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Sample records for high aspect-ratio nanotubes

  1. Aspect ratio has no effect on genotoxicity of multi-wall carbon nanotubes.

    Science.gov (United States)

    Kim, Jin Sik; Lee, Kyu; Lee, Young Hee; Cho, Hyun Sun; Kim, Ki Heon; Choi, Kyung Hee; Lee, Sang Hee; Song, Kyung Seuk; Kang, Chang Soo; Yu, Il Je

    2011-07-01

    Carbon nanotubes (CNTs) have specific physico-chemical and electrical properties that are useful for telecommunications, medicine, materials, manufacturing processes and the environmental and energy sectors. Yet, despite their many advantages, it is also important to determine whether CNTs may represent a hazard to the environment and human health. Like asbestos, the aspect ratio (length:diameter) and metal components of CNTs are known to have an effect on the toxicity of carbon nanotubes. Thus, to evaluate the toxic potential of CNTs in relation to their aspect ratio and metal contamination, in vivo and in vitro genotoxicity tests were conducted using high-aspect-ratio (diameter: 10-15 nm, length: ~10 μm) and low-aspect-ratio multi-wall carbon nanotubes (MWCNTs, diameter: 10-15 nm, length: ~150 nm) according to OECD test guidelines 471 (bacterial reverse mutation test), 473 (in vitro chromosome aberration test), and 474 (in vivo micronuclei test) with a good laboratory practice system. To determine the treatment concentration for all the tests, a solubility and dispersive test was performed, and a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) solution found to be more suitable than distilled water. Neither the high- nor the low-aspect-ratio MWCNTs induced any genotoxicity in a bacterial reverse mutation test (~1,000 μg/plate), in vitro chromosome aberration test (without S9: ~6.25 μg/ml, with S9: ~50 μg/ml), or in vivo micronuclei test (~50 mg/kg). However, the high-aspect-ratio MWCNTs were found to be more toxic than the low-aspect-ratio MWCNTs. Thus, while high-aspect-ratio MWCNTs do not induce direct genotoxicity or metabolic activation-mediated genotoxicity, genotoxicity could still be induced indirectly through oxidative stress or inflammation.

  2. Atomic layer deposition for coating of high aspect ratio TiO.sub.2./sub. nanotube layers

    Czech Academy of Sciences Publication Activity Database

    Zazpe, R.; Knaut, M.; Sopha, H.; Hromádko, L.; Albert, M.; Přikryl, J.; Gärtnerová, Viera; Bartha, J.W.; Macák, J. M.

    2016-01-01

    Roč. 32, č. 41 (2016), s. 10551-10558 ISSN 0743-7463 Institutional support: RVO:68378271 Keywords : aluminum * aluminum coatings * aspect ratio * coatings * nanotubes Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.833, year: 2016

  3. Hyperthermia in low aspect-ratio magnetic nanotubes for biomedical applications

    Science.gov (United States)

    Gutierrez-Guzman, D. F.; Lizardi, L. I.; Otálora, J. A.; Landeros, P.

    2017-03-01

    A simple model for the magnetization reversal process of low aspect-ratio ferromagnetic nanotubes (MNTs) is presented. Because of advantages over other geometries, these structures are interesting for biomedical applications, such as magnetic hyperthermia cancer therapy, where the heat released during magnetic reversal is used to destroy tumors. For example, the tubular geometry provides two independent functional surfaces that may be selectively manipulated and also gives a storage cavity. Owing to their large surface to weight ratio and low mass density, MNTs are not decanted by gravity. We calculated magnetic phase diagrams, energy barriers, nucleation fields, and the amount of dissipated heat and specific absorption rate for magnetite nanotubes. The geometrical parameters were varied, and simple formulae were used to optimize the tube response under alternating excitation, as required for magnetic hyperthermia applications.

  4. A 3-dimensional in vitro model of epithelioid granulomas induced by high aspect ratio nanomaterials

    Directory of Open Access Journals (Sweden)

    Hurt Robert H

    2011-05-01

    Full Text Available Abstract Background The most common causes of granulomatous inflammation are persistent pathogens and poorly-degradable irritating materials. A characteristic pathological reaction to intratracheal instillation, pharyngeal aspiration, or inhalation of carbon nanotubes is formation of epithelioid granulomas accompanied by interstitial fibrosis in the lungs. In the mesothelium, a similar response is induced by high aspect ratio nanomaterials, including asbestos fibers, following intraperitoneal injection. This asbestos-like behaviour of some engineered nanomaterials is a concern for their potential adverse health effects in the lungs and mesothelium. We hypothesize that high aspect ratio nanomaterials will induce epithelioid granulomas in nonadherent macrophages in 3D cultures. Results Carbon black particles (Printex 90 and crocidolite asbestos fibers were used as well-characterized reference materials and compared with three commercial samples of multiwalled carbon nanotubes (MWCNTs. Doses were identified in 2D and 3D cultures in order to minimize acute toxicity and to reflect realistic occupational exposures in humans and in previous inhalation studies in rodents. Under serum-free conditions, exposure of nonadherent primary murine bone marrow-derived macrophages to 0.5 μg/ml (0.38 μg/cm2 of crocidolite asbestos fibers or MWCNTs, but not carbon black, induced macrophage differentiation into epithelioid cells and formation of stable aggregates with the characteristic morphology of granulomas. Formation of multinucleated giant cells was also induced by asbestos fibers or MWCNTs in this 3D in vitro model. After 7-14 days, macrophages exposed to high aspect ratio nanomaterials co-expressed proinflammatory (M1 as well as profibrotic (M2 phenotypic markers. Conclusions Induction of epithelioid granulomas appears to correlate with high aspect ratio and complex 3D structure of carbon nanotubes, not with their iron content or surface area. This model

  5. High aspect ratio piezoelectric strontium-bismuth-tantalate nanotubes

    International Nuclear Information System (INIS)

    Morrison, Finlay D; Ramsay, Laura; Scott, James F

    2003-01-01

    We report the deposition and characterization of transparent ferroelectric/piezoelectric nanotubes of wall thickness about 40 nm, tube diameters ranging from a few hundred nanometres to 4 μm, and length about 100 μm. Comparison with other nanotubes is made and applications in dynamic random access memory trenching and ink-jet printers are discussed. (letter to the editor)

  6. Simulation and Measurement of Neuroelectrodes' Characteristics with Integrated High Aspect Ratio Nano Structures

    Directory of Open Access Journals (Sweden)

    Christoph Nick

    2015-07-01

    Full Text Available Improving the interface between electrodes and neurons has been the focus of research for the last decade. Neuroelectrodes should show small geometrical surface area and low impedance for measuring and high charge injection capacities for stimulation. Increasing the electrochemically active surface area by using nanoporous electrode material or by integrating nanostructures onto planar electrodes is a common approach to improve this interface. In this paper a simulation approach for neuro electrodes' characteristics with integrated high aspect ratio nano structures based on a point-contact-model is presented. The results are compared with experimental findings conducted with real nanostructured microelectrodes. In particular, effects of carbon nanotubes and gold nanowires integrated onto microelectrodes are described. Simulated and measured impedance properties are presented and its effects onto the transfer function between the neural membrane potential and the amplifier output signal are studied based on the point-contact-model. Simulations show, in good agreement with experimental results, that electrode impedances can be dramatically reduced by the integration of high aspect ratio nanostructures such as gold nanowires and carbon nanotubes. This lowers thermal noise and improves the signal-to-noise ratio for measuring electrodes. It also may increase the adhesion of cells to the substrate and thus increase measurable signal amplitudes.

  7. Effect of multi-walled carbon nanotubes aspect ratio and temperature on the dielectric behavior of alternating alkene-carbon monoxide polyketone nanocomposites

    Science.gov (United States)

    Abu-Surrah, Adnan S.; Abdul Jawad, Saadi; Al-Ramahi, Esraa; Hallak, Awni B.; Khattari, Z.

    2015-04-01

    New alternating poly(propylene-alt-carbon monoxide/ethylene-alt-carbon monoxide) (PECO)/multiwalled carbon nanotubes (MWCNTs) composites have been prepared. Dielectric permittivity, electric modulus and ac conductivity of the isolated materials were investigated as a function of fiber aspect ratio, frequency and temperature. For aspect ratio of 30 and 200, a transition from insulator to semiconductor was observed at frequency 1×104. However, for high aspect ratio sample (660), no transition was observed and the conductivity is frequency independent in the measured frequency range of 10-106 Hz. The conductivity increases from about 1×10-4 for the sample that contain fibers of aspect ratio 30 and reaches 5×10-2 (Ω m)-1 for aspect ratio was 660. This behavior can be modeled by a circuit that consists of a contact resistance in series with a parallel combination of resistance (R) and capacitance (C). The calculated activation energy for sample filled with fibers having aspect ratio 30 is about 0.26 eV and decreases to about 0.16 eV when the aspect ratio is 660.

  8. Kramers-Kronig method for determination of optical properties of PZT nanotubes fabricated by sol-gel method and porous anodic alumina with high aspect ratio

    Science.gov (United States)

    Pakizeh, Esmaeil; Moradi, Mahmood

    2018-03-01

    Ferroelectric Pb(ZrTi)O3 (PZT) nanotubes were prepared by sol-gel method and porous anodic alumina (PAA) membrane using spin-coating technique. This method is based on filling-pyrolysis-filling process and the use of one-stage alumina membranes. One of the advantages of this method is its rapidity, which takes only 1 h time before the calcination step. The effect of repeated pores filling was investigated to get the required size of nanotubes. The field emission scanning electron microscope (FE-SEM) images were shown that the PZT nanotubes have inner diameters in the range of 65-90 nm and length of about 50-60 μm. This means that the samples have a significant aspect ratio (700-800). Also the FE-SEM image confirmed that the highly ordered, hexagonally distributed PAA membranes with the pore diameter about 140-150 nm were formed. The X-ray diffraction (XRD) results showed that the PZT nanotubes have a tetragonal structure. The metal oxide bands like ZrO6 and TiO6 of the final PZT nanotubes were detected by Fourier transform infrared (FT-IR) analysis and confirmed the formation of perovskite structure. By using FT-IR spectroscopy and Kramers-Kronig transformation method, the optical constants like real 𝜀1(ω) and imaginary 𝜀2(ω) parts of dielectric function, extinction coefficient k(ω) and refractive index n(ω) were determined. It was shown that the optical constants of PZT nanotubes are different from PZT nanoparticles.

  9. Effect of Aspect Ratio on Electrical, Rheological and Glass Transition Properties of PC/MWCNT Nanocomposites.

    Science.gov (United States)

    Cruz, Heidy; Son, Younggon

    2018-02-01

    Since the discovery of carbon nanotubes (CNT), significant research works have focused on the application of CNT as conductive filler to polymer nanocomposites which can be used in several fields such as electrostatic dissipation (ESD), electrostatic painting and electromagnetic interference shielding (EMI-shielding). However, the main challenge in the large-scale manufacturing of this technology is the poor electrical conductivity of polymer nanocomposites produced by injection molding process. This study aims to investigate the effect of CNT aspect ratio in improving the electrical conductivity of injection molded nanocomposites. In this work, three types of multiwall carbon nanotubes with different lengths were melt-mixed with polycarbonate in a twin screw extruder followed by injection and compression molding. Results show that nanocomposites with higher CNT aspect ratio exhibit higher electrical conductivity. Longer nanotubes form a stronger conductive network during secondary agglomeration which can withstand the high shear forces during injection molding. Higher melt viscosity and storage modulus were observed in nanocomposites with higher CNT aspect ratio which is attributed to the effective constriction of polymer chains by longer nanotubes. It was also found that Tg of the composites increased with nanotube aspect ratio and the addition of CNT causes degradation which leads to the general Tg depression of polycarbonate.

  10. Diffusion of dilute gas in arrays of randomly distributed, vertically aligned, high-aspect-ratio cylinders

    Directory of Open Access Journals (Sweden)

    Wojciech Szmyt

    2017-01-01

    Full Text Available In this work we modelled the diffusive transport of a dilute gas along arrays of randomly distributed, vertically aligned nanocylinders (nanotubes or nanowires as opposed to gas diffusion in long pores, which is described by the well-known Knudsen theory. Analytical expressions for (i the gas diffusion coefficient inside such arrays, (ii the time between collisions of molecules with the nanocylinder walls (mean time of flight, (iii the surface impingement rate, and (iv the Knudsen number of such a system were rigidly derived based on a random-walk model of a molecule that undergoes memoryless, diffusive reflections from nanocylinder walls assuming the molecular regime of gas transport. It can be specifically shown that the gas diffusion coefficient inside such arrays is inversely proportional to the areal density of cylinders and their mean diameter. An example calculation of a diffusion coefficient is delivered for a system of titanium isopropoxide molecules diffusing between vertically aligned carbon nanotubes. Our findings are important for the correct modelling and optimisation of gas-based deposition techniques, such as atomic layer deposition or chemical vapour deposition, frequently used for surface functionalisation of high-aspect-ratio nanocylinder arrays in solar cells and energy storage applications. Furthermore, gas sensing devices with high-aspect-ratio nanocylinder arrays and the growth of vertically aligned carbon nanotubes need the fundamental understanding and precise modelling of gas transport to optimise such processes.

  11. The Young's modulus of high-aspect-ratio carbon/carbon nanotube composite microcantilevers by experimental and modeling validation

    International Nuclear Information System (INIS)

    Zhou, Peng; Yang, Xiao; He, Liang; Hao, Zhimeng; Luo, Wen; Xiong, Biao; Xu, Xu; Niu, Chaojiang; Yan, Mengyu; Mai, Liqiang

    2015-01-01

    This paper reports the Young's modulus of a carbon nanotube (CNT)-reinforced carbon/CNT (C/CNT) composite microcantilevers measured by laser Doppler vibrometer and validated by finite element method. Also, the microfabrication process of the high-aspect-ratio C/CNT microcantilever arrays based on silicon micromolding and pyrolysis is presented in detail. With the in-plane natural resonant frequencies of the microcantilevers measured by a laser Doppler vibrometer, a single degree of freedom (SDoF) model based on Euler-Bernoulli (E-B) beam theory is used to calculate the Young's modulus of this composite. To figure out whether this SDoF model can be applied to these composite microcantilevers, the finite element (FE) simulation of these microcantilevers was performed. The Young's modulus of C/CNT composite microcantilevers fabricated by the pyrolysis process at 600 °C is 9391 MPa, and a good agreement between the results from experiments and FE simulation is obtained

  12. Buckling of ZnS-filled single-walled carbon nanotubes – The influence of aspect ratio

    KAUST Repository

    Monteiro, André O.

    2014-08-16

    The mechanical response of single-walled carbon nanotubes (SWCNT) filled with crystalline zinc sulphide (ZnS) nanowires under uniaxial compression is studied using classical molecular dynamics. These simulations were used to analyse the behaviour of SWCNT, with and without ZnS filling, in terms of critical force and critical strain. Force versus strain curves have been computed for hollow and filled systems, the latter clearly showing an improvement of the mechanical behaviour caused by the ZnS nanowire. The same simulations were repeated for a large range of dimensions in order to evaluate the influence of the aspect ratio on the mechanical response of the tubes.

  13. High aspect ratio spheromak experiments

    International Nuclear Information System (INIS)

    Robertson, S.; Schmid, P.

    1987-05-01

    The Reversatron RFP (R/a = 50cm/8cm) has been operated as an ohmically heated spheromak of high aspect ratio. We find that the dynamo can drive the toroidal field upward at rates as high as 10 6 G/sec. Discharges can be initiated and ramped upward from seed fields as low as 50 G. Small toroidal bias fields of either polarity (-0.2 < F < 0.2) do not significantly affect operation. 5 refs., 3 figs

  14. Systematic in vitro nanotoxicity study on anodic alumina nanotubes with engineered aspect ratio: understanding nanotoxicity by a nanomaterial model.

    Science.gov (United States)

    Wang, Ye; Kaur, Gagandeep; Zysk, Aneta; Liapis, Vasilios; Hay, Shelley; Santos, Abel; Losic, Dusan; Evdokiou, Andreas

    2015-04-01

    Here, we report a detailed and systematic approach for studying the in vitro nanotoxicity study of high aspect ratio (HAR) nanomaterials using anodic alumina nanotubes (AANTs) as a nanomaterial model. AANTs with bio-inert properties and tailored aspect ratios ranging from 7.8 to 63.3 were synthesized by an electrochemical pulse anodization process. Cytotoxicity studies were conducted with RAW 264.7 mouse macrophage cells and MDA-MB 231-TXSA human breast cancer cells through several toxicity parameters, including cell viability and morphology, pro-inflammatory response, mitochondrial depolarization, lysosomal membrane permeabilization (LMP), induction of autophagy and endoplasmic reticulum (ER) stress. The resulting toxicity patterns were cell-type dependent and strongly related with AANTs dose, length of time, and importantly the AR of AANTs. Long AANTs triggered enhanced cell death, morphological changes, tumor necrosis factor α (TNF-α) release, LMP and ER stress than short AANTs. The toxic AR window of AANTs was determined to be 7.8, which is shorter than that of other previously reported HAR nanomaterials. This toxic AR window provides a promising opportunity to control the nanotoxicity of HAR nanomaterials for their advanced drug delivery application. Copyright © 2014 Elsevier Ltd. All rights reserved.

  15. Achieving high aspect ratio wrinkles by modifying material network stress.

    Science.gov (United States)

    Chen, Yu-Cheng; Wang, Yan; McCarthy, Thomas J; Crosby, Alfred J

    2017-06-07

    Wrinkle aspect ratio, or the amplitude divided by the wavelength, is hindered by strain localization transitions when an increasing global compressive stress is applied to synthetic material systems. However, many examples from living organisms show extremely high aspect ratios, such as gut villi and flower petals. We use three experimental approaches to demonstrate that these high aspect ratio structures can be achieved by modifying the network stress in the wrinkle substrate. We modify the wrinkle stress and effectively delay the strain localization transition, such as folding, to larger aspect ratios by using a zero-stress initial wavy substrate, creating a secondary network with post-curing, or using chemical stress relaxation materials. A wrinkle aspect ratio as high as 0.85, almost three times higher than common values of synthetic wrinkles, is achieved, and a quantitative framework is presented to provide understanding the different strategies and predictions for future investigations.

  16. Fabrication of high aspect ratio nanocell lattices by ion beam irradiation

    International Nuclear Information System (INIS)

    Ishikawa, Osamu; Nitta, Noriko; Taniwaki, Masafumi

    2016-01-01

    Highlights: • Nanocell lattice with a high aspect ratio on InSb semiconductor surface was fabricated by ion beam irradiation. • The fabrication technique consisting of top-down and bottom-up processes was performed in FIB. • High aspect ratio of 2 was achieved in nanocell lattice with a 100 nm interval. • The intermediate-flux irradiation is favorable for fabrication of nanocell with a high aspect ratio. - Abstract: A high aspect ratio nanocell lattice was fabricated on the InSb semiconductor surface using the migration of point defects induced by ion beam irradiation. The fabrication technique consisting of the top-down (formation of voids and holes) and bottom-up (growth of voids and holes into nanocells) processes was performed using a focused ion beam (FIB) system. A cell aspect ratio of 2 (cell height/cell diameter) was achieved for the nanocell lattice with a 100 nm dot interval The intermediate-flux ion irradiation during the bottom-up process was found to be optimal for the fabrication of a high aspect ratio nanocell.

  17. Stability of high β large aspect ratio tokamaks

    International Nuclear Information System (INIS)

    Cowley, S.C.

    1991-10-01

    High β(β much-gt ε/q 2 ) large aspect ratio (ε much-gt 1) tokamak equilibria are shown to be always stable to ideal M.H.D. modes that are localized about a flux surface. Both the ballooning and interchange modes are shown to be stable. This work uses the analytic high β large aspect ratio tokamak equilibria developed by Cowley et.al., which are valid for arbitrary pressure and safety factor profiles. The stability results make no assumption about these profiles or the shape of the boundary. 14 refs., 4 figs

  18. Deep Reactive Ion Etching for High Aspect Ratio Microelectromechanical Components

    DEFF Research Database (Denmark)

    Jensen, Søren; Yalcinkaya, Arda Deniz; Jacobsen, S.

    2004-01-01

    A deep reactive ion etch (DRIE) process for fabrication of high aspect ratio trenches has been developed. Trenches with aspect ratios exceeding 20 and vertical sidewalls with low roughness have been demonstrated. The process has successfully been used in the fabrication of silicon-on-insulator (SOI...

  19. Scattering and extinction from high-aspect-ratio trenches

    DEFF Research Database (Denmark)

    Roberts, Alexander Sylvester; Søndergaard, Thomas; Chirumamilla, Manohar

    2015-01-01

    We construct a semi-analytical model describing the scattering, extinction and absorption properties of a high aspect-ratio trench in a metallic film. We find that these trenches act as highly efficient scatterers of free waves. In the perfect conductor limit, which for many metals is approached...

  20. Fabrication of high aspect ratio through-wafer copper interconnects by reverse pulse electroplating

    International Nuclear Information System (INIS)

    Gu, Changdong; Zhang, Tong-Yi; Xu, Hui

    2009-01-01

    This study aims to fabricate high aspect ratio through-wafer copper interconnects by a simple reverse pulse electroplating technique. High aspect-ratio (∼18) through-wafer holes obtained by a two-step deep reactive ion etching (DRIE) process exhibit a taper profile, which might automatically optimize the local current density distribution during the electroplating process, thereby achieving void-free high aspect-ratio copper vias

  1. High aspect ratio silver grid transparent electrodes using UV embossing process

    Directory of Open Access Journals (Sweden)

    Dong Jin Kim

    2017-10-01

    Full Text Available This study presents a UV embossing process to fabricate high aspect ratio silver grid transparent electrodes on a polymer film. Transparent electrodes with a high optical transmittance (93 % and low sheet resistance (4.6 Ω/sq were fabricated without any high temperature or vacuum processes. The strong adhesion force between the UV resin and the silver ink enables the fabrication of silver microstructures with an aspect ratio higher than 3. The high aspect ratio results in a low sheet resistance while maintaining a high optical transmittance. Multi-layer transparent electrodes were fabricated by repeating the proposed UV process. Additionally, a large-area of 8-inch touch panel was fabricated with the proposed UV process. The proposed UV process is a relatively simple and low cost process making it suitable for large-area production as well as mass production.

  2. High aspect ratio titanium nitride trench structures as plasmonic biosensor

    DEFF Research Database (Denmark)

    Shkondin, Evgeniy; Repän, Taavi; Takayama, Osamu

    2017-01-01

    High aspect ratio titanium nitride (TiN) grating structures are fabricated by the combination of deep reactive ion etching (DRIE) and atomic layer deposition (ALD) techniques. TiN is deposited at 500 ◦C on a silicon trench template. Silicon between vertical TiN layers is selectively etched...... to fabricate the high aspect ratio TiN trenches with the pitch of 400 nm and height of around 2.7 µm. Dielectric functions of TiN films with different thicknesses of 18 - 105 nm and post-annealing temperatures of 700 - 900 ◦C are characterized by an ellipsometer. We found that the highest annealing temperature...... of 900 ◦C gives the most pronounced plasmonic behavior with the highest plasma frequency, ωp = 2.53 eV (λp = 490 nm). Such high aspect ratio trench structures function as a plasmonic grating sensor that supports the Rayleigh-Woods anomalies (RWAs), enabling the measurement of changes in the refractive...

  3. Large Aspect Ratio Tokamak Study

    International Nuclear Information System (INIS)

    Reid, R.L.; Holmes, J.A.; Houlberg, W.A.; Peng, Y.K.M.; Strickler, D.J.; Brown, T.G.; Wiseman, G.W.

    1980-06-01

    The Large Aspect Ratio Tokamak Study (LARTS) at Oak Ridge National Laboratory (ORNL) investigated the potential for producing a viable longburn tokamak reactor by enhancing the volt-second capability of the ohmic heating transformer through the use of high aspect ratio designs. The plasma physics, engineering, and economic implications of high aspect ratio tokamaks were assessed in the context of extended burn operation. Using a one-dimensional transport code plasma startup and burn parameters were addressed. The pulsed electrical power requirements for the poloidal field system, which have a major impact on reactor economics, were minimized by optimizing the startup and shutdown portions of the tokamak cycle. A representative large aspect ratio tokamak with an aspect ratio of 8 was found to achieve a burn time of 3.5 h at capital cost only approx. 25% greater than that of a moderate aspect ratio design tokamak

  4. Large aspect ratio tokamak study

    International Nuclear Information System (INIS)

    Reid, R.L.; Holmes, J.A.; Houlberg, W.A.; Peng, Y.K.M.; Strickler, D.J.; Brown, T.G.; Sardella, C.; Wiseman, G.W.

    1979-01-01

    The Large Aspect Ratio Tokamak Study (LARTS) investigated the potential for producing a viable long burn tokamak reactor through enhanced volt-second capability of the ohmic heating transformer by employing high aspect ratio designs. The plasma physics, engineering, and economic implications of high aspect ratio tokamaks were accessed in the context of extended burn operation. Plasma startup and burn parameters were addressed using a one-dimensional transport code. The pulsed electrical power requirements for the poloidal field system, which have a major impact on reactor economics, were minimized by optimizing the field in the ohmic heating coil and the wave shape of the ohmic heating discharge. A high aspect ratio reference reactor was chosen and configured

  5. Nanocomposites with increased energy density through high aspect ratio PZT nanowires.

    Science.gov (United States)

    Tang, Haixiong; Lin, Yirong; Andrews, Clark; Sodano, Henry A

    2011-01-07

    High energy storage plays an important role in the modern electric industry. Herein, we investigated the role of filler aspect ratio in nanocomposites for energy storage. Nanocomposites were synthesized using lead zirconate titanate (PZT) with two different aspect ratio (nanowires, nanorods) fillers at various volume fractions dispersed in a polyvinylidene fluoride (PVDF) matrix. The permittivity constants of composites containing nanowires (NWs) were higher than those with nanorods (NRs) at the same inclusion volume fraction. It was also indicated that the high frequency loss tangent of samples with PZT nanowires was smaller than for those with nanorods, demonstrating the high electrical energy storage efficiency of the PZT NW nanocomposite. The high aspect ratio PZT NWs showed a 77.8% increase in energy density over the lower aspect ratio PZT NRs, under an electric field of 15 kV mm(-1) and 50% volume fraction. The breakdown strength was found to decrease with the increasing volume fraction of PZT NWs, but to only change slightly from a volume fraction of around 20%-50%. The maximum calculated energy density of nanocomposites is as high as 1.158 J cm(-3) at 50% PZT NWs in PVDF. Since the breakdown strength is lower compared to a PVDF copolymer such as poly(vinylidene fluoride-tertrifluoroethylene-terchlorotrifluoroethylene) P(VDF-TreEE-CTFE) and poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP), the energy density of the nanocomposite could be significantly increased through the use of PZT NWs and a polymer with greater breakdown strength. These results indicate that higher aspect ratio fillers show promising potential to improve the energy density of nanocomposites, leading to the development of advanced capacitors with high energy density.

  6. Improving surface acousto-optical interaction by high aspect ratio electrodes

    DEFF Research Database (Denmark)

    Dühring, Maria Bayard; Laude, Vincent; Khelif, Abdelkrim

    2009-01-01

    The acousto-optical interaction of an optical wave confined inside a waveguide and a surface acoustic wave launched by an interdigital transducer (IDT) at the surface of a piezoelectric material is considered. The IDT with high aspect ratio electrodes supports several acoustic modes that are stro......The acousto-optical interaction of an optical wave confined inside a waveguide and a surface acoustic wave launched by an interdigital transducer (IDT) at the surface of a piezoelectric material is considered. The IDT with high aspect ratio electrodes supports several acoustic modes...

  7. Different methods to alter surface morphology of high aspect ratio structures

    Energy Technology Data Exchange (ETDEWEB)

    Leber, M., E-mail: moritz.leber@utah.edu [Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT (United States); Shandhi, M.M.H. [Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT (United States); Hogan, A. [Blackrock Microsystems, Salt Lake City, UT (United States); Solzbacher, F. [Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT (United States); Bhandari, R.; Negi, S. [Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT (United States); Blackrock Microsystems, Salt Lake City, UT (United States)

    2016-03-01

    Graphical abstract: Surface engineering of high aspect ratio silicon structures. - Highlights: • Multiple roughening techniques for high aspect ratio devices were investigated. • Modification of surface morphology of high aspect ratio silicon devices (1:15). • Decrease of 76% in impedance proves significant increase in surface area. - Abstract: In various applications such as neural prostheses or solar cells, there is a need to alter the surface morphology of high aspect ratio structures so that the real surface area is greater than geometrical area. The change in surface morphology enhances the devices functionality. One of the applications of altering the surface morphology is of neural implants such as the Utah electrode array (UEA) that communicate with single neurons by charge injection induced stimulation or by recording electrical neural signals. For high selectivity between single cells of the nervous system, the electrode surface area is required to be as small as possible, while the impedance is required to be as low as possible for good signal to noise ratios (SNR) during neural recording. For stimulation, high charge injection and charge transfer capacities of the electrodes are required, which increase with the electrode surface. Traditionally, researchers have worked with either increasing the roughness of the existing metallization (platinum grey, black) or other materials such as Iridium Oxide and PEDOT. All of these previously investigated methods lead to more complicated metal deposition processes that are difficult to control and often have a critical impact on the mechanical properties of the metal films. Therefore, a modification of the surface underneath the electrode's coating will increase its surface area while maintaining the standard and well controlled metal deposition process. In this work, the surfaces of the silicon micro-needles were engineered by creating a defined microstructure on the electrodes surface using several

  8. Primary response of high-aspect-ratio thermoresistive sensors

    Science.gov (United States)

    Majlesein, H. R.; Mitchell, D. L.; Bhattacharya, Pradeep K.; Singh, A.; Anderson, James A.

    1997-07-01

    There is a growing need for sensors in monitoring performance in modern quality products such as in electronics to monitor heat build up, substrate delaminations, and thermal runaway. In processing instruments, intelligent sensors are needed to measure deposited layer thickness and resistivities for process control, and in environmental electrical enclosures, they are used for climate monitoring and control. A yaw sensor for skid prevention utilizes very fine moveable components, and an automobile engine controller blends a microprocessor and sensor on the same chip. An Active-Pixel Image Sensor is integrated with a digital readout circuit to perform most of the functions in a video camera. Magnetostrictive transducers sense and damp vibrations. Improved acoustic sensors will be used in flow detection of air and other fluids, even at subsonic speeds. Optoelectronic sensor systems are being developed for installation on rocket engines to monitor exhaust gases for signs of wear in the engines. With new freon-free coolants being available the problems of A/C system corrosion have gone up in automobiles and need to be monitored more frequently. Defense cutbacks compel the storage of hardware in safe-custody for an indeterminate period of time, and this makes monitoring more essential. Just-in-time customized manufacturing in modern industries also needs dramatic adjustment in productivity of various selected items, leaving some manufacturing equipment idle for a long time, and therefore, it will be prone to more corrosion, and corrosion sensors are needed. In the medical device industry, development of implantable medical devices using both potentiometric and amperometric determination of parameters has, until now, been used with insufficient micro miniaturization, and thus, requires surgical implantation. In many applications, high-aspect- ratio devices, made possible by the use of synchrotron radiation lithography, allow more useful devices to be produced. High-aspect-ratio

  9. A novel fabrication method for suspended high-aspect-ratio microstructures

    Science.gov (United States)

    Yang, Yao-Joe; Kuo, Wen-Cheng

    2005-11-01

    Suspended high-aspect-ratio structures (suspended HARS) are widely used for MEMS devices such as micro-gyroscopes, micro-accelerometers, optical switches and so on. Various fabrication methods, such as SOI, SCREAM, AIM, SBM and BELST processes, were proposed to fabricate HARS. However, these methods focus on the fabrication of suspended microstructures with relatively small widths of trench opening (e.g. less than 10 µm). In this paper, we propose a novel process for fabricating very high-aspect-ratio suspended structures with large widths of trench opening using photoresist as an etching mask. By enhancing the microtrenching effect, we can easily release the suspended structure without thoroughly removing the floor polymer inside the trenches for the cases with a relatively small trench aspect ratio. All the process steps can be integrated into a single-run single-mask ICP-RIE process, which effectively reduces the process complexity and fabrication cost. We also discuss the phenomenon of corner erosion, which results in the undesired etching of silicon structures during the structure-releasing step. By using the proposed process, 100 µm thick suspended structures with the trench aspect ratio of about 20 are demonstrated. Also, the proposed process can be used to fabricate devices for applications which require large in-plane displacement. This paper was orally presented in the Transducers'05, Seoul, Korea (paper ID: 3B1.3).

  10. Reusable High Aspect Ratio 3-D Nickel Shadow Mask

    Science.gov (United States)

    Shandhi, M.M.H.; Leber, M.; Hogan, A.; Warren, D.J.; Bhandari, R.; Negi, S.

    2017-01-01

    Shadow Mask technology has been used over the years for resistless patterning and to pattern on unconventional surfaces, fragile substrate and biomaterial. In this work, we are presenting a novel method to fabricate high aspect ratio (15:1) three-dimensional (3D) Nickel (Ni) shadow mask with vertical pattern length and width of 1.2 mm and 40 μm respectively. The Ni shadow mask is 1.5 mm tall and 100 μm wide at the base. The aspect ratio of the shadow mask is 15. Ni shadow mask is mechanically robust and hence easy to handle. It is also reusable and used to pattern the sidewalls of unconventional and complex 3D geometries such as microneedles or neural electrodes (such as the Utah array). The standard Utah array has 100 active sites at the tip of the shaft. Using the proposed high aspect ratio Ni shadow mask, the Utah array can accommodate 300 active sites, 200 of which will be along and around the shaft. The robust Ni shadow mask is fabricated using laser patterning and electroplating techniques. The use of Ni 3D shadow mask will lower the fabrication cost, complexity and time for patterning out-of-plane structures. PMID:29056835

  11. Synthesis of high aspect ratio ZnO nanowires with an inexpensive handcrafted electrochemical setup

    Energy Technology Data Exchange (ETDEWEB)

    Taheri, Ali, E-mail: at1361@aut.ac.ir, E-mail: atahery@aeoi.org.ir [Nuclear Science and Technology Institute (Iran, Islamic Republic of); Saramad, Shahyar; Setayeshi, Saeed [Amirkabir University of Technology, Faculty of Energy Engineering and Physics (Iran, Islamic Republic of)

    2016-12-15

    In this work, high aspect ratio zinc oxide nanowires are synthesized using templated one-step electrodeposition technique. Electrodeposition of the nanowires is done using a handcrafted electronic system. Nuclear track-etched polycarbonate membrane is used as a template to form the high aspect ratio nanowires. The result of X-ray diffraction and scanning electron microscopy shows that nanowires with a good crystallinity and an aspect ratio of more than 30 can be achieved in a suitable condition. The height of electrodeposited nanowires reaches to about 11 μm. Based on the obtained results, high aspect ratio ZnO nanowires can be formed using inexpensive electrodeposition setup with an acceptable quality.

  12. Cryogenic Etching of High Aspect Ratio 400 nm Pitch Silicon Gratings.

    Science.gov (United States)

    Miao, Houxun; Chen, Lei; Mirzaeimoghri, Mona; Kasica, Richard; Wen, Han

    2016-10-01

    The cryogenic process and Bosch process are two widely used processes for reactive ion etching of high aspect ratio silicon structures. This paper focuses on the cryogenic deep etching of 400 nm pitch silicon gratings with various etching mask materials including polymer, Cr, SiO 2 and Cr-on-polymer. The undercut is found to be the key factor limiting the achievable aspect ratio for the direct hard masks of Cr and SiO 2 , while the etch selectivity responds to the limitation of the polymer mask. The Cr-on-polymer mask provides the same high selectivity as Cr and reduces the excessive undercut introduced by direct hard masks. By optimizing the etching parameters, we etched a 400 nm pitch grating to ≈ 10.6 μ m depth, corresponding to an aspect ratio of ≈ 53.

  13. High aspect ratio MEMS capacitor for high frequency impedance matching applications

    DEFF Research Database (Denmark)

    Yalcinkaya, Arda Deniz; Jensen, Søren; Hansen, Ole

    2003-01-01

    We present a microelectromechanical tunable capacitor with a low control voltage, a wide tuning range and adequate electrical quality factor. The device is fabricated in a single-crystalline silicon layer using deep reactive ion etching (DRIE) for obtaining high-aspect ratio (> 20) parallel comb...

  14. Simultaneous fabrication of very high aspect ratio positive nano- to milliscale structures.

    Science.gov (United States)

    Chen, Long Qing; Chan-Park, Mary B; Zhang, Qing; Chen, Peng; Li, Chang Ming; Li, Sai

    2009-05-01

    A simple and inexpensive technique for the simultaneous fabrication of positive (i.e., protruding), very high aspect (>10) ratio nanostructures together with micro- or millistructures is developed. The method involves using residual patterns of thin-film over-etching (RPTO) to produce sub-micro-/nanoscale features. The residual thin-film nanopattern is used as an etching mask for Si deep reactive ion etching. The etched Si structures are further reduced in size by Si thermal oxidation to produce amorphous SiO(2), which is subsequently etched away by HF. Two arrays of positive Si nanowalls are demonstrated with this combined RPTO-SiO(2)-HF technique. One array has a feature size of 150 nm and an aspect ratio of 26.7 and another has a feature size of 50 nm and an aspect ratio of 15. No other parallel reduction technique can achieve such a very high aspect ratio for 50-nm-wide nanowalls. As a demonstration of the technique to simultaneously achieve nano- and milliscale features, a simple Si nanofluidic master mold with positive features with dimensions varying continuously from 1 mm to 200 nm and a highest aspect ratio of 6.75 is fabricated; the narrow 200-nm section is 4.5 mm long. This Si master mold is then used as a mold for UV embossing. The embossed open channels are then closed by a cover with glue bonding. A high aspect ratio is necessary to produce unblocked closed channels after the cover bonding process of the nanofluidic chip. The combined method of RPTO, Si thermal oxidation, and HF etching can be used to make complex nanofluidic systems and nano-/micro-/millistructures for diverse applications.

  15. Masks for high aspect ratio x-ray lithography

    International Nuclear Information System (INIS)

    Malek, C.K.; Jackson, K.H.; Bonivert, W.D.; Hruby, J.

    1997-01-01

    Fabrication of very high aspect ratio microstructures, as well as ultra-high precision manufacturing is of increasing interest in a multitude of applications. Fields as diverse as micromechanics, robotics, integrated optics, and sensors benefit from this technology. The scale-length of this spatial regime is between what can be achieved using classical machine tool operations and that which is used in microelectronics. This requires new manufacturing techniques, such as the LIGA process, which combines x-ray lithography, electroforming, and plastic molding

  16. Ultra-high aspect ratio replaceable AFM tips using deformation-suppressed focused ion beam milling

    DEFF Research Database (Denmark)

    Savenko, Alexey; Yildiz, Izzet; Petersen, Dirch Hjorth

    2013-01-01

    Fabrication of ultra-high aspect ratio exchangeable and customizable tips for atomic force microscopy (AFM) using lateral focused ion beam (FIB) milling is presented. While on-axis FIB milling does allow high aspect ratio (HAR) AFM tips to be defined, lateral milling gives far better flexibility...

  17. Jet-Surface Interaction - High Aspect Ratio Nozzle Test: Test Summary

    Science.gov (United States)

    Brown, Clifford A.

    2016-01-01

    The Jet-Surface Interaction High Aspect Ratio Nozzle Test was conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center in the fall of 2015. There were four primary goals specified for this test: (1) extend the current noise database for rectangular nozzles to higher aspect ratios, (2) verify data previously acquired at small-scale with data from a larger model, (3) acquired jet-surface interaction noise data suitable for creating verifying empirical noise models and (4) investigate the effect of nozzle septa on the jet-mixing and jet-surface interaction noise. These slides give a summary of the test with representative results for each goal.

  18. Trade-off analysis of high-aspect-ratio-cooling-channels for rocket engines

    International Nuclear Information System (INIS)

    Pizzarelli, Marco; Nasuti, Francesco; Onofri, Marcello

    2013-01-01

    Highlights: • Aspect ratio has a significant effect on cooling efficiency and hydraulic losses. • Minimizing power loss is of paramount importance in liquid rocket engine cooling. • A suitable quasi-2D model is used to get fast cooling system analysis. • Trade-off with assigned weight, temperature, and channel height or wall thickness. • Aspect ratio is found that minimizes power loss in the cooling circuit. -- Abstract: High performance liquid rocket engines are often characterized by rectangular cooling channels with high aspect ratio (channel height-to-width ratio) because of their proven superior cooling efficiency with respect to a conventional design. However, the identification of the optimum aspect ratio is not a trivial task. In the present study a trade-off analysis is performed on a cooling channel system that can be of interest for rocket engines. This analysis requires multiple cooling channel flow calculations and thus cannot be efficiently performed by CFD solvers. Therefore, a proper numerical approach, referred to as quasi-2D model, is used to have fast and accurate predictions of cooling system properties. This approach relies on its capability of describing the thermal stratification that occurs in the coolant and in the wall structure, as well as the coolant warming and pressure drop along the channel length. Validation of the model is carried out by comparison with solutions obtained with a validated CFD solver. Results of the analysis show the existence of an optimum channel aspect ratio that minimizes the requested pump power needed to overcome losses in the cooling circuit

  19. High aspect ratio channels in glass and porous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Liang, H.D. [Centre for Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Nanoscience and Nanotechnology Initiative (NNI), National University of Singapore, Singapore 117411 (Singapore); Dang, Z.Y. [Centre for Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Wu, J.F. [Centre for Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore); Kan, J.A. van; Qureshi, S. [Centre for Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Ynsa, M.D.; Torres-Costa, V. [Department of Applied Physics, Universidad Autónoma de Madrid, Madrid, Campus de Cantoblanco, 28049 Madrid (Spain); Centro de Micro-Análisis de Materiales (CMAM), Universidad Autónoma de Madrid, Campus de Cantoblanco Edif. 22, Faraday 3, E-28049 Madrid (Spain); Maira, A. [Department of Applied Physics, Universidad Autónoma de Madrid, Madrid, Campus de Cantoblanco, 28049 Madrid (Spain); Venkatesan, T.V. [Nanoscience and Nanotechnology Initiative (NNI), National University of Singapore, Singapore 117411 (Singapore); Breese, M.B.H., E-mail: phymbhb@nus.edu.sg [Centre for Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, Singapore 117542 (Singapore)

    2017-03-01

    We have developed a micromachining process to produce high-aspect-ratio channels and holes in glass and porous silicon. Our process utilizes MeV proton beam irradiation of silicon using direct writing with a focused beam, followed by electrochemical etching. To increase throughput we have also developed another process for large area ion irradiation based on a radiation-resistant gold surface mask, allowing many square inches to be patterned. We present a study of the achievable channel width, depth and period and sidewall verticality for a range of channels which can be over 100 μm deep or 100 nm wide with aspect ratios up to 80. This process overcomes the difficulty of machining glass on a micro- and nanometer scale which has limited many areas of applications in different fields such as microelectronics and microfluidics.

  20. High aspect ratio, remote controlled pumping assembly

    Science.gov (United States)

    Brown, Steve B.; Milanovich, Fred P.

    1995-01-01

    A miniature dual syringe-type pump assembly which has a high aspect ratio and which is remotely controlled, for use such as in a small diameter penetrometer cone or well packer used in water contamination applications. The pump assembly may be used to supply and remove a reagent to a water contamination sensor, for example, and includes a motor, gearhead and motor encoder assembly for turning a drive screw for an actuator which provides pushing on one syringe and pulling on the other syringe for injecting new reagent and withdrawing used reagent from an associated sensor.

  1. Effect of aspect ratio on the uptake and toxicity of hydroxylated-multi walled carbon nanotubes in the nematode,

    Directory of Open Access Journals (Sweden)

    Hyun-Jeong Eom

    2015-03-01

    Full Text Available Objectives In this study, the effect of tube length and outer diameter (OD size of hydroxylated-multi walled carbon nanotubes (OH-MWCNTs on their uptake and toxicity was investigated in the nematode Caenorhabditis elegans using a functional mutant analysis. Methods The physicochemical properties of three different OH-MWCNTs were characterized. Uptake and toxicity were subsequently investigated on C. elegans exposed to MWCNTs with different ODs and tube lengths. Results The results of mutant analysis suggest that ingestion is the main route of MWCNTs uptake. We found that OH-MWCNTs with smaller ODs were more toxic than those with larger ODs, and OH-MWCNTs with shorter tube lengths were more toxic than longer counterparts to C. elegans. Conclusions Overall the results suggest the aspect ratio affects the toxicity of MWCNTs in C. elegans. Further thorough study on the relationship between physicochemical properties and toxicity needs to be conducted for more comprehensive understanding of the uptake and toxicity of MWCNTs.

  2. Synthesis of ultra-long cadmium telluride nanotubes via combinational chemical transformation

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kee-Ryung; Cho, Hong-Baek; Choa, Yong-Ho, E-mail: choa15@hanyang.ac.kr

    2017-03-01

    Synthesis of high-throughput cadmium telluride (CdTe) nanotubes with an ultra-long aspect ratio is presented via a combination process concept combined with electrospinning, electrodeposition, and cationic exchange reaction. Ultra-long sacrificial silver (Ag) nanofibers were synthesized by electrospinning involving two-step calcination, and were then electrodeposited to create silver telluride nanotubes. These nanotubes underwent cationic exchange reaction in cadmium nitrate tetrahydrate solution with the aid of a ligand, tributylphosphine (TBP). Analysis showed that ultra-long pure zinc blende CdTe nanotubes were obtained with controlled dimension and uniform morphology. The thermodynamic driving force induced by the coordination of methanol solvent and TBP attributed to overcome the kinetic barrier between Ag{sub 2}Te and CdTe nanotubes, facilitating the synthesis of CdTe nanotubes. This synthetic process involving a topotactic reaction route paves a way for high-throughput extended synthesis of new chalcogenide hollow nanotubes for application in photodetectors and solar cells. - Highlights: • High throughput synthetic route of hollow CdTe nanotubes with ultra-long aspect ratio. • Chemical combination of electrospinning, electrodeposition & cation exchange reaction. • Pure zinc blende CdTe by controlled dimension & structural variation of Ag nanofibers. • Potential for the high throughput synthesis of new exotic chalcogenide nanotubes.

  3. Flight Loads Prediction of High Aspect Ratio Wing Aircraft Using Multibody Dynamics

    Directory of Open Access Journals (Sweden)

    Michele Castellani

    2016-01-01

    Full Text Available A framework based on multibody dynamics has been developed for the static and dynamic aeroelastic analyses of flexible high aspect ratio wing aircraft subject to structural geometric nonlinearities. Multibody dynamics allows kinematic nonlinearities and nonlinear relationships in the forces definition and is an efficient and promising methodology to model high aspect ratio wings, which are known to be prone to structural nonlinear effects because of the high deflections in flight. The multibody dynamics framework developed employs quasi-steady aerodynamics strip theory and discretizes the wing as a series of rigid bodies interconnected by beam elements, representative of the stiffness distribution, which can undergo arbitrarily large displacements and rotations. The method is applied to a flexible high aspect ratio wing commercial aircraft and both trim and gust response analyses are performed in order to calculate flight loads. These results are then compared to those obtained with the standard linear aeroelastic approach provided by the Finite Element Solver Nastran. Nonlinear effects come into play mainly because of the need of taking into account the large deflections of the wing for flight loads computation and of considering the aerodynamic forces as follower forces.

  4. Comparative study of low and high aspect ratio devices for ITER design options

    International Nuclear Information System (INIS)

    Sugihara, Masayoshi; Tada, Eisuke; Shimomura, Yasuo; Tsunematsu, Toshihide; Nishio, Satoshi; Nakazato, Toshiko; Murakami, Yoshiki; Koizumi, Koichi

    1992-09-01

    Comparative study on the plasma performance and the engineering characteristics of low and high aspect ratio devices for ITER (International Thermonuclear Experimental Reactor) design option is done to examine quantitatively the expected merit and demerit of high aspect ratio device on steady state operation. Device parameters of aspect ratio A=3 and 4 are chosen based on ITER-power scaling law. Improvement of steady state operation with A=4 is found only moderate. Reduction of stability margin in vertical instability is about 20% and plasma elongation must be decreased from 2 down to about 1.8 to recover this reduction of stability margin with A=4. If such lower elongation is employed, single null divertor configuration should be employed to reduce the capacity of poloidal field system. Detailed 2D divertor code calculation shows that peak heat load per unit area of A=4 device with SN configuration increases compared with A=3 device with DN configuration, contrary to the predictions so far made. Preliminary engineering studies indicate that A=4 device would have less space for handling the in-vessel components and doubled toroidal field magnet weight and winding length, and hence is less desirable when compared with the present ITER design (A=3). Based on these examinations, it is concluded that high aspect ratio device does not have remarkable advantage than low aspect ratio device, and the latter device has similar capability for the prospect of future commercial reactor to the former device. (J.P.N.)

  5. Aspect Ratio Scaling of Ideal No-wall Stability Limits in High Bootstrap Fraction Tokamak Plasmas

    International Nuclear Information System (INIS)

    Menard, J.E.; Bell, M.G.; Bell, R.E.; Gates, D.A.; Kaye, S.M.; LeBlanc, B.P.; Maingi, R.; Sabbagh, S.A.; Soukhanovskii, V.; Stutman, D.

    2003-01-01

    Recent experiments in the low aspect ratio National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 (2000) 557] have achieved normalized beta values twice the conventional tokamak limit at low internal inductance and with significant bootstrap current. These experimental results have motivated a computational re-examination of the plasma aspect ratio dependence of ideal no-wall magnetohydrodynamic stability limits. These calculations find that the profile-optimized no-wall stability limit in high bootstrap fraction regimes is well described by a nearly aspect ratio invariant normalized beta parameter utilizing the total magnetic field energy density inside the plasma. However, the scaling of normalized beta with internal inductance is found to be strongly aspect ratio dependent at sufficiently low aspect ratio. These calculations and detailed stability analyses of experimental equilibria indicate that the nonrotating plasma no-wall stability limit has been exceeded by as much as 30% in NSTX in a high bootstrap fraction regime

  6. Formation of high aspect ratio polyamide-6 nanofibers via electrically induced double layer during electrospinning

    International Nuclear Information System (INIS)

    Nirmala, R.; Nam, Ki Taek; Park, Soo-Jin; Shin, Yu-Shik; Navamathavan, R.; Kim, Hak Yong

    2010-01-01

    In the present study, the formation of high aspect ratio nanofibers in polyamide-6 was investigated as a function of applied voltage ranging from 15 to 25 kV using electrospinning technique. All other experimental parameters were kept constant. The electrospun polyamide-6 nanofibers were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). FE-SEM images of polyamide-6 nanofibers showed that the diameter of the electrospun fiber was decreased with increasing applied voltage. At the critical applied voltage, the polymer solution was completely ionized to form the dense high aspect ratio nanofibers in between the main nanofibers. The diameter of the polyamide-6 nanofibers was observed to be in the range of 75-110 nm, whereas the high aspect ratio structures consisted of regularly distributed very fine nanofibers with diameters of about 9-28 nm. Trends in fiber diameter and diameter distribution were discussed for the high aspect ratio nanofibers. TEM results revealed that the formation of double layers in polyamide-6 nanofibers and then split-up into ultrafine fibers. The electrically induced double layer in combination with the polyelectrolytic nature of solution is proposed as the suitable mechanisms for the formation of high aspect ratio nanofibers in polyamide-6.

  7. Transcription and the aspect ratio of DNA

    DEFF Research Database (Denmark)

    Olsen, Kasper Wibeck; Bohr, Jakob

    2013-01-01

    analysis of transcription. It is shown that under certain reasonable assumptions transcription is only possible if the aspect ratio is in the regime corresponding to further twisting. We find this constraint to be in agreement with long-established crystallographic studies of DNA.......Two separate regimes exist for the aspect ratio of DNA. A low aspect regime where DNA will twist further under strain and a high aspect regime where DNA will untwist under strain. The question of the overall geometry, i.e. the aspect ratio, of DNA is revisited from the perspective of a geometrical...

  8. Computational local stiffness analysis of biological cell: High aspect ratio single wall carbon nanotube tip

    Energy Technology Data Exchange (ETDEWEB)

    TermehYousefi, Amin, E-mail: at.tyousefi@gmail.com [Department of Human Intelligence Systems, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology (Kyutech) (Japan); Bagheri, Samira; Shahnazar, Sheida [Nanotechnology & Catalysis Research Centre (NANOCAT), IPS Building, University Malaya, 50603 Kuala Lumpur (Malaysia); Rahman, Md. Habibur [Department of Computer Science and Engineering, University of Asia Pacific, Green Road, Dhaka-1215 (Bangladesh); Kadri, Nahrizul Adib [Department of Biomedical Engineering, Faculty of Engineering, University Malaya, 50603 Kuala Lumpur (Malaysia)

    2016-02-01

    Carbon nanotubes (CNTs) are potentially ideal tips for atomic force microscopy (AFM) due to the robust mechanical properties, nanoscale diameter and also their ability to be functionalized by chemical and biological components at the tip ends. This contribution develops the idea of using CNTs as an AFM tip in computational analysis of the biological cells. The proposed software was ABAQUS 6.13 CAE/CEL provided by Dassault Systems, which is a powerful finite element (FE) tool to perform the numerical analysis and visualize the interactions between proposed tip and membrane of the cell. Finite element analysis employed for each section and displacement of the nodes located in the contact area was monitored by using an output database (ODB). Mooney–Rivlin hyperelastic model of the cell allows the simulation to obtain a new method for estimating the stiffness and spring constant of the cell. Stress and strain curve indicates the yield stress point which defines as a vertical stress and plan stress. Spring constant of the cell and the local stiffness was measured as well as the applied force of CNT-AFM tip on the contact area of the cell. This reliable integration of CNT-AFM tip process provides a new class of high performance nanoprobes for single biological cell analysis. - Graphical abstract: This contribution develops the idea of using CNTs as an AFM tip in computational analysis of the biological cells. The proposed software was ABAQUS 6.13 CAE/CEL provided by Dassault Systems. Finite element analysis employed for each section and displacement of the nodes located in the contact area was monitored by using an output database (ODB). Mooney–Rivlin hyperelastic model of the cell allows the simulation to obtain a new method for estimating the stiffness and spring constant of the cell. Stress and strain curve indicates the yield stress point which defines as a vertical stress and plan stress. Spring constant of the cell and the local stiffness was measured as well

  9. Fabrication of high-aspect-ratio microgrooves using an electrochemical discharge micromilling process

    International Nuclear Information System (INIS)

    Han, Min-Seop; Chae, Ki Woon; Min, Byung-Kwon

    2017-01-01

    In this study, we created high-aspect-ratio microgrooves in hard, brittle materials using an electrochemical discharge machining (ECDM) process by introducing microtextured machining tool. To enhance the electrical discharge activity, the morphology of the tool side surface was treated via micro-electrical discharge machining to produce fine microprotrusive patterns. The resulting microtextured surface morphology enhanced the electric field and played a key role in improving the step milling depth in the ECDM process. Using the FEM analysis, the evaluation of the field enhancement factor is also addressed. Our experimental investigation revealed microgrooves having an aspect ratio of 1:4, with high geometric accuracy and crack-free surfaces, using one-step ECDM. (paper)

  10. Angle resolved mass spectrometry of positive ions transmitted through high aspect ratio channels in a radio frequency discharge

    NARCIS (Netherlands)

    Stoffels - Adamowicz, E.; Stoffels, W.W.; Tachibana, K.; Imai, S.

    1997-01-01

    The behavior of positive ions in high aspect ratio structures, relevant to the reactive ion etching of deep trenches, has been studied by means of energy resolved mass spectrometry. High aspect ratio trenches are simulated by capillary plates with various aspect ratios. Angle resolved measurements

  11. Characterizing the reinforcement mechanisms in multiwall nanotube/polycarbonate composites across different length and time scales

    Science.gov (United States)

    Duncan, Renee Kelly

    The enthusiasm and interest in the potential properties of nanotube (NT)/polymer composites are based on several factors, including the potential for unsurpassed enhancements in mechanical properties together with electrical, thermal and optical properties. Using multiwall nanotubes (MWNTs) grown to a long aspect ratio, the study found that fragmentation tests can be completed in a similar manner to traditional fiber composites. It was found that the fragmentation length does not depend on the angle of the nanotube to the loading direction hence the ISS does not change with the orientation angle of the nanotube in the composite. A critical aspect ratio of 100 and 300 for untreated nanotubes (ARNT) and treated nanotubes (EPNT), respectively was also measured. For nanotubes that are well dispersed in the polycarbonate, it was observed at a critical angle of 60° that there was a change in failure mechanism from pullout to fracture of the nanotubes due to bending shear. Because the tensile strength of a MWNT is unknown a cumulative distribution was used to characterize the relative interfacial shear strength as a function of nanotube chemical modification. The second goal of this thesis is to use Dynamic Mechanical Thermal Analysis (DMTA) with controlled aspect ratios of multiwall nanotubes (MWNT) to isolate and quantify the effects of the interfacial region on modulus enhancements in nanotube-reinforced composites. One major finding of this study was that the shortest aspect ratio showed a significantly broadened relaxation spectrum than the longer aspect ratio nanotubes, despite the longer aspect ratio nanotubes being more percolated at the given weight percent. There is also a direct correlation between the free space parameter of the short aspect ratio nantoubes network and broadening of the relaxation spectrum, concluded to be a result of increased interaction of the interfacial polymer. The study found agreement with the premise that at a constant filler weight

  12. Ultra-high aspect ratio replaceable AFM tips using deformation-suppressed focused ion beam milling

    International Nuclear Information System (INIS)

    Savenko, Alexey; Yildiz, Izzet; Petersen, Dirch Hjorth; Bøggild, Peter; Bartenwerfer, Malte; Krohs, Florian; Oliva, Maria; Harzendorf, Torsten

    2013-01-01

    Fabrication of ultra-high aspect ratio exchangeable and customizable tips for atomic force microscopy (AFM) using lateral focused ion beam (FIB) milling is presented. While on-axis FIB milling does allow high aspect ratio (HAR) AFM tips to be defined, lateral milling gives far better flexibility in terms of defining the shape and size of the tip. Due to beam-induced deformation, it has so far not been possible to define HAR structures using lateral FIB milling. In this work we obtain aspect ratios of up to 45, with tip diameters down to 9 nm, by a deformation-suppressing writing strategy. Several FIB milling strategies for obtaining sharper tips are discussed. Finally, assembly of the HAR tips on a custom-designed probe as well as the first AFM scanning is shown. (paper)

  13. Fabrication process for tall, sharp, hollow, high aspect ratio polymer microneedles on a platform

    International Nuclear Information System (INIS)

    Ceyssens, Frederik; Chaudhri, Buddhadev Paul; Van Hoof, Chris; Puers, Robert

    2013-01-01

    This paper reports on a new lithographic process for fabricating arrays of tall, high aspect ratio (defined as height/wall thickness), hollow, polymer microneedles on a platform. The microneedles feature a high sharpness (down to 3 µm tip radius) and aspect ratio (>65) which is a factor 2 and 4 better than the state of the art, respectively. The maximum achievable needle shaft length is over 1 mm. The improved performance was obtained by using an anisotropically patterned silicon substrate covered with an antireflective layer as mold for the needle tip and an optimized SU-8 lithographic process. Furthermore, a platform containing liquid feedthroughs holding an arbitrary number of needles out of plane can be manufactured with only one additional process step. The high aspect ratio microneedles undergo failure at the critical load of around 230 mN in the case of 1 mm long hollow needles with triangular cross section and a base of 175 µm. Penetration into human skin is demonstrated as well. (paper)

  14. Highly Manufacturable Deep (Sub-Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego-Like Silicon Electronics

    KAUST Repository

    Ghoneim, Mohamed T.; Hussain, Muhammad Mustafa

    2017-01-01

    A highly manufacturable deep reactive ion etching based process involving a hybrid soft/hard mask process technology shows high aspect ratio complex geometry Lego-like silicon electronics formation enabling free-form (physically flexible

  15. Jet-Surface Interaction: High Aspect Ratio Nozzle Test, Nozzle Design and Preliminary Data

    Science.gov (United States)

    Brown, Clifford; Dippold, Vance

    2015-01-01

    The Jet-Surface Interaction High Aspect Ratio (JSI-HAR) nozzle test is part of an ongoing effort to measure and predict the noise created when an aircraft engine exhausts close to an airframe surface. The JSI-HAR test is focused on parameters derived from the Turbo-electric Distributed Propulsion (TeDP) concept aircraft which include a high-aspect ratio mailslot exhaust nozzle, internal septa, and an aft deck. The size and mass flow rate limits of the test rig also limited the test nozzle to a 16:1 aspect ratio, half the approximately 32:1 on the TeDP concept. Also, unlike the aircraft, the test nozzle must transition from a single round duct on the High Flow Jet Exit Rig, located in the AeroAcoustic Propulsion Laboratory at the NASA Glenn Research Center, to the rectangular shape at the nozzle exit. A parametric nozzle design method was developed to design three low noise round-to-rectangular transitions, with 8:1, 12:1, and 16: aspect ratios, that minimizes flow separations and shocks while providing a flat flow profile at the nozzle exit. These designs validated using the WIND-US CFD code. A preliminary analysis of the test data shows that the actual flow profile is close to that predicted and that the noise results appear consistent with data from previous, smaller scale, tests. The JSI-HAR test is ongoing through October 2015. The results shown in the presentation are intended to provide an overview of the test and a first look at the preliminary results.

  16. Hybrid UV Lithography for 3D High-Aspect-Ratio Microstructures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sungmin; Nam, Gyungmok; Kim, Jonghun; Yoon, Sang-Hee [Inha Univ, Incheon (Korea, Republic of)

    2016-08-15

    Three-dimensional (3D) high-aspect-ratio (HAR) microstructures for biomedical applications (e.g., microneedle, microadhesive, etc.) are microfabricated using the hybrid ultraviolet (UV) lithography in which inclined, rotational, and reverse-side UV exposure processes are combined together. The inclined and rotational UV exposure processes are intended to fabricate tapered axisymmetric HAR microstructures; the reverse-side UV exposure process is designed to sharpen the end tip of the microstructures by suppressing the UV reflection on a bottom substrate which is inevitable in conventional UV lithography. Hybrid UV lithography involves fabricating 3D HAR microstructures with an epoxy-based negative photoresist, SU-8, using our customized UV exposure system. The effects of hybrid UV lithography parameters on the geometry of the 3D HAR microstructures (aspect ratio, radius of curvature of the end tip, etc.) are measured. The dependence of the end-tip shape on SU-8 soft-baking condition is also discussed.

  17. Hybrid UV Lithography for 3D High-Aspect-Ratio Microstructures

    International Nuclear Information System (INIS)

    Park, Sungmin; Nam, Gyungmok; Kim, Jonghun; Yoon, Sang-Hee

    2016-01-01

    Three-dimensional (3D) high-aspect-ratio (HAR) microstructures for biomedical applications (e.g., microneedle, microadhesive, etc.) are microfabricated using the hybrid ultraviolet (UV) lithography in which inclined, rotational, and reverse-side UV exposure processes are combined together. The inclined and rotational UV exposure processes are intended to fabricate tapered axisymmetric HAR microstructures; the reverse-side UV exposure process is designed to sharpen the end tip of the microstructures by suppressing the UV reflection on a bottom substrate which is inevitable in conventional UV lithography. Hybrid UV lithography involves fabricating 3D HAR microstructures with an epoxy-based negative photoresist, SU-8, using our customized UV exposure system. The effects of hybrid UV lithography parameters on the geometry of the 3D HAR microstructures (aspect ratio, radius of curvature of the end tip, etc.) are measured. The dependence of the end-tip shape on SU-8 soft-baking condition is also discussed

  18. Framework to model neutral particle flux in convex high aspect ratio structures using one-dimensional radiosity

    Science.gov (United States)

    Manstetten, Paul; Filipovic, Lado; Hössinger, Andreas; Weinbub, Josef; Selberherr, Siegfried

    2017-02-01

    We present a computationally efficient framework to compute the neutral flux in high aspect ratio structures during three-dimensional plasma etching simulations. The framework is based on a one-dimensional radiosity approach and is applicable to simulations of convex rotationally symmetric holes and convex symmetric trenches with a constant cross-section. The framework is intended to replace the full three-dimensional simulation step required to calculate the neutral flux during plasma etching simulations. Especially for high aspect ratio structures, the computational effort, required to perform the full three-dimensional simulation of the neutral flux at the desired spatial resolution, conflicts with practical simulation time constraints. Our results are in agreement with those obtained by three-dimensional Monte Carlo based ray tracing simulations for various aspect ratios and convex geometries. With this framework we present a comprehensive analysis of the influence of the geometrical properties of high aspect ratio structures as well as of the particle sticking probability on the neutral particle flux.

  19. Continuum theory for nanotube piezoelectricity.

    Science.gov (United States)

    Michalski, P J; Sai, Na; Mele, E J

    2005-09-09

    We develop and solve a continuum theory for the piezoelectric response of one-dimensional nanotubes and nanowires, and apply the theory to study electromechanical effects in boron-nitride nanotubes. We find that the polarization of a nanotube depends on its aspect ratio, and a dimensionless constant specifying the ratio of the strengths of the elastic and electrostatic interactions. The solutions of the model as these two parameters are varied are discussed. The theory is applied to estimate the electric potential induced along the length of a boron-nitride nanotube in response to a uniaxial stress.

  20. Fabrication of nanopore and nanoparticle arrays with high aspect ratio AAO masks

    Science.gov (United States)

    Li, Z. P.; Xu, Z. M.; Qu, X. P.; Wang, S. B.; Peng, J.; Mei, L. H.

    2017-03-01

    How to use high aspect ratio anodic aluminum oxide (AAO) membranes as an etching and evaporation mask is one of the unsolved problems in the application of nanostructured arrays. Here we describe the versatile utilizations of the highly ordered AAO membranes with a high aspect ratio of more than 20 used as universal masks for the formation of various nanostructure arrays on various substrates. The result shows that the fabricated nanopore and nanoparticle arrays of substrates inherit the regularity of the AAO membranes completely. The flat AAO substrates and uneven AAO frontages were attached to the Si substrates respectively as an etching mask, which demonstrates that the two kinds of replication, positive and negative, represent the replication of the mirroring of Si substrates relative to the flat AAO substrates and uneven AAO frontages. Our work is a breakthrough for the broad research field of surface nano-masking.

  1. Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

    Science.gov (United States)

    Bridges, James E.

    2015-01-01

    This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly found in embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side (bevel) did produce up to 3 decibels more noise in all directions, while extending the lip on the narrow side (slant) produced up to 2 decibels more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron (notch) produced up to 2decibels increase in the noise. Having internal walls (septae) within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed electric propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

  2. Highly Manufacturable Deep (Sub-Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego-Like Silicon Electronics

    KAUST Repository

    Ghoneim, Mohamed T.

    2017-02-01

    A highly manufacturable deep reactive ion etching based process involving a hybrid soft/hard mask process technology shows high aspect ratio complex geometry Lego-like silicon electronics formation enabling free-form (physically flexible, stretchable, and reconfigurable) electronic systems.

  3. Polymer-Carbon Nanotube Composites, A Literature Review

    National Research Council Canada - National Science Library

    Huber, Trisha A

    2004-01-01

    .... The extraordinary properties arise from the unique tubular structure; the nanotubes may be envisioned as rolled up graphene sheets that are on the order of a nanometer in diameter, and microns in length, resulting in high aspect ratios (length/diameter...

  4. High yield polyol synthesis of round- and sharp-end silver nanowires with high aspect ratio

    Energy Technology Data Exchange (ETDEWEB)

    Nekahi, A.; Marashi, S.P.H., E-mail: pmarashi@aut.ac.ir; Fatmesari, D. Haghshenas

    2016-12-01

    Long silver nanowires (average length of 28 μm, average aspect ratio of 130) with uniform diameter along their length were produced by polyol synthesis of AgNO{sub 3} in ethylene glycol in the presence of PVP as preferential growth agent. Nanowires were produced with no addition of chloride salts such as NaCl or CuCl{sub 2} (or other additives such as Na{sub 2}S) which are usually used for lowering reduction rate of Ag ions by additional etchant of O{sub 2}/Cl{sup −}. Lower reduction rate was obtained by increasing the injection time of PVP and AgNO{sub 3} solutions, which was the significant factor in the formation of nanowires. Therefore, there was enough time for reduced Ag atoms to be deposited preferentially in the direction of PVP chains, resulting in high yield (the fraction of nanowires in the products) of nanowires (more than 95%) with high aspect ratio. The produced nanowires had both round- and sharp-ends with pentagonal cross section. Higher energy level of Ag atoms in borders of MTPs, which increases the dissolution rate of precipitated atoms, in addition to partial melting of MTPs at high synthesis temperatures, leads to the curving of the surfaces of exposed (111) crystalline planes in some MTPs and the formation of round-end silver nanowires. - Highlights: • Long silver nanowires with high aspect ratio of 130 were produced. • More than 95% nanowires were produced in products. • The produced nanowires had round- and sharp-ends with pentagonal cross section. • Additives were needed neither for high yield synthesis nor for round-end nanowires. • Melting and etching of MTPs in high energy borders resulted to round-end nanowires.

  5. Design and Analyses of High Aspect Ratio Nozzles for Distributed Propulsion Acoustic Measurements

    Science.gov (United States)

    Dippold, Vance F., III

    2016-01-01

    A series of three convergent round-to-rectangular high-aspect ratio nozzles were designed for acoustics measurements. The nozzles have exit area aspect ratios of 8:1, 12:1, and 16:1. With septa inserts, these nozzles will mimic an array of distributed propulsion system nozzles, as found on hybrid wing-body aircraft concepts. Analyses were performed for the three nozzle designs and showed that the flow through the nozzles was free of separated flow and shocks. The exit flow was mostly uniform with the exception of a pair of vortices at each span-wise end of the nozzle.

  6. The impact of different multi-walled carbon nanotubes on the X-band microwave absorption of their epoxy nanocomposites.

