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Sample records for tetrahedral amorphous carbon

  1. Mechanical dissipation at elevated temperatures in tetrahedral amorphous carbon.

    Energy Technology Data Exchange (ETDEWEB)

    Sullivan, John P.; Friedmann, Thomas Aquinas; Czaplewski, David A.; Wendt, Joel Robert

    2005-05-01

    We have measured the temperature dependence of mechanical dissipation in tetrahedral amorphous carbon flexural and torsional resonators over the temperature range from 300 to 1023 K. The mechanical dissipation was found to be controlled by defects within the material, and the magnitude and temperature dependence of the dissipation were found to depend on whether flexural or torsional vibrational modes were excited. The defects that were active under flexural stresses have a relatively flat concentration from 0.4 to 0.7 eV with an ever increasing defect concentration up to 1.9 eV. Under shear stresses (torsion), the defect activation energies increase immediately beginning at 0.4 eV, with increasing defect concentration at higher energies.

  2. Stress reduction dependent on incident angles of carbon ions in ultrathin tetrahedral amorphous carbon films

    Science.gov (United States)

    Xu, Shipeng; Li, Xiaowei; Huang, Meidong; Ke, Peiling; Wang, Aiying

    2014-04-01

    We presented the combined experimental and simulation study on stress evolution as a function of incident angles of carbon ions for the ultrathin tetrahedral amorphous carbon films (ta-C). The residual stress was found about 3.6 ± 0.1 GPa for the incident angle of C ions with range of 0°-30°, while it decreased significantly to 2.8 GPa with the incident angle of 60°. Different with the previous reports, noted that in this case both the sp3 content and mechanical properties of film were not deteriorated. Taking molecular dynamics simulation, it was in particularly concluded that the critical relaxation of distorted C-sp3 bond lengths and bond angles played key role on the unusual stress reduction mechanism. The results provide a route to fabricate the ultrathin ta-C films with low stress and high hardness for the precision wear resistant applications.

  3. Microstructure and tribological performance of self-lubricating diamond/tetrahedral amorphous carbon composite film

    Science.gov (United States)

    Chen, Xinchun; Peng, Zhijian; Yu, Xiang; Fu, Zhiqiang; Yue, Wen; Wang, Chengbiao

    2011-02-01

    In order to smooth the rough surface and further improve the wear-resistance of coarse chemical vapor deposition diamond films, diamond/tetrahedral amorphous carbon composite films were synthesized by a two-step preparation technique including hot-filament chemical vapor deposition for polycrystalline diamond (PCD) and subsequent filtered cathodic vacuum arc growth for tetrahedral amorphous carbon (ta-C). The microstructure and tribological performance of the composite films were investigated by means of various characterization techniques. The results indicated that the composite films consisted of a thick well-grained diamond base layer with a thickness up to 150 μm and a thin covering ta-C layer with a thickness of about 0.3 μm, and sp3-C fraction up to 73.93%. Deposition of a smooth ta-C film on coarse polycrystalline diamond films was proved to be an effective tool to lower the surface roughness of the polycrystalline diamond film. The wear-resistance of the diamond film was also enhanced by the self-lubricating effect of the covering ta-C film due to graphitic phase transformation. Under dry pin-on-disk wear test against Si3N4 ball, the friction coefficients of the composite films were much lower than that of the single PCD film. An extremely low friction coefficient (∼0.05) was achieved for the PCD/ta-C composite film. Moreover, the addition of Ti interlayer between the ta-C and the PCD layers can further reduce the surface roughness of the composite film. The main wear mechanism of the composite films was abrasive wear.

  4. Effect of Focussed Vacuum ARC Plasma Deposition on the Properties of Tetrahedral Amorphous Carbon Films

    Science.gov (United States)

    Chua, Daniel H. C.; Teo, K. B. K.; Tsai, T. H.; Robertson, J.; Milne, W. I.

    We have investigated the effect of using a magnetic field to confine and focus the plasma in a Filtered Cathodic Vacuum Arc (FCVA) deposition system used for the preparation of tetrahedrally bonded amorphous carbon (ta-C) thin films. The design of the magnetic field is such that the plasma can be confined into a high-density focussed spot or de-focussed into a lower density wide beam. Increasing the magnetic field directly increases the plasma density and thus increases the deposition rate. The ta-C films grown in the magnetic field were subsequently characterised. EELS and Raman measurement were used to measure the sp3/sp2 ratio and UV-vis spectroscopy for optical bandgap studies. The intrinsic stress and I-V characteristics of the thin films were also studied. The results show that it is possible to deposit the films at rates as high as 2.5 nm/sec without adversely affecting the material properties.

  5. Thickness dependent electronic structure of ultra-thin tetrahedral amorphous carbon (ta-C) films

    Energy Technology Data Exchange (ETDEWEB)

    Soin, Navneet [Nanotechnology and Integrated Bioengineering Centre (NIBEC), University of Ulster at Jordanstown, Shore Road, Newtownabbey BT37 0QB (United Kingdom); Roy, Susanta Sinha, E-mail: sinharoy@ualberta.ca [Micro and Nano-Scale Transport Laboratory, Department of Mechanical Engineering, University of Alberta, Edmonton, T6G 2G8 (Canada); Ray, Sekhar Chandra [School of Physics, University of the Witwatersrand, Private bag 3, Wits 2050, Johannesburg (South Africa); Lemoine, Patrick; Rahman, Md. Anisur; Maguire, Paul D. [Nanotechnology and Integrated Bioengineering Centre (NIBEC), University of Ulster at Jordanstown, Shore Road, Newtownabbey BT37 0QB (United Kingdom); Mitra, Sushanta K. [Micro and Nano-Scale Transport Laboratory, Department of Mechanical Engineering, University of Alberta, Edmonton, T6G 2G8 (Canada); McLaughlin, James A. [Nanotechnology and Integrated Bioengineering Centre (NIBEC), University of Ulster at Jordanstown, Shore Road, Newtownabbey BT37 0QB (United Kingdom)

    2012-01-31

    Microstructural properties of ultrathin (1-10 nm) tetrahedral amorphous carbon (ta-C) films are investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, X-ray Photoelectron Spectroscopy, Raman spectroscopy and Atomic Force Microscopy (AFM). The CK-edge NEXAFS spectra of 1 nm ta-C films provided evidence of surface defects (C-H bonds) which rapidly diminish with increasing film thickness. A critical thickness for stabilization of largely sp{sup 3} matrix structure distorted by sp{sup 2} sites is observed via the change of {pi}*C=C peak behavior. Meanwhile, an increase in the film thickness promotes an enhancement in sp{sup 3} content, the film roughness remains nearly constant as probed by spectroscopic techniques and AFM, respectively. The effect of thickness on local bonding states of ultrathin ta-C films proves to be the limiting factor for their potential use in magnetic and optical storage devices. - Highlights: Black-Right-Pointing-Pointer Filtered Cathodic Vacuum Arc deposited ultra-thin ta-C films (1-10 nm thick). Black-Right-Pointing-Pointer CK-edge NEXAFS provides evidence of surface defects (C-H bonds). Black-Right-Pointing-Pointer Concentration of C-H surface defects decreases with increasing thickness. Black-Right-Pointing-Pointer {pi}*{sub C=C} behavior suggestive of rise and fall of sp{sup 2} bonding configuration. Black-Right-Pointing-Pointer Critical thickness required for stability of sp{sup 3} distorted sp{sup 2} structures.

  6. Effect of tetrahedral amorphous carbon coating on the resistivity and wear of single-walled carbon nanotube network

    Energy Technology Data Exchange (ETDEWEB)

    Iyer, Ajai, E-mail: ajai.iyer@aalto.fi; Etula, Jarkko; Liu, Xuwen; Koskinen, Jari [Department of Materials Science and Engineering, School of Chemical Technology, Aalto University, P.O. Box 16200, 00076 Espoo (Finland); Kaskela, Antti; Kauppinen, Esko I. [NanoMaterials Group, Department of Applied Physics, School of Science, Aalto University, P.O. Box 15100, 00076 Espoo (Finland); Novikov, Serguei [Department of Micro and Nanosciences, Aalto University, P.O. Box 13500, 00076 Aalto (Finland)

    2016-05-14

    Single walled carbon nanotube networks (SWCNTNs) were coated by tetrahedral amorphous carbon (ta-C) to improve the mechanical wear properties of the composite film. The ta-C deposition was performed by using pulsed filtered cathodic vacuum arc method resulting in the generation of C+ ions in the energy range of 40–60 eV which coalesce to form a ta-C film. The primary disadvantage of this process is a significant increase in the electrical resistance of the SWCNTN post coating. The increase in the SWCNTN resistance is attributed primarily to the intrinsic stress of the ta-C coating which affects the inter-bundle junction resistance between the SWCNTN bundles. E-beam evaporated carbon was deposited on the SWCNTNs prior to the ta-C deposition in order to protect the SWCNTN from the intrinsic stress of the ta-C film. The causes of changes in electrical resistance and the effect of evaporated carbon thickness on the changes in electrical resistance and mechanical wear properties have been studied.

  7. Highly conductive ion tracks in tetrahedral amorphous carbon by irradiation with 30 MeV C{sub 60} projectiles

    Energy Technology Data Exchange (ETDEWEB)

    Krauser, J [Hochschule Harz, University of Applied Sciences, 38855 Wernigerode (Germany); Nix, A-K; Gehrke, H-G; Hofsaess, H [II Institute of Physics, University of Goettingen, 37077 Goettingen (Germany); Trautmann, C [Helmholtzzentrum fuer Schwerionenforschung, 64291 Darmstadt (Germany); Weidinger, A, E-mail: jkrauser@hs-harz.de [Helmholtz-Zentrum Berlin fuer Materialien und Energie, 14109 Berlin (Germany)

    2011-08-15

    Electrically conducting ion tracks are produced when high-energy heavy ions pass through a layer of tetrahedral amorphous carbon (ta-C). The tracks are embedded in the insulating ta-C matrix and have a diameter of about 8 nm. Earlier studies showed that the electrical currents through individual tracks produced with Au and U projectiles exhibit rather large track-to-track fluctuations. In striking contrast, 30 MeV C{sub 60} cluster ions are shown to generate conducting tracks of very narrow conductivity distributions. Their current-versus-voltage curves are linear at room temperature. We also investigated ta-C films doped with B, N, Cu and Fe at a concentration of 1 or 2 at.%. In particular, Cu- and Fe-doped samples show increased ion track conductivity.

  8. Conductive tracks of 30-MeV C{sub 60} clusters in doped and undoped tetrahedral amorphous carbon

    Energy Technology Data Exchange (ETDEWEB)

    Krauser, J., E-mail: jkrauser@hs-harz.de [Harz University of Applied Sciences, 38855 Wernigerode (Germany); Gehrke, H.-G.; Hofsäss, H. [II. Institute of Physics, University of Göttingen, 37077 Göttingen (Germany); Trautmann, C. [Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt (Germany); Technische Universität Darmstadt, 64287 Darmstadt (Germany); Weidinger, A. [Helmholtz-Zentrum Berlin GmbH, 14109 Berlin (Germany)

    2013-07-15

    In insulating tetrahedral amorphous carbon (ta-C), the irradiation with 30-MeV C{sub 60} cluster ions leads to the formation of well conducting tracks. While electrical currents through individual tracks produced with monoatomic projectiles (e.g. Au or U) often exhibit rather large track to track fluctuations, C{sub 60} clusters are shown to generate highly conducting tracks with very narrow current distributions. Additionally, all recorded current–voltage curves show linear characteristics. These findings are attributed to the large specific energy loss dE/dx of the 30-MeV C{sub 60} clusters. We also investigated C{sub 60} tracks in ta-C films which were slightly doped with B, N or Fe during film growth. Doping apparently increases the ion track conductivity. However, at the same time the insulating characteristics of the pristine ta-C film can be reduced. The present C{sub 60} results are compared with data from earlier experiments with monoatomic heavy ion beams. The investigations were performed by means of atomic force microscopy including temperature dependent conductivity measurements of single ion tracks.

  9. Conductivity enhancement of ion tracks in tetrahedral amorphous carbon by doping with N, B, Cu and Fe

    Energy Technology Data Exchange (ETDEWEB)

    Krauser, J., E-mail: jkrauser@hs-harz.de [Hochschule Harz, University of Applied Sciences, 38855 Wernigerode (Germany); Nix, A.-K., E-mail: anix@gwdg.de [II. Institute of Physics, University of Goettingen, 37077 Goettingen (Germany); Gehrke, H.-G., E-mail: hgehrke1@gwdg.de [II. Institute of Physics, University of Goettingen, 37077 Goettingen (Germany); Hofsaess, H., E-mail: hans.hofsaess@phys.uni-goettingen.de [II. Institute of Physics, University of Goettingen, 37077 Goettingen (Germany); Trautmann, C., E-mail: C.Trautmann@gsi.de [Helmholtzzentrum fuer Schwerionenforschung GmbH, 64291 Darmstadt (Germany); Weidinger, A., E-mail: alois.weidinger@berlin.de [Helmholtz-Zentrum Berlin GmbH, 14109 Berlin (Germany)

    2012-02-01

    Conducting ion tracks are formed when high-energy heavy ions (e.g. 1 GeV Au) pass through tetrahedral amorphous carbon (ta-C). These nanowires with a diameter of about 8 nm are embedded in the insulating ta-C matrix and of interest for various nanotechnological applications. Usually the overall conductivity of the tracks and the current/voltage characteristics (Ohmic or non-Ohmic) vary strongly from track to track, even when measured on the same sample, indicating that the track formation is neither complete nor homogeneous. To improve the track conductivity, doping of ta-C with N, B, Cu, or Fe is investigated. Beneficial changes in track conductivity after doping compete with a conductivity increase of the surrounding matrix material. Best results are achieved by incorporation of 1 at.% Cu, while for different reasons, the improvement of the tracks remains moderate for N, B, and Fe doping. Conductivity enhancement of the tracks is assumed to develop during the ion track formation process by an increased number of localized states which contribute to the current transport.

  10. Atomic-force-microscopy nanowriting on ultrathin tetrahedral amorphous carbon films

    Science.gov (United States)

    Pivovarov, Pavel A.; Zavedeev, Evgeny V.; Frolov, Vadim D.; Roch, Teja; Scheibe, Hans-Joachim; Pimenov, Sergei M.

    2016-11-01

    We report the atomic-force-microscopy (AFM)-based nanolithography writing of surface patterns on ultrathin (nanoletters') is demonstrated, depending on the magnitude and duration of the voltage pulses applied between the ta-C film and conductive probe, and the relative humidity of ambient air. It is found that the AFM tip-assisted nanowriting process occurring under (1) the presence of adsorbed water layers on the ta-C surface, (2) the applied voltage of >4 V, and (3) the contact pressures in the GPa range results in the formation of a novel carbon phase in a nm-thick surface layer characterized by the lower density, lower mechanical strength, lower electrical conductivity, and increased nanofriction as compared to the original film. The structure of the tip-modified nm-thick layer on the ta-C film is assumed to be a structure of graphite oxide which can be further modified in the presence of water under high contact pressures.

  11. Mixed-mode high-power impulse magnetron sputter deposition of tetrahedral amorphous carbon with pulse-length control of ionization

    Energy Technology Data Exchange (ETDEWEB)

    Tucker, M. D.; Marks, N. A. [Department of Physics and Astronomy, Curtin University, Perth, Western Australia 6102 (Australia); Ganesan, R.; Bilek, M. M. M.; McKenzie, D. R. [School of Physics, The University of Sydney, Sydney, New South Wales 2006 (Australia); McCulloch, D. G.; Partridge, J. G. [School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne, Victoria 3001 (Australia); Stueber, M.; Ulrich, S. [Karlsruhe Institute of Technology—KIT, Institute for Applied Materials—IAM, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2016-04-21

    High-power impulse magnetron sputtering (HiPIMS) is used to deposit amorphous carbon thin films with sp{sup 3} fractions of 13% to 82%. Increasing the pulse length results in a transition from conventional HiPIMS deposition to a “mixed-mode” in which an arc triggers on the target surface, resulting in a large flux of carbon ions. The films are characterized using X-ray photoelectron spectroscopy, Raman spectroscopy, ellipsometry, nanoindentation, elastic recoil detection analysis, and measurements of stress and contact angle. All properties vary in a consistent manner, showing a high tetrahedral character only for long pulses, demonstrating that mixed-mode deposition is the source of the high carbon ion flux. Varying the substrate bias reveals an “energy window” effect, where the sp{sup 3} fraction of the films is greatest for a substrate bias around −100 V and decreases for higher or lower bias values. In the absence of bias, the films' properties show little dependence on the pulse length, showing that energetic ions are the origin of the highly tetrahedral character.

  12. A comparison of mechanical properties of three MEMS materials - silicon carbide, ultrananocrystalline diamond, and hydrogen-free tetrahedral amorphous carbon (Ta-C)

    Energy Technology Data Exchange (ETDEWEB)

    Carlisle, John A. (Argonne National Laboratory, Argonne, IL); Moldovan, N. (Northwestern University, Evanston, IL); Xiao, Xingcheng (Argonne National Laboratory, Argonne, IL); Zorman, C. A. (Case Western Reserve University, Cleveland, OH); Mancini, D. C. (Argonne National Laboratory, Argonne, IL); Peng, B. (Northwestern University, Evanston, IL); Espinosa, H. D. (Northwestern University, Evanston, IL); Friedmann, Thomas Aquinas; Auciello, Orlando, (Argonne National Laboratory, Argonne, IL)

    2004-06-01

    Many MEMS devices are based on polysilicon because of the current availability of surface micromachining technology. However, polysilicon is not the best choice for devices where extensive sliding and/or thermal fields are applied due to its chemical, mechanical and tribological properties. In this work, we investigated the mechanical properties of three new materials for MEMS/NEMS devices: silicon carbide (SiC) from Case Western Reserve University (CWRU), ultrananocrystalline diamond (UNCD) from Argonne National Laboratory (ANL), and hydrogen-free tetrahedral amorphous carbon (ta-C) from Sandia National Laboratories (SNL). Young's modulus, characteristic strength, fracture toughness, and theoretical strength were measured for these three materials using only one testing methodology - the Membrane Deflection Experiment (MDE) developed at Northwestern University. The measured values of Young's modulus were 430GPa, 960GPa, and 800GPa for SiC, UNCD, and ta-C, repectively. Fracture toughness measurments resulted in values of 3.2, 4.5, and 6.2 MPa x m{sup 1/2}, respectively. The strengths were found to follow a Weibull distribution but their scaling was found to be controlled by different specimen size parameters. Therefore, a cross comparison of the strengths is not fully meaningful. We instead propose to compare their theoretical strengths as determined by employing Novozhilov fracture criterion. The estimated theoretical strength for SiC is 10.6GPa at a characteristic length of 58nm, for UNCD is 18.6GPa at a characteristic length of 37nm, and for ta-C is 25.4GPa at a characteristic length of 38nm. The techniques used to obtained these results as well as microscopic fractographic analyses are summarized in the article. We also highlight the importance of characterizing mechanical properties of MEMS materials by means of only one simple and accurate experimental technique.

  13. Tribological properties of amorphous hydrogenated (a-C:H) and hydrogen-free tetrahedral (ta-C) diamond-like carbon coatings under jatropha biodegradable lubricating oil at different temperatures

    Science.gov (United States)

    Mobarak, H. M.; Masjuki, H. H.; Mohamad, E. Niza; Kalam, M. A.; Rashedul, H. K.; Rashed, M. M.; Habibullah, M.

    2014-10-01

    The application of diamond-like carbon (DLC) coatings on automotive components is emerging as a favorable strategy to address the recent challenges in the industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, thereby improving their fuel efficiency and durability. The lubrication of ferrous materials can be enhanced by a large amount of unsaturated and polar components of oils. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetable oil should be investigated. A ball-on-plate tribotester was used to run the experiments. Stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC that slide against 440C stainless steel ball were used to create a ball-on-plate tribotester. The wear track was investigated through scanning electron microscopy. Energy dispersive and X-ray photoelectron spectroscopies were used to analyze the tribofilm inside the wear track. Raman analysis was performed to investigate the structural changes in the coatings. At high temperatures, the CoF in both coatings decreased. The wear rate, however, increased in the a-C:H but decreased in the ta-C DLC-coated plates. The CoF and the wear rate (coated layer and counter surface) were primarily influenced by the graphitization of the coating. Tribochemical films, such as polyphosphate glass, were formed in ta-C and acted as protective layers. Therefore, the wear rate of the ta-C DLC was lower than that of the-C:H DLC.

  14. Amorphous iron (II) carbonate

    DEFF Research Database (Denmark)

    Sel, Ozlem; Radha, A.V.; Dideriksen, Knud

    2012-01-01

    Abstract The synthesis, characterization and crystallization energetics of amorphous iron (II) carbonate (AFC) are reported. AFC may form as a precursor for siderite (FeCO3). The enthalpy of crystallization (DHcrys) of AFC is similar to that of amorphous magnesium carbonate (AMC) and more...

  15. Tribological properties of amorphous hydrogenated (a-C:H) and hydrogen-free tetrahedral (ta-C) diamond-like carbon coatings under jatropha biodegradable lubricating oil at different temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Mobarak, H.M., E-mail: mobarak.ho31@yahoo.com; Masjuki, H.H.; Mohamad, E. Niza, E-mail: edzrol@um.edu.my; Kalam, M.A.; Rashedul, H.K.; Rashed, M.M.; Habibullah, M.

    2014-10-30

    Highlights: • We tested a-C:H and ta-C DLC coatings as a function of temperature. • Jatropha oil contains large amounts of polar components that enhanced the lubricity of coatings. • CoF decreases with increasing temperature for both contacts. • Wear rate increases with increasing temperature in a-C:H and decreases in ta-C DLC. • At high temperature, ta-C coatings confer more protection than a-C:H coatings. - Abstract: The application of diamond-like carbon (DLC) coatings on automotive components is emerging as a favorable strategy to address the recent challenges in the industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, thereby improving their fuel efficiency and durability. The lubrication of ferrous materials can be enhanced by a large amount of unsaturated and polar components of oils. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetable oil should be investigated. A ball-on-plate tribotester was used to run the experiments. Stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC that slide against 440C stainless steel ball were used to create a ball-on-plate tribotester. The wear track was investigated through scanning electron microscopy. Energy dispersive and X-ray photoelectron spectroscopies were used to analyze the tribofilm inside the wear track. Raman analysis was performed to investigate the structural changes in the coatings. At high temperatures, the CoF in both coatings decreased. The wear rate, however, increased in the a-C:H but decreased in the ta-C DLC-coated plates. The CoF and the wear rate (coated layer and counter surface) were primarily influenced by the graphitization of the coating. Tribochemical films, such as polyphosphate glass, were formed in ta-C and acted as protective layers. Therefore, the wear rate of the ta-C DLC was lower than that of the-C:H DLC.

  16. Properties of amorphous carbon

    CERN Document Server

    2003-01-01

    Amorphous carbon has a wide range of properties that are primarily controlled by the different bond hydridisations possible in such materials. This allows for the growth of an extensive range of thin films that can be tailored for specific applications. Films can range from those with high transparency and are hard diamond-like, through to those which are opaque, soft and graphitic-like. Films with a high degree of sp3 bonding giving the diamond-like properties are used widely by industry for hard coatings. Application areas including field emission cathodes, MEMS, electronic devices, medical and optical coatings are now close to market. Experts in amorphous carbon have been drawn together to produce this comprehensive commentary on the current state and future prospects of this highly functional material.

  17. Memristive effects in oxygenated amorphous carbon nanodevices

    Science.gov (United States)

    Bachmann, T. A.; Koelmans, W. W.; Jonnalagadda, V. P.; Le Gallo, M.; Santini, C. A.; Sebastian, A.; Eleftheriou, E.; Craciun, M. F.; Wright, C. D.

    2018-01-01

    Computing with resistive-switching (memristive) memory devices has shown much recent progress and offers an attractive route to circumvent the von-Neumann bottleneck, i.e. the separation of processing and memory, which limits the performance of conventional computer architectures. Due to their good scalability and nanosecond switching speeds, carbon-based resistive-switching memory devices could play an important role in this respect. However, devices based on elemental carbon, such as tetrahedral amorphous carbon or ta-C, typically suffer from a low cycling endurance. A material that has proven to be capable of combining the advantages of elemental carbon-based memories with simple fabrication methods and good endurance performance for binary memory applications is oxygenated amorphous carbon, or a-CO x . Here, we examine the memristive capabilities of nanoscale a-CO x devices, in particular their ability to provide the multilevel and accumulation properties that underpin computing type applications. We show the successful operation of nanoscale a-CO x memory cells for both the storage of multilevel states (here 3-level) and for the provision of an arithmetic accumulator. We implement a base-16, or hexadecimal, accumulator and show how such a device can carry out hexadecimal arithmetic and simultaneously store the computed result in the self-same a-CO x cell, all using fast (sub-10 ns) and low-energy (sub-pJ) input pulses.

  18. Machine learning based interatomic potential for amorphous carbon

    Science.gov (United States)

    Deringer, Volker L.; Csányi, Gábor

    2017-03-01

    We introduce a Gaussian approximation potential (GAP) for atomistic simulations of liquid and amorphous elemental carbon. Based on a machine learning representation of the density-functional theory (DFT) potential-energy surface, such interatomic potentials enable materials simulations with close-to DFT accuracy but at much lower computational cost. We first determine the maximum accuracy that any finite-range potential can achieve in carbon structures; then, using a hierarchical set of two-, three-, and many-body structural descriptors, we construct a GAP model that can indeed reach the target accuracy. The potential yields accurate energetic and structural properties over a wide range of densities; it also correctly captures the structure of the liquid phases, at variance with a state-of-the-art empirical potential. Exemplary applications of the GAP model to surfaces of "diamondlike" tetrahedral amorphous carbon (ta -C) are presented, including an estimate of the amorphous material's surface energy and simulations of high-temperature surface reconstructions ("graphitization"). The presented interatomic potential appears to be promising for realistic and accurate simulations of nanoscale amorphous carbon structures.

  19. Amorphous Carbon-Boron Nitride Nanotube Hybrids

    Science.gov (United States)

    Kim, Jae Woo (Inventor); Siochi, Emilie J. (Inventor); Wise, Kristopher E. (Inventor); Lin, Yi (Inventor); Connell, John (Inventor)

    2016-01-01

    A method for joining or repairing boron nitride nanotubes (BNNTs). In joining BNNTs, the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures. In repairing BNNTs, the damaged site of the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures at the damage site.

  20. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    Science.gov (United States)

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Structural morphology of amorphous conducting carbon film

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 28; Issue 6. Structural ... Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique. X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite.

  2. Structural morphology of amorphous conducting carbon film

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique. X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite. This roughness increases with decrease in preparation temperature.

  3. Characterization of amorphous hydrogenated carbon films ...

    Indian Academy of Sciences (India)

    Amorphous hydrogenated carbon films (-C:H) on -type (100) silicon wafers were prepared with a middle frequency pulsed unbalanced magnetron sputtering technique (MFPUMST) at different ratios of methane–argon gases. The band characteristics, mechanical properties as well as refractive index were measured by ...

  4. Phase transitions in biogenic amorphous calcium carbonate

    Science.gov (United States)

    Gong, Yutao

    Geological calcium carbonate exists in both crystalline phases and amorphous phases. Compared with crystalline calcium carbonate, such as calcite, aragonite and vaterite, the amorphous calcium carbonate (ACC) is unstable. Unlike geological calcium carbonate crystals, crystalline sea urchin spicules (99.9 wt % calcium carbonate and 0.1 wt % proteins) do not present facets. To explain this property, crystal formation via amorphous precursors was proposed in theory. And previous research reported experimental evidence of ACC on the surface of forming sea urchin spicules. By using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), we studied cross-sections of fresh sea urchin spicules at different stages (36h, 48h and 72h after fertilization) and observed the transition sequence of three mineral phases: hydrated ACC → dehydrated ACC → biogenic calcite. In addition, we unexpectedly found hydrated ACC nanoparticles that are surrounded by biogenic calcite. This observation indicates the dehydration from hydrated ACC to dehydrated ACC is inhibited, resulting in stabilization of hydrated ACC nanoparticles. We thought that the dehydration was inhibited by protein matrix components occluded within the biomineral, and we designed an in vitro assay to test the hypothesis. By utilizing XANES-PEEM, we found that SM50, the most abundant occluded matrix protein in sea urchin spicules, has the function to stabilize hydrated ACC in vitro.

  5. Microstructural analyses of amorphic diamond, i-C, and amorphous carbon

    DEFF Research Database (Denmark)

    Collins, C. B.; Davanloo, F.; Jander, D.R.

    1992-01-01

    Recent experiments have identified the microstructure of amorphic diamond with a model of packed nodules of amorphous diamond expected theoretically. However, this success has left in doubt the relationship of amorphic diamond to other noncrystalline forms of carbon. This work reports the compara...

  6. Amorphous calcium carbonate particles form coral skeletons

    Science.gov (United States)

    Mass, Tali; Giuffre, Anthony J.; Sun, Chang-Yu; Stifler, Cayla A.; Frazier, Matthew J.; Neder, Maayan; Tamura, Nobumichi; Stan, Camelia V.; Marcus, Matthew A.; Gilbert, Pupa U. P. A.

    2017-09-01

    Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed “vital effects,” that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene-Eocene Thermal Maximum that occurred 56 Mya.

  7. Deposition of amorphous carbon-silver composites

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Zarco, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Circuito Exterior s/n, Ciudad Universitaria. 04510, Mexico D. F. Mexico (Mexico); Rodil, S.E., E-mail: ser42@iim.unam.m [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Circuito Exterior s/n, Ciudad Universitaria. 04510, Mexico D. F. Mexico (Mexico); Camacho-Lopez, M.A. [Facultad de Quimica, Universidad Autonoma del Estado de Mexico, Tollocan s/n, esq. Paseo Colon, Toluca, Estado de Mexico, 50110 (Mexico)

    2009-12-31

    Composites of amorphous carbon films and silver were deposited by co-sputtering, where the target (10 cm diameter) was of pure graphite with small inclusion of pure silver (less than 1 cm{sup 2}). The films were deposited under different powers, from 40 to 250 W, and different target-substrate distances. The substrate was earthed and rotated in order to obtain a uniform distribution of the silver content. The addition of the Ag piece into the target increased the deposition rate of the carbon films, which could be related to the higher sputter yield of the silver, but there seems to be also a contribution from a larger emission of secondary electrons from the Ag that enhances the plasma and therefore the sputtering process becomes more efficient. Scanning electron micrographs acquired using backscattered electrons showed that the silver was segregated from the carbon matrix, forming nanoparticles or larger clusters as the power was increased. The X-ray diffraction pattern showed that the silver was crystalline and the carbon matrix remained amorphous, although for certain conditions a peak attributed to fullerene-like structures was obtained. Finally, we used Raman spectroscopy to understand the bonding characteristics of the carbon-silver composites, finding that there are variations in the D/G ratio, which can be correlated to the observed structure and X-ray diffraction results.

  8. Protective amorphous carbon coatings on glass substrates

    Directory of Open Access Journals (Sweden)

    Kaspars Silins

    2017-11-01

    Full Text Available Thick amorphous carbon films were deposited by the Magnets-in-Motion (M-M rf linear hollow cathode at varying acetylene contents in Ar in a hybrid PVD/PE-CVD process directly on glass substrates. The hollow cathode plates manufactured from graphite were used as the PVD target. The measurements show that the films can reach thickness of up to 50 μm at deposition rates of up to 2.5 μm/min. Scratch test measurements confirm that well adhering films several μm thick can be achieved at C2H2 contents of up to 0.5%.

  9. Amorphous titania/carbon composite electrode materials

    Science.gov (United States)

    Vaughey, John T.; Jansen, Andrew; Joyce, Christopher D.

    2017-05-09

    An isolated salt comprising a compound of formula (H.sub.2X)(TiO(Y).sub.2) or a hydrate thereof, wherein X is 1,4-diazabicyclo[2.2.2]octane (DABCO), and Y is oxalate anion (C.sub.2O.sub.4.sup.-2), when heated in an oxygen-containing atmosphere at a temperature in the range of at least about 275.degree. C. to less than about 400.degree. C., decomposes to form an amorphous titania/carbon composite material comprising about 40 to about 50 percent by weight titania and about 50 to about 60 percent by weight of a carbonaceous material coating the titania. Heating the composite material at a temperature of about 400 to 500.degree. C. crystallizes the titania component to anatase. The titania materials of the invention are useful as components of the cathode or anode of a lithium or lithium ion electrochemical cell.

  10. Coaxial carbon plasma gun deposition of amorphous carbon films

    Science.gov (United States)

    Sater, D. M.; Gulino, D. A.; Rutledge, S. K.

    1984-01-01

    A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

  11. Unveiling descriptors for predicting the bulk modulus of amorphous carbon

    Science.gov (United States)

    Takahashi, Keisuke; Tanaka, Yuzuru

    2017-02-01

    Descriptors for the bulk modulus of amorphous carbon are investigated through the implementation of data mining where data sets are prepared using first-principles calculations. Data mining reveals that the number of bonds in each C atom and the density of amorphous carbon are found to be descriptors representing the bulk modulus. Support vector regression (SVR) within machine learning is implemented and descriptors are trained where trained SVR is able to predict the bulk modulus of amorphous carbon. An inverse problem, starting from the bulk modulus towards structural information of amorphous carbon, is performed and structural information of amorphous carbon is successfully predicted from the desired bulk modulus. Thus, treating several physics factors in multidimensional space allows for the prediction of physical phenomena. In addition, the reported approach proposes that "big data" can be generated from a small data set using machine learning if descriptors are well defined. This would greatly change how amorphous carbon would be treated and help accelerate further development of amorphous carbon materials.

  12. Novel low Wigner energy amorphous carbon-carbon composite

    Science.gov (United States)

    Dasgupta, Kinshuk; Prakash, Jyoti; Tripathi, B. M.

    2014-02-01

    A novel amorphous carbon-carbon composite has been developed using carbon black dispersed in carbonized phenolic resin matrix in order to avoid Wigner energy problem associated with graphite. The as prepared sample showed a density of 1320 kg m-3. This has been further densified by resin impregnation and chemical vapour infiltration. The effect of processing parameters on final density (1517 kg m-3) has been investigated. This composite possesses the compressive strength of 65 Mpa, coefficient of thermal expansion of 3 × 10-6 K-1 and the specific heat of 1.2 J g-1 K-1. This novel composite was subjected to 145 MeV Ne+6 heavy ion irradiation at different doses. The highest dose was kept at 3 × 10-4 dpa. The stored energy in the composite was found to be 212 J g-1 at the highest dose of irradiation, which is much below than that of graphite. The composite remained amorphous after irradiation as confirmed by X-ray diffraction.

  13. Au nanoparticles improve amorphous carbon to be gas sensors

    Science.gov (United States)

    Liu, Keng-Wen; Lee, Jian-Heng; Chou, Hsiung; Lin, Tzu-Ching; Lin, Si-Ting; Shih-Jye Sun Collaboration

    In order to make the amorphous carbon possess the gas sensing capability transferring some sp3 orbits to sp2 is necessary. It is proposed that the metallic materials having a large charge exchange with sp3 carbon orbits are being catalysts to transfer the carbon orbits. We found embedding gold nanoparticles to the amorphous carbon will induce many compact sp2 orbits around the nanoparticles, which make the amorphous carbon be the candidate material for the gas sensors. The orbits of amorphous carbon near the interface of Au nanoparticles can be changed from sp3 to compact sp2 to reduce the surface energy of Au nanoparticles. Meanwhile, our molecular dynamics simulation has confirmed the fact, when an Au nanoparticle is embedded in the amorphous carbon system the ratio of sp2 orbits increases dramatically. Similar results also have been confirmed from the Raman spectrum measurements. We controlled the carrier transport by changing the hopping barriers formed by amorphous carbon matrix between the Au nanoparticles to modify the resistance. These nanocomposites exhibit a superior sensitivity to NH3 at room temperature as well as good reproducibility and short response/recovery times, which could have potential applications in gas sensors. Dept. of Applied Physics,NUK, Kaohsiung, Taiwan.

  14. Amorphous Calcium Carbonate Based-Microparticles for Peptide Pulmonary Delivery.

    Science.gov (United States)

    Tewes, Frederic; Gobbo, Oliviero L; Ehrhardt, Carsten; Healy, Anne Marie

    2016-01-20

    Amorphous calcium carbonate (ACC) is known to interact with proteins, for example, in biogenic ACC, to form stable amorphous phases. The control of amorphous/crystalline and inorganic/organic ratios in inhalable calcium carbonate microparticles may enable particle properties to be adapted to suit the requirements of dry powders for pulmonary delivery by oral inhalation. For example, an amorphous phase can immobilize and stabilize polypeptides in their native structure and amorphous and crystalline phases have different mechanical properties. Therefore, inhalable composite microparticles made of inorganic (i.e., calcium carbonate and calcium formate) and organic (i.e., hyaluronan (HA)) amorphous and crystalline phases were investigated for peptide and protein pulmonary aerosol delivery. The crystalline/amorphous ratio and polymorphic form of the inorganic component was altered by changing the microparticle drying rate and by changing the ammonium carbonate and HA initial concentration. The bioactivity of the model peptide, salmon calcitonin (sCT), coprocessed with alpha-1-antitrypsin (AAT), a model protein with peptidase inhibitor activity, was maintained during processing and the microparticles had excellent aerodynamic properties, making them suitable for pulmonary aerosol delivery. The bioavailability of sCT after aerosol delivery as sCT and AAT-loaded composite microparticles to rats was 4-times higher than that of sCT solution.

  15. Fracture of Carbon Nanotube - Amorphous Carbon Composites: Molecular Modeling

    Science.gov (United States)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    Carbon nanotubes (CNTs) are promising candidates for use as reinforcements in next generation structural composite materials because of their extremely high specific stiffness and strength. They cannot, however, be viewed as simple replacements for carbon fibers because there are key differences between these materials in areas such as handling, processing, and matrix design. It is impossible to know for certain that CNT composites will represent a significant advance over carbon fiber composites before these various factors have been optimized, which is an extremely costly and time intensive process. This work attempts to place an upper bound on CNT composite mechanical properties by performing molecular dynamics simulations on idealized model systems with a reactive forcefield that permits modeling of both elastic deformations and fracture. Amorphous carbon (AC) was chosen for the matrix material in this work because of its structural simplicity and physical compatibility with the CNT fillers. It is also much stiffer and stronger than typical engineering polymer matrices. Three different arrangements of CNTs in the simulation cell have been investigated: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. The SWNT and MWNT array systems are clearly idealizations, but the SWNT bundle system is a step closer to real systems in which individual tubes aggregate into large assemblies. The effect of chemical crosslinking on composite properties is modeled by adding bonds between the CNTs and AC. The balance between weakening the CNTs and improving fiber-matrix load transfer is explored by systematically varying the extent of crosslinking. It is, of course, impossible to capture the full range of deformation and fracture processes that occur in real materials with even the largest atomistic molecular dynamics simulations. With this limitation in mind, the simulation results reported here provide a plausible upper limit on

  16. Designed synthesis of tunable amorphous carbon nanotubes (a ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Tunable amorphous carbon nanotubes (a-CNTs) were successfully synthesized using V3O7∙H2O and glucose solution as the starting materials by a novel route for the first time. The as-obtained samples were separately characterized by scanning electron microscopy (SEM), transmission electron microscopy ...

  17. Glycolytic intermediates induce amorphous calcium carbonate formation in crustaceans.

    Science.gov (United States)

    Sato, Ai; Nagasaka, Seiji; Furihata, Kazuo; Nagata, Shinji; Arai, Isao; Saruwatari, Kazuko; Kogure, Toshihiro; Sakuda, Shohei; Nagasawa, Hiromichi

    2011-04-01

    It has been thought that phosphorus in biominerals made of amorphous calcium carbonate (ACC) might be related to ACC formation, but no such phosphorus-containing compounds have ever been identified. Crustaceans use ACC biominerals in exoskeleton and gastroliths so that they will have easy access to calcium carbonate inside the body before and after molting. We have identified phosphoenolpyruvate and 3-phosphoglycerate, intermediates of the glycolytic pathway, in exoskeleton and gastroliths and found them important for stabilizing ACC.

  18. Growth, characterisation and electronic applications of amorphous hydrogenated carbon

    CERN Document Server

    Paul, S

    2000-01-01

    temperature on GaAs, has been studied and concluded to be satisfactory on the basis of good adherence and low leakage currents. Such a structure was motivated by the applicability in Metal Insulator Semiconductor Field Effect Transistors (MISFET). My thesis proposes solutions to a number of riddles associated with the material, hydrogenated amorphous carbon, (a-C:H). This material has lately generated interest in the electronic engineering community, owing to some remarkable properties. The characterisation of amorphous carbon films, grown by radio frequency plasma enhanced chemical vapour deposition has been reported. The coexistence of multiple phases in the same a-C:H film manifests itself in the inconsistent electrical behaviour of different parts of the film, thus rendering it difficult to predict the nature of films. For the first time, in this thesis, a reliable prediction of Schottky contact formation on a-C:H films is reported. A novel and simple development on a Scanning Electron Microscope, configu...

  19. Calcium carbonate polyamorphism and its role in biomineralization: how many amorphous calcium carbonates are there?

    Science.gov (United States)

    Cartwright, Julyan H E; Checa, Antonio G; Gale, Julian D; Gebauer, Denis; Sainz-Díaz, C Ignacio

    2012-11-26

    Although the polymorphism of calcium carbonate is well known, and its polymorphs--calcite, aragonite, and vaterite--have been highly studied in the context of biomineralization, polyamorphism is a much more recently discovered phenomenon, and the existence of more than one amorphous phase of calcium carbonate in biominerals has only very recently been understood. Here we summarize what is known about polyamorphism in calcium carbonate as well as what is understood about the role of amorphous calcium carbonate in biominerals. We show that consideration of the amorphous forms of calcium carbonate within the physical notion of polyamorphism leads to new insights when it comes to the mechanisms by which polymorphic structures can evolve in the first place. This not only has implications for our understanding of biomineralization, but also of the means by which crystallization may be controlled in medical, pharmaceutical, and industrial contexts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Strength and Fracture Resistance of Amorphous Diamond-Like Carbon Films for MEMS

    Directory of Open Access Journals (Sweden)

    K. N. Jonnalagadda

    2009-01-01

    Full Text Available The mechanical strength and mixed mode I/II fracture toughness of hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C films, grown by pulsed laser deposition, are discussed in connection to material flaws and its microstructure. The failure properties of ta-C were obtained from films with thicknesses 0.5–3 μm and specimen widths 10–20 μm. The smallest test samples with 10 μm gage section averaged a strength of 7.3 ± 1.2 GPa, while the strength of 20-μm specimens with thicknesses 0.5–3 μm varied between 2.2–5.7 GPa. The scaling of the mechanical strength with specimen thickness and dimensions was owed to deposition-induced surface flaws, and, only in the smallest specimens, RIE patterning generated specimen sidewall flaws. The mode I fracture toughness of ta-C films is KIc=4.4±0.4 MPam, while the results from mixed mode I/II fracture experiments with cracks arbitrarily oriented in the plane of the film compared very well with theoretical predictions.

  1. Novel low Wigner energy amorphous carbon–carbon composite

    Energy Technology Data Exchange (ETDEWEB)

    Dasgupta, Kinshuk, E-mail: kdg@barc.gov.in; Prakash, Jyoti; Tripathi, B.M.

    2014-02-01

    A novel amorphous carbon–carbon composite has been developed using carbon black dispersed in carbonized phenolic resin matrix in order to avoid Wigner energy problem associated with graphite. The as prepared sample showed a density of 1320 kg m{sup −3}. This has been further densified by resin impregnation and chemical vapour infiltration. The effect of processing parameters on final density (1517 kg m{sup −3}) has been investigated. This composite possesses the compressive strength of 65 Mpa, coefficient of thermal expansion of 3 × 10{sup −6} K{sup −1} and the specific heat of 1.2 J g{sup −1} K{sup −1}. This novel composite was subjected to 145 MeV Ne{sup +6} heavy ion irradiation at different doses. The highest dose was kept at 3 × 10{sup −4} dpa. The stored energy in the composite was found to be 212 J g{sup −1} at the highest dose of irradiation, which is much below than that of graphite. The composite remained amorphous after irradiation as confirmed by X-ray diffraction.

  2. Formation of amorphous hydrogenated carbon from compression of benzene

    Science.gov (United States)

    Shinozaki, Ayako; Kagi, Hiroyuki; Mimura, Koichi

    2017-10-01

    Infrared spectra of benzene were measured at pressures up to 25.3 GPa at room temperature using a diamond anvil cell. With decompression from pressures above 18.7 GPa, a new peak of C-H vibration mode appeared at a lower frequency than that of benzene. This indicates that an irreversible chemical change occurred at a pressure that was lower than that reported in previous studies. The IR spectra of the recovered sample after compression up to 20.3 GPa are comparable with those of the amorphous hydrogenated carbon reported in the previous study that was formed by compression of benzene up to approximately 30 GPa.

  3. Intracellular amorphous carbonates uncover a new biomineralization process in eukaryotes.

    Science.gov (United States)

    Martignier, A; Pacton, M; Filella, M; Jaquet, J-M; Barja, F; Pollok, K; Langenhorst, F; Lavigne, S; Guagliardo, P; Kilburn, M R; Thomas, C; Martini, R; Ariztegui, D

    2017-03-01

    Until now, descriptions of intracellular biomineralization of amorphous inclusions involving alkaline-earth metal (AEM) carbonates other than calcium have been confined exclusively to cyanobacteria (Couradeau et al., 2012). Here, we report the first evidence of the presence of intracellular amorphous granules of AEM carbonates (calcium, strontium, and barium) in unicellular eukaryotes. These inclusions, which we have named micropearls, show concentric and oscillatory zoning on a nanometric scale. They are widespread in certain eukaryote phytoplankters of Lake Geneva (Switzerland) and represent a previously unknown type of non-skeletal biomineralization, revealing an unexpected pathway in the geochemical cycle of AEMs. We have identified Tetraselmis cf. cordiformis (Chlorophyta, Prasinophyceae) as being responsible for the formation of one micropearl type containing strontium ([Ca,Sr]CO3 ), which we also found in a cultured strain of Tetraselmis cordiformis. A different flagellated eukaryotic cell forms barium-rich micropearls [(Ca,Ba)CO3 ]. The strontium and barium concentrations of both micropearl types are extremely high compared with the undersaturated water of Lake Geneva (the Ba/Ca ratio of the micropearls is up to 800,000 times higher than in the water). This can only be explained by a high biological pre-concentration of these elements. The particular characteristics of the micropearls, along with the presence of organic sulfur-containing compounds-associated with and surrounding the micropearls-strongly suggest the existence of a yet-unreported intracellular biomineralization pathway in eukaryotic micro-organisms. © 2016 John Wiley & Sons Ltd.