    Science.gov (United States)

    Che, Bien Dong; Nguyen, Bao Quoc; Nguyen, Le-Thu T; Nguyen, Ha Tran; Nguyen, Viet Quoc; Van Le, Thang; Nguyen, Nieu Huu

    2015-01-01

    Carbon nanotube (CNT) characteristics, besides the processing conditions, can change significantly the microwave absorption behavior of CNT/polymer composites. In this study, we investigated the influence of three commercial multi-walled CNT materials with various diameters and length-to-diameter aspect ratios on the X-band microwave absorption of epoxy nanocomposites with CNT contents from 0.125 to 2 wt%, prepared by two dispersion methods, i.e. in solution with surfactant-aiding and via ball-milling. The laser diffraction particle size and TEM analysis showed that both methods produced good dispersions at the microscopic level of CNTs. Both a high aspect ratio resulting in nanotube alignment trend and good infiltration of the matrix in the individual nanotubes, which was indicated by high Brookfield viscosities at low CNT contents of CNT/epoxy dispersions, are important factors to achieve composites with high microwave absorption characteristics. The multi-walled carbon nanotube (MWCNT) with the largest aspect ratio resulted in composites with the best X-band microwave absorption performance, which is considerably better than that of reported pristine CNT/polymer composites with similar or lower thicknesses and CNT loadings below 4 wt%. A high aspect ratio of CNTs resulting in microscopic alignment trend of nanotubes as well as a good level of micro-scale CNT dispersion resulting from good CNT-matrix interactions are crucial to obtain effective microwave absorption performance. This study demonstrated that effective radar absorbing MWCNT/epoxy nanocomposites having small matching thicknesses of 2-3 mm and very low filler contents of 0.25-0.5 wt%, with microwave energy absorption in the X-band region above 90% and maximum absorption peak values above 97%, could be obtained via simple processing methods, which is promising for mass production in industrial applications. Graphical AbstractComparison of the X-band microwave reflection loss of epoxy composites of

  7. Midinfrared Surface Waves on a High Aspect Ratio Nanotrench Platform

    DEFF Research Database (Denmark)

    Takayama, Osamu; Shkondin, Evgeniy; Bodganov, Andrey

    2017-01-01

    ameliorate surface wave propagation and even generate new types of waves. Here, we demonstrate that high aspect ratio (1:20) grating structures with plasmonic lamellas in deep nanoscale trenches, whose pitch is 1/10 – 1/35 of a wavelength, function as a versatile platform supporting both surface and guided...... bulk infrared waves. The surface waves exhibit a unique combination of properties: directionality, broadband existence (from 4 µm to at least 14 μm and beyond) and high localization, making them an attractive tool for effective control of light in an extended range of infrared frequencies....

  8. Highly Manufacturable Deep (Sub-Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego-Like Silicon Electronics.

    Science.gov (United States)

    Ghoneim, Mohamed Tarek; Hussain, Muhammad Mustafa

    2017-04-01

    A highly manufacturable deep reactive ion etching based process involving a hybrid soft/hard mask process technology shows high aspect ratio complex geometry Lego-like silicon electronics formation enabling free-form (physically flexible, stretchable, and reconfigurable) electronic systems. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Finite element analysis of surface acoustic waves in high aspect ratio electrodes

    DEFF Research Database (Denmark)

    Dühring, Maria Bayard; Laude, Vincent; Khelif, Abdelkrim

    2008-01-01

    This paper elaborates on how the finite element method is employed to model surface acoustic waves generated by high aspect ratio electrodes and their interaction with optical waves in a waveguide. With a periodic model it is shown that these electrodes act as a mechanical resonator which slows...

  10. A six degree of freedom nanomanipulator design based on carbon nanotube bundles

    International Nuclear Information System (INIS)

    Artyukhov, Vasilii I

    2010-01-01

    Scanning probe imaging and manipulation of matter is of crucial importance for nanoscale science and technology. However, its resolution and ability to manipulate matter at the atomic scale is limited by rather poor control over the fine structure of the probe. In the present paper, a strategy is proposed to construct a molecular nanomanipulator from ultrathin single-walled carbon nanotubes. Covalent modification of a nanotube cap at predetermined atomic sites makes the nanotube act as a support for a functional 'tooltip' molecule. Then, a small bundle of nanotubes (three or four) with aligned ends can act as an extremely high aspect ratio parallel nanomanipulator for a suspended molecule, where protraction or retraction of individual nanotubes results in controlled tilting of the tooltip in two dimensions. Together with the usual scanning probe microscopy three degrees of freedom and augmented with rotation of the system as a whole, the design offers six degrees of freedom for imaging and manipulation of matter with the precision and freedom so much needed for advanced nanotechnology. A similar design might be possible to implement with other high aspect ratio nanostructures, such as oxide nanowires.

  11. High aspect ratio problem in simulation of a fault current limiter based on superconducting tapes

    Energy Technology Data Exchange (ETDEWEB)

    Velichko, A V; Coombs, T A [Electrical Engineering Division, University of Cambridge (United Kingdom)

    2006-06-15

    We are offering a solution for the high-aspect-ratio problem relevant to the numerical simulation of AC loss in superconductors and metals with high aspect (width-to-thickness) ratio. This is particularly relevant to simulation of fault current limiters (FCLs) based on second generation YBCO tapes on RABiTS. By assuming a linear scaling of the electric and thermal properties with the size of the structure, we can replace the real sample with an effective sample of a reduced aspect ratio by introducing size multipliers into the equations that govern the physics of the system. The simulation is performed using both a proprietary equivalent circuit software and a commercial FEM software. The correctness of the procedure is verified by simulating temperature and current distributions for samples with all three dimensions varying within 10{sup -3}-10{sup 3} of the original size. Qualitatively the distributions for the original and scaled samples are indistinguishable, whereas quantitative differences in the worst case do not exceed 10%.

  12. High aspect ratio problem in simulation of a fault current limiter based on superconducting tapes

    International Nuclear Information System (INIS)

    Velichko, A V; Coombs, T A

    2006-01-01

    We are offering a solution for the high-aspect-ratio problem relevant to the numerical simulation of AC loss in superconductors and metals with high aspect (width-to-thickness) ratio. This is particularly relevant to simulation of fault current limiters (FCLs) based on second generation YBCO tapes on RABiTS. By assuming a linear scaling of the electric and thermal properties with the size of the structure, we can replace the real sample with an effective sample of a reduced aspect ratio by introducing size multipliers into the equations that govern the physics of the system. The simulation is performed using both a proprietary equivalent circuit software and a commercial FEM software. The correctness of the procedure is verified by simulating temperature and current distributions for samples with all three dimensions varying within 10 -3 -10 3 of the original size. Qualitatively the distributions for the original and scaled samples are indistinguishable, whereas quantitative differences in the worst case do not exceed 10%

  13. High aspect ratio nanoholes in glass generated by femtosecond laser pulses with picosecond intervals

    Science.gov (United States)

    Ahn, Sanghoon; Choi, Jiyeon; Noh, Jiwhan; Cho, Sung-Hak

    2018-02-01

    Because of its potential uses, high aspect ratio nanostructures have been interested for last few decades. In order to generate nanostructures, various techniques have been attempted. Femtosecond laser ablation is one of techniques for generating nanostructures inside a transparent material. For generating nanostructures by femtosecond laser ablation, previous studies have been attempted beam shaping such as Bessel beam and temporal tailored beam. Both methods suppress electron excitation at near surface and initiate interference of photons at certain depth. Recent researches indicate that shape of nanostructures is related with temporal change of electron density and number of self-trapped excitons. In this study, we try to use the temporal change of electron density induced by femtosecond laser pulse for generating high aspect ratio nanoholes. In order to reveal the effect of temporal change of electron density, secondary pulses are irradiated from 100 to 1000 ps after the irradiation of first pulse. Our result shows that diameter of nanoholes is increasing and depth of nanoholes is decreasing as pulse to pulse interval is getting longer. With manipulating of pulse to pulse interval, we could generate high aspect ratio nanoholes with diameter of 250-350 nm and depth of 4∼6 μm inside a glass.

  14. Facile preparation of carbon nanotubes-graphene hybrids and the effect of aspect ratio of carbon nanotubes on electrical and thermal properties of silicone rubber based composites

    Science.gov (United States)

    Zhao, Shizhen; Bai, Lu; Zheng, Junping

    2018-01-01

    Thermal exfoliation, as an effective and easily scalable method, was widely used to produce graphene (GE). In order to prevent the severe stacking of GE sheets after thermal exfoliation process, a facile technique was used to solve this problem through the barrier effect of carbon nanotubes (CNTs). Two kinds of CNTs with different aspect ratios (AR) were taken to prepare CNTs-GE hybrids using this technique, and then the effect of AR of CNTs (namely CNTs-L for low AR and CNTs-H for high AR) in the hybrids on the performance of silicone rubber (SR) composites was investigated. The results indicate that the presence of CNTs can effectively impede the stacking of GE sheets and the hybrids are dispersed uniformly in the SR matrix. With the addition of CNTs-GE hybrids, the resulted SR composites exhibit greatly improved electrical and thermal properties, especially for the composites filled with CNTs-H-GE hybrid. At the hybrids content of 3.0 wt%, the volume resistivity of CNTs-H-GE/SR composite is 5 × 104 Ω cm (about 10 orders of magnitude decrease compared with pure SR). And the thermal conductivity increases by 78% compared to the pure SR. But as for the CNTs-L-GE/SR composite, the corresponding values are 3 × 106 Ω cm and 59%, respectively. In terms of thermal stability, the CNTs-H-GE/SR composite containing 1.0 wt% hybrid exhibits the maximum improvement of initial degradation temperature (419 °C) compared with the CNTs-L-GE/SR composite (393 °C) and pure SR (365 °C).

  15. Optimization of HNA etching parameters to produce high aspect ratio solid silicon microneedles

    International Nuclear Information System (INIS)

    Hamzah, A A; Yeop Majlis, B; Yunas, J; Dee, C F; Abd Aziz, N; Bais, B

    2012-01-01

    High aspect ratio solid silicon microneedles with a concave conic shape were fabricated. Hydrofluoric acid–nitric acid–acetic acid (HNA) etching parameters were characterized and optimized to produce microneedles that have long and narrow bodies with smooth surfaces, suitable for transdermal drug delivery applications. The etching parameters were characterized by varying the HNA composition, the optical mask's window size, the etching temperature and bath agitation. An L9 orthogonal Taguchi experiment with three factors, each having three levels, was utilized to determine the optimal fabrication parameters. Isoetch contours for HNA composition with 0% and 10% acetic acid concentrations were presented and a high nitric acid region was identified to produce microneedles with smooth surfaces. It is observed that an increase in window size indiscriminately increases the etch rate in both the vertical and lateral directions, while an increase in etching temperature beyond 35 °C causes the etching to become rapid and uncontrollable. Bath agitation and sample placement could be manipulated to achieve a higher vertical etch rate compared to its lateral counterpart in order to construct high aspect ratio microneedles. The Taguchi experiment performed suggests that a HNA composition of 2:7:1 (HF:HNO 3 :CH 3 COOH), window size of 500 µm and agitation rate of 450 RPM are optimal. Solid silicon microneedles with an average height of 159.4 µm, an average base width of 110.9 µm, an aspect ratio of 1.44, and a tip angle and diameter of 19.2° and 0.38 µm respectively were successfully fabricated. (paper)

  16. Fabrication of high-aspect-ratio microstructures using dielectrophoresis-electrocapillary force-driven UV-imprinting

    International Nuclear Information System (INIS)

    Li, Xiangming; Shao, Jinyou; Tian, Hongmiao; Ding, Yucheng; Li, Xiangmeng

    2011-01-01

    We propose a novel method for fabricating high-aspect-ratio micro-/nano-structures by dielectrophoresis-electrocapillary force (DEP-ECF)-driven UV-imprinting. The force of DEP-ECF, acting on an air–liquid interface and an air–liquid–solid three-phase contact line, is generated by applying voltage between an electrically conductive mold and a substrate, and tends to pull the dielectric liquid (a UV-curable pre-polymer) into the mold micro-cavities. The existence of DEP-ECF is explained theoretically and demonstrated experimentally by the electrically induced reduction of the contact angle. Furthermore, DEP-ECF is proven to play a critical role in forcing the polymer to fill into the mold cavities by the real-time observation of the dynamic filling process. Using the DEP-ECF-driven UV-imprinting process, high-aspect-ratio polymer micro-/nano-structures (more than 10:1) are fabricated with high consistency. This patterning method can overcome the drawbacks of the mechanically induced mold deformation and position shift in conventional imprinting lithography and maximize the pattern uniformity which is usually poor in capillary force lithography

  17. Deep Reactive Ion Etching (DRIE) of High Aspect Ratio SiC Microstructures using a Time-Multiplexed Etch-Passivate Process

    Science.gov (United States)

    Evans, Laura J.; Beheim, Glenn M.

    2006-01-01

    High aspect ratio silicon carbide (SiC) microstructures are needed for microengines and other harsh environment micro-electro-mechanical systems (MEMS). Previously, deep reactive ion etching (DRIE) of low aspect ratio (AR less than or = 1) deep (greater than 100 micron) trenches in SiC has been reported. However, existing DRIE processes for SiC are not well-suited for definition of high aspect ratio features because such simple etch-only processes provide insufficient control over sidewall roughness and slope. Therefore, we have investigated the use of a time-multiplexed etch-passivate (TMEP) process, which alternates etching with polymer passivation of the etch sidewalls. An optimized TMEP process was used to etch high aspect ratio (AR greater than 5) deep (less than 100 micron) trenches in 6H-SiC. Power MEMS structures (micro turbine blades) in 6H-SiC were also fabricated.

  18. Transport in a small aspect ratio torus

    International Nuclear Information System (INIS)

    White, R.B.; Gates, D.A.; Mynick, H.E.

    2005-01-01

    Transport theory in toroidal devices often assumes large aspect ratio and also assumes the poloidal field is small compared to the toroidal field. These assumptions result in transport which in the low collision rate limit is dominated by banana orbits, giving the largest collisionless excursion of a particle from an initial flux surface. However in a small aspect ratio device the gyro radius may be larger than the banana excursion, resulting in significant deviations from the standard neoclassical predictions. In this paper we report numerical simulation of diffusion in low and high beta low aspect ratio equilibria. We also sketch an analytic theory. The diffusion, which we refer to as omniclassical, is a combination of neoclassical and properly averaged classical effects, and can be two or three times the neoclassical value. Good agreement of the analytic theory with numerical simulations is obtained. (author)

  19. Boron Nitride Nanotube: Synthesis and Applications

    Science.gov (United States)

    Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha I.; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; hide

    2014-01-01

    Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800 C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

  20. Dense high-aspect ratio 3D carbon pillars on interdigitated microelectrode arrays

    DEFF Research Database (Denmark)

    Amato, Letizia; Heiskanen, Arto; Hansen, Rasmus

    2015-01-01

    In this work we present high-aspect ratio carbon pillars (1.4 μm in diameter and ∼11 μm in height) on top of interdigitated electrode arrays to be used for electrochemical applications. For this purpose, different types of 2D and 3D pyrolysed carbon structures were fabricated and characterised...... of pyrolysed carbon films with increased film resistance due to oxidation during storage....

  1. Developing Xenopus Embryos Recover by Compacting and Expelling Single-Wall Carbon Nanotubes

    Science.gov (United States)

    Holt, Brian D.; Shawky, Joseph H.; Dahl, Kris Noel; Davidson, Lance A.; Islam, Mohammad F.

    2015-01-01

    Single-wall carbon nanotubes are high aspect ratio nanomaterials that are being developed for use in materials, technological and biological applications due to their high mechanical stiffness, optical properties, and chemical inertness. Because of their prevalence, it is inevitable that biological systems will be exposed to nanotubes, yet studies of the effects of nanotubes on developing embryos have been inconclusive and are lacking for single-wall carbon nanotubes exposed to the widely studied model organism Xenopus laevis (African clawed frog). Microinjection of experimental substances into the Xenopus embryo is a standard technique for toxicology studies and cellular lineage tracing. Here we report the surprising finding that superficial (12.5 ± 7.5 μm below the membrane) microinjection of nanotubes dispersed with Pluronic F127 into one-to-two cell Xenopus embryos resulted in the formation and expulsion of compacted, nanotube-filled, punctate masses, at the blastula to mid-gastrula developmental stages, which we call “boluses”. Such expulsion of microinjected materials by Xenopus embryos has not been reported before and is dramatically different from the typical distribution of the materials throughout the progeny of the microinjected cells. Previous studies of microinjections of nanomaterials such as nanodiamonds, quantum dots or spherical nanoparticles report that nanomaterials often induce toxicity and remain localized within the embryos. In contrast, our results demonstrate an active recovery pathway for embryos after exposure to Pluronic F127-coated nanotubes, which we speculate is due to a combined effect of the membrane activity of the dispersing agent, Pluronic F127, and the large aspect ratio of nanotubes. PMID:26153061

  2. Developing Xenopus embryos recover by compacting and expelling single wall carbon nanotubes.

    Science.gov (United States)

    Holt, Brian D; Shawky, Joseph H; Dahl, Kris Noel; Davidson, Lance A; Islam, Mohammad F

    2016-04-01

    Single wall carbon nanotubes are high aspect ratio nanomaterials being developed for use in materials, technological and biological applications due to their high mechanical stiffness, optical properties and chemical inertness. Because of their prevalence, it is inevitable that biological systems will be exposed to nanotubes, yet studies of the effects of nanotubes on developing embryos have been inconclusive and are lacking for single wall carbon nanotubes exposed to the widely studied model organism Xenopus laevis (African clawed frog). Microinjection of experimental substances into the Xenopus embryo is a standard technique for toxicology studies and cellular lineage tracing. Here we report the surprising finding that superficial (12.5 ± 7.5 µm below the membrane) microinjection of nanotubes dispersed with Pluronic F127 into one- to two-cell Xenopus embryos resulted in the formation and expulsion of compacted, nanotube-filled, punctate masses, at the blastula to mid-gastrula developmental stages, which we call "boluses." Such expulsion of microinjected materials by Xenopus embryos has not been reported before and is dramatically different from the typical distribution of the materials throughout the progeny of the microinjected cells. Previous studies of microinjections of nanomaterials such as nanodiamonds, quantum dots or spherical nanoparticles report that nanomaterials often induce toxicity and remain localized within the embryos. In contrast, our results demonstrate an active recovery pathway for embryos after exposure to Pluronic F127-coated nanotubes, which we speculate is due to a combined effect of the membrane activity of the dispersing agent, Pluronic F127, and the large aspect ratio of nanotubes. Copyright © 2015 John Wiley & Sons, Ltd.

  3. The High Aspect Ratio Design (HARD): A candidate ITER concept with improved technology phase performance

    International Nuclear Information System (INIS)

    Nevins, W.M.; Perkins, L.J.; Wesley, J.C.

    1992-10-01

    The High Aspect Ratio Design (HARD) International Thermonuclear Experimental Reactor (ITER) concept developed by the US ITER team is an alternate to the low-aspect-ratio ITER design developed by the ITER participants during the Conceptual Design Activity (CDA). The CDA design, referred to hereafter as ITER CDA, has an aspect ratio, A, of 2.79, a toroidal magnetic field, B T , of 4.85 T, and a plasma current, I p , of 22 MA for operation with an ignited plasma. In contrast, HARD employs higher aspect ratio, A = 4.0, higher toroidal field, B T = 7.11 T, and lower plasma current, I p = 14.8 MA for ignition operation. The cross sections of the two designs are compared in. The parameters and performance of HARD and ITER CDA for inductively driven ignition operation are compared in. The HARD parameters provide the same ignition performance (ignition margin evaluated against ITER-89P confinement scaling) as ITER CDA in a device with comparable size and cost. However, the reason for advancing HARD rather than ITER CDA as the ITER design concept is not inductively driven ignition performance but HARD's significantly enhanced potential to achieve the technology testing and steady-state operation goals of the ITER objectives with non-inductive current drive

  4. Review on properties, dispersion and toxicology of carbon nanotubes

    International Nuclear Information System (INIS)

    Saeed, K.

    2010-01-01

    Carbon nanotubes (CNTs) have the most intensely studied nano structures because of their unique properties. There are two types of carbon nanotubes CNTs, single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), prepared by chemical-vapour deposition (CVD), plasma enhanced chemical-vapour deposition, thermal chemical vapour deposition, Vapour phase growth, Arc discharge and Lasser ablation. Both single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) possess high mechanical and electrical conductivity, ultra-light weight, high aspect ratio and have excellent chemical and thermal stabilities. They also possess semi- and metallic-conductive properties depending upon their chirality. This review focuses on progress toward functionalization (not only dispersed nano tube but also dramatically improve their solubility), preparation and purification, composites and the toxicity of the carbon nanotubes (CNTs). The functional groups attached to carbon nanotubes (CNTs) should react with polymers and improve the mechanical properties of the nano composites. Carbon nanotubes (CNTs) has significant application in pharmaceutical field such as drug delivery and nano medicine, but the available literature also suggests that carbon nanotubes (CNTs) may have unusual toxicity and have more adverse effects than the same mass of nano size carbon and quartz. (author)

  5. Growth of high-aspect ratio horizontally-aligned ZnO nanowire arrays.

    Science.gov (United States)

    Soman, Pranav; Darnell, Max; Feldman, Marc D; Chen, Shaochen

    2011-08-01

    A method of fabricating horizontally-aligned zinc-oxide (ZnO) nanowire (NW) arrays with full control over the width and length is demonstrated. SEM images reveal the hexagonal structure typical of zinc oxide NWs. Arrays of high-aspect ratio horizontal ZnO NWs are fabricated by making use of the lateral overgrowth from dot patterns created by electron beam lithography (EBL). An array of patterned wires are lifted off and transferred to a flexible PDMS substrate with possible applications in several key nanotechnology areas.

  6. Microfluidic active mixers employing ultra-high aspect-ratio rare-earth magnetic nano-composite polymer artificial cilia

    International Nuclear Information System (INIS)

    Rahbar, Mona; Gray, Bonnie L; Shannon, Lesley

    2014-01-01

    We present a new micromixer based on highly magnetic, flexible, high aspect-ratio, artificial cilia that are fabricated as individual micromixer elements or in arrays for improved mixing performance. These new cilia enable high efficiency, fast mixing in a microchamber, and are controlled by small electromagnetic fields. The artificial cilia are fabricated using a new micromolding process for nano-composite polymers. Cilia fibers with aspect-ratios as high as 8:0.13 demonstrate the fabrication technique's capability in creating ultra-high aspect-ratio microstructures. Cilia, which are realized in polydimethylsiloxane doped with rare-earth magnetic powder, are magnetized to produce permanent magnetic structures with bidirectional deflection capabilities, making them highly suitable as mixers controlled by electromagnetic fields. Due to the high magnetization level of the polarized nano-composite polymer, we are able to use miniature electromagnets providing relatively small magnetic fields of 1.1 to 7 mT to actuate the cilia microstructures over a very wide motion range. Mixing performances of a single cilium, as well as different arrays of multiple cilia ranging from 2 to 8 per reaction chamber, are characterized and compared with passive diffusion mixing performance. The mixer cilia are actuated at different amplitudes and frequencies to optimize mixing performance. We demonstrate that more than 85% of the total volume of the reaction chamber is fully mixed after 3.5 min using a single cilium mixer at 7 mT compared with only 20% of the total volume mixed with passive diffusion. The time to achieve over 85% mixing is further reduced to 70 s using an array of eight cilia microstructures. The novel microfabrication technique and use of rare-earth permanently-magnetizable nano-composite polymers in mixer applications has not been reported elsewhere by other researchers. We further demonstrate improved mixing over other cilia micromixers as enabled by the high

  7. Freestanding bucky paper with high strength from multi-wall carbon nanotubes

    International Nuclear Information System (INIS)

    Li, Zhonglai; Xu, Ju; O'Byrne, Justin P.; Chen, Lan; Wang, Kaixue; Morris, Michael A.; Holmes, Justin D.

    2012-01-01

    Bucky papers have been investigated by some research groups, however, due to different qualities of carbon nanotubes used, various results of strength and electronic properties were reported in the literatures. In this article, the effects of carbon nanotubes synthesized over different catalysts on the qualities of bucky papers were systemically investigated. Multi-wall carbon nanotubes were synthesized over a series of MgO supported catalysts with different weight ratios of Mo and Co. As the ratios of Mo/Co in the catalysts were increased from 0 to 3, the yields of carbon nanotubes were enhanced from 7 wt% to 400 wt%. However, the yield enhancement of carbon nanotubes was achieved at the expense of higher proportion of structural defects within carbon nanotubes, which has been proved by Raman spectroscopy and thermogravimetry analysis. It was demonstrated that the tensile strength of bucky paper composed of numerous MCNTs bundles strongly depends on the structure of carbon nanotubes used. By optimizing reaction conditions, a bucky paper with high strain up to 15.36 MPa and electrical conductivity of 61.17 S cm −1 was obtained by Supercritical Fluid (SCF) drying technique. -- Highlights: ► Multi-wall carbon nanotube bucky paper. ► Structural defects of carbon nanotubes. ► CoMo catalyst. ► Tensile strength of bucky paper.

  8. High beta plasma confinement and neoclassical effects in a small aspect ratio reversed field pinch

    International Nuclear Information System (INIS)

    Hayase, K.; Sugimoto, H.; Ashida, H.

    2003-01-01

    The high β equilibrium and stability of a reversed field pinch (RFP) configuration with a small aspect ratio are theoretically studied. The equilibrium profile, high beta limit and the bootstrap current effect on those are calculated. The Mercier stable critical β decreases with 1/A, but β∼0.2 is permissible at A=2 with help of edge current profile modification. The effect of bootstrap current is evaluated for various pressure and current profiles and cross-sectional shapes of plasma by a self-consistent neoclassical PRSM equilibrium formulation. The high bootstrap current fraction (F bs ) increases the shear stabilization effect in the core region, which enhances significantly the stability β limit compared with that for the classical equilibrium. These features of small aspect ratio RFP, high β and high F bs , and a possibly easier access to the quasi-single helicity state beside the intrinsic compact structure are attractive for the feasible economical RFP reactor concept. (author)

  9. Fabrication of High-Aspect-Ratio 3D Hydrogel Microstructures Using Optically Induced Electrokinetics

    Directory of Open Access Journals (Sweden)

    Yi Li

    2016-04-01

    Full Text Available We present a rapid hydrogel polymerization and prototyping microfabrication technique using an optically induced electrokinetics (OEK chip, which is based on a non-UV hydrogel curing principle. Using this technique, micro-scale high-aspect-ratio three-dimensional polymer features with different geometric sizes can be fabricated within 1–10 min by projecting pre-defined visible light image patterns onto the OEK chip. This method eliminates the need for traditional photolithography masks used for patterning and fabricating polymer microstructures and simplifies the fabrication processes. This technique uses cross-link hydrogels, such as poly(ethylene glycol (PEG-diacrylate (PEGDA, as fabrication materials. We demonstrated that hydrogel micropillar arrays rapidly fabricated using this technique can be used as molds to create micron-scale cavities in PDMS (polydimethylsiloxane substrates. Furthermore, hollow, circular tubes with controllable wall thicknesses and high-aspect ratios can also be fabricated. These results show the potential of this technique to become a rapid prototyping technology for producing microfluidic devices. In addition, we show that rapid prototyping of three-dimensional suspended polymer structures is possible without any sacrificial etching process.

  10. High aspect ratio catalytic reactor and catalyst inserts therefor

    Science.gov (United States)

    Lin, Jiefeng; Kelly, Sean M.

    2018-04-10

    The present invention relates to high efficient tubular catalytic steam reforming reactor configured from about 0.2 inch to about 2 inch inside diameter high temperature metal alloy tube or pipe and loaded with a plurality of rolled catalyst inserts comprising metallic monoliths. The catalyst insert substrate is formed from a single metal foil without a central supporting structure in the form of a spiral monolith. The single metal foil is treated to have 3-dimensional surface features that provide mechanical support and establish open gas channels between each of the rolled layers. This unique geometry accelerates gas mixing and heat transfer and provides a high catalytic active surface area. The small diameter, high aspect ratio tubular catalytic steam reforming reactors loaded with rolled catalyst inserts can be arranged in a multi-pass non-vertical parallel configuration thermally coupled with a heat source to carry out steam reforming of hydrocarbon-containing feeds. The rolled catalyst inserts are self-supported on the reactor wall and enable efficient heat transfer from the reactor wall to the reactor interior, and lower pressure drop than known particulate catalysts. The heat source can be oxygen transport membrane reactors.

  11. Cause and Cure - Deterioration in Accuracy of CFD Simulations With Use of High-Aspect-Ratio Triangular Tetrahedral Grids

    Science.gov (United States)

    Chang, Sin-Chung; Chang, Chau-Lyan; Venkatachari, Balaji Shankar

    2017-01-01

    Traditionally high-aspect ratio triangular/tetrahedral meshes are avoided by CFD re-searchers in the vicinity of a solid wall, as it is known to reduce the accuracy of gradient computations in those regions and also cause numerical instability. Although for certain complex geometries, the use of high-aspect ratio triangular/tetrahedral elements in the vicinity of a solid wall can be replaced by quadrilateral/prismatic elements, ability to use triangular/tetrahedral elements in such regions without any degradation in accuracy can be beneficial from a mesh generation point of view. The benefits also carry over to numerical frameworks such as the space-time conservation element and solution element (CESE), where triangular/tetrahedral elements are the mandatory building blocks. With the requirement of the CESE method in mind, a rigorous mathematical framework that clearly identities the reason behind the difficulties in use of such high-aspect ratio triangular/tetrahedral elements is presented here. As will be shown, it turns out that the degree of accuracy deterioration of gradient computation involving a triangular element is hinged on the value of its shape factor Gamma def = sq sin Alpha1 + sq sin Alpha2 + sq sin Alpha3, where Alpha1; Alpha2 and Alpha3 are the internal angles of the element. In fact, it is shown that the degree of accuracy deterioration increases monotonically as the value of Gamma decreases monotonically from its maximal value 9/4 (attained by an equilateral triangle only) to a value much less than 1 (associated with a highly obtuse triangle). By taking advantage of the fact that a high-aspect ratio triangle is not necessarily highly obtuse, and in fact it can have a shape factor whose value is close to the maximal value 9/4, a potential solution to avoid accuracy deterioration of gradient computation associated with a high-aspect ratio triangular grid is given. Also a brief discussion on the extension of the current mathematical framework to the

  12. Leptothrix sp sheaths modified with iron oxide particles: Magnetically responsive, high aspect ratio functional material

    Czech Academy of Sciences Publication Activity Database

    Šafařík, Ivo; Angelova, R.; Baldíková, Eva; Pospišková, K.; Šafaříková, Miroslava

    2017-01-01

    Roč. 71, FEB (2017), s. 1342-1346 ISSN 0928-4931 R&D Projects: GA ČR(CZ) GA14-11516S; GA MŠk(CZ) LD14075 Institutional support: RVO:67179843 Keywords : removal * Leptothrix * Magnetic modification * Iron oxide * High aspect ratio material Subject RIV: EI - Biotechnology ; Bionics OBOR OECD: Environmental sciences (social aspects to be 5.7) Impact factor: 4.164, year: 2016

  13. Modeling and characterization of dielectrophoretically structured piezoelectric composites using piezoceramic particle inclusions with high aspect ratios

    Science.gov (United States)

    van den Ende, D. A.; Maier, R. A.; van Neer, P. L. M. J.; van der Zwaag, S.; Randall, C. A.; Groen, W. A.

    2013-01-01

    In this work, the piezoelectric properties at high electric fields of dielectrophoretically aligned PZT—polymer composites containing high aspect ratio particles (such as short fibers) are presented. Polarization and strain as a function of electric field are evaluated. The properties of the composites are compared to those of PZT-polymer composites with equiaxed particles, continuous PZT fiber-polymer composites, and bulk PZT ceramics. From high-field polarization and strain measurements, the effective field dependent permittivity and piezoelectric charge constant in the poling direction are determined for dielectrophoresis structured PZT-polymer composites, continuous PZT fiber-polymer composites, and bulk PZT ceramics. The changes in dielectric properties of the inclusions and the matrix at high fields influence the dielectric and piezoelectric properties of the composites. It is found that the permittivity and piezoelectric charge constants increase towards a maximum at an applied field of around 2.5-5 kV/mm. The electric field at which the maximum occurs depends on the aspect ratio and degree of alignment of the inclusions. Experimental values of d33 at low and high applied fields are compared to a model describing the composites as a continuous polymer matrix containing PZT particles of various aspect ratios arranged into chains. Thickness mode coupling factors were determined from measured impedance data using fitted equivalent circuit model simulations. The relatively high piezoelectric strain constants, voltage constants, and thickness coupling factors indicate that such aligned short fiber composites could be useful as flexible large area transducers.

  14. Effects of Conformal Nanoscale Coatings on Thermal Performance of Vertically Aligned Carbon Nanotubes.

    Science.gov (United States)

    Silvestri, Cinzia; Riccio, Michele; Poelma, René H; Jovic, Aleksandar; Morana, Bruno; Vollebregt, Sten; Irace, Andrea; Zhang, Guo Qi; Sarro, Pasqualina M

    2018-04-17

    The high aspect ratio and the porous nature of spatially oriented forest-like carbon nanotube (CNT) structures represent a unique opportunity to engineer a novel class of nanoscale assemblies. By combining CNTs and conformal coatings, a 3D lightweight scaffold with tailored behavior can be achieved. The effect of nanoscale coatings, aluminum oxide (Al 2 O 3 ) and nonstoichiometric amorphous silicon carbide (a-SiC), on the thermal transport efficiency of high aspect ratio vertically aligned CNTs, is reported herein. The thermal performance of the CNT-based nanostructure strongly depends on the achieved porosity, the coating material and its infiltration within the nanotube network. An unprecedented enhancement in terms of effective thermal conductivity in a-SiC coated CNTs has been obtained: 181% compared to the as-grown CNTs and Al 2 O 3 coated CNTs. Furthermore, the integration of coated high aspect ratio CNTs in an epoxy molding compound demonstrates that, next to the required thermal conductivity, the mechanical compliance for thermal interface applications can also be achieved through coating infiltration into foam-like CNT forests. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. A three-dimensional microelectrode array composed of vertically aligned ultra-dense carbon nanotube networks

    Science.gov (United States)

    Nick, C.; Yadav, S.; Joshi, R.; Schneider, J. J.; Thielemann, C.

    2015-07-01

    Electrodes based on carbon nanotubes are a promising approach to manufacture highly sensitive sensors with a low limit of signal detection and a high signal-to-noise ratio. This is achieved by dramatically increasing the electrochemical active surface area without increasing the overall geometrical dimensions. Typically, carbon nanotube electrodes are nearly planar and composed of randomly distributed carbon nanotube networks having a limited surface gain for a specific geometrical surface area. To overcome this limitation, we have introduced vertically aligned carbon nanotube (VACNT) networks as electrodes, which are arranged in a microelectrode pattern of 60 single electrodes. Each microelectrode features a very high aspect ratio of more than 300 and thus a dramatically increased surface area. These microelectrodes composed of VACNT networks display dramatically decreased impedance over the entire frequency range compared to planar microelectrodes caused by the enormous capacity increase. This is experimentally verified by electrochemical impedance spectroscopy and cyclic voltammetry.

  16. Fabrication of silicon-embedded low resistance high-aspect ratio planar copper microcoils

    Science.gov (United States)

    Syed Mohammed, Zishan Ali; Puiu, Poenar Daniel; Aditya, Sheel

    2018-01-01

    Low resistance is an important requirement for microcoils which act as a signal receiver to ensure low thermal noise during signal detection. High-aspect ratio (HAR) planar microcoils entrenched in blind silicon trenches have features that make them more attractive than their traditional counterparts employing electroplating through a patterned thick polymer or achieved through silicon vias. However, challenges met in fabrication of such coils have not been discussed in detail until now. This paper reports the realization of such HAR microcoils embedded in Si blind trenches, fabricated with a single lithography step by first etching blind trenches in the silicon substrate with an aspect ratio of almost 3∶1 and then filling them up using copper electroplating. The electroplating was followed by chemical wet etching as a faster way of removing excess copper than traditional chemical mechanical polishing. Electrical resistance was further reduced by annealing the microcoils. The process steps and challenges faced in the realization of such structures are reported here followed by their electrical characterization. The obtained electrical resistances are then compared with those of other similar microcoils embedded in blind vias.

  17. Nanomagnetic domains of chromium deposited on vertically-aligned carbon nanotubes

    International Nuclear Information System (INIS)

    Wright, Andrew C.; Faulkner, Michael K.; Harris, Robert C.; Goddard, Alex; Abbott, Andrew P.

    2012-01-01

    The drive to create ever smaller magnetic memory devices has led to the development of new nanomagnetic domains on surfaces. This paper reports the development of nano-chromium magnetic domains obtained using electrodeposition on vertically aligned carbon nanofibers arrays. Attempts to achieve this using conventional aqueous solutions were unsuccessful even after thin nickel underlayers were applied. The use of a novel electrolyte, a deep eutectic solvent, made from choline chloride: chromium (III) chloride enabled highly conformal overcoatings of chromium on individual bare carbon nanotubes to be obtained. Very high aspect ratio metal microstructures could be obtained by this novel technology. Magnetic imaging of the coated nanoarrays showed there to be clear magnetic character to the coating when the thin coatings were applied but this disappeared when the deposits were thicker and more contiguous. - Highlights: ► Nanoscale chromium deposited from non-aqueous electrolyte shows magnetic behavior. ► Vertically aligned carbon nanotubes conformally coated with chromium metal. ► Ionic liquid electrolyte superior to chromic acid for plating high aspect ratio structures.

  18. Nanomagnetic domains of chromium deposited on vertically-aligned carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Andrew C., E-mail: a.wright@glyndwr.ac.uk [Advanced Materials Research Laboratory, Materials Science Research Center, Glyndwr University, Wrexham LL11 2AW (United Kingdom); Faulkner, Michael K., E-mail: m.faulkner@manchester.ac.uk [Manchester Materials Science Centre, University of Manchester, Grosvenor Street, Manchester M13 9PL (United Kingdom); Harris, Robert C.; Goddard, Alex; Abbott, Andrew P., E-mail: apa1@le.ac.uk [Department of Chemistry, University of Leicester, Leicester LE1 7RH (United Kingdom)

    2012-12-15

    The drive to create ever smaller magnetic memory devices has led to the development of new nanomagnetic domains on surfaces. This paper reports the development of nano-chromium magnetic domains obtained using electrodeposition on vertically aligned carbon nanofibers arrays. Attempts to achieve this using conventional aqueous solutions were unsuccessful even after thin nickel underlayers were applied. The use of a novel electrolyte, a deep eutectic solvent, made from choline chloride: chromium (III) chloride enabled highly conformal overcoatings of chromium on individual bare carbon nanotubes to be obtained. Very high aspect ratio metal microstructures could be obtained by this novel technology. Magnetic imaging of the coated nanoarrays showed there to be clear magnetic character to the coating when the thin coatings were applied but this disappeared when the deposits were thicker and more contiguous. - Highlights: Black-Right-Pointing-Pointer Nanoscale chromium deposited from non-aqueous electrolyte shows magnetic behavior. Black-Right-Pointing-Pointer Vertically aligned carbon nanotubes conformally coated with chromium metal. Black-Right-Pointing-Pointer Ionic liquid electrolyte superior to chromic acid for plating high aspect ratio structures.

  19. Leptothrix sp sheaths modified with iron oxide particles: Magnetically responsive, high aspect ratio functional material

    Czech Academy of Sciences Publication Activity Database

    Šafařík, Ivo; Angelova, R.; Baldíková, E.; Pospíšková, K.; Šafaříková, Miroslava

    2017-01-01

    Roč. 71, February (2017), s. 1342-1346 ISSN 0928-4931 Institutional support: RVO:60077344 Keywords : Leptothrix * magnetic modification * iron oxide * high aspect ratio material Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Materials engineering Impact factor: 4.164, year: 2016

  20. Fabrication method to create high-aspect ratio pillars for photonic coupling of board level interconnects

    Science.gov (United States)

    Debaes, C.; Van Erps, J.; Karppinen, M.; Hiltunen, J.; Suyal, H.; Last, A.; Lee, M. G.; Karioja, P.; Taghizadeh, M.; Mohr, J.; Thienpont, H.; Glebov, A. L.

    2008-04-01

    An important challenge that remains to date in board level optical interconnects is the coupling between the optical waveguides on printed wiring boards and the packaged optoelectronics chips, which are preferably surface mountable on the boards. One possible solution is the use of Ball Grid Array (BGA) packages. This approach offers a reliable attachment despite the large CTE mismatch between the organic FR4 board and the semiconductor materials. Collimation via micro-lenses is here typically deployed to couple the light vertically from the waveguide substrate to the optoelectronics while allowing for a small misalignment between board and package. In this work, we explore the fabrication issues of an alternative approach in which the vertical photonic connection between board and package is governed by a micro-optical pillar which is attached both to the board substrate and to the optoelectronic chips. Such an approach allows for high density connections and small, high-speed detector footprints while maintaining an acceptable tolerance between board and package. The pillar should exhibit some flexibility and thus a high-aspect ratio is preferred. This work presents and compares different fabrication methods and applies different materials for such high-aspect ratio pillars. The different fabrication methods are: photolithography, direct laser writing and deep proton writing. The selection of optical materials that was investigated is: SU8, Ormocers, PU and a multifunctional acrylate polymer. The resulting optical pillars have diameters ranging from 20um up to 80um, with total heights ranging between 30um and 100um (symbol for micron). The aspect-ratio of the fabricated structures ranges from 1.5 to 5.

  1. Extremely high thermal conductivity anisotropy of double-walled carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Zhaoji Ma

    2017-06-01

    Full Text Available Based on molecular dynamics simulations, we reveal that double-walled carbon nanotubes can possess an extremely high anisotropy ratio of radial to axial thermal conductivities. The mechanism is basically the same as that for the high thermal conductivity anisotropy of graphene layers - the in-plane strong sp2 bonds lead to a very high intralayer thermal conductivity while the weak van der Waals interactions to a very low interlayer thermal conductivity. However, different from flat graphene layers, the tubular structures of carbon nanotubes result in a diameter dependent thermal conductivity. The smaller the diameter, the larger the axial thermal conductivity but the smaller the radial thermal conductivity. As a result, a DWCNT with a small diameter may have an anisotropy ratio of thermal conductivity significantly higher than that for graphene layers. The extremely high thermal conductivity anisotropy allows DWCNTs to be a promising candidate for thermal management materials.

  2. Cooperative simulation of lithography and topography for three-dimensional high-aspect-ratio etching

    Science.gov (United States)

    Ichikawa, Takashi; Yagisawa, Takashi; Furukawa, Shinichi; Taguchi, Takafumi; Nojima, Shigeki; Murakami, Sadatoshi; Tamaoki, Naoki

    2018-06-01

    A topography simulation of high-aspect-ratio etching considering transports of ions and neutrals is performed, and the mechanism of reactive ion etching (RIE) residues in three-dimensional corner patterns is revealed. Limited ion flux and CF2 diffusion from the wide space of the corner is found to have an effect on the RIE residues. Cooperative simulation of lithography and topography is used to solve the RIE residue problem.

  3. Ordered metal nanotube arrays fabricated by PVD.

    Science.gov (United States)

    Marquez, F; Morant, C; Campo, T; Sanz, J M; Elizalde, E

    2010-02-01

    In this work we report a simple method to fabricate ordered arrays of metal nanotubes. This method is based on the deposition of a metal by PVD onto an anodized aluminum oxide (AAO) template. The dimensions of the synthesized nanotubes depend both on the AAO template and on the deposited metal. In fact, it is observed that the aspect ratios of the nanotubes clearly depend significantly on the metal, ranging from 0.6 (Fe) to at least 3 (Zr).

  4. High-speed logic integrated circuits with solution-processed self-assembled carbon nanotubes.

    Science.gov (United States)

    Han, Shu-Jen; Tang, Jianshi; Kumar, Bharat; Falk, Abram; Farmer, Damon; Tulevski, George; Jenkins, Keith; Afzali, Ali; Oida, Satoshi; Ott, John; Hannon, James; Haensch, Wilfried

    2017-09-01

    As conventional monolithic silicon technology struggles to meet the requirements for the 7-nm technology node, there has been tremendous progress in demonstrating the scalability of carbon nanotube field-effect transistors down to the size that satisfies the 3-nm node and beyond. However, to date, circuits built with carbon nanotubes have overlooked key aspects of a practical logic technology and have stalled at simple functionality demonstrations. Here, we report high-performance complementary carbon nanotube ring oscillators using fully manufacturable processes, with a stage switching frequency of 2.82 GHz. The circuit was built on solution-processed, self-assembled carbon nanotube arrays with over 99.9% semiconducting purity, and the complementary feature was achieved by employing two different work function electrodes.

  5. High-speed logic integrated circuits with solution-processed self-assembled carbon nanotubes

    Science.gov (United States)

    Han, Shu-Jen; Tang, Jianshi; Kumar, Bharat; Falk, Abram; Farmer, Damon; Tulevski, George; Jenkins, Keith; Afzali, Ali; Oida, Satoshi; Ott, John; Hannon, James; Haensch, Wilfried

    2017-09-01

    As conventional monolithic silicon technology struggles to meet the requirements for the 7-nm technology node, there has been tremendous progress in demonstrating the scalability of carbon nanotube field-effect transistors down to the size that satisfies the 3-nm node and beyond. However, to date, circuits built with carbon nanotubes have overlooked key aspects of a practical logic technology and have stalled at simple functionality demonstrations. Here, we report high-performance complementary carbon nanotube ring oscillators using fully manufacturable processes, with a stage switching frequency of 2.82 GHz. The circuit was built on solution-processed, self-assembled carbon nanotube arrays with over 99.9% semiconducting purity, and the complementary feature was achieved by employing two different work function electrodes.

  6. Electron percolation in realistic models of carbon nanotube networks

    International Nuclear Information System (INIS)

    Simoneau, Louis-Philippe; Villeneuve, Jérémie; Rochefort, Alain

    2015-01-01

    The influence of penetrable and curved carbon nanotubes (CNT) on the charge percolation in three-dimensional disordered CNT networks have been studied with Monte-Carlo simulations. By considering carbon nanotubes as solid objects but where the overlap between their electron cloud can be controlled, we observed that the structural characteristics of networks containing lower aspect ratio CNT are highly sensitive to the degree of penetration between crossed nanotubes. Following our efficient strategy to displace CNT to different positions to create more realistic statistical models, we conclude that the connectivity between objects increases with the hard-core/soft-shell radii ratio. In contrast, the presence of curved CNT in the random networks leads to an increasing percolation threshold and to a decreasing electrical conductivity at saturation. The waviness of CNT decreases the effective distance between the nanotube extremities, hence reducing their connectivity and degrading their electrical properties. We present the results of our simulation in terms of thickness of the CNT network from which simple structural parameters such as the volume fraction or the carbon nanotube density can be accurately evaluated with our more realistic models

  7. Electron percolation in realistic models of carbon nanotube networks

    Science.gov (United States)

    Simoneau, Louis-Philippe; Villeneuve, Jérémie; Rochefort, Alain

    2015-09-01

    The influence of penetrable and curved carbon nanotubes (CNT) on the charge percolation in three-dimensional disordered CNT networks have been studied with Monte-Carlo simulations. By considering carbon nanotubes as solid objects but where the overlap between their electron cloud can be controlled, we observed that the structural characteristics of networks containing lower aspect ratio CNT are highly sensitive to the degree of penetration between crossed nanotubes. Following our efficient strategy to displace CNT to different positions to create more realistic statistical models, we conclude that the connectivity between objects increases with the hard-core/soft-shell radii ratio. In contrast, the presence of curved CNT in the random networks leads to an increasing percolation threshold and to a decreasing electrical conductivity at saturation. The waviness of CNT decreases the effective distance between the nanotube extremities, hence reducing their connectivity and degrading their electrical properties. We present the results of our simulation in terms of thickness of the CNT network from which simple structural parameters such as the volume fraction or the carbon nanotube density can be accurately evaluated with our more realistic models.

  8. Light emitting diode with high aspect ratio submicron roughness for light extraction and methods of forming

    Science.gov (United States)

    Li, Ting [Ventura, CA

    2011-04-26

    The surface morphology of an LED light emitting surface is changed by applying a reactive ion etch (RIE) process to the light emitting surface. High aspect ratio, submicron roughness is formed on the light emitting surface by transferring a thin film metal hard-mask having submicron patterns to the surface prior to applying a reactive ion etch process. The submicron patterns in the metal hard-mask can be formed using a low cost, commercially available nano-patterned template which is transferred to the surface with the mask. After subsequently binding the mask to the surface, the template is removed and the RIE process is applied for time duration sufficient to change the morphology of the surface. The modified surface contains non-symmetric, submicron structures having high aspect ratio which increase the efficiency of the device.

  9. Microscopic silicon-based lateral high-aspect-ratio structures for thin film conformality analysis

    International Nuclear Information System (INIS)

    Gao, Feng; Arpiainen, Sanna; Puurunen, Riikka L.

    2015-01-01

    Film conformality is one of the major drivers for the interest in atomic layer deposition (ALD) processes. This work presents new silicon-based microscopic lateral high-aspect-ratio (LHAR) test structures for the analysis of the conformality of thin films deposited by ALD and by other chemical vapor deposition means. The microscopic LHAR structures consist of a lateral cavity inside silicon with a roof supported by pillars. The cavity length (e.g., 20–5000 μm) and cavity height (e.g., 200–1000 nm) can be varied, giving aspect ratios of, e.g., 20:1 to 25 000:1. Film conformality can be analyzed with the microscopic LHAR by several means, as demonstrated for the ALD Al 2 O 3 and TiO 2 processes from Me 3 Al/H 2 O and TiCl 4 /H 2 O. The microscopic LHAR test structures introduced in this work expose a new parameter space for thin film conformality investigations expected to prove useful in the development, tuning and modeling of ALD and other chemical vapor deposition processes

  10. Injection molding of high aspect ratio sub-100 nm nanostructures

    DEFF Research Database (Denmark)

    Matschuk, Maria; Larsen, Niels B

    2013-01-01

    We have explored the use of mold coatings and optimized processing conditions to injection mold high aspect ratio nanostructures (height-to-width >1) in cyclic olefin copolymer (COC). Optimizing the molding parameters on uncoated nickel molds resulted in slight improvements in replication quality...... as described by height, width and uniformity of the nanoscopic features. Use of a mold temperature transiently above the polymer glass transition temperature (Tg) was the most important factor in increasing the replication fidelity. Surface coating of the nickel molds with a fluorocarbon-containing thin film...... (FDTS) greatly enhanced the quality of replicated features, in particular at transient mold temperatures above Tg. Injection molding using the latter mold temperature regime resulted in a bimodal distribution of pillar heights, corresponding to either full or very poor replication of the individual...

  11. Evaluation of a Candidate Trace Contaminant Control Subsystem Architecture: The High Velocity, Low Aspect Ratio (HVLA) Adsorption Process

    Science.gov (United States)

    Kayatin, Matthew J.; Perry, Jay L.

    2017-01-01

    Traditional gas-phase trace contaminant control adsorption process flow is constrained as required to maintain high contaminant single-pass adsorption efficiency. Specifically, the bed superficial velocity is controlled to limit the adsorption mass-transfer zone length relative to the physical adsorption bed; this is aided by traditional high-aspect ratio bed design. Through operation in this manner, most contaminants, including those with relatively high potential energy are readily adsorbed. A consequence of this operational approach, however, is a limited available operational flow margin. By considering a paradigm shift in adsorption architecture design and operations, in which flows of high superficial velocity are treated by low-aspect ratio sorbent beds, the range of well-adsorbed contaminants becomes limited, but the process flow is increased such that contaminant leaks or emerging contaminants of interest may be effectively controlled. To this end, the high velocity, low aspect ratio (HVLA) adsorption process architecture was demonstrated against a trace contaminant load representative of the International Space Station atmosphere. Two HVLA concept packaging designs (linear flow and radial flow) were tested. The performance of each design was evaluated and compared against computer simulation. Utilizing the HVLA process, long and sustained control of heavy organic contaminants was demonstrated.

  12. Correlation between MWCNT aspect ratio and the mechanical properties of composites of PMMA and MWCNTs

    Science.gov (United States)

    Mu, Mulan; Teblum, Eti; Figiel, Łukasz; Nessim, Gilbert Daniel; McNally, Tony

    2018-04-01

    The correlation between MWCNT aspect ratio and the quasi-static and dynamic mechanical properties of composites of MWCNTs and PMMA was studied for relatively long MWCNT lengths, in the range 0.3 mm to 5 mm (aspect ratios up to 5 × 105) and at low loading (0.15 wt%). The height of the MWCNTs prepared were modulated by controlling the amount of water vapour introduced in the reactor limiting Ostwald ripening of the catalyst, the formation of amorphous carbon and any increase in CNT diameter. The Tg of PMMA increased by up to 4 °C on addition of the longest tubes as they have the ability to form physical junctions with the polymer chains which lead to enhanced PMMA-MWCNTs interactions and increased mechanical properties, Young’s modulus by 20% on addition of 5 mm long MWCNTs. Predictions of the Young’s modulus of the composites of PMMA and MWCNT with the Mori-Tanaka theory show that future micromechanical models should account for MWCNT agglomeration and polymer-nanotube interactions as a function of CNT length.

  13. Synthesis and electroplating of high resolution insulated carbon nanotube scanning probes for imaging in liquid solutions.

    Science.gov (United States)

    Roberts, N A; Noh, J H; Lassiter, M G; Guo, S; Kalinin, S V; Rack, P D

    2012-04-13

    High resolution and isolated scanning probe microscopy (SPM) is in demand for continued development of energy storage and conversion systems involving chemical reactions at the nanoscale as well as an improved understanding of biological systems. Carbon nanotubes (CNTs) have large aspect ratios and, if leveraged properly, can be used to develop high resolution SPM probes. Isolation of SPM probes can be achieved by depositing a dielectric film and selectively etching at the apex of the probe. In this paper the fabrication of a high resolution and isolated SPM tip is demonstrated using electron beam induced etching of a dielectric film deposited onto an SPM tip with an attached CNT at the apex.

  14. Nanorobotic Manipulation Setup for Pick-and-Place Handling and non-destructive Characterization of Carbon Nanotubes

    DEFF Research Database (Denmark)

    Eicchorn, V.; Carlson, Kenneth; Andersen, Karin Nordström

    2007-01-01

    . The pick-and-place task is carried out by using an electrothermal actuated microgripper, designed for controlled manipulation of nanotubes. The nanotube is picked up from an array of multiwalled carbon nanotubes (MWCNTs) and transferred to the tip of an atomic force microscope (AFM) probe in order...... to assemble a high-aspect ratio AFM supertip. Another application of the nanorobotic setup considered in this paper is the nondestructive mechanical characterization of CNTs. A piezoresistive AFM probe is used to bend MWCNTs, while the bending force is measured, in order to estimate the Young's modulus...

  15. Geckolike high shear strength by carbon nanotube fiber adhesives

    Science.gov (United States)

    Maeno, Y.; Nakayama, Y.

    2009-01-01

    Carbon nanotube adhesives can adhere strongly to surfaces as a gecko does. The number of carbon nanotube layers is an important determinant of the contact area for adhesion. Balancing the catalyst ratio and buffer layer used for chemical vapor deposition processing controls the number of carbon nanotube layers and their distribution. The features of carbon nanotubes determine the shear strength of adhesion. Carbon nanotubes with a broad distribution of layers exhibit enhanced shear strength with equivalent adhesive capability to that of a natural Tokay Gecko (Gekko gecko)

  16. Halloysite nanotube-magnetic iron oxide nanoparticle hybrids for the rapid catalytic decomposition of pentachlorophenol

    NARCIS (Netherlands)

    Tsoufis, T.; Katsaros, F.; Kooi, B. J.; Bletsa, E.; Papageorgiou, S.; Deligiannakis, Y.; Panagiotopoulos, I.

    2017-01-01

    Halloysite clay are a very attractive class of alumino-silicate based, natural nanotubes possessing high aspect ratio, significant thermal and mechanical stability, as well as tunable surface chemistry. We report a novel, facile, synthetic approach involving a modified wet-impregnation method for

  17. Mechanical and electrical properties of low density polyethylene filled with carbon nanotubes

    International Nuclear Information System (INIS)

    Sabet, Maziyar; Soleimani, Hassan

    2014-01-01

    Carbon nanotubes (CNTs) reveal outstanding electrical and mechanical properties in addition to nanometer scale diameter and high aspect ratio, consequently, making it an ideal reinforcing agent for high strength polymer composites. Low density polyethylene (LDPE)/CNT composites were prepared via melt compounding. Mechanical and electrical properties of (LDPE)/CNT composites with different CNT contents were studied in this research

  18. Revealing properties of single-walled carbon nanotubes under high pressure

    CERN Document Server

    Tang Jie; Sasaki, T; Yudasaka, M; Matsushita, A; Iijima, S

    2002-01-01

    It was found by the x-ray diffraction experiment under hydrostatic pressure that the carbon nanotubes are compressed easily with a high volume compressibility of 0.024 GPa sup - sup 1. The single-walled carbon nanotubes are polygonized when they form bundles of hexagonal close-packed structure and the inter-tubular gap is smaller than the equilibrium spacing of graphite. Under high pressure, further polygonization occurs to accommodate the extra amount of volume reduction. The ratio of the short and the long diagonals in the hexagonalized cross section is found to have changed from 0.991 at zero pressure to 0.982 at 1.5 GPa pressure, when the Bragg reflection from the nanotube lattice diminished. Accompanying polygonization, a discontinuous change in electrical resistivity was observed at 1.5 GPa pressure, suggesting a phase transition had occurred.

  19. Fabrication of high aspect ratio micro electrode by using EDM

    International Nuclear Information System (INIS)

    Elsiti, Nagwa Mejid; Noordin, M.Y.; Alkali, Adam Umar

    2016-01-01

    The electrical discharge machining (EDM) process inherits characteristics that make it a promising micro-machining technique. Micro electrical discharge machining (micro- EDM) is a derived form of EDM, which is commonly used to manufacture micro and miniature parts and components by using the conventional electrical discharge machining fundamentals. Moving block electro discharge grinding (Moving BEDG) is one of the processes that can be used to fabricate micro-electrode. In this study, a conventional die sinker EDM machine was used to fabricate the micro-electrode. Modifications are made to the moving BEDG, which include changing the direction of movements and control gap in one electrode. Consequently current was controlled due to the use of roughing, semi-finishing and finishing parameters. Finally, a high aspect ratio micro-electrode with a diameter of 110.49μm and length of 6000μm was fabricated. (paper)

  20. Analytic free-form lens design for imaging applications with high aspect ratio

    Science.gov (United States)

    Duerr, Fabian; Benítez, Pablo; Miñano, Juan Carlos; Meuret, Youri; Thienpont, Hugo

    2012-10-01

    A new three-dimensional analytic optics design method is presented that enables the coupling of three ray sets with only two free-form lens surfaces. Closely related to the Simultaneous Multiple Surface method in three dimensions (SMS3D), it is derived directly from Fermat's principle, leading to multiple sets of functional differential equations. The general solution of these equations makes it possible to calculate more than 80 coefficients for each implicit surface function. Ray tracing simulations of these free-form lenses demonstrate superior imaging performance for applications with high aspect ratio, compared to conventional rotational symmetric systems.

  1. Development of a virtual probe tip with an application to high aspect ratio microscale features

    International Nuclear Information System (INIS)

    Bauza, Marcin B.; Hocken, Robert J.; Smith, Stuart T.; Woody, Shane C.

    2005-01-01

    Nondestructive measurement of microscale features remains a challenging metrology problem. For example, to assess a high aspect ratio small hole it is currently common to cut a cross section and measure the features of interest using an atomic force microscope, scanning probe microscope, or scanning electron microscope. Typically, these metrology tools may be suitable for surface finish measurement but often lack the capability for dimensional metrology. The aim of this article is to discuss the development of a high aspect-ratio microscale probe for measurement of microscale features. A 700:1 high aspect ratio probe shank is fabricated with a 7 μm diameter, and attached at one end to an oscillator. The oscillator produces a standing wave in the oscillating probe shank as opposed to conventional probes that use a microscale sphere on the end of a comparatively rigid shank. As a result of the standing wave formed in steady state vibration, the free end of the shank generates an amplitude of oscillation greater than the probe shank diameter. Thus, the probe does not require a spherical ball to serve as the contact point and simply uses the contact diameter of the free end of the vibrating shank. This methodology is referred to as a virtual probe tip. The virtual probe tip in conjunction with a nanopositioning scanner is used to measure surface profile measurements over traverse lengths of 130 μm. In this article, results from profiles of a 500 nm step height and a ruby sphere of diameter 1 mm are presented. Experiments in this article indicate the ability to repeatedly resolve surface features of less than 5 nm while maintaining bandwidths greater than 1 kHz. Furthermore, adhesion problems often encountered with micrometer scaled probes were not observed during profile measurements with this virtual probe

  2. High aspect ratio 10-nm-scale nanoaperture arrays with template-guided metal dewetting.

    Science.gov (United States)

    Wang, Ying Min; Lu, Liangxing; Srinivasan, Bharathi Madurai; Asbahi, Mohamed; Zhang, Yong Wei; Yang, Joel K W

    2015-04-10

    We introduce an approach to fabricate ordered arrays of 10-nm-scale silica-filled apertures in a metal film without etching or liftoff. Using low temperature (dewetting of metal films guided by nano-patterned templates, apertures with aspect ratios up to 5:1 are demonstrated. Apertures form spontaneously during the thermal process without need for further processing. Although the phenomenon of dewetting has been well studied, this is the first demonstration of its use in the fabrication of nanoapertures in a spatially controllable manner. In particular, the achievement of 10-nm length-scale patterning at high aspect ratio with thermal dewetting is unprecedented. By varying the nanotemplate design, we show its strong influence over the positions and sizes of the nanoapertures. In addition, we construct a three-dimensional phase field model of metal dewetting on nano-patterned substrates. The simulation data obtained closely corroborates our experimental results and reveals new insights to template dewetting at the nanoscale. Taken together, this fabrication method and simulation model form a complete toolbox for 10-nm-scale patterning using template-guided dewetting that could be extended to a wide range of material systems and geometries.

  3. Hydrotalcites: a highly efficient ecomaterial for effluent treatment originated from carbon nanotubes chemical processing

    Energy Technology Data Exchange (ETDEWEB)

    Alves, O L; Stefani, D; Parizotto, N V; Filho, A G Souza, E-mail: oalves@iqm.unicamp.br [Solid State Chemistry Laboratory, Institute of Chemistry, University of Campinas - UNICAMP, P. O. Box 6154, 13083-970, Campinas-SP (Brazil)

    2011-07-06

    It has been reported that a mixture of carboxylated carbonaceous fragments (CCFs), so called oxidation debris, are generated during carbon nanotubes chemical processing using oxidant agents such as HNO{sub 3}. The elimination of these fragments from carbon nanotubes surface has been point out to be a crucial step for an effective functionalization of the nanotubes as well as for improving the material. However, this process can introduce a potential environmental problem related water contamination because these CCFs can be viewed as a mixture of carbonaceous polyaromatic systems similar to humic substances and dissolved organic matter (DOM). The negative aspects of humic substances and DOM to water quality and wastewater treatment are well known. Since carbon nanotubes industry expands at high rates it is expected that effluent containing oxidation debris will increase since HNO{sub 3} chemical processing is the most applied method for purification and functionalization of carbon nanotubes. In this work, we have demonstrated that Hydrotalcites (HT) are highly efficient to remove oxidation debris from effluent solution originated from HNO{sub 3}-treated multiwalled carbon nanotubes. The strategy presented here is a contribution towards green chemistry practices and life cycle studies in carbon nanotubes field.

  4. Buckling of ZnS-filled single-walled carbon nanotubes – The influence of aspect ratio

    KAUST Repository

    Monteiro, André O.; Da Costa, Pedro M. F. J.; Cachim, Paulo B.; Holec, David

    2014-01-01

    The mechanical response of single-walled carbon nanotubes (SWCNT) filled with crystalline zinc sulphide (ZnS) nanowires under uniaxial compression is studied using classical molecular dynamics. These simulations were used to analyse the behaviour

  5. Thermal effect on transverse vibrations of double-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Zhang, Y Q; Liu, X; Liu, G R

    2007-01-01

    Based on the theory of thermal elasticity mechanics, a double-elastic beam model is developed for transverse vibrations of double-walled carbon nanotubes with large aspect ratios. The thermal effect is incorporated in the formulation. With this double-elastic beam model, explicit expressions are derived for natural frequencies and associated amplitude ratios of the inner to the outer tubes for the case of simply supported double-walled carbon nanotubes. The influence of temperature change on the properties of transverse vibrations is discussed. It is demonstrated that some properties of transverse vibrations of double-walled carbon nanotubes are dependent on the change of temperature

  6. High-aspect-ratio microstructures with versatile slanting angles on silicon by uniform metal-assisted chemical etching

    Science.gov (United States)

    Li, Liyi; Zhang, Cheng; Tuan, Chia-Chi; Chen, Yun; Wong, C.-P.

    2018-05-01

    High-aspect-ratio (HAR) microstructures on silicon (Si) play key roles in photonics and electromechanical devices. However, it has been challenging to fabricate HAR microstructures with slanting profiles. Here we report successful fabrication of uniform HAR microstructures with controllable slanting angles on (1 0 0)-Si by slanted uniform metal-assisted chemical etching (SUMaCE). The trenches have width of 2 µm, aspect ratio greater than 20:1 and high geometric uniformity. The slanting angles can be adjusted between 2-70° with respect to the Si surface normal. The results support a fundamental hypothesis that under the UMaCE condition, the preferred etching direction is along the normal of the thin film catalysts, regardless of the relative orientation of the catalyst to Si substrates or the crystalline orientation of the substrates. The SUMaCE method paves the way to HAR 3D microfabrication with arbitrary slanting profiles inside Si.

  7. Relationship between BaTiO₃ nanowire aspect ratio and the dielectric permittivity of nanocomposites.

    Science.gov (United States)

    Tang, Haixiong; Zhou, Zhi; Sodano, Henry A

    2014-04-23

    The aspect ratio of barium titanate (BaTiO3) nanowires is demonstrated to be successfully controlled by adjusting the temperature of the hydrothermal growth from 150 to 240 °C, corresponding to aspect ratios from 9.3 to 45.8, respectively. Polyvinylidene fluoride (PVDF) nanocomposites are formed from the various aspect ratio nanowires and the relationship between the dielectric constant of the nanocomposite and the aspect ratio of the fillers is quantified. It was found that the dielectric constant of the nanocomposite increases with the aspect ratio of the nanowires. Nanocomposites with 30 vol % BaTiO3 nanowires and an aspect ratio of 45.8 can reach a dielectric constant of 44.3, which is 30.7% higher than samples with an aspect ratio of 9.3 and 352% larger than the polymer matrix. These results demonstrate that using high-aspect-ratio nanowires is an effective way to control and improve the dielectric performance of nanocomposites for future capacitor applications.

  8. High-aspect ratio microstructures in p-type GaAs and InP created by proton beam writing

    International Nuclear Information System (INIS)

    Menzel, F.; Spemann, D.; Butz, T.

    2011-01-01

    With proton beam writing (PBW) and subsequent electrochemical etching in HF-solution the creation of high-aspect ratio microstructures in p-type InP was performed for the first time. Microstructures with high surface quality as well as high-aspect ratio possessing lateral dimensions down to 1 μm were produced. Furthermore, free-standing microstructures were created in this material by a combined irradiation with 2.25 MeV protons and 1.125 MeV H 2 + molecules, were the smallest structure dimension of 0.6 μm was achieved for a horizontal needle. The creation of nearly perfect circular microstructures indicates that the crystal structure has little effect on the structuring process by PBW in this material. Moreover, the effect of reduced etching inside of closed irradiation patterns, already known from Si and GaAs, was observed also in InP. In further PBW experiments and subsequent electrochemical etching with KOH-solution p-type GaAs microstructures were produced. By using a 4-fold higher etch current density of 45 mA/cm 2 compared to former PBW experiments on this material the quality of the microstructures could be improved significantly leading to high aspect-ratio structures with minimum lateral sizes of ∼1 μm, nearly vertical side walls as well as circular microstructures. This shows the reduced influence of the crystal structure on the shape of the microstructures compared to experiments with lower etch current density where only flat microstructures with inclined side walls determined by the crystal structure could be created.

  9. Fabrication of novel AFM probe with high-aspect-ratio ultra-sharp three-face silicon nitride tips

    NARCIS (Netherlands)

    Vermeer, Rolf; Berenschot, Johan W.; Sarajlic, Edin; Tas, Niels Roelof; Jansen, Henricus V.

    In this paper we present the wafer-scale fabrication of molded AFM probes with high aspect ratio ultra-sharp three-plane silicon nitride tips. Using $\\langle$111$\\rangle$ silicon wafers a dedicated process is developed to fabricate molds in the silicon wafer that have a flat triangular bottom

  10. A hypothetical model for predicting the toxicity of high aspect ratio nanoparticles (HARN)

    Science.gov (United States)

    Tran, C. L.; Tantra, R.; Donaldson, K.; Stone, V.; Hankin, S. M.; Ross, B.; Aitken, R. J.; Jones, A. D.

    2011-12-01

    The ability to predict nanoparticle (dimensional structures which are less than 100 nm in size) toxicity through the use of a suitable model is an important goal if nanoparticles are to be regulated in terms of exposures and toxicological effects. Recently, a model to predict toxicity of nanoparticles with high aspect ratio has been put forward by a consortium of scientists. The High aspect ratio nanoparticles (HARN) model is a platform that relates the physical dimensions of HARN (specifically length and diameter ratio) and biopersistence to their toxicity in biological environments. Potentially, this model is of great public health and economic importance, as it can be used as a tool to not only predict toxicological activity but can be used to classify the toxicity of various fibrous nanoparticles, without the need to carry out time-consuming and expensive toxicology studies. However, this model of toxicity is currently hypothetical in nature and is based solely on drawing similarities in its dimensional geometry with that of asbestos and synthetic vitreous fibres. The aim of this review is two-fold: (a) to present findings from past literature, on the physicochemical property and pathogenicity bioassay testing of HARN (b) to identify some of the challenges and future research steps crucial before the HARN model can be accepted as a predictive model. By presenting what has been done, we are able to identify scientific challenges and research directions that are needed for the HARN model to gain public acceptance. Our recommendations for future research includes the need to: (a) accurately link physicochemical data with corresponding pathogenicity assay data, through the use of suitable reference standards and standardised protocols, (b) develop better tools/techniques for physicochemical characterisation, (c) to develop better ways of monitoring HARN in the workplace, (d) to reliably measure dose exposure levels, in order to support future epidemiological

  11. A hypothetical model for predicting the toxicity of high aspect ratio nanoparticles (HARN)

    International Nuclear Information System (INIS)

    Tran, C. L.; Tantra, R.; Donaldson, K.; Stone, V.; Hankin, S. M.; Ross, B.; Aitken, R. J.; Jones, A. D.

    2011-01-01

    The ability to predict nanoparticle (dimensional structures which are less than 100 nm in size) toxicity through the use of a suitable model is an important goal if nanoparticles are to be regulated in terms of exposures and toxicological effects. Recently, a model to predict toxicity of nanoparticles with high aspect ratio has been put forward by a consortium of scientists. The High aspect ratio nanoparticles (HARN) model is a platform that relates the physical dimensions of HARN (specifically length and diameter ratio) and biopersistence to their toxicity in biological environments. Potentially, this model is of great public health and economic importance, as it can be used as a tool to not only predict toxicological activity but can be used to classify the toxicity of various fibrous nanoparticles, without the need to carry out time-consuming and expensive toxicology studies. However, this model of toxicity is currently hypothetical in nature and is based solely on drawing similarities in its dimensional geometry with that of asbestos and synthetic vitreous fibres. The aim of this review is two-fold: (a) to present findings from past literature, on the physicochemical property and pathogenicity bioassay testing of HARN (b) to identify some of the challenges and future research steps crucial before the HARN model can be accepted as a predictive model. By presenting what has been done, we are able to identify scientific challenges and research directions that are needed for the HARN model to gain public acceptance. Our recommendations for future research includes the need to: (a) accurately link physicochemical data with corresponding pathogenicity assay data, through the use of suitable reference standards and standardised protocols, (b) develop better tools/techniques for physicochemical characterisation, (c) to develop better ways of monitoring HARN in the workplace, (d) to reliably measure dose exposure levels, in order to support future epidemiological

  12. Key Techniques on Preparing High Aspect Ratio Micro and Nano Structures

    DEFF Research Database (Denmark)

    Jian, Zhao; Lianhe, Dong; Xiaoli, Zhu

    2016-01-01

    effectively. The mechanism of action between NaCl and HSQ was analyzed. The collapse and adhesion of resist structure due to the effect of gas-liquid interfacial capillary surface tension were suppressed by the CO2 supercritical drying method. Large-area dense nano-structures with the aspect ratio of 12...

  13. Oscillatory convection in low aspect ratio Czochralski melts

    Science.gov (United States)

    Anselmo, A.; Prasad, V.; Koziol, J.; Gupta, K. P.

    1993-11-01

    Modeling of the crucible in bulk crystal growth simulations as a right circular cylinder may be adequate for high aspect ratio melts but this may be unrealistic when the melt height is low. Low melt height is a unique feature of a solid feed continuous Czochralski growth process for silicon single crystals currently under investigation. At low melt heights, the crucible bottom curvature has a dampening effect on the buoyancy-induced oscillations, a source of inhomogeneities in the grown crystal. The numerical results demonstrate how the mode of convection changes from vertical wall-dominated recirculating flows to Benard convection as the aspect ratio is lowered. This phenomenon is strongly dependent on the boundary condition at the free surface of the melt, which has been generally considered to be either adiabatic or radiatively cooled. A comparison of the flow oscillations in crucibles with and without curved bottoms at aspect ratios in the range of 0.25 to 0.50, and at realistic Grashof numbers (10 7 < Gr < 10 8) illustrate that changing the shape of the crucible may be an effective means of suppressing oscillations and controlling the melt flow.

  14. Novel bamboo structured TiO2 nanotubes for energy storage/production applications

    Science.gov (United States)

    Samuel, J. J.; Beh, K. P.; Cheong, Y. L.; Yusuf, W. A. A.; Yam, F. K.

    2018-04-01

    Nanostructured TiO2 received much attention owing to its high surface-to-volume ratio, which can be advantageous in energy storage and production applications. However, the increase in energy consumption at present and possibly the foreseeable future has demanded energy storage and production devices of even higher performance. A direct approach would be manipulating the physical aspects of TiO2 nanostructures, particularly, nanotubes. In this work, dual voltage anodization system has been implemented to fabricate bamboo shaped TiO2 nanotubes, which offers even greater surface area. This unique nanostructure would be used in Dye Sensitized Solar Cell (DSSC) fabrication and its performance will be evaluated and compared along other forms of TiO2 nanotubes. The results showed that bamboo shaped nanotubes indeed are superior morphologically, with an increase of efficiency of 107% at 1.130% efficiency when compared to smooth walled nanotubes at 0.546% efficiency.

  15. Carbon nanotube based gecko inspired self-cleaning adhesives

    Science.gov (United States)

    Sethi, Sunny; Ge, Liehui; Ajayan, Pulickel; Ali, Dhinojwala

    2008-03-01

    Wall climbing organisms like geckos have unique ability to attach to different surfaces without use of any viscoelastic material. The hairy structure found in gecko feet allows them to obtain intimate contact over a large area thus allowing then to adhere using van der Waals interactions. Not only high adhesion, the geometry of the hairs makes gecko feet self cleaning, thus allowing them to walk continuously without worrying about loosing adhesive strength. Such properties if mimicked synthetically could form basis of a new class of materials, which, unlike conventional adhesives would show two contradictory properties, self cleaning and high adhesion. Such materials would form essential component of applications like wall climbing robot. We tried to synthesize such material using micropatterened vertically aligned carbon nanotubes. When dealing with large areas, probability of defects in the structure increase, forming patterns instead of using uniform film of carbon nanotubes helps to inhibit crack propagation, thus gives much higher adhesive strength than a uniform film. When carbon nanotube patterns with optimized aspect ratio are used, both high adhesion and self cleaning properties are observed.

  16. Growth of highly oriented carbon nanotubes by plasma-enhanced hot filament chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Z.P.; Xu, J.W.; Ren, Z.F.; Wang, J.H. [Materials Synthesis Laboratory, Departments of Physics and Chemistry, and Center for Advanced Photonic and Electronic Materials (CAPEM), State University of New York at Buffalo, Buffalo, New York 14260 (United States); Siegal, M.P.; Provencio, P.N. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States)

    1998-12-01

    Highly oriented, multiwalled carbon nanotubes were grown on polished polycrystalline and single crystal nickel substrates by plasma enhanced hot filament chemical vapor deposition at temperatures below 666 {degree}C. The carbon nanotubes range from 10 to 500 nm in diameter and 0.1 to 50 {mu}m in length depending on growth conditions. Acetylene is used as the carbon source for the growth of the carbon nanotubes and ammonia is used for dilution gas and catalysis. The plasma intensity, acetylene to ammonia gas ratio, and their flow rates, etc. affect the diameters and uniformity of the carbon nanotubes. {copyright} {ital 1998 American Institute of Physics.}

  17. Shear modulus and damping ratio of natural rubber containing carbon nanotubes

    Science.gov (United States)

    Ismail, R.; Ibrahim, A.; Rusop, M.; Adnan, A.

    2018-05-01

    This paper presents the results of an investigation into the potential application of Natural rubber (NR) containing Carbon Nanotubes (CNTs) by measuring its shear modulus and damping ratio. Four different types of rubber specimens which fabricated with different MWCNT loadings: 0 wt% (pure natural rubber), 1 wt%, 3 wt%, and 5 wt%. It is observed that the shear modulus and damping ratio of CNTs filled rubber composites are remarkably higher than that of raw rubber indicating the inherent reinforcing potential of CNTs.

  18. High performance transistors via aligned polyfluorene-sorted carbon nanotubes

    Science.gov (United States)

    Brady, Gerald J.; Joo, Yongho; Singha Roy, Susmit; Gopalan, Padma; Arnold, Michael S.

    2014-02-01

    We evaluate the performance of exceptionally electronic-type sorted, semiconducting, aligned single-walled carbon nanotubes (s-SWCNTs) in field effect transistors (FETs). High on-conductance and high on/off conductance modulation are simultaneously achieved at channel lengths which are both shorter and longer than individual s-SWCNTs. The s-SWCNTs are isolated from heterogeneous mixtures using a polyfluorene-derivative as a selective agent and aligned on substrates via dose-controlled, floating evaporative self-assembly at densities of ˜50 s-SWCNTs μm-1. At a channel length of 9 μm the s-SWCNTs percolate to span the FET channel, and the on/off ratio and charge transport mobility are 2.2 × 107 and 46 cm2 V-1 s-1, respectively. At a channel length of 400 nm, a large fraction of the s-SWCNTs directly span the channel, and the on-conductance per width is 61 μS μm-1 and the on/off ratio is 4 × 105. These results are considerably better than previous solution-processed FETs, which have suffered from poor on/off ratio due to spurious metallic nanotubes that bridge the channel. 4071 individual and small bundles of s-SWCNTs are tested in 400 nm channel length FETs, and all show semiconducting behavior, demonstrating the high fidelity of polyfluorenes as selective agents and the promise of assembling s-SWCNTs from solution to create high performance semiconductor electronic devices.

  19. Stable equilibria for bootstrap-current-driven low aspect ratio tokamaks

    International Nuclear Information System (INIS)

    Miller, R.L.; Lin-Liu, Y.R.; Turnbull, A.D.; Chan, V.S.; Pearlstein, L.D.; Sauter, O.; Villard, L.

    1997-01-01

    Low aspect ratio tokamaks (LATs) can potentially provide a high ratio of plasma pressure to magnetic pressure β and high plasma current I at a modest size. This opens up the possibility of a high-power density compact fusion power plant. For the concept to be economically feasible, bootstrap current must be a major component of the plasma current, which requires operating at high β p . A high value of the Troyon factor β N and strong shaping is required to allow simultaneous operation at a high-β and high bootstrap fraction. Ideal magnetohydrodynamic stability of a range of equilibria at aspect ratio 1.4 is systematically explored by varying the pressure profile and shape. The pressure and current profiles are constrained in such a way as to assure complete bootstrap current alignment. Both β N and β are defined in terms of the vacuum toroidal field. Equilibria with β N ≥8 and β∼35%endash 55% exist that are stable to n=∞ ballooning modes. The highest β case is shown to be stable to n=0,1,2,3 kink modes with a conducting wall. copyright 1997 American Institute of Physics

  20. High-aspect ratio micro- and nanostructures enabled by photo-electrochemical etching for sensing and energy harvesting applications

    Science.gov (United States)

    Alhalaili, Badriyah; Dryden, Daniel M.; Vidu, Ruxandra; Ghandiparsi, Soroush; Cansizoglu, Hilal; Gao, Yang; Saif Islam, M.

    2018-03-01

    Photo-electrochemical (PEC) etching can produce high-aspect ratio features, such as pillars and holes, with high anisotropy and selectivity, while avoiding the surface and sidewall damage caused by traditional deep reactive ion etching (DRIE) or inductively coupled plasma (ICP) RIE. Plasma-based techniques lead to the formation of dangling bonds, surface traps, carrier leakage paths, and recombination centers. In pursuit of effective PEC etching, we demonstrate an optical system using long wavelength (λ = 975 nm) infra-red (IR) illumination from a high-power laser (1-10 W) to control the PEC etching process in n-type silicon. The silicon wafer surface was patterned with notches through a lithography process and KOH etching. Then, PEC etching was introduced by illuminating the backside of the silicon wafer to enhance depth, resulting in high-aspect ratio structures. The effect of the PEC etching process was optimized by varying light intensities and electrolyte concentrations. This work was focused on determining and optimizing this PEC etching technique on silicon, with the goal of expanding the method to a variety of materials including GaN and SiC that are used in designing optoelectronic and electronic devices, sensors and energy harvesting devices.

  1. Control-surface hinge-moment calculations for a high-aspect-ratio supercritical wing

    Science.gov (United States)

    Perry, B., III

    1978-01-01

    The hinge moments, at selected flight conditions, resulting from deflecting two trailing edge control surfaces (one inboard and one midspan) on a high aspect ratio, swept, fuel conservative wing with a supercritical airfoil are estimated. Hinge moment results obtained from procedures which employ a recently developed transonic analysis are given. In this procedure a three dimensional inviscid transonic aerodynamics computer program is combined with a two dimensional turbulent boundary layer program in order to obtain an interacted solution. These results indicate that trends of the estimated hinge moment as a function of deflection angle are similar to those from experimental hinge moment measurements made on wind tunnel models with swept supercritical wings tested at similar values of free stream Mach number and angle of attack.

  2. Atomic structures and mechanical properties of single-crystal GaN nanotubes

    International Nuclear Information System (INIS)

    Xu, B.; Lu, A.J.; Pan, B.C.; Yu, Q.X.

    2005-01-01

    An approach is proposed to theoretically construct a realistic single-crystal GaN nanotube at atomic scale. The generated atomic structures of the single-crystal GaN nanotubes match the structural aspects from experiment very well. Our energetic calculations show that a single-crystal GaN nanotube with [100]-oriented lateral facets is more stable than that with [110]-oriented lateral facets, when they have around the same wall thickness. For a specified orientation of the lateral facets on the single-crystal GaN nanotubes, the energetic stabilities of the tubes obey a P rule, in which P is the ratio of the number of four-coordinated atoms to the number of three-coordinated atoms. Furthermore, the Young's modulus of the considered GaN nanotubes decrease with increasing the ratio of the number of bulk atoms to the number of surface atoms in each type of tube. Our calculations and analysis demonstrate that the surface effect of a single-crystal nanotube enhances its Young's modulus significantly

  3. Effect of tip vortices on membrane vibration of flexible wings with different aspect ratios

    Directory of Open Access Journals (Sweden)

    Genç Mustafa Serdar

    2016-01-01

    Full Text Available In this study, the effect of the aspect ratio on the aerodynamics characteristic of flexible membrane wings with different aspect ratios (AR = 1 and AR = 3 is experimentally investigated at Reynolds number of 25000. Time accurate measurements of membrane deformation using Digital Image Correlation system (DIC is carried out while normal forces of the wing will be measured by helping a load-cell system and flow on the wing was visualized by means of smoke wire technic. The characteristics of high aspect ratio wings are shown to be affected by leading edge separation bubbles at low Reynolds number. It is concluded that the camber of membrane wing excites the separated shear layer and this situation increases the lift coefficient relatively more as compared to rigid wings. In membrane wings with low aspect ratio, unsteadiness included tip vortices and vortex shedding, and the combination of tip vortices and vortex shedding causes complex unsteady deformations of these membrane wings. The characteristic of high aspect ratio wings was shown to be affected by leading edge separation bubbles at low Reynolds numbers whereas the deformations of flexible wing with low aspect ratio affected by tip vortices and leading edge separation bubbles.

  4. Electrochemical fabrication of Sn nanowires on titania nanotube guide layers

    International Nuclear Information System (INIS)

    Djenizian, Thierry; Hanzu, Ilie; Premchand, Yesudas D; Vacandio, Florence; Knauth, Philippe

    2008-01-01

    We describe a novel approach for the fabrication of tailored nanowires using a two-step electrochemical process. It is demonstrated that self-organized TiO 2 nanotubes can be used to activate and guide the electrochemical growth of Sn crystallites, leading to the formation of vertical features with a high aspect ratio. We show that the dimensions and the density of Sn crystallites depend on the electrodeposition parameters

  5. Hot embossing of photonic crystal polymer structures with a high aspect ratio

    DEFF Research Database (Denmark)

    Schelb, Mauno; Vannahme, Christoph; Kolew, Alexander

    2011-01-01

    ). A nickel tool for the replication of structures with lateral dimensions of 110 nm and heights of approximately 370 nm is fabricated via electroplating of a nanostructured sample resulting in an aspect ratio of approximately 3.5. The structures are subsequently hot embossed into PMMA and COC substrates....

  6. Calculation of stress intensity factors for circumferential semi-elliptical cracks with high aspect ratio in pipes

    International Nuclear Information System (INIS)

    Zareei, A.; Nabavi, S.M.

    2016-01-01

    In this paper, stress intensity factors are calculated at the deepest point of an internal circumferential semi-elliptical crack in a pipe subjected to any arbitrary load. Based on the three dimensional finite element analysis, a weight function is proposed for high aspect ratio semi-elliptical cracks in pipes. An effective expression is developed analytically to evaluate the stress intensity factor using the weight function method. For several crack face stress fields and welding residual stress distributions, the weight function is validated against finite element data and those in the literature. Based on the comparison results, it can be concluded that the solution proposed in this paper is effective in engineering applications. - Highlights: • Analysis of internal circumferential semi-elliptical cracks with high aspect ratio in pipes. • A weight function is proposed for the calculation of the stress intensity factors for the deepest point of the crack. • An effective closed form expression is proposed to evaluate the stress intensity factors. • Prediction of stress intensity factors for any applied stress gradients through the wall thickness without any limitations. • A three-dimensional finite element modeling employs to calculate the stress intensity factors for different geometries.

  7. High performance transistors via aligned polyfluorene-sorted carbon nanotubes

    International Nuclear Information System (INIS)

    Brady, Gerald J.; Joo, Yongho; Singha Roy, Susmit; Gopalan, Padma; Arnold, Michael S.

    2014-01-01

    We evaluate the performance of exceptionally electronic-type sorted, semiconducting, aligned single-walled carbon nanotubes (s-SWCNTs) in field effect transistors (FETs). High on-conductance and high on/off conductance modulation are simultaneously achieved at channel lengths which are both shorter and longer than individual s-SWCNTs. The s-SWCNTs are isolated from heterogeneous mixtures using a polyfluorene-derivative as a selective agent and aligned on substrates via dose-controlled, floating evaporative self-assembly at densities of ∼50 s-SWCNTs μm −1 . At a channel length of 9 μm the s-SWCNTs percolate to span the FET channel, and the on/off ratio and charge transport mobility are 2.2 × 10 7 and 46 cm 2  V −1  s −1 , respectively. At a channel length of 400 nm, a large fraction of the s-SWCNTs directly span the channel, and the on-conductance per width is 61 μS μm −1 and the on/off ratio is 4 × 10 5 . These results are considerably better than previous solution-processed FETs, which have suffered from poor on/off ratio due to spurious metallic nanotubes that bridge the channel. 4071 individual and small bundles of s-SWCNTs are tested in 400 nm channel length FETs, and all show semiconducting behavior, demonstrating the high fidelity of polyfluorenes as selective agents and the promise of assembling s-SWCNTs from solution to create high performance semiconductor electronic devices

  8. High performance transistors via aligned polyfluorene-sorted carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Brady, Gerald J.; Joo, Yongho; Singha Roy, Susmit; Gopalan, Padma; Arnold, Michael S., E-mail: msarnold@wisc.edu [Department of Materials Science and Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, Wisconsin 53706 (United States)

    2014-02-24

    We evaluate the performance of exceptionally electronic-type sorted, semiconducting, aligned single-walled carbon nanotubes (s-SWCNTs) in field effect transistors (FETs). High on-conductance and high on/off conductance modulation are simultaneously achieved at channel lengths which are both shorter and longer than individual s-SWCNTs. The s-SWCNTs are isolated from heterogeneous mixtures using a polyfluorene-derivative as a selective agent and aligned on substrates via dose-controlled, floating evaporative self-assembly at densities of ∼50 s-SWCNTs μm{sup −1}. At a channel length of 9 μm the s-SWCNTs percolate to span the FET channel, and the on/off ratio and charge transport mobility are 2.2 × 10{sup 7} and 46 cm{sup 2} V{sup −1} s{sup −1}, respectively. At a channel length of 400 nm, a large fraction of the s-SWCNTs directly span the channel, and the on-conductance per width is 61 μS μm{sup −1} and the on/off ratio is 4 × 10{sup 5}. These results are considerably better than previous solution-processed FETs, which have suffered from poor on/off ratio due to spurious metallic nanotubes that bridge the channel. 4071 individual and small bundles of s-SWCNTs are tested in 400 nm channel length FETs, and all show semiconducting behavior, demonstrating the high fidelity of polyfluorenes as selective agents and the promise of assembling s-SWCNTs from solution to create high performance semiconductor electronic devices.

  9. Analytical and numerical techniques for predicting the interfacial stresses of wavy carbon nanotube/polymer composites

    NARCIS (Netherlands)

    Yazdchi, K.; Salehi, M.; Shokrieh, M.M.

    2009-01-01

    By introducing a new simplified 3D representative volume element for wavy carbon nanotubes, an analytical model is developed to study the stress transfer in single-walled carbon nanotube-reinforced polymer composites. Based on the pull-out modeling technique, the effects of waviness, aspect ratio,

  10. The vortex structure and flux creep within superconducting permanent-magnet high aspect-ratio discs

    International Nuclear Information System (INIS)

    Watson, J.H.P.; Younas, I.

    1997-01-01

    Inhomogeneous type II superconducting discs magnetized by an applied field will retain some magnetization when field is switched off so the superconducting disc will behave as a permanent magnet after flux creep has reduced to a low value.This paper examines the superconducting vortex structure within superconducting permanent-magnet high aspect-ratio discs which is consistent with the calculated magnetic field distribution.The discs, with radius R, have the axis along the z-direction and the mid-plane of the disc corresponds to z = 0. These discs with large aspect ratios in the remnant state have a region between radius r l and R where the magnetic field is reversed. Surrounding the line r = r l and z = 0 there is a region where H cl which is in the Meissner state. Near r l the vortex lines are strongly curved. For radii r l vortex lines creep to larger values of r. For radii r > r l vortex lines creep to smaller values of r, meet at r l with vortex lines of opposite sign and form a continuous loop which decreases in size and is finally annihilated in the Meissner region. Flux creep induces lossless currents in the Meissner region. (author)

  11. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio.

    Science.gov (United States)

    Kruyt, Jan W; van Heijst, GertJan F; Altshuler, Douglas L; Lentink, David

    2015-04-06

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  12. High-aspect-ratio HfC nanobelts accompanied by HfC nanowires: Synthesis, characterization and field emission properties

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Song, E-mail: tiansong22@126.com [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China); School of Materials Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China); Zhang, Yulei; Ren, Jincui; Qiang, Xinfa; Zhang, Shouyang [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China); Li, Hejun, E-mail: lihejun@nwpu.edu.cn [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China)

    2017-04-30

    Highlights: • HfC naobelts accompanied by HfC nanowires were synthesized by a catalytic CVD method. • HfC nanobelts as a novel structure of HfC ceramic are reported for the first time. • HfC nanobelts have 100–200 μm in lengths and reach up to 10 μm in widths. • The synthesized product is promising field nanoemitters. - Abstract: As a key refractory carbide, hafnium carbide (HfC) is commonly used as structural materials while the field emission (FE) application of HfC in the field of vacuum microelectronics is almost the only one for functional material purposes. Based on its outstanding physical and chemical characteristics, HfC is identified as a potential candidate with satisfactory mechanical properties and long-term and/or high-temperature FE stability for future applications in high-performance field emitters. However, the development of HfC in various FE applications is hindered because it is not facile to fabricate large-scale low-dimensional HfC field nanoemitters. Herein, High-aspect-ratio HfC nanobelts accompanied by HfC nanowires were synthesized on a large scale by a traditional and simple catalytic chemical vapor deposition (CVD) method. Classical vapor–liquid–solid (VLS) theory was employed to explain the growth of the HfC nanowires and nanobelts along axial direction. The thin HfO{sub 2} shell and thin C layer surrounding the nanostructures might give rise to the diameter fluctuation of HfC nanowires and the width increase of HfC nanobelts in lateral direction. Field emission results show that the high-aspect-ratio HfC nanobelts accompanied by the nanowires are promising field nanoemitters, which exhibit excellent field emission properties with a fairly low turn-on field of ∼1.5 V μm{sup −1} and a low current fluctuation less than ∼10%. This suggests that HfC ceramics with high-aspect-ratio nanostructures are ideal cathode material for various field emission applications.

  13. Gas-Assisted Heating Technology for High Aspect Ratio Microstructure Injection Molding

    Directory of Open Access Journals (Sweden)

    Shia-Chung Chen

    2013-01-01

    Full Text Available A hot gas is used for heating the cavity surface of a mold. Different mold gap sizes were designed. The mold surface temperature was heated to above the glass transition temperature of the plastic material, and the mold then closed for melt filling. The cavity surface can be heated to 130°C to assist the melt filling of the microfeatures. Results show that hot gas heating can improve the filling process and achieve 91% of the high aspect ratio microgrooves (about 640.38 μm of the maximum of 700 μm. The mold gap size strongly affects the heating speed and heating uniformity. Without surface preheating, the center rib is the highest. When the heating target temperature is 90°C or 100°C, the three microribs have a good uniformity of height. However, when the target temperature exceeds 100°C, the left side rib is higher than the other ribs.

  14. Boron nitride nanotube-mediated stimulation modulates F/G-actin ratio and mechanical properties of human dermal fibroblasts

    Science.gov (United States)

    Ricotti, Leonardo; das Neves, Ricardo Pires; Ciofani, Gianni; Canale, Claudio; Nitti, Simone; Mattoli, Virgilio; Mazzolai, Barbara; Ferreira, Lino; Menciassi, Arianna

    2014-02-01

    F/G-actin ratio modulation is known to have an important role in many cell functions and in the regulation of specific cell behaviors. Several attempts have been made in the latest decades to finely control actin production and polymerization, in order to promote certain cell responses. In this paper we demonstrate the possibility of modulating F/G-actin ratio and mechanical properties of normal human dermal fibroblasts by using boron nitride nanotubes dispersed in the culture medium and by stimulating them with ultrasound transducers. Increasing concentrations of nanotubes were tested with the cells, without any evidence of cytotoxicity up to 10 μg/ml concentration of nanoparticles. Cells treated with nanoparticles and ultrasound stimulation showed a significantly higher F/G-actin ratio in comparison with the controls, as well as a higher Young's modulus. Assessment of Cdc42 activity revealed that actin nucleation/polymerization pathways, involving Rho GTPases, are probably influenced by nanotube-mediated stimulation, but they do not play a primary role in the significant increase of F/G-actin ratio of treated cells, such effect being mainly due to actin overexpression.

  15. Dipolar interaction in arrays of magnetic nanotubes

    International Nuclear Information System (INIS)

    Velázquez-Galván, Y; Martínez-Huerta, J M; Encinas, A; De La Torre Medina, J; Danlée, Y; Piraux, L

    2014-01-01

    The dipolar interaction field in arrays of nickel nanotubes has been investigated on the basis of expressions derived from the effective demagnetizing field of the assembly as well as magnetometry measurements. The model incorporates explicitly the wall thickness and aspect ratio, as well as the spatial order of the nanotubes. The model and experiment show that the interaction field in nanotubes is smaller than that in solid nanowires due to the packing fraction reduction in tubes related to their inner cavity. Finally, good agreement between the model and experiment is found for the variation of the interaction field as a function of the tube wall thickness. (paper)

  16. Electrochemical Deposition of Conformal and Functional Layers on High Aspect Ratio Silicon Micro/Nanowires.

    Science.gov (United States)

    Ozel, Tuncay; Zhang, Benjamin A; Gao, Ruixuan; Day, Robert W; Lieber, Charles M; Nocera, Daniel G

    2017-07-12

    Development of new synthetic methods for the modification of nanostructures has accelerated materials design advances to furnish complex architectures. Structures based on one-dimensional (1D) silicon (Si) structures synthesized using top-down and bottom-up methods are especially prominent for diverse applications in chemistry, physics, and medicine. Yet further elaboration of these structures with distinct metal-based and polymeric materials, which could open up new opportunities, has been difficult. We present a general electrochemical method for the deposition of conformal layers of various materials onto high aspect ratio Si micro- and nanowire arrays. The electrochemical deposition of a library of coaxial layers comprising metals, metal oxides, and organic/inorganic semiconductors demonstrate the materials generality of the synthesis technique. Depositions may be performed on wire arrays with varying diameter (70 nm to 4 μm), pitch (5 μ to 15 μ), aspect ratio (4:1 to 75:1), shape (cylindrical, conical, hourglass), resistivity (0.001-0.01 to 1-10 ohm/cm 2 ), and substrate orientation. Anisotropic physical etching of wires with one or more coaxial shells yields 1D structures with exposed tips that can be further site-specifically modified by an electrochemical deposition approach. The electrochemical deposition methodology described herein features a wafer-scale synthesis platform for the preparation of multifunctional nanoscale devices based on a 1D Si substrate.

  17. High Aspect Ratio Sub-15 nm Silicon Trenches From Block Copolymer Templates

    Science.gov (United States)

    Gu, Xiaodan; Liu, Zuwei; Gunkel, Ilja; Olynick, Deirdre; Russell, Thomas; University of Massachusetts Amherst Collaboration; Oxford Instrument Collaboration; Lawrence Berkeley National Lab Collaboration

    2013-03-01

    High-aspect-ratio sub-15 nm silicon trenches are fabricated directly from plasma etching of a block copolymer (BCP) mask. Polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) 40k-b-18k was spin coated and solvent annealed to form cylindrical structures parallel to the silicon substrate. The BCP thin film was reconstructed by immersion in ethanol and then subjected to an oxygen and argon reactive ion etching to fabricate the polymer mask. A low temperature ion coupled plasma with sulfur hexafluoride and oxygen was used to pattern transfer block copolymer structure to silicon with high selectivity (8:1) and fidelity. The silicon pattern was characterized by scanning electron microscopy and grazing incidence x-ray scattering. We also demonstrated fabrication of silicon nano-holes using polystyrene-b-polyethylene oxide (PS-b-PEO) using same methodology described above for PS-b-P2VP. Finally, we show such silicon nano-strucutre serves as excellent nano-imprint master template to pattern various functional materials like poly 3-hexylthiophene (P3HT).

  18. Inverse metal-assisted chemical etching produces smooth high aspect ratio InP nanostructures.

    Science.gov (United States)

    Kim, Seung Hyun; Mohseni, Parsian K; Song, Yi; Ishihara, Tatsumi; Li, Xiuling

    2015-01-14

    Creating high aspect ratio (AR) nanostructures by top-down fabrication without surface damage remains challenging for III-V semiconductors. Here, we demonstrate uniform, array-based InP nanostructures with lateral dimensions as small as sub-20 nm and AR > 35 using inverse metal-assisted chemical etching (I-MacEtch) in hydrogen peroxide (H2O2) and sulfuric acid (H2SO4), a purely solution-based yet anisotropic etching method. The mechanism of I-MacEtch, in contrast to regular MacEtch, is explored through surface characterization. Unique to I-MacEtch, the sidewall etching profile is remarkably smooth, independent of metal pattern edge roughness. The capability of this simple method to create various InP nanostructures, including high AR fins, can potentially enable the aggressive scaling of InP based transistors and optoelectronic devices with better performance and at lower cost than conventional etching methods.

  19. Fabrication of high-aspect-ratio nano structures using a nano x-ray shadow mask

    International Nuclear Information System (INIS)

    Kim, Yong Chul; Lee, Seung S

    2008-01-01

    This paper describes a novel method for the fabrication of high-aspect-ratio nano structures (HAR-nano structures) using a nano x-ray shadow mask and deep x-ray lithography (DXRL). The nano x-ray shadow mask is fabricated by depositing an x-ray absorber layer (Au, 3 µm) onto the back side of a nano shadow mask. The nano shadow mask is produced with nano-sized apertures whose dimensions are reduced to several tens of nanometers by the accumulation of low-stress silicon nitride (Si x N y ) using the LPCVD process on the shadow mask. A shadow mask containing apertures with a size of 1 µm is fabricated on a bulk micromachined Si x N y membrane. The thickness of an absorber layer must be in the range of several tens of micrometers in order to obtain a contrast of more than 100 for the conventional DXRL process at the Pohang Light Source (PLS). However, a 3 µm thick absorber layer can provide a sufficient contrast if the modified DXRL of the central beam-stop method is used, which blocks high-energy x-rays. A nano shadow mask with 30 nm sized apertures is fabricated and a nano x-ray shadow mask with 250 nm sized apertures is fabricated by depositing a 3 µm thick absorber layer on a nano shadow mask with 500 nm sized apertures. HAR-nano structures (circles with a diameter of 420 nm and lines with a width of 274 nm) with aspect ratios of over 10:1 on a 3.2 µm SU-8 are successfully fabricated by using the nano x-ray shadow mask and the central beam-stop method

  20. Microwave dynamics of high aspect ratio superconducting nanowires studied using self-resonance

    Science.gov (United States)

    Santavicca, Daniel F.; Adams, Jesse K.; Grant, Lierd E.; McCaughan, Adam N.; Berggren, Karl K.

    2016-06-01

    We study the microwave impedance of extremely high aspect ratio (length/width ≈ 5000) superconducting niobium nitride nanowires. The nanowires are fabricated in a compact meander geometry that is in series with the center conductor of a 50 Ω coplanar waveguide transmission line. The transmission coefficient of the sample is measured up to 20 GHz. At high frequency, a peak in the transmission coefficient is seen. Numerical simulations show that this is a half-wave resonance along the length of the nanowire, where the nanowire acts as a high impedance, slow wave transmission line. This resonance sets the upper frequency limit for these nanowires as inductive elements. Fitting simulations to the measured resonance enables a precise determination of the nanowire's complex sheet impedance at the resonance frequency. The real part is a measure of dissipation, while the imaginary part is dominated by kinetic inductance. We characterize the dependence of the sheet resistance and sheet inductance on both temperature and current and compare the results to recent theoretical predictions for disordered superconductors. These results can aid in the understanding of high frequency devices based on superconducting nanowires. They may also lead to the development of novel superconducting devices such as ultra-compact resonators and slow-wave structures.

  1. Template directed synthesis of plasmonic gold nanotubes with tunable IR absorbance.

    Science.gov (United States)

    Bridges, Colin R; Schon, Tyler B; DiCarmine, Paul M; Seferos, Dwight S

    2013-04-01

    A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates, as well as a wide range of other fields such as photo-thermal heating, permselective transport, catalysis, microfluidics, and electrochemical sensing. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening.

  2. Rapid prototyping of nanotube-based devices using topology-optimized microgrippers

    DEFF Research Database (Denmark)

    Sardan, Özlem; Eichhorn, Volkmar; Petersen, D.H.

    2008-01-01

    Nanorobotic handling of carbon nanotubes (CNTs) using microgrippers is one of the most promising approaches for the rapid characterization of the CNTs and also for the assembly of prototypic nanotube-based devices. In this paper, we present pick-and-place nanomanipulation of multi-walled CNTs...... in a rapid and a reproducible manner. We placed CNTs on copper TEM grids for structural analysis and on AFM probes for the assembly of AFM super-tips. We used electrothermally actuated polysilicon microgrippers designed using topology optimization in the experiments. The microgrippers are able to open...... with an amorphous carbon layer, which is locally removed at the contact points with the microgripper. The assembled AFM super-tips are used for AFM measurements of microstructures with high aspect ratios....

  3. Nitrogen in highly crystalline carbon nanotubes

    International Nuclear Information System (INIS)

    Ducati, C; Koziol, K; Stavrinadis, A; Friedrichs, S; Windle, A H; Midgley, P A

    2006-01-01

    Multiwall carbon nanotubes (MWCNTs) with an unprecedented degree of internal order were synthesised by chemical vapour deposition (CVD) adding a nitrogen-containing compound to the hydrocarbon feedstock. Ferrocene was used as the metal catalyst precursor. The remarkable crystallinity of these nanotubes lies both in the isochirality and in the crystallographic register of their walls, as demonstrated by electron diffraction and high resolution electron microscopy experiments. High resolution transmission electron microscopy analysis shows that the walls of the nanotubes consist of truncated stacked cones, instead of perfect cylinders, with a range of apex angles that appears to be related to the nitrogen concentration in the synthesis process. The structure of armchair, zigzag and chiral nanotubes is modelled and discussed in terms of density of topological defects, providing an interesting comparison with our microscopy experiments. A growth mechanism based on the interplay of base- and tip-growth is proposed to account for our experimental observations

  4. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

    NARCIS (Netherlands)

    Kruyt, J.W.; Heijst, Van G.F.; Altshuler, D.L.; Lentink, David

    2015-01-01

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle

  5. New Vehicle Detection Method with Aspect Ratio Estimation for Hypothesized Windows

    Directory of Open Access Journals (Sweden)

    Jisu Kim

    2015-12-01

    Full Text Available All kinds of vehicles have different ratios of width to height, which are called the aspect ratios. Most previous works, however, use a fixed aspect ratio for vehicle detection (VD. The use of a fixed vehicle aspect ratio for VD degrades the performance. Thus, the estimation of a vehicle aspect ratio is an important part of robust VD. Taking this idea into account, a new on-road vehicle detection system is proposed in this paper. The proposed method estimates the aspect ratio of the hypothesized windows to improve the VD performance. Our proposed method uses an Aggregate Channel Feature (ACF and a support vector machine (SVM to verify the hypothesized windows with the estimated aspect ratio. The contribution of this paper is threefold. First, the estimation of vehicle aspect ratio is inserted between the HG (hypothesis generation and the HV (hypothesis verification. Second, a simple HG method named a signed horizontal edge map is proposed to speed up VD. Third, a new measure is proposed to represent the overlapping ratio between the ground truth and the detection results. This new measure is used to show that the proposed method is better than previous works in terms of robust VD. Finally, the Pittsburgh dataset is used to verify the performance of the proposed method.

  6. Stability of highly shifted equilibria in a large aspect ratio low-field tokamak

    International Nuclear Information System (INIS)

    Gourdain, P.-A.; Leboeuf, J.-N.; Neches, R. Y.

    2007-01-01

    In the long run, the economics of fusion will dictate that reactors confine large plasma pressure rather efficiently. A possible route manifests itself as equilibria with large shift of the plasma magnetic axis. This shift compresses the flux surfaces on the outer part of the plasma, hereby increasing the allowable plasma pressure a machine can confine for a given toroidal magnetic field, which is the main cost of the device. As a first step toward a reactor, we propose investigating the stability of such configurations in a low magnetic field high aspect ratio machine. By focusing our arguments solely on the shape of the toroidal plasma current density profile we discuss the stability of highly shifted equilibria and their robustness to current profile variations that could occur in actual experiments. The evolution of the plasma parameters, as the beta poloidal is increased, is also examined to give a better understanding of the difference in performance between the various regimes

  7. Modeling and optimization of atomic layer deposition processes on vertically aligned carbon nanotubes.

    Science.gov (United States)

    Yazdani, Nuri; Chawla, Vipin; Edwards, Eve; Wood, Vanessa; Park, Hyung Gyu; Utke, Ivo

    2014-01-01

    Many energy conversion and storage devices exploit structured ceramics with large interfacial surface areas. Vertically aligned carbon nanotube (VACNT) arrays have emerged as possible scaffolds to support large surface area ceramic layers. However, obtaining conformal and uniform coatings of ceramics on structures with high aspect ratio morphologies is non-trivial, even with atomic layer deposition (ALD). Here we implement a diffusion model to investigate the effect of the ALD parameters on coating kinetics and use it to develop a guideline for achieving conformal and uniform thickness coatings throughout the depth of ultra-high aspect ratio structures. We validate the model predictions with experimental data from ALD coatings of VACNT arrays. However, the approach can be applied to predict film conformality as a function of depth for any porous topology, including nanopores and nanowire arrays.

  8. Interaction forces and conduction properties between multi wall carbon nanotube tips and Au(1 1 1)

    Energy Technology Data Exchange (ETDEWEB)

    Luna, M.; Pablo, P.J. de; Colchero, J.; Gomez-Herrero, J.; Baro, A.M.; Tokumoto, H.; Jarvis, S.P

    2003-07-15

    We have studied the interaction forces and electrical conduction properties arising between multiwall carbon nanotube tips and the Au(1 1 1) surface in air, by means of amplitude modulation scanning force microscopy, also called intermittent contact. We have centered our work on tips with metallic electronic structure and for the specific parameters used we have found a preliminary interaction range where there is no contact between tip and surface. Stable imaging in this non-contact range is possible with multiwall carbon nanotube tips. These tips have also been used to obtain simultaneous topographic and current maps of the surface. They show excellent properties as tips due to their high aspect ratio and durability, as a result of their elastic and non-reactive properties. Correspondingly, multiwall carbon nanotube tips allow high resolution local analysis of electrical conductivity on a nanometer scale.

  9. Random walks in nanotube composites: Improved algorithms and the role of thermal boundary resistance

    International Nuclear Information System (INIS)

    Duong, Hai M.; Papavassiliou, Dimitrios V.; Lee, Lloyd L.; Mullen, Kieran J.

    2005-01-01

    Random walk simulations of thermal walkers are used to study the effect of interfacial resistance on heat flow in randomly dispersed carbon nanotube composites. The adopted algorithm effectively makes the thermal conductivity of the nanotubes themselves infinite. The probability that a walker colliding with a matrix-nanotube interface reflects back into the matrix phase or crosses into the carbon nanotube phase is determined by the thermal boundary (Kapitza) resistance. The use of 'cold' and 'hot' walkers produces a steady state temperature profile that allows accurate determination of the thermal conductivity. The effects of the carbon nanotube orientation, aspect ratio, volume fraction, and Kapitza resistance on the composite effective conductivity are quantified

  10. High pressure synthesis of amorphous TiO2 nanotubes

    Directory of Open Access Journals (Sweden)

    Quanjun Li

    2015-09-01

    Full Text Available Amorphous TiO2 nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO2 nanotubes. The structural phase transitions of anatase TiO2 nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO2 nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO2 phase was revealed by high-resolution transmission electron microscopy (HRTEM study. In addition, the bulk modulus (B0 = 158 GPa of the anatase TiO2 nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa. We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO2 nanotubes.

  11. Plasma features and alpha particle transport in low-aspect ratio tokamak reactor

    International Nuclear Information System (INIS)

    Xu Qiang; Wang Shaojie

    1997-06-01

    The results of the experiment and theory from low-aspect ratio tokamak devices have proved that the MHD stability will be improved. Based on present plasma physics and extrapolation to reduced aspect ratio, the feature of physics of low-aspect ratio tokamak reactor is discussed primarily. Alpha particle confinement and loss in the self-justified low-aspect ratio tokamak reactor parameters and the effect of alpha particle confinement and loss for different aspect ratio are calculated. The results provide a reference for the feasible research of compact tokamak reactor. (9 refs., 2 figs., 3 tabs.)

  12. Dynamic Response of Functionally Graded Carbon Nanotube Reinforced Sandwich Plate

    Science.gov (United States)

    Mehar, Kulmani; Panda, Subrata Kumar

    2018-03-01

    In this article, the dynamic response of the carbon nanotube-reinforced functionally graded sandwich composite plate has been studied numerically with the help of finite element method. The face sheets of the sandwich composite plate are made of carbon nanotube- reinforced composite for two different grading patterns whereas the core phase is taken as isotropic material. The final properties of the structure are calculated using the rule of mixture. The geometrical model of the sandwich plate is developed and discretized suitably with the help of available shell element in ANSYS library. Subsequently, the corresponding numerical dynamic responses computed via batch input technique (parametric design language code in ANSYS) of ANSYS including Newmark’s integration scheme. The stability of the sandwich structural numerical model is established through the proper convergence study. Further, the reliability of the sandwich model is checked by comparison study between present and available results from references. As a final point, some numerical problems have been solved to examine the effect of different design constraints (carbon nanotube distribution pattern, core to face thickness ratio, volume fractions of the nanotube, length to thickness ratio, aspect ratio and constraints at edges) on the time-responses of sandwich plate.

  13. Facile fabrication of self-assembled polyaniline nanotubes doped with D-tartaric acid for high-performance supercapacitors

    Science.gov (United States)

    Mu, Jingjing; Ma, Guofu; Peng, Hui; Li, Jiajia; Sun, Kanjun; Lei, Ziqiang

    2013-11-01

    Polyaniline (PANI) nanotubes with outstanding electrochemical properties have been successfully synthesized via a simple chemical template-free method in the presence of D-tartaric acid (D-TA) as the dopant, and ammonium persulfate ((NH4)2S2O8) as the oxidant. The morphologies and structures of PANI-(D-TA) with different [D-TA]/[aniline] molar ratios are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD). To assess the electrochemical properties of PANI-(D-TA) materials, cyclic voltammetry (CV) and galvanostatic charging-discharging measurements are performed. The PANI-(D-TA) nanotubes electrode, with [D-TA]/[aniline] molar ratio of 1:1, exhibits larger specific capacitance (as high as 625 F g-1 at 1 A g-1) and higher capacitance retention (77% of its initial capacitance after 500 cycles) in 1 M H2SO4 aqueous solution. The remarkable electrochemical characteristics of PANI-(D-TA) are mainly attributed to their unique nanotubular structures, which provide a high electrode/electrolyte contact area and short ions diffusion path. These novel PANI-(D-TA) nanotubes will be promising electrode materials for high-performance supercapacitors.

  14. Progress in nanoscale dry processes for fabrication of high-aspect-ratio features: How can we control critical dimension uniformity at the bottom?

    Science.gov (United States)

    Ishikawa, Kenji; Karahashi, Kazuhiro; Ishijima, Tatsuo; Cho, Sung Il; Elliott, Simon; Hausmann, Dennis; Mocuta, Dan; Wilson, Aaron; Kinoshita, Keizo

    2018-06-01

    In this review, we discuss the progress of emerging dry processes for nanoscale fabrication of high-aspect-ratio features, including emerging design technology for manufacturability. Experts in the fields of plasma processing have contributed to addressing the increasingly challenging demands of nanoscale deposition and etching technologies for high-aspect-ratio features. The discussion of our atomic-scale understanding of physicochemical reactions involving ion bombardment and neutral transport presents the major challenges shared across the plasma science and technology community. Focus is placed on advances in fabrication technology that control surface reactions on three-dimensional features, as well as state-of-the-art techniques used in semiconductor manufacturing with a brief summary of future challenges.

  15. Carbon nanotube/carbon nanotube composite AFM probes prepared using ion flux molding

    Science.gov (United States)

    Chesmore, Grace; Roque, Carrollyn; Barber, Richard

    The performance of carbon nanotube-carbon nanotube composite (CNT/CNT composite) atomic force microscopy (AFM) probes is compared to that of conventional Si probes in AFM tapping mode. The ion flux molding (IFM) process, aiming an ion beam at the CNT probe, aligns the tip to a desired angle. The result is a relatively rigid tip that is oriented to offset the cantilever angle. Scans using these probes reveal an improvement in image accuracy over conventional tips, while allowing higher aspect ratio imaging of 3D surface features. Furthermore, the lifetimes of CNT-CNT composite tips are observed to be longer than both conventional tips and those claimed for other CNT technologies. Novel applications include the imaging of embiid silk. Supported by the Clare Boothe Luce Research Scholars Award and Carbon Design Innovations.

  16. Carbon Nanotubes Filled with Different Ferromagnetic Alloys Affect the Growth and Development of Rice Seedlings by Changing the C:N Ratio and Plant Hormones Concentrations.

    Science.gov (United States)

    Hao, Yi; Yu, Feifan; Lv, Ruitao; Ma, Chuanxin; Zhang, Zetian; Rui, Yukui; Liu, Liming; Cao, Weidong; Xing, Baoshan

    2016-01-01

    The aim of this study was to investigate the phytotoxicity of thin-walled carbon nanotubes (CNTs) to rice (Oryza sativa L.) seedlings. Three different CNTs, including hollow multi-walled carbon nanotubes (MWCNTs), Fe-filled carbon nanotubes (Fe-CNTs), and Fe-Co-filled carbon nanotubes (FeCo-CNTs), were evaluated. The CNTs significantly inhibited rice growth by decreasing the concentrations of endogenous plant hormones. The carbon to nitrogen ratio (C:N ratio) significantly increased in rice roots after treatments with CNTs, and all three types of CNTs had the same effects on the C:N ratio. Interestingly, the increase in the C:N ratio in roots was largely because of decreased N content, indicating that the CNTs significantly decreased N assimilation. Analyses of the Fe and Co contents in plant tissues, transmission electron microscope (TEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis proved that the CNTs could penetrate the cell wall and the cell membrane, and then enter the root cells. According to the author's knowledge, this is the first time to study the relationship between carbon nanotubes and carbon nitrogen ratio and plant hormones.

  17. SIP Shear Walls: Cyclic Performance of High-Aspect-Ratio Segments and Perforated Walls

    Science.gov (United States)

    Vladimir Kochkin; Douglas R. Rammer; Kevin Kauffman; Thomas Wiliamson; Robert J. Ross

    2015-01-01

    Increasing stringency of energy codes and the growing market demand for more energy efficient buildings gives structural insulated panel (SIP) construction an opportunity to increase its use in commercial and residential buildings. However, shear wall aspect ratio limitations and lack of knowledge on how to design SIPs with window and door openings are barriers to the...

  18. Solution Process Synthesis of High Aspect Ratio ZnO Nanorods on Electrode Surface for Sensitive Electrochemical Detection of Uric Acid

    Science.gov (United States)

    Ahmad, Rafiq; Tripathy, Nirmalya; Ahn, Min-Sang; Hahn, Yoon-Bong

    2017-04-01

    This study demonstrates a highly stable, selective and sensitive uric acid (UA) biosensor based on high aspect ratio zinc oxide nanorods (ZNRs) vertical grown on electrode surface via a simple one-step low temperature solution route. Uricase enzyme was immobilized on the ZNRs followed by Nafion covering to fabricate UA sensing electrodes (Nafion/Uricase-ZNRs/Ag). The fabricated electrodes showed enhanced performance with attractive analytical response, such as a high sensitivity of 239.67 μA cm-2 mM-1 in wide-linear range (0.01-4.56 mM), rapid response time (~3 s), low detection limit (5 nM), and low value of apparent Michaelis-Menten constant (Kmapp, 0.025 mM). In addition, selectivity, reproducibility and long-term storage stability of biosensor was also demonstrated. These results can be attributed to the high aspect ratio of vertically grown ZNRs which provides high surface area leading to enhanced enzyme immobilization, high electrocatalytic activity, and direct electron transfer during electrochemical detection of UA. We expect that this biosensor platform will be advantageous to fabricate ultrasensitive, robust, low-cost sensing device for numerous analyte detection.

  19. Analysis of high aspect ratio jet flap wings of arbitrary geometry.

    Science.gov (United States)

    Lissaman, P. B. S.

    1973-01-01

    Paper presents a design technique for rapidly computing lift, induced drag, and spanwise loading of unswept jet flap wings of arbitrary thickness, chord, twist, blowing, and jet angle, including discontinuities. Linear theory is used, extending Spence's method for elliptically loaded jet flap wings. Curves for uniformly blown rectangular wings are presented for direct performance estimation. Arbitrary planforms require a simple computer program. Method of reducing wing to equivalent stretched, twisted, unblown planform for hand calculation is also given. Results correlate with limited existing data, and show lifting line theory is reasonable down to aspect ratios of 5.

  20. Mechanisms involved in the hydrothermal growth of ultra-thin and high aspect ratio ZnO nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Demes, Thomas [Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, F-38000 Grenoble (France); Ternon, Céline, E-mail: celine.ternon@grenoble-inp.fr [Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, F-38000 Grenoble (France); Univ. Grenoble Alpes, CNRS, LTM, F-38000 Grenoble (France); Morisot, Fanny [Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, F-38000 Grenoble (France); Univ. Grenoble Alpes, CNRS, Grenoble-INP" 2, IMEP-LaHC, F-38000 Grenoble (France); Riassetto, David [Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, F-38000 Grenoble (France); Legallais, Maxime [Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, F-38000 Grenoble (France); Univ. Grenoble Alpes, CNRS, Grenoble-INP" 2, IMEP-LaHC, F-38000 Grenoble (France); Roussel, Hervé; Langlet, Michel [Univ. Grenoble Alpes, CNRS, Grenoble-INP, LMGP, F-38000 Grenoble (France)

    2017-07-15

    Highlights: • ZnO nanowires are grown on sol-gel ZnO seed layers by hydrothermal synthesis. • Ultra-thin and high aspect ratio nanowires are obtained without using additives. • Nanowire diameter is 20–25 nm regardless of growth time and seed morphology. • A nanowire growth model is developed on the basis of thermodynamic considerations. • The nanowires are intended for integration into electrically conductive nanonets. - Abstract: Hydrothermal synthesis of ZnO nanowires (NWs) with tailored dimensions, notably high aspect ratios (AR) and small diameters, is a major concern for a wide range of applications and still represents a challenging and recurring issue. In this work, an additive-free and reproducible hydrothermal procedure has been developed to grow ultra-thin and high AR ZnO NWs on sol-gel deposited ZnO seed layers. Controlling the substrate temperature and using a low reagent concentration (1 mM) has been found to be essential for obtaining such NWs. We show that the NW diameter remains constant at about 20–25 nm with growth time contrary to the NW length that can be selectively increased leading to NWs with ARs up to 400. On the basis of investigated experimental conditions along with thermodynamic and kinetic considerations, a ZnO NW growth mechanism has been developed which involves the formation and growth of nuclei followed by NW growth when the nuclei reach a critical size of about 20–25 nm. The low reagent concentration inhibits NW lateral growth leading to ultra-thin and high AR NWs. These NWs have been assembled into electrically conductive ZnO nanowire networks, which opens attractive perspectives toward the development of highly sensitive low-cost gas- or bio-sensors.

  1. Application of carbon nanotubes flexible strain sensor in smart textiles

    Directory of Open Access Journals (Sweden)

    Qiong CHENG

    2017-10-01

    Full Text Available Smart textiles have not only the necessary functions of daily wear, but also the intelligence. The focus of the current textile materials research is the selection of flexible material. For flexible materials, carbon material is one of the ideal materials for preparing flexible strain gauges. The application of flexible strain sensor prepared by carbon nanotubes as a flexible material in smart textiles is the research content. The research status of carbon nanotubes flexible strain sensor is introduced from the aspects of the structure, properties and application. The characteristics and functions of flexible strain gages prepared with carbon nanotube fibers and carbon nanotube films as flexible materials are discussed in terms of selection, preparation method, performance test and application. At the same time, the advantages and disadvantages of the flexible strain sensor of carbon nanotubes are reviewed from the aspects of preparation difficulty, production cost and practical application effect. High sensitivity with high strain will be a key research direction for carbon nanotube flexible strain sensors.

  2. Water entry of cylindrical bodies with various aspect ratios

    Science.gov (United States)

    Kim, Nayoung; Park, Hyungmin

    2017-11-01

    We experimentally investigate the water entry of cylindrical bodies with different aspect ratio (1.0-8.0), focusing on the deformation of free surface and resulting phenomena over and under the surface. The experiment is performed using a high-speed imaging (upto 10000 fps) and PIV. The head and tail of bodies are hemispherical and the nose part is additionally roughened with a sandpaper to see the effect of roughness as well. The release height is also adjusted to change the impact velocity at the free surface (Reynolds number is order of 105). For smooth surface (without cavity formation), a thin liquid film rises up the body after impacting, gathers at the pole and forms a jet over the free surfaces. The jet is created in the form of a thick and thin jet. The thin jet is produced by a water film riding up the surface of an object, and a thick jet is produced by rising water from underwater as the object sinks. However, as the aspect ratio increases, the liquid film does not fully ride up the body and cannot close, so there is an empty space below the free surface. With roughness (with cavity), the liquid film is detached from the body and splash/dome is formed above the free surface. The splash height and its collapsing time decrease with increasing the aspect ratio. Supported by Grants (MPSS-CG-2016-02, NRF-2017R1A4A1015523) of the Korea government.

  3. Electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes: FFT-impedance spectroscopy of the growth process and magnetic properties.

    Science.gov (United States)

    Gerngross, Mark-Daniel; Carstensen, Jürgen; Föll, Helmut

    2014-01-01

    The electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes has been investigated by fast Fourier transform-impedance spectroscopy (FFT-IS) in the frequency range from 75 Hz to 18.5 kHz. The impedance data could be fitted very well using an electric circuit equivalent model with a series resistance connected in series to a simple resistor-capacitor (RC) element and a Maxwell element. Based on the impedance data, the Co deposition in ultra-high aspect ratio InP membranes can be divided into two different Co deposition processes. The corresponding share of each process on the overall Co deposition can be determined directly from the transfer resistances of the two processes. The impedance data clearly show the beneficial impact of boric acid on the Co deposition and also indicate a diffusion limitation of boric acid in ultra-high aspect ratio InP membranes. The grown Co nanowires are polycrystalline with a very small grain size. They show a narrow hysteresis loop with a preferential orientation of the easy magnetization direction along the long nanowire axis due to the arising shape anisotropy of the Co nanowires.

  4. High aspect ratio micro tool manufacturing for polymer replication using mu EDM of silicon, selective etching and electroforming

    DEFF Research Database (Denmark)

    Tosello, Guido; Bissacco, Giuliano; Tang, Peter Torben

    2008-01-01

    Mass fabrication of polymer micro components with high aspect ratio micro-structures requires high performance micro tools allowing the use of low cost replication processes such as micro injection moulding. In this regard an innovative process chain, based on a combination of micro electrical di...... discharge machining (mu EDM) of a silicon substrate, electroforming and selective etching was used for the manufacturing of a micro tool. The micro tool was employed for polymer replication by means of the injection moulding process....

  5. Effects of aspect ratio and specimen size on uniaxial failure stress of iron green bodies at high strain rates

    Directory of Open Access Journals (Sweden)

    Kuroyanagi Yuki

    2015-01-01

    Full Text Available Powder metallurgy is used for the production of a number of mechanical parts and is an essential production method. These are great advantages such as product cost effectiveness and product uniqueness. In general, however parts created by powder metallurgy have low strength because of low density. In order to increase strength as well as density, new techniques such as high-velocity-compaction (HVC was developed and further investigation has been conducted on improvement of techniques and optimum condition using computer simulation. In this study, the effects of aspect ratio and specimen size of iron green bodies on failure strength of uniaxial compression and failure behavior were examined using a split Hopkinson pressure Bar. The diameters of specimens were 12.5 mm and 25 mm the aspect ratios (thickness/diameter were 0.8 and 1.2.

  6. High frequency conductivity in carbon nanotubes

    Directory of Open Access Journals (Sweden)

    S. S. Abukari

    2012-12-01

    Full Text Available We report on theoretical analysis of high frequency conductivity in carbon nanotubes. Using the kinetic equation with constant relaxation time, an analytical expression for the complex conductivity is obtained. The real part of the complex conductivity is initially negative at zero frequency and become more negative with increasing frequency, until it reaches a resonance minimum at ω ∼ ωB for metallic zigzag CNs and ω < ωB for armchair CNs. This resonance enhancement is indicative for terahertz gain without the formation of current instabilities induced by negative dc conductivity. We noted that due to the high density of states of conduction electrons in metallic zigzag carbon nanotubes and the specific dispersion law inherent in hexagonal crystalline structure result in a uniquely high frequency conductivity than the corresponding values for metallic armchair carbon nanotubes. We suggest that this phenomenon can be used to suppress current instabilities that are normally associated with a negative dc differential conductivity.

  7. Sacrificial structures for deep reactive ion etching of high-aspect ratio kinoform silicon x-ray lenses

    DEFF Research Database (Denmark)

    Stöhr, Frederik; Michael-Lindhard, Jonas; Hübner, Jörg

    2015-01-01

    This article describes the realization of complex high-aspect ratio silicon structures with feature dimensions from 100 lm to 100nm by deep reactive ion etching using the Bosch process. As the exact shape of the sidewall profiles can be crucial for the proper functioning of a device, the authors...... of the sacrificial structures was accomplished by thermal oxidation and subsequent selective wet etching. The effects of the dimensions and relative placement of sacrificial walls and pillars on the etching result were determined through systematic experiments. The authors applied this process for exact sidewall...

  8. The elastic buckling of super-graphene and super-square carbon nanotube networks

    International Nuclear Information System (INIS)

    Li Ying; Qiu Xinming; Yin Yajun; Yang Fan; Fan Qinshan

    2010-01-01

    The super-graphene (SG) and super-square (SS) carbon nanotube network are built by the straight single-walled carbon nanotubes and corresponding junctions. The elastic buckling behaviors of these carbon nanotube networks under different boundary conditions are explored through the molecular structural mechanics method. The following results are obtained: (a) The critical buckling forces of the SG and SS networks decrease as the side lengths or aspect ratios of the networks increase. The continuum plate theory could give good predictions to the buckling of the SS network but not the SG network with non-uniform buckling modes. (b) The carbon nanotube networks are more stable structures than the graphene structures with less carbon atoms.

  9. Evaluation of RANS and LES models for Natural Convection in High-Aspect-Ratio Parallel Plate Channels

    Science.gov (United States)

    Fradeneck, Austen; Kimber, Mark

    2017-11-01

    The present study evaluates the effectiveness of current RANS and LES models in simulating natural convection in high-aspect ratio parallel plate channels. The geometry under consideration is based on a simplification of the coolant and bypass channels in the very high-temperature gas reactor (VHTR). Two thermal conditions are considered, asymmetric and symmetric wall heating with an applied heat flux to match Rayleigh numbers experienced in the VHTR during a loss of flow accident (LOFA). RANS models are compared to analogous high-fidelity LES simulations. Preliminary results demonstrate the efficacy of the low-Reynolds number k- ɛ formulations and their enhancement to the standard form and Reynolds stress transport model in terms of calculating the turbulence production due to buoyancy and overall mean flow variables.

  10. Modeling and optimization of atomic layer deposition processes on vertically aligned carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Nuri Yazdani

    2014-03-01

    Full Text Available Many energy conversion and storage devices exploit structured ceramics with large interfacial surface areas. Vertically aligned carbon nanotube (VACNT arrays have emerged as possible scaffolds to support large surface area ceramic layers. However, obtaining conformal and uniform coatings of ceramics on structures with high aspect ratio morphologies is non-trivial, even with atomic layer deposition (ALD. Here we implement a diffusion model to investigate the effect of the ALD parameters on coating kinetics and use it to develop a guideline for achieving conformal and uniform thickness coatings throughout the depth of ultra-high aspect ratio structures. We validate the model predictions with experimental data from ALD coatings of VACNT arrays. However, the approach can be applied to predict film conformality as a function of depth for any porous topology, including nanopores and nanowire arrays.

  11. Scaling model for high-aspect-ratio microballoon direct-drive implosions at short laser wavelengths

    International Nuclear Information System (INIS)

    Schirmann, D.; Juraszek, D.; Lane, S.M.; Campbell, E.M.

    1992-01-01

    A scaling model for hot spherical ablative implosions in direct-drive mode is presented. The model results have been compared with experiments from LLE, ILE, and LLNL. Reduction of the neutron yield due to illumination nonuniformities is taken into account by the assumption that the neutron emission is cut off when the gas shock wave reflected off the center meets the incoming pusher, i.e., at a time when the probability of shell breakup is greatly enhanced. The main advantage of this semiempirical scaling model is that it elucidates the principal features of these simple implosions and permits one to estimate very quickly the performance of a high-aspect-ratio direct-drive target illuminated by short-wavelength laser light. (Author)

  12. The experimental research on electrodischarge drilling of high aspect ratio holes in Inconel 718

    Science.gov (United States)

    Lipiec, Piotr; Machno, Magdalena; Skoczypiec, Sebastian

    2018-05-01

    In recent years the drilling operations become important area of electrodischarge machining (EDM) application. This especially concerns drilling of, small (D 10) holes in difficult-to-cut materials (i.e. nickel or titanium alloys). Drilling of such a holes is significantly beyond mechanical drilling capabilities. Therefore electrodischarge machining is good and cost efficient alternative for such application. EDM gives possibility to drill accurate, burr free and high aspect ratio holes and is applicable to machine wide range of conductive materials, irrespective of their hardness and toughness. However it is worth to underline its main disadvantages such as: significant tool wear, low material removal rate and poor surface integrity. The last one is especially important in reliable applications in aircraft or medical industry.

  13. Vertically aligned BCN nanotubes with high capacitance.

    Science.gov (United States)

    Iyyamperumal, Eswaramoorthi; Wang, Shuangyin; Dai, Liming

    2012-06-26

    Using a chemical vapor deposition method, we have synthesized vertically aligned BCN nanotubes (VA-BCNs) on a Ni-Fe-coated SiO(2)/Si substrate from a melamine diborate precursor. The effects of pyrolysis conditions on the morphology and thermal property of grown nanotubes, as well as the nanostructure and composition of an individual BCN nanotube, were systematically studied. It was found that nitrogen atoms are bonded to carbons in both graphitic and pyridinic forms and that the resultant VA-BCNs grown at 1000 °C show the highest specific capacitance (321.0 F/g) with an excellent rate capability and high durability with respect to nonaligned BCN (167.3 F/g) and undoped multiwalled carbon nanotubes (117.3 F/g) due to synergetic effects arising from the combined co-doping of B and N in CNTs and the well-aligned nanotube structure.

  14. Design studies of low-aspect ratio quasi-omnigenous stellarators

    International Nuclear Information System (INIS)

    Spong, D.A.; Hirshman, S.; Whitson, J.C.

    2001-01-01

    Significant progress has been made in the development of new modest-size compact stellarator devices that could test optimization principles for the design of a more attractive reactor. These are 3 and 4 field period low-aspect-ratio quasi-omnigenous (QO) stellarators based on an optimization method that targets improved confinement, stability, ease of coil design, low-aspect-ratio, and low bootstrap current. (author)

  15. Synthesis of carbon nanotubes from acetylene on the FeCoMgO catalytic system obtained by ball milling

    Energy Technology Data Exchange (ETDEWEB)

    Biris, A R; Simon, S; Lupu, D; Misan, I [National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath, 400293 Cluj-Napoca (Romania); Biris, A S; Dervishi, E; Li, Z; Watanabe, F [UALR Nanotechnology Center, University of Arkansas, 2801 S University Ave, Little Rock, AR 72204 (United States); Lucaci, M, E-mail: alexandru.biris@itim-cj.r [National Institute for Research and Development in Electrical Engineering ICPE-CA 313 Splaiul Unirii, 030138 Bucharest (Romania)

    2009-08-01

    Highly crystalline multi wall carbon nanotubes have been synthesized by RF-CVD from acetylene at 850{sup 0}C over a Fe:Co:MgO catalyst. The catalytic system was obtained by mixing for 100 h Fe, Co and MgO powders in a ball milling device under petroleum ether environment, followed by oxidation in air at 500{sup 0}C for 24 h. Most of the nanotubes had external diameters in order of dozens of nm and lengths of microns, resulting in an aspect ration of over 1000. Their external to internal diameter ratio varied between 2.5 and 3.

  16. Weight of evidence analysis for assessing the genotoxic potential of carbon nanotubes

    DEFF Research Database (Denmark)

    Møller, Peter; Jacobsen, Nicklas Raun

    2017-01-01

    Carbon nanotube (CNT) is a nanomaterial that has received interest because of its high-tensile strength and low weight. Although CNTs differ substantially in physico-chemical properties, they share high aspect ratio which resembles that of asbestos and other fibers causing lung cancer...... and insufficient mechanistic evidence. Damage to DNA is considered to be a key mechanistic step in the development of fiber-induced cancer. Thus, the genotoxic potential can be a cornerstone in the evaluation of hazards of CNTs. The present study used a weight of evidence (WoE) analysis to evaluate...

  17. Synthesis and characterization of carbon nanotube from coconut shells activated carbon

    Science.gov (United States)

    Melati, A.; Hidayati, E.

    2016-03-01

    Carbon nanotubes (CNTs) have been explored in almost every single cancer treatment modality, including drug delivery, lymphatic targeted chemotherapy, photodynamic therapy, and gene therapy. They are considered as one of the most promising nanomaterial with the capability of both detecting the cancerous cells and delivering drugs or small therapeutic molecules to the cells. CNTs have unique physical and chemical properties such as high aspect ratio, ultralight weight, high mechanical strength, high electrical conductivity, and high thermal conductivity. Coconut Shell was researched as active carbon source on 500 - 600°C. These activated carbon was synthesized becomes carbon nanotube and have been proposed as a promising tool for detecting the expression of indicative biological molecules at early stage of cancer. Clinically, biomarkers cancer can be detected by CNT Biosensor. We are using pyrolysis methods combined with CVD process or Wet Chemical Process on 600°C. Our team has successfully obtained high purity, and aligned MWCNT (Multi Wall Nanotube) bundles on synthesis CNT based on coconut shells raw materials. CNTs can be used to cross the mammalian cell membrane by endocytosis or other mechanisms. SEM characterization of these materials have 179 nm bundles on phase 83° and their materials compound known by using FTIR characterization.

  18. Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations

    Directory of Open Access Journals (Sweden)

    S. Nishizawa

    2015-10-01

    Full Text Available We examine the influence of the grid aspect ratio of horizontal to vertical grid spacing on turbulence in the planetary boundary layer (PBL in a large-eddy simulation (LES. In order to clarify and distinguish them from other artificial effects caused by numerical schemes, we used a fully compressible meteorological LES model with a fully explicit scheme of temporal integration. The influences are investigated with a series of sensitivity tests with parameter sweeps of spatial resolution and grid aspect ratio. We confirmed that the mixing length of the eddy viscosity and diffusion due to sub-grid-scale turbulence plays an essential role in reproducing the theoretical −5/3 slope of the energy spectrum. If we define the filter length in LES modeling based on consideration of the numerical scheme, and introduce a corrective factor for the grid aspect ratio into the mixing length, the theoretical slope of the energy spectrum can be obtained; otherwise, spurious energy piling appears at high wave numbers. We also found that the grid aspect ratio has influence on the turbulent statistics, especially the skewness of the vertical velocity near the top of the PBL, which becomes spuriously large with large aspect ratio, even if a reasonable spectrum is obtained.

  19. High adhesion transparent conducting films using graphene oxide hybrid carbon nanotubes

    International Nuclear Information System (INIS)

    Da, Shi-Xun; Wang, Jie; Geng, Hong-Zhang; Jia, Song-Lin; Xu, Chun-Xia; Li, Lin-Ge; Shi, Pei-Pei; Li, Guangfen

    2017-01-01

    Graphical abstract: The GO hybrid CNTs to fabricate TCFs could dramatically enhance the conductivity, adhesion, flatness, and wettability of the films, all these improvements are advantageous for optoelectronic applications. - Highlights: • TCFs were fabricated using GO/CNT hybrid inks by a simple spray method. • Conductivity of TCFs was improved through the hybrid of GO/CNT, sheet resistance of TCFs was 146 Ω/sq at the transmittance of 86.0% when the ratio of GO/CNT got 1.5:1.0. • The flatness and wettability of TCFs were improved dramatically, which is advantageous for the solution-based processing of organic electronics for spraying and printing. • The adhesion of the TCFs increased dramatically with the raise of the ratio GO/CNT hybrid. - Abstract: Flexible transparent conducting films (TCFs) with carbon nanotubes (CNTs) have attracted more and more attention for their wide range of potential applications. While, there are still some problems to be solved on several aspects. In this study, a graphene oxide/carbon nanotube (GO/CNT) hybrid TCF was fabricated through the simple spray coating method. GO sheets were introduced to form new electron transporting channels. It was found that the best optoelectronic property films were fabricated when the ratio of GO/CNT is 1.5:1.0, which the sheet resistance of the film was found to be 146 Ω/sq at the transmittance of 86.0%. Due to the two-dimensional structure and the oxidation groups of GO sheets, flatness and wettability of the electrode surface was improved obviously. Adhesion factor of the TCFs was calculated by the change of transparent and sheet resistance after trial test, the addition of GO sheets enhanced the adhesion dramatically and the mechanism was analyzed. Improvements of conductivity, flatness, wettability and adhesion above are all advantageous for the solution-based processing of organic electronics for spraying and printing.