  4. Structural characterization of amorphous calcium carbonate-binding protein: an insight into the mechanism of amorphous calcium carbonate formation.

    Science.gov (United States)

    Su, Jingtan; Liang, Xiao; Zhou, Qiang; Zhang, Guiyou; Wang, Hongzhong; Xie, Liping; Zhang, Rongqing

    2013-07-15

    ACC (amorphous calcium carbonate) plays an important role in biomineralization process for its function as a precursor for calcium carbonate biominerals. However, it is unclear how biomacromolecules regulate the formation of ACC precursor in vivo. In the present study, we used biochemical experiments coupled with bioinformatics approaches to explore the mechanisms of ACC formation controlled by ACCBP (ACC-binding protein). Size-exclusion chromatography, chemical cross-linking experiments and negative staining electron microscopy reveal that ACCBP is a decamer composed of two adjacent pentamers. Sequence analyses and fluorescence quenching results indicate that ACCBP contains two Ca²⁺-binding sites. The results of in vitro crystallization experiments suggest that one Ca²⁺-binding site is critical for ACC formation and the other site affects the ACC induction efficiency. Homology modelling demonstrates that the Ca²⁺-binding sites of pentameric ACCBP are arranged in a 5-fold symmetry, which is the structural basis for ACC formation. To the best of our knowledge, this is the first report on the structural basis for protein-induced ACC formation and it will significantly improve our understanding of the amorphous precursor pathway.

  5. Amorphous carbon nanofibres inducing high specific capacitance of deposited hydrous ruthenium oxide

    Energy Technology Data Exchange (ETDEWEB)

    Barranco, V. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), Sor Juan Ines de la Cruz 3, Cantoblanco, E-28049-Madrid (Spain); Pico, F.; Ibanez, J. [Centro Nacional de Investigaciones Metalurgicas, CSIC, Avda. Gregorio del Amo 8, E-28040-Madrid (Spain); Lillo-Rodenas, M.A.; Linares-Solano, A. [MCMA, Departamento de Quimica Inorganica, Universidad de Alicante, P.O. Box 99, E-03080-Alicante (Spain); Kimura, M. [Gun Ei Chemical Ind. Co., Ltd., Takasaki, Gunma 370 (Japan); Oya, A. [Faculty of Engineering, Gunma University, Gunma 376 (Japan); Rojas, R.M.; Amarilla, J.M. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), Sor Juan Ines de la Cruz 3, Cantoblanco, E-28049-Madrid (Spain); Rojo, J.M., E-mail: jmrojo@icmm.csic.e [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), Sor Juan Ines de la Cruz 3, Cantoblanco, E-28049-Madrid (Spain)

    2009-12-01

    Composites consisting of ruthenium oxide particles deposited on amorphous carbon nanofibres are prepared by a repetitive impregnation procedure. The choice of amorphous carbon nanofibres as support of amorphous ruthenium oxide leads to composites in which the deposited oxide consists of aggregates of extremely small primary particles (1-1.5 nm-size) and showing high porosity (specific surface area of 450 m{sup 2} g{sup -1}). This special deposition of the oxide seems to favour: (i) high oxide capacitance (1000 Fg{sup -1}) at high oxide loadings (up to 20 wt%) and (ii) high capacitance retention (ca. 80% from the initial oxide capacitance) at high current densities (200 mA cm{sup -2}). Amorphous carbon nanofibres are suitable supports for amorphous ruthenium oxide and perhaps for other amorphous oxides acting as active electrode materials.

  6. Infrared analysis of thin films amorphous, hydrogenated carbon on silicon

    CERN Document Server

    Jacob, W; Schwarz-Selinger, T

    2000-01-01

    The infrared analysis of thin films on a thick substrate is discussed using the example of plasma-deposited, amorphous, hydrogenated carbon layers (a-C:H) on silicon substrates. The framework for the optical analysis of thin films is presented. The main characteristic of thin film optics is the occurrence of interference effects due to the coherent superposition of light multiply reflected at the various internal and external interfaces of the optical system. These interference effects lead to a sinusoidal variation of the transmitted and reflected intensity. As a consequence, the Lambert-Beer law is not applicable for the determination of the absorption coefficient of thin films. Furthermore, observable changes of the transmission and reflection spectra occur in the vicinity of strong absorption bands due to the Kramers-Kronig relation. For a sound data evaluation these effects have to be included in the analysis. To be able to extract the full information contained in a measured optical thin film spectrum, ...

  7. Presence of Amorphous Carbon Nanoparticles in Food Caramels

    Science.gov (United States)

    Sk, Md Palashuddin; Jaiswal, Amit; Paul, Anumita; Ghosh, Siddhartha Sankar; Chattopadhyay, Arun

    2012-01-01

    We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4–30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe. PMID:22540029

  8. Amorphous carbon interlayers for gold on elastomer stretchable conductors

    Energy Technology Data Exchange (ETDEWEB)

    Manzoor, M U; Tuinea-Bobe, C L; McKavanagh, F; Byrne, C P; Dixon, D; Maguire, P D; Lemoine, P, E-mail: Manzoor-m@email.ulster.ac.uk [NIBEC, University of Ulster at Jordanstown, Shore Road, Newtownabbey, Co. Antrim, BT37 0QB, Northern Ireland (United Kingdom)

    2011-06-22

    Gold on polydimethylsiloxane (PDMS) stretchable conductors were prepared using a novel approach by interlacing an hydrogenated amorphous carbon (a-C : H) layer between the deposited metal layer and the elastomer. AFM analysis of the a-C : H film surface before gold deposition shows nanoscale buckling, the corresponding increase in specific surface area corresponds to a strain compensation for the first 4-6% of bi-axial tensile loading. Without this interlayer, the deposited gold films show much smaller and uni-directional ripples as well as more cracks and delaminations. With a-C : H interlayer, the initial electrical resistivity of the metal film decreases markedly (280-fold decrease to 8 x 10{sup -6} {Omega} cm). This is not due to conduction within the carbon interlayer; both a-C : H/PDMS and PDMS substrates are electrically insulating. Upon cyclic tensile loading, both films become more resistive, but return to their initial state after 20 tensile cycles up to 60% strain. Profiling experiments using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy indicate that the a-C : H layer intermixes with the PDMS, resulting in a graded layer of decreasing stiffness. We believe that both this graded layer and the surface buckling contribute to the observed improvement in the electrical performance of these stretchable conductors.

  9. Incidence Angle Effect of Energetic Carbon Ions on Deposition Rate, Topography, and Structure of Ultrathin Amorphous Carbon Films Deposited by Filtered Cathodic Vacuum Arc

    KAUST Repository

    Wang, N.

    2012-07-01

    The effect of the incidence angle of energetic carbon ions on the thickness, topography, and structure of ultrathin amorphous carbon (a-C) films synthesized by filtered cathodic vacuum arc (FCVA) was examined in the context of numerical and experimental results. The thickness of a-C films deposited at different incidence angles was investigated in the light of Monte Carlo simulations, and the calculated depth profiles were compared with those obtained from high-resolution transmission electron microscopy (TEM). The topography and structure of the a-C films were studied by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The film thickness decreased with the increase of the incidence angle, while the surface roughness increased and the content of tetrahedral carbon hybridization (sp 3) decreased significantly with the increase of the incidence angle above 45° , measured from the surface normal. TEM, AFM, and XPS results indicate that the smoothest and thinnest a-C films with the highest content of sp 3 carbon bonding were produced for an incidence angle of 45°. The findings of this study have direct implications in ultrahigh-density magnetic recording, where ultrathin and smooth a-C films with high sp 3 contents are of critical importance. © 2012 IEEE.

  10. Carbon-nanotube-templated deposition of amorphous aluminum oxide with linear photo transmittance

    Science.gov (United States)

    Lan, Zhuyao; Zhang, Xin; Zhang, Haiyan; Ye, Xiang; Zhang, Xiaohua

    2017-11-01

    Atomic layer deposition on free-standing carbon nanotube (CNT) sheets produced highly amorphous Al2O3 nanostructures. The hybrid sheets maintained amorphousness for Al2O3 at 700 °C and robustness as well by thermally decomposing the CNTs. Higher temperatures (above 1000 °C) induced crystalline transformations into γ- and α Al2O3 phases. As each amorphous structure could contribute an absorption peak, the hybrid sheets with a mixture of amorphousness interestingly showed a linear photo-transmittance/absorbance when increasing the wavelength from 200 to 800 nm.

  11. Wake potential of swift ion in amorphous carbon target

    Science.gov (United States)

    Al-Bahnam, Nabil janan; Ahmad, Khalid A.; Aboo Al-Numan, Abdullah Ibrahim

    2017-02-01

    The wake potential and wake phenomena for swift proton in an amorphous carbon target were studied by utilising various dielectric function formalisms, including the Drude dielectric function, the Drude-Lorentz dielectric function and quantum dielectric function. The Drude model results exhibited a damped oscillatory behaviour in the longitudinal direction behind the projectile; the pattern of these oscillations decreases exponentially in the transverse direction. In addition, the wake potential extends slightly ahead of the projectile which also depends on the proton coordinate and velocity. The effect of electron binding on the wake potential, characterised by the ratio ωp2/ω02 = 10 to 0.1, has been studied alongside the Drude-Lorentz dielectric function and quantum dielectric function formalisms; the results evidently show that the wake potential dip depth decreases with more oscillations when the electron density ratio ωp2/ω02 decreases from 10 to 0.1. One of the primary objectives of the present work is to construct a reasonably realistic procedure for simulating the response of target to swift ions by combining an expression for the induced wake potential along with several important dielectric function models; the aim of this research is to reduce computational complexity without sacrificing accuracy. This is regarded as being an efficient strategy in that it creates suitable computer simulation procedures which are relevant to actual solids. After comparing this method with other models, the main differences and similarities have been noted while the end results have proved encouraging.

  12. Electromagnetic Wave Absorbing Properties of Amorphous Carbon Nanotubes

    Science.gov (United States)

    Zhao, Tingkai; Hou, Cuilin; Zhang, Hongyan; Zhu, Ruoxing; She, Shengfei; Wang, Jungao; Li, Tiehu; Liu, Zhifu; Wei, Bingqing

    2014-01-01

    Amorphous carbon nanotubes (ACNTs) with diameters in the range of 7–50 nm were used as absorber materials for electromagnetic waves. The electromagnetic wave absorbing composite films were prepared by a dip-coating method using a uniform mixture of rare earth lanthanum nitrate doped ACNTs and polyvinyl chloride (PVC). The microstructures of ACNTs and ACNT/PVC composites were characterized using transmission electron microscope and X-ray diffraction, and their electromagnetic wave absorbing properties were measured using a vector-network analyzer. The experimental results indicated that the electromagnetic wave absorbing properties of ACNTs are superior to multi-walled CNTs, and greatly improved by doping 6 wt% lanthanum nitrate. The reflection loss (R) value of a lanthanum nitrate doped ACNT/PVC composite was −25.02 dB at 14.44 GHz, and the frequency bandwidth corresponding to the reflector loss at −10 dB was up to 5.8 GHz within the frequency range of 2–18 GHz. PMID:25007783

  13. Thermal decomposition of fullerene nanowhiskers protected by amorphous carbon mask

    Science.gov (United States)

    Guo, Hongxuan; Wang, Chengxiang; Miyazawa, Kun'Ichi; Wang, Hongxin; Masuda, Hideki; Fujita, Daisuke

    2016-12-01

    Fullerene nanostructures are well known for their unique morphology, physical and mechanical properties. The thermal stability of fullerene nanostructures, such as their sublimation at high temperature is also very important for studying their structures and applications. In this work, We observed fullerene nanowhiskers (FNWs) in situ with scanning helium ion microscopy (HIM) at elevated temperatures. The FNWs exhibited different stabilities with different thermal histories during the observation. The pristine FNWs were decomposed at the temperatures higher than 300 °C in a vacuum environment. Other FNWs were protected from decomposition with an amorphous carbon (aC) film deposited on the surface. Based on high spacial resolution, aC film with periodic structure was deposited by helium ion beam induced deposition (IBID) on the surface of FNWs. Annealed at the high temperature, the fullerene molecules were selectively sublimated from the FNWs. The periodic structure was formed on the surface of FNWs and observed by HIM. Monte Carlo simulation and Raman characterization proved that the morphology of the FNWs was changed by helium IBID at high temperature. This work provides a new method of fabricating artificial structure on the surface of FNWs with periodic aC film as a mask.

  14. Revealing the 1 nm/s Extensibility of Nanoscale Amorphous Carbon in a Scanning Electron Microscope

    DEFF Research Database (Denmark)

    Zhang, Wei

    2013-01-01

    In an ultra-high vacuum scanning electron microscope, the edged branches of amorphous carbon film (∼10 nm thickness) can be continuously extended with an eye-identifying speed (on the order of ∼1 nm/s) under electron beam. Such unusual mobility of amorphous carbon may be associated with deformati...... positive implications to explore some amorphous carbon as electron field emission device. SCANNING 35: 261-264, 2013. © 2012 Wiley Periodicals, Inc.......In an ultra-high vacuum scanning electron microscope, the edged branches of amorphous carbon film (∼10 nm thickness) can be continuously extended with an eye-identifying speed (on the order of ∼1 nm/s) under electron beam. Such unusual mobility of amorphous carbon may be associated with deformation...... promoted by the electric field, which resulted from an inner secondary electron potential difference from the main trunk of carbon film to the tip end of branches under electron beam. This result demonstrates importance of applying electrical effects to modify properties of carbon materials. It may have...

  15. Silicon and aluminum doping effects on the microstructure and properties of polymeric amorphous carbon films

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiaoqiang, E-mail: lxq_suse@sina.com [Material Corrosion and Protection Key Laboratory of Sichuan province, Sichuan University of Science and Engineering, Zigong 643000 (China); Hao, Junying, E-mail: jyhao@licp.cas.cn [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Xie, Yuntao [Material Corrosion and Protection Key Laboratory of Sichuan province, Sichuan University of Science and Engineering, Zigong 643000 (China)

    2016-08-30

    Highlights: • Evolution of nanostructure and properties of the polymeric amorphous carbon films were firstly studied. • Si doping enhanced polymerization of the hydrocarbon chains and Al doping resulted in increase in the ordered carbon clusters of polymeric amorphous carbon films. • Soft polymeric amorphous carbon films exhibited an unconventional frictional behaviors with a superior wear resistance. • The mechanical and vacuum tribological properties of the polymeric amorphous carbon films were significantly improved by Si and Al co-doping. - Abstract: Polymeric amorphous carbon films were prepared by radio frequency (R.F. 13.56 MHz) magnetron sputtering deposition. The microstructure evolution of the deposited polymeric films induced by silicon (Si) and aluminum(Al) doping were scrutinized through infrared spectroscopy, multi-wavelength Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The comparative results show that Si doping can enhance polymerization and Al doping results in an increase in the ordered carbon clusters. Si and Al co-doping into polymeric films leads to the formation of an unusual dual nanostructure consisting of cross-linked polymer-like hydrocarbon chains and fullerene-like carbon clusters. The super-high elasticity and super-low friction coefficients (<0.002) under a high vacuum were obtained through Si and Al co-doping into the films. Unconventionally, the co-doped polymeric films exhibited a superior wear resistance even though they were very soft. The relationship between the microstructure and properties of the polymeric amorphous carbon films with different elements doping are also discussed in detail.

  16. Recent progress in the synthesis and characterization of amorphous and crystalline carbon nitride coatings

    CERN Document Server

    Widlow, I

    2000-01-01

    This review summarizes our most recent findings in the structure and properties of amorphous and crystalline carbon nitride coatings, synthesized by reactive magnetron sputtering. By careful control of the plasma conditions via proper choice of process parameters such as substrate bias, target power and gas pressure, one can precisely control film structure and properties. With this approach, we were able to produce amorphous carbon nitride films with controlled hardness and surface roughness. In particular, we can synthesize ultrathin (1 nm thick) amorphous carbon nitride films to be sufficiently dense and uniform that they provide adequate corrosion protection for hard disk applications. We demonstrated the strong correlation between ZrN (111) texture and hardness in CN sub x /ZrN superlattice coatings. Raman spectroscopy and near-edge X-ray absorption show the predominance of sp sup 3 -bonded carbon in these superlattice coatings.

  17. Highly conductive carbon black supported amorphous molybdenum disulfide for efficient hydrogen evolution reaction

    Science.gov (United States)

    Cao, Pengfei; Peng, Jing; Li, Jiuqiang; Zhai, Maolin

    2017-04-01

    Molybdenum disulfide (MoS2) is a promising electrocatalyst for hydrogen evolution reaction (HER), however, the catalytic activity of reported MoS2-based materials towards HER still can't satisfy the requirement of practical application. Herein, highly conductive carbon black (CB) supported amorphous MoS2 nanocomposite is synthesized by a facile one-pot hydrothermal process. XRD and TEM analysis proves the amorphous morphology of MoS2. XPS further confirms both hexagonal and orthorhombic S ligands exist in the amorphous MoS2. Compared with crystalline MoS2, amorphous MoS2/CB shows an onset overpotential of 78 mV and current density of 470 mA cm-2 at the overpotential of 200 mV, which is even 50% higher than that of the commercial 20% Pt/C catalyst. Furthermore, a fairly stable performance can be achieved even after 5000 CV cycles. The outstanding HER activity and stability of the amorphous MoS2/CB nanocomposite can be attributed to these advantages: (1) amorphous structure offers more active sites in MoS2; (2) highly conductive CB reduces the charge transfer resistance (RCT); (3) relative hydrophilic CB can largely reduce the resistance between catalyst/electrolyte interface and allows rapid mass transport; (4) electron penetration effect between amorphous MoS2 and CB increases the intrinsic activity of amorphous MoS2 by two orders of magnitude.

  18. Molecular dynamics simulations of amorphous hydrogenated carbon under high hydrogen fluxes

    NARCIS (Netherlands)

    de Rooij, E. D.; von Toussaint, U.; Kleyn, A. W.; W. J. Goedheer,

    2009-01-01

    We study the flux dependence of the carbon erosion yield and the hydrogen enrichment of the surface in the high flux regime at 10(28) ions per m(2) s and higher by using molecular dynamics (MD). We simulate an amorphous hydrogenated carbon sample exposed to high flux hydrogen bombardment with a

  19. Fabrication of barium/strontium carbonate coated amorphous carbon nanotubes as an improved field emitter

    Energy Technology Data Exchange (ETDEWEB)

    Maity, S. [Jadavpur University, Thin Film and Nanoscience Laboratory, Department of Physics, Kolkata (India); Jha, A.; Das, N.S. [Jadavpur University, School of Materials Science and Nanotechnology, Kolkata (India); Chattopadhyay, K.K. [Jadavpur University, Thin Film and Nanoscience Laboratory, Department of Physics, Kolkata (India); Jadavpur University, School of Materials Science and Nanotechnology, Kolkata (India)

    2013-02-15

    Amorphous carbon nanotubes (aCNTs) were synthesized by a chemical reaction between ferrocene and ammonium chloride at a temperature {proportional_to}250 {sup circle} C in an air furnace. As-synthesized aCNTs were coated with the barium/strontium carbonate through a simple chemical process. The coating of barium/strontium carbonate was confirmed by a high resolution transmission electron microscopy, X-ray diffraction, and Fourier transformed infrared spectroscopy. Morphology of the as-prepared samples was studied by field emission scanning electron microscopy. Thermal gravimetric analysis showed that barium/strontium carbonate coated aCNTs are more stable than the pristine aCNTs. As-prepared barium/strontium carbonate coated aCNTs showed significantly improved field emission properties with a turn-on field as low as 2.5 V/{mu}m. The variation of field emission characteristics of the barium/strontium carbonate coated aCNTs with interelectrode distances was also studied. (orig.)

  20. Study on the excimer laser annealed amorphous hydrogenated silicon carbon films deposited by PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Ambrosone, G. [CNR-INFM CRS-Coherentia, Complesso Universitario MSA, Napoli (Italy); Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , Complesso Universitario MSA, Napoli (Italy); Basa, D.K. [Utkal University, Bhubaneswar (India); Coscia, U. [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , Complesso Universitario MSA, Napoli (Italy); CNISM Unita' di Napoli, Complesso Universitario MSA, Napoli (Italy); Tresso, E.; Celasco, E. [Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino (Italy); Chiodoni, A. [Materials and Microsystems Laboratory, chi-LAB, Politecnico di Torino (Italy); Pinto, N.; Murri, R. [Dipartimento di Fisica, Universita' di Camerino (Italy)

    2010-04-15

    Hydrogenated amorphous silicon carbon films of different carbon content were deposited by plasma enhanced chemical vapour deposition at low substrate temperature (200 C) and were subjected to excimer laser annealing. X-ray diffraction spectra and field emission scanning electron microscopy images demonstrate that carbon content plays an important role in facilitating the crystallization process induced by the excimer laser treatment (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. In vitro cytocompatibility assessment of amorphous carbon structures using neuroblastoma and Schwann cells.

    Science.gov (United States)

    Jain, Shilpee; Sharma, Ashutosh; Basu, Bikramjit

    2013-05-01

    The development of scaffolds for neural tissue engineering application requires an understanding of cell adhesion, proliferation, and migration of neuronal cells. Considering the potential application of carbon as scaffold materials and the lack of understanding of compatibility of amorphous carbon with neuronal cells, the carbon-based materials in the forms of carbon films and continuous electrospun carbon nanofibers having average diameter of ~200 nm are being investigated with or without ultraviolet (UV) and oxy-plasma (OP) treatments for cytocompatibility property using mouse Neuroblastoma (N2a) and rat Schwann cells (RT4-D6P2T). The use of Raman spectroscopy in combination with Fourier transform infrared (FTIR) and X-ray diffraction establishes the amorphous nature and surface-bonding characteristics of the studied carbon materials. Although both UV and OP treatments make carbon surfaces more hydrophilic, the cell viability of N2a cells is statistically more significant on OP treated fibers/films compared to UV fiber/film substrates after 4 days in culture. The electrospun carbon fibrous substrate provides the physical guidance to the cultured Schwann cells. Overall, the experimental results of this study demonstrate that the electrospun amorphous carbon nanofibrous scaffolds can be used as a suitable biomaterial substrate for supporting cell adhesion and proliferation of neuronal cells in the context of their applications as artificial nerve implants. Copyright © 2013 Wiley Periodicals, Inc.

  2. Revealing the multi hydrogen bonding state within iron doped amorphous carbon

    Science.gov (United States)

    Miyazato, Itsuki; Takahashi, Keisuke

    2018-01-01

    Hydrogenated Fe doped amorphous carbon is synthesized via mechanically alloying. XANES analysis suggests that Fe is considered to bond with either C or H atom where the first principle calculations reveals that two types of H-C bonding is confirmed. Weak H-C bond is observed near Fe atom while strong H-C bond is seen far from Fe atom. Electronic structure discovered that weak H-C bonding is induced by Fe atoms where Fe form ionic like bond with surrounding C, resulting in the weak H-C interaction. Thus, two different types of H-C bonding is confirmed within Fe doped amorphous carbon.

  3. Low-Temperature Production of Genuinely Amorphous Carbon from Highly Reactive Nanoacetylide Precursors

    Directory of Open Access Journals (Sweden)

    Ken Judai

    2016-01-01

    Full Text Available Copper acetylide is a well-known explosive compound. However, when the size of it crystals is reduced to the nanoscale, its explosive nature is lost, owing to a much lower thermal conductance that inhibits explosive chain reactions. This less explosive character can be exploited for the production of new carbon materials. Generally, amorphous carbon is prepared by carbonization of organic compounds exposed to high temperature, which can induce partial crystallization in graphite. In this work, we present a new method in which the carbonization reaction can proceed at a lower annealing temperature (under 150°C owing to the highly reactive nature of copper acetylide, thus avoiding crystallization processes and enabling the production of genuinely amorphous carbon materials.

  4. Strong Metal-Support Interaction: Growth of Individual Carbon Nanofibers from Amorphous Carbon Interacting with an Electron Beam

    DEFF Research Database (Denmark)

    Zhang, Wei; Kuhn, Luise Theil

    2013-01-01

    The article discusses the growth behavior of carbon nanofibers (CNFs). It mentions that CNFs can be synthesized using methods such as arc-discharge, laser ablation and chemical vapor deposition. It further states that CNFs can be grown from a physical mixing of amorphous carbon and CGO....../Ni nanoparticles, devoid of any gaseous carbon source and external heating and stimulated by an electron beam in a 300 kilo volt transmission electron microscope....

  5. Design of Amorphous Manganese Oxide@Multiwalled Carbon Nanotube Fiber for Robust Solid-State Supercapacitor.

    Science.gov (United States)

    Shi, Peipei; Li, Li; Hua, Li; Qian, Qianqian; Wang, Pengfei; Zhou, Jinyuan; Sun, Gengzhi; Huang, Wei

    2017-01-24

    Solid-state fiber-based supercapacitors have been considered promising energy storage devices for wearable electronics due to their lightweight and amenability to be woven into textiles. Efforts have been made to fabricate a high performance fiber electrode by depositing pseudocapacitive materials on the outer surface of carbonaceous fiber, for example, crystalline manganese oxide/multiwalled carbon nanotubes (MnO2/MWCNTs). However, a key challenge remaining is to achieve high specific capacitance and energy density without compromising the high rate capability and cycling stability. In addition, amorphous MnO2 is actually preferred due to its disordered structure and has been proven to exhibit superior electrochemical performance over the crystalline one. Herein, by incorporating amorphous MnO2 onto a well-aligned MWCNT sheet followed by twisting, we design an amorphous MnO2@MWCNT fiber, in which amorphous MnO2 nanoparticles are distributed in MWCNT fiber uniformly. The proposed structure gives the amorphous MnO2@MWCNT fiber good mechanical reliability, high electrical conductivity, and fast ion-diffusion. Solid-state supercapacitor based on amorphous MnO2@MWCNT fibers exhibits improved energy density, superior rate capability, exceptional cycling stability, and excellent flexibility. This study provides a strategy to design a high performance fiber electrode with microstructure control for wearable energy storage devices.

  6. Hard graphitelike hydrogenated amorphous carbon grown at high rates by a remote plasma

    DEFF Research Database (Denmark)

    Singh, Shailendra Vikram; Zaharia, T.; Creatore, M.

    2010-01-01

    Hydrogenated amorphous carbon (a-C:H) deposited from an Ar-C 2H2 expanding thermal plasma chemical vapor deposition (ETP-CVD) is reported. The downstream plasma region of an ETP is characterized by a low electron temperature (∼0.3 eV), which leads to an ion driven chemistry and negligible physical...

  7. Low-Temperature Synthesis of Hierarchical Amorphous Basic Nickel Carbonate Particles for Water Oxidation Catalysis.

    Science.gov (United States)

    Yang, Yisu; Liang, Fengli; Li, Mengran; Rufford, Thomas E; Zhou, Wei; Zhu, Zhonghua

    2015-07-08

    Amorphous nickel carbonate particles are catalysts for the oxygen evolution reaction (OER), which plays a critical role in the electrochemical splitting of water. The amorphous nickel carbonate particles can be prepared at a temperature as low as 60 °C by an evaporation-induced precipitation (EIP) method. The products feature hierarchical pore structures. The mass-normalized activity of the catalysts, measured at an overpotential of 0.35 V, was 55.1 A g(-1) , with a Tafel slope of only 60 mV dec(-1) . This catalytic activity is superior to the performance of crystalline NiOx particles and β-Ni(OH)2 particles, and compares favorably to state-of-the-art RuO2 catalysts. The activity of the amorphous nickel carbonate is remarkably stable during a 10 000 s chronoamperometry test. Further optimization of synthesis parameters reveals that the amorphous structure can be tuned by adjusting the H2 O/Ni ratio in the precursor mixture. These results suggest the potential application of easily prepared hierarchical basic nickel carbonate particles as cheap and robust OER catalysts with high activity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Amorphous calcium carbonate controls avian eggshell mineralization: A new paradigm for understanding rapid eggshell calcification.

    Science.gov (United States)

    Rodríguez-Navarro, Alejandro B; Marie, Pauline; Nys, Yves; Hincke, Maxwell T; Gautron, Joel

    2015-06-01

    Avian eggshell mineralization is the fastest biogenic calcification process known in nature. How this is achieved while producing a highly crystalline material composed of large calcite columnar single crystals remains largely unknown. Here we report that eggshell mineral originates from the accumulation of flat disk-shaped amorphous calcium carbonate (ACC) particles on specific organic sites on the eggshell membrane, which are rich in proteins and sulfated proteoglycans. These structures known as mammillary cores promote the nucleation and stabilization of a amorphous calcium carbonate with calcitic short range order which predetermine the calcite composition of the mature eggshell. The amorphous nature of the precursor phase was confirmed by the diffuse scattering of X-rays and electrons. The nascent calcitic short-range order of this transient mineral phase was revealed by infrared spectroscopy and HRTEM. The ACC mineral deposited around the mammillary core sites progressively transforms directly into calcite crystals without the occurrence of any intermediate phase. Ionic speciation data suggest that the uterine fluid is equilibrated with amorphous calcium carbonate, throughout the duration of eggshell mineralization process, supporting that this mineral phase is constantly forming at the shell mineralization front. On the other hand, the transient amorphous calcium carbonate mineral deposits, as well as the calcite crystals into which they are converted, form by the ordered aggregation of nanoparticles that support the rapid mineralization of the eggshell. The results of this study alter our current understanding of avian eggshell calcification and provide new insights into the genesis and formation of calcium carbonate biominerals in vertebrates. Copyright © 2015 Elsevier Inc. All rights reserved.

  9. Effects of Atomic-Scale Structure on the Fracture Properties of Amorphous Carbon - Carbon Nanotube Composites

    Science.gov (United States)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    The fracture of carbon materials is a complex process, the understanding of which is critical to the development of next generation high performance materials. While quantum mechanical (QM) calculations are the most accurate way to model fracture, the fracture behavior of many carbon-based composite engineering materials, such as carbon nanotube (CNT) composites, is a multi-scale process that occurs on time and length scales beyond the practical limitations of QM methods. The Reax Force Field (ReaxFF) is capable of predicting mechanical properties involving strong deformation, bond breaking and bond formation in the classical molecular dynamics framework. This has been achieved by adding to the potential energy function a bond-order term that varies continuously with distance. The use of an empirical bond order potential, such as ReaxFF, enables the simulation of failure in molecular systems that are several orders of magnitude larger than would be possible in QM techniques. In this work, the fracture behavior of an amorphous carbon (AC) matrix reinforced with CNTs was modeled using molecular dynamics with the ReaxFF reactive forcefield. Care was taken to select the appropriate simulation parameters, which can be different from those required when using traditional fixed-bond force fields. The effect of CNT arrangement was investigated with three systems: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. For each arrangement, covalent bonds are added between the CNTs and AC, with crosslink fractions ranging from 0-25% of the interfacial CNT atoms. The SWNT and MWNT array systems represent ideal cases with evenly spaced CNTs; the SWNT bundle system represents a more realistic case because, in practice, van der Waals interactions lead to the agglomeration of CNTs into bundles. The simulation results will serve as guidance in setting experimental processing conditions to optimize the mechanical properties of CNT

  10. Sea Urchin Spine Calcite Forms via a Transient Amorphous Calcium Carbonate Phase

    Science.gov (United States)

    Politi, Yael; Arad, Talmon; Klein, Eugenia; Weiner, Steve; Addadi, Lia

    2004-11-01

    The skeletons of adult echinoderms comprise large single crystals of calcite with smooth convoluted fenestrated morphologies, raising many questions about how they form. By using water etching, infrared spectroscopy, electron diffraction, and environmental scanning electron microscopy, we show that sea urchin spine regeneration proceeds via the initial deposition of amorphous calcium carbonate. Because most echinoderms produce the same type of skeletal material, they probably all use this same mechanism. Deposition of transient amorphous phases as a strategy for producing single crystals with complex morphology may have interesting implications for the development of sophisticated materials.

  11. Unlocking the Electrocatalytic Activity of Chemically Inert Amorphous Carbon-Nitrogen for Oxygen Reduction: Discerning and Refactoring Chaotic Bonds

    DEFF Research Database (Denmark)

    Zhang, Caihong; Zhang, Wei; Wang, Dong

    2017-01-01

    Mild annealing enables inactive nitrogen (N)-doped amorphous carbon (a-C) films abundant with chaotic bonds prepared by magnetron sputtering to become effective for the oxygen reduction reaction (ORR) by virtue of generating pyridinic N. The rhythmic variation of ORR activity elaborates well...... on the subtle evolution of the amorphous C−N bonds conferred by spectroscopic analysis....

  12. Amorphous Carbon Gold Nanocomposite Thin Films: Structural and Spectro-ellipsometric Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Montiel-Gonzalez, Z., E-mail: zeuzmontiel@hotmail.com [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Circuito exterior s/n, Ciudad Universitaria, Coyoacan 04510, Mexico D.F (Mexico); Rodil, S.E.; Muhl, S. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Circuito exterior s/n, Ciudad Universitaria, Coyoacan 04510, Mexico D.F (Mexico); Mendoza-Galvan, A. [Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Unidad Queretaro, 76010 Queretaro, Queretaro (Mexico); Rodriguez-Fernandez, L. [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Circuito de la Investigacion Cientifica, Ciudad Universitaria, 04510, Mexico D.F (Mexico)

    2011-07-01

    Spectroscopic Ellipsometry was used to determine the optical and structural properties of amorphous carbon:gold nanocomposite thin films deposited by dc magnetron co-sputtering at different deposition power. The incorporation of gold as small particles distributed in the amorphous carbon matrix was confirmed by X-ray Diffraction, Rutherford Backscattering measurements and High Resolution Transmission Electron Microscopy. Based on these results, an optical model for the films was developed using the Maxwell-Garnett effective medium with the Drude-Lorentz model representing the optical response of gold and the Tauc-Lorentz model for the amorphous carbon. The gold volume fraction and particle size obtained from the fitting processes were comparable to those from the physical characterization. The analysis of the ellipsometric spectra for all the samples showed strong changes in the optical properties of the carbon films as a consequence of the gold incorporation. These changes were correlated to the structural modification observed by Raman Spectroscopy, which indicated a clustering of the sp{sup 2} phase with a subsequent decrease in the optical gap. Finally, measurements of Reflection and Transmission Spectroscopy were carried out and Transmission Electron Microscopy images were obtained in order to support the ellipsometric model results.

  13. Study of SEY degradation of amorphous carbon coatings

    CERN Document Server

    Bundaleski, N.; Santos, A.; Teodoro, O.M.N.D.; Silva, A.G.

    2013-04-22

    Deposition of low secondary electron yield (SEY) carbon coatings by magnetron sputtering onto the inner walls of the accelerator seems to be the most promising solution for suppressing the electron cloud problem. However, these coatings change their electron emission properties during long term exposure to air. The ageing process of carbon coated samples with initial SEY of about 0.9 received from CERN is studied as a function of exposure to different environments. It is shown that samples having the same initial SEY may age with different rates. The SEY increase can be correlated with the surface concentration of oxygen. Annealing of samples in air at 100-200 {\\deg}C reduces the ageing rate and even recovers previously degraded samples. The result of annealing is reduction of the hydrogen content in the coatings by triggering its surface segregation followed by desorption.

  14. Tetrahedral modular graph functions

    Science.gov (United States)

    Kleinschmidt, Axel; Verschinin, Valentin

    2017-09-01

    The low-energy expansion of one-loop amplitudes in type II string theory generates a series of world-sheet integrals whose integrands can be represented by world-sheet Feynman diagrams. These integrands are modular invariant and understanding the structure of the action of the modular Laplacian on them is important for determining their contribution to string scattering amplitudes. In this paper we study a particular infinite family of such integrands associated with three-loop scalar vacuum diagrams of tetrahedral topology and find closed forms for the action of the Laplacian. We analyse the possible eigenvalues and degeneracies of the Laplace operator by group- and representation-theoretic means.

  15. In situ mechanical property measurements of amorphous carbon-boron nitride nanotube nanostructures

    Science.gov (United States)

    Kim, Jae-Woo; Carpena Núñez, Jennifer; Siochi, Emilie J.; Wise, Kristopher E.; Lin, Yi; Connell, John W.; Smith, Michael W.

    2012-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  16. In Situ Mechanical Property Measurements of Amorphous Carbon-Boron Nitride Nanotube Nanostructures

    Science.gov (United States)

    Kim, Jae-Woo; Lin, Yi; Nunez, Jennifer Carpena; Siochi, Emilie J.; Wise, Kristopher E.; Connell, John W.; Smith, Michael W.

    2011-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  17. Synthesis and Characterization of Amorphous Carbon Films for Magnetic Storage Technology

    OpenAIRE

    Xie, Jun

    2015-01-01

    Increasing demands for high magnetic storage capacity have led to the increase of the recording area density, mainly by reducing the distance between the magnetic media on the hard disk and the magnetic transducer of the head. A factor that has greatly contributed to the profound decrease of the magnetic spacing is excessive thinning of the protective amorphous carbon (a-C) overcoat. However, the remarkable decrease in overcoat thickness raises a concern about its quality and protective capab...

  18. Facile fabrication of boron nitride nanosheets-amorphous carbon hybrid film for optoelectronic applications

    KAUST Repository

    Wan, Shanhong

    2015-01-01

    A novel boron nitride nanosheets (BNNSs)-amorphous carbon (a-C) hybrid film has been deposited successfully on silicon substrates by simultaneous electrochemical deposition, and showed a good integrity of this B-C-N composite film by the interfacial bonding. This synthesis can potentially provide the facile control of the B-C-N composite film for the potential optoelectronic devices. This journal is

  19. Short pulse laser-induced optical damage and fracto-emission of amorphous, diamond-like carbon

    Energy Technology Data Exchange (ETDEWEB)

    SOKOLOWSKI-TINTEN,K.; VON DER LINDE,D.; SIEGAL,MICHAEL P.; OVERMYER,DONALD L.

    2000-02-07

    Short pulse laser damage and ablation of amorphous, diamond-like carbon films is investigated. Material removal is due to fracture of the film and ejection of large fragments, which exhibit a broadband emission of microsecond duration.

  20. Parallel Anisotropic Tetrahedral Adaptation

    Science.gov (United States)

    Park, Michael A.; Darmofal, David L.

    2008-01-01

    An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.

  1. Real-time observation of tubule formation from amorphous carbon nanowires under high-bias Joule heating.

    Science.gov (United States)

    Huang, J Y; Chen, S; Ren, Z F; Chen, G; Dresselhaus, M S

    2006-08-01

    The tubule formation process from amorphous carbon nanowires under high-bias-caused Joule heating was observed in real time in a high-resolution transmission electron microscope. The crystallization of the amorphous carbon nanowires occurred in two distinct ways: the formation of tubular graphitic basal planes parallel to the nanowire axis on the surface and the formation of nano-onions in the interior of the nanowire. The tubule formation mechanism is a process of solid-state atom diffusion at high temperatures. Energetically, the tubule formation is caused by the exceptionally low surface energy of the (0002) plane of graphite. Higher input power to the amorphous nanowires generally leads to improved graphitization and, in turn, to increased conductance. The results suggest that nanotube formation in the arc-discharge growth process may involve the formation and crystallization of amorphous carbon.

  2. Cell survival in carbon beams - comparison of amorphous track model predictions

    DEFF Research Database (Denmark)

    Grzanka, L.; Greilich, S.; Korcyl, M.

    neutrons, stopped pions, and heavy ion beams. Nucl Instrum Meth. 1973;111:93-116. 2.Weyrather WK, Kraft G. RBE of carbon ions: experimental data and the strategy of RBE calculation for treatment planning. Radiother Oncol. 2004;73(Suppl 2):161-9. 3.Greilich S, Grzanka L, Bassler N, Andersen CE, Jäkel O......Introduction: Predictions of the radiobiological effectiveness (RBE) play an essential role in treatment planning with heavy charged particles. Amorphous track models ( [1] , [2] , also referred to as track structure models) provide currently the most suitable description of cell survival under ion....... [2] . In addition, a new approach based on microdosimetric distributions is presented and investigated [3] . Material and methods: A suitable software library embrasing the mentioned amorphous track models including numerous submodels with respect to delta-electron range models, radial dose...

  3. Crystalline and Amorphous Phosphorus – Carbon Nanotube Composites as Promising Anodes for Lithium-Ion Batteries

    KAUST Repository

    Smajic, Jasmin

    2016-05-04

    Battery research has been going full steam and with that the search for alternative anodes. Among many proposed electrode materials, little attention has been given to phosphorus. Phosphorus boasts the third highest gravimetric charge capacity and the highest volumetric charge capacity of all elements. Because of that, it would be an attractive battery anode material were it not for its poor cyclability with significant capacity loss immediately after the first cycle. This is known to be the consequence of considerable volume changes of phosphorus during charge/discharge cycles. In this work, we propose circumventing this issue by mixing amorphous red phosphorus with carbon nanotubes. By employing a non-destructive sublimation-deposition method, we have synthesized composites where the synergetic effect between phosphorus and carbon nanotubes allow for an improvement in the electrochemical performance of battery anodes. In fact, it has been shown that carbon nanotubes can act as an effective buffer to phosphorus volumetric expansions and contractions during charging and discharging of the half-cells [1]. By modifying the synthesis parameters, we have also been able to change the degree of crystallinity of the phosphorus matrix in the composites. In fact, the less common phase of red phosphorus, named fibrous phosphorus, was obtained, and that explains some of the varying electrochemical performances observed in the composites. Overall, it is found that a higher surface area of amorphous phosphorus allows for a better anode material when using single-walled carbon nanotubes as fillers.

  4. Amorphous calcium carbonate precipitation by cellular biomineralization in mantle cell cultures of Pinctada fucata.

    Directory of Open Access Journals (Sweden)

    Liang Xiang

    Full Text Available The growth of molluscan shell crystals is generally thought to be initiated from the extrapallial fluid by matrix proteins, however, the cellular mechanisms of shell formation pathway remain unknown. Here, we first report amorphous calcium carbonate (ACC precipitation by cellular biomineralization in primary mantle cell cultures of Pinctada fucata. Through real-time PCR and western blot analyses, we demonstrate that mantle cells retain the ability to synthesize and secrete ACCBP, Pif80 and nacrein in vitro. In addition, the cells also maintained high levels of alkaline phosphatase and carbonic anhydrase activity, enzymes responsible for shell formation. On the basis of polarized light microscopy and scanning electron microscopy, we observed intracellular crystals production by mantle cells in vitro. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the crystals to be ACC, and de novo biomineralization was confirmed by following the incorporation of Sr into calcium carbonate. Our results demonstrate the ability of mantle cells to perform fundamental biomineralization processes via amorphous calcium carbonate, and these cells may be directly involved in pearl oyster shell formation.

  5. Activated carbon as a carrier for amorphous drug delivery: Effect of drug characteristics and carrier wettability.

    Science.gov (United States)

    Miriyala, Nikhila; Ouyang, Defang; Perrie, Yvonne; Lowry, Deborah; Kirby, Daniel J

    2017-06-01

    Recent research on porous silica materials as drug carriers for amorphous and controlled drug delivery has shown promising results. However, due to contradictory literature reports on toxicity and high costs of production, it is important to explore alternative safe and inexpensive porous carriers. In this study, the potential of activated carbon (AC) as an amorphous drug carrier was investigated using paracetamol (PA) and ibuprofen (IBU) as model drugs. The solution impregnation method was used for drug loading, with loading efficiency determined by UV spectroscopy and drug release kinetics studied using USP II dissolution apparatus. The physical state of the drug in the complex was characterised using differential scanning calorimetry and X-ray diffractions techniques, whilst sites of drug adsorption were studied using Fourier transform infrared spectroscopy and N 2 adsorption techniques. In addition, the cytotoxicity of AC on human colon carcinoma (Caco-2) cells was assessed using the MTT assay. Results presented here reveal that, for PA/AC and IBU/AC complexes, the saturation solubility of the drug in the loading solvent appears to have an effect on the drug loading efficiency and the physical state of the drug loaded, whilst drug release kinetics were affected by the wettability of the activated carbon particles. Furthermore, activated carbon microparticles exhibited very low cytotoxicity on Caco-2 cells at the concentrations tested (10-800μg/mL). This study, therefore, supports the potential of activated carbon as a carrier for amorphous drug delivery. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

    Science.gov (United States)

    Rietmeijer, Frans J. M.

    1990-04-01

    Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous

  7. Effects of heating time on the growth and behavior of amorphous carbon nanostructures from ferrocene

    Science.gov (United States)

    Rafiqul Islam, Md; Rashid, A. K. M. B.; Ferdous, Md; Shafiul Azam, Md

    2017-05-01

    Heating time is one of the crucial factors in various methods employed for the synthesis of carbon nanostructures (CNSs) from ferrocene. However, the effects of heating time on the growth and morphology of the nanostructured materials has not been well explored yet, particularly for amorphous carbon. Herein, we investigate how the variation of heating time impacts the growth of CNSs by carrying out the reaction between ferrocene and ammonium chloride in a solvent free condition at 250 °C. Several different forms of carbon nanostructures yielded from this reaction at 25 min (CNS-25), 30 min (CNS-30), 35 min (CNS-35) and 40 min (CNS-40) were analyzed by means of field emission scanning electron microscopy (FESEM) coupled with energy-dispersive x-ray (EDX), Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy. The final product CNS-40 was washed several times with concentrated hydrochloric acid solution to remove the impurities and then characterized by the means of similar techniques. FTIR spectra of all the nanostructures confirmed the presence of several functional groups such as C  =  C, C-O and -OH etc, which are common in carbonaceous nanostructures. However, the FESEM images obtained are significantly different and suggest a gradual growth of the carbon nanostructures ending up with long carbon nanotubes after 40 min. No absorption peak in the visible region of the UV-Vis spectra of the final product confirms the amorphous nature, which is also supported by XRD of the synthesized nanotube. Moreover, a noteworthy redshift in the UV-Vis peaks reflecting a huge increase in length and diameter of the nanostructures indicates the maximum longitudinal growth of the carbon nanotubes occurs during 35 min to 40 min.