  20. High adhesion transparent conducting films using graphene oxide hybrid carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Da, Shi-Xun; Wang, Jie; Geng, Hong-Zhang, E-mail: genghz@tjpu.edu.cn; Jia, Song-Lin; Xu, Chun-Xia; Li, Lin-Ge; Shi, Pei-Pei; Li, Guangfen

    2017-01-15

    Graphical abstract: The GO hybrid CNTs to fabricate TCFs could dramatically enhance the conductivity, adhesion, flatness, and wettability of the films, all these improvements are advantageous for optoelectronic applications. - Highlights: • TCFs were fabricated using GO/CNT hybrid inks by a simple spray method. • Conductivity of TCFs was improved through the hybrid of GO/CNT, sheet resistance of TCFs was 146 Ω/sq at the transmittance of 86.0% when the ratio of GO/CNT got 1.5:1.0. • The flatness and wettability of TCFs were improved dramatically, which is advantageous for the solution-based processing of organic electronics for spraying and printing. • The adhesion of the TCFs increased dramatically with the raise of the ratio GO/CNT hybrid. - Abstract: Flexible transparent conducting films (TCFs) with carbon nanotubes (CNTs) have attracted more and more attention for their wide range of potential applications. While, there are still some problems to be solved on several aspects. In this study, a graphene oxide/carbon nanotube (GO/CNT) hybrid TCF was fabricated through the simple spray coating method. GO sheets were introduced to form new electron transporting channels. It was found that the best optoelectronic property films were fabricated when the ratio of GO/CNT is 1.5:1.0, which the sheet resistance of the film was found to be 146 Ω/sq at the transmittance of 86.0%. Due to the two-dimensional structure and the oxidation groups of GO sheets, flatness and wettability of the electrode surface was improved obviously. Adhesion factor of the TCFs was calculated by the change of transparent and sheet resistance after trial test, the addition of GO sheets enhanced the adhesion dramatically and the mechanism was analyzed. Improvements of conductivity, flatness, wettability and adhesion above are all advantageous for the solution-based processing of organic electronics for spraying and printing.

  1. Fabrication of high aspect ratio TiO2 and Al2O3 nanogratings by atomic layer deposition

    DEFF Research Database (Denmark)

    Shkondin, Evgeniy; Takayama, Osamu; Michael-Lindhard, Jonas

    2016-01-01

    The authors report on the fabrication of TiO2 and Al2O3 nanostructured gratings with an aspect ratio of up to 50. The gratings were made by a combination of atomic layer deposition (ALD) and dry etch techniques. The workflow included fabrication of a Si template using deep reactive ion etching...... spectroscopy. The approach presented opens the possibility to fabricate high quality optical metamaterials and functional nanostructures....

  2. A small perturbation based optimization approach for the frequency placement of high aspect ratio wings

    Science.gov (United States)

    Goltsch, Mandy

    Design denotes the transformation of an identified need to its physical embodiment in a traditionally iterative approach of trial and error. Conceptual design plays a prominent role but an almost infinite number of possible solutions at the outset of design necessitates fast evaluations. The corresponding practice of empirical equations and low fidelity analyses becomes obsolete in the light of novel concepts. Ever increasing system complexity and resource scarcity mandate new approaches to adequately capture system characteristics. Contemporary concerns in atmospheric science and homeland security created an operational need for unconventional configurations. Unmanned long endurance flight at high altitudes offers a unique showcase for the exploration of new design spaces and the incidental deficit of conceptual modeling and simulation capabilities. Structural and aerodynamic performance requirements necessitate light weight materials and high aspect ratio wings resulting in distinct structural and aeroelastic response characteristics that stand in close correlation with natural vibration modes. The present research effort evolves around the development of an efficient and accurate optimization algorithm for high aspect ratio wings subject to natural frequency constraints. Foundational corner stones are beam dimensional reduction and modal perturbation redesign. Local and global analyses inherent to the former suggest corresponding levels of local and global optimization. The present approach departs from this suggestion. It introduces local level surrogate models to capacitate a methodology that consists of multi level analyses feeding into a single level optimization. The innovative heart of the new algorithm originates in small perturbation theory. A sequence of small perturbation solutions allows the optimizer to make incremental movements within the design space. It enables a directed search that is free of costly gradients. System matrices are decomposed

  3. Elliptic nozzle aspect ratio effect on controlled jet propagation

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S M Aravindh; Rathakrishnan, Ethirajan, E-mail: aravinds@iitk.ac.in, E-mail: erath@iitk.ac.in [Department of Aerospace Engineering, Indian Institute of Technology, Kanpur (India)

    2017-04-15

    The present study deals with the control of a Mach 2 elliptic jet from a convergent–divergent elliptic nozzle of aspect ratio 4 using tabs at the nozzle exit. The experiments were carried out for rectangular and triangular tabs of the same blockage, placed along the major and minor axes of the nozzle exit, at different levels of nozzle expansion. The triangular tabs along the minor axis promoted superior mixing compared to the other controlled jets and caused substantial core length reduction at all the nozzle pressure ratios studied. The rectangular tabs along the minor axis caused core length reduction at all pressure ratios, but the values were minimal compared to that of triangular tabs along the minor axis. For all the test conditions, the mixing promotion caused by tabs along the major axis was inferior to that of tabs along the minor axis. The waves present in the core of controlled jets were visualized using a shadowgraph. Comparison of the present results with the results of a controlled Mach 2 elliptic jet of aspect ratio 2 (Aravindh Kumar and Sathakrishnan 2016 J. Propulsion Power 32 121–33, Aravindh Kumar and Rathakrishnan 2016 J. Aerospace Eng. at press (doi:10.1177/0954410016652921)) show that for all levels of expansion, the mixing effectiveness of triangular tabs along the minor axis of an aspect ratio 4 nozzle is better than rectangular or triangular tabs along the minor axis of an aspect ratio 2 nozzle. (paper)

  4. Elliptic nozzle aspect ratio effect on controlled jet propagation

    International Nuclear Information System (INIS)

    Kumar, S M Aravindh; Rathakrishnan, Ethirajan

    2017-01-01

    The present study deals with the control of a Mach 2 elliptic jet from a convergent–divergent elliptic nozzle of aspect ratio 4 using tabs at the nozzle exit. The experiments were carried out for rectangular and triangular tabs of the same blockage, placed along the major and minor axes of the nozzle exit, at different levels of nozzle expansion. The triangular tabs along the minor axis promoted superior mixing compared to the other controlled jets and caused substantial core length reduction at all the nozzle pressure ratios studied. The rectangular tabs along the minor axis caused core length reduction at all pressure ratios, but the values were minimal compared to that of triangular tabs along the minor axis. For all the test conditions, the mixing promotion caused by tabs along the major axis was inferior to that of tabs along the minor axis. The waves present in the core of controlled jets were visualized using a shadowgraph. Comparison of the present results with the results of a controlled Mach 2 elliptic jet of aspect ratio 2 (Aravindh Kumar and Sathakrishnan 2016 J. Propulsion Power 32 121–33, Aravindh Kumar and Rathakrishnan 2016 J. Aerospace Eng. at press (doi:10.1177/0954410016652921)) show that for all levels of expansion, the mixing effectiveness of triangular tabs along the minor axis of an aspect ratio 4 nozzle is better than rectangular or triangular tabs along the minor axis of an aspect ratio 2 nozzle. (paper)

  5. High pressure synthesis of amorphous TiO{sub 2} nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Li, Quanjun; Liu, Ran; Wang, Tianyi; Xu, Ke; Dong, Qing; Liu, Bo; Liu, Bingbing, E-mail: liubb@jlu.edu.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012 (China); Liu, Jing [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2015-09-15

    Amorphous TiO{sub 2} nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO{sub 2} nanotubes. The structural phase transitions of anatase TiO{sub 2} nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD) method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA) form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO{sub 2} nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO{sub 2} phase was revealed by high-resolution transmission electron microscopy (HRTEM) study. In addition, the bulk modulus (B{sub 0} = 158 GPa) of the anatase TiO{sub 2} nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa). We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO{sub 2} nanotubes.

  6. A multiscale method for modeling high-aspect-ratio micro/nano flows

    Science.gov (United States)

    Lockerby, Duncan; Borg, Matthew; Reese, Jason

    2012-11-01

    In this paper we present a new multiscale scheme for simulating micro/nano flows of high aspect ratio in the flow direction, e.g. within long ducts, tubes, or channels, of varying section. The scheme consists of applying a simple hydrodynamic description over the entire domain, and allocating micro sub-domains in very small ``slices'' of the channel. Every micro element is a molecular dynamics simulation (or other appropriate model, e.g., a direct simulation Monte Carlo method for micro-channel gas flows) over the local height of the channel/tube. The number of micro elements as well as their streamwise position is chosen to resolve the geometrical features of the macro channel. While there is no direct communication between individual micro elements, coupling occurs via an iterative imposition of mass and momentum-flux conservation on the macro scale. The greater the streamwise scale of the geometry, the more significant is the computational speed-up when compared to a full MD simulation. We test our new multiscale method on the case of a converging/diverging nanochannel conveying a simple Lennard-Jones liquid. We validate the results from our simulations by comparing them to a full MD simulation of the same test case. Supported by EPSRC Programme Grant, EP/I011927/1.

  7. Bump Bonding Using Metal-Coated Carbon Nanotubes

    Science.gov (United States)

    Lamb, James L.; Dickie, Matthew R.; Kowalczyk, Robert S.; Liao, Anna; Bronikowski, Michael J.

    2012-01-01

    Bump bonding hybridization techniques use arrays of indium bumps to electrically and mechanically join two chips together. Surface-tension issues limit bump sizes to roughly as wide as they are high. Pitches are limited to 50 microns with bumps only 8-14 microns high on each wafer. A new process uses oriented carbon nanotubes (CNTs) with a metal (indium) in a wicking process using capillary actions to increase the aspect ratio and pitch density of the connections for bump bonding hybridizations. It merges the properties of the CNTs and the metal bumps, providing enhanced material performance parameters. By merging the bumps with narrow and long CNTs oriented in the vertical direction, higher aspect ratios can be obtained if the metal can be made to wick. Possible aspect ratios increase from 1:1 to 20:1 for most applications, and to 100:1 for some applications. Possible pitch density increases of a factor of 10 are possible. Standard capillary theory would not normally allow indium or most other metals to be drawn into the oriented CNTs, because they are non-wetting. However, capillary action can be induced through the ability to fabricate oriented CNT bundles to desired spacings, and the use of deposition techniques and temperature to control the size and mobility of the liquid metal streams and associated reservoirs. This hybridization of two technologies (indium bumps and CNTs) may also provide for some additional benefits such as improved thermal management and possible current density increases.

  8. Effects of Aspect Ratio on Water Immersion into Deep Silica Nanoholes.

    Science.gov (United States)

    Zheng, Jing; Zhang, Junqiao; Tan, Lu; Li, Debing; Huang, Liangliang; Wang, Qi; Liu, Yingchun

    2016-08-30

    Understanding the influence of aspect ratio on water immersion into silica nanoholes is of significant importance to the etching process of semiconductor fabrication and other water immersion-related physical and biological processes. In this work, the processes of water immersion into silica nanoholes with different height/width aspect ratios (ϕ = 0.87, 1.92, 2.97, 4.01, 5.06) and different numbers of water molecules (N = 9986, 19972, 29958, 39944) were studied by molecular dynamics simulations. A comprehensive analysis has been conducted about the detailed process of water immersion and the influence of aspect ratios on water immersion rates. Five distinguishable stages were identified for the immersion process with all studied models. The results reveal that water can easily immerse into the silica nanoholes with larger ϕ and smaller N. The calculation also suggests that aspect ratios have a greater effect on water immersion rates for larger N numbers. The mechanism of the water immersion process is discussed in this work. We also propose a mathematical model to correlate the complete water immersion process for different aspect ratios.

  9. INFLUENCE OF SCALE RATIO, ASPECT RATIO, AND PLANFORM ON THE PERFORMANCE OF SUPERCAVITATING HYDROFOILS.

    Science.gov (United States)

    performance of supercavitating hydrofoils. No appreciable scale effect was found for scale ratios up to 3 in the fully-cavitating flow region. The...overall performance of the hydrofoil by increasing the aspect ratio above 3, and (2) moderate taper ratio seems to be advantageous in view of the overall performance of supercavitating hydrofoils. (Author)

  10. Blade tip, finite aspect ratio, and dynamic stall effects on the Darrieus rotor

    Science.gov (United States)

    Paraschivoiu, I.; Desy, P.; Masson, C.

    1988-02-01

    The objective of the work described in this paper was to apply the Boeing-Vertol dynamic stall model in an asymmetric manner to account for the asymmetry of the flow between the left and right sides of the rotor. This phenomenon has been observed by the flow visualization of a two-straight-bladed Darrieus rotor in the IMST water tunnel. Also introduced into the aerodynamic model are the effects of the blade tip and finite aspect ratio on the aerodynamic performance of the Darrieus wind turbine. These improvements are compatible with the double-multiple-streamtube model and have been included in the CARDAAV computer code for predicting the aerodynamic performance. Very good agreement has been observed between the test data (Sandia 17 m) and theoretical predictions; a significant improvement over the previous dynamic stall model was obtained for the rotor power at low tip speed ratios, while the inclusion of the finite aspect ratio effects enhances the prediction of the rotor power for high tip speed ratios. The tip losses and finite aspect ratio effects were also calculated for a small-scale vertical-axis wind turbine, with a two-straight-bladed (NACA 0015) rotor.

  11. Omniclassical Diffusion in Low Aspect Ratio Tokamaks

    International Nuclear Information System (INIS)

    Mynick, H.E.; White, R.B.; Gates, D.A.

    2004-01-01

    Recently reported numerical results for axisymmetric devices with low aspect ratio A found radial transport enhanced over the expected neoclassical value by a factor of 2 to 3. In this paper, we provide an explanation for this enhancement. Transport theory in toroidal devices usually assumes large A, and that the ratio B p /B t of the poloidal to the toroidal magnetic field is small. These assumptions result in transport which, in the low collision limit, is dominated by banana orbits, giving the largest collisionless excursion of a particle from an initial flux surface. However in a small aspect ratio device one may have B p /B t ∼ 1, and the gyroradius may be larger than the banana excursion. Here, we develop an approximate analytic transport theory valid for devices with arbitrary A. For low A, we find that the enhanced transport, referred to as omniclassical, is a combination of neoclassical and properly generalized classical effects, which become dominant in the low-A, B p /B t ∼ 1 regime. Good agreement of the analytic theory with numerical simulations is obtained

  12. Impact of aspect ratio and solar heating on street canyon air temperature

    International Nuclear Information System (INIS)

    Memon, R.A.; Lal, K.

    2011-01-01

    The results obtained from RNG (Re-Normalization Group) version of k-and turbulence model are reported in this study. The model is adopted to elucidate the impact of different building aspect ratios (i.e., ratio of building-height-to-street-canyon-width) and solar heating on temperatures in street canyon. The validation of Navier-Stokes and energy an sport equations showed that the model prediction for air-temperature and ambient wind provides reasonable accuracy. The model was applied on AR (Aspect Ratios) one to eight and surface temperature difference (delta and theta/sub s-a/)) of 2 -8. Notably, air-temperatures were higher in high AR street canyons in particular on the leeward side of the street canyon. Further investigation showed that the difference between the air-temperature 'high and low AR street canyons (AR) was positive and high with higher delta and theta/sub s-a/) conversely, the AR become negative and low gradually with lower values of delta and theta(/sub s-a/). These results could be very beneficial for the city and regional planners, civil engineers Id HVAC experts who design street canyons and strive for human thermal comfort with minimum possible energy requirements. (author)

  13. Impact of Aspect Ratio and Solar Heating on Street Conyn Air Temperature

    Directory of Open Access Journals (Sweden)

    Rizwan Ahmed Memon

    2011-01-01

    Full Text Available The results obtained from RNG (Re-Normalization Group version of k-? turbulence model are reported in this study. The model is adopted to elucidate the impact of different building aspect ratios (i.e., ratio of building-height-to-street-canyon-width and solar heating on temperatures in street canyon. The validation of Navier-Stokes and energy transport equations showed that the model prediction for air-temperature and ambient wind provides reasonable accuracy. The model was applied on AR (Aspect Ratios one to eight and surface temperature difference (??s-a of 2 -8. Notably, air-temperatures were higher in high AR street canyons in particular on the leeward side of the street canyon. Further investigation showed that the difference between the air-temperature of high and low AR street canyons ( AR was positive and high with higher ??s-a. Conversely, the AR become negative and low gradually with lower values of ??s-a. These results could be very beneficial for the city and regional planners, civil engineers and HVAC experts who design street canyons and strive for human thermal comfort with minimum possible energy requirements.

  14. Subsonic and transonic pressure measurements on a high-aspect-ratio supercritical-wing model with oscillating control surfaces

    Science.gov (United States)

    Sandford, M. C.; Ricketts, R. H.; Watson, J. J.

    1981-01-01

    A high aspect ratio supercritical wing with oscillating control surfaces is described. The semispan wing model was instrumented with 252 static orifices and 164 in situ dynamic pressure gases for studying the effects of control surface position and sinusoidal motion on steady and unsteady pressures. Data from the present test (this is the second in a series of tests on this model) were obtained in the Langley Transonic Dynamics Tunnel at Mach numbers of 0.60 and 0.78 and are presented in tabular form.

  15. Effect of aspect ratio in free-swimming plunging flexible plates

    Science.gov (United States)

    Yeh, Peter; Alexeev, Alexander

    2015-11-01

    Using three dimensional fully-coupled fluid-structure interaction simulations, we investigate the free swimming of plunging elastic rectangular plates with aspect ratios ranging from 0.5 to 5 in a viscous fluid with Reynolds number 250. We find that maximum velocity occurs near the first natural frequency regardless of aspect ratio, while the maximum swimming economy occurs away from the first natural frequency and corresponds to a specific swimmer bending pattern characterized by reduced displacement of the swimmer's center of mass. Furthermore, we find that swimmers with wider span are both faster and more economical than narrow swimmers. These faster speeds are due to decreased drag for low aspect ratio plunging swimmers, which is in agreement with a recently proposed vortex-induced drag model that suggests that the smaller relative size of side vortices in low aspect ratio swimmers creates less drag per unit width. Our results are useful for the design of small autonomous micro-swimming devices and also provide insights on the physics of aquatic locomotion using oscillating fins.

  16. A low aspect ratio electrothermal gun for metal plasma vapor discharge and ceramic nanopowder production

    International Nuclear Information System (INIS)

    Kim, Kyoung Jin; Peterson, Dennis R.

    2008-01-01

    Traditionally, the electrothermal gun design has the bore of a large aspect ratio: however, a low aspect ratio design with a shorter bore length has been employed for efficient production of metal plasma vapors and synthesis of nanomaterials. In a comparison of the arc resistance-current relationship, a low aspect ratio design is found to exhibit distinctively different characteristics compared to a high aspect ratio design, and this trend is explained by the scaling law of plasma properties including theory of plasma electrical conductivity. A one-dimensional isothermal model has been applied to the present experiments to confirm the scaling laws, and it was found that the present modification of the electrothermal gun is able to produce fully ionized metal plasma vapor, while the plasma vapor produced in a conventional design is partially ionized. Also, by reacting metal plasma vapors with the controlled gases in the reaction chamber, nanoscale materials such as aluminum oxide, aluminum nitride, and titanium oxide were synthesized successfully

  17. Mechanical properties investigation on single-wall ZrO2 nanotubes: A finite element method with equivalent Poisson's ratio for chemical bonds

    Science.gov (United States)

    Yang, Xiao; Li, Huijian; Hu, Minzheng; Liu, Zeliang; Wärnå, John; Cao, Yuying; Ahuja, Rajeev; Luo, Wei

    2018-04-01

    A method to obtain the equivalent Poisson's ratio in chemical bonds as classical beams with finite element method was proposed from experimental data. The UFF (Universal Force Field) method was employed to calculate the elastic force constants of Zrsbnd O bonds. By applying the equivalent Poisson's ratio, the mechanical properties of single-wall ZrNTs (ZrO2 nanotubes) were investigated by finite element analysis. The nanotubes' Young's modulus (Y), Poisson's ratio (ν) of ZrNTs as function of diameters, length and chirality have been discussed, respectively. We found that the Young's modulus of single-wall ZrNTs is calculated to be between 350 and 420 GPa.

  18. Low-temperature plasma etching of high aspect-ratio densely packed 15 to sub-10 nm silicon features derived from PS-PDMS block copolymer patterns

    International Nuclear Information System (INIS)

    Liu, Zuwei; Sassolini, Simone; Olynick, Deirdre L; Gu, Xiaodan; Hwu, Justin

    2014-01-01

    The combination of block copolymer (BCP) lithography and plasma etching offers a gateway to densely packed sub-10 nm features for advanced nanotechnology. Despite the advances in BCP lithography, plasma pattern transfer remains a major challenge. We use controlled and low substrate temperatures during plasma etching of a chromium hard mask and then the underlying substrate as a route to high aspect ratio sub-10 nm silicon features derived from BCP lithography. Siloxane masks were fabricated using poly(styrene-b-siloxane) (PS-PDMS) BCP to create either line-type masks or, with the addition of low molecular weight PS-OH homopolymer, dot-type masks. Temperature control was essential for preventing mask migration and controlling the etched feature’s shape. Vertical silicon wire features (15 nm with feature-to-feature spacing of 26 nm) were etched with aspect ratios up to 17 : 1; higher aspect ratios were limited by the collapse of nanoscale silicon structures. Sub-10 nm fin structures were etched with aspect ratios greater than 10 : 1. Transmission electron microscopy images of the wires reveal a crystalline silicon core with an amorphous surface layer, just slightly thicker than a native oxide. (paper)

  19. Influence of obstacle aspect ratio on tripped cylinder wakes

    International Nuclear Information System (INIS)

    Araújo, Tiago B.; Sicot, Christophe; Borée, Jacques; Martinuzzi, Robert J.

    2012-01-01

    Highlights: ► Influence of a tripwire on wake properties of a surface-mounted circular cylinder. ► Height-to-diameter aspect ratios of 3 and 6 are considered. ► Critical positions for the tripwire lead to an abrupt change in the wake structure. ► Results further suggest that the tripwire can strengthen 2D wake properties. - Abstract: The influence of an asymmetrically mounted, single tripwire on the shedding and wake characteristics of a vertical, surface-mounted finite circular cylinder is investigated experimentally. Height-to-diameter aspect ratios of 3 and 6 are considered. It is shown that a critical position for the tripwire exists, which is characterised in an abrupt change in the shedding frequency and wake structure. Results further suggest that the tripwire can strengthen 2D wake properties. The influence of the aspect ratio is due to tip-wake flow interactions and thus differs fundamentally from two-dimensional geometries.

  20. Analysis of high-aspect-ratio jet-flap wings of arbitrary geometry

    Science.gov (United States)

    Lissaman, P. B. S.

    1973-01-01

    An analytical technique to compute the performance of an arbitrary jet-flapped wing is developed. The solution technique is based on the method of Maskell and Spence in which the well-known lifting-line approach is coupled with an auxiliary equation providing the extra function needed in jet-flap theory. The present method is generalized to handle straight, uncambered wings of arbitrary planform, twist, and blowing (including unsymmetrical cases). An analytical procedure is developed for continuous variations in the above geometric data with special functions to exactly treat discontinuities in any of the geometric and blowing data. A rational theory for the effect of finite wing thickness is introduced as well as simplified concepts of effective aspect ratio for rapid estimation of performance.

  1. Low Aspect-Ratio Wings for Wing-Ships

    DEFF Research Database (Denmark)

    Filippone, Antonino; Selig, M.

    1998-01-01

    Flying on ground poses technical and aerodynamical challenges. The requirements for compactness, efficiency, manouverability, off-design operation,open new areas of investigations in the fieldof aerodynamic analysis and design. A review ofthe characteristics of low-aspect ratio wings, in- and out...

  2. Epitaxial growth of quantum rods with high aspect ratio and compositional contrast

    International Nuclear Information System (INIS)

    Li, L. H.; Patriarche, G.; Fiore, A.

    2008-01-01

    The epitaxial growth of quantum rods (QRs) on GaAs was investigated. It was found that GaAs thickness in the GaAs/InAs superlattice used for QR formation plays a key role in improving the QR structural properties. Increasing the GaAs thickness results in both an increased In compositional contrast between the QRs and surrounding layer, and an increased QR length. QRs with an aspect ratio of up to 10 were obtained, representing quasiquantum wires in a GaAs matrix. Due to modified confinement and strain potential, such nanostructure is promising for controlling gain polarization

  3. Second regime tokamak operation at large aspect ratio

    International Nuclear Information System (INIS)

    Navratil, G.A.

    1989-01-01

    This paper reviews the need for high beta in economic tokamak reactors and summarizes recent results on the scaling of the second regime beta limit for high-n ballooning modes using optimized pressure profiles as well as results on low-n mode stability at the first regime beta limit from the Columbia HBT tokamak. While several experiments have studied ballooning limits using high εβ p plasmas, the most important question for the use of the second stability regime for tokamak reactor improvement is how to achieve these high values of εβ p while at the same time increasing the value of beta to several times the Troyon beta limit. An approach to the study of this key question on beta limits using modest sized, large aspect ratio tokamaks is described. (author). 28 refs, 7 figs, 1 tab

  4. Potential of Carbon Nanotube Reinforced Cement Composites as Concrete Repair Material

    Directory of Open Access Journals (Sweden)

    Tanvir Manzur

    2016-01-01

    Full Text Available Carbon nanotubes (CNTs are a virtually ideal reinforcing agent due to extremely high aspect ratios and ultra high strengths. It is evident from contemporary research that utilization of CNT in producing new cement-based composite materials has a great potential. Consequently, possible practical application of CNT reinforced cementitious composites has immense prospect in the field of applied nanotechnology within construction industry. Several repair, retrofit, and strengthening techniques are currently available to enhance the integrity and durability of concrete structures with cracks and spalling, but applicability and/or reliability is/are often limited. Therefore, there is always a need for innovative high performing concrete repair materials with good mechanical, rheological, and durability properties. Considering the mechanical properties of carbon nanotubes (CNTs and the test results of CNT reinforced cement composites, it is apparent that such composites could be used conveniently as concrete repair material. With this end in view, the applicability of multiwalled carbon nanotube (MWNT reinforced cement composites as concrete repair material has been evaluated in this study in terms of setting time, bleeding, and bonding strength (slant shear tests. It has been found that MWNT reinforced cement mortar has good prospective as concrete repair material since such composites exhibited desirable behavior in setting time, bleeding, and slant shear.

  5. Carbon nanotube feedback-gate field-effect transistor: suppressing current leakage and increasing on/off ratio.

    Science.gov (United States)

    Qiu, Chenguang; Zhang, Zhiyong; Zhong, Donglai; Si, Jia; Yang, Yingjun; Peng, Lian-Mao

    2015-01-27

    Field-effect transistors (FETs) based on moderate or large diameter carbon nanotubes (CNTs) usually suffer from ambipolar behavior, large off-state current and small current on/off ratio, which are highly undesirable for digital electronics. To overcome these problems, a feedback-gate (FBG) FET structure is designed and tested. This FBG FET differs from normal top-gate FET by an extra feedback-gate, which is connected directly to the drain electrode of the FET. It is demonstrated that a FBG FET based on a semiconducting CNT with a diameter of 1.5 nm may exhibit low off-state current of about 1 × 10(-13) A, high current on/off ratio of larger than 1 × 10(8), negligible drain-induced off-state leakage current, and good subthreshold swing of 75 mV/DEC even at large source-drain bias and room temperature. The FBG structure is promising for CNT FETs to meet the standard for low-static-power logic electronics applications, and could also be utilized for building FETs using other small band gap semiconductors to suppress leakage current.

  6. The Use of Multi-Walled Carbon Nanotubes as Possible Carrier in Drug Delivery System for Aspirin

    Science.gov (United States)

    Yusof, Alias Mohd.; Buang, Nor Aziah; Yean, Lee Sze; Ibrahim, Mohd. Lokman

    2009-06-01

    Carbon nanotubes (CNTs) have raised great interest in a number of applications, including field emission, energy storage, molecular electronics, sensors, biochips and drug delivery systems. This is due to their remarkable mechanical properties, chemical stability and biofunctionalizability. This nanomaterial is low in weight, has high strength and a high aspect ratio (long length compared to a small diameter). This paper will present a brief overview of drugs adsorbed onto the surface of carbon nanotubes via sonication method. The surface area of carbon nanotubes was measured by methylene blue method, Carbon nanotubes synthesized by catalytic chemical vapor deposition (CCVD) method were purified and functionalized in a mixture of concentrated acids (H2SO4:HNO3 = 3:1) at room temperature (25° C) via sonication in water bath, yielding carboxylic acid group on the CNTs' surface. CNT was successfully loaded with 48 %(w/w) aspirin molecules by suspending CNTs in a solution of aspirin in alcohol. Analysis of loaded CNTs by Field Emission-Scanning Electron Microscope (FESEM), Fourier Transform Infrared Spectrum (FITR) and UV-visible Spectroscopy confirmed the loading of the drug onto the CNTs. The work presented is a prelude to the direction of using carbon nanotubes as a drug delivery system to desired sites in human body.

  7. Material versatility using replica molding for large-scale fabrication of high aspect-ratio, high density arrays of nano-pillars

    International Nuclear Information System (INIS)

    Li, Y; Menon, C; Ng, H W; Gates, B D

    2014-01-01

    Arrays of high aspect-ratio (AR) nano-pillars have attracted a lot of interest for various applications, such as for use in solar cells, surface acoustic sensors, tissue engineering, bio-inspired adhesives and anti-reflective surfaces. Each application may require a different structural material, which can vary in the required chemical composition and mechanical properties. In this paper, a low cost fabrication procedure is proposed for large scale, high AR and high density arrays of nano-pillars. The proposed method enables the replication of a master with high fidelity, using the subsequent replica molds multiple times, and preparing arrays of nano-pillars in a variety of different materials. As an example applied to bio-inspired dry adhesion, polymeric arrays of nano-pillars are prepared in this work. Thermoset and thermoplastic nano-pillar arrays are examined using an atomic force microscope to assess their adhesion strength and its uniformity. Results indicate the proposed method is robust and can be used to reliably prepare nano-structures with a high AR. (paper)

  8. Recent Developments in Carbon Nanotube Membranes for Water Purification and Gas Separation

    Science.gov (United States)

    Sears, Kallista; Dumée, Ludovic; Schütz, Jürg; She, Mary; Huynh, Chi; Hawkins, Stephen; Duke, Mikel; Gray, Stephen

    2010-01-01

    Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i) CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii) isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented.

  9. Alternative method for variable aspect ratio vias using a vortex mask

    Science.gov (United States)

    Schepis, Anthony R.; Levinson, Zac; Burbine, Andrew; Smith, Bruce W.

    2014-03-01

    Historically IC (integrated circuit) device scaling has bridged the gap between technology nodes. Device size reduction is enabled by increased pattern density, enhancing functionality and effectively reducing cost per chip. Exemplifying this trend are aggressive reductions in memory cell sizes that have resulted in systems with diminishing area between bit/word lines. This affords an even greater challenge in the patterning of contact level features that are inherently difficult to resolve because of their relatively small area and complex aerial image. To accommodate these trends, semiconductor device design has shifted toward the implementation of elliptical contact features. This empowers designers to maximize the use of free device space, preserving contact area and effectively reducing the via dimension just along a single axis. It is therefore critical to provide methods that enhance the resolving capacity of varying aspect ratio vias for implementation in electronic design systems. Vortex masks, characterized by their helically induced propagation of light and consequent dark core, afford great potential for the patterning of such features when coupled with a high resolution negative tone resist system. This study investigates the integration of a vortex mask in a 193nm immersion (193i) lithography system and qualifies its ability to augment aspect ratio through feature density using aerial image vector simulation. It was found that vortex fabricated vias provide a distinct resolution advantage over traditionally patterned contact features employing a 6% attenuated phase shift mask (APM). 1:1 features were resolvable at 110nm pitch with a 38nm critical dimension (CD) and 110nm depth of focus (DOF) at 10% exposure latitude (EL). Furthermore, iterative source-mask optimization was executed as means to augment aspect ratio. By employing mask asymmetries and directionally biased sources aspect ratios ranging between 1:1 and 2:1 were achievable, however, this

  10. Single-Run Single-Mask Inductively-Coupled-Plasma Reactive-Ion-Etching Process for Fabricating Suspended High-Aspect-Ratio Microstructures

    Science.gov (United States)

    Yang, Yao-Joe; Kuo, Wen-Cheng; Fan, Kuang-Chao

    2006-01-01

    In this work, we present a single-run single-mask (SRM) process for fabricating suspended high-aspect-ratio structures on standard silicon wafers using an inductively coupled plasma-reactive ion etching (ICP-RIE) etcher. This process eliminates extra fabrication steps which are required for structure release after trench etching. Released microstructures with 120 μm thickness are obtained by this process. The corresponding maximum aspect ratio of the trench is 28. The SRM process is an extended version of the standard process proposed by BOSCH GmbH (BOSCH process). The first step of the SRM process is a standard BOSCH process for trench etching, then a polymer layer is deposited on trench sidewalls as a protective layer for the subsequent structure-releasing step. The structure is released by dry isotropic etching after the polymer layer on the trench floor is removed. All the steps can be integrated into a single-run ICP process. Also, only one mask is required. Therefore, the process complexity and fabrication cost can be effectively reduced. Discussions on each SRM step and considerations for avoiding undesired etching of the silicon structures during the release process are also presented.

  11. Surface tension-induced high aspect-ratio PDMS micropillars with concave and convex lens tips

    KAUST Repository

    Li, Huawei; Fan, Yiqiang; Yi, Ying; Foulds, Ian G.

    2013-01-01

    This paper reports a novel method for the fabrication of 3-dimensional (3D) Polydimethylsiloxane (PDMS) micropillars with concave and convex lens tips in a one-step molding process, using a CO2 laser-machined Poly(methyl methacrylate) (PMMA) mold with through holes. The PDMS micropillars are 4 mm high and have an aspect ratio of 251. The micropillars are formed by capillary force drawing up PDMS into the through hole mold. The concave and convex lens tips of the PDMS cylindrical micropillars are induced by surface tension and are controllable by changing the surface wetting properties of the through holes in the PMMA mold. This technique eliminates the requirements of expensive and complicated facilities to prepare a 3D mold, and it provides a simple and rapid method to fabricate 3D PDMS micropillars with controllable dimensions and tip shapes. © 2013 IEEE.

  12. Surface tension-induced high aspect-ratio PDMS micropillars with concave and convex lens tips

    KAUST Repository

    Li, Huawei

    2013-04-01

    This paper reports a novel method for the fabrication of 3-dimensional (3D) Polydimethylsiloxane (PDMS) micropillars with concave and convex lens tips in a one-step molding process, using a CO2 laser-machined Poly(methyl methacrylate) (PMMA) mold with through holes. The PDMS micropillars are 4 mm high and have an aspect ratio of 251. The micropillars are formed by capillary force drawing up PDMS into the through hole mold. The concave and convex lens tips of the PDMS cylindrical micropillars are induced by surface tension and are controllable by changing the surface wetting properties of the through holes in the PMMA mold. This technique eliminates the requirements of expensive and complicated facilities to prepare a 3D mold, and it provides a simple and rapid method to fabricate 3D PDMS micropillars with controllable dimensions and tip shapes. © 2013 IEEE.

  13. Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

    NARCIS (Netherlands)

    Kruyt, J.W.; Quicazan Rubio, E.M.; Heijst, van G.J.F.; Altshuler, D.L.; Lentink, D.

    2014-01-01

    Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy.

  14. Fabrication of high thermal conductivity arrays of carbon nanotubes and their composites

    Science.gov (United States)

    Geohegan, David B [Knoxville, TN; Ivanov, Ilya N [Knoxville, TN; Puretzky, Alexander A [Knoxville, TN

    2010-07-27

    Methods and apparatus are described for fabrication of high thermal conductivity arrays of carbon nanotubes and their composites. A composition includes a vertically aligned nanotube array including a plurality of nanotubes characterized by a property across substantially all of the vertically aligned nanotube array. A method includes depositing a vertically aligned nanotube array that includes a plurality of nanotubes; and controlling a deposition rate of the vertically aligned nanotubes array as a function of an in situ monitored property of the plurality of nanotubes.

  15. Dimensional measurement of micro parts with high aspect ratio in HIT-UOI

    Science.gov (United States)

    Dang, Hong; Cui, Jiwen; Feng, Kunpeng; Li, Junying; Zhao, Shiyuan; Zhang, Haoran; Tan, Jiubin

    2016-11-01

    Micro parts with high aspect ratios have been widely used in different fields including aerospace and defense industries, while the dimensional measurement of these micro parts becomes a challenge in the field of precision measurement and instrument. To deal with this contradiction, several probes for the micro parts precision measurement have been proposed by researchers in Center of Ultra-precision Optoelectronic Instrument (UOI), Harbin Institute of Technology (HIT). In this paper, optical fiber probes with structures of spherical coupling(SC) with double optical fibers, micro focal-length collimation (MFL-collimation) and fiber Bragg grating (FBG) are described in detail. After introducing the sensing principles, both advantages and disadvantages of these probes are analyzed respectively. In order to improve the performances of these probes, several approaches are proposed. A two-dimensional orthogonal path arrangement is propounded to enhance the dimensional measurement ability of MFL-collimation probes, while a high resolution and response speed interrogation method based on differential method is used to improve the accuracy and dynamic characteristics of the FBG probes. The experiments for these special structural fiber probes are given with a focus on the characteristics of these probes, and engineering applications will also be presented to prove the availability of them. In order to improve the accuracy and the instantaneity of the engineering applications, several techniques are used in probe integration. The effectiveness of these fiber probes were therefore verified through both the analysis and experiments.

  16. Bosch-like method for creating high aspect ratio poly(methyl methacrylate) (PMMA) structures

    KAUST Repository

    Haiducu, Marius

    2012-02-02

    This paper presents a method for etching millimetre-deep trenches in commercial grade PMMA using deep-UV at 254 nm. The method is based on consecutive cycles of irradiation and development of the exposed areas, respectively. The exposure segment is performed using an inexpensive, in-house built irradiation box while the development part is accomplished using an isopropyl alcohol (IPA):H2O developer. The method was tested and characterized by etching various dimension square test structures in commercial grade, mirrored acrylic. The undercut of the sidewalls due to the uncollimated nature of the irradiation light was dramatically alleviated by using a honeycomb metallic grid in between the irradiation source and the acrylic substrate and by rotating the latter using a direct current (DC) motor-driven stage. By using an extremely affordable set-up and non-toxic, environmentally friendly materials and substances, this process represents an excellent alternative to microfabricating microfluidic devices in particular and high aspect ratio structures in general using PMMA as substrate. © 2012 SPIE.

  17. The unexpected stability of multiwall nanotubes under high pressure and shear deformation

    International Nuclear Information System (INIS)

    Pashkin, E. Y.; Pankov, A. M.; Kulnitskiy, B. A.; Mordkovich, V. Z.; Perezhogin, I. A.; Karaeva, A. R.; Popov, M. Y.; Sorokin, P. B.; Blank, V. D.

    2016-01-01

    The behavior of multiwall carbon nanotubes under a high pressure (up to 55 GPa) combined with shear deformation was studied by experimental and theoretical methods. The unexpectedly high stability of the nanotubes' structure under high stresses was observed. After the pressure was released, we observed that the nanotubes had restored their shapes. Atomistic simulations show that the hydrostatic and shear stresses affect the nanotubes' structure in a different way. It was found that the shear stress load in the multiwall nanotubes' outer walls can induce their connection and formation of an amorphized sp"3-hybridized region but internal core keeps the tubular structure.

  18. The unexpected stability of multiwall nanotubes under high pressure and shear deformation

    Energy Technology Data Exchange (ETDEWEB)

    Pashkin, E. Y.; Pankov, A. M.; Kulnitskiy, B. A.; Mordkovich, V. Z. [Technological Institute for Superhard and Novel Carbon Materials, 7a Centralnaya Street, Troitsk, Moscow 142190 (Russian Federation); Moscow Institute of Physics and Technology, 9 Institutsky Lane, Dolgoprudny 141700 (Russian Federation); Perezhogin, I. A. [Technological Institute for Superhard and Novel Carbon Materials, 7a Centralnaya Street, Troitsk, Moscow 142190 (Russian Federation); Lomonosov Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Karaeva, A. R. [Technological Institute for Superhard and Novel Carbon Materials, 7a Centralnaya Street, Troitsk, Moscow 142190 (Russian Federation); Popov, M. Y.; Sorokin, P. B.; Blank, V. D. [Technological Institute for Superhard and Novel Carbon Materials, 7a Centralnaya Street, Troitsk, Moscow 142190 (Russian Federation); Moscow Institute of Physics and Technology, 9 Institutsky Lane, Dolgoprudny 141700 (Russian Federation); National University of Science and Technology MISiS, 4 Leninskiy Prospekt, Moscow 119049 (Russian Federation)

    2016-08-22

    The behavior of multiwall carbon nanotubes under a high pressure (up to 55 GPa) combined with shear deformation was studied by experimental and theoretical methods. The unexpectedly high stability of the nanotubes' structure under high stresses was observed. After the pressure was released, we observed that the nanotubes had restored their shapes. Atomistic simulations show that the hydrostatic and shear stresses affect the nanotubes' structure in a different way. It was found that the shear stress load in the multiwall nanotubes' outer walls can induce their connection and formation of an amorphized sp{sup 3}-hybridized region but internal core keeps the tubular structure.

  19. Configuration studies for a small-aspect-ratio tokamak stellarator hybrid

    International Nuclear Information System (INIS)

    Carreras, B.A.; Lynch, V.E.; Ware, A.

    1996-08-01

    The use of modulated toroidal coils offers a new path to the tokamak-stellarator hybrids. Low-aspect-ratio configurations can be found with robust vacuum flux surfaces and rotational transform close to the transform of a reverse-shear tokamak. These configurations have clear advantages in minimizing disruptions and their effect and in reducing tokamak current drive needs. They also allow the study of low-aspect-ratio effects on stellarator confinement in small devices

  20. Trade-off between Photon Management Efficacy and Material Quality in Thin-Film Solar Cells on Nanostructured Substrates of High Aspect Ratio Structures

    Directory of Open Access Journals (Sweden)

    Alan H. Chin

    2018-04-01

    Full Text Available Although texturing of the transparent electrode of thin-film solar cells has long been used to enhance light absorption via light trapping, such texturing has involved low aspect ratio features. With the recent development of nanotechnology, nanostructured substrates enable improved light trapping and enhanced optical absorption via resonances, a process known as photon management, in thin-film solar cells. Despite the progress made in the development of photon management in thin-film solar cells using nanostructures substrates, the structural integrity of the thin-film solar cells deposited onto such nanostructured substrates is rarely considered. Here, we report the observation of the reduction in the open circuit voltage of amorphous silicon solar cells deposited onto a nanostructured substrate with increasing areal number density of high aspect ratio structures. For a nanostructured substrate with the areal number density of such nanostructures increasing in correlation with the distance from one edge of the substrate, a correlation between the open circuit voltage reduction and the increase of the areal number density of high aspect ratio nanostructures of the front electrode of the small-size amorphous silicon solar cells deposited onto different regions of the substrate with graded nanostructure density indicates the effect of the surface morphology on the material quality, i.e., a trade-off between photon management efficacy and material quality. This observed trade-off highlights the importance of optimizing the morphology of the nanostructured substrate to ensure conformal deposition of the thin-film solar cell.

  1. Current drive and profile control in low aspect ratio tokamaks

    International Nuclear Information System (INIS)

    Chan, V.S.; Chiu, S.C.; Lin-Liu, Y.R.; Miller, R.L.; Turnbull, A.D.

    1995-07-01

    The key to the theoretically predicted high performance of a low aspect ratio tokamak (LAT) is its ability to operate at very large plasma current*I p . The plasma current at low aspect ratios follows the approximate formula: I p ∼ (5a 2 B t /Rqψ) [(1 + κ 2 )/2] [A/(A - 1)] where A quadruple-bond R/a which was derived from equilibrium studies. For constant qψ and B t , I p can increase by an order of magnitude over the case of tokamaks with A approx-gt 2.5. The large current results in a significantly enhanced β t (quadruple-bond β N I p /aB t ) possibly of order unity. It also compensates for the reduction in A to maintain the same confinement performance assuming the confinement time τ follows the generic form ∼ HI p P -1 / 2 R 3 / 2 κ 1 / 2 . The initiation and maintenance of such a large current is therefore a key issue for LATs

  2. Strong geographical variation in wing aspect ratio of a damselfly, Calopteryx maculata (Odonata: Zygoptera

    Directory of Open Access Journals (Sweden)

    Christopher Hassall

    2015-08-01

    Full Text Available Geographical patterns in body size have been described across a wide range of species, leading to the development of a series of fundamental biological rules. However, shape variables are less well-described despite having substantial consequences for organism performance. Wing aspect ratio (AR has been proposed as a key shape parameter that determines function in flying animals, with high AR corresponding to longer, thinner wings that promote high manoeuvrability, low speed flight, and low AR corresponding to shorter, broader wings that promote high efficiency long distance flight. From this principle it might be predicted that populations living in cooler areas would exhibit low AR wings to compensate for reduced muscle efficiency at lower temperatures. I test this hypothesis using the riverine damselfly, Calopteryx maculata, sampled from 34 sites across its range margin in North America. Nine hundred and seven male specimens were captured from across the 34 sites (mean = 26.7 ± 2.9 SE per site, dissected and measured to quantify the area and length of all four wings. Geometric morphometrics were employed to investigate geographical variation in wing shape. The majority of variation in wing shape involved changes in wing aspect ratio, confirmed independently by geometric morphometrics and wing measurements. There was a strong negative relationship between wing aspect ratio and the maximum temperature of the warmest month which varies from west-east in North America, creating a positive relationship with longitude. This pattern suggests that higher aspect ratio may be associated with areas in which greater flight efficiency is required: regions of lower temperatures during the flight season. I discuss my findings in light of research of the functional ecology of wing shape across vertebrate and invertebrate taxa.

  3. Piezoelectric Nanotube Array for Broadband High-Frequency Ultrasonic Transducer.

    Science.gov (United States)

    Liew, Weng Heng; Yao, Kui; Chen, Shuting; Tay, Francis Eng Hock

    2018-03-01

    Piezoelectric materials are vital in determining ultrasonic transducer and imaging performance as they offer the function for conversion between mechanical and electrical energy. Ultrasonic transducers with high-frequency operation suffer from performance degradation and fabrication difficulty of the demanded piezoelectric materials. Hence, we propose 1-D polymeric piezoelectric nanostructure with controlled nanoscale features to overcome the technical limitations of high-frequency ultrasonic transducers. For the first time, we demonstrate the integration of a well-aligned piezoelectric nanotube array to produce a high-frequency ultrasonic transducer with outstanding performance. We find that nanoconfinement-induced polarization orientation and unique nanotube structure lead to significantly improved piezoelectric and ultrasonic transducing performance over the conventional piezoelectric thin film. A large bandwidth, 126% (-6 dB), is achieved at high center frequency, 108 MHz. Transmission sensitivity of nanotube array is found to be 46% higher than that of the monolithic thin film transducer attributed to the improved electromechanical coupling effectiveness and impedance match. We further demonstrate high-resolution scanning, ultrasonic imaging, and photoacoustic imaging using the obtained nanotube array transducers, which is valuable for biomedical imaging applications in the future.

  4. Patterned growth of carbon nanotubes obtained by high density plasma chemical vapor deposition

    Science.gov (United States)

    Mousinho, A. P.; Mansano, R. D.

    2015-03-01

    Patterned growth of carbon nanotubes by chemical vapor deposition represents an assembly approach to place and orient nanotubes at a stage as early as when they are synthesized. In this work, the carbon nanotubes were obtained at room temperature by High Density Plasmas Chemical Vapor Deposition (HDPCVD) system. This CVD system uses a new concept of plasma generation, where a planar coil coupled to an RF system for plasma generation was used with an electrostatic shield for plasma densification. In this mode, high density plasmas are obtained. We also report the patterned growth of carbon nanotubes on full 4-in Si wafers, using pure methane plasmas and iron as precursor material (seed). Photolithography processes were used to pattern the regions on the silicon wafers. The carbon nanotubes were characterized by micro-Raman spectroscopy, the spectra showed very single-walled carbon nanotubes axial vibration modes around 1590 cm-1 and radial breathing modes (RBM) around 120-400 cm-1, confirming that high quality of the carbon nanotubes obtained in this work. The carbon nanotubes were analyzed by atomic force microscopy and scanning electron microscopy too. The results showed that is possible obtain high-aligned carbon nanotubes with patterned growth on a silicon wafer with high reproducibility and control.

  5. Effect of channel aspect ratio on chemical recuperation process in advanced aeroengines

    International Nuclear Information System (INIS)

    Zhang, Silong; Cui, Naigang; Xiong, Yuefei; Feng, Yu; Qin, Jiang; Bao, Wen

    2017-01-01

    The working process of an advanced aeroengine such as scramjet with endothermic hydrocarbon fuel cooling is a chemical recuperative cycle. The design of cooling channel in terms of engine real working conditions is very important for the chemical recuperation process. To study the effects of channel aspect ratio (AR) on chemical recuperation process of advanced aeroengines, three dimensional model of pyrolysis coolant flow inside asymmetrical rectangular cooling channels with fins is introduced and validated through experiments. Cases when AR varies from 1 to 8 are carried out. In the pyrolysis zone of the cooling channel, decreasing the channel aspect ratio can reduce the temperature difference and non-uniformity of fuel conversion in the channel cross section, and it can also increase the final conversion and corresponding chemical heat absorption. A small channel aspect ratio is beneficial for the chemical recuperation process and can guarantee the engine cooling performance in the pyrolysis zone of the cooling channel. - Highlights: • Large non-uniformity of conversion is bad for the chemical recuperation. • Small channel aspect ratio is beneficial for improving the chemical recuperation effectiveness. • Small channel aspect ratio is also beneficial for reducing the engine wall temperature.

  6. Propagation of Elastic Waves in a One-Dimensional High Aspect Ratio Nanoridge Phononic Crystal

    Directory of Open Access Journals (Sweden)

    Abdellatif Gueddida

    2018-05-01

    Full Text Available We investigate the propagation of elastic waves in a one-dimensional (1D phononic crystal constituted by high aspect ratio epoxy nanoridges that have been deposited at the surface of a glass substrate. With the help of the finite element method (FEM, we calculate the dispersion curves of the modes localized at the surface for propagation both parallel and perpendicular to the nanoridges. When the direction of the wave is parallel to the nanoridges, we find that the vibrational states coincide with the Lamb modes of an infinite plate that correspond to one nanoridge. When the direction of wave propagation is perpendicular to the 1D nanoridges, the localized modes inside the nanoridges give rise to flat branches in the band structure that interact with the surface Rayleigh mode, and possibly open narrow band gaps. Filling the nanoridge structure with a viscous liquid produces new modes that propagate along the 1D finite height multilayer array.

  7. Confinement of hydrogen at high pressure in carbon nanotubes

    Science.gov (United States)

    Lassila, David H [Aptos, CA; Bonner, Brian P [Livermore, CA

    2011-12-13

    A high pressure hydrogen confinement apparatus according to one embodiment includes carbon nanotubes capped at one or both ends thereof with a hydrogen-permeable membrane to enable the high pressure confinement of hydrogen and release of the hydrogen therethrough. A hydrogen confinement apparatus according to another embodiment includes an array of multi-walled carbon nanotubes each having first and second ends, the second ends being capped with palladium (Pd) to enable the high pressure confinement of hydrogen and release of the hydrogen therethrough as a function of palladium temperature, wherein the array of carbon nanotubes is capable of storing hydrogen gas at a pressure of at least 1 GPa for greater than 24 hours. Additional apparatuses and methods are also presented.

  8. Study on morphology of high-aspect-ratio grooves fabricated by using femtosecond laser irradiation and wet etching

    International Nuclear Information System (INIS)

    Chen, Tao; Pan, An; Li, Cunxia; Si, Jinhai; Hou, Xun

    2015-01-01

    Highlights: • We studied morphologies of silicon grooves fabricated by laser irradiation and wet etching. • We found nano-ripple structures formed on the groove sidewall. • Formations of nano-ripples were due to the formation of standing wave and nanoplanes. • Remaining debris on the groove bottom was removed by KOH etching. - Abstract: Morphologies of high-aspect-ratio silicon grooves fabricated by using femtosecond laser irradiation and selective chemical etching of hydrofluoric acid (HF) were studied. Oxygen was deeply doped into silicon under femtosecond laser irradiation in air, and then the oxygen-doped regions were removed by HF etching to form high-aspect-ratio grooves. After HF etching, periodic nano-ripples which were induced in silicon by femtosecond laser were observed on the groove sidewalls. The ripple orientation was perpendicular or parallel to the laser propagation direction (z direction), which depended on the relative direction between the laser polarization direction and the scanning direction. The formation of nano-ripples with orientations perpendicular to z direction could be attributed to the standing wave generated by the interference of the incident light and the reflected light in z direction. The formation of nano-ripples with orientations parallel to z direction could be attributed to the formation of self-organized periodic nanoplanes (bulk nanogratings) induced by femtosecond laser inside silicon. Materials in the tail portion of laser-induced oxygen doping (LIOD) regions were difficult to be etched by HF solution due to low oxygen concentration. The specimen was etched further in KOH solution to remove remaining materials in LIOD regions and all-silicon grooves were fabricated

  9. Carbon nanotube based composites for electricity storage in supercapacitors

    OpenAIRE

    Zhang, Shengwen

    2010-01-01

    In the context of fossil-fuel shortage and climate change, the production, conversion, storage and distribution of energy have become the focus of today's world. Supercapacitors, with their unique energy and power density specifications, cover the application gap between batteries and conventional capacitors and hence making valuable contributions in energy storage and distribution. Caron nanotubes (CNTs), with their unique aspect ratio and other distinctive physical, electrochemical and...

  10. Cause and Cure-Deterioration in Accuracy of CFD Simulations with Use of High-Aspect-Ratio Triangular/Tetrahedral Grids

    Science.gov (United States)

    Chang, Sin-Chung; Chang, Chau-Lyan; Venkatachari, Balaji

    2017-01-01

    In the multi-dimensional space-time conservation element and solution element16 (CESE) method, triangles and tetrahedral mesh elements turn out to be the most natural building blocks for 2D and 3D spatial grids, respectively. As such, the CESE method is naturally compatible with the simplest 2D and 3D unstructured grids and thus can be easily applied to solve problems with complex geometries. However, because (a) accurate solution of a high-Reynolds number flow field near a solid wall requires that the grid intervals along the direction normal to the wall be much finer than those in a direction parallel to the wall and, as such, the use of grid cells with extremely high aspect ratio (103 to 106) may become mandatory, and (b) unlike quadrilateral hexahedral grids, it is well-known that accuracy of gradient computations involving triangular tetrahedral grids tends to deteriorate rapidly as cell aspect ratio increases. As a result, the use of triangular tetrahedral grid cells near a solid wall has long been deemed impractical by CFD researchers. In view of (a) the critical role played by triangular tetrahedral grids in the CESE development, and (b) the importance of accurate resolution of high-Reynolds number flow field near a solid wall, as will be presented in the main paper, a comprehensive and rigorous mathematical framework that clearly identifies the reasons behind the accuracy deterioration as described above has been developed for the 2D case involving triangular cells. By avoiding the pitfalls identified by the 2D framework, and its 3D extension, it has been shown numerically.

  11. Feasibility of multi-walled carbon nanotube probes in AFM anodization lithography

    International Nuclear Information System (INIS)

    Choi, Ji Sun; Bae, Sukjong; Ahn, Sang Jung; Kim, Dal Hyun; Jung, Ki Young; Han, Cheolsu; Chung, Chung Choo; Lee, Haiwon

    2007-01-01

    Multi-walled carbon nanotube (CNT) tips were used in atomic force microscope (AFM) anodization lithography to investigate their advantages over conventional tips. The CNT tip required a larger threshold voltage than the mother silicon tip due to the Schottky barrier at the CNT-Si interface. Current-to-voltage curves distinguished the junction property between CNTs and mother tips. The CNT-platinum tip, which is more conductive than the CNT-silicon tip, showed promising results for AFM anodization lithography. Finally, the nanostructures with high aspect ratio were fabricated using a pulsed bias voltage technique as well as the CNT tip

  12. Wave-driver options for low-aspect-ratio steady-state tokamak reactors

    International Nuclear Information System (INIS)

    Ehst, D.A.

    1981-02-01

    Low aspect ratio designs are proposed for steady-state tokamak reactors. Benefits stem from reduced major radius and lessened stresses in the toroidal field coils, resulting in possible cost savings in the tokamak construction. In addition, a low aspect ratio (A = 2.6) permits the application of a bundle divertor capable of diverting 3-T fields to a power reactor using STARFIRE technology. Such a low aspect ratio is possible with the elimination of poloidal field coils in the central hole of the tokamak, which implies a need for noninductive current drive. Several plasma waves are considered for this application, and it appears likely that a candidate can be found which reduces the electric power for current maintenance to an acceptable value

  13. Recent Developments in Carbon Nanotube Membranes for Water Purification and Gas Separation

    Directory of Open Access Journals (Sweden)

    Stephen Gray

    2010-01-01

    Full Text Available Carbon nanotubes (CNTs are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented.

  14. Enhanced performance of starter lighting ignition type lead-acid batteries with carbon nanotubes as an additive to the active mass

    Science.gov (United States)

    Marom, Rotem; Ziv, Baruch; Banerjee, Anjan; Cahana, Beni; Luski, Shalom; Aurbach, Doron

    2015-11-01

    Addition of various carbon materials into lead-acid battery electrodes was studied and examined in order to enhance the power density, improve cycle life and stability of both negative and positive electrodes in lead acid batteries. High electrical-conductivity, high-aspect ratio, good mechanical properties and chemical stability of multi-wall carbon nanotubes (MWCNT, unmodified and mofified with carboxylic groups) position them as viable additives to enhance the electrodes' electrical conductivity, to mitigate the well-known sulfation failure mechanism and improve the physical integration of the electrodes. In this study, we investigated the incorporation-effect of carbon nanotubes (CNT) to the positive and the negative active materials in lead-acid battery prototypes in a configuration of flooded cells, as well as gelled cells. The cells were tested at 25% and 30% depth-of-discharge (DOD). The positive effect of the carbon nanotubes (CNT) utilization as additives to both positive and negative electrodes of lead-acid batteries was clearly demonstrated and is explained herein based on microscopic studies.

  15. Role of substrate aspect ratio on the robustness of capillary alignment

    International Nuclear Information System (INIS)

    Broesch, David J.; Shiang, Edward; Frechette, Joelle

    2014-01-01

    Capillary forces associated with liquid bridges formed across solid substrates are routinely exploited to align and assemble micro- and nanoscale devices. The magnitude of these forces plays a critical role in minimizing substrate misalignment and therefore should be controlled for robust and reliable fabrication process. We explore through simulations and experiments the role of the substrate aspect ratio (L/W) on capillary restoring forces and torques. Simulations show that increasing the aspect ratio of the substrates increases the capillary torques and forces when the substrates are misaligned through either lateral or rotational perturbations. The effect of substrate area, perimeter, and liquid volume are also systematically explored to show that the increase in restoring torque is caused by an increase in aspect ratio. A simple theoretical model based on the geometry of the system shows excellent agreement with Surface Evolver simulations. Finally, parameters from experimental flip-chip devices [Josell, D. Wallace, W.E. Warren, J.A. Wheeler, D. Powell, A.C. J. Electron. Packag. 124, 227, (2002)] are used in our simulations to show how current capillary self-alignment schemes could benefit from using rectangular substrate shapes with aspect ratio greater than one

  16. Carbon Micronymphaea: Graphene on Vertically Aligned Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Jong Won Choi

    2013-01-01

    Full Text Available This paper describes the morphology of carbon nanomaterials such as carbon nanotube (CNT, graphene, and their hybrid structure under various operating conditions during a one-step synthesis via plasma-enhanced chemical vapor deposition (PECVD. We focus on the synthetic aspects of carbon hybrid material composed of heteroepitaxially grown graphene on top of a vertical array of carbon nanotubes, called carbon micronymphaea. We characterize the structural features of this unique nanocomposite by uses of electron microscopy and micro-Raman spectroscopy. We observe carbon nanofibers, poorly aligned and well-aligned vertical arrays of CNT sequentially as the growth temperature increases, while we always discover the carbon hybrids, called carbon micronymphaea, at specific cooling rate of 15°C/s, which is optimal for the carbon precipitation from the Ni nanoparticles in this study. We expect one-pot synthesized graphene-on-nanotube hybrid structure poses great potential for applications that demand ultrahigh surface-to-volume ratios with intact graphitic nature and directional electronic and thermal transports.

  17. Progress in the fabrication of high aspect ratio zone plates by soft x-ray lithography

    International Nuclear Information System (INIS)

    Divan, R.; Mancini, D. C.; Moldovan, N. A.; Lai, B.; Assoufid, L.; Leondard, Q.; Cerrina, F.

    2002-01-01

    Fabrication of Fresnel zone plates for the hard x-ray spectral region combines the challenge of high lateral resolution (∼100 nm) with a large thickness requirement for the phase-shifting material (0.5-3 (micro)m). For achieving a high resolution, the initial mask was fabricated by e-beam lithography and gold electroforming. To prevent the collapse of the structures between the developing and electroforming processes, drying was completely eliminated. Fabrication errors, such as nonuniform gold electroplating and collapse of structures, were systematically analyzed and largely eliminated. We optimized the exposure and developing processes for 950k and 2200k polymethylmethacrylate of different thicknesses and various adhesion promoters. We discuss the effects of these fabrication steps on the zone plate's resolution and aspect ratio. Fresnel zone plates with 110 nm outermost zone width, 150 (micro)m diameter, and 1.3 (micro)m gold thickness were fabricated. Preliminary evaluation of the FZPs was done by scanning electron microscopy and atomic force microscopy. The FZP focusing performance was characterized at the Advanced Photon Source at Argonne National Laboratory

  18. Carbon Nanofiber-Based, High-Frequency, High-Q, Miniaturized Mechanical Resonators

    Science.gov (United States)

    Kaul, Anupama B.; Epp, Larry W.; Bagge, Leif

    2011-01-01

    High Q resonators are a critical component of stable, low-noise communication systems, radar, and precise timing applications such as atomic clocks. In electronic resonators based on Si integrated circuits, resistive losses increase as a result of the continued reduction in device dimensions, which decreases their Q values. On the other hand, due to the mechanical construct of bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators, such loss mechanisms are absent, enabling higher Q-values for both BAW and SAW resonators compared to their electronic counterparts. The other advantages of mechanical resonators are their inherently higher radiation tolerance, a factor that makes them attractive for NASA s extreme environment planetary missions, for example to the Jovian environments where the radiation doses are at hostile levels. Despite these advantages, both BAW and SAW resonators suffer from low resonant frequencies and they are also physically large, which precludes their integration into miniaturized electronic systems. Because there is a need to move the resonant frequency of oscillators to the order of gigahertz, new technologies and materials are being investigated that will make performance at those frequencies attainable. By moving to nanoscale structures, in this case vertically oriented, cantilevered carbon nanotubes (CNTs), that have larger aspect ratios (length/thickness) and extremely high elastic moduli, it is possible to overcome the two disadvantages of both bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators. Nano-electro-mechanical systems (NEMS) that utilize high aspect ratio nanomaterials exhibiting high elastic moduli (e.g., carbon-based nanomaterials) benefit from high Qs, operate at high frequency, and have small force constants that translate to high responsivity that results in improved sensitivity, lower power consumption, and im - proved tunablity. NEMS resonators have recently been demonstrated using topdown

  19. Direct injection in organic SU8 nanowires and nanotubes for waveguiding properties investigation

    Science.gov (United States)

    Bigeon, J.; Huby, N.; Duvail, Jean-Luc; Bêche, Bruno

    2014-05-01

    We report photonic concepts related to injection and sub-wavelength propagation in nanofibers (nanowires and nanotubes). These nanostructures are fabricated by the wetting template method leading to aspect ratio of over 250. At first, injection into nanowires and nanotubes of SU8, a photoresist used for integrated photonics, was successfully achieved by using polymer microlensed fibers with sub-micronic radius of curvature. Theoret- ical simulation by finite domain time-dependent (FDTD) method was used to determine the sub-wavelength propagation for nanowires and nanotubes and corroborate this coupling phenomena. The original confinement of energy density into SU8 nanotubes is highlighted. Finally, characterisation of propagation losses is reported by using a cut-back method transposed to such nanotubes and determined to range between 1 and 2 dB/mm. Both injection and cut-back method developed here are compatible with any sub-micronic structures. This work on SU8 nanofibers suggests broader perspectives for future nanophotonics.

  20. ASPECT RATIO DEPENDENCE OF THE FREE-FALL TIME FOR NON-SPHERICAL SYMMETRIES

    Energy Technology Data Exchange (ETDEWEB)

    Pon, Andy; Johnstone, Doug [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, STN CSC, Victoria, BC V8W 3P6 (Canada); Toala, Jesus A. [Instituto de Astrofisica de Andalucia, CSIC, Glorieta de la Astronomia s/n, E-18008, Granada (Spain); Vazquez-Semadeni, Enrique; Gomez, Gilberto C. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Campus Morelia Apartado Postal 3-72, 58090 Morelia, Michoacan (Mexico); Heitsch, Fabian, E-mail: arpon@uvic.ca, E-mail: Douglas.Johnstone@nrc-cnrc.gc.ca, E-mail: toala@iaa.es, E-mail: e.vazquez@crya.unam.mx, E-mail: g.gomez@crya.unam.mx, E-mail: fheitsch@unc.edu [Department of Physics and Astronomy, University of North Carolina Chapel Hill, CB 3255, Phillips Hall, Chapel Hill, NC 27599 (United States)

    2012-09-10

    We investigate the collapse of non-spherical substructures, such as sheets and filaments, which are ubiquitous in molecular clouds. Such non-spherical substructures collapse homologously in their interiors but are influenced by an edge effect that causes their edges to be preferentially accelerated. We analytically compute the homologous collapse timescales of the interiors of uniform-density, self-gravitating filaments and find that the homologous collapse timescale scales linearly with the aspect ratio. The characteristic timescale for an edge-driven collapse mode in a filament, however, is shown to have a square-root dependence on the aspect ratio. For both filaments and circular sheets, we find that selective edge acceleration becomes more important with increasing aspect ratio. In general, we find that lower dimensional objects and objects with larger aspect ratios have longer collapse timescales. We show that estimates for star formation rates, based upon gas densities, can be overestimated by an order of magnitude if the geometry of a cloud is not taken into account.

  1. ASPECT RATIO DEPENDENCE OF THE FREE-FALL TIME FOR NON-SPHERICAL SYMMETRIES

    International Nuclear Information System (INIS)

    Pon, Andy; Johnstone, Doug; Toalá, Jesús A.; Vázquez-Semadeni, Enrique; Gómez, Gilberto C.; Heitsch, Fabian

    2012-01-01

    We investigate the collapse of non-spherical substructures, such as sheets and filaments, which are ubiquitous in molecular clouds. Such non-spherical substructures collapse homologously in their interiors but are influenced by an edge effect that causes their edges to be preferentially accelerated. We analytically compute the homologous collapse timescales of the interiors of uniform-density, self-gravitating filaments and find that the homologous collapse timescale scales linearly with the aspect ratio. The characteristic timescale for an edge-driven collapse mode in a filament, however, is shown to have a square-root dependence on the aspect ratio. For both filaments and circular sheets, we find that selective edge acceleration becomes more important with increasing aspect ratio. In general, we find that lower dimensional objects and objects with larger aspect ratios have longer collapse timescales. We show that estimates for star formation rates, based upon gas densities, can be overestimated by an order of magnitude if the geometry of a cloud is not taken into account.

  2. Long-range forces affecting equilibrium inertial focusing behavior in straight high aspect ratio microfluidic channels

    Energy Technology Data Exchange (ETDEWEB)

    Reece, Amy E.; Oakey, John, E-mail: joakey@uwyo.edu [Department of Chemical Engineering, University of Wyoming, Laramie, Wyoming 82071 (United States)

    2016-04-15

    The controlled and directed focusing of particles within flowing fluids is a problem of fundamental and technological significance. Microfluidic inertial focusing provides passive and precise lateral and longitudinal alignment of small particles without the need for external actuation or sheath fluid. The benefits of inertial focusing have quickly enabled the development of miniaturized flow cytometers, size-selective sorting devices, and other high-throughput particle screening tools. Straight channel inertial focusing device design requires knowledge of fluid properties and particle-channel size ratio. Equilibrium behavior of inertially focused particles has been extensively characterized and the constitutive phenomena described by scaling relationships for straight channels of square and rectangular cross section. In concentrated particle suspensions, however, long-range hydrodynamic repulsions give rise to complex particle ordering that, while interesting and potentially useful, can also dramatically diminish the technique’s effectiveness for high-throughput particle handling applications. We have empirically investigated particle focusing behavior within channels of increasing aspect ratio and have identified three scaling regimes that produce varying degrees of geometrical ordering between focused particles. To explore the limits of inertial particle focusing and identify the origins of these long-range interparticle forces, we have explored equilibrium focusing behavior as a function of channel geometry and particle concentration. Experimental results for highly concentrated particle solutions identify equilibrium thresholds for focusing that scale weakly with concentration and strongly with channel geometry. Balancing geometry mediated inertial forces with estimates for interparticle repulsive forces now provide a complete picture of pattern formation among concentrated inertially focused particles and enhance our understanding of the fundamental limits

  3. A Sense of Proportion: Aspect Ratio and the Framing of Television Space

    OpenAIRE

    Cardwell, Sarah E. F.