  8. Distinct Short-Range Order Is Inherent to Small Amorphous Calcium Carbonate Clusters (<2 nm)

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Shengtong [Physical Chemistry, University of Konstanz, Universitätsstrasse 10 78457 Konstanz Germany; School of Chemical Engineering, State Key Laboratory of Chemical Engineering, Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, 130 Meilong Road Shanghai 200237 P.R. China; Chevrier, Daniel M. [Department of Chemistry and Institute for Research in Materials, Dalhousie University, Halifax Nova Scotia B3H 4R2 Canada; Zhang, Peng [Department of Chemistry and Institute for Research in Materials, Dalhousie University, Halifax Nova Scotia B3H 4R2 Canada; Gebauer, Denis [Physical Chemistry, University of Konstanz, Universitätsstrasse 10 78457 Konstanz Germany; Cölfen, Helmut [Physical Chemistry, University of Konstanz, Universitätsstrasse 10 78457 Konstanz Germany

    2016-09-09

    Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in such small CaCO3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.

  9. Stress reduction behavior in metal-incorporated amorphous carbon films: first-principles approach

    Energy Technology Data Exchange (ETDEWEB)

    Choi, J-H; Ahn, H-S; Lee, S-C; Lee, K-R [Future Technology Research Division, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650 (Korea, Republic of)

    2006-01-01

    The stress reduction behavior in metal-incorporated amorphous carbon films was investigated by the first-principle calculation. We calculated the total energy of the system with changes in bond angles between the incorporated metal (Ti, Mo, Cr, W, Ag, Au, Al, Si, etc) and the carbon atoms by using DMOL{sup 3}computational software package. The four carbon atoms are arranged as a tetrahedron, with a carbon or metal atom at the center. The total energy increased substantially as the bond angle deviated from the equilibrium value when a carbon atom is located at the tetrahedron center. However, with a replacement by a metal atom at the center of the tetrahedron, the increase in the total energy due to the distortion in bond angle was significantly reduced. The pivotal action of the metal atoms dissolved in the carbon matrix would be more significant when noble metals having filled d-shells are incorporated compared to the transition metals having unfilled d-shells. These atoms have a weak and more isotropic bond with carbon atoms as confirmed by the electron density distribution.

  10. Synthesis and structure of synthetically pure and deuterated amorphous (basic) calcium carbonates.

    Science.gov (United States)

    Wang, Hsiu-Wen; Daemen, Luke L; Cheshire, Michael C; Kidder, Michelle K; Stack, Andrew G; Allard, Lawrence F; Neuefeind, Jörg; Olds, Daniel; Liu, Jue; Page, Katharine

    2017-03-07

    It is generally believed that H2O and OH- are the key species stabilizing and controlling amorphous calcium carbonate "polyamorph" forms, and may in turn control the ultimate crystallization products during synthesis and in natural systems. Yet, the locations and hydrogen-bonding network of these species in ACC have never been measured directly using neutron diffraction. We report a synthesis route that overcomes the existing challenges with respect to yield quantities and deuteration, both of which are critically necessary for high quality neutron studies.

  11. MoO2 nanosheets embedded in amorphous carbon matrix for sodium-ion batteries

    Science.gov (United States)

    He, Hong; Man, Yuhong; Yang, Jingang; Xie, Jiale; Xu, Maowen

    2017-10-01

    MoO2 nanosheets embedded in the amorphous carbon matrix (MoO2/C) are successfully synthesized via a facile hydrothermal method and investigated as an anode for sodium-ion batteries. Because of the efficient ion transport channels and good volume change accommodation, MoO2/C delivers a discharge/charge capacity of 367.8/367.0 mAh g-1 with high coulombic efficiency (99.4%) after 100 cycles at a current density of 50 mA g-1.

  12. Precipitation of Co(2+) carbonates from aqueous solution: insights on the amorphous to crystalline transformation.

    Science.gov (United States)

    González-López, Jorge; Fernández-González, Ángeles; Jiménez, Amalia

    2016-04-01

    Cobalt is toxic metal that is present only as a trace in the Earth crust. However, Co might concentrate on specific areas due to both natural and anthropogenic factors and thus, soils and groundwater can be contaminated. It is from this perspective that we are interested in the precipitation of cobalt carbonates, since co-precipitation with minerals phases is a well-known method for metal immobilization in the environment. In particular, the carbonates are widely used due to its reactivity and natural abundance. In order to evaluate the cobalt carbonate precipitation at room temperature, a simple experimental work was carried out in this work. The precipitation occurred via reaction of two common salts: 0.05M of CoCl2 and 0.05M of Na2CO3 in aqueous solution. After reaction, the precipitated solid was kept in the remaining water at 25 oC and under constant stirring for different aging times of 5 min, 1 and 5 hours, 1, 2, 4, 7, 30 and 60 days. In addition to the aging and precipitation experiments, we carried out experiments to determine the solubility of the solids. In these experiments each precipitate was dissolved in Milli-Q water until equilibrium was reached and then the aqueous solution was analyzed regarding Co2+ and total alkalinity. Furthermore, acid solution calorimetry of the products were attained. Finally, we modeled the results using the PHREEQC code. Solid and aqueous phase identification and characterization have been extensively reported in a previous work (González-López et al., 2015). The main results of our investigation were the initial precipitation of an amorphous cobalt carbonate that evolve towards a poorly crystalline cobalt hydroxide carbonate with aging treatment. Solubility of both phases have been calculated under two different approaches: precipitation and dissolution. Values of solubility from each approach were obtained with a general error due to differences in experiment conditions, for instance, ionic strength, temperature and

  13. Vertical electric field stimulated neural cell functionality on porous amorphous carbon electrodes.

    Science.gov (United States)

    Jain, Shilpee; Sharma, Ashutosh; Basu, Bikramjit

    2013-12-01

    We demonstrate the efficacy of amorphous macroporous carbon substrates as electrodes to support neuronal cell proliferation and differentiation in electric field mediated culture conditions. The electric field was applied perpendicular to carbon substrate electrode, while growing mouse neuroblastoma (N2a) cells in vitro. The placement of the second electrode outside of the cell culture medium allows the investigation of cell response to electric field without the concurrent complexities of submerged electrodes such as potentially toxic electrode reactions, electro-kinetic flows and charge transfer (electrical current) in the cell medium. The macroporous carbon electrodes are uniquely characterized by a higher specific charge storage capacity (0.2 mC/cm(2)) and low impedance (3.3 kΩ at 1 kHz). The optimal window of electric field stimulation for better cell viability and neurite outgrowth is established. When a uniform or a gradient electric field was applied perpendicular to the amorphous carbon substrate, it was found that the N2a cell viability and neurite length were higher at low electric field strengths (≤ 2.5 V/cm) compared to that measured without an applied field (0 V/cm). While the cell viability was assessed by two complementary biochemical assays (MTT and LDH), the differentiation was studied by indirect immunostaining. Overall, the results of the present study unambiguously establish the uniform/gradient vertical electric field based culture protocol to either enhance or to restrict neurite outgrowth respectively at lower or higher field strengths, when neuroblastoma cells are cultured on porous glassy carbon electrodes having a desired combination of electrochemical properties. Copyright © 2013 Elsevier Ltd. All rights reserved.

  14. Computational Evaluation of Amorphous Carbon Coating for Durable Silicon Anodes for Lithium-Ion Batteries

    Directory of Open Access Journals (Sweden)

    Jeongwoon Hwang

    2015-10-01

    Full Text Available We investigate the structural, mechanical, and electronic properties of graphite-like amorphous carbon coating on bulky silicon to examine whether it can improve the durability of the silicon anodes of lithium-ion batteries using molecular dynamics simulations and ab-initio electronic structure calculations. Structural models of carbon coating are constructed using molecular dynamics simulations of atomic carbon deposition with low incident energies (1–16 eV. As the incident energy decreases, the ratio of sp2 carbons increases, that of sp3 decreases, and the carbon films become more porous. The films prepared with very low incident energy contain lithium-ion conducting channels. Also, those films are electrically conductive to supplement the poor conductivity of silicon and can restore their structure after large deformation to accommodate the volume change during the operations. As a result of this study, we suggest that graphite-like porous carbon coating on silicon will extend the lifetime of the silicon anodes of lithium-ion batteries.

  15. Fabrication of periodical surface structures by picosecond laser irradiation of carbon thin films: transformation of amorphous carbon in nanographite

    Energy Technology Data Exchange (ETDEWEB)

    Popescu, C.; Dorcioman, G. [National Institute for Lasers, Plasma and Radiation Physics, 409 Atomistilor Street, Magurele RO-077125 (Romania); Bita, B. [National Institute for Research and Development in Microtechnologies, 126A Erou Iancu Nicolae Street, Voluntari RO-077190 (Romania); Faculty of Physics, 405 Atomistilor Street, Magurele RO-077125 (Romania); Besleaga, C.; Zgura, I. [National Institute of Materials Physics, 105bis Atomistilor Street, Magurele RO-077125 (Romania); Himcinschi, C. [Institute of Theoretical Physics, TU Bergakademie Freiberg, Freiberg D-09596 (Germany); Popescu, A.C., E-mail: andrei.popescu@inflpr.ro [National Institute for Lasers, Plasma and Radiation Physics, 409 Atomistilor Street, Magurele RO-077125 (Romania)

    2016-12-30

    Highlights: • Ripples obtained on carbon films after irradiation with visible ps laser pulses. • Amorphous carbon was transformed in nanographite following irradiation. • Ripples had a complex morphology, being made of islands of smaller ripples. • Hydrophilic carbon films became hydrophobic after surface structuring. - Abstract: Thin films of carbon were synthesized by ns pulsed laser deposition in vacuum on silicon substrates, starting from graphite targets. Further on, the films were irradiated with a picosecond laser source emitting in visible at 532 nm. After tuning of laser parameters, we obtained a film surface covered by laser induced periodical surface structures (LIPSS). They were investigated by optical, scanning electron and atomic force microscopy. It was observed that changing the irradiation angle influences the LIPSS covered area. At high magnification it was revealed that the LIPSS pattern was quite complex, being composed of other small LIPSS islands, interconnected by bridges of nanoparticles. Raman spectra for the non-irradiated carbon films were typical for a-C type of diamond-like carbon, while the LIPSS spectra were characteristic to nano-graphite. The pristine carbon film was hydrophilic, while the LIPSS covered film surface was hydrophobic.

  16. Effect of metal doping on structural characteristics of amorphous carbon system: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiaowei; Zhang, Dong [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Lee, Kwang-Ryeol, E-mail: krlee@kist.re.kr [Computational Science Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Wang, Aiying, E-mail: aywang@nimte.ac.cn [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

    2016-05-31

    First-principles calculation was performed to investigate the effect of metal doping on the structural characteristics of amorphous carbon system, and the 3d transition metals (TM) were particularly selected as representative case. Results showed that the total energy in TM–C systems caused by distorting the bond angles was reduced distinctly for comparison with that in C–C system. Further electronic structure revealed that as the 3d electrons of doped TM increased, the bond characteristic of highest occupied molecular orbital changed from bonding (Sc, Ti) to nonbonding (V, Cr, Mn, Fe) and finally to antibonding (Co, Ni, Cu) between the TM and C atoms. Meanwhile, the TM–C bond presented a mixture of the covalent and ionic characters. The decrease of strength and directionality of TM–C bonds resulted in the total energy change upon bond angle distortion, which demonstrated that the bond characteristics played an important role in reducing residual stress of TM-doped amorphous carbon systems. - Highlights: • The bond characteristics as 3d electrons changed from bonding, nonbonding to antibonding. • The TM–C bond was a mixture of covalent and ionic characters. • Reduced strength and directionality of TM–C bond led to small distortion energy change. • The weak TM–C bond accounted for the reduced compressive stress caused by TM.

  17. Controlled fluoridation of amorphous carbon films deposited at reactive plasma conditions

    Directory of Open Access Journals (Sweden)

    Yoffe Alexander

    2015-09-01

    Full Text Available A study of the correlations between plasma parameters, gas ratios, and deposited amorphous carbon film properties is presented. The injection of a C4F8/Ar/N2 mixture of gases was successfully used in an inductively coupled plasma system for the preparation of amorphous carbon films with different fluoride doping at room-temperature, using silicon as a substrate. This coating was formed at low-pressure and low-energy using an inductively coupled plasma process. A strong dependence between the ratios of gases during deposition and the composition of the substrate compounds was shown. The values of ratios between Ar (or Ar+N2 and C4F8 - 1:1 and between N2 and Ar - 1:2 in the N2/Ar/C4F8 mixture were found as the best for low fluoridated coatings. In addition, an example of improving the etch-passivation in the Bosch procedure was described. Scanning electron microscopy with energy dispersive spectroscopy options, X-ray diffraction, and X-ray reflectivity were used for quantitative analysis of the deposited films.

  18. Electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride

    Directory of Open Access Journals (Sweden)

    Buiculescu Raluca

    2011-01-01

    Full Text Available Abstract The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima.

  19. Study on effects of carbon impurities and oxygen vacancies in amorphous alumina phosphor prepared via a solution method

    Energy Technology Data Exchange (ETDEWEB)

    Wakui, Yoshinori; Takahashi, Kanako [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Shan, Yue Jin, E-mail: shan@cc.utsunomiya-u.ac.jp [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Tezuka, Keitaro; Imoto, Hideo [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Hosokawa, Shogo; Shinozaki, Norifumi [Tatsumori Ltd., 50 Minami-Kawada, Kami-Yukiai, Tamura-cho, Koriyama-shi, Fukushima 963-0724 (Japan); Ando, Mariko; Maekawa, Hideki [Graduate School of Engineering, Tohoku University, 6-6-04 Aramaki Aoba, Sendai-shi, Miyagi 980-8579 (Japan)

    2015-01-15

    The amorphous alumina phosphors without containing expensive or toxic elements were prepared via a solution method. The obtained sample indicates bluish-white emission centered at 390–430 nm by UV excitation. According to the measurement results of Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FT-IR) and organic microanalysis, it is found that the carbon impurities exist in the sample and they are essential for luminescence. On the other hand, {sup 27}Al NMR measurements indicate the presence of Al of 5-coordination. Moreover, there is good correspondence among the excitation spectra of the emission samples, the experimental optical properties of amorphous alumina, and the calculated oxygen vacancies levels in amorphous alumina model. Therefore, the new luminescence mechanism can be proposed as follows; the electrons in valence band are excited to oxygen vacancies bands by UV light and return to ground state through the carbon impurities band, being accompanied by the bluish-white emission. - Highlights: • The amorphous alumina prepared via solution method shows bluish-white emission. • According to the ESR results, carbon impurities are necessary for luminescence. • FT-IR, NMR and UV–vis measurements of the samples were conducted. • Our results indicated that oxygen vacancies play an important role. • We proposed the new luminescence mechanism for amorphous alumina phosphor.

  20. Study of CVD diamond layers with amorphous carbon admixture by Raman scattering spectroscopy

    Directory of Open Access Journals (Sweden)

    Dychalska Anna

    2015-12-01

    Full Text Available Raman spectroscopy is a most often used standard technique for characterization of different carbon materials. In this work we present the Raman spectra of polycrystalline diamond layers of different quality, synthesized by Hot Filament Chemical Vapor Deposition method (HF CVD. We show how to use Raman spectroscopy for the analysis of the Raman bands to determine the structure of diamond films as well as the structure of amorphous carbon admixture. Raman spectroscopy has become an important technique for the analysis of CVD diamond films. The first-order diamond Raman peak at ca. 1332 cm−1 is an unambiguous evidence for the presence of diamond phase in the deposited layer. However, the existence of non-diamond carbon components in a CVD diamond layer produces several overlapping peaks in the same wavenumber region as the first order diamond peak. The intensities, wavenumber, full width at half maximum (FWHM of these bands are dependent on quality of diamond layer which is dependent on the deposition conditions. The aim of the present work is to relate the features of diamond Raman spectra to the features of Raman spectra of non-diamond phase admixture and occurrence of other carbon structures in the obtained diamond thin films.

  1. Fast deposition of amorphous carbon films by an expanding cascaded arc plasma jet

    Science.gov (United States)

    Buuron, A. J. M.; van de Sanden, M. C. M.; van Ooij, W. J.; Driessens, R. M. A.; Schram, D. C.

    1995-07-01

    Using an expanding cascaded arc plasma jet, amorphous hydrogenated and fluorohydrogenated carbon films were deposited on silicon, glass, and steel substrates at high rates of tens of nanometers per second and on large areas of up to 100 cm2. The present work was aimed at depositing amorphous carbon films suited for optical and protective applications. Films deposited with the common argon/methane or argon/acetylene mixture tend to delaminate from the substrate when the film is thicker than about 1 μm. For this reason, also trials using other compounds like C7H8 (toluene), CF4, and H2, and mixtures of these, were carried out. Using toluene, several-μm-thick films with good adhesion to the substrate were deposited. With spectroscopic ellipsometry and infrared absorption spectroscopy optical parameters were obtained. Appropriate numerical models were developed for analyzing the data, taking into account interference fringes in the spectra due to multiple reflections in the thin film. The hydrogen and oxygen content in the films were determined with nuclear recoil techniques. Films deposited with the use of methane and acetylene are diamondlike with mainly sp3 bonding types, and a hydrogen content ranging from 36 to 26 at. % (with a low oxygen contamination of 1-2 at. %). Films deposited with the use of toluene are more polymerlike, with also sp1 and sp2 bonding types. These films have a high hydrogen content (35 at. %), and can be partially oxidized (up to 13 at. %). In general, going from the polymerlike to the more diamondlike films, the refractive index increases from 1.3 to 2.2, and the band gap decreases from about 2 to 1 eV. By the admixture of hydrogen in the deposition plasma diamondlike films were produced with a larger band gap of 2.2 eV. The corrosion performance of the films was studied by storing them in a humidity cabinet. The corrosion resistance of films deposited with hydrocarbon/argon plasma mixtures appears to be limited. Thick films with a good

  2. Transformation and Crystallization Energetics of Synthetic and Biogenic Amorphous Calcium Carbonate

    Energy Technology Data Exchange (ETDEWEB)

    Radha, A. V. [Peter A. Rock Thermochemistry Lab. and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), Univ. of California, Davis, CA (United States); Forbes, Tori Z. [Peter A. Rock Thermochemistry Lab. and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), Univ. of California, Davis, CA (United States); Killian, Christopher E. [Univ. of Wisconsin, Madison, WI (United States); Gilbert, P.U.P.A [Univ. of Wisconsin, Madison, WI (United States); Navrotsky, Alexandra [Peter A. Rock Thermochemistry Lab. and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), Univ. of California, Davis, CA (United States)

    2010-01-01

    Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC→anhydrous ACC ~ biogenic anhydrous ACC→vaterite → aragonite → calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO₂ sequestration.

  3. Highly ordered amorphous silicon-carbon alloys obtained by RF PECVD

    CERN Document Server

    Pereyra, I; Carreno, M N P; Prado, R J; Fantini, M C A

    2000-01-01

    We have shown that close to stoichiometry RF PECVD amorphous silicon carbon alloys deposited under silane starving plasma conditions exhibit a tendency towards c-Si C chemical order. Motivated by this trend, we further explore the effect of increasing RF power and H sub 2 dilution of the gaseous mixtures, aiming to obtain the amorphous counterpart of c-Si C by the RF-PECVD technique. Doping experiments were also performed on ordered material using phosphorus and nitrogen as donor impurities and boron and aluminum as acceptor ones. For nitrogen a doping efficiency close to device quality a-Si:H was obtained, the lower activation energy being 0,12 eV with room temperature dark conductivity of 2.10 sup - sup 3 (OMEGA.cm). Nitrogen doping efficiency was higher than phosphorous for all studied samples. For p-type doping, results indicate that, even though the attained conductivity values are not device levels, aluminum doping conducted to a promising shift in the Fermi level. Also, aluminum resulted a more efficie...

  4. Highly ordered amorphous silicon-carbon alloys obtained by RF PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Pereyra, I.; Villacorta, C.A.; Carreno, M.N.P. [Sao Paulo Univ., SP (Brazil). Escola Politecnica. Dept. de Engenharia de Sistemas Eletronicos; Prado, R.J.; Fantini, M.C.A. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica

    2000-09-01

    We have shown that close to stoichiometry RF PECVD amorphous silicon carbon alloys deposited under silane starving plasma conditions exhibit a tendency towards c-Si C chemical order. Motivated by this trend, we further explore the effect of increasing RF power and H{sub 2} dilution of the gaseous mixtures, aiming to obtain the amorphous counterpart of c-Si C by the RF-PECVD technique. Doping experiments were also performed on ordered material using phosphorus and nitrogen as donor impurities and boron and aluminum as acceptor ones. For nitrogen a doping efficiency close to device quality a-Si:H was obtained, the lower activation energy being 0,12 eV with room temperature dark conductivity of 2.10{sup -3} ({omega}.cm). Nitrogen doping efficiency was higher than phosphorous for all studied samples. For p-type doping, results indicate that, even though the attained conductivity values are not device levels, aluminum doping conducted to a promising shift in the Fermi level. Also, aluminum resulted a more efficient acceptor than boron, in accordance to observations in crystalline Si C material. (author)

  5. A Low-Stress, Elastic, and Improved Hardness Hydrogenated Amorphous Carbon Film

    Directory of Open Access Journals (Sweden)

    Qi Wang

    2015-01-01

    Full Text Available The evolution of hydrogenated amorphous carbon films with fullerene-like microstructure was investigated with a different proportion of hydrogen supply in deposition. The results showed at hydrogen flow rate of 50 sccm, the deposited films showed a lower compressive stress (lower 48.6%, higher elastic recovery (higher 19.6%, near elastic recovery rate 90%, and higher hardness (higher 7.4% compared with the films deposited without hydrogen introduction. Structural analysis showed that the films with relatively high sp2 content and low bonded hydrogen content possessed high hardness, elastic recovery rate, and low compressive stress. It was attributed to the curved graphite microstructure, which can form three-dimensional covalently bonded network.

  6. A Selective Metasurface Absorber with An Amorphous Carbon Interlayer for Solar Thermal Applications

    CERN Document Server

    Wan, Chenglong; Nunez-Sanchez, S; Chen, Lifeng; Lopez-Garcia, M; Pugh, J; Zhu, Bofeng; Selvaraj, P; Mallick, T; Senthilarasu, S; Cryan, M J

    2016-01-01

    This paper presents fabrication, measurement and modelling results for a metal-dielectric-metal metasurface absorber for solar thermal applications. The structure uses amorphous carbon as an inter-layer between thin gold films with the upper film patterned with a 2D periodic array using focused ion beam etching. The patterned has been optimised to give high absorptance from 400-1200nm and low absorptance above this wavelength range to minimise thermal radiation and hence obtain higher temperature performance. Wide angle absorptance results are shown and detailed modelling of a realistic nanostructured upper layer results in excellent agreement between measured and modelled results. The use of gold in this paper is a first step towards a high temperature metasurface where gold can be replaced by other refractory metals such as tungsten or chrome.

  7. Increased sensitivity of amorphous carbon based gas-sensors due to different Au nanostructures

    Science.gov (United States)

    Liu, K. W.; Chen, B. Y.; Hsu, H. S.; Ju, S. P.; Sun, S. J.; Chou, H.; Spintronics lab Collaboration

    We reported that gold nanoparticles attached with the amorphous carbon (a-C) could promote sp2 bonds around the gold nanoparticles. This can change the hopping characteristics and can control the carrier transport which results in increased conductivity. These nanocomposites exhibit a superior sensitivity towards NH3 at room temperature, as well as good reproducibility and short response/recovery time. To increase the sensitivity of gas-sensors we need to increase the interface effect between gold nanostructures and a-C. To increase this interface effect we choose gold nanorods instead of nanoparticles. To grow the gold nanorods along z-direction perpendicular to the substrate surface we use low temperature deposition technique. Improvement in the interfacial effect will greatly improve the sensitivity of gas-sensors.

  8. Sizeable magnetic circular dichroism of artificially precipitated Co clusters in amorphous carbon

    Directory of Open Access Journals (Sweden)

    H. S. Hsu

    2012-09-01

    Full Text Available This study examines sizeable magnetic circular dichroism (MCD in Co(20%-doped amorphous carbon (a-C films. While as-grown films exhibit a non-detectable MCD signal, films that undergo rapid thermal annealing (RTA at 600°C in a vacuum yield broad MCD spectra with a large amplitude of ∼3.9 × 104 deg/cm in saturation field 0.78 T at the σ-σ* gap transition (∼5.5 eV. In such films after RTA, the metastable Co-C bonding is decomposed and suitable Co nanoparticles/a-C interfaces are thus formed. Our results indicate that the large change in MCD is contributed from Co nanoparticles and associated with the spin-dependent electronic structure at the Co/a-C interfaces.

  9. Mechanism of wiggling enhancement due to HBr gas addition during amorphous carbon etching

    Science.gov (United States)

    Kofuji, Naoyuki; Ishimura, Hiroaki; Kobayashi, Hitoshi; Une, Satoshi

    2015-06-01

    The effect of gas chemistry during etching of an amorphous carbon layer (ACL) on wiggling has been investigated, focusing especially on the changes in residual stress. Although the HBr gas addition reduces critical dimension loss, it enhances the surface stress and therefore increases wiggling. Attenuated total reflectance Fourier transform infrared spectroscopy revealed that the increase in surface stress was caused by hydrogenation of the ACL surface with hydrogen radicals. Three-dimensional (3D) nonlinear finite element method analysis confirmed that the increase in surface stress is large enough to cause the wiggling. These results also suggest that etching with hydrogen compound gases using an ACL mask has high potential to cause the wiggling.

  10. Correlation between bonding structure and mechanical properties of amorphous carbon nitride thin films

    Energy Technology Data Exchange (ETDEWEB)

    Quiros, C.; Nunez, R.; Prieto, P. [Universidad Autonoma de Madrid (Spain). Dept. de Fisica Aplicada; Vergara, I.; Caceres, D. [Dpto. de Fisica, Universidad Carlos III de Madrid, C/ Butarque 15, E-28915 Leganes, Madrid (Spain); Soriano, L.; Fuentes, G.G.; Elizalde, E.; Sanz, J.M. [Dpto. de Fisica Aplicada, C-XII, Universidad Autonoma de Madrid, E-28049, Madrid (Spain)

    2000-03-01

    Amorphous carbon nitride thin films were prepared in a dual ion beam sputtering (DIBS) system. The N/C atomic concentration ratio ranged between 0.3 and 0.5 as determined by quantitative X-ray photoelectron spectroscopy (XPS) of the surface. Fourier transform infrared spectroscopy (FT-IR), XPS and X-ray absorption spectroscopy (XAS) were used to obtain information about the different types of bonding present in the films. The hardness and the Young's modulus of the samples were determined by nanoindentation measurements. The hardness varied in the range 15-30 GPa with Young's modulus between 170 and 250 GPa. In order to explain the measured hardness, some of the films are considered as heterogeneous, in good agreement with the XPS, FT-IR and XAS data. (orig.)

  11. Improved adhesion and tribological properties of fast-deposited hard graphite-like hydrogenated amorphous carbon films

    NARCIS (Netherlands)

    Zaharia, T.; Kudlacek, P.; Creatore, M.; Groenen, R.; Persoone, P.; M. C. M. van de Sanden,

    2011-01-01

    Graphite-like hard hydrogenated amorphous carbon (a-C:H) was deposited using an Ar-C(2)H(2) expanding thermal plasma chemical vapour deposition (ETP-CVD) process. The relatively high hardness of the fast deposited a-C:H material leads to high compressive stress resulting in poor adhesion between the

  12. Nanoindentation behaviors of amorphous carbon films containing nanocrystalline graphite and diamond clusters prepared by radio frequency sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Xue [Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049 (China); Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656 (Japan); Nose, Kenji [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); Diao, Dongfeng, E-mail: dfdiao@szu.edu.cn [Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049 (China); Nanosurface Science and Engineering Research Institute, Shenzhen University, Shenzhen 518060 (China); Yoshida, Toyonobu [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656 (Japan)

    2013-05-15

    Amorphous carbon (a-C) films were prepared by a radio-frequency sputtering method. Nano structures in the films were controlled by changing the ion irradiation energy and deposition temperature. It was found that nanocrystalline graphite and diamond clusters were embedded in the pure amorphous structure with sizes of approximately 5 nm. a-C films contained nanocrystalline graphite clusters (a-C:NCG) were obtained with the ion energy ranging from 50 to 120 eV and temperature in 300–370 K. a-C film contained nanocrystalline diamond clusters (a-C:NCD) was obtained with 120 eV at 570 K. Nanoindentation behaviors of these carbon films were compared with pure amorphous structured carbon film. The percentage of elastic recoveries of a-C:NCD, a-C, and a-C:NCG films were obtained to be 81.9%, 84.3%, and 87.5%, respectively. Pop-in steps with about 3 nm displacement appeared in loading curves for a-C:NCG film, and 10 nm for a-C:NCD film. These results showed that the nanoindentation behaviors of amorphous carbon film containing cross-linked nanocrystalline graphite clusters is better than that of diamond clusters.

  13. A mixed flow reactor method to synthesize amorphous calcium carbonate under controlled chemical conditions.

    Science.gov (United States)

    Blue, Christina R; Rimstidt, J Donald; Dove, Patricia M

    2013-01-01

    This study describes a new procedure to synthesize amorphous calcium carbonate (ACC) from well-characterized solutions that maintain a constant supersaturation. The method uses a mixed flow reactor to prepare ACC in significant quantities with consistent compositions. The experimental design utilizes a high-precision solution pump that enables the reactant solution to continuously flow through the reactor under constant mixing and allows the precipitation of ACC to reach steady state. As a proof of concept, we produced ACC with controlled Mg contents by regulating the Mg/Ca ratio of the input solution and the carbonate concentration and pH. Our findings show that the Mg/Ca ratio of the reactant solution is the primary control for the Mg content in ACC, as shown in previous studies, but ACC composition is further regulated by the carbonate concentration and pH of the reactant solution. The method offers promise for quantitative studies of ACC composition and properties and for investigating the role of this phase as a reactive precursor to biogenic minerals. © 2013 Elsevier Inc. All rights reserved.

  14. Characterization and antibacterial performance of ZrCN/amorphous carbon coatings deposited on titanium implants

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Chih-Ho [School of Medicine, China Medical University, Taichung, 404 Taiwan (China); Chang, Yin-Yu, E-mail: yinyu@mail2000.com.tw [Department of Mechanical and Computer-Aided Engineering, National Formosa University, Yunlin, Taiwan (China); Huang, Heng-Li [School of Dentistry, China Medical University, Taichung, Taiwan (China); Kao, Ho-Yi [Department of Materials Science and Engineering, Mingdao University, Changhua, Taiwan (China)

    2011-12-30

    Titanium (Ti)-based materials have been used for dental/orthopedic implants due to their excellent biological compatibility, superior mechanical strength and high corrosion resistance. The osseointegration of Ti implants is related to their composition and surface treatment. Better biocompatibility and anti-bacterial performances of Ti implant are beneficial for the osseointegration and for avoiding the infection after implantation surgery. In this study, nanocomposite ZrCN/amorphous carbon (a-C) coatings with different carbon contents were deposited on a bio-grade pure Ti implant material. A cathodic-arc evaporation system with plasma enhanced duct equipment was used for the deposition of ZrCN/a-C coatings. Reactive gas (N{sub 2}) and C{sub 2}H{sub 2} activated by the zirconium plasma in the evaporation process were used to deposit the ZrCN/a-C coatings. To verify the susceptibility of implant surface to bacterial adhesion, Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans), one of the major pathogen frequently found in the dental implant-associated infections, was chosen for in vitro anti-bacterial analyses. In addition, the biocompatibility of human gingival fibroblast (HGF) cells on coatings was also evaluated by a cell proliferation assay. The results suggested that the ZrCN/a-C coatings with carbon content higher than 12.7 at.% can improve antibacterial performance with excellent HGF cell compatibility as well.

  15. Phototransformation-Induced Aggregation of Functionalized Single-Walled Carbon Nanotubes: The Importance of Amorphous Carbon

    Science.gov (United States)

    Single-walled carbon nanotubes (SWCNTs) with proper functionalization are desirable for applications that require dispersion in aqueous and biological environments, and functionalized SWCNTs also serve as building blocks for conjugation with specific molecules in these applicatio...

  16. Highly Efficient Performance and Conversion Pathway of Photocatalytic NO Oxidation on SrO-Clusters@Amorphous Carbon Nitride.

    Science.gov (United States)

    Cui, Wen; Li, Jieyuan; Dong, Fan; Sun, Yanjuan; Jiang, Guangming; Cen, Wanglai; Lee, S C; Wu, Zhongbiao

    2017-09-19

    This work demonstrates the first molecular-level conversion pathway of NO oxidation over a novel SrO-clusters@amorphous carbon nitride (SCO-ACN) photocatalyst, which is synthesized via copyrolysis of urea and SrCO 3 . The inclusion of SrCO 3 is crucial in the formation of the amorphous carbon nitride (ACN) and SrO clusters by attacking the intralayer hydrogen bonds at the edge sites of graphitic carbon nitride (CN). The amorphous nature of ACN can promote the transportation, migration, and transformation of charge carriers on SCO-ACN. And the SrO clusters are identified as the newly formed active centers to facilitate the activation of NO via the formation of Sr-NO δ(+) , which essentially promotes the conversion of NO to the final products. The combined effects of the amorphous structure and SrO clusters impart outstanding photocatalytic NO removal efficiency to the SCO-ACN under visible-light irradiation. To reveal the photocatalytic mechanism, the adsorption and photocatalytic oxidation of NO over CN and SCO-ACN are analyzed by in situ DRIFTS, and the intermediates and conversion pathways are elucidated and compared. This work presents a novel in situ DRIFTS-based strategy to explore the photocatalytic reaction pathway of NO oxidation, which is quite beneficial to understand the mechanism underlying the photocatalytic reaction and advance the development of photocatalytic technology for environmental remediation.

  17. Formation of self-supporting porous graphite structures by Spark Plasma Sintering of nickel-amorphous carbon mixtures

    Science.gov (United States)

    Bokhonov, Boris B.; Dudina, Dina V.; Ukhina, Arina V.; Korchagin, Michail A.; Bulina, Natalia V.; Mali, Vyacheslav I.; Anisimov, Alexander G.

    2015-01-01

    Graphitization of amorphous carbon in the presence of nickel has been reported for various configurations of the metal-carbon interface; however, no study has been performed to evaluate a possibility of forming self-supporting networks by sintering of the in situ formed graphite. In this work, we have shown that Spark Plasma Sintering (SPS) of nickel-amorphous carbon mixtures containing 50 vol% of Ni at 1000 °C results in the formation of networks formed by sintered graphite platelets 50-200 nm thick and 0.3-2 μm in diameter. Upon selective dissolution of nickel, a self-supporting porous 3D skeleton was revealed in 20 mm-diameter compacts. Starting from the mechanically milled Ni-C mixture, porous graphite of uniform microstructure and containing submicron pores was obtained. A model study has been performed, in which a thin amorphous carbon film graphitized during annealing and formed a continuous graphite film with micron-sized grains covering an area of 2 cm×2 cm of the surface of a Ni foil. We discuss the role of the in situ formation of graphite by nickel-assisted graphitization in the formation of networks consisting of well sintered platelets during the SPS and the design possibilities of porous carbon materials produced by phase separation in nickel-graphite composites.

  18. Spectroscopic properties of nitrogen doped hydrogenated amorphous carbon films grown by radio frequency plasma-enhanced chemical vapor deposition

    Science.gov (United States)

    Hayashi, Y.; Yu, G.; Rahman, M. M.; Krishna, K. M.; Soga, T.; Jimbo, T.; Umeno, M.

    2001-06-01

    Nitrogen doped hydrogenated amorphous carbon thin films have been deposited by rf plasma-enhanced chemical vapor deposition using CH4 as the source of carbon and with different nitrogen flow rates (N2/CH4 gas ratios between 0 and 3), at 300 K. The dependence modifications of the optical and the structural properties on nitrogen incorporation were investigated using different spectroscopic techniques, such as, Raman spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy, electron spin resonance (ESR), photoluminescence (PL) and spectroscopic ellipsometry (SE). Raman spectroscopy and IR absorption reveal an increase in sp2-bonded carbon or a change in sp2 domain size with increasing nitrogen flow rate. It is found that the configuration of nitrogen atoms incorporated into an amorphous carbon network gradually changes from nitrogen atoms surrounded by three (σ bonded) to two (π bonded) neighboring carbons with increasing nitrogen flow rate. Tauc optical gap is reduced from 2.6 to 2.0 eV, and the ESR spin density and the peak-to-peak linewidth increase sharply with increasing nitrogen flow rate. Excellent agreement has been found between the measured SE data and modeled spectra, in which an empirical dielectric function of amorphous materials and a linear void distribution along the thickness have been assumed. The influence of nitrogen on the electronic density of states is explained based on the optical properties measured by UV-VIS and PL including nitrogen lone pair band.

  19. Characterization and evaluation of amorphous carbon thin film (ACTF) for sodium ion adsorption

    Science.gov (United States)

    Fathy, Mahmoud; Mousa, Mahmoud Ahmed; Moghny, Th. Abdel; Awadallah, Ahmed E.

    2017-07-01

    The removal of sodium ions from aqueous solutions by adsorption onto amorphous carbon thin film (ACTF) has been studied in batch mode. In this work, the ACTF as new adsorbent was synthesized based on rice straw, then its structure and properties were taken into consideration to study its ability to adsorb sodium ions from synthetic water. The influence of pH, contact time, and temperature of the ion adsorption on ACTF was also studied using batch tests. We found that the contact time of sodium adsorption and its isothermal adsorption studied were described by pseudo-second-order kinetic model and Langmuir isotherm, respectively. Our results indicated that the adsorption of sodium ions on ACTF become be stronger and depends on pH, furthermore, the maximum adsorption capacities of sodium on ACTF recorded 107, 120 and 135 mg g-1 at 35, 45, and 65 °C. The thermodynamic parameters explain that the adsorption of sodium ions on ACTF is a spontaneous process and endothermic reaction. According to adsorption studies, we found that the ACTF can be used effectively for ion chromatography or desalinate sodium ion using ion exchange process in the hybrid desalination process with insignificant loss of adsorption capacity. However, the ACTF has better properties than any other carbon materials obtained from an agricultural byproduct.

  20. Transformation of Graphitic and Amorphous Carbon Dust to Complex Organic Molecules in a Massive Carbon Cycle in Protostellar Nebulae

    Science.gov (United States)

    Nuth, Joseph A., III; Johnson, Natasha M.

    2012-01-01

    More than 95% of silicate minerals and other oxides found in meteorites were melted, or vaporized and recondensed in the Solar Nebula prior to their incorporation into meteorite parent bodies. Gravitational accretion energy and heating via radioactive decay further transformed oxide minerals accreted into planetesimals. In such an oxygen-rich environment the carbonaceous dust that fell into the nebula as an intimate mixture with oxide grains should have been almost completely converted to CO. While some pre-collapse, molecular-cloud carbonaceous dust does survive, much in the same manner as do pre-solar oxide grains, such materials constitute only a few percent of meteoritic carbon and are clearly distinguished by elevated D/H, N-15/N-16, C-13/C-12 ratios or noble gas patterns. Carbonaceous Dust in Meteorites: We argue that nearly all of the carbon in meteorites was synthesized in the Solar Nebula from CO and that this CO was generated by the reaction of carbonaceous dust with solid oxides, water or OH. It is probable that some fraction of carbonaceous dust that is newly synthesized in the Solar Nebula is also converted back into CO by additional thermal processing. CO processing might occur on grains in the outer nebula through irradiation of CO-containing ice coatings or in the inner nebula via Fischer-Tropsch type (FTT) reactions on grain surfaces. Large-scale transport of both gaseous reaction products and dust from the inner nebula out to regions where comets formed would spread newly formed carbonaceous materials throughout the solar nebula. Formation of Organic Carbon: Carbon dust in the ISM might easily be described as inorganic graphite or amorphous carbon, with relatively low structural abundances of H, N, O and S . Products of FTT reactions or organics produced via irradiation of icy grains contain abundant aromatic and aliphatic hydrocarbons. aldehydes, keytones, acids, amines and amides.. The net result of the massive nebular carbon cycle is to convert

  1. Amorphous and crystalline calcium carbonate phases during carbonation of nanolimes: implications in heritage conservation

    Czech Academy of Sciences Publication Activity Database

    Rodriguez-Navarro, C.; Elert, K.; Ševčík, Radek

    2016-01-01

    Roč. 18, č. 35 (2016), s. 6594-6607 ISSN 1466-8033 R&D Projects: GA ČR(CZ) GP14-20374P; GA MŠk(CZ) LO1219 Keywords : carbonation * nanolime * kinetics * CaCO3 polymorphs Subject RIV: AL - Art, Architecture, Cultural Heritage Impact factor: 3.474, year: 2016 http://pubs.rsc.org/en/Content/ArticleLanding/2016/CE/c6ce01202g#!divAbstract

  2. Synthesis and electrochemical property of amorphous carbon nanotubes wrapped sulfur particles as cathode material for lithium-sulfur batteries

    Science.gov (United States)

    Hu, Jingtian; Zhao, Tingkai; Ji, Xianglin; Peng, Xiarong; Jin, Wenbo; Yang, Wenbo; Zhang, Lei; Gao, Junjie; Dang, Alei; Li, Hao; Li, Tiehu

    2017-11-01

    Amorphous carbon nanotube (ACNT)/sulfur composites were prepared by solution reaction method. The electrochemical results showed that both ACNT/S composite and ACNT/S mixture had a first reversible capacity of 1020 mA h·g-1, and the capacity retention of ACNT/S composite was 77% after 100 cycles while that of ACNT/S mixture was only 35% with the initial capacity being 850 mA h·g-1. The experimental results showed that the reversible lithium insertion capacity of the composite was obviously high and the cycling stability was good, which was mainly due to the solid and uniform dispersion of the sulfur and amorphous carbon nanotube matrix in the composite.

  3. Mapping residual organics and carbonate at grain boundaries and in the amorphous interphase in mouse incisor enamel

    Directory of Open Access Journals (Sweden)

    Lyle M Gordon

    2015-03-01

    Full Text Available Dental enamel has evolved to resist the most grueling conditions of mechanical stress, fatigue, and wear. Adding insult to injury, it is exposed to the frequently corrosive environment of the oral cavity. While its hierarchical structure is unrivaled in its mechanical resilience, heterogeneity in the distribution of magnesium ions and the presence of Mg-substituted amorphous calcium phosphate (Mg-ACP as an intergranular phase have recently been shown to increase the susceptibility of mouse enamel to acid attack. Herein we investigate the distribution of two important constituents of enamel, residual organic matter and inorganic carbonate. We find that organics, carbonate, and possibly water show distinct distribution patterns in the mouse enamel crystallites, at simple grain boundaries, and in the amorphous interphase at multiple grain boundaries. This has implications for the resistance to acid corrosion, mechanical properties, and the mechanism by which enamel crystals grow during amelogenesis.

  4. Acid polysaccharide-induced amorphous calcium carbonate (ACC) films: colloidal nanoparticle self-organization process.

    Science.gov (United States)

    Zhong, Chao; Chu, C Chang

    2009-03-03

    Amorphous calcium carbonate (ACC) plays important roles in biomineralization, and its synthesis in vitro has been of keen interest in the field of biomimetic materials. In this report, we describe the synthesis of ACC films using a novel acid polysaccharide, maleic chitosan, as an additive. We prepared the films by directly depositing them onto TEM grids and examined them using polarized optical microscopy (POM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED). This enabled us to examine their formation and mesostructure without introducing artifacts. We observed that, in the presence of maleic chitosan, the ACC films are formed through a particle buildup process, with aggregation and coalescence occurring simultaneously. Nanoparticles with a size of less than 10 nm appear to be the basic units responsible for such self-organization. We suggest that the acid polysaccharide plays an important role in forming and stabilizing these nanoparticles, and we propose a colloidal nanoparticle self-organization model to explain the formation of the ACC films.

  5. Thermal stability of perfluorinated molecular monolayers immobilized on pulsed laser deposited amorphous carbon surfaces

    Science.gov (United States)

    Godet, Christian; Sabbah, Hussein; Hervé, Marie; Ababou-Girard, Soraya; Députier, Stéphanie; Perrin, André; Guilloux-Viry, Maryline; Solal, Francine

    2010-11-01

    Amorphous carbon (a-C) films grown by Pulsed Laser Deposition were optimized to get smooth surfaces with sp3-rich hybridization, sp3/(sp2+sp3) = 0.45-0.65. Under UHV annealing conditions, some sp3-to-sp2 conversion mechanism becomes efficient above 350°C. Covalent immobilization of linear alkene molecular layers was performed by a thermally-assisted (160-300°C) process, using perfluorodecene (PFD) in the gas phase, with no physical or chemical surface preparation of a-C films. Quantitative XPS analysis indicates the immobilization of a dense molecular monolayer. Thermal stability of the grafted PFD monolayer is investigated by using UHV annealing steps to derive the desorption rate constant k(T) and the temperature corresponding to half initial coverage (T1/2 = 460°C). The slower desorption rate of perfluorodecene monolayers immobilized on a-C as compared with a-Si:H surfaces reveals the role of the covalent C-C interface bond in the robustness of the molecule / semiconductor assembly.

  6. Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

    Energy Technology Data Exchange (ETDEWEB)

    Caro, Miguel A., E-mail: mcaroba@gmail.com [Department of Electrical Engineering and Automation, Aalto University, Espoo (Finland); Department of Applied Physics, COMP Centre of Excellence in Computational Nanoscience, Aalto University, Espoo (Finland); Määttä, Jukka [Department of Chemistry, Aalto University, Espoo (Finland); Lopez-Acevedo, Olga [Department of Applied Physics, COMP Centre of Excellence in Computational Nanoscience, Aalto University, Espoo (Finland); Laurila, Tomi [Department of Electrical Engineering and Automation, Aalto University, Espoo (Finland)

    2015-01-21

    In this paper, we obtain the energy band positions of amorphous carbon (a–C) surfaces in vacuum and in aqueous environment. The calculations are performed using a combination of (i) classical molecular dynamics (MD), (ii) Kohn-Sham density functional theory with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, and (iii) the screened-exchange hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE). PBE allows an accurate generation of a-C and the evaluation of the local electrostatic potential in the a-C/water system, HSE yields an improved description of energetic positions which is critical in this case, and classical MD enables a computationally affordable description of water. Our explicit calculation shows that, both in vacuo and in aqueous environment, the a-C electronic states available in the region comprised between the H{sub 2}/H{sub 2}O and O{sub 2}/H{sub 2}O levels of water correspond to both occupied and unoccupied states within the a-C pseudogap region. These are localized states associated to sp{sup 2} sites in a-C. The band realignment induces a shift of approximately 300 meV of the a-C energy band positions with respect to the redox levels of water.