    2015-01-01

    Aspect ratio’ is frequently overlooked or naively characterised. Yet it plays a fundamental, determining role in forming and framing television’s spaces. A balanced reappraisal of television’s varied aspect ratios and their unique dramatic and aesthetic possibilities can enhance our close analyses and our understanding of television’s ‘art history’. This paper challenges myths, misunderstandings and preconceptions about TV’s aspect ratios and their spatial properties. Countering prevailing p...

  4. Highly ordered Ni–Ti–O nanotubes for non-enzymatic glucose detection

    Energy Technology Data Exchange (ETDEWEB)

    Hang, Ruiqiang, E-mail: hangruiqiang@tyut.edu.cn [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Liu, Yanlian [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Gao, Ang [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Bai, Long; Huang, Xiaobo; Zhang, Xiangyu; Lin, Naiming [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Tang, Bin, E-mail: tangbin@tyut.edu.cn [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

    2015-06-01

    Anodization is used to fabricate Ni–Ti–O nanotube (NT) electrodes for non-enzymatic glucose detection. The morphology, microstructure and composition of the materials are characterized by field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Our results show amorphous and highly ordered NTs with diameter of 50 nm, length of 800 nm, and Ni/Ti ratio (at %) of 0.35 can be fabricated in ethylene glycol electrolyte supplemented with 0.2 wt.% NH{sub 4}F and 0.5 vol.% H{sub 2}O at 30 °C and 25 V for 1 h. Electrochemical experiments indicate that at an applied potential of 0.60 V vs. Ag/AgCl, the electrode exhibits a linear response window for glucose concentrations from 0.002 mM to 0.2 mM with a response time of 10 s, detection limit of 0.13 μM (S/N = 3), and sensitivity of 83 μA mM{sup −1} cm{sup −2}. The excellent performance of the electrode is attributed to its large specific area and fast electron transfer between the NT walls. The good electrochemical performance of the Ni–Ti–O NTs as well as their simple and low-cost preparation method make the strategy promising in non-enzymatic glucose detection. - Highlights: • Highly ordered Ni–Ti–O nanotubes have been fabricated by one-step anodization. • We find H{sub 2}O contents in the electrolyte is critical to successful fabrication of the NTs. • The Ni–Ti–O nanotubes are ideal electrode materials for non-enzymatic glucose detection.

  5. High-aspect-ratio, silicon oxide-enclosed pillar structures in microfluidic liquid chromatography.

    Science.gov (United States)

    Taylor, Lisa C; Lavrik, Nickolay V; Sepaniak, Michael J

    2010-11-15

    The present paper discusses the ability to separate chemical species using high-aspect-ratio, silicon oxide-enclosed pillar arrays. These miniaturized chromatographic systems require smaller sample volumes, experience less flow resistance, and generate superior separation efficiency over traditional packed bed liquid chromatographic columns, improvements controlled by the increased order and decreased pore size of the systems. In our distinctive fabrication sequence, plasma-enhanced chemical vapor deposition (PECVD) of silicon oxide is used to alter the surface and structural properties of the pillars for facile surface modification while improving the pillar mechanical stability and increasing surface area. The separation behavior of model compounds within our pillar systems indicated an unexpected hydrophobic-like separation mechanism. The effects of organic modifier, ionic concentration, and pressure-driven flow rate were studied. A decrease in the organic content of the mobile phase increased peak resolution while detrimentally effecting peak shape. A resolution of 4.7 (RSD = 3.7%) was obtained for nearly perfect Gaussian shaped peaks, exhibiting plate heights as low as 1.1 and 1.8 μm for fluorescein and sulforhodamine B, respectively. Contact angle measurements and DART mass spectrometry analysis indicate that our employed elastomeric soft bonding technique modifies pillar properties, creating a fortuitous stationary phase. This discovery provides evidence supporting the ability to easily functionalize PECVD oxide surfaces by gas-phase reactions.

  6. The effect of particle aspect ratio on the electroelastic properties of piezoelectric nanocomposites

    International Nuclear Information System (INIS)

    Andrews, C; Lin, Y; Sodano, H A

    2010-01-01

    Piezoelectric materials offer exceptional sensing and actuation properties; however, they are prone to breakage and difficult to apply on curved surfaces in their monolithic form. One method of alleviating these issues is through the use of 0–3 nanocomposites, which are formed by embedding piezoelectric particles into a polymer matrix. Material of this class offers certain advantages over monolithic materials; however, it has seen little use due to its low coupling. Here we develop micromechanics and finite element models to study the electroelastic properties of an active nanocomposite, as a function of the aspect ratio and alignment of the piezoelectric filler. Our results show that the aspect ratio is critical for achieving high electromechanical coupling, and with an increase from 1 to 10 at 30% volume fraction of piezoelectric filler the coupling can increase to 60 times its initial value and achieve a bulk composite coupling as high as 90% for a pure PZT-7A piezoelectric constituent

  7. High quantum yield graphene quantum dots decorated TiO_2 nanotubes for enhancing photocatalytic activity

    International Nuclear Information System (INIS)

    Qu, Ailan; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan

    2016-01-01

    Highlights: • High concentration yellow GQDs and TiO_2 nanotubes were achieved by a simple and green method. • High quantum yield GQDs enhanced the photodegradation capacity of TiO_2 nanotube. • The catalytic performance of GQDs/TiO_2 depends on the GQDs loading. • The improved photocatalytic activity of GQDs/TiO_2 was attributed to three aspects. - Abstract: Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO_2 nanotubes (GQDs/TiO_2 NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600–800 nm. The photocatalytic activity of prepared GQDs/TiO_2 NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO_2 nanotubes (TiO_2 NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV–vis light irradiation (λ = 380–780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO_2 NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO_2 NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO_2 composite.

  8. Facile Route to Vertically Aligned High-Aspect Ratio Block Copolymer Films via Dynamic Zone Annealing

    Science.gov (United States)

    Singh, Gurpreet; Kulkarni, Manish; Yager, Kevin; Smilgies, Detlef; Bucknall, David; Karim, Alamgir

    2012-02-01

    Directed assembly of block copolymers (BCP) can be used to fabricate a diversity of nanostructures useful for nanotech applications. The ability to vertically orient etchable high aspect ratio (˜30) ordered BCP domains on flexible substrates via continuous processing methods are particularly attractive for nanomanufacturing. We apply sharp dynamic cold zone annealing (CZA-S) to create etchable, and predominantly vertically oriented 30nm cylindrical domains in 1 μm thick poly(styrene-b-methylmethacrylate) films on low thermal conductivity rigid (quartz) and flexible (PDMS & Kapton) substrates. Under similar static conditions, temporally stable vertical cylinders form within a narrow zone above a critical temperature gradient. Primary ordering mechanism of CZA-S involves sweeping this vertically orienting zone created at maximum thermal gradient. An optimal speed is needed since the process competes with preferential surface wetting dynamics that favors parallel orientation. GISAXS of etched BCP films confirms internal morphology.

  9. Effect of aspect ratio on the laminar-to-turbulent transition in rectangular channel

    International Nuclear Information System (INIS)

    Wang Chang; Gao Puzhen; Tan Sichao; Xu Chao

    2012-01-01

    Highlights: ► Effect of aspect ratio on the transition Reynolds number in rectangular channel is studied. ► Prediction correlation for transition Reynolds number is proposed. ► The initiation location of flow transition is studied. - Abstract: The critical Reynolds number of the laminar-to-turbulent transition in the rectangular channel is investigated based on the energy gradient method. The results show that the critical Reynolds number decreases with the increasing aspect ratio. However, the relative location of laminar breakdown does not migrate significantly with the variation of the aspect ratio. In addition, a theoretical correlation as a function of the aspect ratio is proposed to calculate the transition Reynolds number, and the predicted values are in good agreement with the experimental data obtained in the published literatures.

  10. Tight aspect ratio tokamak power reactor with superconducting TF coils

    International Nuclear Information System (INIS)

    Nishio, S.; Tobita, K.; Konishi, S.; Ando, T.; Hiroki, S.; Kuroda, T.; Yamauchi, M.; Azumi, M.; Nagata, M.

    2003-01-01

    Tight aspect ratio tokamak power reactor with super-conducting toroidal field (TF) coils has been proposed. A center solenoid coil system and an inboard blanket were discarded. The key point was how to find the engineering design solution of the TF coil system with the high field and high current density. The coil system with the center post radius of less than 1 m can generate the maximum field of ∼ 20 T. This coil system causes a compact reactor concept, where the plasma major and minor radii of 3.75 m and 1.9 m, respectively and the fusion power of 1.8 GW. (author)

  11. Filament Winding Multifunctional Carbon Nanotube Composites of Various Dimensionality

    Science.gov (United States)

    Wells, Brian David

    Carbon nanotubes (CNT) have been long considered an optimal material for composites due to their high strength, high modulus, and electrical/thermal conductivity. These composite materials have the potential to be used in the aerospace, computer, automotive, medical industry as well as many others. The nano dimensions of these structures make controlled alignment and distribution difficult using many production techniques. An area that shows promise for controlled alignment is the formation of CNT yarns. Different approaches have been used to create yarns with various winding angles and diameters. CNTs resemble traditional textile fiber structures due to their one-dimensional dimensions, axial strength and radial flexibility. One difference is, depending on the length, CNTs can have aspect ratios that far exceed those of traditional textile fibers. This can complicate processing techniques and cause agglomeration which prevents optimal structures from being created. However, with specific aspect ratios and spatial distributions a specific type of CNT, vertically aligned spinnable carbon nanotubes (VASCNTs), have interesting properties that allow carbon nanotubes to be drawn from an array in a continuous aligned web. This dissertation examines the feasibility of combining VASCNTs with another textile manufacturing process, filament winding, to create structures with various levels of dimensionality. While yarn formation with CNTs has been largely studied, there has not been significant work studying the use of VASCNTs to create composite materials. The studies that have been produces revolve around mixing CNTs into epoxy or creating uni-directional wound structures. In this dissertation VASCNTs are used to create filament wound materials with various degrees of alignment. These structures include 1 dimensional coatings applied to non-conductive polymer monofilaments, two dimensional multifunctional adhesive films, and three dimensional hybrid-nano composites. The

  12. Aspect Ratio Dependence of Impact Fragmentation

    International Nuclear Information System (INIS)

    Inaoka, H.; Toyosawa, E.; Takayasu, H.; Inaoka, H.

    1997-01-01

    A numerical model of three-dimensional impact fragmentation produces a power-law cumulative fragment mass distribution followed by a flat tail. The result is consistent with an experimental result in a recent paper by Meibom and Balslev [Phys. Rev. Lett. 76, 2492 (1996)]. Our numerical simulation also implies that the fragment mass distribution changes from a power law with a flat tail to a power law with a sudden cutoff, depending on the aspect ratio of the fractured object. copyright 1997 The American Physical Society

  13. Durability and inflammogenic impact of carbon nanotubes compared with asbestos fibres

    Directory of Open Access Journals (Sweden)

    Clark Steve

    2011-05-01

    Full Text Available Abstract Background It has been suggested that carbon nanotubes might conform to the fibre pathogenicity paradigm that explains the toxicities of asbestos and other fibres on a continuum based on length, aspect ratio and biopersistence. Some types of carbon nanotubes satisfy the first two aspects of the fibre paradigm but only recently has their biopersistence begun to be investigated. Biopersistence is complex and requires in vivo testing and analysis. However durability, the chemical mimicking of the process of fibre dissolution using in vitro treatment, is closely related to biopersistence and more readily determined. Here, we describe an experimental process to determine the durability of four types of carbon nanotubes in simulated biological fluid (Gambles solution, and their subsequent pathogenicity in vivo using a mouse model sensitive to inflammogenic effects of fibres. The in vitro and in vivo results were compared with well-characterised glass wool and asbestos fibre controls. Results After incubation for up to 24 weeks in Gambles solution, our control fibres were recovered at percentages consistent with their known in vitro durabilities and/or in vivo persistence, and three out of the four types of carbon nanotubes tested (single-walled (CNTSW and multi-walled (CNTTANG2, CNTSPIN showed no, or minimal, loss of mass or change in fibre length or morphology when examined by electron microscopy. However, the fourth type [multi-walled (CNTLONG1] lost 30% of its original mass within the first three weeks of incubation, after which there was no further loss. Electron microscopy of CNTLONG1 samples incubated for 10 weeks confirmed that the proportion of long fibres had decreased compared to samples briefly exposed to the Gambles solution. This loss of mass and fibre shortening was accompanied by a loss of pathogenicity when injected into the peritoneal cavities of C57Bl/6 mice compared to fibres incubated briefly. CNTSW did not elicit an

  14. Fowler Nordheim theory of carbon nanotube based field emitters

    Energy Technology Data Exchange (ETDEWEB)

    Parveen, Shama; Kumar, Avshish [Department of Physics, Jamia Millia Islamia (Central University), New Delhi (India); Husain, Samina [Centre for Nanoscience and Nanotechnology, Jamia Millia Islamia (Central University), New Delhi (India); Husain, Mushahid, E-mail: mush_reslab@rediffmail.com [Department of Physics, Jamia Millia Islamia (Central University), New Delhi (India)

    2017-01-15

    Field emission (FE) phenomena are generally explained in the frame-work of Fowler Nordheim (FN) theory which was given for flat metal surfaces. In this work, an effort has been made to present the field emission mechanism in carbon nanotubes (CNTs) which have tip type geometry at nanoscale. High aspect ratio of CNTs leads to large field enhancement factor and lower operating voltages because the electric field strength in the vicinity of the nanotubes tip can be enhanced by thousand times. The work function of nanostructure by using FN plot has been calculated with reverse engineering. With the help of modified FN equation, an important formula for effective emitting area (active area for emission of electrons) has been derived and employed to calculate the active emitting area for CNT field emitters. Therefore, it is of great interest to present a state of art study on the complete solution of FN equation for CNTs based field emitter displays. This manuscript will also provide a better understanding of calculation of different FE parameters of CNTs field emitters using FN equation.

  15. Electron diffraction from carbon nanotubes

    International Nuclear Information System (INIS)

    Qin, L-C

    2006-01-01

    The properties of a carbon nanotube are dependent on its atomic structure. The atomic structure of a carbon nanotube can be defined by specifying its chiral indices (u, v), that specify its perimeter vector (chiral vector), with which the diameter and helicity are also determined. The fine electron beam available in a modern transmission electron microscope (TEM) offers a unique probe to reveal the atomic structure of individual nanotubes. This review covers two aspects related to the use of the electron probe in the TEM for the study of carbon nanotubes: (a) to understand the electron diffraction phenomena for inter-pretation of the electron diffraction patterns of carbon nanotubes and (b) to obtain the chiral indices (u, v), of the carbon nanotubes from the electron diffraction patterns. For a nanotube of a given structure, the electron scattering amplitude from the carbon nanotube is first described analytically in closed form using the helical diffraction theory. From a known structure as given by the chiral indices (u, v), its electron diffraction pattern can be calculated and understood. The reverse problem, i.e. assignment of the chiral indices from an electron diffraction pattern of a carbon nanotube, is approached from the relationship between the electron scattering intensity distribution and the chiral indices (u, v). We show that electron diffraction patterns can provide an accurate and unambiguous assignment of the chiral indices of carbon nanotubes. The chiral indices (u, v) can be read indiscriminately with a high accuracy from the intensity distribution on the principal layer lines in an electron diffraction pattern. The symmetry properties of electron diffraction from carbon nanotubes and the electron diffraction from deformed carbon nanotubes are also discussed in detail. It is shown that 2mm symmetry is always preserved for single-walled carbon nanotubes, but it can break down for multiwalled carbon nanotubes under some special circumstances

  16. High dispersity of carbon nanotubes diminishes immunotoxicity in spleen.

    Science.gov (United States)

    Lee, Soyoung; Khang, Dongwoo; Kim, Sang-Hyun

    2015-01-01

    From the various physiochemical material properties, the chemical functionalization order of single-walled carbon nanotubes (swCNTs) has not been considered as a critical factor for modulating immunological responses and toxicological aspects in drug delivery applications. Although most nanomaterials, including carbon nanotubes, are specifically accumulated in spleen, few studies have focused on spleen immunotoxicity. For this reason, this study demonstrated that the dispersity of swCNTs significantly influenced immunotoxicity in vitro and in vivo. For cytotoxicity of swCNTs, MTT assay, reactive oxygen species production, superoxide dismutase activity, cellular uptake, and confocal microscopy were used in macrophages. In the in vivo study, female BALB/c mice were intravenously administered with 1 mg/kg/day of swCNTs for 2 weeks. The body weight, organ weight, hematological change, reverse-transcription polymerase chain reaction, and lymphocyte population were evaluated. Different orders of chemical functionalization of swCNTs controlled immunotoxicity. In short, less-dispersed swCNTs caused cytotoxicity in macrophages and abnormalities in immune organs such as spleen, whereas highly dispersed swCNTs did not result in immunotoxicity. This study clarified that increasing carboxyl groups on swCNTs significantly mitigated immunotoxicity in vitro and in vivo. Our findings clarified the effective immunotoxicological factors of swCNTs by increasing dispersity of swCNTs and provided useful guidelines for the effective use of nanomaterials.

  17. Experimental observations of electron-backscatter effects from high-atomic-number anodes in large-aspect-ratio, electron-beam diodes

    Energy Technology Data Exchange (ETDEWEB)

    Cooperstein, G; Mosher, D; Stephanakis, S J; Weber, B V; Young, F C [Naval Research Laboratory, Washington, DC (United States); Swanekamp, S B [JAYCOR, Vienna, VA (United States)

    1997-12-31

    Backscattered electrons from anodes with high-atomic-number substrates cause early-time anode-plasma formation from the surface layer leading to faster, more intense electron beam pinching, and lower diode impedance. A simple derivation of Child-Langmuir current from a thin hollow cathode shows the same dependence on the diode aspect ratio as critical current. Using this fact, it is shown that the diode voltage and current follow relativistic Child-Langmuir theory until the anode plasma is formed, and then follows critical current after the beam pinches. With thin hollow cathodes, electron beam pinching can be suppressed at low voltages (< 800 kV) even for high currents and high-atomic-number anodes. Electron beam pinching can also be suppressed at high voltages for low-atomic-number anodes as long as the electron current densities remain below the plasma turn-on threshold. (author). 8 figs., 2 refs.

  18. On/off ratio enhancement in single-walled carbon nanotube field-effect transistor by controlling network density via sonication

    Science.gov (United States)

    Jang, Ho-Kyun; Choi, Jun Hee; Kim, Do-Hyun; Kim, Gyu Tae

    2018-06-01

    Single-walled carbon nanotube (SWCNT) is generally used as a networked structure in the fabrication of a field-effect transistor (FET) since it is known that one-third of SWCNT is electrically metallic and the remains are semiconducting. In this case, the presence of metallic paths by metallic SWCNT (m-SWCNT) becomes a significant technical barrier which hinders the networks from achieving a semiconducting behavior, resulting in a low on/off ratio. Here, we report on an easy method of controlling the on/off ratio of a FET where semiconducting SWCNT (s-SWCNT) and m-SWCNT constitute networks between source and drain electrodes. A FET with SWCNT networks was simply sonicated under water to control the on/off ratio and network density. As a result, the FET having an almost metallic behavior due to the metallic paths by m-SWCNT exhibited a p-type semiconducting behavior. The on/off ratio ranged from 1 to 9.0 × 104 along sonication time. In addition, theoretical calculations based on Monte-Carlo method and circuit simulation were performed to understand and explain the phenomenon of a change in the on/off ratio and network density by sonication. On the basis of experimental and theoretical results, we found that metallic paths contributed to a high off-state current which leads to a low on/off ratio and that sonication formed sparse SWCNT networks where metallic paths of m-SWCNT were removed, resulting in a high on/off ratio. This method can open a chance to save the device which has been considered as a failed one due to a metallic behavior by a high network density leading to a low on/off ratio.

  19. Nano-scaled graphene platelets with a high length-to-width aspect ratio

    Science.gov (United States)

    Zhamu, Aruna; Guo, Jiusheng; Jang, Bor Z.

    2010-09-07

    This invention provides a nano-scaled graphene platelet (NGP) having a thickness no greater than 100 nm and a length-to-width ratio no less than 3 (preferably greater than 10). The NGP with a high length-to-width ratio can be prepared by using a method comprising (a) intercalating a carbon fiber or graphite fiber with an intercalate to form an intercalated fiber; (b) exfoliating the intercalated fiber to obtain an exfoliated fiber comprising graphene sheets or flakes; and (c) separating the graphene sheets or flakes to obtain nano-scaled graphene platelets. The invention also provides a nanocomposite material comprising an NGP with a high length-to-width ratio. Such a nanocomposite can become electrically conductive with a small weight fraction of NGPs. Conductive composites are particularly useful for shielding of sensitive electronic equipment against electromagnetic interference (EMI) or radio frequency interference (RFI), and for electrostatic charge dissipation.

  20. High aspect ratio silicon nanowires control fibroblast adhesion and cytoskeleton organization

    Science.gov (United States)

    Andolfi, Laura; Murello, Anna; Cassese, Damiano; Ban, Jelena; Dal Zilio, Simone; Lazzarino, Marco

    2017-04-01

    Cell-cell and cell-matrix interactions are essential to the survival and proliferation of most cells, and are responsible for triggering a wide range of biochemical pathways. More recently, the biomechanical role of those interactions was highlighted, showing, for instance, that adhesion forces are essential for cytoskeleton organization. Silicon nanowires (Si NWs) with their small size, high aspect ratio and anisotropic mechanical response represent a useful model to investigate the forces involved in the adhesion processes and their role in cellular development. In this work we explored and quantified, by single cell force spectroscopy (SCFS), the interaction of mouse embryonic fibroblasts with a flexible forest of Si NWs. We observed that the cell adhesion forces are comparable to those found on collagen and bare glass coverslip, analogously the membrane tether extraction forces are similar to that on collagen but stronger than that on bare flat glass. Cell survival did not depend significantly on the substrate, although a reduced proliferation after 36 h was observed. On the contrary both cell morphology and cytoskeleton organization revealed striking differences. The cell morphology on Si-NW was characterized by a large number of filopodia and a significant decrease of the cell mobility. The cytoskeleton organization was characterized by the absence of actin fibers, which were instead dominant on collagen and flat glass support. Such findings suggest that the mechanical properties of disordered Si NWs, and in particular their strong asymmetry, play a major role in the adhesion, morphology and cytoskeleton organization processes. Indeed, while adhesion measurements by SCFS provide out-of-plane forces values consistent with those measured on conventional substrates, weaker in-plane forces hinder proper cytoskeleton organization and migration processes.

  1. Large-scale synthesis of lead telluride (PbTe) nanotube-based nanocomposites with tunable morphology, crystallinity and thermoelectric properties

    Science.gov (United States)

    Park, Kee-Ryung; Cho, Hong-Baek; Song, Yoseb; Kim, Seil; Kwon, Young-Tae; Ryu, Seung Han; Lim, Jae-Hong; Lee, Woo-Jin; Choa, Yong-Ho

    2018-04-01

    A few millimeter-long lead telluride (PbTe) hollow nanofibers with thermoelectric properties was synthesized for the first time with high through manner via three-step sequential process of electrospinning, electrodeposition and cationic exchange reaction. As-synthesized electrospun Ag nanofibers with ultra-long aspect ratio of 10,000 were Te electrodeposited to obtain silver telluride nanotubes and underwent cationic exchange reaction in Pb(NO3)2 solution to obtain polycrystalline PbTe nanotubes with average diameter of 100 nm with 20 nm of wall thickness. Variation of the Ag-to-Pb ratio in the AgxTey-PbTe nanocomposites during the cationic exchange reaction enabled to control the thermoelectric properties of resulting 1D hollow nanofibers. The diameter of Ag nanofiber is the key factor to determine the final dimension of the PbTe nanotubes in the topotactic transformation and the content of Ag ion leads to the enhancement of thermoelectric properties in the AgxTey-PbTe nanocomposites. The synthesized 1D nanocomposite mats showed the highest value of Seebeck coefficient of 433 μV/K (at 300 K) when the remained Ag content was 30%, while the power factor reached highest to 0.567 μW/mK2 for the pure PbTe nanotubes. The enhancement of thermoelectric properties and the composite crystallinity are elucidated with relation to Ag contents in the resulting 1D nanocomposites.

  2. Study by the Prandtl-Glauert method of compressibility effects and critical Mach number for ellipsoids of various aspect ratios and thickness ratios

    Science.gov (United States)

    Hess, Robert V; Gardner, Clifford S

    1947-01-01

    By using the Prandtl-Glauert method that is valid for three-dimensional flow problems, the value of the maximum incremental velocity for compressible flow about thin ellipsoids at zero angle of attack is calculated as a function of the Mach number for various aspect ratios and thickness ratios. The critical Mach numbers of the various ellipsoids are also determined. The results indicate an increase in critical Mach number with decrease in aspect ratio which is large enough to explain experimental results on low-aspect-ratio wings at zero lift.

  3. Study of blade aspect ratio on a compressor front stage aerodynamic and mechanical design report

    Science.gov (United States)

    Burger, G. D.; Lee, D.; Snow, D. W.

    1979-01-01

    A single stage compressor was designed with the intent of demonstrating that, for a tip speed and hub-tip ratio typical of an advanced core compressor front stage, the use of low aspect ratio can permit high levels of blade loading to be achieved at an acceptable level of efficiency. The design pressure ratio is 1.8 at an adiabatic efficiency of 88.5 percent. Both rotor and stator have multiple-circular-arc airfoil sections. Variable IGV and stator vanes permit low speed matching adjustments. The design incorporates an inlet duct representative of an engine transition duct between fan and high pressure compressor.

  4. Fabrication of mesoporous and high specific surface area lanthanum carbide-carbon nanotube composites

    International Nuclear Information System (INIS)

    Biasetto, L.; Carturan, S.; Maggioni, G.; Zanonato, P.; Bernardo, P. Di; Colombo, P.; Andrighetto, A.; Prete, G.

    2009-01-01

    Mesoporous lanthanum carbide-carbon nanotube composites were produced by means of carbothermal reaction of lanthanum oxide, graphite and multi-walled carbon nanotube mixtures under high vacuum. Residual gas analysis revealed the higher reactivity of lanthanum oxide towards carbon nanotubes compared to graphite. After sintering, the composites revealed a specific surface area increasing with the amount of carbon nanotubes introduced. The meso-porosity of carbon nanotubes was maintained after thermal treatment.

  5. Collisional Transport in a Low Aspect Ratio Tokamak -- Beyond the Drift Kinetic Formalism

    International Nuclear Information System (INIS)

    Gates, D.A.; White, R.B.

    2004-01-01

    Calculations of collisional thermal and particle diffusivities in toroidal magnetic plasma confinement devices order the toroidal gyroradius to be small relative to the poloidal gyroradius. This ordering is central to what is usually referred to as neoclassical transport theory. This ordering is incorrect at low aspect ratio, where it can often be the case that the toroidal gyroradius is larger than the poloidal gyroradius. We calculate the correction to the particle and thermal diffusivities at low aspect ratio by comparing the diffusivities as determined by a full orbit code (which we refer to as omni-classical diffusion) with those from a gyroaveraged orbit code (neoclassical diffusion). In typical low aspect ratio devices the omni-classical diffusion can be up to 2.5 times the calculated neoclassical value. We discuss the implications of this work on the analysis of collisional transport in low aspect ratio magnetic confinement experiments

  6. High-performance carbon nanotube-reinforced bioplastic

    CSIR Research Space (South Africa)

    Ramontja, J

    2009-12-01

    Full Text Available -1 High-Performance Carbon Nanotube-Reinforced Bioplastic 1. James Ramontja1,2, 2. Suprakas Sinha Ray1,*, 3. Sreejarani K. Pillai1, 4. Adriaan S. Luyt2 1. 1 DST/CSIR Nanotechnology Innovation Centre, National Centre for Nano-Structured Materials...

  7. Improved tensile and buckling behavior of defected carbon nanotubes utilizing boron nitride coating – A molecular dynamic study

    Energy Technology Data Exchange (ETDEWEB)

    Badjian, H.; Setoodeh, A.R., E-mail: setoodeh@sutech.ac.ir

    2017-02-15

    Synthesizing inorganic nanostructures such as boron nitride nanotubes (BNNTs) have led to immense studies due to their many interesting functional features such as piezoelectricity, high temperature resistance to oxygen, electrical insulation, high thermal conductivity and very long lengths as physical features. In order to utilize the superior properties of pristine and defected carbon nanotubes (CNTs), a hybrid nanotube is proposed in this study by forming BNNTs surface coating on the CNTs. The benefits of such coating on the tensile and buckling behavior of single-walled CNTs (SWCNTs) are illustrated through molecular dynamics (MD) simulations of the resulted nanostructures during the deformation. The AIREBO and Tersoff-Brenner potentials are employed to model the interatomic forces between the carbon and boron nitride atoms, respectively. The effects of chiral indices, aspect ratio, presence of mono-vacancy defects and coating dimension on coated/non-coated CNTs are examined. It is demonstrated that the coated defective CNTs exhibit remarkably enhanced ultimate strength, buckling load capacity and Young's modulus. The proposed coating not only enhances the mechanical properties of the resulted nanostructure, but also conceals it from few external factors impacting the behavior of the CNT such as humidity and high temperature.

  8. Poly(3,4-ethylenedioxythiophene) nanotubes as electrode materials for a high-powered supercapacitor

    International Nuclear Information System (INIS)

    Liu Ran; Cho, Seung Il; Lee, Sang Bok

    2008-01-01

    We report the fast charging/discharging capability of poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes during the redox process and their potential application to a high-powered supercapacitor. PEDOT nanotubes were electrochemically synthesized in a porous alumina membrane, and their structures were characterized using electron microscopes. Cyclic voltammetry was used to characterize the specific capacitance of the PEDOT nanotubes at various scan rates. A type I supercapacitor (two symmetric electrodes) based on PEDOT nanotube electrodes was fabricated, and its energy density and power density were evaluated by galvanostatic charge/discharge cycles at various current densities. We show that the PEDOT-nanotube-based supercapacitor can achieve a high power density of 25 kW kg -1 while maintaining 80% energy density (5.6 W h kg -1 ). This high power capability is attributed to the fast charge/discharge of nanotubular structures: hollow nanotubes allow counter-ions to readily penetrate into the polymer and access their internal surfaces, while the thin wall provides a short diffusion distance to facilitate the ion transport. Impedance spectroscopy shows that nanotubes have much lower diffusional resistance to charging ions than solid nanowires shielded by an alumina template, providing supporting information for the high charging/discharging efficiency of nanotubular structures

  9. A model for roll stall and the inherent stability modes of low aspect ratio wings at low Reynolds numbers

    Science.gov (United States)

    Shields, Matt

    The development of Micro Aerial Vehicles has been hindered by the poor understanding of the aerodynamic loading and stability and control properties of the low Reynolds number regime in which the inherent low aspect ratio (LAR) wings operate. This thesis experimentally evaluates the static and damping aerodynamic stability derivatives to provide a complete aerodynamic model for canonical flat plate wings of aspect ratios near unity at Reynolds numbers under 1 x 105. This permits the complete functionality of the aerodynamic forces and moments to be expressed and the equations of motion to solved, thereby identifying the inherent stability properties of the wing. This provides a basis for characterizing the stability of full vehicles. The influence of the tip vortices during sideslip perturbations is found to induce a loading condition referred to as roll stall, a significant roll moment created by the spanwise induced velocity asymmetry related to the displacement of the vortex cores relative to the wing. Roll stall is manifested by a linearly increasing roll moment with low to moderate angles of attack and a subsequent stall event similar to a lift polar; this behavior is not experienced by conventional (high aspect ratio) wings. The resulting large magnitude of the roll stability derivative, Cl,beta and lack of roll damping, Cl ,rho, create significant modal responses of the lateral state variables; a linear model used to evaluate these modes is shown to accurately reflect the solution obtained by numerically integrating the nonlinear equations. An unstable Dutch roll mode dominates the behavior of the wing for small perturbations from equilibrium, and in the presence of angle of attack oscillations a previously unconsidered coupled mode, referred to as roll resonance, is seen develop and drive the bank angle? away from equilibrium. Roll resonance requires a linear time variant (LTV) model to capture the behavior of the bank angle, which is attributed to the

  10. Microwave synthesis and photocatalytic activities of ZnO bipods with different aspect ratios

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Fazhe; Zhao, Zengdian [Analysis and Testing Center, Shandong University of Technology, Zibo 255100 (China); Qiao, Xueliang, E-mail: xuelqiao@163.com [State Key Laboratory of Plastic Forming Simulation and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, Hubei (China); Tan, Fatang; Wang, Wei [State Key Laboratory of Plastic Forming Simulation and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, Hubei (China)

    2016-02-15

    Highlights: • We synthesized linked ZnO nanorods by a facile microwave method. • The effect of reaction parameters on ZnO was investigated. • ZnO bipods with different aspect ratios were prepared. • The photocatalytic performance of ZnO bipods was evaluated. - Abstract: Linked ZnO nanorods have been successfully prepared via a facile microwave method without any post-synthesis treatment. The X-ray diffraction (XRD) patterns indicated the precursor had completely transformed into the pure ZnO crystal. The images of field emitting scanning electron microscope (FESEM) and transmission electron microscope (TEM) showed that linked ZnO nanorods consisted predominantly of ZnO bipods. The formation process of the ZnO bipods was clearly discussed. ZnO bipods with different aspect ratios have been obtained by tuning the concentrations of reagents and microwave power. Moreover, the photocatalytic performance of ZnO bipods with different aspect ratios for degradation of methylene blue was systematically evaluated. The results of photocatalytic experiments showed that the photocatalytic activity increased with the aspect ratios of ZnO bipods increased. The reason is that ZnO bipods with larger aspect ratio have higher surface area, which can absorb more MB molecules to react with ·OH radicals.

  11. Carbon hybridized halloysite nanotubes for high-performance hydrogen storage capacities

    Science.gov (United States)

    Jin, Jiao; Fu, Liangjie; Yang, Huaming; Ouyang, Jing

    2015-01-01

    Hybrid nanotubes of carbon and halloysite nanotubes (HNTs) with different carbon:HNTs ratio were hydrothermally synthesized from natural halloysite and sucrose. The samples display uniformly cylindrical hollow tubular structure with different morphologies. These hybrid nanotubes were concluded to be promising medium for physisorption-based hydrogen storage. The hydrogen adsorption capacity of pristine HNTs was 0.35% at 2.65 MPa and 298 K, while that of carbon coated HNTs with the pre-set carbon:HNTs ratio of 3:1 (3C-HNTs) was 0.48% under the same condition. This carbon coated method could offer a new pattern for increasing the hydrogen adsorption capacity. It was also possible to enhance the hydrogen adsorption capacity through the spillover mechanism by incorporating palladium (Pd) in the samples of HNTs (Pd-HNTs) and 3C-HNTs (Pd-3C-HNTs and 3C-Pd-HNTs are the samples with different location of Pd nanoparticles). The hydrogen adsorption capacity of the Pd-HNTs was 0.50% at 2.65 MPa and 298 K, while those of Pd-3C-HNTs and 3C-Pd-HNTs were 0.58% and 0.63%, respectively. In particular, for this spillover mechanism of Pd-carbon-HNTs ternary system, the bidirectional transmission of atomic and molecular hydrogen (3C-Pd-HNTs) was concluded to be more effective than the unidirectional transmission (Pd-3C-HNTs) in this work for the first time. PMID:26201827

  12. A modal analysis of carbon nanotube using elastic network model

    International Nuclear Information System (INIS)

    Kim, Min Hyeok; Seo, Sang Jae; Lim, Byeong Soo; Choi, Jae Boong; Kim, Moon Ki; Liu, Wing Kam

    2012-01-01

    Although it is widely known that both size and chirality play significant roles in vibration behaviors of single walled carbon nanotubes (SWCNTs), there haven't been yet enough studies specifying the relationship between structure and vibration mode shape of SWCNTs. We have analyzed the chirality and length dependence of SWCNT by using normal mode analysis based elastic network model in which all interatomic interactions of the given SWCNTs structure are represented by a network of linear spring connections. As this method requires relatively short computation time compared to molecular dynamics simulation, we can efficiently analyze vibration behavior of SWCNTs. To ensure the relationship between SWCNT structure and its vibration mode shapes, we simulated more than one hundred SWCNTs having different types of chirality and length. Results indicated that the first two major mode shapes are bending and breathing. The minimum length of nanotube for maintaining the bending mode does not depend on chirality but on its diameter. Our simulations pointed out that there is a critical aspect ratio between diameter and length to determine vibration mode shapes, and it can be empirically formulated as a function of nanotube length and diameter. Therefore, uniformity control is the most important premise in order to utilize vibration features of SWCNTs. It is also expected that the obtained vibration aspect will play an important role in designing nanotube based devices such as resonators and sensors more accurately

  13. Axial buckling scrutiny of doubly orthogonal slender nanotubes via nonlocal continuum theory

    Energy Technology Data Exchange (ETDEWEB)

    Kiani, Keivan [K.N. Toosi University of Technolog, Tehran (Iran, Islamic Republic of)

    2015-10-15

    Using nonlocal Euler-Bernoulli beam theory, buckling behavior of elastically embedded Doubly orthogonal single-walled carbon nanotubes (DOSWCNTs) is studied. The nonlocal governing equations are obtained. In fact, these are coupled fourth-order integroordinary differential equations which are very difficult to be solved explicitly. As an alternative solution, Galerkin approach in conjunction with assumed mode method is employed, and the axial compressive buckling load of the nanosystem is evaluated. For DOSWCNTs with simply supported tubes, the influences of the slenderness ratio, aspect ratio, intertube free space, small-scale parameter, and properties of the surrounding elastic matrix on the axial buckling load of the nanosystem are addressed. The proposed model could be considered as a pivotal step towards better understanding the buckling behavior of more complex nanosystems such as doubly orthogonal membranes or even jungles of carbon nanotubes.

  14. Aspect Ratio Model for Radiation-Tolerant Dummy Gate-Assisted n-MOSFET Layout.

    Science.gov (United States)

    Lee, Min Su; Lee, Hee Chul

    2014-01-01

    In order to acquire radiation-tolerant characteristics in integrated circuits, a dummy gate-assisted n-type metal oxide semiconductor field effect transistor (DGA n-MOSFET) layout was adopted. The DGA n-MOSFET has a different channel shape compared with the standard n-MOSFET. The standard n-MOSFET has a rectangular channel shape, whereas the DGA n-MOSFET has an extended rectangular shape at the edge of the source and drain, which affects its aspect ratio. In order to increase its practical use, a new aspect ratio model is proposed for the DGA n-MOSFET and this model is evaluated through three-dimensional simulations and measurements of the fabricated devices. The proposed aspect ratio model for the DGA n-MOSFET exhibits good agreement with the simulation and measurement results.

  15. Study of modification methods of probes for critical-dimension atomic-force microscopy by the deposition of carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Ageev, O. A., E-mail: ageev@sfedu.ru [Southern Federal University, Institute for Nanotechnologies, Electronics, and Electronic Equipment Engineering (Russian Federation); Bykov, Al. V. [NT-MDT (Russian Federation); Kolomiitsev, A. S.; Konoplev, B. G.; Rubashkina, M. V.; Smirnov, V. A.; Tsukanova, O. G. [Southern Federal University, Institute for Nanotechnologies, Electronics, and Electronic Equipment Engineering (Russian Federation)

    2015-12-15

    The results of an experimental study of the modification of probes for critical-dimension atomicforce microscopy (CD-AFM) by the deposition of carbon nanotubes (CNTs) to improve the accuracy with which the surface roughness of vertical walls is determined in submicrometer structures are presented. Methods of the deposition of an individual CNT onto the tip of an AFM probe via mechanical and electrostatic interaction between the probe and an array of vertically aligned carbon nanotubes (VACNTs) are studied. It is shown that, when the distance between the AFM tip and a VACNT array is 1 nm and the applied voltage is within the range 20–30 V, an individual carbon nanotube is deposited onto the tip. On the basis of the results obtained in the study, a probe with a carbon nanotube on its tip (CNT probe) with a radius of 7 nm and an aspect ratio of 1:15 is formed. Analysis of the CNT probe demonstrates that its use improves the resolution and accuracy of AFM measurements, compared with the commercial probe, and also makes it possible to determine the roughness of the vertical walls of high-aspect structures by CD-AFM. The results obtained can be used to develop technological processes for the fabrication and reconditioning of special AFM probes, including those for CD-AFM, and procedures for the interoperational express monitoring of technological process parameters in the manufacturing of elements for micro- and nanoelectronics and micro- and nanosystem engineering.

  16. Flutter analysis of hybrid metal-composite low aspect ratio trapezoidal wings in supersonic flow

    Directory of Open Access Journals (Sweden)

    Shokrollahi Saeed

    2017-02-01

    Full Text Available An effective 3D supersonic Mach box approach in combination with non-classical hybrid metal-composite plate theory has been used to investigate flutter boundaries of trapezoidal low aspect ratio wings. The wing structure is composed of two main components including aluminum material (in-board section and laminated composite material (out-board section. A global Ritz method is used with simple polynomials being employed as the trial functions. The most important objective of the present research is to study the effect of composite to metal proportion of hybrid wing structure on flutter boundaries in low supersonic regime. In addition, the effect of some important geometrical parameters such as sweep angle, taper ratio and aspect ratio on flutter boundaries were studied. The results obtained by present approach for special cases like pure metallic wings and results for high supersonic regime based on piston theory show a good agreement with those obtained by other investigators.

  17. Radio frequency and linearity performance of transistors using high-purity semiconducting carbon nanotubes.

    Science.gov (United States)

    Wang, Chuan; Badmaev, Alexander; Jooyaie, Alborz; Bao, Mingqiang; Wang, Kang L; Galatsis, Kosmas; Zhou, Chongwu

    2011-05-24

    This paper reports the radio frequency (RF) and linearity performance of transistors using high-purity semiconducting carbon nanotubes. High-density, uniform semiconducting nanotube networks are deposited at wafer scale using our APTES-assisted nanotube deposition technique, and RF transistors with channel lengths down to 500 nm are fabricated. We report on transistors exhibiting a cutoff frequency (f(t)) of 5 GHz and with maximum oscillation frequency (f(max)) of 1.5 GHz. Besides the cutoff frequency, the other important figure of merit for the RF transistors is the device linearity. For the first time, we report carbon nanotube RF transistor linearity metrics up to 1 GHz. Without the use of active probes to provide the high impedance termination, the measurement bandwidth is therefore not limited, and the linearity measurements can be conducted at the frequencies where the transistors are intended to be operating. We conclude that semiconducting nanotube-based transistors are potentially promising building blocks for highly linear RF electronics and circuit applications.

  18. Mechanisms involved in the hydrothermal growth of ultra-thin and high aspect ratio ZnO nanowires

    Science.gov (United States)

    Demes, Thomas; Ternon, Céline; Morisot, Fanny; Riassetto, David; Legallais, Maxime; Roussel, Hervé; Langlet, Michel

    2017-07-01

    Hydrothermal synthesis of ZnO nanowires (NWs) with tailored dimensions, notably high aspect ratios (AR) and small diameters, is a major concern for a wide range of applications and still represents a challenging and recurring issue. In this work, an additive-free and reproducible hydrothermal procedure has been developed to grow ultra-thin and high AR ZnO NWs on sol-gel deposited ZnO seed layers. Controlling the substrate temperature and using a low reagent concentration (1 mM) has been found to be essential for obtaining such NWs. We show that the NW diameter remains constant at about 20-25 nm with growth time contrary to the NW length that can be selectively increased leading to NWs with ARs up to 400. On the basis of investigated experimental conditions along with thermodynamic and kinetic considerations, a ZnO NW growth mechanism has been developed which involves the formation and growth of nuclei followed by NW growth when the nuclei reach a critical size of about 20-25 nm. The low reagent concentration inhibits NW lateral growth leading to ultra-thin and high AR NWs. These NWs have been assembled into electrically conductive ZnO nanowire networks, which opens attractive perspectives toward the development of highly sensitive low-cost gas- or bio-sensors.

  19. Computational modelling of a non-viscous fluid flow in a multi-walled carbon nanotube modelled as a Timoshenko beam

    International Nuclear Information System (INIS)

    Khosravian, N; Rafii-Tabar, H

    2008-01-01

    In the design of nanotube-based fluidic devices, a critical issue is the effect of the induced vibrations in the nanotube arising from the fluid flow, since these vibrations can promote structural instabilities, such as buckling transitions. It is known that the induced resonant frequencies depend on the fluid flow velocity in a significant manner. We have studied, for the first time, the flow of a non-viscous fluid in stubby multi-walled carbon nanotubes, using the Timoshenko classical beam theory to model the nanotubes as a continuum structure. We have obtained the variations of the resonant frequencies with the fluid flow velocity under several experimentally interesting boundary conditions and aspect ratios of the nanotube. The main finding from our work is that, compared to an Euler-Bernoulli classical beam model of a nanotube, the Timoshenko beam predicts the loss of stability at lower fluid flow velocities

  20. Computational modelling of a non-viscous fluid flow in a multi-walled carbon nanotube modelled as a Timoshenko beam

    Energy Technology Data Exchange (ETDEWEB)

    Khosravian, N; Rafii-Tabar, H [Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: rafii-tabar@nano.ipm.ac.ir

    2008-07-09

    In the design of nanotube-based fluidic devices, a critical issue is the effect of the induced vibrations in the nanotube arising from the fluid flow, since these vibrations can promote structural instabilities, such as buckling transitions. It is known that the induced resonant frequencies depend on the fluid flow velocity in a significant manner. We have studied, for the first time, the flow of a non-viscous fluid in stubby multi-walled carbon nanotubes, using the Timoshenko classical beam theory to model the nanotubes as a continuum structure. We have obtained the variations of the resonant frequencies with the fluid flow velocity under several experimentally interesting boundary conditions and aspect ratios of the nanotube. The main finding from our work is that, compared to an Euler-Bernoulli classical beam model of a nanotube, the Timoshenko beam predicts the loss of stability at lower fluid flow velocities.

  1. Effects of finite aspect ratio on wind turbine airfoil measurements

    DEFF Research Database (Denmark)

    Kiefer, Janik; Miller, Mark A.; Hultmark, Marcus

    2016-01-01

    Wind turbines partly operate in stalled conditions within their operational cycle. To simulate these conditions, it is also necessary to obtain 2-D airfoil data in terms of lift and drag coefficients at high angles of attack. Such data has been obtained previously, but often at low aspect ratios...... and only barely past the stall point, where strong wall boundary layer influence is expected. In this study, the influence of the wall boundary layer on 2D airfoil data, especially in the post stall domain, is investigated. Here, a wind turbine airfoil is tested at different angles of attack and with two...

  2. Origin of the outer layer of martian low-aspect ratio layered ejecta craters

    Science.gov (United States)

    Boyce, Joseph M.; Wilson, Lionel; Barlow, Nadine G.

    2015-01-01

    Low-aspect ratio layered ejecta (LARLE) craters are one of the most enigmatic types of martian layered ejecta craters. We propose that the extensive outer layer of these craters is produced through the same base surge mechanism as that which produced the base surge deposits generated by near-surface, buried nuclear and high-explosive detonations. However, the LARLE layers have higher aspect ratios compared with base surge deposits from explosion craters, a result of differences in thicknesses of these layers. This characteristics is probably caused by the addition of large amounts of small particles of dust and ice derived from climate-related mantles of snow, ice and dust in the areas where LARLE craters form. These deposits are likely to be quickly stabilized (order of a few days to a few years) from eolian erosion by formation of duricrust produced by diffusion of water vapor out of the deposits.

  3. Nanotube structures, methods of making nanotube structures, and methods of accessing intracellular space

    Science.gov (United States)

    VanDersarl, Jules J.; Xu, Alexander M.; Melosh, Nicholas A.; Tayebi, Noureddine

    2016-02-23

    In accordance with the purpose(s) of the present disclosure, as embodied and broadly described herein, embodiments of the present disclosure, in one aspect, relate to methods of making a structure including nanotubes, a structure including nanotubes, methods of delivering a fluid to a cell, methods of removing a fluid to a cell, methods of accessing intracellular space, and the like.

  4. Effect of mixture ratios and nitrogen carrier gas flow rates on the morphology of carbon nanotube structures grown by CVD

    CSIR Research Space (South Africa)

    Malgas, GF

    2008-02-01

    Full Text Available This paper reports on the growth of carbon nanotubes (CNTs) by thermal Chemical Vapour Deposition (CVD) and investigates the effects of nitrogen carrier gas flow rates and mixture ratios on the morphology of CNTs on a silicon substrate by vaporizing...

  5. Secondary flow in turbulent ducts with increasing aspect ratio

    Science.gov (United States)

    Vinuesa, R.; Schlatter, P.; Nagib, H. M.

    2018-05-01

    Direct numerical simulations of turbulent duct flows with aspect ratios 1, 3, 5, 7, 10, and 14.4 at a center-plane friction Reynolds number Reτ,c≃180 , and aspect ratios 1 and 3 at Reτ,c≃360 , were carried out with the spectral-element code nek5000. The aim of these simulations is to gain insight into the kinematics and dynamics of Prandtl's secondary flow of the second kind and its impact on the flow physics of wall-bounded turbulence. The secondary flow is characterized in terms of the cross-plane component of the mean kinetic energy, and its variation in the spanwise direction of the flow. Our results show that averaging times of around 3000 convective time units (based on duct half-height h ) are required to reach a converged state of the secondary flow, which extends up to a spanwise distance of around ≃5 h measured from the side walls. We also show that if the duct is not wide enough to accommodate the whole extent of the secondary flow, then its structure is modified as reflected through a different spanwise distribution of energy. Another confirmation of the extent of the secondary flow is the decay rate of kinetic energy of any remnant secondary motions for zc/h >5 (where zc is the spanwise distance from the corner) in aspect ratios 7, 10, and 14.4, which exhibits a decreasing level of energy with increasing averaging time ta, and in its rapid rate of decay given by ˜ta-1 . This is the same rate of decay observed in a spanwise-periodic channel simulation, which suggests that at the core, the kinetic energy of the secondary flow integrated over the cross-sectional area, , behaves as a random variable with zero mean, with rate of decay consistent with central limit theorem. Long-time averages of statistics in a region of rectangular ducts extending about the width of a well-designed channel simulation (i.e., extending about ≃3 h on each side of the center plane) indicate that ducts or experimental facilities with aspect ratios larger than 10 may

  6. Electro-Thermal Transport in Nanotube Based Composites for Macroelectronic Applications

    OpenAIRE

    Kumar, Satish

    2007-01-01

    Dispersions of particles of different shapes and sizes in fluids or solids modify the transport properties of the underlying matrix. A remarkable enhancement in the electrical, thermal and other transport properties of the matrix due to the long aspect ratio dispersions like nanotube/nanowires has been observed my many research groups. This has motivated tremendous research to explore these composites for various macro-electronic and micro-electronic applications in the last decade. Carbon na...

  7. Fabrication of a novel aluminum surface covered by numerous high-aspect-ratio anodic alumina nanofibers

    Science.gov (United States)

    Nakajima, Daiki; Kikuchi, Tatsuya; Natsui, Shungo; Sakaguchi, Norihito; Suzuki, Ryosuke O.

    2015-11-01

    The formation behavior of anodic alumina nanofibers via anodizing in a concentrated pyrophosphoric acid under various conditions was investigated using electrochemical measurements and SEM/TEM observations. Pyrophosphoric acid anodizing at 293 K resulted in the formation of numerous anodic alumina nanofibers on an aluminum substrate through a thin barrier oxide and honeycomb oxide with narrow walls. However, long-term anodizing led to the chemical dissolution of the alumina nanofibers. The density of the anodic alumina nanofibers decreased as the applied voltage increased in the 10-75 V range. However, active electrochemical dissolution of the aluminum substrate occurred at a higher voltage of 90 V. Low temperature anodizing at 273 K resulted in the formation of long alumina nanofibers measuring several micrometers in length, even though a long processing time was required due to the low current density during the low temperature anodizing. In contrast, high temperature anodizing easily resulted in the formation and chemical dissolution of alumina nanofibers. The structural nanofeatures of the anodic alumina nanofibers were controlled by choosing of the appropriate electrochemical conditions, and numerous high-aspect-ratio alumina nanofibers (>100) can be successfully fabricated. The anodic alumina nanofibers consisted of a pure amorphous aluminum oxide without anions from the employed electrolyte.

  8. An Analysis of the Effects of Wing Aspect Ratio and Tail Location on Static Longitudinal Stability Below the Mach Number of Lift Divergence

    Science.gov (United States)

    Axelson, John A.; Crown, J. Conrad

    1948-01-01

    An analysis is presented of the influence of wing aspect ratio and tail location on the effects of compressibility upon static longitudinal stability. The investigation showed that the use of reduced wing aspect ratios or short tail lengths leads to serious reductions in high-speed stability and the possibility of high-speed instability.

  9. High-performance supercapacitors based on vertically aligned carbon nanotubes and nonaqueous electrolytes

    International Nuclear Information System (INIS)

    Kim, Byungwoo; Kim, Woong; Chung, Haegeun

    2012-01-01

    We demonstrate the high performance of supercapacitors fabricated with vertically aligned carbon nanotubes and nonaqueous electrolytes such as ionic liquids and conventional organic electrolytes. Specific capacitance, maximum power and energy density of the supercapacitor measured in ionic liquid were ∼75 F g −1 , ∼987 kW kg −1 and ∼27 W h kg −1 , respectively. The high power performance was consistently indicated by a fast relaxation time constant of 0.2 s. In addition, electrochemical oxidation of the carbon nanotubes improved the specific capacitance (∼158 F g −1 ) and energy density (∼53 W h kg −1 ). Both high power and energy density could be attributed to the fast ion transport realized by the alignment of carbon nanotubes and the wide operational voltage defined by the ionic liquid. The demonstrated carbon-nanotube- and nonaqueous-electrolyte-based supercapacitors show great potential for the development of high-performance energy storage devices. (paper)

  10. High-performance supercapacitors based on vertically aligned carbon nanotubes and nonaqueous electrolytes.

    Science.gov (United States)

    Kim, Byungwoo; Chung, Haegeun; Kim, Woong

    2012-04-20

    We demonstrate the high performance of supercapacitors fabricated with vertically aligned carbon nanotubes and nonaqueous electrolytes such as ionic liquids and conventional organic electrolytes. Specific capacitance, maximum power and energy density of the supercapacitor measured in ionic liquid were ~75 F g(-1), ~987 kW kg(-1) and ~27 W h kg(-1), respectively. The high power performance was consistently indicated by a fast relaxation time constant of 0.2 s. In addition, electrochemical oxidation of the carbon nanotubes improved the specific capacitance (~158 F g(-1)) and energy density (~53 W h kg(-1)). Both high power and energy density could be attributed to the fast ion transport realized by the alignment of carbon nanotubes and the wide operational voltage defined by the ionic liquid. The demonstrated carbon-nanotube- and nonaqueous-electrolyte-based supercapacitors show great potential for the development of high-performance energy storage devices. © 2012 IOP Publishing Ltd

  11. High-performance supercapacitors based on vertically aligned carbon nanotubes and nonaqueous electrolytes

    Science.gov (United States)

    Kim, Byungwoo; Chung, Haegeun; Kim, Woong

    2012-04-01

    We demonstrate the high performance of supercapacitors fabricated with vertically aligned carbon nanotubes and nonaqueous electrolytes such as ionic liquids and conventional organic electrolytes. Specific capacitance, maximum power and energy density of the supercapacitor measured in ionic liquid were ˜75 F g-1, ˜987 kW kg-1 and ˜27 W h kg-1, respectively. The high power performance was consistently indicated by a fast relaxation time constant of 0.2 s. In addition, electrochemical oxidation of the carbon nanotubes improved the specific capacitance (˜158 F g-1) and energy density (˜53 W h kg-1). Both high power and energy density could be attributed to the fast ion transport realized by the alignment of carbon nanotubes and the wide operational voltage defined by the ionic liquid. The demonstrated carbon-nanotube- and nonaqueous-electrolyte-based supercapacitors show great potential for the development of high-performance energy storage devices.

  12. Effects of aspect ratio and concentration on rheology of epoxy suspensions containing model plate-like nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    White, K. L.; Takahara, A. [International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 819-0395 (Japan); Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 819-0395 (Japan); Hawkins, S.; Sue, H.-J., E-mail: hjsue@tamu.edu [Department of Materials Science and Engineering, Texas A& M University, College Station, Texas 77843 (United States); Miyamoto, M. [Kaneka US Materials Research Center, Kaneka America Holdings, Inc., College Station, Texas 77843 (United States)

    2015-12-15

    Hexagonal 2-dimensional α-zirconium phosphate crystals were prepared with lateral diameters ranging from 110 nm to 1.5 μm to investigate the effect of particle size on suspension rheology. The nanoplatelets were exfoliated to individual sheets with monodisperse thickness and dispersed in a Newtonian epoxy fluid. The steady shear response of dilute and semi-dilute suspensions was measured and compared to expressions obtained from theory for infinitely dilute suspensions. For suspensions containing the smaller nanoplatelets, aspect ratio ∼160, the low shear rate viscosity and transition to shear thinning behavior were well described by theory for loadings up to 0.5 vol. %. The agreement was improved by assuming a moderate polydispersity in lateral diameter, ∼30%–50%, which is consistent with experimental observation. For the higher aspect ratio nanoplatelets, good agreement between theory and experiment was observed only at high shear rates. At lower shear rate, theory consistently over-predicted viscosity, which was attributed to a progressive shift to non-isotropic initial conditions with increasing particle size. The results suggest that at a fixed Peclet number, there is an increasing tendency for the nanoplatelets to form transient, local stacks as particle size increases. The largest particles, aspect ratio ∼2200, showed unusual shear thinning and thickening behaviors that were attributed to particle flexibility. The findings demonstrate the surprising utility of theory for infinitely dilute suspensions to interpret, and in some cases quantitatively describe, the non-Newtonian viscosity of real suspensions containing high aspect ratio plate-like particles. A simple framework is proposed to interpret deviations from ideal behavior based on the local and collective behavior of the suspended nanoplatelets.

  13. High quantum yield graphene quantum dots decorated TiO{sub 2} nanotubes for enhancing photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Qu, Ailan, E-mail: qal67@163.com; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan

    2016-07-01

    Highlights: • High concentration yellow GQDs and TiO{sub 2} nanotubes were achieved by a simple and green method. • High quantum yield GQDs enhanced the photodegradation capacity of TiO{sub 2} nanotube. • The catalytic performance of GQDs/TiO{sub 2} depends on the GQDs loading. • The improved photocatalytic activity of GQDs/TiO{sub 2} was attributed to three aspects. - Abstract: Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO{sub 2} nanotubes (GQDs/TiO{sub 2} NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600–800 nm. The photocatalytic activity of prepared GQDs/TiO{sub 2} NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO{sub 2} nanotubes (TiO{sub 2} NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV–vis light irradiation (λ = 380–780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO{sub 2} NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO{sub 2} NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO{sub 2} composite.

  14. Length-scale and strain rate-dependent mechanism of defect formation and fracture in carbon nanotubes under tensile loading

    Energy Technology Data Exchange (ETDEWEB)

    Javvaji, Brahmanandam [Indian Institute of Science, Department of Aerospace Engineering (India); Raha, S. [Indian Institute of Science, Department of Computational and Data Sciences (India); Mahapatra, D. Roy, E-mail: droymahapatra@aero.iisc.ernet.in [Indian Institute of Science, Department of Aerospace Engineering (India)

    2017-02-15

    Electromagnetic and thermo-mechanical forces play a major role in nanotube-based materials and devices. Under high-energy electron transport or high current densities, carbon nanotubes fail via sequential fracture. The failure sequence is governed by certain length scale and flow of current. We report a unified phenomenological model derived from molecular dynamic simulation data, which successfully captures the important physics of the complex failure process. Length-scale and strain rate-dependent defect nucleation, growth, and fracture in single-walled carbon nanotubes with diameters in the range of 0.47 to 2.03 nm and length which is about 6.17 to 26.45 nm are simulated. Nanotubes with long length and small diameter show brittle fracture, while those with short length and large diameter show transition from ductile to brittle fracture. In short nanotubes with small diameters, we observe several structural transitions like Stone-Wales defect initiation, its propagation to larger void nucleation, formation of multiple chains of atoms, conversion to monatomic chain of atoms, and finally complete fracture of the carbon nanotube. Hybridization state of carbon-carbon bonds near the end cap evolves, leading to the formation of monatomic chain in short nanotubes with small diameter. Transition from ductile to brittle fracture is also observed when strain rate exceeds a critical value. A generalized analytical model of failure is established, which correlates the defect energy during the formation of atomic chain with aspect ratio of the nanotube and strain rate. Variation in the mechanical properties such as elastic modulus, tensile strength, and fracture strain with the size and strain rate shows important implications in mitigating force fields and ways to enhance the life of electronic devices and nanomaterial conversion via fracture in manufacturing.

  15. All Metal Iron Core For A Low Aspect Ratio Tokamak

    International Nuclear Information System (INIS)

    Gates, D.A.; Jun, C.; Zatz, I.; Zolfaghari, A.

    2010-01-01

    A novel concept for incorporating a iron core transformer within a axisymmetric toroidal plasma containment device with a high neutron flux is described. This design enables conceptual design of low aspect ratio devices which employ standard transformer-driven plasma startup by using all-metal high resistance separators between the toroidal field windings. This design avoids the inherent problems of a multiturn air core transformer which will inevitably suffer from strong neutron bombardment and hence lose the integrity of its insulation, both through long term material degradation and short term neutron-induced conductivity. A full 3-dimensional model of the concept has been developed within the MAXWELL program and the resultant loop voltage calculated. The utility of the result is found to be dependent on the resistivity of the high resistance separators. Useful loop voltage time histories have been obtained using achievable resistivities.

  16. Carbon nanotubes from synthesis to in vivo biomedical applications.

    Science.gov (United States)

    Sajid, Muhammad Imran; Jamshaid, Usama; Jamshaid, Talha; Zafar, Nadiah; Fessi, H; Elaissari, Abdelhamid

    2016-03-30

    Owing to their unique and interesting properties, extensive research round the globe has been carried out on carbon nanotubes and carbon nanotubes based systems to investigate their practical usefulness in biomedical applications. The results from these studies demonstrate a great promise in their use in targeted drug delivery systems, diagnostic techniques and in bio-analytical applications. Although, carbon nanotubes possess quite interesting properties, which make them potential candidates in the biomedical science, but they also have some inherent properties which arise great concern regarding their biosafety. In this comprehensive review, we have discussed different aspects of carbon nanotubes and carbon nanotube based systems related to biomedical applications. In the beginning, a short historical account of these tiny yet powerful particles is given followed by discussion regarding their types, properties, methods of synthesis, large scale production method, purification techniques and characterization aspects of carbon nanotubes. In the second part of the review, the functionalization of carbon nanotubes is reviewed in detail, which is not only important to make them biocompatible and stable in biological systems but also render them a great property of loading various biomolecules, diagnostic and therapeutic moieties resulting in diversified applications. In the final part of the review, emphasis is given on the pharmacokinetic aspects of carbon nanotubes including administration routes, absorption mechanisms, distribution and elimination of carbon nanotubes based systems. Lastly, a comprehensive account about the potential biomedical applications has been given followed by insights into the future. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Attachment of carbon nanotubes to atomic force microscope probes

    International Nuclear Information System (INIS)

    Gibson, Christopher T.; Carnally, Stewart; Roberts, Clive J.

    2007-01-01

    In atomic force microscopy (AFM) the accuracy of data is often limited by the tip geometry and the effect on this geometry of wear. One way to improve the tip geometry is to attach carbon nanotubes (CNT) to AFM tips. CNTs are ideal because they have a small diameter (typically between 1 and 20 nm), high aspect ratio, high strength, good conductivity, and almost no wear. A number of methods for CNT attachment have been proposed and explored including chemical vapour deposition (CVD), dielectrophoresis, arc discharge and mechanical attachment. In this work we will use CVD to deposit nanotubes onto a silicon surface and then investigate improved methods to pick-up and attach CNTs to tapping mode probes. Conventional pick-up methods involve using standard tapping mode or non-contact mode so as to attach only those CNTs that are aligned vertically on the surface. We have developed improved methods to attach CNTs using contact mode and reduced set-point tapping mode imaging. Using these techniques the AFM tip is in contact with a greater number of CNTs and the rate and stability of CNT pick-up is improved. The presence of CNTs on the modified AFM tips was confirmed by high-resolution AFM imaging, analysis of the tips dynamic force curves and scanning electron microscopy (SEM)

  18. On the high charge-carrier mobility in polyaniline molecular channels in nanogaps between carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Emelianov, A. V., E-mail: emmsowton@gmail.com; Romashkin, A. V.; Tsarik, K. A. [National Research University of Electronic Technology (MIET) (Russian Federation); Nasibulin, A. G. [Skolkovo Institute of Science and Technology (Russian Federation); Nevolin, V. K.; Bobrinetskiy, I. I. [National Research University of Electronic Technology (MIET) (Russian Federation)

    2017-04-15

    This study is devoted to the fabrication of molecular semiconductor channels based on polymer molecules with nanoscale electrodes made of single-walled carbon nanotubes. A reproducible technology for forming nanoscale gaps in carbon nanotubes using a focused Ga{sup +} ion beam is proposed. Polyaniline molecules are deposited into nanogaps up to 30 nm wide between nanotubes by electrophoresis from N-methyl-2-pyrrolidone solution. As a result, molecular organic transistors are fabricated, in which the field effect is studied and the molecular-channel mobility is determined as 0.1 cm{sup 2}/(V s) at an on/off current ratio of 5 × 10{sup 2}.

  19. An innovative approach to synthesize highly-ordered TiO2 nanotubes.

    Science.gov (United States)

    Isimjan, Tayirjan T; Yang, D Q; Rohani, Sohrab; Ray, Ajay K

    2011-02-01

    An innovative route to prepare highly-ordered and dimensionally controlled TiO2 nanotubes has been proposed using a mild sonication method. The nanotube arrays were prepared by the anodization of titanium in an electrolyte containing 3% NH4F and 5% H2O in glycerol. It is demonstrated that the TiO2 nanostructures has two layers: the top layer is TiO2 nanowire and underneath is well-ordered TiO2 nanotubes. The top layer can easily fall off and form nanowires bundles by implementing a mild sonication after a short annealing time. We found that the dimensions of the TiO2 nanotubes were only dependent on the anodizing condition. The proposed technique may be extended to fabricate reproducible well-ordered TiO2 nanotubes with large area on other metals.

  20. Fabrication of high aspect ratio TiO{sub 2} and Al{sub 2}O{sub 3} nanogratings by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Shkondin, Evgeniy, E-mail: eves@fotonik.dtu.dk [Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark and Danish National Center for Micro- and Nanofabrication (DANCHIP), DK-2800 Kongens Lyngby (Denmark); Takayama, Osamu; Lavrinenko, Andrei V. [Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Lindhard, Jonas Michael; Larsen, Pernille Voss; Mar, Mikkel Dysseholm; Jensen, Flemming [Danish National Center for Micro- and Nanofabrication (DANCHIP), DK-2800 Kongens Lyngby (Denmark)

    2016-05-15

    The authors report on the fabrication of TiO{sub 2} and Al{sub 2}O{sub 3} nanostructured gratings with an aspect ratio of up to 50. The gratings were made by a combination of atomic layer deposition (ALD) and dry etch techniques. The workflow included fabrication of a Si template using deep reactive ion etching followed by ALD of TiO{sub 2} or Al{sub 2}O{sub 3}. Then, the template was etched away using SF{sub 6} in an inductively coupled plasma tool, which resulted in the formation of isolated ALD coatings, thereby achieving high aspect ratio grating structures. SF{sub 6} plasma removes silicon selectively without any observable influence on TiO{sub 2} or Al{sub 2}O{sub 3}, thus revealing high selectivity throughout the fabrication. Scanning electron microscopy was used to analyze every fabrication step. Due to nonreleased stress in the ALD coatings, the top parts of the gratings were observed to bend inward as the Si template was removed, thus resulting in a gradual change in the pitch value of the structures. The pitch on top of the gratings is 400 nm, and it gradually reduces to 200 nm at the bottom. The form of the bending can be reshaped by Ar{sup +} ion beam etching. The chemical purity of the ALD grown materials was analyzed by x-ray photoelectron spectroscopy. The approach presented opens the possibility to fabricate high quality optical metamaterials and functional nanostructures.

  1. Alignment of muscle precursor cells on the vertical edges of thick carbon nanotube films

    Energy Technology Data Exchange (ETDEWEB)

    Holt, Ian, E-mail: ian.holt@rjah.nhs.uk [Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, Shropshire SY10 7AG (United Kingdom); Institute for Science and Technology in Medicine, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Gestmann, Ingo, E-mail: Ingo.Gestmann@fei.com [FEI Europe B.V., Achtseweg Noord 5, 5651 Eindhoven (Netherlands); Wright, Andrew C., E-mail: a.wright@glyndwr.ac.uk [Advanced Materials Research Laboratory, Glyndwr University, Plas Coch, Mold Rd, Wrexham LL11 2AW (United Kingdom)

    2013-10-15

    The development of scaffolds and templates is an essential aspect of tissue engineering. We show that thick (> 0.5 mm) vertically aligned carbon nanotube films, made by chemical vapour deposition, can be used as biocompatible substrates for the directional alignment of mouse muscle cells where the cells grow on the exposed sides of the films. Ultra high resolution scanning electron microscopy reveals that the films themselves consist mostly of small diameter (10 nm) multi-wall carbon nanotubes of wavy morphology with some single wall carbon nanotubes. Our findings show that for this alignment to occur the nanotubes must be in pristine condition. Mechanical wiping of the films to create directional alignment is detrimental to directional bioactivity. Larger areas for study have been formed from a composite of multiply stacked narrow strips of nanotubes wipe-transferred onto elastomer supports. These composite substrates appear to show a useful degree of alignment of the cells. Highlights: • Highly oriented muscle precursor cells grown on edges of carbon nanotube pads • Mechanical treatment of nanotube pads highly deleterious to cell growth on edges • Larger areas created from wipe-transfer of narrow strips of nanotubes onto elastomer supports • Very high resolution SEM reveals clues to aligned cell growth.

  2. Alignment of muscle precursor cells on the vertical edges of thick carbon nanotube films

    International Nuclear Information System (INIS)

    Holt, Ian; Gestmann, Ingo; Wright, Andrew C.

    2013-01-01

    The development of scaffolds and templates is an essential aspect of tissue engineering. We show that thick (> 0.5 mm) vertically aligned carbon nanotube films, made by chemical vapour deposition, can be used as biocompatible substrates for the directional alignment of mouse muscle cells where the cells grow on the exposed sides of the films. Ultra high resolution scanning electron microscopy reveals that the films themselves consist mostly of small diameter (10 nm) multi-wall carbon nanotubes of wavy morphology with some single wall carbon nanotubes. Our findings show that for this alignment to occur the nanotubes must be in pristine condition. Mechanical wiping of the films to create directional alignment is detrimental to directional bioactivity. Larger areas for study have been formed from a composite of multiply stacked narrow strips of nanotubes wipe-transferred onto elastomer supports. These composite substrates appear to show a useful degree of alignment of the cells. Highlights: • Highly oriented muscle precursor cells grown on edges of carbon nanotube pads • Mechanical treatment of nanotube pads highly deleterious to cell growth on edges • Larger areas created from wipe-transfer of narrow strips of nanotubes onto elastomer supports • Very high resolution SEM reveals clues to aligned cell growth

  3. Modeling of finite aspect ratio effects on current drive

    International Nuclear Information System (INIS)

    Wright, J.C.; Phillips, C.K.

    1996-01-01

    Most 2D RF modeling codes use a parameterization of current drive efficiencies to calculate fast wave driven currents. This parameterization assumes a uniform diffusion coefficient and requires a priori knowledge of the wave polarizations. These difficulties may be avoided by a direct calculation of the quasilinear diffusion coefficient from the Kennel-Englemann form with the field polarizations calculated by a full wave code. This eliminates the need to use the approximation inherent in the parameterization. Current profiles are then calculated using the adjoint formulation. This approach has been implemented in the FISIC code. The accuracy of the parameterization of the current drive efficiency, η, is judged by a comparison with a direct calculation: where χ is the adjoint function, ε is the kinetic energy, and rvec Γ is the quasilinear flux. It is shown that for large aspect ratio devices (ε → 0), the parameterization is nearly identical to the direct calculation. As the aspect ratio approaches unity, visible differences between the two calculations appear

  4. Diagnostics of BubbleMode Vortex Breakdown in Swirling Flow in a Large-Aspect-Ratio Cylinder

    DEFF Research Database (Denmark)

    Kulikov, D. V.; Mikkelsen, Robert Flemming; Naumov, Igor

    2014-01-01

    We report for the first time on the possible formation of regions with counterflow (bubble-mode vortex breakdown or explosion) at the center of strongly swirling flow generated by a rotating endwall in a large-aspect-ratio cylindrical cavity filled with a liquid medium. Previously, the possibility...... of bubble-mode breakdown was studied in detail for cylindrical cavities of moderate aspect ratio (length to radius ratios up to H/R ∼ 3.5), while flows in large-aspect-ratio cylinders were only associated with regimes of self-organized helical vortex multiplets. In the present study, a regime...

  5. Sub-nanometer-resolution imaging of peptide nanotubes in water using frequency modulation atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sugihara, Tomoki; Hayashi, Itsuho; Onishi, Hiroshi [Department of Chemistry, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501 (Japan); Kimura, Kenjiro, E-mail: kimura@gold.kobe-u.ac.jp [Department of Chemistry, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501 (Japan); Tamura, Atsuo [Department of Chemistry, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501 (Japan)

    2013-06-20

    Highlights: ► Peptide nanotubes were aligned on highly oriented pyrolytic graphite surface. ► We visualized sub-nanometer-scale structure on peptide nanotube surface in water. ► We observed hydration structure at a peptide nanotube/water interface. - Abstract: Peptide nanotubes are self-assembled fibrous materials composed of cyclic polypeptides. Recently, various aspects of peptide nanotubes have been studied, in particular the utility of different methods for making peptide nanotubes with diverse designed functions. In order to investigate the relationship between formation, function and stability, it is essential to analyze the precise structure of peptide nanotubes. Atomic-scale surface imaging in liquids was recently achieved using frequency modulation atomic force microscopy with improved force sensing. Here we provide a precise surface structural analysis of peptide nanotubes in water without crystallizing them obtained by imaging the nanotubes at the sub-nanometer scale in water. In addition, the local hydration structure around the peptide nanotubes was observed at the nanotube/water interface.

  6. Carbon nanotube stationary phases for microchip electrochromatography

    DEFF Research Database (Denmark)

    Mogensen, Klaus Bo; Bøggild, Peter; Kutter, Jörg Peter

    , microfluidic devices with microfabricated carbon nanotube columns for electrochromatographic separations will be presented. The electrically conductive carbon nanotube layer has been patterned into hexoganol micropillars in order to support electroosmotic flow without forming gas bubbles from electrolysis......The use of nanomaterials in separation science has increased rapidly in the last decade. The reason for this is to take advantage of the unique properties of these materials, such as a very high surface-to-volume ratio and favourable sorbent behaviour. Carbon nanostructures, such as carbon...

  7. A PIV Study of Baseline and Controlled Flow over the Highly Deflected Flap of a Generic Low Aspect Ratio Trapezoidal Wing

    Science.gov (United States)

    Tewes, Philipp; Genschow, Konstantin; Little, Jesse; Wygnanski, Israel

    2017-11-01

    A detailed flow survey using PIV was conducted over a highly-deflected flap (55°) of a low-aspect ratio trapezoidal wing. The wing section is a NACA 0012 with 45° sweep at both the leading and trailing edges, an aspect ratio of 1.5 and a taper ratio of 0.27. The main element is equipped with 7 equally spaced fluidic oscillators, covering the inner 60 % of the span, located near the flap hinge. Experiments were carried out at 0° and 8° incidence at a Reynolds number of 1.7 .106 for both baseline and active flow control (AFC) cases. Velocity ISO-surfaces, x-vorticity and streamlines are analyzed / discussed. A flap leading edge vortex governs the baseline flow field for 0°. This vortical structure interacts with the jets emitted by the actuators (Cμ = 1 %). Its development is hampered and the vortex is redirected toward the trailing edge resulting in a CL increase. At 8°, the dominant flap leading edge vortex could not be detected and is believed to have already merged with the tip vortex. AFC attached the flow over the flap and enhanced the lift by up to 20 % while maintaining longitudinal stability. The dominant flow features in the AFC cases are actuator-generated streamwise vortices which appear stronger at 8°. This work was supported by the Office of Naval Research under ONR Grant No. N00014-14-1-0387.

  8. Pressure effects on dynamics behavior of multiwall boron nitride nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Talebian, Taha [Faculty of Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur (Iran, Islamic Republic of)

    2016-01-15

    The dynamic behavior of Multiwall boron nitride nanotubes (MWBNNTs) is investigated by employing multiple elastic shells model. The influences of van der Waals interactions on layers are shown as nonlinear functions of the interlayer distance of MWBNNTs. Governing equations are solved by using the developed finite element method and by employing time history diagrams. The radial wave speed from the outermost layer to the innermost layer is computed. The effects of geometrical factors such as diameter-to-thickness ratio on dynamic behavior of MWBNNTs are determined. The magnification aspects of MWBNNTs are computed, and the effects of surrounding pressures on wave speed and magnification aspect of MWBNNTs are discussed.

  9. Comparison of cellular toxicity between multi-walled carbon nanotubes and onion-like shell-shaped carbon nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Seunghyon [Seoul National University, School of Mechanical and Aerospace Engineering (Korea, Republic of); Kim, Ji-Eun [Korea Research Institute of Standard and Science, Center for NanoSafety Metrology, Division of Convergence Technology (Korea, Republic of); Kim, Daegyu [LG Electronics (Korea, Republic of); Woo, Chang Gyu [Korea Institute of Machinery and Materials, Environmental and Energy Systems Research Division (Korea, Republic of); Pikhitsa, Peter V. [Seoul National University, School of Mechanical and Aerospace Engineering (Korea, Republic of); Cho, Myung-Haing, E-mail: mchotox@snu.ac.kr [Seoul National University, Laboratory of Toxicology, College of Veterinary Medicine (Korea, Republic of); Choi, Mansoo, E-mail: mchoi@snu.ac.kr [Seoul National University, School of Mechanical and Aerospace Engineering (Korea, Republic of)

    2015-09-15

    The cellular toxicity of multi-walled carbon nanotubes (MWCNTs) and onion-like shell-shaped carbon nanoparticles (SCNPs) was investigated by analyzing the comparative cell viability. For the reasonable comparison, physicochemical characteristics were controlled thoroughly such as crystallinity, carbon bonding characteristic, hydrodynamic diameter, and metal contents of the particles. To understand relation between cellular toxicity of the particles and generation of reactive oxygen species (ROS), we measured unpaired singlet electrons of the particles and intracellular ROS, and analyzed cellular toxicity with/without the antioxidant N-acetylcysteine (NAC). Regardless of the presence of NAC, the cellular toxicity of SCNPs was found to be lower than that of MWCNTs. Since both particles show similar crystallinity, hydrodynamic size, and Raman signal with negligible contribution of remnant metal particles, the difference in cell viability would be ascribed to the difference in morphology, i.e., spherical shape (aspect ratio of one) for SCNP and elongated shape (high aspect ratio) for MWCNT.

  10. Comparison of cellular toxicity between multi-walled carbon nanotubes and onion-like shell-shaped carbon nanoparticles

    International Nuclear Information System (INIS)

    Kang, Seunghyon; Kim, Ji-Eun; Kim, Daegyu; Woo, Chang Gyu; Pikhitsa, Peter V.; Cho, Myung-Haing; Choi, Mansoo

    2015-01-01

    The cellular toxicity of multi-walled carbon nanotubes (MWCNTs) and onion-like shell-shaped carbon nanoparticles (SCNPs) was investigated by analyzing the comparative cell viability. For the reasonable comparison, physicochemical characteristics were controlled thoroughly such as crystallinity, carbon bonding characteristic, hydrodynamic diameter, and metal contents of the particles. To understand relation between cellular toxicity of the particles and generation of reactive oxygen species (ROS), we measured unpaired singlet electrons of the particles and intracellular ROS, and analyzed cellular toxicity with/without the antioxidant N-acetylcysteine (NAC). Regardless of the presence of NAC, the cellular toxicity of SCNPs was found to be lower than that of MWCNTs. Since both particles show similar crystallinity, hydrodynamic size, and Raman signal with negligible contribution of remnant metal particles, the difference in cell viability would be ascribed to the difference in morphology, i.e., spherical shape (aspect ratio of one) for SCNP and elongated shape (high aspect ratio) for MWCNT

  11. Computational modelling of the flow of viscous fluids in carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Khosravian, N [Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5531, Tehran (Iran, Islamic Republic of); Rafii-Tabar, H [Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5531, Tehran (Iran, Islamic Republic of)

    2007-11-21

    Carbon nanotubes will have extensive application in all areas of nano-technology, and in particular in the field of nano-fluidics, wherein they can be used for molecular separation, nano-scale filtering and as nano-pipes for conveying fluids. In the field of nano-medicine, nanotubes can be functionalized with various types of receptors to act as bio-sensors for the detection and elimination of cancer cells, or be used as bypasses and even neural connections. Modelling fluid flow inside nanotubes is a very challenging problem, since there is a complex interplay between the motion of the fluid and the stability of the walls. A critical issue in the design of nano-fluidic devices is the induced vibration of the walls, due to the fluid flow, which can promote structural instability. It has been established that the resonant frequencies depend on the flow velocity. We have studied, for the first time, the flow of viscous fluids through multi-walled carbon nanotubes, using the Euler-Bernoulli classical beam theory to model the nanotube as a continuum structure. Our aim has been to compute the effect of the fluid flow on the structural stability of the nanotubes, without having to consider the details of the fluid-walls interaction. The variations of the resonant frequencies with the flow velocity are obtained for both unembedded nanotubes, and when they are embedded in an elastic medium. It is found that a nanotube conveying a viscous fluid is more stable against vibration-induced buckling than a nanotube conveying a non-viscous fluid, and that the aspect ratio plays the same role in both cases.

  12. Computational modelling of the flow of viscous fluids in carbon nanotubes

    International Nuclear Information System (INIS)

    Khosravian, N; Rafii-Tabar, H

    2007-01-01

    Carbon nanotubes will have extensive application in all areas of nano-technology, and in particular in the field of nano-fluidics, wherein they can be used for molecular separation, nano-scale filtering and as nano-pipes for conveying fluids. In the field of nano-medicine, nanotubes can be functionalized with various types of receptors to act as bio-sensors for the detection and elimination of cancer cells, or be used as bypasses and even neural connections. Modelling fluid flow inside nanotubes is a very challenging problem, since there is a complex interplay between the motion of the fluid and the stability of the walls. A critical issue in the design of nano-fluidic devices is the induced vibration of the walls, due to the fluid flow, which can promote structural instability. It has been established that the resonant frequencies depend on the flow velocity. We have studied, for the first time, the flow of viscous fluids through multi-walled carbon nanotubes, using the Euler-Bernoulli classical beam theory to model the nanotube as a continuum structure. Our aim has been to compute the effect of the fluid flow on the structural stability of the nanotubes, without having to consider the details of the fluid-walls interaction. The variations of the resonant frequencies with the flow velocity are obtained for both unembedded nanotubes, and when they are embedded in an elastic medium. It is found that a nanotube conveying a viscous fluid is more stable against vibration-induced buckling than a nanotube conveying a non-viscous fluid, and that the aspect ratio plays the same role in both cases

  13. Carbon nanotube transistor based high-frequency electronics

    Science.gov (United States)

    Schroter, Michael

    At the nanoscale carbon nanotubes (CNTs) have higher carrier mobility and carrier velocity than most incumbent semiconductors. Thus CNT based field-effect transistors (FETs) are being considered as strong candidates for replacing existing MOSFETs in digital applications. In addition, the predicted high intrinsic transit frequency and the more recent finding of ways to achieve highly linear transfer characteristics have inspired investigations on analog high-frequency (HF) applications. High linearity is extremely valuable for an energy efficient usage of the frequency spectrum, particularly in mobile communications. Compared to digital applications, the much more relaxed constraints for CNT placement and lithography combined with already achieved operating frequencies of at least 10 GHz for fabricated devices make an early entry in the low GHz HF market more feasible than in large-scale digital circuits. Such a market entry would be extremely beneficial for funding the development of production CNTFET based process technology. This talk will provide an overview on the present status and feasibility of HF CNTFET technology will be given from an engineering point of view, including device modeling, experimental results, and existing roadblocks. Carbon nanotube transistor based high-frequency electronics.

  14. The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing.

    Science.gov (United States)

    Phillips, Nathan; Knowles, Kevin; Bomphrey, Richard J

    2015-10-09

    Insect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean wing chord (c). We investigated the impact of aspect ratio, AR, on the induced flow field around a flapping wing using a robotic device. Rigid rectangular wings ranging from AR = 1.5 to 7.5 were flapped with insect-like kinematics in air with a constant Reynolds number (Re) of 1400, and a dimensionless stroke amplitude of 6.5c (number of chords traversed by the wingtip). Pseudo-volumetric, ensemble-averaged, flow fields around the wings were captured using particle image velocimetry at 11 instances throughout simulated downstrokes. Results confirmed the presence of a high-lift, separated flow field with a leading-edge vortex (LEV), and revealed that the conical, primary LEV grows in size and strength with increasing AR. In each case, the LEV had an arch-shaped axis with its outboard end originating from a focus-sink singularity on the wing surface near the tip. LEV detachment was observed for AR > 1.5 around mid-stroke at ~70% span, and initiated sooner over higher aspect ratio wings. At AR > 3 the larger, stronger vortex persisted under the wing surface well into the next half-stroke leading to a reduction in lift. Circulatory lift attributable to the LEV increased with AR up to AR = 6. Higher aspect ratios generated proportionally less lift distally because of LEV breakdown, and also less lift closer to the wing root due to the previous LEV's continuing presence under the wing. In nature, insect wings go no higher than AR ~ 5, likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings.

  15. Field emission from carbon nanotube bundle arrays grown on self-aligned ZnO nanorods

    International Nuclear Information System (INIS)

    Li Chun; Fang Guojia; Yuan Longyan; Liu Nishuang; Ai Lei; Xiang Qi; Zhao Dongshan; Pan Chunxu; Zhao Xingzhong

    2007-01-01

    The field emission (FE) properties of carbon nanotube (CNT) bundle arrays grown on vertically self-aligned ZnO nanorods (ZNRs) are reported. The ZNRs were first synthesized on ZnO-seed-coated Si substrate by the vapour phase transport method, and then the radically grown CNTs were grown directly on the surface of the ZNRs from ethanol flames. The CNT/ZNR composite showed a turn-on field of 1.5 V μm -1 (at 0.1 μA cm -2 ), a threshold field of 4.5 V μm -1 (at 1 mA cm -2 ) and a stable emission current with fluctuations of 5%, demonstrating significantly enhanced FE of ZNRs due to the low work function and high aspect ratio of the CNTs, and large surface-to-volume ratio of the underlying ZNRs

  16. Large-area fluidic assembly of single-walled carbon nanotubes through dip-coating and directional evaporation

    Science.gov (United States)

    Kim, Pilnam; Kang, Tae June

    2017-12-01

    We present a simple and scalable fluidic-assembly approach, in which bundles of single-walled carbon nanotubes (SWCNTs) are selectively aligned and deposited by directionally controlled dip-coating and solvent evaporation processes. The patterned surface with alternating regions of hydrophobic polydimethyl siloxane (PDMS) (height 100 nm) strips and hydrophilic SiO2 substrate was withdrawn vertically at a constant speed ( 3 mm/min) from a solution bath containing SWCNTs ( 0.1 mg/ml), allowing for directional evaporation and subsequent selective deposition of nanotube bundles along the edges of horizontally aligned PDMS strips. In addition, the fluidic assembly was applied to fabricate a field effect transistor (FET) with highly oriented SWCNTs, which demonstrate significantly higher current density as well as high turn-off ratio (T/O ratio 100) as compared to that with randomly distributed carbon nanotube bundles (T/O ratio <10).

  17. Self-Assembled Cu-Sn-S Nanotubes with High (De)Lithiation Performance.

    Science.gov (United States)

    Lin, Jie; Lim, Jin-Myoung; Youn, Duck Hyun; Kawashima, Kenta; Kim, Jun-Hyuk; Liu, Yang; Guo, Hang; Henkelman, Graeme; Heller, Adam; Mullins, Charles Buddie

    2017-10-24

    Through a gelation-solvothermal method without heteroadditives, Cu-Sn-S composites self-assemble to form nanotubes, sub-nanotubes, and nanoparticles. The nanotubes with a Cu 3-4 SnS 4 core and Cu 2 SnS 3 shell can tolerate long cycles of expansion/contraction upon lithiation/delithiation, retaining a charge capacity of 774 mAh g -1 after 200 cycles with a high initial Coulombic efficiency of 82.5%. The importance of the Cu component for mitigation of the volume expansion and structural evolution upon lithiation is informed by density functional theory calculations. The self-generated template and calculated results can inspire the design of analogous Cu-M-S (M = metal) nanotubes for lithium batteries or other energy storage systems.

  18. Self-combustion synthesis and oxygen storage properties of mesoporous gadolinia-doped ceria nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Yang Tao [College of Environmental and Energy Engineering, Beijing University of Technology (BUT-CEEE), Chaoyang District 100124, Beijing (China); Xia Dingguo, E-mail: yangtaophoenix@yahoo.com.cn [College of Environmental and Energy Engineering, Beijing University of Technology (BUT-CEEE), Chaoyang District 100124, Beijing (China)

    2010-10-01

    Ethyl glycol and citric acid, along with metal nitrates have been used to prepare Ce{sub 0.9}Gd{sub 0.1}O{sub 2-x} nanotubes directed at the anodic alumina oxide (AAO) template by combustion route. The tubes produced by the self-combustion route do not need any further calcination step. XRD patterns show the doped-ceria tubes have the flurite-type structure and no impurities are detected. The specific surface area of the tube is 112.7 m{sup 2} g{sup -1} and N{sub 2} adsorption-desorption profiles of the BET measurement shows the tubes are mesoporous. The largest aspect ratio of a nanotube reaches 20:1 and the TEM observation reveals the hollow structure. The Ce:Gd molar ratio calculated from the EDS and ICP-AES is 9:1 and the selected area electron diffraction confirms the flurite-type structure from the XRD characterization. The combined thermogravimetry-differential thermal analysis has been carried out to study the combustion reactions in the tube-forming process. The thermal stability of the nanotubes under both reductive and oxidative atmospheres is tested using the dynamic reduction/reoxidation reactions. At last, the oxygen storage capacity (OSC) of the nanotubes is calculated to be 695 {mu}mol-O{sup 2} g{sup -1} from the temperature-programed reduction reaction.

  19. Preparation and desalination performance of multiwall carbon nanotubes

    International Nuclear Information System (INIS)

    Zhang Dengsong; Shi Liyi; Fang Jianhui; Dai Kai; Li Xuanke

    2006-01-01

    Multiwall carbon nanotubes (MWCNTs) were prepared by catalytic decomposition of methane at 680-700 deg. C, using nickel oxide-silica binary aerogels as the catalyst. The morphological structure of MWCNTs was investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results revealed that MWCNTs had a diameter of 40-60 nm, with high quality and high length/diameter ratio, and some metal catalyst particles were encapsulated at the tip of nanotubes. Using MWCNTs as the electrodes of flow-through capacitor (FTC), desalination performance was investigated. The results showed that modification methods had great effect on desalination performance of MWCNTs. The removal amount of NaCl was generally dependent on the surface area and pore volume of MWCNTs. After modification in diluted HNO 3 solution with ultrasonic and then ball milling, the metal catalyst particles at the tip of nanotubes disappeared, the nanotube length became short, the cap at the tip of nanotubes was opened, the internal surface area could be effectively used, leading to increasing the specific surface area and pore volume for MWCNTs, and thus, the desalination performance thereof was the best of all

  20. Aspects of the Fracture Toughness of Carbon Nanotube Modified Epoxy Polymer Composites

    Science.gov (United States)

    Mirjalili, Vahid

    Epoxy resins used in fibre reinforced composites exhibit a brittle fracture behaviour, because they show no sign of damage prior to a catastrophic failure. Rubbery materials and micro-particles have been added to epoxy resins to improve their fracture toughness, which reduces strength and elastic properties. In this research, carbon nanotubes (CNTs) are investigated as a potential toughening agent for epoxy resins and carbon fibre reinforced composites, which can also enhance strength and elastic properties. More specifically, the toughening mechanisms of CNTs are investigated theoretically and experimentally. The effect of aligned and randomly oriented carbon nanotubes (CNTs) on the fracture toughness of polymers was modelled using Elastic Plastic Fracture Mechanics. Toughening from CNT pull-out and rupture were considered, depending on the CNTs critical length. The model was used to identify the effect of CNTs geometrical and mechanical properties on the fracture toughness of CNT-modified epoxies. The modelling results showed that a uniform dispersion and alignment of a high volume fraction of CNTs normal to the crack growth plane would lead to the maximum fracture toughness enhancement. To achieve a uniform dispersion, the effect of processing on the dispersion of single walled and multi walled CNTs in epoxy resins was investigated. An instrumented optical microscope with a hot stage was used to quantify the evolution of the CNT dispersion during cure. The results showed that the reduction of the resin viscosity at temperatures greater than 100 °C caused an irreversible re-agglomeration of the CNTs in the matrix. The dispersion quality was then directly correlated to the fracture toughness of the modified resin. It was shown that the fine tuning of the ratio of epoxy resin, curing agent and CNT content was paramount to the improvement of the base resin fracture toughness. For the epoxy resin (MY0510 from Hexcel), an improvement of 38% was achieved with 0.3 wt

  1. Polymer-Sorted Semiconducting Carbon Nanotube Networks for High-Performance Ambipolar Field-Effect Transistors

    Science.gov (United States)

    2014-01-01

    Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm2·V–1·s–1, low ohmic contact resistance, steep subthreshold swings (0.12–0.14 V/dec) and high on/off ratios (106) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61. PMID:25493421

  2. Hydrodynamic thrust generation and power consumption investigations for piezoelectric fins with different aspect ratios

    Science.gov (United States)

    Shahab, S.; Tan, D.; Erturk, A.

    2015-12-01

    Bio-inspired hydrodynamic thrust generation using piezoelectric transduction has recently been explored using Macro-Fiber Composite (MFC) actuators. The MFC technology strikes a balance between the actuation force and structural deformation levels for effective swimming performance, and additionally offers geometric scalability, silent operation, and ease of fabrication. Recently we have shown that mean thrust levels comparable to biological fish of similar size can be achieved using MFC fins. The present work investigates the effect of length-to-width (L/b) aspect ratio on the hydrodynamic thrust generation performance of MFC cantilever fins by accounting for the power consumption level. It is known that the hydrodynamic inertia and drag coefficients are controlled by the aspect ratio especially for L/bdrag coefficients from the vibration response to harmonic actuation for the first bending mode. Experiments are then conducted for various actuation voltage levels to quantify the mean thrust resultant and power consumption levels for different aspect ratios. Variation of the thrust coefficient of the MFC bimorph fins with changing aspect ratio is also semi-empirically modeled and presented.

  3. Carbon nanotube-based black coatings

    Science.gov (United States)

    Lehman, J.; Yung, C.; Tomlin, N.; Conklin, D.; Stephens, M.

    2018-03-01

    Coatings comprising carbon nanotubes are very black, that is, characterized by uniformly low reflectance over a broad range of wavelengths from the visible to far infrared. Arguably, there is no other material that is comparable. This is attributable to the intrinsic properties of graphitic material as well as the morphology (density, thickness, disorder, and tube size). We briefly describe a history of other coatings such as nickel phosphorous, gold black, and carbon-based paints and the comparable structural morphology that we associate with very black coatings. The need for black coatings is persistent for a variety of applications ranging from baffles and traps to blackbodies and thermal detectors. Applications for space-based instruments are of interest and we present a review of space qualification and the results of outgassing measurements. Questions of nanoparticle safety depend on the nanotube size and aspect ratio as well as the nature and route of exposure. We describe the growth of carbon nanotube forests along with the catalyst requirements and temperature limitations. We also describe coatings derived from carbon nanotubes and applied like paint. Building the measurement apparatus and determining the optical properties of something having negligible reflectance are challenging and we summarize the methods and means for such measurements. There exists information in the literature for effective media approximations to model the dielectric function of vertically aligned arrays. We summarize this along with the refractive index of graphite from the literature that is necessary for modeling the optical properties. In our experience, the scientific questions can be overshadowed by practical matters, so we provide an appendix of recipes for making as-grown and sprayed coatings along with an example of reflectance measurements.

  4. Electrochemical Capacitors Based on Aligned Carbon Nanotubes Directly Synthesized on Tantalum Substrates

    International Nuclear Information System (INIS)

    Kim, Byung Woo; Chung, Hae Geun; Kim, Woong; Min, Byoung Koun; Kim, Hong Gon

    2010-01-01

    We demonstrate that vertically aligned carbon nanotubes can be synthesized directly on tantalum substrate via waterassisted chemical vapor deposition and evaluate their properties as electrochemical capacitors. The mean diameter of the carbon nanotubes was 7.1 ± 1.5 nm, and 70% of them had double walls. The intensity ratio of G-band to D-band in Raman spectra was as high as 5, indicating good quality of the carbon nanotubes. Owing to the alignment and low equivalent series resistance, the carbon nanotube based supercapacitors showed good rate performance. Rectangular shape of cyclic voltammogram was maintained even at the scan rate of > 1 V/s in 1 M sulfuric acid aqueous solution. Specific capacitance was well-retained (∼94%) even when the discharging current density dramatically increased up to 145 A/g. Consequently, specific power as high as 60 kW/kg was obtained from as-grown carbon nanotubes in aqueous solution. Maximum specific energy of ∼20 Wh/kg was obtained when carbon nanotubes were electrochemically oxidized and operated in organic solution. Demonstration of direct synthesis of carbon nanotubes on tantalum current collectors and their applications as supercapacitors could be an invaluable basis for fabrication of high performance carbon nanotube supercapacitors

  5. THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY

    Energy Technology Data Exchange (ETDEWEB)

    WONG,SK; CHAN,VS

    2002-11-01

    OAK B202 THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY. This article presents a comprehensive description of neoclassical transport theory in the banana regime for large aspect ratio flux surfaces of arbitrary shapes. The method of matched asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates discussion of the treatment of dynamical constraints. it is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard.

  6. THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY

    International Nuclear Information System (INIS)

    WONG, S.K.; CHAN, V.S.

    2002-01-01

    OAK B202 THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY. This article presents a comprehensive description of neoclassical transport theory in the banana regime for large aspect ratio flux surfaces of arbitrary shapes. The method of matched asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates discussion of the treatment of dynamical constraints. it is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard

  7. Forces and Moments on Flat Plates of Small Aspect Ratio with Application to PV Wind Loads and Small Wind Turbine Blades

    Directory of Open Access Journals (Sweden)

    Xavier Ortiz

    2015-03-01

    Full Text Available To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 104 to 2 × 105. Measurements were made for angles of attack between 0° and 90° both in the free stream and in wall proximity with increased turbulence and mean shear. The ratio of drag to lift closely follows the inverse tangent of the angle of incidence for virtually all measurements. This implies that the forces of interest are due largely to the instantaneous pressure distribution around the plate and are not significantly influenced by shear stresses. The instantaneous forces appear most complex for the smaller aspect ratios but the intensity of the normal force fluctuations is between 10% and 20% in the free-steam but can exceed 30% near the wall. As the wind tunnel floor is approached, the lift and drag reduce with increasing aspect ratio, and there is a reduction in the high frequency components of the forces. It is shown that the centre of pressure is closer to the centre of the plates than the quarter-chord position for nearly all cases.

  8. High-performance thin-film-transistors based on semiconducting-enriched single-walled carbon nanotubes processed by electrical-breakdown strategy

    Energy Technology Data Exchange (ETDEWEB)

    Aïssa, B., E-mail: aissab@emt.inrs.ca [Centre Énergie, Matériaux et Télécommunications, INRS, 1650, boulevard Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada); Qatar Environment and Energy Research Institute (QEERI), Qatar Foundation, P.O. Box 5825, Doha (Qatar); Nedil, M. [Telebec Wireless Underground Communication Laboratory, UQAT, 675, 1" è" r" e Avenue, Val d’Or, Québec J9P 1Y3 (Canada); Habib, M.A. [Computer Sciences and Engineering Department, Yanbu University College, P.O. Box 30031 (Saudi Arabia); Abdul-Hafidh, E.H. [High Energy Physics Department, Yanbu University College, P.O. Box 30031 (Saudi Arabia); Rosei, F. [Centre Énergie, Matériaux et Télécommunications, INRS, 1650, boulevard Lionel-Boulet, Varennes, Quebec J3X 1S2 (Canada)

    2015-02-15

    Highlights: • We selectively burn metallic single wall carbon nanotubes (SWCNT) by electrical breakdown. • We successfully achieve a semiconducting enriched-SWCNT in TFT configuration. • High performance, like On/Off of 10{sup 5} and a subthreshold swing of 165 mV/decades were obtained. • After PMMA coating, the SWCNT–TFTs were found stables for more than 4 months. - Abstract: Over the past two decades, among remarkable variety of nanomaterials, single-walled carbon nanotubes (SWCNTs) remain the most intriguing and uniquely well suited materials for applications in high-performance electronics. The most advanced technologies require the ability to form purely semiconducting SWCNTs. Here, we report on our strategy based on the well known progressive electrical breakdown process that offer this capability and serves as highly efficient means for selectively removing metallic carbon nanotubes from electronically heterogeneous random networks, deposited on silicon substrates in a thin film transistor (TFT) configuration. We demonstrate the successful achievement of semiconducting enriched-SWCNT networks in TFT scheme that reach On/Off switching ratios of ∼100,000, on-conductance of 20 μS, and a subthreshold swing of less than 165 mV/decades. The obtained TFT devices were then protected with thin film poly(methyl methacrylate) (PMMA) to keep the percolation level of the SWCNTs network spatially and temporally stable, while protecting it from atmosphere exchanges. TFT devices were found to be air-stable and maintained their excellent characteristics in ambient atmosphere for more than 4 months. This approach could work as a platform for future nanotube-based nanoelectronics.

  9. A modified atmospheric non-hydrostatic model on low aspect ratio grids: part II

    Directory of Open Access Journals (Sweden)

    Wen-Yih Sun

    2013-06-01

    Full Text Available Sun et al. (2012 proposed a modified non-hydrostatic model (MNH, in which the left-hand side of the continuity equation is multiplied by a parameter δ (4≤δ≤16 in the article to suppress high-frequency acoustic waves. They showed that the MNH allows a longer time step than the original non-hydrostatic model (NH. The MNH is also more accurate and efficient than the horizontal explicit and vertical implicit scheme (HE–VI when the aspect ratio (Δx/Δz is small. In addition to multiplying a parameter δ, here we propose to add a smoothing on the right-hand side of the continuity equation in the MNH to damp shortest sound waves. Linear stability analysis and non-linear model simulations show that the MNH with smoothing (henceforth abbreviated as MNHS can use twice the time interval of the MNH while maintaining the same accuracy. The MNHS is also more accurate and efficient than HE–VI when the aspect ratio is small.

  10. Control of size and aspect ratio in hydroquinone-based synthesis of gold nanorods

    International Nuclear Information System (INIS)

    Morasso, Carlo; Picciolini, Silvia; Schiumarini, Domitilla; Mehn, Dora; Ojea-Jiménez, Isaac; Zanchetta, Giuliano; Vanna, Renzo; Bedoni, Marzia; Prosperi, Davide; Gramatica, Furio

    2015-01-01

    In this article, we describe how it is possible to tune the size and the aspect ratio of gold nanorods obtained using a highly efficient protocol based on the use of hydroquinone as a reducing agent by varying the amounts of CTAB and silver ions present in the “seed-growth” solution. Our approach not only allows us to prepare nanorods with a four times increased Au 3+ reduction yield, when compared with the commonly used protocol based on ascorbic acid, but also allows a remarkable reduction of 50–60 % of the amount of CTAB needed. In fact, according to our findings, the concentration of CTAB present in the seed-growth solution do not linearly influence the final aspect ratio of the obtained nanorods, and an optimal concentration range between 30 and 50 mM has been identified as the one that is able to generate particles with more elongated shapes. On the optimized protocol, the effect of the concentration of Ag + ions in the seed-growth solution and the stability of the obtained particles has also been investigated

  11. High-performance radio frequency transistors based on diameter-separated semiconducting carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Yu; Che, Yuchi; Zhou, Chongwu, E-mail: chongwuz@usc.edu [Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Seo, Jung-Woo T.; Hersam, Mark C. [Department of Materials Science and Engineering and Department of Chemistry, Northwestern University, Evanston, Illinois 60208 (United States); Gui, Hui [Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States)

    2016-06-06

    In this paper, we report the high-performance radio-frequency transistors based on the single-walled semiconducting carbon nanotubes with a refined average diameter of ∼1.6 nm. These diameter-separated carbon nanotube transistors show excellent transconductance of 55 μS/μm and desirable drain current saturation with an output resistance of ∼100 KΩ μm. An exceptional radio-frequency performance is also achieved with current gain and power gain cut-off frequencies of 23 GHz and 20 GHz (extrinsic) and 65 GHz and 35 GHz (intrinsic), respectively. These radio-frequency metrics are among the highest reported for the carbon nanotube thin-film transistors. This study provides demonstration of radio frequency transistors based on carbon nanotubes with tailored diameter distributions, which will guide the future application of carbon nanotubes in radio-frequency electronics.

  12. Flutter analysis of low aspect ratio wings

    Science.gov (United States)

    Parnell, L. A.

    1986-01-01

    Several very low aspect ratio flat plate wing configurations are analyzed for their aerodynamic instability (flutter) characteristics. All of the wings investigated are delta planforms with clipped tips, made of aluminum alloy plate and cantilevered from the supporting vehicle body. Results of both subsonic and supersonic NASTRAN aeroelastic analyses as well as those from another version of the program implementing the supersonic linearized aerodynamic theory are presented. Results are selectively compared with the experimental data; however, supersonic predictions of the Mach Box method in NASTRAN are found to be erratic and erroneous, requiring the use of a separate program.

  13. Seed-mediated synthesis of gold nanorods: control of the aspect ratio by variation of the reducing agent

    International Nuclear Information System (INIS)

    Koeppl, Susanne; Ghielmetti, Nico; Caseri, Walter; Spolenak, Ralph

    2013-01-01

    Seed-mediated growth methods involving reduction of tetrachloroaurate(III) with ascorbic acid are common for the synthesis of gold nanorods. This study shows, however, that simply by appropriate choice of the reducing agent a drastic influence on the aspect ratio can be attained. Weaker reducing agents, such as dihydroxybenzene isomers (hydroquinone, catechol or resorcinol) or glucose can increase the aspect ratio of the nanorods by an order of magnitude, up to values as high as 100 (nanowires). The increase in aspect ratio is mainly a consequence of an increase in length of the particles (up to 1–3 μm). This effect is probably associated with a decrease in the reduction rate of gold(III) species by dihydroxybenzenes or glucose compared to ascorbic acid. The reduction potential of the reducing agents strongly depends on the pH value, and related effects on the dimensions of the nanoparticles are also reflected in this study. The nanorods exhibited penta-twinned nature without noteworthy defects (e.g. stacking faults and dislocations).

  14. Stability of low aspect ratio inverted flags and rods in a uniform flow

    Science.gov (United States)

    Huertas-Cerdeira, Cecilia; Sader, John E.; Gharib, Morteza

    2016-11-01

    Cantilevered elastic plates and rods in an inverted configuration, where the leading edge is free to move and the trailing edge is clamped, undergo complex dynamics when subjected to a uniform flow. The stability of low aspect ratio inverted plates and rods is theoretically examined, showing that it is markedly different from that of their large aspect ratio counterpart. In the limit of zero aspect ratio, the undeflected equilibrium position is found to be stable for all wind speeds. A saddle-node bifurcation emerges at finite wind speed, giving rise to a strongly deflected stable and a weakly deflected unstable equilibria. This theory is compared to experimental measurements, where good agreement is found. This research was supported by a Grant of the Gordon and Betty Moore Foundation, the Australian Research Council Grants scheme and a "la Caixa" Fellowship Grant for Post-Graduate Studies of "la Caixa" Banking Foundation.

  15. Optimized aspect ratios of restrained thick-wall cylinders by virtue of Poisson's ratio selection. Part two: Temperature application

    International Nuclear Information System (INIS)

    Whitty, J.P.M.; Henderson, B.; Francis, J.

    2011-01-01

    Highlights: → Incontrovertible evidence is presented that thermal stresses in cylindrical components which include nuclear reactors and containment vessels are shown to be highly dependent on the Poisson's ratio of the materials. → The key novelty is concerned with the identification of a new potential thermal applications for negative Poisson's ratio (auxetic) materials; i.e. those that get fatter when they are stretched. → Negative Poisson's ratio (auxetic) materials exhibit lower thermal stress build-up than conventional positive Poisson's ratio materials, this conjecture being proven using thermal surface plots. - Abstract: Analytical and numerical modelling have been employed to show that the choice of Poisson's ratio is one of the principal design criteria in order to reduce thermal stress build-up in isotropic materials. The modelling procedures are all twofold; consisting of a solution to a steady-state heat conduction problem followed by a linear static solution. The models developed take the form of simplistic thick-wall cylinders such model systems are applicable at macro-structural and micro-structural levels as the underlining formulations are based on the classical theory of elasticity. Generally, the results show that the Poisson's ratio of the material has a greater effect on the magnitude of the principal stresses than the aspect ratio of the cylinders investigated. Constraining the outside of these models significantly increases the thermal stresses induced. The most significant and original finding presented is that the for both freely expanding and constrained thick-wall cylinders the optimum Poisson's ratio is minus unity.

  16. Forces and Moments on Flat Plates of Small Aspect Ratio with Application to PV Wind Loads and Small Wind Turbine Blades

    OpenAIRE

    Xavier Ortiz; David Rival; David Wood

    2015-01-01

    To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 10 4 to 2 × 10 5 . Measurements were made for angles of attack between 0°...

  17. Stable magnetization of iron filled carbon nanotube MFM probes in external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Wolny, Franziska; Weissker, Uhland; Muehl, Thomas; Lutz, Matthias U; Mueller, Christian; Leonhardt, Albrecht; Buechner, Bernd, E-mail: f.wolny@ifw-dresden.d [Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Helmholtzstrasse 20, 01069 Dresden (Germany)

    2010-01-01

    We present results on the application of an iron filled carbon nanotube (Fe-CNT) as a probe for magnetic force microscopy (MFM) in an external magnetic field. If an external field is applied parallel to the sample surface, conventional ferromagnetically coated MFM probes often have the disadvantage that the magnetization of the coating turns towards the direction of the applied field. Then it is difficult to distinguish the effect of the external field on the sample from those on the MFM probe. The Fe-CNT MFM probe has a large shape anisotropy due to the high aspect ratio of the enclosed iron nanowire. Thanks to this the direction of the magnetization stays mainly oriented along the long nanotube axis in in-plane fields up to our experimental limit of 250 mT. Thus, the quality of the MFM images remains unchanged. Apart from this, it is shown that Fe-CNT MFM probe yields a very good magnetic resolution of about 25 nm due to the small diameter of the iron filling.

  18. Metallic conductivity transition of carbon nanotube yarns coated with silver particles

    International Nuclear Information System (INIS)

    Zhang, Daohong; Zhang, Yunhe; Miao, Menghe

    2014-01-01

    Dry spun carbon nanotube yarns made from vertically aligned multiwalled carbon nanotube forests possess high mechanical strength and behave like semiconductors with electrical conductivity of the order of 4 × 10 4 S m −1 . Coating a submicron-thick film of silver particle-filled polymer on the surface increased the electrical conductivity of the carbon nanotube yarn by 60-fold without significantly sacrificing its mechanical strength. The transitional characteristics of the silver-coated carbon nanotube yarn were investigated by varying the take-up ratio of the silver coating. A step change in conductivity was observed when the silver content in the coated yarn was between 7 and 10 wt% as a result of the formation of connected silver particle networks on the carbon nanotube yarn surface. (papers)

  19. Facile synthesis of polyaniline nanotubes using reactive oxide templates for high energy density pseudocapacitors

    KAUST Repository

    Chen, Wei

    2013-01-01

    A remarkable energy density of 84 W h kg(cell) -1 and a power density of 182 kW kg(cell) -1 have been achieved for full-cell pseudocapacitors using conducting polymer nanotubes (polyaniline) as electrode materials and ionic liquid as electrolytes. The polyaniline nanotubes were synthesized by a one-step in situ chemical polymerization process utilizing MnO2 nanotubes as sacrificial templates. The polyaniline-nanotube pseudocapacitors exhibit much better electrochemical performance than the polyaniline-nanofiber pseudocapacitors in both acidic aqueous and ionic liquid electrolytes. Importantly, the incorporation of ionic liquid with polyaniline-nanotubes has drastically improved the energy storage capacity of the PAni-nanotube pseudocapacitors by a factor of ∼5 times compared to that of the PAni-nanotube pseudocapacitors in the acidic aqueous electrolyte. Furthermore, even after 10000 cycles, the PAni-nanotube pseudocapacitors in the ionic liquid electrolyte maintain sufficient high energy density and can light LEDs for several minutes, with only 30 s quick charge. © 2013 The Royal Society of Chemistry.

  20. Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods

    Directory of Open Access Journals (Sweden)

    Magnus Willander

    2009-11-01

    Full Text Available ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.

  1. Applications of carbon nanotubes-based biomaterials in biomedical nanotechnology.

    Science.gov (United States)

    Polizu, Stefania; Savadogo, Oumarou; Poulin, Philippe; Yahia, L'Hocine

    2006-07-01

    One of the facets of nanotechnology applications is the immense opportunities they offer for new developments in medicine and health sciences. Carbon nanotubes (CNTs) have particularly attracted attention for designing new monitoring systems for environment and living cells as well as nanosensors. Carbon nanotubes-based biomaterials are also employed as support for active prosthesis or functional matrices in reparation of parts of the human body. These nanostructures are studied as molecular-level building blocks for the complex and miniaturized medical device, and substrate for stimulation of cellular growth. The CNTs are cylindrical shaped with caged molecules which can act as nanoscale containers for molecular species, well required for biomolecular recognition and drug delivery systems. Endowed with very large aspect ratios, an excellent electrical conductivity and inertness along with mechanical robustness, nanotubes found enormous applications in molecular electronics and bioelectronics. The ballistic electrical behaviour of SWNTs conjugated with functionalization promotes a large variety of biosensors for individual molecules. Actuative response of CNTs is considered very promising feature for nanodevices, micro-robots and artificial muscles. An description of CNTs based biomaterials is attempted in this review, in order to point out their enormous potential for biomedical nanotechnology and nanobiotechnology.

  2. Enhancing the wettability of high aspect-ratio through-silicon vias lined with LPCVD silicon nitride or PE-ALD titanium nitride for void-free bottom-up copper electroplating

    NARCIS (Netherlands)

    Saadaoui, M.; Zeijl, H. van; Wien, W.H.A.; Pham, H.T.M.; Kwakernaak, C.; Knoops, H.C.M.; Erwin Kessels, W.M.M.; Sanden, R.M.C.M. van de; Voogt, F.C.; Roozeboom, F.; Sarro, P.M.

    2011-01-01

    One of the critical steps toward producing void-free and uniform bottom-up copper electroplating in high aspect-ratio (AR) through-silicon vias (TSVs) is the ability of the copper electrolyte to spontaneously flow through the entire depth of the via. This can be accomplished by reducing the

  3. Enhancing the Wettability of High Aspect-Ratio Through-Silicon Vias Lined with LPCVD Silicon Nitride or PE-ALD Titanium Nitride for Void-Free Bottom-Up Copper Electroplating

    NARCIS (Netherlands)

    Saadaoui, M.; van Zeijl, H.; Wien, W. H. A.; Pham, H. T. M.; Kwakernaak, C.; Knoops, H. C. M.; Kessels, W. M. M.; R. van de Sanden,; Voogt, F. C.; Roozeboom, F.; Sarro, P. M.

    2011-01-01

    One of the critical steps toward producing void-free and uniform bottom-up copper electroplating in high aspect-ratio (AR) through-silicon vias (TSVs) is the ability of the copper electrolyte to spontaneously flow through the entire depth of the via. This can be accomplished by reducing the

  4. Thermal performance analysis of a flat heat pipe working with carbon nanotube-water nanofluid for cooling of a high heat flux heater

    Science.gov (United States)

    Arya, A.; Sarafraz, M. M.; Shahmiri, S.; Madani, S. A. H.; Nikkhah, V.; Nakhjavani, S. M.

    2018-04-01

    Experimental investigation on the thermal performance of a flat heat pipe working with carbon nanotube nanofluid is conducted. It is used for cooling a heater working at high heat flux conditions up to 190 kW/m2. The heat pipe is fabricated from aluminium and is equipped with rectangular fin for efficient cooling of condenser section. Inside the heat pipe, a screen mesh was inserted as a wick structure to facilitate the capillary action of working fluid. Influence of different operating parameters such as heat flux, mass concentration of carbon nanotubes and filling ratio of working fluid on thermal performance of heat pipe and its thermal resistance are investigated. Results showed that with an increase in heat flux, the heat transfer coefficient in evaporator section of the heat pipe increases. For filling ratio, however, there is an optimum value, which was 0.8 for the test heat pipe. In addition, CNT/water enhanced the heat transfer coefficient up to 40% over the deionized water. Carbon nanotubes intensified the thermal performance of wick structure by creating a fouling layer on screen mesh structure, which changes the contact angle of liquid with the surface, intensifying the capillary forces.

  5. Nanotube cathodes.

    Energy Technology Data Exchange (ETDEWEB)

    Overmyer, Donald L.; Lockner, Thomas Ramsbeck; Siegal, Michael P.; Miller, Paul Albert

    2006-11-01

    Carbon nanotubes have shown promise for applications in many diverse areas of technology. In this report we describe our efforts to develop high-current cathodes from a variety of nanotubes deposited under a variety of conditions. Our goal was to develop a one-inch-diameter cathode capable of emitting 10 amperes of electron current for one second with an applied potential of 50 kV. This combination of current and pulse duration significantly exceeds previously reported nanotube-cathode performance. This project was planned for two years duration. In the first year, we tested the electron-emission characteristics of nanotube arrays fabricated under a variety of conditions. In the second year, we planned to select the best processing conditions, to fabricate larger cathode samples, and to test them on a high-power relativistic electron beam generator. In the first year, much effort was made to control nanotube arrays in terms of nanotube diameter and average spacing apart. When the project began, we believed that nanotubes approximately 10 nm in diameter would yield sufficient electron emission properties, based on the work of others in the field. Therefore, much of our focus was placed on measured field emission from such nanotubes grown on a variety of metallized surfaces and with varying average spacing between individual nanotubes. We easily reproduced the field emission properties typically measured by others from multi-wall carbon nanotube arrays. Interestingly, we did this without having the helpful vertical alignment to enhance emission; our nanotubes were randomly oriented. The good emission was most likely possible due to the improved crystallinity, and therefore, electrical conductivity, of our nanotubes compared to those in the literature. However, toward the end of the project, we learned that while these 10-nm-diameter CNTs had superior crystalline structure to the work of others studying field emission from multi-wall CNT arrays, these nanotubes still

  6. Nanotube cathodes

    International Nuclear Information System (INIS)

    Overmyer, Donald L.; Lockner, Thomas Ramsbeck; Siegal, Michael P.; Miller, Paul Albert

    2006-01-01

    Carbon nanotubes have shown promise for applications in many diverse areas of technology. In this report we describe our efforts to develop high-current cathodes from a variety of nanotubes deposited under a variety of conditions. Our goal was to develop a one-inch-diameter cathode capable of emitting 10 amperes of electron current for one second with an applied potential of 50 kV. This combination of current and pulse duration significantly exceeds previously reported nanotube-cathode performance. This project was planned for two years duration. In the first year, we tested the electron-emission characteristics of nanotube arrays fabricated under a variety of conditions. In the second year, we planned to select the best processing conditions, to fabricate larger cathode samples, and to test them on a high-power relativistic electron beam generator. In the first year, much effort was made to control nanotube arrays in terms of nanotube diameter and average spacing apart. When the project began, we believed that nanotubes approximately 10 nm in diameter would yield sufficient electron emission properties, based on the work of others in the field. Therefore, much of our focus was placed on measured field emission from such nanotubes grown on a variety of metallized surfaces and with varying average spacing between individual nanotubes. We easily reproduced the field emission properties typically measured by others from multi-wall carbon nanotube arrays. Interestingly, we did this without having the helpful vertical alignment to enhance emission; our nanotubes were randomly oriented. The good emission was most likely possible due to the improved crystallinity, and therefore, electrical conductivity, of our nanotubes compared to those in the literature. However, toward the end of the project, we learned that while these 10-nm-diameter CNTs had superior crystalline structure to the work of others studying field emission from multi-wall CNT arrays, these nanotubes still

  7. Quantum transport in carbon nanotubes

    DEFF Research Database (Denmark)

    Laird, Edward A.; Kuemmeth, Ferdinand; Steele, Gary A.

    2015-01-01

    Carbon nanotubes are a versatile material in which many aspects of condensed matter physics come together. Recent discoveries, enabled by sophisticated fabrication, have uncovered new phenomena that completely change our understanding of transport in these devices, especially the role of the spin...... blockade. This can be exploited to read out spin and valley qubits, and to measure the decay of these states through coupling to nuclear spins and phonons. A second unique property of carbon nanotubes is that the combination of valley freedom and electron-electron interactions in one dimension strongly...... and valley degrees of freedom. This review describes the modern understanding of transport through nanotube devices. Unlike conventional semiconductors, electrons in nanotubes have two angular momentum quantum numbers, arising from spin and from valley freedom. We focus on the interplay between the two...

  8. High-Fidelity Multidisciplinary Design Optimization of Aircraft Configurations

    Science.gov (United States)

    Martins, Joaquim R. R. A.; Kenway, Gaetan K. W.; Burdette, David; Jonsson, Eirikur; Kennedy, Graeme J.

    2017-01-01

    To evaluate new airframe technologies we need design tools based on high-fidelity models that consider multidisciplinary interactions early in the design process. The overarching goal of this NRA is to develop tools that enable high-fidelity multidisciplinary design optimization of aircraft configurations, and to apply these tools to the design of high aspect ratio flexible wings. We develop a geometry engine that is capable of quickly generating conventional and unconventional aircraft configurations including the internal structure. This geometry engine features adjoint derivative computation for efficient gradient-based optimization. We also added overset capability to a computational fluid dynamics solver, complete with an adjoint implementation and semiautomatic mesh generation. We also developed an approach to constraining buffet and started the development of an approach for constraining utter. On the applications side, we developed a new common high-fidelity model for aeroelastic studies of high aspect ratio wings. We performed optimal design trade-o s between fuel burn and aircraft weight for metal, conventional composite, and carbon nanotube composite wings. We also assessed a continuous morphing trailing edge technology applied to high aspect ratio wings. This research resulted in the publication of 26 manuscripts so far, and the developed methodologies were used in two other NRAs. 1

  9. Nanotube phonon waveguide

    Science.gov (United States)

    Chang, Chih-Wei; Zettl, Alexander K.

    2013-10-29

    Disclosed are methods and devices in which certain types of nanotubes (e.g., carbon nanotubes and boron nitride nanotubes conduct heat with high efficiency and are therefore useful in electronic-type devices.

  10. FERROMAGNETIC NANOTUBES IN PORES OF TRACK MEMBRANES FOR THE FLEXIBLE ELECTRONIC ELEMENTS

    Directory of Open Access Journals (Sweden)

    E. Yu. Kaniukov

    2017-01-01

    Full Text Available In the paper the template synthesis of ferromagnetic (Fe, Co, Ni nanotubes in the pores of track membranes were studied. The aim of this work was determination of nanotubes basic structural and magnetic parameters and demonstration of the possibility of application in the flexible electronics elements.By electrochemical deposition, ferromagnetic nanotubes with a diameter of 110 nm and an aspect ratio of 100 were formed in the pores of polyethylene terephthalate track membranes. The morphology of the obtained nanostructures were studied by scanning electron microscopy, the elemental composition was determined by the energy-dispersion analysis. Using the X-ray structural analysis, the main parameters of the crystal structure were established: lattice type, lattice parameter and average crystallite size. The magnetic properties were studied by the method of vibrational magnetometry.It was shown that in the selected conditions of synthesis without reference to the type of ferromagnetic metals nanotubes had the same dimensions – length, diameter and wall thickness. The produced nanotubes consisted of iron, cobalt and nickel, respectively without oxides impurities. Nanotubes had a polycrystalline structure of walls with a body-centered cubic (iron, face-centered cubic (cobalt and nickel crystal lattice. According to the main magnetic parameters, nanotubes belonged to a group of soft magnetic materials. Also, the presence of magnetic anisotropy, which is caused by the features of crystalline structure and shape of the nanostructures.Based on the analysis of structural and magnetic characteristics of ferromagnetic nanotubes which were synthesized in the pores of track membranes, were proposed the main principles of their using in the elements’ of flexible electronics constructing (magnetic field direction sensors and magnetic memory elements. 

  11. A Review: Carbon Nanotube-Based Piezoresistive Strain Sensors

    Directory of Open Access Journals (Sweden)

    Waris Obitayo

    2012-01-01

    Full Text Available The use of carbon nanotubes for piezoresistive strain sensors has acquired significant attention due to its unique electromechanical properties. In this comprehensive review paper, we discussed some important aspects of carbon nanotubes for strain sensing at both the nanoscale and macroscale. Carbon nanotubes undergo changes in their band structures when subjected to mechanical deformations. This phenomenon makes them applicable for strain sensing applications. This paper signifies the type of carbon nanotubes best suitable for piezoresistive strain sensors. The electrical resistivities of carbon nanotube thin film increase linearly with strain, making it an ideal material for a piezoresistive strain sensor. Carbon nanotube composite films, which are usually fabricated by mixing small amounts of single-walled or multiwalled carbon nanotubes with selected polymers, have shown promising characteristics of piezoresistive strain sensors. Studies also show that carbon nanotubes display a stable and predictable voltage response as a function of temperature.

  12. pH-Dependent Toxicity of High Aspect Ratio ZnO Nanowires in Macrophages Due to Intracellular Dissolution

    KAUST Repository

    H. Müller, Karin

    2010-11-23

    High-aspect ratio ZnO nanowires have become one of the most promising products in the nanosciences within the past few years with a multitude of applications at the interface of optics and electronics. The interaction of zinc with cells and organisms is complex, with both deficiency and excess causing severe effects. The emerging significance of zinc for many cellular processes makes it imperative to investigate the biological safety of ZnO nanowires in order to guarantee their safe economic exploitation. In this study, ZnO nanowires were found to be toxic to human monocyte macrophages (HMMs) at similar concentrations as ZnCl2. Confocal microscopy on live cells confirmed a rise in intracellular Zn2+ concentrations prior to cell death. In vitro, ZnO nanowires dissolved very rapidly in a simulated body fluid of lysosomal pH, whereas they were comparatively stable at extracellular pH. Bright-field transmission electron microscopy (TEM) showed a rapid macrophage uptake of ZnO nanowire aggregates by phagocytosis. Nanowire dissolution occurred within membrane-bound compartments, triggered by the acidic pH of the lysosomes. ZnO nanowire dissolution was confirmed by scanning electron microscopy/energy-dispersive X-ray spectrometry. Deposition of electron-dense material throughout the ZnO nanowire structures observed by TEM could indicate adsorption of cellular components onto the wires or localized zinc-induced protein precipitation. Our study demonstrates that ZnO nanowire toxicity in HMMs is due to pH-triggered, intracellular release of ionic Zn2+ rather than the high-aspect nature of the wires. Cell death had features of necrosis as well as apoptosis, with mitochondria displaying severe structural changes. The implications of these findings for the application of ZnO nanowires are discussed. © 2010 American Chemical Society.

  13. Controlled nanostructure and high loading of single-walled carbon nanotubes reinforced polycarbonate composite

    International Nuclear Information System (INIS)

    Wang Shiren; Liang Zhiyong; Pham, Giang; Park, Young-Bin; Wang, Ben; Zhang, Chuck; Kramer, Leslie; Funchess, Percy

    2007-01-01

    This paper presents an effective technique to fabricate thermoplastic nanocomposites with high loading of well-dispersed single-walled carbon nanotubes (SWNTs). SWNT membranes were made from a multi-step dispersion and filtration method, and then impregnated with polycarbonate solution to make thermoplastic nanocomposites. High loading of nanotubes was achieved by controlling the viscosity of polycarbonate solution. SEM and AFM characterization results revealed the controlled nanostructure in the resultant nanocomposites. Dynamic mechanical property tests indicated that the storage modulus of the resulting nanocomposites at 20 wt% nanotubes loading was improved by a factor of 3.4 compared with neat polycarbonate material. These results suggest the developed approach is an effective way to fabricate thermoplastic nanocomposites with good dispersion and high SWNT loading

  14. Influence of aspect ratio and surface defect density on hydrothermally grown ZnO nanorods towards amperometric glucose biosensing applications

    Science.gov (United States)

    Shukla, Mayoorika; Pramila; Dixit, Tejendra; Prakash, Rajiv; Palani, I. A.; Singh, Vipul

    2017-11-01

    In this work, hydrothermally grown ZnO Nanorods Array (ZNA) has been synthesized over Platinum (Pt) coated glass substrate, for biosensing applications. In-situ addition of strong oxidizing agent viz KMnO4 during hydrothermal growth was found to have profound effect on the physical properties of ZNA. Glucose oxidase (GOx) was later immobilized over ZNA by means of physical adsorption process. Further influence of varying aspect ratio, enzyme loading and surface defects on amperometric glucose biosensor has been analyzed. Significant variation in biosensor performance was observed by varying the amount of KMnO4 addition during the growth. Moreover, investigations revealed that the suppression of surface defects and aspect ratio variation of the ZNA played key role towards the observed improvement in the biosensor performance, thereby significantly affecting the sensitivity and response time of the fabricated biosensor. Among different biosensors fabricated having varied aspect ratio and surface defect density of ZNA, the best electrode resulted into sensitivity and response time to be 18.7 mA cm-2 M-1 and <5 s respectively. The observed results revealed that apart from high aspect ratio nanostructures and the extent of enzyme loading, surface defect density also hold a key towards ZnO nanostructures based bio-sensing applications.

  15. Carbon nanotube based photocathodes

    International Nuclear Information System (INIS)

    Hudanski, Ludovic; Minoux, Eric; Schnell, Jean-Philippe; Xavier, Stephane; Pribat, Didier; Legagneux, Pierre; Gangloff, Laurent; Teo, Kenneth B K; Robertson, John; Milne, William I

    2008-01-01

    This paper describes a novel photocathode which is an array of vertically aligned multi-walled carbon nanotubes (MWCNTs), each MWCNT being associated with one p-i-n photodiode. Unlike conventional photocathodes, the functions of photon-electron conversion and subsequent electron emission are physically separated. Photon-electron conversion is achieved with p-i-n photodiodes and the electron emission occurs from the MWCNTs. The current modulation is highly efficient as it uses an optically controlled reconfiguration of the electric field at the MWCNT locations. Such devices are compatible with high frequency and very large bandwidth operation and could lead to their application in compact, light and efficient microwave amplifiers for satellite telecommunication. To demonstrate this new photocathode concept, we have fabricated the first carbon nanotube based photocathode using silicon p-i-n photodiodes and MWCNT bunches. Using a green laser, this photocathode delivers 0.5 mA with an internal quantum efficiency of 10% and an I ON /I OFF ratio of 30

  16. Control of size and aspect ratio in hydroquinone-based synthesis of gold nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Morasso, Carlo, E-mail: cmorasso@dongnocchi.it; Picciolini, Silvia; Schiumarini, Domitilla [Fondazione Don Carlo Gnocchi ONLUS, Laboratory of Nanomedicine and Clinical Biophotonics (LABION) (Italy); Mehn, Dora; Ojea-Jiménez, Isaac [European Commission Joint Research Centre, Institute for Health and Consumer Protection (IHCP) (Italy); Zanchetta, Giuliano [Universitá degli Studi di Milano, Dipartimento di Biotecnologie Mediche e Medicina Traslazionale (Italy); Vanna, Renzo; Bedoni, Marzia [Fondazione Don Carlo Gnocchi ONLUS, Laboratory of Nanomedicine and Clinical Biophotonics (LABION) (Italy); Prosperi, Davide [Università degli Studi di Milano Bicocca, NanoBioLab, Dipartimento di Biotecnologie e Bioscienze (Italy); Gramatica, Furio [Fondazione Don Carlo Gnocchi ONLUS, Laboratory of Nanomedicine and Clinical Biophotonics (LABION) (Italy)

    2015-08-15

    In this article, we describe how it is possible to tune the size and the aspect ratio of gold nanorods obtained using a highly efficient protocol based on the use of hydroquinone as a reducing agent by varying the amounts of CTAB and silver ions present in the “seed-growth” solution. Our approach not only allows us to prepare nanorods with a four times increased Au{sup 3+} reduction yield, when compared with the commonly used protocol based on ascorbic acid, but also allows a remarkable reduction of 50–60 % of the amount of CTAB needed. In fact, according to our findings, the concentration of CTAB present in the seed-growth solution do not linearly influence the final aspect ratio of the obtained nanorods, and an optimal concentration range between 30 and 50 mM has been identified as the one that is able to generate particles with more elongated shapes. On the optimized protocol, the effect of the concentration of Ag{sup +} ions in the seed-growth solution and the stability of the obtained particles has also been investigated.

  17. High pressure Raman spectroscopy of single-walled carbon nanotubes: Effect of chemical environment on individual nanotubes and the nanotube bundle

    Science.gov (United States)

    Proctor, John E.; Halsall, Matthew P.; Ghandour, Ahmad; Dunstan, David J.

    2006-12-01

    The pressure-induced tangential mode Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using a variety of different solvents as hydrostatic pressure-transmitting media. The variation in the nanotube response to hydrostatic pressure with different pressure transmitting media is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [J. Chem. Phys. 121 (2004) 2752], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at lower pressures. We also find that the role of cohesive energy density in the solvent nanotube interaction is more complex than previously thought.

  18. Electrolytic Manganese Dioxide Coatings on High Aspect Ratio Micro-Pillar Arrays for 3D Thin Film Lithium Ion Batteries

    Directory of Open Access Journals (Sweden)

    Yafa Zargouni

    2017-05-01

    Full Text Available In this work, we present the electrochemical deposition of manganese dioxide (MnO2 thin films on carbon-coated TiN/Si micro-pillars. The carbon buffer layer, grown by plasma enhanced chemical vapor deposition (PECVD, is used as a protective coating for the underlying TiN current collector from oxidation, during the film deposition, while improving the electrical conductivity of the stack. A conformal electrolytic MnO2 (EMD coating is successfully achieved on high aspect ratio C/TiN/Si pillar arrays by tailoring the deposition process. Lithiation/Delithiation cycling tests have been performed. Reversible insertion and extraction of Li+ through EMD structure are observed. The fabricated stack is thus considered as a good candidate not only for 3D micorbatteries but also for other energy storage applications.

  19. Electrolytic Manganese Dioxide Coatings on High Aspect Ratio Micro-Pillar Arrays for 3D Thin Film Lithium Ion Batteries.

    Science.gov (United States)

    Zargouni, Yafa; Deheryan, Stella; Radisic, Alex; Alouani, Khaled; Vereecken, Philippe M

    2017-05-27

    In this work, we present the electrochemical deposition of manganese dioxide (MnO₂) thin films on carbon-coated TiN/Si micro-pillars. The carbon buffer layer, grown by plasma enhanced chemical vapor deposition (PECVD), is used as a protective coating for the underlying TiN current collector from oxidation, during the film deposition, while improving the electrical conductivity of the stack. A conformal electrolytic MnO₂ (EMD) coating is successfully achieved on high aspect ratio C/TiN/Si pillar arrays by tailoring the deposition process. Lithiation/Delithiation cycling tests have been performed. Reversible insertion and extraction of Li⁺ through EMD structure are observed. The fabricated stack is thus considered as a good candidate not only for 3D micorbatteries but also for other energy storage applications.

  20. Tuning the Slide-Roll Motion Mode of Carbon Nanotubes via Hydroxyl Groups

    Science.gov (United States)

    Li, Rui; Wang, Shiwei; Peng, Qing

    2018-05-01

    Controlling the motion of carbon nanotubes is critical in manipulating nanodevices, including nanorobots. Herein, we investigate the motion behavior of SWCNT (10,10) on Si substrate utilizing molecular dynamics simulations. We show that hydroxyl groups have sensitive effect on the carbon nanotube's motion mode. When the hydroxyl groups' ratio on carbon nanotube and silicon substrate surfaces is larger than 10 and 20%, respectively, the motion of carbon nanotube transforms from sliding to rolling. When the hydroxyl groups' ratio is smaller, the slide or roll mode can be controlled by the speed of carbon nanotube, which is ultimately determined by the competition between the interface potential energy and kinetic energy. The change of motion mode holds true for different carbon nanotubes with hydroxyl groups. The chirality has little effect on the motion behavior, as opposed to the diameter, attributed to the hydroxyl groups' ratio. Our study suggests a new route to control the motion behavior of carbon nanotube via hydroxyl groups.

  1. High yield growth of patterned vertically aligned carbon nanotubes using inkjet-printed catalyst.

    Science.gov (United States)

    Beard, James D; Stringer, Jonathan; Ghita, Oana R; Smith, Patrick J

    2013-10-09

    This study reports on the fabrication of vertically aligned carbon nanotubes localized at specific sites on a growth substrate by deposition of a nanoparticle suspension using inkjet printing. Carbon nanotubes were grown with high yield as vertically aligned forests to a length of approximately 400 μm. The use of inkjet printing for catalyst fabrication considerably improves the production rate of vertically aligned patterned nanotube forests compared with conventional patterning techniques, for example, electron beam lithography or photolithography.

  2. Flow and Pollutant Transport in Urban Street Canyons of Different Aspect Ratios with Ground Heating: Large-Eddy Simulation

    Science.gov (United States)

    Li, Xian-Xiang; Britter, Rex E.; Norford, Leslie K.; Koh, Tieh-Yong; Entekhabi, Dara

    2012-02-01

    A validated large-eddy simulation model was employed to study the effect of the aspect ratio and ground heating on the flow and pollutant dispersion in urban street canyons. Three ground-heating intensities (neutral, weak and strong) were imposed in street canyons of aspect ratio 1, 2, and 0.5. The detailed patterns of flow, turbulence, temperature and pollutant transport were analyzed and compared. Significant changes of flow and scalar patterns were caused by ground heating in the street canyon of aspect ratio 2 and 0.5, while only the street canyon of aspect ratio 0.5 showed a change in flow regime (from wake interference flow to skimming flow). The street canyon of aspect ratio 1 does not show any significant change in the flow field. Ground heating generated strong mixing of heat and pollutant; the normalized temperature inside street canyons was approximately spatially uniform and somewhat insensitive to the aspect ratio and heating intensity. This study helps elucidate the combined effects of urban geometry and thermal stratification on the urban canyon flow and pollutant dispersion.

  3. Zirconium oxide nanotube-Nafion composite as high performance membrane for all vanadium redox flow battery

    Science.gov (United States)

    Aziz, Md. Abdul; Shanmugam, Sangaraju

    2017-01-01

    A high-performance composite membrane for vanadium redox flow battery (VRB) consisting of ZrO2 nanotubes (ZrNT) and perfluorosulfonic acid (Nafion) was fabricated. The VRB operated with a composite (Nafion-ZrNT) membrane showed the improved ion-selectivity (ratio of proton conductivity to permeability), low self-discharge rate, high discharge capacity and high energy efficiency in comparison with a pristine commercial Nafion-117 membrane. The incorporation of zirconium oxide nanotubes in the Nafion matrix exhibits high proton conductivity (95.2 mS cm-1) and high oxidative stability (99.9%). The Nafion-ZrNT composite membrane exhibited low vanadium ion permeability (3.2 × 10-9 cm2 min-1) and superior ion selectivity (2.95 × 107 S min cm-3). The VRB constructed with a Nafion-ZrNT composite membrane has lower self-discharge rate maintaining an open-circuit voltage of 1.3 V for 330 h relative to a pristine Nafion membrane (29 h). The discharge capacity of Nafion-ZrNT membrane (987 mAh) was 3.5-times higher than Nafion-117 membrane (280 mAh) after 100 charge-discharge cycles. These superior properties resulted in higher coulombic and voltage efficiencies with Nafion-ZrNT membranes compared to VRB with Nafion-117 membrane at a 40 mA cm-2 current density.