  7. Pseudo first ordered adsorption of noxious textile dyes by low-temperature synthesized amorphous carbon nanotubes

    Science.gov (United States)

    Banerjee, D.; Bhowmick, P.; Pahari, D.; Santra, S.; Sarkar, S.; Das, B.; Chattopadhyay, K. K.

    2017-03-01

    Amorphous carbon nanotubes (a-CNTs) were synthesized by solid state reaction. The as prepared a-CNTs were characterized by X-ray diffraction, field emission scanning and high resolution transmission electron microscope and Raman spectroscopy. As-synthesized a-CNTs were used for, the first time, for removing different organic dyes from water. The dyes mainly include Rhodamine B and Methyl Orange and systematic batch mode studies of a-CNTs assisted adsorption have been executed in detail. The removing efficiency of a-CNTs has also been investigated for various sorption parameters like contact time, dosage, pH, initial dye concentration, contact time etc. It is seen that a-CNTs can be material of potential for removal of dyes. In case of Rhodamine B, the maximum time for removal was 45 min whereas for Methyl orange rapid removal was plausible in about 30 min even in ambient condition. The experimental data have been well correlated with classical Langmuir-Freundlich and Temkin adsorption models.

  8. Chemical bonding and humidity sensing properties of amorphous carbon nitride (a-CNx) by acetylene gas

    Science.gov (United States)

    Aziz, Siti Aisyah Abd; Purhanudin, Noorain; Awang, Rozidawati

    2017-05-01

    Amorphous carbon nitride (a-CNx) thin films were deposited by radio frequency plasma enhance chemical vapor deposition (RF-PECVD) using a fixed mixture of acetylene (C2H2) at 20 sccm and nitrogen (N2) gases at 50 sccm. The films were deposited at different RF power of 60, 70, 80, 90 and 100 W. The deposition pressure, deposition time and substrate temperature were kept constant at 0.8 mbar, 30 minutes and 100°C, respectively. The chemical bonding of the a-CNx thin films was characterized using Fourier transform infrared spectroscopy (FTIR) and its sensing properties was determined using a home built humidity sensor system. The increase of RF powers leads to an increment of formation of double (C=N) and triple (C≡N) bonds as compared to a-CNx deposited using methane (CH4) or ethane (C2H6) gas. This is due to a higher ratio of C to H atoms in C2H2. The humidity sensing performance show the sensitivity of the films is the highest at low deposition power in changes of relative humidity (%RH). The a-CNx thin film show good repeatability and high sensitivity as a humidity sensing materials which prepared at low RF power.

  9. The multilayered structure of ultrathin amorphous carbon films synthesized by filtered cathodic vacuum arc deposition

    KAUST Repository

    Wang, Na

    2013-08-01

    The structure of ultrathin amorphous carbon (a-C) films synthesized by filtered cathodic vacuum arc (FCVA) deposition was investigated by high-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy. Results of the plasmon excitation energy shift and through-thickness elemental concentration show a multilayered a-C film structure comprising an interface layer consisting of C, Si, and, possibly, SiC, a buffer layer with continuously increasing sp 3 fraction, a relatively thicker layer (bulk film) of constant sp 3 content, and an ultrathin surface layer rich in sp 2 hybridization. A detailed study of the C K-edge spectrum indicates that the buffer layer between the interface layer and the bulk film is due to the partial backscattering of C+ ions interacting with the heavy atoms of the silicon substrate. The results of this study provide insight into the minimum thickness of a-C films deposited by FCVA under optimum substrate bias conditions. Copyright © 2013 Materials Research Society.

  10. Enhanced electrochemical performance of amorphous carbon nanotube-manganese-di-oxide-poly-pyrrole ternary nanohybrid

    Science.gov (United States)

    Pahari, D.; Das, N. S.; Das, B.; Howli, P.; Chattopadhyay, K. K.; Banerjee, D.

    2017-12-01

    Amorphous carbon nanotubes (a-CNTs) manganese di oxide (MnO2)-poly pyrrole (PPy) ternary nanocomposites have been synthesized by a simple chemical route. The as prepared samples have been characterized with different characterization tools that include field emission scanning and high resolution transmission electron microscopy, Raman, Fourier transformed infrared as well as UV-Vis spectroscopy. The electrochemical performance of all the as prepared pure and hybrid samples have been studied in detail. It has been seen that the ternary hybrid shows efficient electrochemical performance with high value of specific capacitance with good stability even up to 2000 cycles. The superior performance of the hybrid samples can be attributed to the strong synergistic effect between the components resulting electron shuttling along PPy main chains and inter-chain raising built-in continuous conductive network. The ternary composite approach offers an effective solution to enhance the device performance of metal-oxide based supercapacitors for long cycling applications. These studies can well speculate the existence of another supercapacitor hybrid for the use in environment friendly electrode and thus a pollution free nature.

  11. Preparation of Amorphous Carbon Films and Evaluation of Its Optical Properties and Gas Barrier Property

    Science.gov (United States)

    Ohsone, Yuuki; Nishi, Hidetaka; Saito, Masanori; Suzuki, Masaki; Murakami, Hiroya; Ohtake, Naoto

    Hydrogenerated amorphous carbon (a-C:H) films can improve oxygen gas barrier characteristics of plastic food containers, by coating it on the surfaces of such containers, and is intended to enhance the preservative quality. However, it has a problem that the degradation of optical transparency in the visible light range blocks the view of the inner content. In this study, we aimed to reduce the oxygen transmission rate (OTR) as well as to improve optical transparency, and fabricated a-C:H films by the pulse plasma chemical vapor deposition (CVD) method on polyethylene terephthalate (PET) films. First, it is clarified that the gas barrier performance in the a-C:H film in the vicinity of the PET boundary surface was lower than that of bulk a-C:H film. Secondly, the OTR and optical transparency of a-C:H films deposited not only from C2H2 but also from Si(CH3)4 were investigated in detail. The a-C:H film deposited from Si(CH3)4 shows high transmittance of 87% for visible light with a relatively low OTR of 3.2 cc/(m2·atm·day).

  12. Introducing novel amorphous carbon nanoparticles as energy acceptors into a chemiluminescence resonance energy transfer immunoassay system.

    Science.gov (United States)

    Wang, Zhenxing; Gao, Hongfei; Fu, Zhifeng

    2013-11-21

    A novel chemiluminescence resonance energy transfer (CRET) system for competitive immunoassay of biomolecules was developed by using novel amorphous carbon nanoparticles (CNPs) prepared from candle soot as energy acceptors. The CNPs were firstly prepared to bind with the antigen (Ag) for obtaining the nanocomposite CNP-Ag, and this obtained CNP-Ag was then reacted with the horseradish peroxidase-labeled antibody (HRP-Ab) to assemble the CRET system. The luminol catalyzed by HRP serving as the energy donor for CNPs triggered the CRET phenomenon between luminol and CNPs, which led to the chemiluminescence signal decrease. Due to the competitive immunoreaction of the target antigen and the CNP-Ag, a part of the CNP-Ag was replaced from the HRP-Ab, and then resulted in a weaker interaction between luminol and CNPs. Thus the competitive immunoreaction led to a higher chemiluminescence emission. This CNP-based CRET system was successfully applied to detect the human IgG as a model analyte, and a linear range of 10-200 ng mL(-1) and a detection limit of 1.9 ng mL(-1) (S/N = 3) were obtained. The results for real sample analysis demonstrated its application potential in some important areas such as clinical diagnosis.

  13. Carboxylated molecules regulate magnesium content of amorphous calcium carbonates during calcification.

    Science.gov (United States)

    Wang, Dongbo; Wallace, Adam F; De Yoreo, James J; Dove, Patricia M

    2009-12-22

    With the realization that many calcified skeletons form by processes involving a precursor phase of amorphous calcium carbonate (ACC), a new paradigm for mineralization is emerging. There is evidence the Mg content in biogenic ACC is regulated by carboxylated (acidic) proteins and other macromolecules, but the physical basis for such a process is unknown. We test the hypothesis that ACC compositions express a systematic relationship to the chemistry of carboxyl-rich biomolecules. A series of inorganic control experiments were conducted to establish the dependence of Mg/Ca ratios in ACC on solution composition. We then determined the influence of a suite of simple carboxylated organic acids on Mg content. Molecules with a strong affinity for binding Ca compared with Mg promote the formation of Mg-enriched ACC that is compositionally equivalent to high-magnesium calcites and dolomite. Measurements show Mg/Ca ratios are controlled by a predictable dependence upon the binding properties of the organic molecules. The trend appears rooted in the conformation and electrostatic potential topology of each molecule, but dynamic factors also may be involved. The dependence suggests a physical basis for reports that specific sequences of calcifying proteins are critical to modulating mineralization. Insights from this study may provide a plausible explanation for why some biogenic carbonates and carbonaceous cements often contain higher Mg signatures than those that are possible by classical crystal growth processes. The findings reiterate the controls of microenvironment on mineralization and suggest an origin of compositional offsets, or vital effects, long recognized by the paleoclimate community.

  14. Rational design of coaxial mesoporous birnessite manganese dioxide/amorphous-carbon nanotubes arrays for advanced asymmetric supercapacitors

    KAUST Repository

    Zhu, Shijin

    2015-03-01

    Coaxial mesoporous MnO2/amorphous-carbon nanotubes have been synthesized via a facile and cost-effective strategy at room temperature. The coaxial double nanotubes of inner (outer) MnO2 and outer (inner) amorphous carbon can be obtained via fine tuning the preparative factors (e.g., deposition order and processing temperature). Furthermore, the electrochemical properties of the coaxial nanotubes were evaluated by cycle voltammetric (CV) and galvanostatic charge-discharge (GC) measurements. The as-prepared coaxial double nanotubes of outer MnO2 and inner amorphous carbon exhibit the optimized pseudocapacitance performance (362 F g-1) with good cycling stability, and ideal rate capability owning to the unique nanostructures. When assembled into two-electrode asymmetric supercapacitor, an energy density of 22.56 W h kg-1 at a power density of 224.9 W kg-1 is obtained. These findings provide a new and facile approach to fabricate high-performance electrode for supercapacitors.

  15. The transformation of amorphous calcium carbonate, ACC, to crystalline phases as function of time and temperature.

    Science.gov (United States)

    Gies, Hermann; Happel, Marian; Niedermayr, Andrea; Immenhauser, Adrian

    2017-04-01

    We present results from a structural study of the transformation of freeze dried amorphous calcium carbonate, ACC, in crystalline material using pair distribution function analysis, PDF analysis, of X-ray powder diffraction data, XPD data. PDF analysis allows for the analysis of local order of structural subunit in the range between molecular unit (1. and 2. coordination sphere) and long range periodicity as in crystalline materials. ACC was precipitated from aqueous solutions at 298 K and 278 K using different amounts of Mg cations as stabilizer. The samples were immediately separated from the solution and freeze dried. For the transformation study, the samples were heated and analysed using XPD until they were crystallized. The radial distribution obtained from the XPD data were compared to simulated radial distributions of the calcium carbonate polymorphs and their hydrated phases. An ACC precipitated from a solution with Ca:Mg:CO3 = 1:5:4 at 298 K (ration in mmol, pH = 8.2) and freeze dried right after isolation from the solution revealed a close resemblance with ikaite in its local order. Another ACC with Ca:Mg:CO3 = 1:10:1.4 (T = 298, pH = 8.7) showed distinctly different local order resembling monohydrocalcite. Both ACC, however, still had considerable amounts of water dominating the Ca-coordination sphere. During the transformation to calcite, the structural changes in the sample concerned the hydrate water coordinating Ca which was removed and replaced by the carbonate oxygens. The study shows that ACC obtained from different starting solutions show specific local order. Freeze drying leads to solid ACC powder which still contain considerable amounts of hydrate water. Structural subunits are distinct in ACC and different from the crystalline phase. The study supplements recent reports presented by Konrad et al., Purgstaller et al., and Tobler et al.. F. Konrad et al., Cryst. Growth Des. 16, 6310-6317(2016) B. Purgstaller et al., Geochimica et Cosmochimica

  16. Biogenic fish-gut calcium carbonate is a stable amorphous phase in the gilt-head seabream, Sparus aurata.

    Science.gov (United States)

    Foran, Elizabeth; Weiner, Steve; Fine, Maoz

    2013-01-01

    The main source of calcium carbonate (CaCO₃) in the ocean comes from the shells of calcifying planktonic organisms, but substantial amounts of CaCO₃ are also produced in fish intestines. The precipitation of CaCO₃ assists fish in intestinal water absorption and aids in whole body Ca²⁺ homeostasis. Here we report that the product formed in the intestinal lumen of the gilt-head seabream, Sparus aurata, is an amorphous calcium carbonate (ACC) phase. With FTIR spectroscopy and SEM imaging, our study shows that the fish-derived carbonates from S. aurata are maintained as a stable amorphous phase throughout the intestinal tract. Moreover, intestinal deposits contained up to 54 mol% Mg²⁺, the highest concentration yet reported in biogenic ACC. Mg is most likely responsible for stabilizing this inherently unstable mineral. The fish carbonates also displayed initial rapid dissolution when exposed to seawater, exhibiting a significant increase in carbonate concentration.

  17. The Kontsevich tetrahedral flow revisited

    Science.gov (United States)

    Bouisaghouane, A.; Buring, R.; Kiselev, A.

    2017-09-01

    We prove that the Kontsevich tetrahedral flow P ˙ =Qa:b(P) , the right-hand side of which is a linear combination of two differential monomials of degree four in a bi-vector P on an affine real Poisson manifold Nn, does infinitesimally preserve the space of Poisson bi-vectors on Nn if and only if the two monomials in Qa:b(P) are balanced by the ratio a : b = 1 : 6. The proof is explicit; it is written in the language of Kontsevich graphs.

  18. Development of amorphous carbon protective coatings on poly(vinyl)chloride

    Energy Technology Data Exchange (ETDEWEB)

    Rangel, Elidiane C., E-mail: elidiane@sorocaba.unesp.b [Laboratorio de Plasmas Tecnologicos, Universidade Estadual Paulista, UNESP, Av. Tres de Marco, 511, 18087-180 Sorocaba, SP (Brazil); Souza, Eduardo S. de; Moraes, Francine S. de [Laboratorio de Plasmas Tecnologicos, Universidade Estadual Paulista, UNESP, Av. Tres de Marco, 511, 18087-180 Sorocaba, SP (Brazil); Marins, Nazir M.S. [Laboratorio de Plasmas, Departamento de Fisica e Quimica, Universidade Estadual Paulista, UNESP, Av. Dr. Ariberto Pereira da Silva, 333, 12516-410 Guaratingueta, SP (Brazil); Schreiner, Wido H. [Laboratorio de Superficies e Interfaces, Departamento de Fisica, Universidade Federal do Parana, 81531-990 Curitiba, PR (Brazil); Cruz, Nilson C. [Laboratorio de Plasmas Tecnologicos, Universidade Estadual Paulista, UNESP, Av. Tres de Marco, 511, 18087-180 Sorocaba, SP (Brazil)

    2010-03-01

    The great versatility of polymers has promoted their application in a series of ordinary situations. The development of specific devices from polymers, however, requires modifications to fit specific stipulations. In this work the surface properties of thin films grown onto polyvinylchloride (PVC) were investigated. Hydrogenated amorphous carbon films were deposited onto commercial PVC plates from acetylene and argon plasmas excited by radiofrequency (13.56 MHz, 70 W) power. The proportion of acetylene in the gas feed was varied against that of argon, keeping the total pressure constant at 2.5 Pa. Deposition time was 1800 s. Film elemental composition was analyzed by X-ray photoelectron spectroscopy, XPS. Water contact angle measurements were performed using the sessile drop technique. The root mean squared roughness was derived from 50 x 50 {mu}m{sup 2} surface topographic images, acquired by scanning probe microscopy. Nanoindentation and pin-on-disk techniques were employed on the determination of film hardness and sliding wear, respectively. Oxidation resistance was obtained through the etching rate of the samples in oxygen radiofrequency (1.3 Pa, 50 W) plasmas. From XPS analysis it was detected oxygen and nitrogen contamination in all the samples. It was also found that sp{sup 3}/sp{sup 2} ratio depends on the proportion of argon in the plasma. At lower argon concentrations, hardness, wear and oxidation resistances were all improved with respect to the uncoated PVC. In such conditions, the surface wettability is low indicating a moderate receptivity to water. This combination of properties, ascribed to a balance between the ion bombardment and deposition processes, is suitable for materials exposed to rigorous weathering conditions.

  19. Impact of sodium polyacrylate on the amorphous calcium carbonate formation from supersaturated solution.

    Science.gov (United States)

    Liu, J; Pancera, S; Boyko, V; Gummel, J; Nayuk, R; Huber, K

    2012-02-21

    A detailed in situ scattering study has been carried out on the formation of amorphous calcium carbonate (ACC) particles modulated by the presence of small amounts of sodium polyacrylate chains. The work is aiming at an insight into the modulation of ACC formation by means of two polyacrylate samples differing in their molecular weight by a factor of 50. The ACC formation process was initiated by an in situ generation of CO(3)(2-) ions via hydrolysis of 10 mM dimethylcarbonate in the presence of 10 mM CaCl(2). Analysis of the formation process by means of time-resolved small-angle X-ray and light scattering in the absence of any additives provided evidence for a monomer addition mechanism for the growth of ACC particles. ACC formation under these conditions sets in after a lag-period of some 350 s. In the presence of sodium polyacrylate chains, calcium polyacrylate aggregates are formed during the lag-period, succeeded by a modulated ACC growth in a second step. The presence of anionic polyacrylate chains changed the shape of the growing particles toward loose and less homogeneous entities. In the case of low amounts (1.5-7.5 mg/L) of the long chain additive with 97 kDa, the size of the aggregates is comparable to the size of the successively formed hybrid particles. No variation of the lag-period has been observed in this case. Use of the short chain additive with 2 kDa enabled increase of the additive concentration up to 100 mg/L and resulted in a significant increase of the lag-period. This fact, together with the finding that the resulting hybrid particles remained stable in the latter case, identified short chain sodium polyacrylates as more efficient modulators than long chain polyacrylates.

  20. Multiplex Lateral Flow Immunoassays Based on Amorphous Carbon Nanoparticles for Detecting Three Fusarium Mycotoxins in Maize.

    Science.gov (United States)

    Zhang, Xiya; Yu, Xuezhi; Wen, Kai; Li, Chenglong; Mujtaba Mari, Ghulam; Jiang, Haiyang; Shi, Weimin; Shen, Jianzhong; Wang, Zhanhui

    2017-09-13

    The detecting labels used for lateral flow immunoassays (LFAs) have been traditionally gold nanoparticles (GNPs) and, more recently, luminescent nanoparticles, such as quantum dots (QDs). However, these labels have low sensitivity and are costly, in particular, for trace detection of mycotoxins in cereals. Here, we provided a simple preparation procedure for amorphous carbon nanoparticles (ACNPs) and described multiplex LFAs employing ACNPs as labels (ACNP-LFAs) for detecting three Fusarium mycotoxins. The analytical performance of ACNPs in LFA was compared to GNPs and QDs using the same immunoreagents, except for the labels, allowing for their analytical characteristics to be objectively compared. The visual limit of detection for ACNP-LFAs in buffer was 8-fold better than GNPs and 2-fold better than QDs. Under optimized conditions, the quantitative limit of detection of ACNP-LFAs in maize was as low as 20 μg/kg for deoxynivalenol, 13 μg/kg for T-2 toxin, and 1 μg/kg for zearalenone. These measurements were much lower than the action level of these mycotoxins in maize. The accuracy and precision of the ACNP-LFAs were evaluated by analysis of spiked and incurred maize samples with recoveries of 84.6-109% and coefficients of variation below 13%. The results of ACNP-LFAs using naturally incurred maize samples showed good agreement with results from high-performance liquid chromatography-tandem mass spectrometry, indicating that ACNPs were more sensitive labels than and a promising alternative to GNPs used in LFAs for detecting mycotoxins in cereals.

  1. Efficient Production of N-Butyl Levulinate Fuel Additive from Levulinic Acid Using Amorphous Carbon Enriched with Oxygenated Groups

    Directory of Open Access Journals (Sweden)

    Jinfan Yang

    2018-01-01

    Full Text Available The aim of this study was to develop an effective carbonaceous solid acid for synthesizing green fuel additive through esterification of lignocellulose-derived levulinic acid (LA and n-butanol. Two different sulfonated carbons were prepared from glucose-derived amorphous carbon (GC400 and commercial active carbon (AC400. They were contrastively studied by a series of characterizations (N2 adsorption, X-ray diffraction, elemental analysis, transmission electron microscopy, Fourier transform infrared spectroscopy and NH3 temperature programmed desorption. The results indicated that GC400 possessed stronger acidity and higher –SO3H density than AC400, and the amorphous structure qualified GC400 for good swelling capacity in the reaction solution. Assessment experiments showed that GC400 displayed remarkably higher catalytic efficiency than AC400 and other typical solid acids (HZSM-5, Hβ, Amberlyst-15 and Nafion-212 resin. Up to 90.5% conversion of LA and 100% selectivity of n-butyl levulinate could be obtained on GC400 under the optimal reaction conditions. The sulfonated carbon retained 92% of its original catalytic activity even after five cycles.

  2. Amorphous ZnO Quantum Dot/Mesoporous Carbon Bubble Composites for a High-Performance Lithium-Ion Battery Anode.

    Science.gov (United States)

    Tu, Zhiming; Yang, Gongzheng; Song, Huawei; Wang, Chengxin

    2017-01-11

    Due to its high theoretical capacity (978 mA h g-1), natural abundance, environmental friendliness, and low cost, zinc oxide is regarded as one of the most promising anode materials for lithium-ion batteries (LIBs). A lot of research has been done in the past few years on this topic. However, hardly any research on amorphous ZnO for LIB anodes has been reported despite the fact that the amorphous type could have superior electrochemical performance due to its isotropic nature, abundant active sites, better buffer effect, and different electrochemical reaction details. In this work, we develop a simple route to prepare an amorphous ZnO quantum dot (QDs)/mesoporous carbon bubble composite. The composite consists of two parts: mesoporous carbon bubbles as a flexible skeleton and monodisperse amorphous zinc oxide QDs (smaller than 3 nm) encapsulated in an amorphous carbon matrix as a continuous coating tightly anchored on the surface of mesoporous carbon bubbles. With the benefits of abundant active sites, amorphous nature, high specific surface area, buffer effect, hierarchical pores, stable interconnected conductive network, and multidimensional electron transport pathways, the amorphous ZnO QD/mesoporous carbon bubble composite delivers a high reversible capacity of nearly 930 mA h g-1 (at current density of 100 mA g-1) with almost 90% retention for 85 cycles and possesses a good rate performance. This work opens the possibility to fabricate high-performance electrode materials for LIBs, especially for amorphous metal oxide-based materials.