  4. Mirage effect from thermally modulated transparent carbon nanotube sheets.

    Science.gov (United States)

    Aliev, Ali E; Gartstein, Yuri N; Baughman, Ray H

    2011-10-28

    The single-beam mirage effect, also known as photothermal deflection, is studied using a free-standing, highly aligned carbon nanotube aerogel sheet as the heat source. The extremely low thermal capacitance and high heat transfer ability of these transparent forest-drawn carbon nanotube sheets enables high frequency modulation of sheet temperature over an enormous temperature range, thereby providing a sharp, rapidly changing gradient of refractive index in the surrounding liquid or gas. The advantages of temperature modulation using carbon nanotube sheets are multiple: in inert gases the temperature can reach > 2500 K; the obtained frequency range for photothermal modulation is ~100 kHz in gases and over 100 Hz in high refractive index liquids; and the heat source is transparent for optical and acoustical waves. Unlike for conventional heat sources for photothermal deflection, the intensity and phase of the thermally modulated beam component linearly depends upon the beam-to-sheet separation over a wide range of distances. This aspect enables convenient measurements of accurate values for thermal diffusivity and the temperature dependence of refractive index for both liquids and gases. The remarkable performance of nanotube sheets suggests possible applications as photo-deflectors and for switchable invisibility cloaks, and provides useful insights into their use as thermoacoustic projectors and sonar. Visibility cloaking is demonstrated in a liquid.

  5. Single macroscopic pillars as model system for bioinspired adhesives: influence of tip dimension, aspect ratio, and tilt angle.

    Science.gov (United States)

    Micciché, Maurizio; Arzt, Eduard; Kroner, Elmar

    2014-05-28

    The goal of our study is to better understand the design parameters of bioinspired dry adhesives inspired by geckos. For this, we fabricated single macroscopic pillars of 400 μm diameter with different aspect ratios and different tip shapes (i.e., flat tips, spherical tips with different radii, and mushroom tips with different diameters). Tilt-angle-dependent adhesion measurements showed that although the tip shape of the pillars strongly influences the pull-off force, the pull-off strength is similar for flat and mushroom-shaped tips. We found no tilt-angle dependency of adhesion for spherical tip structures and, except for high tilt angle and low preload experiments, no tilt-angle effect for mushroom-tip pillars. For flat-tip pillars, we found a strong influence of tilt angle on adhesion, which decreased linearly with increasing aspect ratio. The experiments show that for the tested aspect ratios between 1 and 5, a linear decrease of tilt-angle dependency is found. The results of our studies will help to design bioinspired adhesives for application on smooth and rough surfaces.

  6. Nanoscale Soldering of Positioned Carbon Nanotubes using Highly Conductive Electron Beam Induced Gold Deposition

    DEFF Research Database (Denmark)

    Madsen, Dorte Nørgaard; Mølhave, Kristian; Mateiu, Ramona Valentina

    2003-01-01

    We have developed an in-situ method for controlled positioning of carbon nanotubes followed by highly conductive contacting of the nanotubes, using electron beam assisted deposition of gold. The positioning and soldering process takes place inside an Environmental Scanning Electron Microscope (E...... in a carbon matrix. Nanoscale soldering of multi-walled carbon nanotubes (MWNT) onto microelectrodes was achieved by deposition of a conducting gold line across a contact point between nanotube and electrode. The solderings were found to be mechanically stronger than the carbon nanotubes. We have positioned...... MWNTs to bridge the gap between two electrodes, and formed soldering bonds between the tube and each of the electrodes. All nanotube bridges showed ohmic resistances in the range 10-30 kΩ. We observed no increase in resistance after exposing the MWNT bridge to air for days....

  7. Fringing-field dielectrophoretic assembly of ultrahigh-density semiconducting nanotube arrays with a self-limited pitch

    Science.gov (United States)

    Cao, Qing; Han, Shu-Jen; Tulevski, George S.

    2014-09-01

    One key challenge of realizing practical high-performance electronic devices based on single-walled carbon nanotubes is to produce electronically pure nanotube arrays with both a minuscule and uniform inter-tube pitch for sufficient device-packing density and homogeneity. Here we develop a method in which the alternating voltage-fringing electric field formed between surface microelectrodes and the substrate is utilized to assemble semiconducting nanotubes into well-aligned, ultrahigh-density and submonolayered arrays, with a consistent pitch as small as 21±6 nm determined by a self-limiting mechanism, based on the unique field focusing and screening effects of the fringing field. Field-effect transistors based on such nanotube arrays exhibit record high device transconductance (>50 μS μm-1) and decent on current per nanotube (~1 μA per tube) together with high on/off ratios at a drain bias of -1 V.

  8. New approach to synthesis of carbon nanotubes

    International Nuclear Information System (INIS)

    Ha, Jong Keun; Choi, Kyo Hong; Cho, Kwon Koo; Kim, Ki Won; Nam, Tae Hyun; Ahn, Hyo Jun; Ahn, Jou Hyun; Cho, Gyu Bong

    2007-01-01

    Carbon nanotubes (CNTs) have been synthesized through chemical vapor deposition in argon gas atmosphere using Fe-2.5%Mo alloyed nanoparticles as a catalyst and H 2 /CH 4 gas mixture as a reaction gas. Fe-2.5 wt.%Mo alloyed nanoparticles with average diameter of 7, 20, 45 and 85 nm are prepared by the chemical vapor condensation process using the pyrolysis of iron pentacarbonyl (Fe(CO) 5 ) and molybdenum hexacarbonyl (Mo(CO) 6 ). The morphologies of the CNTs are controlled by adjusting the nanoparticle size, reaction gas ratio and reaction temperature. With decreasing nanoparticle size under the same experimental conditions, the degree of crystalline perfection increases gradually and the morphologies of the carbon nanotubes vary from multi wall carbon nanotubes to single wall carbon nanotubes. Also, the ratio of reaction gas has an effect on the morphology and the degree of crystallinity of CNTs. In this work, it is suggested that morphology, diameter and degree of crystallinity of CNTs could be controlled by adjusting the reaction gas ratio, reaction temperature and catalyst size

  9. Physically unclonable cryptographic primitives using self-assembled carbon nanotubes

    Science.gov (United States)

    Hu, Zhaoying; Comeras, Jose Miguel M. Lobez; Park, Hongsik; Tang, Jianshi; Afzali, Ali; Tulevski, George S.; Hannon, James B.; Liehr, Michael; Han, Shu-Jen

    2016-06-01

    Information security underpins many aspects of modern society. However, silicon chips are vulnerable to hazards such as counterfeiting, tampering and information leakage through side-channel attacks (for example, by measuring power consumption, timing or electromagnetic radiation). Single-walled carbon nanotubes are a potential replacement for silicon as the channel material of transistors due to their superb electrical properties and intrinsic ultrathin body, but problems such as limited semiconducting purity and non-ideal assembly still need to be addressed before they can deliver high-performance electronics. Here, we show that by using these inherent imperfections, an unclonable electronic random structure can be constructed at low cost from carbon nanotubes. The nanotubes are self-assembled into patterned HfO2 trenches using ion-exchange chemistry, and the width of the trench is optimized to maximize the randomness of the nanotube placement. With this approach, two-dimensional (2D) random bit arrays are created that can offer ternary-bit architecture by determining the connection yield and switching type of the nanotube devices. As a result, our cryptographic keys provide a significantly higher level of security than conventional binary-bit architecture with the same key size.

  10. Wakes behind surface-mounted obstacles: Impact of aspect ratio, incident angle, and surface roughness

    Science.gov (United States)

    Tobin, Nicolas; Chamorro, Leonardo P.

    2018-03-01

    The so-called wake-moment coefficient C˜h and lateral wake deflection of three-dimensional windbreaks are explored in the near and far wake. Wind-tunnel experiments were performed to study the functional dependence of C˜h with windbreak aspect ratio, incidence angle, and the ratio of the windbreak height and surface roughness (h /z0 ). Supported with the data, we also propose basic models for the wake deflection of the windbreak in the near and far fields. The near-wake model is based on momentum conservation considering the drag on the windbreak, whereas the far-wake counterpart is based on existing models for wakes behind surface-mounted obstacles. Results show that C˜h does not change with windbreak aspect ratios of 10 or greater; however, it may be lower for an aspect ratio of 5. C˜h is found to change roughly with the cosine of the incidence angle, and to depend strongly on h /z0 . The data broadly support the proposed wake-deflection models, though better predictions could be made with improved knowledge of the windbreak drag coefficient.

  11. Engineering Design Study of Quasi-Axisymmetric Stellarator with Low Aspect Ratio

    International Nuclear Information System (INIS)

    Matsuoka, Keisuke; Okamura, Shoichi; Nishimura, Shin; Isobe, Mitsutaka; Suzuki, Chihiro; Shimizu, Akihiro; Tanaka, Nobuo; Hasegawa, Mitsuru; Naito, Hideji; Urata, Kazuhiro; Suzuki, Yutaka; Tsukamoto, Tadanori

    2004-01-01

    The engineering design of the quasi-axisymmetric stellarator CHS-qa is described, having a toroidal period number of 2, major radius of 1.5 m, and plasma aspect ratio of 3.2. Although the entire structure of the machine is highly nonaxisymmetric and deformative, the following major engineering concerns for the modular coils and the vacuum vessel have been resolved: (a) modular coil design (curvature and twist of conductors), (b) supporting structures for modular coils, (c) errors due to electromagnetic forces and misalignment in manufacturing processes (analysis shows that the magnetic surface is robust against such disturbances), (d) construction procedure for vacuum vessel and modular coils, and (e) ports for heating and diagnostics

  12. High performance bulk metallic glass/carbon nanotube composite cathodes for electron field emission

    International Nuclear Information System (INIS)

    Hojati-Talemi, Pejman; Gibson, Mark A.; East, Daniel; Simon, George P.

    2011-01-01

    We report the preparation of new nanocomposites based on a combination of bulk metallic glass and carbon nanotubes for electron field emission applications. The use of bulk metallic glass as the matrix ensures high electrical and thermal conductivity, high thermal stability, and ease of processing, whilst the well dispersed carbon nanotubes act as highly efficient electron emitters. These advantages, alongside excellent electron emission properties, make these composites one of the best reported options for electron emission applications to date.

  13. High performance bulk metallic glass/carbon nanotube composite cathodes for electron field emission

    Energy Technology Data Exchange (ETDEWEB)

    Hojati-Talemi, Pejman [Department of Materials Engineering, Monash University, Clayton, Vic 3800 (Australia); Mawson Institute, University of South Australia, Mawson Lakes, SA 5095 (Australia); Gibson, Mark A. [Process Science and Engineering, Commonwealth Scientific and Industrial Research Organisation, Clayton, Vic 3168 (Australia); East, Daniel; Simon, George P. [Department of Materials Engineering, Monash University, Clayton, Vic 3800 (Australia)

    2011-11-07

    We report the preparation of new nanocomposites based on a combination of bulk metallic glass and carbon nanotubes for electron field emission applications. The use of bulk metallic glass as the matrix ensures high electrical and thermal conductivity, high thermal stability, and ease of processing, whilst the well dispersed carbon nanotubes act as highly efficient electron emitters. These advantages, alongside excellent electron emission properties, make these composites one of the best reported options for electron emission applications to date.

  14. Anodization parameters influencing the morphology and electrical properties of TiO{sub 2} nanotubes for living cell interfacing and investigations

    Energy Technology Data Exchange (ETDEWEB)

    Khudhair, D. [Deakin University, Waurn Ponds Campus, Vic 3216 (Australia); Bhatti, A., E-mail: asim.bhatti@deakin.edu.au [Deakin University, Waurn Ponds Campus, Vic 3216 (Australia); Li, Y. [RMIT University, Bundoora, Victoria 3083 (Australia); Hamedani, H. Amani; Garmestani, H. [Georgia Institute of Technology, GA 30332 (United States); Hodgson, P.; Nahavandi, S. [Deakin University, Waurn Ponds Campus, Vic 3216 (Australia)

    2016-02-01

    Nanotube structures have attracted tremendous attention in recent years in many applications. Among such nanotube structures, titania nanotubes (TiO{sub 2}) have received paramount attention in the medical domain due to their unique properties, represented by high corrosion resistance, good mechanical properties, high specific surface area, as well as great cell proliferation, adhesion and mineralization. Although lot of research has been reported in developing optimized titanium nanotube structures for different medical applications, however there is a lack of unified literature source that could provide information about the key parameters and experimental conditions required to develop such optimized structure. This paper addresses this gap, by focussing on the fabrication of TiO{sub 2} nanotubes through anodization process on both pure titanium and titanium alloys substrates to exploit the biocompatibility and electrical conductivity aspects, critical factors for many medical applications from implants to in-vivo and in-vitro living cell studies. It is shown that the morphology of TiO{sub 2} directly impacts the biocompatibility aspects of the titanium in terms of cell proliferation, adhesion and mineralization. Similarly, TiO{sub 2} nanotube wall thickness of 30–40 nm has shown to exhibit improved electrical behaviour, a critical factor in brain mapping and behaviour investigations if such nanotubes are employed as micro–nano-electrodes. - Highlights: • We spotlight on the importance of TiO{sub 2} nanotubes in medical applications. • The influence of nanotubes morphology on the electrical conductivity and biocompatibility properties • Influence of key anodizing parameters on the nanotube morphology • Methods to improve the electrical conductivity of TiO{sub 2} nanotubes • Potential of employment of TiO{sub 2} nanotubes as micro–nano-electrodes.

  15. Optimization of laser energy deposition for single-shot high aspect-ratio microstructuring of thick BK7 glass

    Energy Technology Data Exchange (ETDEWEB)

    Garzillo, Valerio; Grigutis, Robertas [Dipartimento di Scienza e Alta Tecnologia, University of Insubria, Via Valleggio 11, I-22100 Como (Italy); Jukna, Vytautas [Centre de Physique Theorique, CNRS, Ecole Polytechnique, Université Paris-Saclay, F-91128 Palaiseau (France); LOA, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Université Paris Saclay, F-91762 Palaiseau (France); Couairon, Arnaud [Centre de Physique Theorique, CNRS, Ecole Polytechnique, Université Paris-Saclay, F-91128 Palaiseau (France); Di Trapani, Paolo [Dipartimento di Scienza e Alta Tecnologia, University of Insubria and CNISM UdR Como, Via Valleggio 11, I-22100 Como (Italy); Jedrkiewicz, Ottavia, E-mail: ottavia.jedrkiewicz@ifn.cnr.it [Istituto di Fotonica e Nanotecnologie, CNR and CNISM UdR Como, Via Valleggio 11, I-22100 Como (Italy)

    2016-07-07

    We investigate the generation of high aspect ratio microstructures across 0.7 mm thick glass by means of single shot Bessel beam laser direct writing. We study the effect on the photoinscription of the cone angle, as well as of the energy and duration of the ultrashort laser pulse. The aim of the study is to optimize the parameters for the writing of a regular microstructure due to index modification along the whole sample thickness. By using a spectrally resolved single pulse transmission diagnostics at the output surface of the glass, we correlate the single shot material modification with observations of the absorption in different portions of the retrieved spectra, and with the absence or presence of spectral modulation. Numerical simulations of the evolution of the Bessel pulse intensity and of the energy deposition inside the sample help us interpret the experimental results that suggest to use picosecond pulses for an efficient and more regular energy deposition. Picosecond pulses take advantage of nonlinear plasma absorption and avoid temporal dynamics effects which can compromise the stationarity of the Bessel beam propagation.

  16. Physics Issues in the Design of Low Aspect-Ratio, High-Beta, Quasi-Axisymmetric Stellarators

    International Nuclear Information System (INIS)

    Zarnstorff, M.C.; Berry, L.A.; Boozer, A.; Brooks, A.; Cooper, W.A.

    2000-01-01

    Compact stellarators have the potential to combine the best features of the stellarator and the advanced tokamak, offering steady state operation without current drive and potentially without disruptions at an aspect ratio similar to tokamaks. A quasi-axisymmetric stellarator is developed that is consistent with the boot-strap current and passively stable to the ballooning, kink, Mercier, vertical, and neoclassical tearing modes at b=4.1 % without need for conducting walls or external feedback. The configuration has good flux surfaces and fast ion confinement. Thermal transport analysis indicates that the confinement should be similar to tokamaks of the same size, allowing access to the b-limit with moderate power. Coils have been designed to reproduce the physics properties. Initial analysis indicates the coils have considerable flexibility to manipulate the configuration properties. Simulations of the current evolution indicate the kink-mode can remain stable during the approach to h igh-beta

  17. Guided proliferation and bone-forming functionality on highly ordered large diameter TiO2 nanotube arrays

    International Nuclear Information System (INIS)

    Zhang, Ruopeng; Wu, Hongliu; Ni, Jiahua; Zhao, Changli; Chen, Yifan; Zheng, Chengjunyi; Zhang, Xiaonong

    2015-01-01

    The significantly enhanced osteoblast adhesion, proliferation and alkaline phosphatase (ALP) activity were observed on TiO 2 nanotube surface in recent studies in which the scale of nanotube diameter was restricted under 100 nm. In this paper, a series of highly ordered TiO 2 nanotube arrays with larger diameters ranging from 150 nm to 470 nm were fabricated via high voltage anodization. The behaviors of MC3T3-E1 cells in response to the diameter-controlled TiO 2 nanotubes were investigated. A contrast between the trend of proliferation and the trend of cell elongation was observed. The highest cell elongation (nearly 10:1) and the lowest cell number were observed on the TiO 2 nanotube arrays with 150 nm diameter. While, the lowest cell elongation and highest cell number were achieved on the TiO 2 nanotube arrays with 470 nm diameter. Furthermore, the ALP activity peaked on the 150 nm diameter TiO 2 nanotube arrays and decreased dramatically with the increase of nanotube diameter. Thus a narrow range of diameter (100–200 nm) that could induce the greatest bone-forming activity is determined. It is expected that more delicate design of orthopedic implant with regional abduction of cell proliferation or bone forming could be achieved by controlling the diameter of TiO 2 nanotubes. - Highlights: • Improved anodization methods leading to more ordered large diameter TiO 2 nanotubes • Significantly enhanced ALP activity was observed on 150 nm diameter TiO 2 nanotubes. • The highest cell density was observed on 470 nm diameter TiO 2 nanotube arrays. • Similar cell response was observed on the amorphous and anatase phased nanotube surface

  18. Synthesis of highly ordered TiO2 nanotube in malonic acid solution by anodization.

    Science.gov (United States)

    Ryu, Won Hee; Park, Chan Jin; Kwon, Hyuk Sang

    2008-10-01

    We synthesized TiO2 nanotube array by anodizing in a solution of malonic acid (HOOCCH2COOH) and NH4F, and analyzed the morphology of the nanotube using scanning electron microscopy (SEM). The morphology of TiO2 nanotube was largely affected by anodizing time, anodizing voltage, and malonic acid concentration. With increasing the anodizing voltage from 5 V to 20 V, the diameter of TiO2 nanotube was increased from about 20 nm to 110 nm and its length from about 10 nm to 700 nm. In addition, the length of TiO2 nanotube was increased with increasing anodizing time up to 6 h at 20 V. We obtained the longest and the most highly ordered nanotube structure when anodizing Ti in a solution of 0.5 wt% NH4F and 1 M malonic acid at 20 V for 6 h.

  19. Comparison of analytical and experimental subsonic steady and unsteady pressure distributions for a high-aspect-ratio-supercritical wing model with oscillating control surfaces

    Science.gov (United States)

    Mccain, W. E.

    1982-01-01

    The results of a comparative study using the unsteady aerodynamic lifting surface theory, known as the Doublet Lattice method, and experimental subsonic steady- and unsteady-pressure measurements, are presented for a high-aspect-ratio supercritical wing model. Comparisons of pressure distributions due to wing angle of attack and control-surface deflections were made. In general, good correlation existed between experimental and theoretical data over most of the wing planform. The more significant deviations found between experimental and theoretical data were in the vicinity of control surfaces for both static and oscillatory control-surface deflections.

  20. Highly ordered and ultra-long carbon nanotube arrays as air cathodes for high-energy-efficiency Li-oxygen batteries

    Science.gov (United States)

    Yu, Ruimin; Fan, Wugang; Guo, Xiangxin; Dong, Shaoming

    2016-02-01

    Carbonaceous air cathodes with rational architecture are vital for the nonaqueous Li-O2 batteries to achieve large energy density, high energy efficiency and long cycle life. In this work, we report the cathodes made of highly ordered and vertically aligned carbon nanotubes grown on permeable Ta foil substrates (VACNTs-Ta) via thermal chemical vapour deposition. The VACNTs-Ta, composed of uniform carbon nanotubes with approximately 240 μm in superficial height, has the super large surface area. Meanwhile, the oriented carbon nanotubes provide extremely outstanding passageways for Li ions and oxygen species. Electrochemistry tests of VACNTs-Ta air cathodes show enhancement in discharge capacity and cycle life compared to those made from short-range oriented and disordered carbon nanotubes. By further combining with the LiI redox mediator that is dissolved in the tetraethylene dimethyl glycol based electrolytes, the batteries exhibit more than 200 cycles at the current density of 200 mA g-1 with a cut-off discharge capacity of 1000 mAh g-1, and their energy efficiencies increase from 50% to 82%. The results here demonstrate the importance of cathode construction for high-energy-efficiency and long-life Li-O2 batteries.

  1. Transonic steady- and unsteady-pressure measurements on a high-aspect-ratio supercritical-wing model with oscillating control surfaces

    Science.gov (United States)

    Sandford, M. C.; Ricketts, R. H.; Cazier, F. W., Jr.

    1980-01-01

    A supercritical wing with an aspect ratio of 10.76 and with two trailing-edge oscillating control surfaces is described. The semispan wing is instrumented with 252 static orifices and 164 in situ dynamic-pressure gages for studying the effects of control-surface position and motion on steady- and unsteady-pressures at transonic speeds. Results from initial tests conducted in the Langley Transonic Dynamics Tunnel at two Reynolds numbers are presented in tabular form.

  2. AC magnetic losses in Bi-2223/Ag tapes with different aspect ratios

    Energy Technology Data Exchange (ETDEWEB)

    Fang, J.; Luo, X.M.; Chen, D.X.; Collings, E.W.; Lee, E.; Sumption, M.D.; Alamgir, A.K.M.; Yi, H.P.; Fang, J.G.; Gu, C.; Guo, S.Q.; Liu, M.L.; Xin, Y.; Han, Z

    2004-10-01

    AC losses in multi-filamentary tapes depend on various parameters. Among them, the overall tape width and thickness are expected to have an important influence. In order to study this geometrical effect, five Bi-2223/Ag tapes with different aspect ratios from 5 to 26 have been prepared. AC losses have been measured at 77 K when a perpendicular AC magnetic field is applied. It has been found that at any frequencies the magnetic loss per cycle increases as the aspect ratio increases. For AC magnetic loss, with increasing frequency from 3 to 9000 Hz the losses as a function of frequency show a maximum if the field amplitude is much less than the full penetration field or increase continuously if the field amplitude is larger.

  3. AC magnetic losses in Bi-2223/Ag tapes with different aspect ratios

    International Nuclear Information System (INIS)

    Fang, J.; Luo, X.M.; Chen, D.X.; Collings, E.W.; Lee, E.; Sumption, M.D.; Alamgir, A.K.M.; Yi, H.P.; Fang, J.G.; Gu, C.; Guo, S.Q.; Liu, M.L.; Xin, Y.; Han, Z.

    2004-01-01

    AC losses in multi-filamentary tapes depend on various parameters. Among them, the overall tape width and thickness are expected to have an important influence. In order to study this geometrical effect, five Bi-2223/Ag tapes with different aspect ratios from 5 to 26 have been prepared. AC losses have been measured at 77 K when a perpendicular AC magnetic field is applied. It has been found that at any frequencies the magnetic loss per cycle increases as the aspect ratio increases. For AC magnetic loss, with increasing frequency from 3 to 9000 Hz the losses as a function of frequency show a maximum if the field amplitude is much less than the full penetration field or increase continuously if the field amplitude is larger

  4. Numerical Investigation of Mixing Characteristics in Cavity Flow at Various Aspect Ratios

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Myung Seob [Dongyang Mirae University, Seoul (Korea, Republic of); Yang, Seung Deok; Yoon, Joon Yong [Hanyang University, Seoul (Korea, Republic of)

    2015-01-15

    This study numerically examined the mixing characteristics of rectangular cavity flows by using the hybrid lattice Boltzmann method (HLBM) applied to the finite difference method (FDM). Multi-relaxation time was used along with a passive scalar method which assumes that two substances have the same mass and that there is no interaction. First, we studied numerical results such as the stream function, position of vortices, and velocity profile for a square cavity and rectangular cavity with an aspect ratio of 2. The data were compared with previous numerical results that have been proven to be reliable. We also studied the mixing characteristics of a rectangular cavity flow such as the concentration profile and average Sherwood number at various Pe numbers and aspect ratios.

  5. Manufacturing High-Quality Carbon Nanotubes at Lower Cost

    Science.gov (United States)

    Benavides, Jeanette M.; Lidecker, Henning

    2004-01-01

    A modified electric-arc welding process has been developed for manufacturing high-quality batches of carbon nanotubes at relatively low cost. Unlike in some other processes for making carbon nanotubes, metal catalysts are not used and, consequently, it is not necessary to perform extensive cleaning and purification. Also, unlike some other processes, this process is carried out at atmospheric pressure under a hood instead of in a closed, pressurized chamber; as a result, the present process can be implemented more easily. Although the present welding-based process includes an electric arc, it differs from a prior electric-arc nanotube-production process. The welding equipment used in this process includes an AC/DC welding power source with an integral helium-gas delivery system and circulating water for cooling an assembly that holds one of the welding electrodes (in this case, the anode). The cathode is a hollow carbon (optionally, graphite) rod having an outside diameter of 2 in. (approximately equal to 5.1 cm) and an inside diameter of 5/8 in. (approximately equal to 1.6 cm). The cathode is partly immersed in a water bath, such that it protrudes about 2 in. (about 5.1 cm) above the surface of the water. The bottom end of the cathode is held underwater by a clamp, to which is connected the grounding cable of the welding power source. The anode is a carbon rod 1/8 in. (approximately equal to 0.3 cm) in diameter. The assembly that holds the anode includes a thumbknob- driven mechanism for controlling the height of the anode. A small hood is placed over the anode to direct a flow of helium downward from the anode to the cathode during the welding process. A bell-shaped exhaust hood collects the helium and other gases from the process. During the process, as the anode is consumed, the height of the anode is adjusted to maintain an anode-to-cathode gap of 1 mm. The arc-welding process is continued until the upper end of the anode has been lowered to a specified height

  6. Novel Magnetic Zinc Oxide Nanotubes for Phenol Adsorption: Mechanism Modeling

    Directory of Open Access Journals (Sweden)

    Marwa F. Elkady

    2017-11-01

    Full Text Available Considering the great impact of a material’s surface area on adsorption processes, hollow nanotube magnetic zinc oxide with a favorable surface area of 78.39 m2/g was fabricated with the assistance of microwave technology in the presence of poly vinyl alcohol (PVA as a stabilizing agent followed by sonic precipitation of magnetite nano-particles. Scanning electron microscopy (SEM and transmission electron microscopy (TEM micrographs identified the nanotubes’ morphology in the synthesized material with an average aspect ratio of 3. X-ray diffraction (XRD analysis verified the combination of magnetite material with the hexagonal wurtzite structure of ZnO in the prepared material. The immobilization of magnetite nanoparticles on to ZnO was confirmed using vibrating sample magnetometry (VSM. The sorption affinity of the synthesized magnetic ZnO nanotube for phenolic compounds from aqueous solutions was examined as a function of various processing factors. The degree of acidity of the phenolic solution has great influence on the phenol sorption process on to magnetic ZnO. The calculated value of ΔH0 designated the endothermic nature of the phenol uptake process on to the magnetic ZnO nanotubes. Mathematical modeling indicated a combination of physical and chemical adsorption mechanisms of phenolic compounds on to the fabricated magnetic ZnO nanotubes. The kinetic process correlated better with the second-order rate model compared to the first-order rate model. This result indicates the predominance of the chemical adsorption process of phenol on to magnetic ZnO nanotubes.

  7. Heat transfer characteristics of rectangular coolant channels with various aspect ratios in the plasma-facing components under fully developed MHD laminar flow

    International Nuclear Information System (INIS)

    Takase, K.; Hasan, M.Z.

    1995-01-01

    Convective heat transfer in MHD laminar flow through rectangular channels in the plasma-facing components of a fusion reactor has been analyzed numerically to investigate the effects of channel aspect ratio, defined as the ratio of the lengths of the plasma-facing side to the other side. The adverse effect of the nonuniformity of surface heat flus on Nusselt number (Nu) at the plasma-facing side can be alleviated by increasing the aspect ratio of a rectangular duct. At the center and corner of the plasma-facing side of a square duct, the Nu of non-MHD flow are 6.8 and 2.2, respectively, for uniform surface heat flux. In the presence of a strong magnetic field, Nu at the center and corner increases to 22 and 3.6, respectively. However, when the heat flux is highly nonuniform, as in the plasma-facing components, Nu decreases from 22 to 3.1 at the center and from 3.6 to 3.1 at the corner. When the aspect ratio is increased to 4, Nu at the center and corner increase to 5 and 4.7. Along the circumference of a rectangular channel, there are locations where the wall temperature is equal to or less than the bulk coolant temperature, thus making the Nu with conventional definition infinity or negative. The ratio between Nu of MHD flow and Nu of non-MHD flow for various aspect ratios is constant in the region of Hartmann number of more than 200 at least. On the other hand, its ratio increases monotonously with increasing the aspect ratio

  8. Power plant design study of a high aspect ratio Tokamak using a SiC composite structure

    International Nuclear Information System (INIS)

    Murakami, Y.; Takase, H.; Shinya, K.

    1998-01-01

    The DREAM (drastically easy maintenance) tokamak is a fusion power plant which is designed from the viewpoint of maintenance feasibility. For this purpose, the DREAM reactor uses a plasma with a very high aspect ratio (A) and adopts SiC as a structural material. The choice of SiC affects the design of the core plasma, i.e. large inboard shield thickness, low synchrotron radiation reflectivity, and small plasma elongation for positional stability. The objectives of this study are to explore the feasibility of a high-A device, such as a power plant, and to clarify the technological impact of SiC material on the plasma design. Plasma size is optimized by the physics guidelines similar to ITER. The plasma major and minor radii of DREAM are 16 m and 2 m, respectively, and the average neutron wall load is 2.5 MW m -2 , the maximum toroidal field is 20 T, and the fusion power is 5.5 GW. Steady-state operation is obtained with 50 MW of external current-drive power and 90% bootstrap current. The divertor heat load is estimated to be about 10 MW m -2 . A radiative divertor concept is adopted to achieve a low divertor plasma temperature. The DREAM tokamak concept is found to be a possible candidate for a future power plant with more than 5 GW of fusion power and an acceptable divertor condition. (orig.)

  9. A helium-cooled blanket design of the low aspect ratio reactor

    International Nuclear Information System (INIS)

    Wong, C.P.; Baxi, C.B.; Reis, E.E.; Cerbone, R.; Cheng, E.T.

    1998-03-01

    An aggressive low aspect ratio scoping fusion reactor design indicated that a 2 GW(e) reactor can have a major radius as small as 2.9 m resulting in a device with competitive cost of electricity at 49 mill/kWh. One of the technology requirements of this design is a high performance high power density first wall and blanket system. A 15 MPa helium-cooled, V-alloy and stagnant LiPb breeder first wall and blanket design was utilized. Due to the low solubility of tritium in LiPb, there is the concern of tritium migration and the formation of V-hydride. To address these issues, a lithium breeder system with high solubility of tritium has been evaluated. Due to the reduction of blanket energy multiplication to 1.2, to maintain a plant Q of > 4, the major radius of the reactor has to be increased to 3.05 m. The inlet helium coolant temperature is raised to 436 C in order to meet the minimum V-alloy temperature limit everywhere in the first wall and blanket system. To enhance the first wall heat transfer, a swirl tape coolant channel design is used. The corresponding increase in friction factor is also taken into consideration. To reduce the coolant system pressure drop, the helium pressure is increased from 15 to 18 MPa. Thermal structural analysis is performed for a simple tube design. With an inside tube diameter of 1 cm and a wall thickness of 1.5 mm, the lithium breeder can remove an average heat flux and neutron wall loading of 2 and 8 MW/m(2), respectively. This reference design can meet all the temperature and material structural design limits, as well as the coolant velocity limits. Maintaining an outlet coolant temperature of 650 C, one can expect a gross closed cycle gas turbine thermal efficiency of 45%. This study further supports the use of helium coolant for high power density reactor design. When used with the low aspect ratio reactor concept a competitive fusion reactor can be projected at 51.9 mill/kWh

  10. Developing polymer composite materials: carbon nanotubes or graphene?

    Science.gov (United States)

    Sun, Xuemei; Sun, Hao; Li, Houpu; Peng, Huisheng

    2013-10-04

    The formation of composite materials represents an efficient route to improve the performances of polymers and expand their application scopes. Due to the unique structure and remarkable mechanical, electrical, thermal, optical and catalytic properties, carbon nanotube and graphene have been mostly studied as a second phase to produce high performance polymer composites. Although carbon nanotube and graphene share some advantages in both structure and property, they are also different in many aspects including synthesis of composite material, control in composite structure and interaction with polymer molecule. The resulting composite materials are distinguished in property to meet different applications. This review article mainly describes the preparation, structure, property and application of the two families of composite materials with an emphasis on the difference between them. Some general and effective strategies are summarized for the development of polymer composite materials based on carbon nanotube and graphene. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Industrial-scale separation of high-purity single-chirality single-wall carbon nanotubes for biological imaging

    Science.gov (United States)

    Yomogida, Yohei; Tanaka, Takeshi; Zhang, Minfang; Yudasaka, Masako; Wei, Xiaojun; Kataura, Hiromichi

    2016-01-01

    Single-chirality, single-wall carbon nanotubes are desired due to their inherent physical properties and performance characteristics. Here, we demonstrate a chromatographic separation method based on a newly discovered chirality-selective affinity between carbon nanotubes and a gel containing a mixture of the surfactants. In this system, two different selectivities are found: chiral-angle selectivity and diameter selectivity. Since the chirality of nanotubes is determined by the chiral angle and diameter, combining these independent selectivities leads to high-resolution single-chirality separation with milligram-scale throughput and high purity. Furthermore, we present efficient vascular imaging of mice using separated single-chirality (9,4) nanotubes. Due to efficient absorption and emission, blood vessels can be recognized even with the use of ∼100-fold lower injected dose than the reported value for pristine nanotubes. Thus, 1 day of separation provides material for up to 15,000 imaging experiments, which is acceptable for industrial use. PMID:27350127

  12. Cellular cytotoxic response induced by highly purified multi-wall carbon nanotube in human lung cells.

    Science.gov (United States)

    Tsukahara, Tamotsu; Haniu, Hisao

    2011-06-01

    Carbon nanotubes, a promising nanomaterial with unique characteristics, have applications in a variety of fields. The cytotoxic effects of carbon nanotubes are partially due to the induction of oxidative stress; however, the detailed mechanisms of nanotube cytotoxicity and their interaction with cells remain unclear. In this study, the authors focus on the acute toxicity of vapor-grown carbon fiber, HTT2800, which is one of the most highly purified multi-wall carbon nanotubes (MWCNT) by high-temperature thermal treatment. The authors exposed human bronchial epithelial cells (BEAS-2B) to HTT2800 and measured the cellular uptake, mitochondrial function, cellular LDH release, apoptotic signaling, reactive oxygen species (ROS) generation and pro-inflammatory cytokine release. The HTT2800-exposed cells showed cellular uptake of the carbon nanotube, increased cell death, enhanced DNA damage, and induced cytokine release. However, the exposed cells showed no obvious intracellular ROS generation. These cellular and molecular findings suggest that HTT2800 could cause a potentially adverse inflammatory response in BEAS-2B cells.

  13. Low-loss saturable absorbers based on tapered fibers embedded in carbon nanotube/polymer composites

    Science.gov (United States)

    Martinez, Amos; Al Araimi, Mohammed; Dmitriev, Artemiy; Lutsyk, Petro; Li, Shen; Mou, Chengbo; Rozhin, Alexey; Sumetsky, Misha; Turitsyn, Sergei

    2017-12-01

    The emergence of low-dimensional materials has opened new opportunities in the fabrication of compact nonlinear photonic devices. Single-walled carbon nanotubes were among the first of those materials to attract the attention of the photonics community owing to their high third order susceptibility, broadband operation, and ultrafast response. Saturable absorption, in particular, has become a widespread application for nanotubes in the mode-locking of a fiber laser where they are used as nonlinear passive amplitude modulators to initiate pulsed operation. Numerous approaches have been proposed for the integration of nanotubes in fiber systems; these can be divided into those that rely on direct interaction (where the nanotubes are sandwiched between fiber connectors) and those that rely on lateral interaction with the evanescence field of the propagating wave. Tapered fibers, in particular, offer excellent flexibility to adjust the nonlinearity of nanotube-based devices but suffer from high losses (typically exceeding 50%) and poor saturable to non-saturable absorption ratios (typically above 1:5). In this paper, we propose a method to fabricate carbon nanotube saturable absorbers with controllable saturation power, low-losses (as low as 15%), and large saturable to non-saturable loss ratios approaching 1:1. This is achieved by optimizing the procedure of embedding tapered fibers in low-refractive index polymers. In addition, this study sheds light in the operation of these devices, highlighting a trade-off between losses and saturation power and providing guidelines for the design of saturable absorbers according to their application.

  14. Carbon nanotubes for high-performance logic

    OpenAIRE

    Chen, Zhihong; Wong, H.S. Phillip; Mitra, Subhasish; Bol, Aggeth; Peng, Lianmao; Hills, Gage; Thissen, Nick

    2014-01-01

    Single-wall carbon nanotubes (CNTs) were discovered in 1993 and have been an area of intense research since then. They offer the right dimensions to explore material science and physical chemistry at the nanoscale and are the perfect system to study low-dimensional physics and transport. In the past decade, more attention has been shifted toward making use of this unique nanomaterial in real-world applications. In this article, we focus on potential applications of CNTs in the high-performanc...

  15. Highly stretchable carbon nanotube transistors enabled by buckled ion gel gate dielectrics

    International Nuclear Information System (INIS)

    Wu, Meng-Yin; Chang, Tzu-Hsuan; Ma, Zhenqiang; Zhao, Juan; Xu, Feng; Jacobberger, Robert M.; Arnold, Michael S.

    2015-01-01

    Deformable field-effect transistors (FETs) are expected to facilitate new technologies like stretchable displays, conformal devices, and electronic skins. We previously demonstrated stretchable FETs based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes as the channel, buckled metal films as electrodes, and unbuckled flexible ion gel films as the dielectric. The FETs were stretchable up to 50% without appreciable degradation in performance before failure of the ion gel film. Here, we show that by buckling the ion gel, the integrity and performance of the nanotube FETs are extended to nearly 90% elongation, limited by the stretchability of the elastomer substrate. The FETs maintain an on/off ratio of >10 4 and a field-effect mobility of 5 cm 2 V −1 s −1 under elongation and demonstrate invariant performance over 1000 stretching cycles

  16. Radial breathing vibration of double-walled carbon nanotubes subjected to pressure

    International Nuclear Information System (INIS)

    Lei, Xiao-Wen; Natsuki, Toshiaki; Shi, Jin-Xing; Ni, Qing-Qing

    2011-01-01

    A theoretical vibrational analysis of the radial breathing mode (RBM) of double-walled carbon nanotubes (DWCNTs) subjected to pressure is presented based on an elastic continuum model. The results agree with reported experimental results obtained under different conditions. Frequencies of the RBM in DWCNTs subjected to increasing pressure depend strongly on circumferential wave numbers, but weakly on the aspect ratio and axial half-wave numbers. For the inner and outer tubes of DWCNTs, the frequency of the RBM increases obviously as the pressure increases under different conditions. The range of variation is smaller for the inner tube than the outer tube. -- Highlights: → An elastic continuum model is used in the theoretical analysis of RBM of DWCNTs. → The RBM of DWCNTs subjected to pressure is analyzed. → Frequency of RBM depends on wave number and aspect ratio. → Frequencies of RBM in inner and outer tubes change in different trends and ranges.

  17. Dynamic response of low aspect ratio piezoelectric microcantilevers actuated in different liquid environments

    International Nuclear Information System (INIS)

    Vázquez, J; Rivera, M A; Hernando, J; Sánchez-Rojas, J L

    2009-01-01

    The response of commercial piezoelectric AFM probes for potential applications in the field of chemical or biological sensors operating in liquids is investigated using laser Doppler vibrometry. The present work investigates the roles played in the frequency response by the density and the viscosity of different water–glycerol mixtures, in a frequency range of up to 1 MHz in air. Since the width of the tested probes is relatively large (and hence the aspect ratio remains small), inertial loading effects dominate viscous effects, unlike in cantilevers characterized by larger aspect ratios. Measurements are compared with results provided by a simplified computer model of a probe immersed in an inviscid surrounding fluid

  18. Properties of single-walled carbon nanotube-based aerogels as a function of nanotube loading

    International Nuclear Information System (INIS)

    Worsley, Marcus A.; Pauzauskie, Peter J.; Kucheyev, Sergei O.; Zaug, Joseph M.; Hamza, Alex V.; Satcher, Joe H.; Baumann, Theodore F.

    2009-01-01

    Here, we present the synthesis and characterization of low-density single-walled carbon nanotube-based aerogels (SWNT-CA). Aerogels with varying nanotube loading (0-55 wt.%) and density (20-350 mg cm -3 ) were fabricated and characterized by four-probe method, electron microscopy, Raman spectroscopy and nitrogen porosimetry. Several properties of the SWNT-CAs were highly dependent upon nanotube loading. At nanotube loadings of 55 wt.%, shrinkage of the aerogel monoliths during carbonization and drying was almost completely eliminated. Electrical conductivities are improved by an order of magnitude for the SWNT-CA (55 wt.% nanotubes) compared to those of foams without nanotubes. Surface areas as high as 184 m 2 g -1 were achieved for SWNT-CAs with greater than 20 wt.% nanotube loading.

  19. Carbon Nanotubes: A Review on Structure and Their Interaction with Proteins

    Directory of Open Access Journals (Sweden)

    N. Saifuddin

    2013-01-01

    Full Text Available Carbon nanotubes (CNTs are allotropes of carbon with a nanostructure that can have a length-to-diameter ratio greater than 1,000,000. Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, and chemical vapor deposition. Developments in the past few years have illustrated the potentially revolutionizing impact of nanomaterials, especially in biomedical imaging, drug delivery, biosensing, and the design of functional nanocomposites. Methods to effectively interface proteins with nanomaterials for realizing these applications continue to evolve. The high surface-to-volume ratio offered by nanoparticles resulted in the concentration of the immobilized entity being considerably higher than that afforded by other materials. There has also been an increasing interest in understanding the influence of nanomaterials on the structure and function of proteins. Various immobilization methods have been developed, and in particular, specific attachment of enzymes on carbon nanotubes has been an important focus of attention. With the growing attention paid to cascade enzymatic reaction, it is possible that multienzyme coimmobilization would be one of the next goals in the future. In this paper, we focus on advances in methodology for enzyme immobilization on carbon nanotubes.

  20. Influence of the aspect ratio of bioactive nanofillers on rheological behavior of PMMA-based orthopedic materials.

    Science.gov (United States)

    Liu, Tse-Ying; Chen, San-Yuan; Liu, Dean-Mo

    2004-10-15

    In this investigation, calcium-deficient hydroxyapatite (CDHA) nanocrystals with needle-like geometry were synthesized and incorporated with Poly(methyl methacrylate), PMMA, to form CDHA-PMMA nanocomposites. Rheological behaviors of the PMMA-CDHA melting suspensions were systematically investigated in terms of solid loading and aspect ratio of the CDHA nanoparticles. The maximum solid loadings of nano-CDHA particles with aspect ratios of 7.2, 10.4, and 17 were determined to be 28, 31, and 57%, respectively. An increase in solid concentrations causes pronounced shear-thinning behavior. This result suggests that a strong interaction, including Van der Waals attraction and mechanical interlocking, between the nano-CDHA particles makes the nanocomposite mixture more non-Newtonian. Furthermore, it was found that packing efficiency and yield strength in the suspension were strongly influenced by the aspect ratio, especially above the critical value of 8.8. The obtained critical aspect ratio and solid content provide not only appropriate design in the PMMA-CDHA polymeric suspension for fabrication process but also optimal conditions for the fabrication of orthopedic devices via injection molding or extrusion.

  1. Engineering feasibility of tight aspect ratio Tokamak (spherical torus) reactors

    International Nuclear Information System (INIS)

    Peng, Y-K.M.; Hicks, J.B.

    1990-01-01

    Engineering solutions are identified and analyzed for key high-power-density components of tight aspect ratio tokamak reactors (spherical torus reactors). The potentially extreme divertor heat loads can be reduced to about 3 MW/m 2 in expanded divertors using coils inside the demountable toroidal field coils. Given the long and narrow divertor channels, gaseous divertor targets become possible, which eliminate sputtering and increase the divertor life. The unshielded centre conductor post (CCP) of the toroidal field coil can be made of a single dispersion strengthened copper conductor cooled by high-velocity pressurized water to maintain acceptable copper temperature and strength. Damage and activation of the CCP at a neutron fluence of 10 MW-a/m 2 are also tolerable. Annual replacement of the centre post, the divertor assemblies and the blanket can be accomplished with vertical access for all torus components, which are modularized to reduce size and weight. The technical requirements of these solutions are shown to be comparable with, if not less demanding than, those estimated for conventional tokamak reactors. (author)

  2. Synthetic cation-selective nanotube: permeant cations chaperoned by anions.

    Science.gov (United States)

    Hilder, Tamsyn A; Gordon, Dan; Chung, Shin-Ho

    2011-01-28

    The ability to design ion-selective, synthetic nanotubes which mimic biological ion channels may have significant implications for the future treatment of bacteria, diseases, and as ultrasensitive biosensors. We present the design of a synthetic nanotube made from carbon atoms that selectively allows monovalent cations to move across and rejects all anions. The cation-selective nanotube mimics some of the salient properties of biological ion channels. Before practical nanodevices are successfully fabricated it is vital that proof-of-concept computational studies are performed. With this in mind we use molecular and stochastic dynamics simulations to characterize the dynamics of ion permeation across a single-walled (10, 10), 36 Å long, carbon nanotube terminated with carboxylic acid with an effective radius of 5.08 Å. Although cations encounter a high energy barrier of 7 kT, its height is drastically reduced by a chloride ion in the nanotube. The presence of a chloride ion near the pore entrance thus enables a cation to enter the pore and, once in the pore, it is chaperoned by the resident counterion across the narrow pore. The moment the chaperoned cation transits the pore, the counterion moves back to the entrance to ferry another ion. The synthetic nanotube has a high sodium conductance of 124 pS and shows linear current-voltage and current-concentration profiles. The cation-anion selectivity ratio ranges from 8 to 25, depending on the ionic concentrations in the reservoirs.

  3. High-density carbon nanotube wet-laid buckypapers with enhanced strength and conductivity using a high-pressure homogenization process

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jun; Jang, Si Hoon; Park, No Hyung; Jeong, Won Young; Lim, Dae Young [Human and Culture Convergence Technology Group, Korea Institute of Industrial Technology (KITECH), Ansan (Korea, Republic of); Oh, Jun Young; Yang, Seung Jae [Dept. of Applied Organic Materials Engineering, Inha University, Incheon (Korea, Republic of)

    2017-04-15

    In this work, we prepared homogeneously dispersed carbon nanotubes in water using a high-pressure homogenizer, while high-density carbon nanotube buckypapers were prepared by wet-laid process. The strength and conductivity of the buckypaper were increased dramatically after the high-pressure homogenization because of the increased density and uniformity of the paper. In addition, the buckypapers containing various additives and treated with SOCl{sub 2} exhibited further increase of strength and conductivity resulting from the binding and the p-type doping effect. The buckypapers with high electrical conductivity exhibited superior electromagnetic interference shielding effectiveness that could be applied for structural shielding materials.

  4. Analytical modeling of glucose biosensors based on carbon nanotubes.

    Science.gov (United States)

    Pourasl, Ali H; Ahmadi, Mohammad Taghi; Rahmani, Meisam; Chin, Huei Chaeng; Lim, Cheng Siong; Ismail, Razali; Tan, Michael Loong Peng

    2014-01-15

    In recent years, carbon nanotubes have received widespread attention as promising carbon-based nanoelectronic devices. Due to their exceptional physical, chemical, and electrical properties, namely a high surface-to-volume ratio, their enhanced electron transfer properties, and their high thermal conductivity, carbon nanotubes can be used effectively as electrochemical sensors. The integration of carbon nanotubes with a functional group provides a good and solid support for the immobilization of enzymes. The determination of glucose levels using biosensors, particularly in the medical diagnostics and food industries, is gaining mass appeal. Glucose biosensors detect the glucose molecule by catalyzing glucose to gluconic acid and hydrogen peroxide in the presence of oxygen. This action provides high accuracy and a quick detection rate. In this paper, a single-wall carbon nanotube field-effect transistor biosensor for glucose detection is analytically modeled. In the proposed model, the glucose concentration is presented as a function of gate voltage. Subsequently, the proposed model is compared with existing experimental data. A good consensus between the model and the experimental data is reported. The simulated data demonstrate that the analytical model can be employed with an electrochemical glucose sensor to predict the behavior of the sensing mechanism in biosensors.

  5. Formation and sustainment of a low aspect ratio tokamak by a series of plasma injections

    International Nuclear Information System (INIS)

    Shimamura, Shin; Taniguchi, Makoto; Takahashi, Tsutomu; Nogi, Yasuyuki

    1995-01-01

    A low aspect ratio tokamak plasma was generated and sustained by injecting a series of plasmas from a magnetized coaxial gun into a flux conserver with toroidal field. The magnetized coaxial gun was supplied by an oscillating current with a d.c. component. The first few current pulses injected plasma and helicity into the flux conserver. This pulse helicity injection method worked effectively to maintain the low aspect ratio tokamak. 8 refs., 5 figs

  6. Modeling the Effects of Interfacial Characteristics on Gas Permeation Behavior of Nanotube-Mixed Matrix Membranes.

    Science.gov (United States)

    Chehrazi, Ehsan; Sharif, Alireza; Omidkhah, Mohammadreza; Karimi, Mohammad

    2017-10-25

    Theoretical approaches that accurately predict the gas permeation behavior of nanotube-containing mixed matrix membranes (nanotube-MMMs) are scarce. This is mainly due to ignoring the effects of nanotube/matrix interfacial characteristics in the existing theories. In this paper, based on the analogy of thermal conduction in polymer composites containing nanotubes, we develop a model to describe gas permeation through nanotube-MMMs. Two new parameters, "interfacial thickness" (a int ) and "interfacial permeation resistance" (R int ), are introduced to account for the role of nanotube/matrix interfacial interactions in the proposed model. The obtained values of a int , independent of the nature of the permeate gas, increased by increasing both the nanotubes aspect ratio and polymer-nanotube interfacial strength. An excellent correlation between the values of a int and polymer-nanotube interaction parameters, χ, helped to accurately reproduce the existing experimental data from the literature without the need to resort to any adjustable parameter. The data includes 10 sets of CO 2 /CH 4 permeation, 12 sets of CO 2 /N 2 permeation, 3 sets of CO 2 /O 2 permeation, and 2 sets of CO 2 /H 2 permeation through different nanotube-MMMs. Moreover, the average absolute relative errors between the experimental data and the predicted values of the proposed model are very small (less than 5%) in comparison with those of the existing models in the literature. To the best of our knowledge, this is the first study where such a systematic comparison between model predictions and such extensive experimental data is presented. Finally, the new way of assessing gas permeation data presented in the current work would be a simple alternative to complex approaches that are usually utilized to estimate interfacial thickness in polymer composites.

  7. A novel method for the fabrication of a high-density carbon nanotube microelectrode array

    Directory of Open Access Journals (Sweden)

    Adam Khalifa

    2015-09-01

    Full Text Available We present a novel method for fabricating a high-density carbon nanotube microelectrode array (MEA chip. Vertically aligned carbon nanotubes (VACNTs were synthesized by microwave plasma-enhanced chemical vapor deposition and thermal chemical vapor deposition. The device was characterized using electrochemical experiments such as cyclic voltammetry, impedance spectroscopy and potential transient measurements. Through-silicon vias (TSVs were fabricated and partially filled with polycrystalline silicon to allow electrical connection from the high-density electrodes to a stimulator microchip. In response to the demand for higher resolution implants, we have developed a unique process to obtain a high-density electrode array by making the microelectrodes smaller in size and designing new ways of routing the electrodes to current sources. Keywords: Microelectrode array, Neural implant, Carbon nanotubes, Through-silicon via interconnects, Microfabrication

  8. A graphene oxide-carbon nanotube grid for high-resolution transmission electron microscopy of nanomaterials

    International Nuclear Information System (INIS)

    Zhang Lina; Zhang Haoxu; Zhou Ruifeng; Chen Zhuo; Li Qunqing; Fan Shoushan; Jiang Kaili; Ge Guanglu; Liu Renxiao

    2011-01-01

    A novel grid for use in transmission electron microscopy is developed. The supporting film of the grid is composed of thin graphene oxide films overlying a super-aligned carbon nanotube network. The composite film combines the advantages of graphene oxide and carbon nanotube networks and has the following properties: it is ultra-thin, it has a large flat and smooth effective supporting area with a homogeneous amorphous appearance, high stability, and good conductivity. The graphene oxide-carbon nanotube grid has a distinct advantage when characterizing the fine structure of a mass of nanomaterials over conventional amorphous carbon grids. Clear high-resolution transmission electron microscopy images of various nanomaterials are obtained easily using the new grids.

  9. High aspect ratio lead zirconate titanate tube structures: I. Template assisted fabrication - vacuum infiltration method

    Directory of Open Access Journals (Sweden)

    Vladimír Kovaľ

    2012-03-01

    Full Text Available Polycrystalline Pb(Zr0.52Ti0.48O3 (PZT microtubes are fabricated by a vacuum infiltration method. The method is based on repeated infiltration of precursor solution into macroporous silicon (Si templates at a sub-atmospheric pressure. The pyrolyzed PZT tubes of a 2-µm outer diameter, extending to over 30 µm in length were released from the template using a selective isotropic-pulsed XeF2 reactive ion etching of silicon. Free-standing microtubes, partially anchored at the bottom of the Si template, were then crystallized in pure oxygen atmosphere at 750 °C for 2 min using a rapid thermal annealer. The perovskite phase of the final PZT tubes was confirmed by X-ray diffraction (XRD analysis. The XRD spectrum also revealed a small amount of the pyrochlore phase in the structure and signs of possible fluoride contamination caused most likely by the XeF2 etching process. The surface morphology was examined using scanning electron microscopy. It was demonstrated that the whole surface of the pore walls was conformally coated during the repeated infiltration of templates, resulting in straight tubes with closed tips formed on the opposite ends as replicas of the pore bottoms. These high aspect ratio ferroelectric structures are suggested as building units for developing miniaturized electronic devices, such as memory storage (DRAM trenched capacitors, piezoelectric scanners and actuators, and are of fundamental value for the theory of ferroelectricity in systems with low dimensionality.

  10. Facile fabrication of single-crystal-diamond nanostructures with ultrahigh aspect ratio.

    OpenAIRE

    Tao Ye; Degen Christian

    2013-01-01

    A robust and facile approach for making single crystal diamond MEMS and NEMS devices is presented. The approach relies entirely on commercial diamond material and standard cleanroom processes. As an example batch fabrication of cantilever beams of thickness down to 45 nm and aspect ratios exceeding 2000:1 is demonstrated.

  11. Imperceptible and Ultraflexible p-Type Transistors and Macroelectronics Based on Carbon Nanotubes.

    Science.gov (United States)

    Cao, Xuan; Cao, Yu; Zhou, Chongwu

    2016-01-26

    Flexible thin-film transistors based on semiconducting single-wall carbon nanotubes are promising for flexible digital circuits, artificial skins, radio frequency devices, active-matrix-based displays, and sensors due to the outstanding electrical properties and intrinsic mechanical strength of carbon nanotubes. Nevertheless, previous research effort only led to nanotube thin-film transistors with the smallest bending radius down to 1 mm. In this paper, we have realized the full potential of carbon nanotubes by making ultraflexible and imperceptible p-type transistors and circuits with a bending radius down to 40 μm. In addition, the resulted transistors show mobility up to 12.04 cm(2) V(-1) S(-1), high on-off ratio (∼10(6)), ultralight weight (transistors and circuits have great potential to work as indispensable components for ultraflexible complementary electronics.

  12. Flow patterns and heat transfer characteristics of flat plate pulsating heat pipes with various asymmetric and aspect ratios of the channels

    International Nuclear Information System (INIS)

    Jang, Dong Soo; Lee, Joo Seong; Ahn, Jae Hwan; Kim, Dongwoo; Kim, Yongchan

    2017-01-01

    Highlights: • Flat plate pulsating heat pipes with asymmetric and aspect ratios were tested. • Flow patterns were investigated according to channel geometry and flow condition. • Heat transfer characteristics were analyzed with various heat inputs. • Optimum asymmetric and aspect ratios were suggested for maximum thermal performance. - Abstract: The thermal performance of flat plate pulsating heat pipes (PHPs) in compact electronic devices can be improved by adopting asymmetric channels with increased pressure differences and an unbalanced driving force. The objective of this study is to investigate the heat transfer characteristics of flat plate PHPs with various asymmetric ratios and aspect ratios in the channels. The thermal performance and flow pattern of the flat plate PHPs were measured by varying the asymmetric ratio from 1.0 to 4.0, aspect ratio from 2.5 to 5.0, and heat input from 2 to 28 W. The effects of the asymmetric ratio and aspect ratio on the thermal resistance were analyzed with the measured evaporator temperature and flow patterns at various heat inputs. With heat inputs of 6 W and 12 W, the optimum asymmetric ratio and aspect ratio for the flat plate PHPs were determined to be 4.0 and 2.5, respectively. With the heat input of 18 W, the optimum asymmetric ratio and aspect ratio were determined to be 1.5 and 2.5, respectively.

  13. Examination of the high-frequency capability of carbon nanotube FETs

    Science.gov (United States)

    Pulfrey, David L.; Chen, Li

    2008-09-01

    New results are added to a recent critique of the high-frequency performance of carbon nanotube field-effect transistors (CNFETs). On the practical side, reduction of the number of metallic tubes in CNFETs fashioned from multiple nanotubes has allowed the measured fT to be increased to 30 GHz. On the theoretical side, the opinion that the band-structure-determined velocity limits the high-frequency performance has been reinforced by corrections to recent simulation results for doped-contact CNFETs, and by the ruling out of the possibility of favourable image-charge effects. Inclusion in the simulations of the features of finite gate-metal thickness and source/drain contact resistance has given an indication of likely practical values for fT. A meaningful comparison between CNFETs with doped-contacts and metallic contacts has been made.

  14. Highly stretchable carbon nanotube transistors enabled by buckled ion gel gate dielectrics

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Meng-Yin; Chang, Tzu-Hsuan; Ma, Zhenqiang [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Zhao, Juan [School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Xu, Feng; Jacobberger, Robert M.; Arnold, Michael S., E-mail: michael.arnold@wisc.edu [Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

    2015-08-03

    Deformable field-effect transistors (FETs) are expected to facilitate new technologies like stretchable displays, conformal devices, and electronic skins. We previously demonstrated stretchable FETs based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes as the channel, buckled metal films as electrodes, and unbuckled flexible ion gel films as the dielectric. The FETs were stretchable up to 50% without appreciable degradation in performance before failure of the ion gel film. Here, we show that by buckling the ion gel, the integrity and performance of the nanotube FETs are extended to nearly 90% elongation, limited by the stretchability of the elastomer substrate. The FETs maintain an on/off ratio of >10{sup 4} and a field-effect mobility of 5 cm{sup 2} V{sup −1} s{sup −1} under elongation and demonstrate invariant performance over 1000 stretching cycles.

  15. A highly durable fuel cell electrocatalyst based on double-polymer-coated carbon nanotubes.

    Science.gov (United States)

    Berber, Mohamed R; Hafez, Inas H; Fujigaya, Tsuyohiko; Nakashima, Naotoshi

    2015-11-23

    Driven by the demand for the commercialization of fuel cell (FC) technology, we describe the design and fabrication of a highly durable FC electrocatalyst based on double-polymer-coated carbon nanotubes for use in polymer electrolyte membrane fuel cells. The fabricated electrocatalyst is composed of Pt-deposited polybenzimidazole-coated carbon nanotubes, which are further coated with Nafion. By using this electrocatalyst, a high FC performance with a power density of 375 mW/cm(2) (at 70 ˚C, 50% relative humidity using air (cathode)/H2(anode)) was obtained, and a remarkable durability of 500,000 accelerated potential cycles was recorded with only a 5% loss of the initial FC potential and 20% loss of the maximum power density, which were far superior properties compared to those of the membrane electrode assembly prepared using carbon black in place of the carbon nanotubes. The present study indicates that the prepared highly durable fuel cell electrocatalyst is a promising material for the next generation of PEMFCs.

  16. The Use of Carbon Nanotubes to Reinforce 45S5 Bioglass-Based Scaffolds for Tissue Engineering Applications

    Directory of Open Access Journals (Sweden)

    R. Touri

    2013-01-01

    Full Text Available Bioglass has been used for bone-filling material in bone tissue engineering, but its lean mechanical strength limits its applications in load-bearing positions. Carbon nanotubes (CNTs, with their high aspect ratio and excellent mechanical properties, have the potential to strengthen and toughen bioactive glass material without offsetting its bioactivity. Therefore, in this research, multiwall carbon nanotube (MWCNT/45S5 Bioglass composite scaffolds have been successfully prepared by means of freeze casting process. 45S5 Bioglass was synthesized by the sol-gel processing method. The obtained material was characterized with X-ray powder diffraction (XRD. The mechanical properties of the scaffolds, such as compression strength and elastic modulus, were measured. Finally, compared with the scaffolds prepared by 100% 45S5 Bioglass powders, the addition of 0.25 wt.% MWCNTs increases the compressive strength and elastic modulus of 45S5 Bioglass scaffolds from 2.08 to 4.56 MPa (a 119% increase and 111.50 to 266.59 MPa (a 139% increase, respectively.

  17. Decorating Mg/Fe oxide nanotubes with nitrogen-doped carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Cao Yong, E-mail: caoyangel@126.com [Institute of Environment and Municipal Engineering, North China Institute of Water Conservancy and Hydroelectric Power, Zhengzhou 450011 (China); Jiao Qingze, E-mail: jiaoqz@bit.edu.cn [School of Chemical Engineering and the Environment, Beijing Institute of Technology, Beijing 100081 (China); Zhao Yun [School of Chemical Engineering and the Environment, Beijing Institute of Technology, Beijing 100081 (China); Dong Yingchao [Materials and Surface Science Institute (MSSI), University of Limerick, Limerick (Ireland)

    2011-09-22

    Graphical abstract: Highlights: > Mg/Fe oxide nanotubes arrayed parallel to each other were prepared by an AAO template method. > The Mg/Fe oxide nanotubes decorated with CN{sub x} were realized by CVD of ethylenediamine on the outer surface of oxide nanotubes. > The magnetic properties of Mg/Fe oxide nanotubes were highly improved after being decorated. - Abstract: Mg/Fe oxide nanotubes decorated with nitrogen-doped carbon nanotubes (CN{sub x}) were fabricated by catalytic chemical vapor deposition of ethylenediamine on the outer surface of oxide nanotubes. Mg/Fe oxide nanotubes were prepared using a 3:1 molar precursor solution of Mg(NO{sub 3}){sub 2} and Fe(NO{sub 3}){sub 3} and anodic aluminum oxide as the substrate. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). The XRD pattern shows that the oxide nanotubes are made up of MgO and Fe{sub 2}O{sub 3}. TEM and SEM observations indicate the oxide nanotubes are arrayed roughly parallel to each other, and the outer surface of oxide nanotubes are decorated with CN{sub x}. XPS results show the nitrogen-doped level in CN{sub x} is about 7.3 at.%. Magnetic measurements with VSM demonstrate the saturated magnetization, remanence and coercivity of oxide nanotubes are obvious improved after being decorated with CN{sub x}.

  18. Porous carbon nanotube/graphene composites for high-performance supercapacitors

    Science.gov (United States)

    Li, Jing; Tang, Jie; Yuan, Jinshi; Zhang, Kun; Yu, Xiaoliang; Sun, Yige; Zhang, Han; Qin, Lu-Chang

    2018-02-01

    Carbon nanotubes (CNTs) are an effective spacer to prevent the re-stacking of graphene layers. However, the aggregation of CNTs always reduces the specific surface area of resulting CNT/graphene composites. Meanwhile, different pores always have different contributions to the specific capacitance. In this study, CNT/graphene composites with different porous structures are synthesized by co-reduction of oxidized CNTs and graphene oxide with different mixing ratios. With an optimized CNT content of 20%, the CNT/graphene composite shows 206 F g-1 in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte. It is found that pores larger than twice the size of electrolyte ions can make greater contributions to the specific capacitance.

  19. Non-inductive current drive via helicity injection by Alfven waves in low aspects ratio Tokamak

    International Nuclear Information System (INIS)

    Cuperman, S.; Bruma, C.; Komoshvili, K.

    1996-01-01

    A theoretical investigation of radio frequency (RF) current drive via helicity injection in low aspect ratio tokamaks was carried out. A current-carrying cylindrical plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell was considered. Toroidal features of low aspect ratio tokamaks were simulated by incorporation of the following effects: (i) arbitrarily small aspect ratio, R o /a ≡ 1/ε (ii) strongly sheared equilibrium magnetic field; and (iii) relatively large poloidal component of the equilibrium magnetic field. The study concentrates on the Alfven continuum, i.e. the case in which the wave frequency satisfies the condition {ω Alf (r)} min ≤ω≥{ω Alf (r)} max , where ω Alf (r)≡ω[n(r),B o (o)] is an eigenfrequency of the shear Alfven wave (SAW). Thus, using low-p, ideal magneto-hydrodynamics, the wave equation with correct boundary (matching) conditions was solved, the RF field components were found and subsequently, current drive , power deposition and efficiency were computed. The results of our investigation clearly demonstrate the possibility of generation of RF-driven currents via helicity injection by Alfven waves in low aspect ratio tokamaks, in the SAW mode. A special algorithm was developed which enables the selection of the antenna parameters providing optimal current drive efficiency. (authors)

  20. Low-loss saturable absorbers based on tapered fibers embedded in carbon nanotube/polymer composites

    Directory of Open Access Journals (Sweden)

    Amos Martinez

    2017-12-01

    Full Text Available The emergence of low-dimensional materials has opened new opportunities in the fabrication of compact nonlinear photonic devices. Single-walled carbon nanotubes were among the first of those materials to attract the attention of the photonics community owing to their high third order susceptibility, broadband operation, and ultrafast response. Saturable absorption, in particular, has become a widespread application for nanotubes in the mode-locking of a fiber laser where they are used as nonlinear passive amplitude modulators to initiate pulsed operation. Numerous approaches have been proposed for the integration of nanotubes in fiber systems; these can be divided into those that rely on direct interaction (where the nanotubes are sandwiched between fiber connectors and those that rely on lateral interaction with the evanescence field of the propagating wave. Tapered fibers, in particular, offer excellent flexibility to adjust the nonlinearity of nanotube-based devices but suffer from high losses (typically exceeding 50% and poor saturable to non-saturable absorption ratios (typically above 1:5. In this paper, we propose a method to fabricate carbon nanotube saturable absorbers with controllable saturation power, low-losses (as low as 15%, and large saturable to non-saturable loss ratios approaching 1:1. This is achieved by optimizing the procedure of embedding tapered fibers in low-refractive index polymers. In addition, this study sheds light in the operation of these devices, highlighting a trade-off between losses and saturation power and providing guidelines for the design of saturable absorbers according to their application.

  1. GPU based 3D feature profile simulation of high-aspect ratio contact hole etch process under fluorocarbon plasmas

    Science.gov (United States)

    Chun, Poo-Reum; Lee, Se-Ah; Yook, Yeong-Geun; Choi, Kwang-Sung; Cho, Deog-Geun; Yu, Dong-Hun; Chang, Won-Seok; Kwon, Deuk-Chul; Im, Yeon-Ho

    2013-09-01

    Although plasma etch profile simulation has been attracted much interest for developing reliable plasma etching, there still exist big gaps between current research status and predictable modeling due to the inherent complexity of plasma process. As an effort to address this issue, we present 3D feature profile simulation coupled with well-defined plasma-surface kinetic model for silicon dioxide etching process under fluorocarbon plasmas. To capture the realistic plasma surface reaction behaviors, a polymer layer based surface kinetic model was proposed to consider the simultaneous polymer deposition and oxide etching. Finally, the realistic plasma surface model was used for calculation of speed function for 3D topology simulation, which consists of multiple level set based moving algorithm, and ballistic transport module. In addition, the time consumable computations in the ballistic transport calculation were improved drastically by GPU based numerical computation, leading to the real time computation. Finally, we demonstrated that the surface kinetic model could be coupled successfully for 3D etch profile simulations in high-aspect ratio contact hole plasma etching.

  2. Facile fabrication of polyaniline nanotubes using the self-assembly behavior based on the hydrogen bonding: a mechanistic study and application in high-performance electrochemical supercapacitor electrode

    International Nuclear Information System (INIS)

    Wu, Wenling; Pan, Duo; Li, Yanfeng; Zhao, Guanghui; Jing, Lingyun; Chen, Suli

    2015-01-01

    At present, the in situ synthesis of polyaniline (PANI) nanotubes via self-assembly of organic dopant acid is a particularly charming task in supercapacitors. Herein, we report the formation of uniform PANI nanotubes doped with malic acid (MA) and other organic acids, such as propionic acid (PA), succinic acid (SA), tartaric acid (TA) and citric acid (CA), which simultaneously acts as a dopant acid as well as a structure-directing agent. The morphology, structure and thermal stability of PANI nanotubes were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectra, Ultraviolet-visible spectra (UV–vis), X-ray diffraction (XRD), thermogravimetric analysis (TGA). Meanwhile, the electrochemical performance of the fabricated electrodes was evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). Furthermore, the PANI-MA and PANI-CA nanotubes, with [aniline]/[acid] molar ratio of 4:1, possessed highest specific capacitance of 658 F/g and 617 F/g at the current density of 0.1 A/g in 1.0 M H 2 SO 4 electrolyte due to their unique nanotubular structures. It makes PANI nanotubes a promising electrode material for high performance supercapacitors

  3. Aligned Carbon Nanotubes for High-Performance Films and Composites

    Science.gov (United States)

    Zhang, Liwen

    Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or

  4. Multiwall carbon nanotube-filled natural rubber: Electrical and mechanical properties

    Directory of Open Access Journals (Sweden)

    L. Bokobza

    2012-03-01

    Full Text Available The influence of multiwall carbon nanotube (MWNTs contents on electrical and mechanical properties of MWNTs-reinforced natural rubber (NR composites is studied. The volume resistivity of the composites decreases with increasing the MWNTs content and the electrical percolation threshold is reached at less than 1 phr of MWNTs (phr = parts of filler by weight per hundred parts of rubber. This is caused by the formation of conductive chains in the composites. Electrical measurements under uniaxial deformation of a composite carried out at a filler loading above the percolation threshold, indicate a gradual disconnection of the conducting network with the bulk deformation. The drop in the storage modulus G' with the shear strain amplitude (Payne effect is also attributed to a breakdown of the filler network. Considerable improvement in the stiffness is obtained upon incorporation of MWNTs in the polymer matrix but the main factor for reinforcement of NR by MWNTs appears to be their high aspect ratio rather than strong interfacial interaction with rubber. The tensile strength and the elongation at break of the composites are reduced with regard to the unfilled sample. This is probably due to the presence of some agglomerates that increase with the nanotube content. This hypothesis is confirmed by a cyclic loading of the composites where it is seen that the deformation at break occurs at a much higher level of strain in the second stretch than in the first one. The overall significant property improvements are the result of a better nanotube dispersion attributed to the combined use of tip sonication and cyclohexane as dispersion aids during composite processing.

  5. A Photodetector Based on p-Si/n-ZnO Nanotube Heterojunctions with High Ultraviolet Responsivity

    KAUST Repository

    Flemban, Tahani H.

    2017-09-19

    Enhanced ultraviolet (UV) photodetectors (PDs) with high responsivity comparable to that of visible and infrared photodetectors are needed for commercial applications. n-Type ZnO nanotubes (NTs) with high-quality optical, structural, and electrical properties on a p-type Si(100) substrate are successfully fabricated by pulsed laser deposition (PLD) to produce a UV PD with high responsivity, for the first time. We measure the current–voltage characteristics of the device under dark and illuminated conditions and demonstrated the high stability and responsivity (that reaches ∼101.2 A W–1) of the fabricated UV PD. Time-resolved spectroscopy is employed to identify exciton confinement, indicating that the high PD performance is due to optical confinement, the high surface-to-volume ratio, the high structural quality of the NTs, and the high photoinduced carrier density. The superior detectivity and responsivity of our NT-based PD clearly demonstrate that fabrication of high-performance UV detection devices for commercial applications is possible.

  6. Novel catalytic route to bulk production of high purity carbon nanotube

    International Nuclear Information System (INIS)

    Dasgupta, Kinshuk; Venugopalan, Ramani; Dey, G. K.; Sathiyamoorthy, D.

    2008-01-01

    Carbon nanotubes have been synthesized by catalytic chemical vapour deposition of acetylene diluted with argon using three different catalysts, namely, nickel formate, cobalt formate and ferrocene. The synthesis was carried out at 700 deg. C in a quartz reactor for 30 minutes. Thermal analysis was carried out in order to determine the yield of the nanotube. It was found that the deposit contains 86% nanotube, with nickel-based catalyst, which was the maximum. The yield of nanotube was 71 times that of the nickel loading. The TEM images reveal helical type of nanotubes with iron catalyst while cobalt and nickel catalysts yielded straight nanotubes. This technique can be explored for the bulk production of carbon nanotube in an economic way

  7. Nano-Reinforcement of Interfaces in Prepreg-Based Composites Using a Carbon Nanotubes Spraying Method

    KAUST Repository

    Almuhammadi, Khaled

    2012-01-01

    of epoxy resins used as matrix materials for CFRP composites can be increased by the addition of nano-sized fillers such as Carbon nanotubes (CNTs). CNTs are particularly well suited for this purpose because of their nano-scale diameter and high aspect

  8. Novel iron oxide nanotube arrays as high-performance anodes for lithium ion batteries

    Science.gov (United States)

    Zhong, Yuan; Fan, Huiqing; Chang, Ling; Shao, Haibo; Wang, Jianming; Zhang, Jianqing; Cao, Chu-nan

    2015-11-01

    Nanostructured iron oxides can be promising anode materials for lithium ion batteries (LIBs). However, improvement on the rate capability and/or electrochemical cycling stability of iron oxide anode materials remains a key challenge because of their poor electrical conductivities and large volume expansion during cycling. Herein, the vertically aligned arrays of one-dimensional (1D) iron oxide nanotubes with 5.8 wt% carbon have been fabricated by a novel surfactant-free self-corrosion process and subsequent thermal treatment. The as-fabricated nanotube array electrode delivers a reversible capacity of 932 mAh g-1 after 50 charge-discharge cycles at a current of 0.6 A g-1. The electrode still shows a reversible capacity of 610 mAh g-1 even at a very high rate (8.0 A g-1), demonstrating its prominent rate capability. Furthermore, the nanotube array electrode also exhibits the excellent electrochemical cycling stability with a reversible capacity of 880 mAh g-1 after 500 cycles at a current of 4 A g-1. The nanotube array electrode with superior lithium storage performance reveals the promising potential as a high-performance anode for LIBs.

  9. Safety considerations for graphene: lessons learnt from carbon nanotubes.

    Science.gov (United States)

    Bussy, Cyrill; Ali-Boucetta, Hanene; Kostarelos, Kostas

    2013-03-19

    Many consider carbon nanomaterials the poster children of nanotechnology, attracting immense scientific interest from many disciplines and offering tremendous potential in a diverse range of applications due to their extraordinary properties. Graphene is the youngest in the family of carbon nanomaterials. Its isolation, description, and mass fabrication has followed that of fullerenes and carbon nanotubes. Graphene's development and its adoption by many industries will increase unintended or intentional human exposure, creating the need to determine its safety profile. In this Account, we compare the lessons learned from the development of carbon nanotubes with what is known about graphene, based on our own investigations and those of others. Despite both being carbon-based, nanotubes and graphene are two very distinct nanomaterials. We consider the key physicochemical characteristics (structure, surface, colloidal properties) for graphene and carbon nanotubes at three different physiological levels: cellular, tissue, and whole body. We summarize the evidence for health effects of both materials at all three levels. Overall, graphene and its derivatives are characterized by a lower aspect ratio, larger surface area, and better dispersibility in most solvents compared to carbon nanotubes. Dimensions, surface chemistry, and impurities are equally important for graphene and carbon nanotubes in determining both mechanistic (aggregation, cellular processes, biodistribution, and degradation kinetics) and toxicological outcomes. Colloidal dispersions of individual graphene sheets (or graphene oxide and other derivatives) can easily be engineered without metallic impurities, with high stability and less aggregation. Very importantly, graphene nanostructures are not fiber-shaped. These features theoretically offer significant advantages in terms of safety over inhomogeneous dispersions of fiber-shaped carbon nanotubes. However, studies that directly compare graphene with

  10. Template-directed formation of functional complex metal-oxide nanostructures by combination of sol-gel processing and spin coating

    International Nuclear Information System (INIS)

    Choi, Y.C.; Kim, J.; Bu, S.D.

    2006-01-01

    We report the template-based formation of functional complex metal-oxide nanostructures by a combination of sol-gel processing and spin coating. This method employs the spin-coating of a sol-gel solution into an anodic aluminum oxide membrane (SSAM). Various metal-oxide nanowires and nanotubes with a high aspect-ratio were prepared. The aspect-ratios of the PbO 2 nanowires and Pb(Zr 0.52 Ti 0.48 )O 3 nanowires were about 300 and 400, respectively, and their diameters were about 50 nm. The fabricated PbTiO 3 nanotubes have a relatively constant wall thickness of about 20 nm with an outer diameter of about 60 nm. The deposition time for all of the fabricated metal-oxide nanowires and nanotubes is less than 120 s, which is far shorter than those required in both the sol-gel dipping and sol-gel electrophoretic methods. These results indicate that the SSAM method can be a versatile pathway to prepare functional complex metal-oxide nanowires and nanotubes with a high aspect-ratio. The possible formation process for the one-dimensional nanostructures by SSAM is discussed

  11. A vacuum sealed high emission current and transmission efficiency carbon nanotube triode

    Energy Technology Data Exchange (ETDEWEB)

    Di, Yunsong [School of Electronic Science & Engineering, Southeast University, Nanjing 210096 (China); Jiangsu Key Laboratory of Optoelectronic Technology, Nanjing Normal University, Nanjing 210023 (China); Wang, Qilong; Zhang, Xiaobing, E-mail: bell@seu.edu.cn; Lei, Wei; Du, Xiaofei; Yu, Cairu [School of Electronic Science & Engineering, Southeast University, Nanjing 210096 (China)

    2016-04-15

    A vacuum sealed carbon nanotubes (CNTs) triode with a concave and spoke-shaped Mo grid is presented. Due to the high aperture ratio of the grid, the emission current could be modulated at a relatively high electric field. Totally 75 mA emission current has been obtained from the CNTs cathode with the average applied field by the grid shifting from 8 to 13 V/μm. Whilst with the electron transmission efficiency of the grid over 56%, a remarkable high modulated current electron beam over 42 mA has been collected by the anode. Also contributed by the high aperture ration of the grid, desorbed gas molecules could flow away from the emission area rapidly when the triode has been operated at a relative high emission current, and finally collected by a vacion pump. The working pressure has been maintained at ∼1 × 10{sup −7} Torr, seldom spark phenomena occurred. Nearly perfect I-V curve and corresponding Fowler-Nordheim (FN) plot confirmed the accuracy of the measured data, and the emission current was long term stable and reproducible. Thusly, this kind of triode would be used as a high-power electron source.

  12. Influence of external toroidal flux on low-aspect-ratio toroidal plasma

    International Nuclear Information System (INIS)

    Ikuno, S.; Natori, M.; Kamitani, A.

    1999-01-01

    In the HIST device, the external flux is generated by two kinds of currents: the current I s flowing along the symmetry axis and the bias coil current I D . The influence of the external flux on the MHD equilibrium and stability of the low-aspect-ratio toroidal plasma in the HIST device is investigated numerically. Equilibrium configurations of the low-aspect-ratio toroidal plasma in the HIST device are numerically determined by means of the combination of FDM and BEM. The influence of I s and I D on their stability is also investigated by using the Mercier criterion. The results of computations show that the Mercier limit decreases to zero with increasing I s and with decreasing I D . Moreover, either a further increase in I s or a further decrease in I D raises the Mercier limit considerably. Besides, the equilibrium configuration in the HIST device changes its state from spheromak through ultra-low q to tokamak with increasing I s and with decreasing I D . (author)

  13. Pt–Al2O3 dual layer atomic layer deposition coating in high aspect ratio nanopores

    International Nuclear Information System (INIS)

    Pardon, Gaspard; Gatty, Hithesh K; Stemme, Göran; Wijngaart, Wouter van der; Roxhed, Niclas

    2013-01-01

    Functional nanoporous materials are promising for a number of applications ranging from selective biofiltration to fuel cell electrodes. This work reports the functionalization of nanoporous membranes using atomic layer deposition (ALD). ALD is used to conformally deposit platinum (Pt) and aluminum oxide (Al 2 O 3 ) on Pt in nanopores to form a metal–insulator stack inside the nanopore. Deposition of these materials inside nanopores allows the addition of extra functionalities to nanoporous materials such as anodic aluminum oxide (AAO) membranes. Conformal deposition of Pt on such materials enables increased performances for electrochemical sensing applications or fuel cell electrodes. An additional conformal Al 2 O 3 layer on such a Pt film forms a metal–insulator–electrolyte system, enabling field effect control of the nanofluidic properties of the membrane. This opens novel possibilities in electrically controlled biofiltration. In this work, the deposition of these two materials on AAO membranes is investigated theoretically and experimentally. Successful process parameters are proposed for a reliable and cost-effective conformal deposition on high aspect ratio three-dimensional nanostructures. A device consisting of a silicon chip supporting an AAO membrane of 6 mm diameter and 1.3 μm thickness with 80 nm diameter pores is fabricated. The pore diameter is reduced to 40 nm by a conformal deposition of 11 nm Pt and 9 nm Al 2 O 3 using ALD. (paper)

  14. Pt-Al2O3 dual layer atomic layer deposition coating in high aspect ratio nanopores

    Science.gov (United States)

    Pardon, Gaspard; Gatty, Hithesh K.; Stemme, Göran; van der Wijngaart, Wouter; Roxhed, Niclas

    2013-01-01

    Functional nanoporous materials are promising for a number of applications ranging from selective biofiltration to fuel cell electrodes. This work reports the functionalization of nanoporous membranes using atomic layer deposition (ALD). ALD is used to conformally deposit platinum (Pt) and aluminum oxide (Al2O3) on Pt in nanopores to form a metal-insulator stack inside the nanopore. Deposition of these materials inside nanopores allows the addition of extra functionalities to nanoporous materials such as anodic aluminum oxide (AAO) membranes. Conformal deposition of Pt on such materials enables increased performances for electrochemical sensing applications or fuel cell electrodes. An additional conformal Al2O3 layer on such a Pt film forms a metal-insulator-electrolyte system, enabling field effect control of the nanofluidic properties of the membrane. This opens novel possibilities in electrically controlled biofiltration. In this work, the deposition of these two materials on AAO membranes is investigated theoretically and experimentally. Successful process parameters are proposed for a reliable and cost-effective conformal deposition on high aspect ratio three-dimensional nanostructures. A device consisting of a silicon chip supporting an AAO membrane of 6 mm diameter and 1.3 μm thickness with 80 nm diameter pores is fabricated. The pore diameter is reduced to 40 nm by a conformal deposition of 11 nm Pt and 9 nm Al2O3 using ALD.

  15. Large quantity production of carbon and boron nitride nanotubes by mechano-thermal process

    International Nuclear Information System (INIS)

    Chen, Y.; Fitzgerald, J.D.; Chadderton, L.; Williams, J.S.; Campbell, S.J.

    2002-01-01

    Full text: Nanotube materials including carbon and boron nitride have excellent properties compared with bulk materials. The seamless graphene cylinders with a high length to diameter ratio make them as superstrong fibers. A high amount of hydrogen can be stored into nanotubes as future clean fuel source. Theses applications require large quantity of nanotubes materials. However, nanotube production in large quantity, fully controlled quality and low costs remains challenges for most popular synthesis methods such as arc discharge, laser heating and catalytic chemical decomposition. Discovery of new synthesis methods is still crucial for future industrial application. The new low-temperature mechano-thermal process discovered by the current author provides an opportunity to develop a commercial method for bulk production. This mechano-thermal process consists of a mechanical ball milling and a thermal annealing processes. Using this method, both carbon and boron nitride nanotubes were produced. I will present the mechano-thermal method as the new bulk production technique in the conference. The lecture will summarise main results obtained. In the case of carbon nanotubes, different nanosized structures including multi-walled nanotubes, nanocells, and nanoparticles have been produced in a graphite sample using a mechano-thermal process, consisting of I mechanical milling at room temperature for up to 150 hours and subsequent thermal annealing at 1400 deg C. Metal particles have played an important catalytic effect on the formation of different tubular structures. While defect structure of the milled graphite appears to be responsible for the formation of small tubes. It is found that the mechanical treatment of graphite powder produces a disordered and microporous structure, which provides nucleation sites for nanotubes as well as free carbon atoms. Multiwalled carbon nanotubes appear to grow via growth of the (002) layers during thermal annealing. In the case of BN

  16. Soldering of Nanotubes onto Microelectrodes

    DEFF Research Database (Denmark)

    Madsen, Dorte Nørgaard; Mølhave, Kristian; Mateiu, Ramona Valentina

    2003-01-01

    Suspended bridges of individual multiwalled carbon nanotubes were fabricated inside a scanning electron microscope by soldering the nanotube onto microelectrodes with highly conducting gold-carbon material. By the decomposition of organometallic vapor with the electron beam, metal-containing sold...... bonds were consistently found to be mechanically stronger than the carbon nanotubes.......Suspended bridges of individual multiwalled carbon nanotubes were fabricated inside a scanning electron microscope by soldering the nanotube onto microelectrodes with highly conducting gold-carbon material. By the decomposition of organometallic vapor with the electron beam, metal-containing solder...... bonds were formed at the intersection of the nanotube and the electrodes. Current-voltage curves indicated metallic conduction of the nanotubes, with resistances in the range of 9-29 kOmega. Bridges made entirely of the soldering material exhibited resistances on the order of 100 Omega, and the solder...

  17. Use of tapered Pyrex capillary tubes to increase the mechanical stability of multiwall carbon nanotubes field emitters

    Science.gov (United States)

    Mousa, M. S.; Bani Ali, E. S.; Hagmann, M. J.

    2018-02-01

    In this study, NanocylTM NC 7000 Thin Multiwall Carbon Nanotubes (MWCNTs) were used with a high aspect ratio (>150) made by the process of catalytic chemical vapor deposition (CCVD). The field emitter tips were prepared by inserting these MWCT into fine glass capillary tubes that were pulled at high temperatures and then cut. Measurements were carried out under ultra-high vacuum (UHV) conditions with a base pressure of 10-9 mbar. The data show the effects of initial conditioning of MWCNT and hysteresis. Compression of the MWCNT by the capillary tubes appears to provide adequate mechanical support without requiring the use of a low-melting point electrically-conductive binder as has been used previously. Emission currents in excess of 1 μA were obtained so this technique shows promise as a reliable, stable, powerful electron source.

  18. Well-Shaped Sulfonic Organosilica Nanotubes with High Activity for Hydrolysis of Cellobiose

    Directory of Open Access Journals (Sweden)

    Jing Sun

    2017-04-01

    Full Text Available Sulfonic organosilica nanotubes with different acidity densities could be synthesized through the co-condensation of ethenyl- or phenylene-bridged organosilane and 3-mercaptopropyltrimethoxysilane followed by sulfhydryl (–SH oxidation. Transmission electron microscopy (TEM analysis and nitrogen adsorption-desorption experiment clearly exhibit the hollow nanotube structures with the diameters of about 5 nm. The compositions of the nanotube frameworks are confirmed by solid state 13C nuclear magnetic resonance (NMR while X-ray photoelectron spectroscopy (XPS shows that about 60–80% of SH groups were oxidized to sulfonic acid (SO3H. The acid contents were measured by both elemental analysis (CHNS mode and acid-base titration experiment, which revealed that the acid density was in the range of 0.74 to 4.37 μmol·m−2 on the solid. These nanotube-based acid catalysts exhibited excellent performances in the hydrolysis of cellobiose with the highest conversion of 92% and glucose selectivity of 96%. In addition, the catalysts could maintain high activity (65% conversion with 92% selectivity even after six recycles.

  19. A self-propagation high-temperature synthesis and annealing route to synthesis of wave-like boron nitride nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jilin; Zhang, Laiping [School of Materials Science and Engineering, Wuhan Institute of Technology, Wuhan, Hubei, 430073 (China); Gu, Yunle, E-mail: ncm@mail.wit.edu.cn [School of Materials Science and Engineering, Wuhan Institute of Technology, Wuhan, Hubei, 430073 (China); Pan, Xinye; Zhao, Guowei; Zhang, Zhanhui [School of Materials Science and Engineering, Wuhan Institute of Technology, Wuhan, Hubei, 430073 (China)

    2013-03-15

    Highlights: ► Large quantities of wave-like BN nanotubes were synthesized by SHS-annealing method. ► The catalytic boron-containing porous precursor was produced by self-propagation high-temperature synthesis method. ► Three growth models were proposed to explain the growth mechanism of the wave-like BN nanotubes. - Abstract: Large quantities of boron nitride (BN) nanotubes were synthesized by annealing a catalytic boron-containing porous precursor in flowing NH{sub 3} gas at 1180 °C. The porous precursor was prepared by self-propagation high-temperature synthesis (SHS) method at 800 °C using Mg, B{sub 2}O{sub 3} and amorphous boron powder (α-B) as the starting materials. The porous precursor played an important role in large quantities synthesis of BN nanotubes. The as-synthesized product was characterized by X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FTIR), Raman, Scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM). Characterization results indicated that the BN nanotubes displayed wave-like inner structures with diameters in the range of 50–300 nm and average lengths of more than 10 μm. The possible growth mechanism of the BN nanotubes was also discussed.

  20. Multifunctional Electroactive Nanocomposites Based on Piezoelectric Boron Nitride Nanotubes

    Science.gov (United States)

    Kang, Jin Ho; Sauti, Godfrey; Park, Cheol; Yamakov, Vesselin I.; Wise, Kristopher E.; Lowther, Sharon E.; Fay, Catharine C.; Thibeault, Sheila A.; Bryant, Robert G.

    2015-01-01

    Space exploration missions require sensors and devices capable of stable operation in harsh environments such as those that include high thermal fluctuation, atomic oxygen, and high-energy ionizing radiation. However, conventional or state-of-the-art electroactive materials like lead zirconate titanate, poly(vinylidene fluoride), and carbon nanotube (CNT)-doped polyimides have limitations on use in those extreme applications. Theoretical studies have shown that boron nitride nanotubes (BNNTs) have strength-to-weight ratios comparable to those of CNTs, excellent high-temperature stability (to 800 C in air), large electroactive characteristics, and excellent neutron radiation shielding capability. In this study, we demonstrated the experimental electroactive characteristics of BNNTs in novel multifunctional electroactive nanocomposites. Upon application of an external electric field, the 2 wt % BNNT/polyimide composite was found to exhibit electroactive strain composed of a superposition of linear piezoelectric and nonlinear electrostrictive components. When the BNNTs were aligned by stretching the 2 wt % BNNT/polyimide composite, electroactive characteristics increased by about 460% compared to the nonstretched sample. An all-nanotube actuator consisting of a BNNT buckypaper layer between two single-walled carbon nanotube buck-paper electrode layers was found to have much larger electroactive properties. The additional neutron radiation shielding properties and ultraviolet/visible/near-infrared optical properties of the BNNT composites make them excellent candidates for use in the extreme environments of space missions. utilizing the unique characteristics of BNNTs.

  1. Invariant Imbedding T-Matrix Method for Axial Symmetric Hydrometeors with Extreme Aspect Ratios

    Science.gov (United States)

    Pelissier, C.; Clune, T.; Kuo, K. S.; Munchak, S. J.; Adams, I. S.

    2017-12-01

    The single-scattering properties (SSPs) of hydrometeors are the fundamental quantities for physics-based precipitation retrievals. Thus, efficient computation of their electromagnetic scattering is of great value. Whereas the semi-analytical T-Matrix methods are likely the most efficient for nonspherical hydrometeors with axial symmetry, they are not suitable for arbitrarily shaped hydrometeors absent of any significant symmetry, for which volume integral methods such as those based on Discrete Dipole Approximation (DDA) are required. Currently the two leading T-matrix methods are the Extended Boundary Condition Method (EBCM) and the Invariant Imbedding T-matrix Method incorporating Lorentz-Mie Separation of Variables (IITM+SOV). EBCM is known to outperform IITM+SOV for hydrometeors with modest aspect ratios. However, in cases when aspect ratios become extreme, such as needle-like particles with large height to diameter values, EBCM fails to converge. Such hydrometeors with extreme aspect ratios are known to be present in solid precipitation and their SSPs are required to model the radiative responses accurately. In these cases, IITM+SOV is shown to converge. An efficient, parallelized C++ implementation for both EBCM and IITM+SOV has been developed to conduct a performance comparison between EBCM, IITM+SOV, and DDSCAT (a popular implementation of DDA). We present the comparison results and discuss details. Our intent is to release the combined ECBM & IITM+SOV software to the community under an open source license.

  2. Non-inductive current drive via helicity injection by Alfven waves in low-aspect-ratio tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Cuperman, S.; Bruma, C.; Komoshvili, K. [Tel Aviv Univ. (Israel). Sackler Faculty of Exact Sciences

    1996-08-01

    A theoretical investigation of radio-frequency (RF) current drive via helicity injection in low aspect ratio tokamaks is carried out. A current-carrying cylindrical plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell is considered. Toroidal features of low-aspect-ratio tokamaks are simulated by incorporating the following effects: (i) arbitrarily small aspect ratio, R{sub O}/a ``identical to`` 1/{epsilon}; (ii) strongly sheared equilibrium magnetic field; and (iii) relatively large poloidal component of the equilibrium magnetic field. This study concentrates on the Alfven continuum, i.e. the case in which the wave frequency satisfies the condition {l_brace}{omega}{sub Alf}({tau}){r_brace}{sub min}{r_brace} {<=} {omega} {<=} {l_brace}{omega}{sub Alf}({tau}){r_brace}{sub max}, where {omega}{sub Alf}({tau}) ``identical to`` {omega}{sub Alf}[n({tau}), B{sub O}({tau})] is an eigenfrequency of the shear Alfven wave (SAW). Thus, using low-{beta} magnetohydrodynamics, the wave equation with correct boundary (matching) conditions is solved, the RF field components are found, and subsequently current drive, power deposition and efficiency are computed. The results of our investigation clearly demonstrate the possibility of generation of RF-driven currents via helicity injection by Alfven waves in low-aspect-ratio tokamaks, in the SAW mode. A special algorithm is developed that enables one to select the antenna parameters providing optimal current drive efficiency. (Author).

  3. All carbon nanotubes are not created equal

    International Nuclear Information System (INIS)

    Geohegan, David B.; Puretzky, Alexander A.; Rouleau, Christopher M.

    2010-01-01

    This chapter presents the various factors that enter into consideration when choosing the source of carbon nanotubes for a specific application. Carbon nanotubes are giant molecules made of pure carbon. They have captured the imagination of the scientific community by the unique structure that provides superior physical, chemical, and electrical properties. However, a surprisingly wide disparity exists between the intrinsic properties determined under ideal conditions and the properties that carbon nanotubes exhibit in real world situations. The lack of uniformity in carbon nanotube properties is likely to be the main obstacle holding back the development of carbon nanotube applications. This tutorial addresses the nonuniformity of carbon nanotube properties from the synthesis standpoint. This synthesis-related nonuniformity is on top of the intrinsic chirality distribution that gives the ∼1:2 ratio of metallic to semiconducting nanotubes. From the standpoint of carbon bonding chemistry the variation in the quality and reproducibility of carbon nanotube materials is not unexpected. It is an intrinsic feature that is related to the metastability of carbon structures. The extent to which this effect is manifested in carbon nanotube formation is governed by the type and the kinetics of the carbon nanotube synthesis reaction. Addressing this variation is critical if nanotubes are to live up to the potential already demonstrated by their phenomenal physical properties.

  4. Functional materials based on carbon nanotubes: Carbon nanotube actuators and noncovalent carbon nanotube modification

    Science.gov (United States)

    Fifield, Leonard S.

    Carbon nanotubes have attractive inherent properties that encourage the development of new functional materials and devices based on them. The use of single wall carbon nanotubes as electromechanical actuators takes advantage of the high mechanical strength, surface area and electrical conductivity intrinsic to these molecules. The work presented here investigates the mechanisms that have been discovered for actuation of carbon nanotube paper: electrostatic, quantum chemical charge injection, pneumatic and viscoelastic. A home-built apparatus for the measurement of actuation strain is developed and utilized in the investigation. An optical fiber switch, the first demonstrated macro-scale device based on the actuation of carbon nanotubes, is described and its performance evaluated. Also presented here is a new general process designed to modify the surface of carbon nanotubes in a non-covalent, non-destructive way. This method can be used to impart new functionalities to carbon nanotube samples for a variety of applications including sensing, solar energy conversion and chemical separation. The process described involves the achievement of large degrees of graphitic surface coverage with polycyclic aromatic hydrocarbons through the use of supercritical fluids. These molecules are bifunctional agents that anchor a desired chemical group to the aromatic surface of the carbon nanotubes without adversely disrupting the conjugated backbone that gives rise the attractive electronic and physical properties of the nanotubes. Both the nanotube functionalization work and the actuator work presented here emphasize how an understanding and control of nanoscale structure and phenomena can be of vital importance in achieving desired performance for active materials. Opportunities for new devices with improved function over current state-of-the-art can be envisioned and anticipated based on this understanding and control.

  5. Numerical analysis on effect of aspect ratio of planar solid oxide fuel cell fueled with decomposed ammonia

    Science.gov (United States)

    Tan, Wee Choon; Iwai, Hiroshi; Kishimoto, Masashi; Brus, Grzegorz; Szmyd, Janusz S.; Yoshida, Hideo

    2018-04-01

    Planar solid oxide fuel cells (SOFCs) with decomposed ammonia are numerically studied to investigate the effect of the cell aspect ratio. The ammonia decomposer is assumed to be located next to the SOFCs, and the heat required for the endothermic decomposition reaction is supplied by the thermal radiation from the SOFCs. Cells with aspect ratios (ratios of the streamwise length to the spanwise width) between 0.130 and 7.68 are provided with the reactants at a constant mass flow rate. A parametric study is conducted by varying the cell temperature and fuel utility factor to investigate their effects on the cell performance in terms of the voltage efficiency. The effect of the heat supply to the ammonia decomposer is also studied. The developed model shows good agreement, in terms of the current-voltage curve, with the experimental data obtained from a short stack without parameter tuning. The simulation study reveals that the cell with the highest aspect ratio achieves the highest performance under furnace operation. On the other hand, the 0.750 aspect ratio cell with the highest voltage efficiency of 0.67 is capable of thermally sustaining the ammonia decomposers at a fuel utility of 0.80 using the thermal radiation from both sidewalls.

  6. Enhanced field emission properties of carbon nanotube bundles confined in SiO2 pits

    Science.gov (United States)

    Lim, Yu Dian; Grapov, Dmitry; Hu, Liangxing; Kong, Qinyu; Tay, Beng Kang; Labunov, Vladimir; Miao, Jianmin; Coquet, Philippe; Aditya, Sheel

    2018-02-01

    It has been widely reported that carbon nanotubes (CNTs) exhibit superior field emission (FE) properties due to their high aspect ratios and unique structural properties. Among the various types of CNTs, random growth CNTs exhibit promising FE properties due to their reduced inter-tube screening effect. However, growing random growth CNTs on individual catalyst islands often results in spread out CNT bundles, which reduces overall field enhancement. In this study, significant improvement in FE properties in CNT bundles is demonstrated by confining them in microfabricated SiO2 pits. Growing CNT bundles in narrow (0.5 μm diameter and 2 μm height) SiO2 pits achieves FE current density of 1-1.4 A cm-2, which is much higher than for freestanding CNT bundles (76.9 mA cm-2). From the Fowler Nordheim plots, confined CNT bundles show a higher field enhancement factor. This improvement can be attributed to the reduced bundle diameter by SiO2 pit confinement, which yields bundles with higher aspect ratios. Combining the obtained outcomes, it can be conclusively summarized that confining CNTs in SiO2 pits yields higher FE current density due to the higher field enhancement of confined CNTs.

  7. Study on photocatalysis of TiO2 nanotubes prepared by methanol ...

    Indian Academy of Sciences (India)

    Titanate nanotubes were synthesized in methanol–water volume ratios of 10:90, 20:80 and 30:70 which still .... atmospheric pressure. .... pore volume of the largest titania nanotubes were observed ... affect phase structure and microstructure of titanate nanotubes .... Left inset in figure 7 is an enlarged picture of a tube wall.

  8. Recent Development in the CESE Method for the Solution of the Navier-Stokes Equations Using Unstructured Triangular or Tetrahedral Meshes With High Aspect Ratio

    Science.gov (United States)

    Chang, Sin-Chung; Chang, Chau-Lyan; Yen, Joseph C.

    2013-01-01

    In the multidimensional CESE development, triangles and tetrahedra turn out to be the most natural building blocks for 2D and 3D spatial meshes. As such the CESE method is compatible with the simplest unstructured meshes and thus can be easily applied to solve problems with complex geometries. However, because the method uses space-time staggered stencils, solution decoupling may become a real nuisance in applications involving unstructured meshes. In this paper we will describe a simple and general remedy which, according to numerical experiments, has removed any possibility of solution decoupling. Moreover, in a real-world viscous flow simulation near a solid wall, one often encounters a case where a boundary with high curvature or sharp corner is surrounded by triangular/tetrahedral meshes of extremely high aspect ratio (up to 106). For such an extreme case, the spatial projection of a space-time compounded conservation element constructed using the original CESE design may become highly concave and thus its centroid (referred to as a spatial solution point) may lie far outside of the spatial projection. It could even be embedded beyond a solid wall boundary and causes serious numerical difficulties. In this paper we will also present a new procedure for constructing conservation elements and solution elements which effectively overcomes the difficulties associated with the original design. Another difficulty issue which was addressed more recently is the wellknown fact that accuracy of gradient computations involving triangular/tetrahedral grids deteriorates rapidly as the aspect ratio of grid cells increases. The root cause of this difficulty was clearly identified and several remedies to overcome it were found through a rigorous mathematical analysis. However, because of the length of the current paper and the complexity of mathematics involved, this new work will be presented in another paper.

  9. Titania nanotubes with adjustable dimensions for drug reservoir sites and enhanced cell adhesion.

    Science.gov (United States)

    Çalışkan, Nazlı; Bayram, Cem; Erdal, Ebru; Karahaliloğlu, Zeynep; Denkbaş, Emir Baki

    2014-02-01

    This study aims to generate a bactericidal agent releasing surface via nanotube layer on titanium metal and to investigate how aspect ratio of nanotubes affects drug elution time and cell proliferation. Titania nanotube layers were generated on metal surfaces by anodic oxidation at various voltage and time parameters. Gentamicin loading was carried out via simple pipetting and the samples were tested against S. aureus for the efficacy of the applied modification. Drug releasing time and cell proliferation were also tested in vitro. Titania nanotube layers with varying diameters and lengths were prepared after anodization and anodizing duration was found as the most effective parameter for amount of loaded drug and drug releasing time. Drug elution lasted up to 4 days after anodizing for 80 min of the samples, whereas release completed in 24 h when the samples were anodized for 20 min. All processed samples had bactericidal properties against S. aureus organism except unmodified titanium, which was also subjected to drug incorporation step. The anodization also enhanced water wettability and cell adhesion results. Anodic oxidation is an effective surface modification to enhance tissue-implant interactions and also resultant titania layer can act as a drug reservoir for the release of bactericidal agents. The use of implants as local drug eluting devices is promising but further in vivo testing is required. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. Fast fabrication of long TiO2 nanotube array with high photoelectrochemical property on flexible stainless steel.

    Science.gov (United States)

    Tao, Jie; Wu, Tao; Gao, Peng

    2012-03-01

    Oriented highly ordered long TiO2 nanotube array films with nanopore structure and high photoelectrochemical property were fabricated on flexible stainless steel substrate (50 microm) by anodization treatment of titanium thin films in a short time. The samples were characterized by means of field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and photoelectrochemical methods, respectively. The results showed that Ti films deposited at the condition of 0.7 Pa Ar pressure and 96 W sputtering power at room temperature was uniform and dense with good homogeneity and high crystallinity. The voltage and the anodization time both played significant roles in the formation of TiO2 nanopore-nanotube array film. The optimal voltage was 60 V and the anodization time is less than 30 min by anodizing Ti films in ethylene glycerol containing 0.5% (w) NH4F and 3% (w) H2O. The growth rate of TiO2 nanotube array was as high as 340 nm/min. Moreover, the photocurrent-potential curves, photocurrent response curves and electrochemical impedance spectra results indicated that the TiO2 nanotube array film with the nanoporous structure exhibited a better photo-response ability and photoelectrochemical performance than the ordinary TiO2 nanotube array film. The reason is that the nanoporous structure on the surface of the nanotube array can separate the photo electron-hole pairs more efficiently and completely than the tubular structure.

  11. Quantum transport in carbon nanotubes

    NARCIS (Netherlands)

    Laird, E.A.; Kuemmeth, F.; Steele, G.A.; Grove-Rasmussen, K.; Nygard, J.; Flensberg, K.; Kouwenhoven, L.P.

    2015-01-01

    Carbon nanotubes are a versatile material in which many aspects of condensed matter physics come together. Recent discoveries have uncovered new phenomena that completely change our understanding of transport in these devices, especially the role of the spin and valley degrees of freedom. This

  12. A fully MEMS-compatible process for 3D high aspect ratio micro coils obtained with an automatic wire bonder

    International Nuclear Information System (INIS)

    Kratt, K; Badilita, V; Burger, T; Wallrabe, U; Korvink, J G

    2010-01-01

    We report the fabrication of 3D micro coils made with an automatic wire bonder. Using standard MEMS processes such as spin coating and UV lithography on silicon and Pyrex® wafers results in high aspect ratio SU-8 posts with diameters down to 100 µm that serve as mechanical stabilization yokes for the coils. The wire bonder is employed to wind 25 µm insulated gold wire around the posts in an arbitrary (e.g. solenoidal) path, yielding arrays of micro coils. Each micro coil is bonded directly on-chip, so that loose wire ends are avoided and, compared to other winding methods, coil re-soldering is unnecessary. The manufacturing time for a single coil is about 200 ms, and although the process is serial, it is batch fabrication compatible due to the high throughput of the machine. Despite the speed of manufacture we obtain high manufacturing precision and reliability. The micro air-core solenoids show an RF quality factor of over 50 when tested at 400 MHz. We present a flexible coil making method where the number of windings is only limited by the post height. The coil diameter is restricted by limits defined by lithography and the mechanical strength of the posts. Based on this technique we present coils ranging from 100 µm diameter and 1 winding up to 1000 µm diameter and 20 windings

  13. High power density supercapacitor electrodes of carbon nanotube films by electrophoretic deposition

    International Nuclear Information System (INIS)

    Du Chunsheng; Pan Ning

    2006-01-01

    Carbon nanotube thin films have been successfully fabricated by the electrophoretic deposition technique. The supercapacitors built from such thin film electrodes have a very small equivalent series resistance, and a high specific power density over 20 kW kg -1 was thus obtained. More importantly, the supercapacitors showed superior frequency response. Our study also demonstrated that these carbon nanotube thin films can serve as coating layers over ordinary current collectors to drastically enhance the electrode performance, indicating a huge potential in supercapacitor and battery manufacturing

  14. High activity of novel Pd/TiO2 nanotube catalysts for methanol electro-oxidation

    International Nuclear Information System (INIS)

    Wang Mei; Guo Daojun; Li Hulin

    2005-01-01

    Electro-oxidation of methanol in sulfuric acid solution was studied using palladium well-dispersed on titanium nanotubes, in relation to methanol oxidation processes in the direct oxidation methanol fuel cell. Pd dispersed on titania nanotubes, which leads to high surface area substrates, showed excellent catalytic activities compared to those of pure Pd and Pd-TiO 2 nanoparticles. TEM results show a narrow distribution of TiO 2 nanoparticles whose particle size is about 10nm, and uniform nano-sized TiO 2 nanotubes with 10nm in diameters are seen from HRTEM . A homogeneous structure in the composite nanomaterials is indicated by XRD analysis. The composite electrode activities were measured by cyclic voltammetry (CV) and at 25 deg. C it was found that 3wt% Pd in titania nanotubes had the best activity for methanol oxidation

  15. The impact of changing solar screen rotation angle and its opening aspect ratios on Daylight Availability in residential desert buildings

    KAUST Repository

    Sherif, Ahmed H.

    2012-11-01

    In desert sunny clear-sky regions solar penetration can become excessive. This can cause non-uniform daylight distribution, glare and high solar heat gain, affecting both visual and thermal comfort. Shading devices, such as solar screens, were usually used to diffuse and prevent direct solar penetration into spaces. This paper investigates the impact of changing solar screen axial rotation angle and screen opening aspect ratio on daylighting performance in a typical residential living room space under the desert sunny clear-sky. The larger aim is to arrive at efficient solar screen designs that suit the different orientations.The study was divided into three consecutive phases. In phase one, the effect of the two parameters on Daylight Availability was tested. The solar screen was axially rotated by three different angles at 10° increments. Also, the aspect ratio of the screen opening in both horizontal and vertical directions was changed systematically. Simulation was conducted using the annual Daylight Dynamic Performance Metrics (DDPMs). In phase two, the Annual Daylight Glare Probability (DGP) metric was evaluated for the cases that were found adequate in phase one. In the third phase, the annual solar energy transmittance through the screen was calculated for the cases that achieved acceptable performance in the two previous phases in order to identify the more energy efficient screens.Solar screens with openings having horizontal aspect ratios were found to be the most effective, while those with vertical aspect ratios were achieved the lowest performance. In the North orientation, since almost all the cases that were tested in this research provided acceptable daylighting performance, the designer now have a variety of options to choose from. Preference should be given to screen openings of horizontal aspect ratios, especially the 12:1 and 18:1 (H:V) screens that achieved the best performance where 92% of the space was " daylit" in comparison with only 53

  16. The influence of streamwise vortices on turbulent heat transfer in rectangular ducts with various aspect ratios

    International Nuclear Information System (INIS)

    Choi, Hang Seok; Park, Tae Seon

    2013-01-01

    Highlights: ► With changing aspect ratio, the effect of secondary flows on the turbulent heat transfer is scrutinized by a LES. ► The conditional sampling technique of instantaneous near-wall streamwise vortices is developed. ► Clockwise and counter-clockwise rotating streamwise vortices are sampled and discussed with the wall heat transfer. ► The hot-sweep motions of CW and CCW vortices clearly appear with increasing aspect ratio. -- Abstract: The effect of aspect ratio of rectangular duct on the turbulent flow and heat transfer is very important for its engineering applications. But the turbulent thermal fields have not been fundamentally scrutinized in spite of its engineering significance especially for cooling device. Hence, in the present study, large eddy simulation is applied to the turbulent flow and heat transfer in rectangular ducts with varying aspect ratio. The turbulent statistics of the flow and thermal quantities are calculated and the characteristics of wall Nusselt number are investigated for each rectangular duct. Especially, to scrutinize near-wall streamwise vortices, a conditional sampling technique is developed and adopted. Clockwise and counter-clockwise rotating streamwise vortices are sampled and the probability density function of the vortex circulation Reynolds number and wall Nusselt number are calculated. From the results, the time-averaged secondary flow caused by instantaneous vortical motions has a great effect on the heat and momentum transport of the flow in the rectangular ducts. Hence, the wall Nusselt number is enhanced near the downwash flow region of the secondary flow. However, with increasing the aspect ratio, the effects of the hot-sweep flow of the clockwise and counter-clockwise rotating vortices become equally dominant near the wall normal bisector of the ducts. During time averaging process, these two counter-rotating vortices are canceled out each other diminishing a secondary flow but they still enhance the

  17. Au nanoparticles attached carbon nanotubes as a high performance active element in field effect transistor

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Myeongsoon; Kim, Don, E-mail: donkim@pknu.ac.kr

    2016-08-15

    The Au nanoparticles attached carbon nanotubes (Au-CNTs), diameter ranged from 40 to 250 nm, were prepared and discussed their chemical and electrical properties. The shape and crystallinity of the carbon nanotubes (CNTs) phase depended main2ly on the diameter of CNTs (r{sub Au-CNT}). Highly crystalline, straight CNTs were observed when the r{sub Au-CNT} exceeded 80 nm, and less crystalline noodle-shaped CNTs were observed when the r{sub Au-CNT} was smaller than 80 nm. The crystallinity of the CNT phase was confirmed by analyzing the G and D bands in their Raman spectra and the electrical conductivities of the Au-CNTs. The electrical conductivity of the highly crystalline carbon phase of Au-CNTs (r{sub Au-CNT} = 250 nm) was ∼10{sup 4} S/cm. The back-gated field effect transistors (FETs) based on the Au-CNTs, which were assembled on a SiO{sub 2}/Si wafer using the dielectrophoresis technique, showed that the Au-CNTs would be a good functional electronic material for future electronic and sensing applications. The transconductance and hole mobility of the FETs, which were assembled with the highly crystalline Au-CNTs (r{sub Au-CNT} = 250 nm), reached to 3.6 × 10{sup −4} A/V and 3.1 × 10{sup 4} cm{sup 2}/V s, respectively. These values are in the middle of those of reported for single walled carbon nanotubes and graphene. However, we could not find any field effect in a CNTFET, which assembled without Au nanoparticles, through the same process. - Highlights: • The shape and crystallinity of the CNTs depended mainly on the diameter of CNTs. • The electrical conductivity of the highly crystalline Au-CNTs was ∼10{sup 4} S/cm. • The Au-CNT FET shows typical p-channel gate effect with the on/off ratio of ∼10{sup 4}. • The Au-CNT FET shows very high transconductance (g{sub m}) and carrier mobility (μ{sub h}).

  18. Au nanoparticles attached carbon nanotubes as a high performance active element in field effect transistor

    International Nuclear Information System (INIS)

    Lee, Myeongsoon; Kim, Don

    2016-01-01

    The Au nanoparticles attached carbon nanotubes (Au-CNTs), diameter ranged from 40 to 250 nm, were prepared and discussed their chemical and electrical properties. The shape and crystallinity of the carbon nanotubes (CNTs) phase depended main2ly on the diameter of CNTs (r_A_u_-_C_N_T). Highly crystalline, straight CNTs were observed when the r_A_u_-_C_N_T exceeded 80 nm, and less crystalline noodle-shaped CNTs were observed when the r_A_u_-_C_N_T was smaller than 80 nm. The crystallinity of the CNT phase was confirmed by analyzing the G and D bands in their Raman spectra and the electrical conductivities of the Au-CNTs. The electrical conductivity of the highly crystalline carbon phase of Au-CNTs (r_A_u_-_C_N_T = 250 nm) was ∼10"4 S/cm. The back-gated field effect transistors (FETs) based on the Au-CNTs, which were assembled on a SiO_2/Si wafer using the dielectrophoresis technique, showed that the Au-CNTs would be a good functional electronic material for future electronic and sensing applications. The transconductance and hole mobility of the FETs, which were assembled with the highly crystalline Au-CNTs (r_A_u_-_C_N_T = 250 nm), reached to 3.6 × 10"−"4 A/V and 3.1 × 10"4 cm"2/V s, respectively. These values are in the middle of those of reported for single walled carbon nanotubes and graphene. However, we could not find any field effect in a CNTFET, which assembled without Au nanoparticles, through the same process. - Highlights: • The shape and crystallinity of the CNTs depended mainly on the diameter of CNTs. • The electrical conductivity of the highly crystalline Au-CNTs was ∼10"4 S/cm. • The Au-CNT FET shows typical p-channel gate effect with the on/off ratio of ∼10"4. • The Au-CNT FET shows very high transconductance (g_m) and carrier mobility (μ_h).

  19. Sharp burnout failure observed in high current-carrying double-walled carbon nanotube fibers

    Science.gov (United States)

    Song, Li; Toth, Geza; Wei, Jinquan; Liu, Zheng; Gao, Wei; Ci, Lijie; Vajtai, Robert; Endo, Morinobu; Ajayan, Pulickel M.

    2012-01-01

    We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 µm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 105 S m - 1 and over 1 × 105 A cm - 2 in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers.

  20. Inkjet Printing of High Aspect Ratio Superparamagnetic SU-8 Microstructures with Preferential Magnetic Directions

    Directory of Open Access Journals (Sweden)

    Loïc Jacot-Descombes

    2014-08-01

    Full Text Available Structuring SU-8 based superparamagnetic polymer composite (SPMPC containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing and thermal curing for the fabrication of much thicker hemispherical microstructures of SPMPC. The microstructures are fabricated by inkjet printing the nanoparticle-doped SU-8 onto flat substrates functionalized to reduce the surface energy and thus the wetting. The thickness and the aspect ratio of the printed structures are further increased by printing the composite onto substrates with confinement pedestals. Fully crosslinked microstructures with a thickness up to 88.8 μm and edge angle of 112° ± 4° are obtained. Manipulation of the microstructures by an external field is enabled by creating lines of densely aggregated nanoparticles inside the composite. To this end, the printed microstructures are placed within an external magnetic field directly before crosslinking inducing the aggregation of dense Fe3O4 nanoparticle lines with in-plane and out-of-plane directions.

  1. Vertically aligned carbon nanotube probes for monitoring blood cholesterol

    Science.gov (United States)

    Roy, Somenath; Vedala, Harindra; Choi, Wonbong

    2006-02-01

    Detection of blood cholesterol is of great clinical significance. The amperometric detection technique was used for the enzymatic assay of total cholesterol. Multiwall carbon nanotubes (MWNTs), vertically aligned on a silicon platform, promote heterogeneous electron transfer between the enzyme and the working electrode. Surface modification of the MWNT with a biocompatible polymer, polyvinyl alcohol (PVA), converted the hydrophobic nanotube surface into a highly hydrophilic one, which facilitates efficient attachment of biomolecules. The fabricated working electrodes showed a linear relationship between cholesterol concentration and the output signal. The efficacy of the multiwall carbon nanotubes in promoting heterogeneous electron transfer was evident by distinct electrochemical peaks and higher signal-to-noise ratio as compared to the Au electrode with identical enzyme immobilization protocol. The selectivity of the cholesterol sensor in the presence of common interferents present in human blood, e.g. uric acid, ascorbic acid and glucose, is also reported.

  2. Synthesis of PbI(2) single-layered inorganic nanotubes encapsulated within carbon nanotubes.

    Science.gov (United States)

    Cabana, Laura; Ballesteros, Belén; Batista, Eudar; Magén, César; Arenal, Raúl; Oró-Solé, Judith; Rurali, Riccardo; Tobias, Gerard

    2014-04-02

    The template assisted growth of single-layered inorganic nanotubes is reported. Single-crystalline lead iodide single-layered nanotubes have been prepared using the inner cavities of carbon nanotubes as hosting templates. The diameter of the resulting inorganic nanotubes is merely dependent on the diameter of the host. This facile method is highly versatile opening up new horizons in the preparation of single-layered nanostructures. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. High-performance supercapacitors of Cu-based porous coordination polymer nanowires and the derived porous CuO nanotubes.

    Science.gov (United States)

    Wu, Meng-Ke; Zhou, Jiao-Jiao; Yi, Fei-Yan; Chen, Chen; Li, Yan-Li; Li, Qin; Tao, Kai; Han, Lei

    2017-12-12

    Electrode materials for supercapacitors with one-dimensional porous nanostructures, such as nanowires and nanotubes, are very attractive for high-efficiency storage of electrochemical energy. Herein, ultralong Cu-based porous coordination polymer nanowires (copper-l-aspartic acid) were used as the electrode material for supercapacitors, for the first time. The as-prepared material exhibits a high specific capacitance of 367 F g -1 at 0.6 A g -1 and excellent cycling stability (94% retention over 1000 cycles). Moreover, porous CuO nanotubes were successfully fabricated by the thermal decomposition of this nanowire precursor. The CuO nanotube exhibits good electrochemical performance with high rate capacity (77% retention at 12.5 A g -1 ) and long-term stability (96% retention over 1000 cycles). The strategy developed here for the synthesis of porous nanowires and nanotubes can be extended to the construction of other electrode materials for more efficient energy storage.

  4. Hardness of high-pressure high-temperature treated single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Kawasaki, S.; Nojima, Y.; Yokomae, T.; Okino, F.; Touhara, H.

    2007-01-01

    We have performed high-pressure high-temperature (HPHT) treatments of high quality single-walled carbon nanotubes (SWCNTs) over a wide pressure-temperature range up to 13 GPa-873 K and have investigated the hardness of the HPHT-treated SWCNTs using a nanoindentation technique. It was found that the hardness of the SWCNTs treated at pressures greater than 11 GPa and at temperatures higher than 773 K is about 10 times greater than that of the SWCNTs treated at low temperature. It was also found that the hardness change of the SWCNTs is related to the structural change by the HPHT treatments which was based on synchrotron X-ray diffraction measurements

  5. A Study on Aspect Ratio of Heat Dissipation Fin for the Heat Dissipation Performance of Ultra Constant Discharge Lamp

    Science.gov (United States)

    Ko, Dong Guk; Cong Ge, Jun; Im, Ik Tae; Choi, Nag Jung; Kim, Min Soo

    2018-01-01

    In this study, we analyzed the heat dissipation performance of UCD lamp ballast fin with various aspect ratios. The minimum grid size was 0.02 mm and the number of grid was approximately 11,000. In order to determine the influence of the aspect ratio on the heat dissipation performance of UCD lamp ballast fin, the heat transfer area of the fin was kept constant at 4 mm2. The aspect ratios of the fin were 2 mm: 2 mm (basic model), 1.5 mm: 2.7 mm and 2.7 mm: 1.5 mm, respectively. The heat flux and heat flux time at fin were kept constant at 1×105 W/m2 and 10 seconds, respectively. The heat dissipation performance by the fin was the best at an aspect ratio of 1.5 mm: 2.7 mm.

  6. Morphology and growth of titania nanotubes. Nanostructuring and applications

    Energy Technology Data Exchange (ETDEWEB)

    Albu, Sergiu P.

    2012-10-26

    this nanostructure. It draws attention to important aspects that should be considered when using organic electrolytes, poses specific questions regarding the electrochemical methods and provides some solutions to them. The second part is focused on the growth of TiO{sub 2} nanotubes under different conditions. This part deals with a wide range of parameters that influence the formation of nanotubes, their chemical composition, geometry, etc. The most important factors in nanotube growth were found to be the applied voltage, water content, temperature and background electrolyte. Oxidation and metal ion dissolution are reactions governing the anodic process and the efficiency of oxide growth which is directly connected with these reactions determines whether self-ordering takes place or not. Many high-end technologies such as scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy were adopted for the detailed characterization of the nanotubes. In the third part, the crystallization of ''as grown'' amorphous TiO{sub 2} nanotubes is addressed. In addition to the influence of well-known annealing parameters (final temperature, heating ramp-rate) on nanotube crystallization, some specific aspects are provided which may drastically affect the efficiency of devices based on TiO{sub 2} nanotubes. Here it is shown that heat treatment can be successfully used to control the size of the anatase crystals inside nanotube walls or to alter completely the nanotubular structure. In the last chapter, advanced nanostructures based on TiO{sub 2} nanotubes are investigated. Many of these nanostructures are formed via manipulation of electrochemical parameters such as the applied voltage or the chemical etching. Novel ''nanolace'' and ''bamboo-type nanotube'' structures are shown and characterized here. In order to demonstrate the advantageous features of these nanotubes, some

  7. Experimental simulation of air quality in street canyon under changes of building orientation and aspect ratio.

    Science.gov (United States)

    Yassin, Mohamed F; Ohba, Masaake

    2012-09-01

    To assist validation of numerical simulations of urban pollution, air quality in a street canyon was investigated using a wind tunnel as a research tool under neutral atmospheric conditions. We used tracer gas techniques from a line source without buoyancy. Ethylene (C(2)H(4)) was used as the tracer gas. The street canyon model was formed of six parallel building rows of the same length. The flow and dispersion field was analyzed and measured using a hot-wire anemometer with split fiber probe and fast flame ionization detector. The diffusion flow field in the boundary layer within the street canyon was examined at different locations, with varying building orientations (θ=90°, 112.5°, 135° and 157.5°) and street canyon aspect ratios (W/H=1/2, 3/4 and 1) downwind of the leeward side of the street canyon model. Results show that velocity increases with aspect ratio, and with θ>90°. Pollutant concentration increases as aspect ratio decreases. This concentration decreases exponentially in the vertical direction, and decreases as θ increases from 90°. Measured pollutant concentration distributions indicate that variability of building orientation and aspect ratio in the street canyon are important for estimating air quality in the canyon. The data presented here can be used as a comprehensive database for validation of numerical models.

  8. Toroidal Dielectric Tensor-Operator for Arbitrary Aspect-Ratio and Wave Frequency an Anisotropic-Resistivity MHD Formulation

    International Nuclear Information System (INIS)

    Komoshvili, K.; Cuperman, S.

    1998-01-01

    Motivated by the recently increased interest in small aspect ratio tokamaks, we have derived a 2(1/2)D dielectric tensor-operator which can properly describe the plasma response to r.f. waves, under conditions prevailing in the pre-heated stages of arbitrary aspect ratio, axisymmetric toroidal fusion devices. The derived dielectric tensor elements are based on a two-fluid, weakly collisional plasma description, with the Hall term included. They are characterized by the following features: (i) They are cast in a form evidencing the dielectric (non-operator) and operator contributions - the latter being due to the toroidal structure of the V-operators present in Maxwell's equations, on the background of equilibrium currents and pressure gradients; (ii) They are not subject to any I imitation on the (relative) magnitude of the toroidal effects - no expansion in the inverse aspect ratio parameter is used for their derivation; (iii) They include anisotropic - parallel and perpendicular to the magnetic field - contributions to the plasma resistivity; (iv) They are not Iimited by any restriction on the (relative) value of the wave frequency. The explicit, physically transparent formulation of the dielectric tensor is intended for the numerical solution of the full (E ll ≠ 0) wave equation and subsequently, evaluation of the Alfven wave current drive in small aspect ratio tokamaks

  9. Numerical modeling on air quality in an urban environment with changes of the aspect ratio and wind direction.

    Science.gov (United States)

    Yassin, Mohamed F

    2013-06-01

    Due to heavy traffic emissions within an urban environment, air quality during the last decade becomes worse year by year and hazard to public health. In the present work, numerical modeling of flow and dispersion of gaseous emissions from vehicle exhaust in a street canyon were investigated under changes of the aspect ratio and wind direction. The three-dimensional flow and dispersion of gaseous pollutants were modeled using a computational fluid dynamics (CFD) model which was numerically solved using Reynolds-averaged Navier-Stokes (RANS) equations. The diffusion flow field in the atmospheric boundary layer within the street canyon was studied for different aspect ratios (W/H=1/2, 3/4, and 1) and wind directions (θ=90°, 112.5°, 135°, and 157.5°). The numerical models were validated against wind tunnel results to optimize the turbulence model. The numerical results agreed well with the wind tunnel results. The simulation demonstrated that the minimum concentration at the human respiration height within the street canyon was on the windward side for aspect ratios W/H=1/2 and 1 and wind directions θ=112.5°, 135°, and 157.5°. The pollutant concentration level decreases as the wind direction and aspect ratio increase. The wind velocity and turbulence intensity increase as the aspect ratio and wind direction increase.

  10. Investigating the Inter-Tube Conduction Mechanism in Polycarbonate Nanocomposites Prepared with Conductive Polymer-Coated Carbon Nanotubes

    KAUST Repository

    Ventura, Isaac Aguilar

    2015-12-16

    A well-known strategy to improve the electrical conductivity of polymers is to dope them with high-aspect-ratio and conductive nanoparticles such as carbon nanotubes (CNTs). However, these nanocomposites also exhibit undesirable properties such as damage-sensitive and history-dependent conductivity because their macroscopic electrical conductivity is largely determined by the tunneling effect at the tube/tube interface. To reduce these issues, new nanocomposites have been developed with CNTs that have been coated with a conductive layer of poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT/PSS). It has been posited that the insulating region between the CNTs is replaced by a conductive polymer bridge; this has not been proven up to now. We propose here to investigate in-depth how the macroscopic conductivity of these materials is changing when (1) varying the frequency of the electrical loading (impedance spectroscopy), (2) varying the mechanical hydrostatic pressure, and (3) varying the voltage of the electrical loading. The response is systematically compared to the one of conventional carbon nanotube/polycarbonate (CNT/PC) nanocomposites so we can clarify how efficiently the tunneling effect is suppressed from these composites. The objective is to elucidate further the mechanism for conduction in such material formulations.

  11. Free vibration of a single-walled carbon nanotube containing a fluid flow using the Timoshenko beam model

    International Nuclear Information System (INIS)

    Chang, W.-J.; Lee, H.-L.

    2009-01-01

    The flexural vibration of the fluid-conveying single-walled carbon nanotube (SWCNT) is derived by the Timoshenko beam model, including rotary inertia and transverse shear deformation. The effects of the flow velocity and the aspect ratio of length to diameter on the vibration frequency and mode shape of the SWCNT are analyzed. Results show that the effects of rotary inertia and transverse shear deformation result in a reduction of the vibration frequencies, especially for higher modes of vibration and short nanotubes. The frequency is also compared with the previous study based on Euler beam model. In addition, if the ratio of length to diameter increased to 60, the influence of the shear deformation and rotary inertia on the mode shape and the resonant frequencies can be neglected. However, the influence is very obvious when the ratio decreased to 20. As the flow velocity of the fluid increases in the vicinity of 2π, the SWCNT reveals the divergence instability. It regains stability when the flow velocity reaches about 9. As the velocity increases further, the SWCNT undergoes a coupled-mode flutter and results in a larger amplitude

  12. Investigation of Chirality Selection Mechanism of Single-Walled Carbon Nanotube

    Science.gov (United States)

    2015-07-17

    Final 3. DATES COVERED (From - To) 01-June-2014 to 31-May-2015 4. TITLE AND SUBTITLE Investigation of Chirality Selection Mechanism of...of two significant mechanistic aspects of carbon nanotube (CNT) array growth under chemical vapor deposition conditions: chirality selectivity and...affected by the morphological evolution of catalyst particles. 15. SUBJECT TERMS Carbon Nanotubes, Chirality , Processing, Catalysis

  13. Hydrogen adsorption in metal-decorated silicon carbide nanotubes

    Science.gov (United States)

    Singh, Ram Sevak; Solanki, Ankit

    2016-09-01

    Hydrogen storage for fuel cell is an active area of research and appropriate materials with excellent hydrogen adsorption properties are highly demanded. Nanotubes, having high surface to volume ratio, are promising storage materials for hydrogen. Recently, silicon carbide nanotubes have been predicted as potential materials for future hydrogen storage application, and studies in this area are ongoing. Here, we report a systematic study on hydrogen adsorption properties in metal (Pt, Ni and Al) decorated silicon carbide nanotubes (SiCNTs) using first principles calculations based on density functional theory. The hydrogen adsorption properties are investigated by calculations of adsorption energy, electronic band structure, density of states (DOS) and Mulliken charge population analysis. Our findings show that hydrogen adsorptions on Pt, Ni and Al-decorated SiCNTs undergo spontaneous exothermic reactions with significant modulation of electronic structure of SiCNTs in all cases. Importantly, according to the Mulliken charge population analysis, dipole-dipole interaction causes chemisorptions of hydrogen in Pt, Ni and Al decorated SiCNTs with formation of chemical bonds. The study is a platform for the development of metal decorated SiCNTs for hydrogen adsorption or hydrogen storage application.

  14. Carbon nanotubes as cancer therapeutic carriers and mediators

    Science.gov (United States)

    Son, Kuk Hui; Hong, Jeong Hee; Lee, Jin Woo

    2016-01-01

    Carbon nanotubes (CNTs) have received increasing attention in biomedical fields because of their unique structures and properties, including high aspect ratios, large surface areas, rich surface chemical functionalities, and size stability on the nanoscale. Particularly, they are attractive as carriers and mediators for cancer therapy. Through appropriate functionalization, CNTs have been used as nanocarriers for anticancer drugs including doxorubicin, camptothecin, carboplatin, cisplatin, paclitaxel, Pt(II), and Pt(IV), and genes including plasmid DNA, small-interfering RNA, oligonucleotides, and RNA/DNA aptamers. CNTs can also deliver proteins and immunotherapy components. Using combinations of light energy, they have also been applied as mediators for photothermal therapy and photodynamic therapy to directly destroy cancer cells without severely damaging normal tissue. If limitations such as a long-term cytotoxicity in the body, lack of size uniformity during the synthetic process, loading deviations for drug–CNT complexes, and release controllability at the target point are overcome, CNTs will become one of the strongest tools that are available for various other biomedical fields as well as for cancer therapy. PMID:27785021

  15. Crosslinked Carbon Nanotubes/Polyaniline Composites as a Pseudocapacitive Material with High Cycling Stability

    Directory of Open Access Journals (Sweden)

    Dong Liu

    2015-06-01

    Full Text Available The poor cycling stability of polyaniline (PANI limits its practical application as a pseudocapacitive material due to the volume change during the charge-discharge procedure. Herein, crosslinked carbon nanotubes/polyaniline (C-CNTs/PANI composites had been designed by the in situ chemical oxidative polymerization of aniline in the presence of crosslinked carbon nanotubes (C-CNTs, which were obtained by coupling of the functionalized carbon nanotubes with 1,4-benzoquinone. The composite showed a specific capacitance of 294 F/g at the scan rate of 10 mV/s, and could retain 95% of its initial specific capacitance after 1000 CV cycles. Such high electrochemical cycling stability resulting from the crosslinked skeleton of the C-CNTs makes them potential electrode materials for a supercapacitor.

  16. Effect of Collector Aspect Ratio on the Thermal Performance of Wavy Finned Absorber Solar Air Heater

    OpenAIRE

    Abhishek Priyam; Prabha Chand

    2016-01-01

    A theoretical investigation on the effect of collector aspect ratio on the thermal performance of wavy finned absorber solar air heaters has been performed. For the constant collector area, the various performance parameters have been calculated for plane and wavy finned solar air heaters. It has been found that the performance of wavy finned solar air heater improved with the increase in the collector aspect ratio. The performance of wavy finned solar air heater has been found 30 percent hig...

  17. Titania nanotubes with adjustable dimensions for drug reservoir sites and enhanced cell adhesion

    Energy Technology Data Exchange (ETDEWEB)

    Çalışkan, Nazlı; Bayram, Cem; Erdal, Ebru; Karahaliloğlu, Zeynep; Denkbaş, Emir Baki, E-mail: denkbas@hacettepe.edu.tr

    2014-02-01

    This study aims to generate a bactericidal agent releasing surface via nanotube layer on titanium metal and to investigate how aspect ratio of nanotubes affects drug elution time and cell proliferation. Titania nanotube layers were generated on metal surfaces by anodic oxidation at various voltage and time parameters. Gentamicin loading was carried out via simple pipetting and the samples were tested against S. aureus for the efficacy of the applied modification. Drug releasing time and cell proliferation were also tested in vitro. Titania nanotube layers with varying diameters and lengths were prepared after anodization and anodizing duration was found as the most effective parameter for amount of loaded drug and drug releasing time. Drug elution lasted up to 4 days after anodizing for 80 min of the samples, whereas release completed in 24 h when the samples were anodized for 20 min. All processed samples had bactericidal properties against S. aureus organism except unmodified titanium, which was also subjected to drug incorporation step. The anodization also enhanced water wettability and cell adhesion results. Anodic oxidation is an effective surface modification to enhance tissue–implant interactions and also resultant titania layer can act as a drug reservoir for the release of bactericidal agents. The use of implants as local drug eluting devices is promising but further in vivo testing is required. - Highlights: • Titanium surfaces were anodized and a nanotubular titania layer was obtained. • Drug eluting time was found to be increasing with anodizaton time. • Varying nanotube diameters has no effect in drug elution time but amount of incorporated drug.

  18. Titania nanotubes with adjustable dimensions for drug reservoir sites and enhanced cell adhesion

    International Nuclear Information System (INIS)

    Çalışkan, Nazlı; Bayram, Cem; Erdal, Ebru; Karahaliloğlu, Zeynep; Denkbaş, Emir Baki

    2014-01-01

    This study aims to generate a bactericidal agent releasing surface via nanotube layer on titanium metal and to investigate how aspect ratio of nanotubes affects drug elution time and cell proliferation. Titania nanotube layers were generated on metal surfaces by anodic oxidation at various voltage and time parameters. Gentamicin loading was carried out via simple pipetting and the samples were tested against S. aureus for the efficacy of the applied modification. Drug releasing time and cell proliferation were also tested in vitro. Titania nanotube layers with varying diameters and lengths were prepared after anodization and anodizing duration was found as the most effective parameter for amount of loaded drug and drug releasing time. Drug elution lasted up to 4 days after anodizing for 80 min of the samples, whereas release completed in 24 h when the samples were anodized for 20 min. All processed samples had bactericidal properties against S. aureus organism except unmodified titanium, which was also subjected to drug incorporation step. The anodization also enhanced water wettability and cell adhesion results. Anodic oxidation is an effective surface modification to enhance tissue–implant interactions and also resultant titania layer can act as a drug reservoir for the release of bactericidal agents. The use of implants as local drug eluting devices is promising but further in vivo testing is required. - Highlights: • Titanium surfaces were anodized and a nanotubular titania layer was obtained. • Drug eluting time was found to be increasing with anodizaton time. • Varying nanotube diameters has no effect in drug elution time but amount of incorporated drug

  19. Investigation of the influence of geometric parameters of carbon nanotube arrays on their adhesion properties

    Science.gov (United States)

    Il’ina, M. V.; Konshin, A. A.; Il’in, O. I.; Rudyk, N. N.; Fedotov, A. A.; Ageev, O. A.

    2018-03-01

    The results of experimental studies of adhesion of carbon nanotube (CNT) arrays with different geometric parameters and orientations using atomic-force microscopy are presented. The adhesion values of CNT arrays were determined, which were from 82 to 1315 nN depending on the parameters of the array. As a result, it was established that the adhesion of a CNT array increases with an increase in branching and disorientation of the array, as well as with the growth of the aspect ratio of CNTs in the array.

  20. Nanocomposite fibers and film containing polyolefin and surface-modified carbon nanotubes

    Science.gov (United States)

    Chu,Benjamin; Hsiao, Benjamin S.

    2010-01-26

    Methods for modifying carbon nanotubes with organic compounds are disclosed. The modified carbon nanotubes have enhanced compatibility with polyolefins. Nanocomposites of the organo-modified carbon nanotubes and polyolefins can be used to produce both fibers and films having enhanced mechanical and electrical properties, especially the elongation-to-break ratio and the toughness of the fibers and/or films.