  3. Correlation between luminescence properties and microstructure of hydrogenated amorphous carbon films investigated by X-ray diffraction and infrared ellipsometry

    Science.gov (United States)

    Godet, C.; Heitz, T.; Bourée, J. E.; Bouchet, B.; Dixmier, J.; Drévillon, B.

    1999-07-01

    Plasma deposited polymer-like amorphous carbon (PLC) films show a strong photoluminescence (PL) in the visible range at room temperature. However, the origin of the luminescence in terms of microstructure is poorly understood. In this study, by varying the plasma conditions, hydrogenated carbon (a-C:H) films, ranging from soft and transparent to denser and more absorbent materials, have been grown. Steady-state PL measurements reveal a steep quenching of the luminescence intensity when film density is higher than 1.3 g cm -3. Using in situ infrared ellipsometry, C-H bonding analysis shows that this quenching corresponds to a strong decrease of the sp 3 CH n=2,3 group concentrations, consistent with a network crosslinking and to an enrichment of the methyl group environment in π bonds. In correlation, the evolution of the carbon skeleton has been studied using X-ray diffraction measurements. Structure factors and pair correlation functions evidence clear differences in the network structure, in particular a shortening of the carbon-carbon bond when density increases.

  4. Derivation of Hamaker Dispersion Energy of Amorphous Carbon Surfaces in Contact with Liquids Using Photoelectron Energy-Loss Spectra

    Science.gov (United States)

    Godet, Christian; David, Denis

    2017-12-01

    Hamaker interaction energies and cutoff distances have been calculated for disordered carbon films, in contact with purely dispersive (diiodomethane) or polar (water) liquids, using their experimental dielectric functions ɛ ( q, ω) obtained over a broad energy range. In contrast with previous works, a q-averaged q is derived from photoelectron energy-loss spectroscopy (XPS-PEELS) where the energy loss function (ELF) q is a weighted average over allowed transferred wave vector values, q, given by the physics of bulk plasmon excitation. For microcrystalline diamond and amorphous carbon films with a wide range of (sp3/sp2 + sp3) hybridization, non-retarded Hamaker energies, A 132 ( L < 1 nm), were calculated in several configurations, and distance and wavenumber cutoff values were then calculated based on A 132 and the dispersive work of adhesion obtained from contact angles. A geometric average approximation, H 0 CVL = ( H 0 CVC H 0 LVL )1/2, holds for the cutoff separation distances obtained for carbon-vacuum-liquid (CVL), carbon-vacuum-carbon (CVC) and liquid-vacuum-liquid (LVL) equilibrium configurations. The linear dependence found for A CVL, A CLC and A CLV values as a function of A CVC, for each liquid, allows predictive relationships for Hamaker energies (in any configuration) using experimental determination of the dispersive component of the surface tension, {γ}_{CV}^d , and a guess value of the cutoff distance H 0 CVC of the solid. [Figure not available: see fulltext.

  5. A tetrapyridine ligand with a rigid tetrahedral core forms metal-organic frameworks with PtS type architecture.

    Science.gov (United States)

    Caputo, Christopher B; Vukotic, V Nicholas; Sirizzotti, Natalie M; Loeb, Stephen J

    2011-08-14

    A new tetradentate, pyridine ligand with a rigid tetrahedral core can be prepared in good yield by a cross-coupling methodology. Two metal organic framework structures of Cu(II) with PtS-type topology having a carbon atom as the tetrahedral node have been characterized utilising this ligand. This journal is © The Royal Society of Chemistry 2011

  6. Nitrogen-doped amorphous carbon-silicon core-shell structures for high-power supercapacitor electrodes.

    Science.gov (United States)

    Tali, S A Safiabadi; Soleimani-Amiri, S; Sanaee, Z; Mohajerzadeh, S

    2017-02-10

    We report successful deposition of nitrogen-doped amorphous carbon films to realize high-power core-shell supercapacitor electrodes. A catalyst-free method is proposed to deposit large-area stable, highly conformal and highly conductive nitrogen-doped amorphous carbon (a-C:N) films by means of a direct-current plasma enhanced chemical vapor deposition technique (DC-PECVD). This approach exploits C2H2 and N2 gases as the sources of carbon and nitrogen constituents and can be applied to various micro and nanostructures. Although as-deposited a-C:N films have a porous surface, their porosity can be significantly improved through a modification process consisting of Ni-assisted annealing and etching steps. The electrochemical analyses demonstrated the superior performance of the modified a-C:N as a supercapacitor active material, where specific capacitance densities as high as 42 F/g and 8.5 mF/cm2 (45 F/cm3) on silicon microrod arrays were achieved. Furthermore, this supercapacitor electrode showed less than 6% degradation of capacitance over 5000 cycles of a galvanostatic charge-discharge test. It also exhibited a relatively high energy density of 2.3 × 103 Wh/m3 (8.3 × 106 J/m3) and ultra-high power density of 2.6 × 108 W/m3 which is among the highest reported values.

  7. Immobilization of sericin molecules via amorphous carbon plasma modified-polystyrene dish for serum-free culture

    Energy Technology Data Exchange (ETDEWEB)

    Tunma, Somruthai [The Graduate School, Chiang Mai University, 239 Huay Kaew Road, Muang District, Chiang Mai 50200 (Thailand); Thailand Center of Excellence in Physics (ThEP), 239 Huay Kaew Road, Muang District, Chiang Mai 50200 (Thailand); Song, Doo-Hoon [Research Center for Orofacial Hard Tissue Regeneration, College of Dentistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752 (Korea, Republic of); Kim, Si-Eun; Kim, Kyoung-Nam [Research Center for Orofacial Hard Tissue Regeneration, College of Dentistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752 (Korea, Republic of); Department and Research Institute of Dental Biomaterials and Bioengineering, College of Dentistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752 (Korea, Republic of); Han, Jeon-Geon [Center for Advanced Plasma Surface Technology, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746 (Korea, Republic of); Boonyawan, Dheerawan, E-mail: dheerawan.b@cmu.ac.th [Thailand Center of Excellence in Physics (ThEP), 239 Huay Kaew Road, Muang District, Chiang Mai 50200 (Thailand); Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, 239 Huay Kaew Road, Muang District, Chiang Mai 50200 (Thailand)

    2013-10-15

    In this study, we focused on sericin hydrolysates, originating from silkworm used in serum-free human bone marrow-derived mesenchymal stem cells (hBM-MSCs) culture. We reported the effect of a covalent linkage between a bioactive protein molecule and polystyrene dish surface via a carbon intermediate layer which can slow down the release rate of protein compounds into the phosphate buffer saline (PBS) solution. Films of amorphous carbon (a-C) and functionalized-carbon were deposited on PS culture dish surfaces by using a DC magnetron sputtering system and RF PECVD system. We found that a-C based-films can increase the hydrophilicity and biocompatibility of polystyrene (PS) dishes, especially a-C films and a-C:N{sub 2} films showed good attachment of hBM-MSCs at 24 h. However, in the case of silica surface (a-C:SiO{sub x} films), the cells showed a ragged and unattached boundary resulting from the presence of surface silanol groups. For the UV–vis absorbance, all carbon modified-PS dishes showed a lower release rate of sericin molecules into PBS solution than PS control. This revealed that the functionalized carbon could be enhanced by specific binding properties with given molecules. The carbon-coated PS dishes grafting with sericin protein were used in a serum-free condition. We also found that hBM-MSCs have higher percentage of proliferated cells at day 7 for the modified dishes with carbon films and coated with sericin than the PS control coated with sericin. The physical film properties were measured by atomic force microscopy (AFM), scanning electron microscope (SEM) and contact angle measurement. The presence of -NH{sub 2} groups of sericin compounds on the PS dish was revealed by Fourier transform infrared spectroscopy (FTIR). The stability of covalent bonds of sericin molecules after washing out ungrafted sericin was confirmed by X-ray photoelectron spectroscopy (XPS).

  8. NEW RSW & Wall Medium Fully Tetrahedral Grid

    Data.gov (United States)

    National Aeronautics and Space Administration — New Medium Fully Tetrahedral RSW Grid with viscous wind tunnel wall at the root. This grid is for a node-based unstructured solver. Medium Tet: Quad Surface Faces= 0...

  9. NEW RSW & Wall Fine Fully Tetrahedral Grid

    Data.gov (United States)

    National Aeronautics and Space Administration — NEW RSW Fine Fully Tetrahedral Grid with Viscous Wind Tunnel wall at the root. This grid is for a node-based unstructured solver. Note that the CGNS file is very...

  10. Efficient cold cathode emission in crystalline-amorphous hybrid: Study on carbon nanotube-cadmium selenide system

    Science.gov (United States)

    Sarkar, S.; Banerjee, D.; Das, N. S.; Ghorai, U. K.; Sen, D.; Chattopadhyay, K. K.

    2018-03-01

    Cadmium Selenide (CdSe) quantum dot (QD) decorated amorphous carbon nanotubes (a-CNTs) hybrids have been synthesized by simple chemical process. The samples were characterized by field emission scanning and transmission electron microscopy, Fourier transformed infrared spectroscopy, Raman and UV-Vis spectroscopy. Lattice image obtained from transmission electron microscopic study confirms the successful attachment of CdSe QDs. It is seen that hybrid samples show an enhanced cold emission properties with good stability. The results have been explained in terms of increased roughness, more numbers of emitting sites and favorable band bending induced electron transport. ANSYS software based calculation has also supported the result. Also a first principle based study has been done which shows that due to the formation of hybrid structure there is a profound upward shift in the Fermi level, i.e. a decrease of work function, which is believed to be another key reason for the observed improved field emission performance.

  11. Neutron and X-ray diffraction and empirical potential structure refinement modelling of magnesium stabilised amorphous calcium carbonate

    DEFF Research Database (Denmark)

    Cobourne, G.; Mountjoy, G.; Rodriguez Blanco, Juan Diego

    2014-01-01

    Amorphous calcium carbonate (ACC) plays a key role in biomineralisation processes in sea organisms. Neutron and X-ray diffraction have been performed for a sample of magnesium-stabilised ACC, which was prepared with a Mg:Ca ratio of 0.05:1 and 0.25 H2O molecules per molecule of CO3. The empirical...... potential structure refinement method has been used to make a model of magnesium-stabilised ACC and the results revealed a fair agreement with the experimental diffraction data. The model has well-defined CO3 and H2O molecules. The average coordination number of Ca is 7.4 and is composed of 6.8 oxygen atoms...

  12. Understanding the Atomic Scale Mechanisms that Control the Attainment of Ultralow Friction and Wear in Carbon-Based Materials

    Science.gov (United States)

    2016-01-16

    2015. 15. Invited. New Insights into Friction and Wear through In-Situ Nanotribology. Joint Symposium of the Surface Science Society of Japan and...and Carpick, R.W. Influence of Surface Passivation on the Friction and Wear Behavior of Ultrananocrystalline Diamond and Tetrahedral Amorphous Carbon...AFRL-AFOSR-JP-TR-2016-0053 Understanding the Atomic Scale Mechanism that controls the attainment of ultralow friction and wear in carbon based

  13. Structural stability of hydrogenated amorphous carbon overcoats used in heat-assisted magnetic recording investigated by rapid thermal annealing

    KAUST Repository

    Wang, N.

    2013-01-01

    Ultrathin amorphous carbon (a-C) films are extensively used as protective overcoats of magnetic recording media. Increasing demands for even higher storage densities have necessitated the development of new storage technologies, such as heat-assisted magnetic recording (HAMR), which uses laser-assisted heating to record data on high-stability media that can store single bits in extremely small areas (∼1 Tbit/in.2). Because HAMR relies on locally changing the coercivity of the magnetic medium by raising the temperature above the Curie temperature for data to be stored by the magnetic write field, it raises a concern about the structural stability of the ultrathin a-C film. In this study, rapid thermal annealing (RTA) experiments were performed to examine the thermal stability of ultrathin hydrogenated amorphous carbon (a-C:H) films deposited by plasma-enhanced chemical vapor deposition. Structural changes in the a-C:H films caused by RTA were investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, x-ray reflectivity, and conductive atomic force microscopy. The results show that the films exhibit thermal stability up to a maximum temperature in the range of 400-450 °C. Heating above this critical temperature leads to hydrogen depletion and sp 2 clustering. The critical temperature determined by the results of this study represents an upper bound of the temperature rise due to laser heating in HAMR hard-disk drives and the Curie temperature of magnetic materials used in HAMR hard disks. © 2013 American Institute of Physics.

  14. Biological characteristics of the MG-63 human osteosarcoma cells on composite tantalum carbide/amorphous carbon films.

    Directory of Open Access Journals (Sweden)

    Yin-Yu Chang

    Full Text Available Tantalum (Ta is a promising metal for biomedical implants or implant coating for orthopedic and dental applications because of its excellent corrosion resistance, fracture toughness, and biocompatibility. This study synthesizes biocompatible tantalum carbide (TaC and TaC/amorphous carbon (a-C coatings with different carbon contents by using a twin-gun magnetron sputtering system to improve their biological properties and explore potential surgical implant or device applications. The carbon content in the deposited coatings was regulated by controlling the magnetron power ratio of the pure graphite and Ta cathodes. The deposited TaC and TaC/a-C coatings exhibited better cell viability of human osteosarcoma cell line MG-63 than the uncoated Ti and Ta-coated samples. Inverted optical and confocal imaging was used to demonstrate the cell adhesion, distribution, and proliferation of each sample at different time points during the whole culture period. The results show that the TaC/a-C coating, which contained two metastable phases (TaC and a-C, was more biocompatible with MG-63 cells compared to the pure Ta coating. This suggests that the TaC/a-C coatings exhibit a better biocompatible performance for MG-63 cells, and they may improve implant osseointegration in clinics.

  15. Biological Characteristics of the MG-63 Human Osteosarcoma Cells on Composite Tantalum Carbide/Amorphous Carbon Films

    Science.gov (United States)

    Chang, Yin-Yu; Huang, Heng-Li; Chen, Ya-Chi; Hsu, Jui-Ting; Shieh, Tzong-Ming; Tsai, Ming-Tzu

    2014-01-01

    Tantalum (Ta) is a promising metal for biomedical implants or implant coating for orthopedic and dental applications because of its excellent corrosion resistance, fracture toughness, and biocompatibility. This study synthesizes biocompatible tantalum carbide (TaC) and TaC/amorphous carbon (a-C) coatings with different carbon contents by using a twin-gun magnetron sputtering system to improve their biological properties and explore potential surgical implant or device applications. The carbon content in the deposited coatings was regulated by controlling the magnetron power ratio of the pure graphite and Ta cathodes. The deposited TaC and TaC/a-C coatings exhibited better cell viability of human osteosarcoma cell line MG-63 than the uncoated Ti and Ta-coated samples. Inverted optical and confocal imaging was used to demonstrate the cell adhesion, distribution, and proliferation of each sample at different time points during the whole culture period. The results show that the TaC/a-C coating, which contained two metastable phases (TaC and a-C), was more biocompatible with MG-63 cells compared to the pure Ta coating. This suggests that the TaC/a-C coatings exhibit a better biocompatible performance for MG-63 cells, and they may improve implant osseointegration in clinics. PMID:24760085

  16. Hydrogen and Hydrocarbon Gases, Polycyclic Aromatic Hydrocarbons, and Amorphous Carbon Produced by Multiple Shock Compression of Liquid Benzene up to 27.4 GPa.

    Science.gov (United States)

    Mimura, Koichi; Nishida, Tamihito

    2017-08-31

    Phase diagrams of benzene have been reported on the basis of data mainly obtained from static compression at various pressure-temperature, P-T, conditions. However, there are few data in the high-pressure and high temperature-region of the phase diagram. To understand the physical and chemical behavior of benzene in that region, multiple shock compression of benzene was evaluated by a recovery experimental system that directly analyzed the shocked samples. The shocked samples were composed of the remaining benzene, gases (H2, CH4, C2H4, C2H6, C3H6, and C3H8), polycyclic aromatic hydrocarbons with molecular weights from 128 (naphthalene) to 300 (coronene), and amorphous carbon. The abundances of these chemical species varied according to the P-T conditions induced by shock compression. Samples in the lower-pressure and lower-temperature region of the a-C:H phase in the phase diagram contained a significant amount of benzene as well as amorphous carbon. In the higher-pressure and higher-temperature region of the a-C:H phase, benzene was mostly converted into amorphous carbon (H/C = 0.2), H2, and CH4. Therefore, the amorphous carbon in the present study was produced by a different pathway than that in previous studies that have detected hydrogenated amorphous carbon (H/C = 1). For earth sciences, the present study can provide basic information on the delivery to the early earth of extraterrestrial organic materials related to the origin of life.

  17. Microcellular Foaming of Amorphous High-Tg Polymers Using Carbon Dioxyde

    NARCIS (Netherlands)

    Krause, B.; Mettinkhof, R.; van der Vegt, N.F.A.; Wessling, Matthias

    2001-01-01

    The foaming of thin (~100 m) polysulfone (PSU), poly(ether sulfone) (PES), and cyclic olefin copolymer (COC) films using carbon dioxide as a physical blowing agent has been studied. Microcellular foam morphologies were obtained by saturating the polymer with carbon dioxide and heating the sample

  18. Formation, Structure and Properties of Amorphous Carbon Char from Polymer Materials in Extreme Atmospheric Reentry Environments

    Science.gov (United States)

    Lawson, John W.

    2010-01-01

    Amorphous carbonaceous char produced from the pyrolysis of polymer solids has many desirable properties for ablative heat shields for space vehicles. Molecular dynamics simulations are presented to study the transformation of the local atomic structure from virgin polymer to a dense, disordered char [1]. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated char structure. Mechanisms of the char formation process and the morphology of the resulting structures are elucidated. Thermal conductivity and mechanical response of the resulting char are evaluated [2]. During reenty, the optical response and oxidative reactivity of char are also important properties. Results of ab initio computations of char optical functions [3] and char reactivity [4] are also presented.

  19. An ab initio study of the nickel-catalyzed transformation of amorphous carbon into graphene in rapid thermal processing

    Science.gov (United States)

    Chen, Shuang; Xiong, Wei; Zhou, Yun Shen; Lu, Yong Feng; Zeng, Xiao Cheng

    2016-05-01

    Ab initio molecular dynamics (AIMD) simulations are employed to investigate the chemical mechanism underlying the Ni-catalyzed transformation of amorphous carbon (a-C) into graphene in the rapid thermal processing (RTP) experiment to directly grow graphene on various dielectric surfaces via the evaporation of surplus Ni and C at 1100 °C (below the melting point of bulk Ni). It is found that the a-C-to-graphene transformation entails the metal-induced crystallization and layer exchange mechanism, rather than the conventional dissolution/precipitation mechanism typically involved in Ni-catalyzed chemical vapor deposition (CVD) growth of graphene. The multi-layer graphene can be tuned by changing the relative thicknesses of deposited a-C and Ni thin films. Our AIMD simulations suggest that the easy evaporation of surplus Ni with excess C is likely attributed to the formation of a viscous-liquid-like Ni-C solution within the temperature range of 900-1800 K and to the faster diffusion of C atoms than that of Ni atoms above 600 K. Even at room temperature, sp3-C atoms in a-C are quickly converted to sp2-C atoms in the course of the simulation, and the graphitic C formation can occur at low temperature. When the temperature is as high as 1200 K, the grown graphitic structures reversely dissolve into Ni. Because the rate of temperature increase is considerably faster in the AIMD simulations than in realistic experiments, defects in the grown graphitic structures are kinetically trapped. In this kinetic growth stage, the carbon structures grown from sp3-carbon or from sp2-carbon exhibit marked differences.Ab initio molecular dynamics (AIMD) simulations are employed to investigate the chemical mechanism underlying the Ni-catalyzed transformation of amorphous carbon (a-C) into graphene in the rapid thermal processing (RTP) experiment to directly grow graphene on various dielectric surfaces via the evaporation of surplus Ni and C at 1100 °C (below the melting point of bulk

  20. Increased calcium absorption from synthetic stable amorphous calcium carbonate: double-blind randomized crossover clinical trial in postmenopausal women.

    Science.gov (United States)

    Vaisman, Nachum; Shaltiel, Galit; Daniely, Michal; Meiron, Oren E; Shechter, Assaf; Abrams, Steven A; Niv, Eva; Shapira, Yami; Sagi, Amir

    2014-10-01

    Calcium supplementation is a widely recognized strategy for achieving adequate calcium intake. We designed this blinded, randomized, crossover interventional trial to compare the bioavailability of a new stable synthetic amorphous calcium carbonate (ACC) with that of crystalline calcium carbonate (CCC) using the dual stable isotope technique. The study was conducted in the Unit of Clinical Nutrition, Tel Aviv Sourasky Medical Center, Israel. The study population included 15 early postmenopausal women aged 54.9 ± 2.8 (mean ± SD) years with no history of major medical illness or metabolic bone disorder, excess calcium intake, or vitamin D deficiency. Standardized breakfast was followed by randomly provided CCC or ACC capsules containing 192 mg elemental calcium labeled with 44Ca at intervals of at least 3 weeks. After swallowing the capsules, intravenous CaCl2 labeled with 42Ca on was administered on each occasion. Fractional calcium absorption (FCA) of ACC and CCC was calculated from the 24-hour urine collection following calcium administration. The results indicated that FCA of ACC was doubled (± 0.96 SD) on average compared to that of CCC (p calcium supplementation. © 2014 American Society for Bone and Mineral Research.

  1. Molecular-scale tribology of amorphous carbon coatings: effects of film thickness, adhesion, and long-range interactions.

    Science.gov (United States)

    Gao, G T; Mikulski, Paul T; Harrison, Judith A

    2002-06-19

    Classical molecular dynamics simulations have been conducted to investigate the atomic-scale friction and wear when hydrogen-terminated diamond (111) counterfaces are in sliding contact with diamond (111) surfaces coated with amorphous, hydrogen-free carbon films. Two films, with approximately the same ratio of sp(3)-to-sp(2) carbon, but different thicknesses, have been examined. Both systems give a similar average friction in the load range examined. Above a critical load, a series of tribochemical reactions occur resulting in a significant restructuring of the film. This restructuring is analogous to the "run-in" observed in macroscopic friction experiments and reduces the friction. The contribution of adhesion between the probe (counterface) and the sample to friction was examined by varying the saturation of the counterface. Decreasing the degree of counterface saturation, by reducing the hydrogen termination, increases the friction. Finally, the contribution of long-range interactions to friction was examined by using two potential energy functions that differ only in their long-range forces to examine friction in the same system.

  2. Hydrogenated amorphous carbon films on steel balls and Si substrates: Nanostructural evolutions and their trigging tribological behaviors

    Science.gov (United States)

    Wang, Yongfu; Wang, Yan; Zhang, Xingkai; Shi, Jing; Gao, Kaixiong; Zhang, Bin; Zhang, Junyan

    2017-10-01

    In this study, we prepared hydrogenated amorphous carbon films on steel balls and Si substrates (steel ball- and Si substrate-films) with different deposition time, and discussed their carbon nanostructural evolutions and tribological behaviors. The steel ball-film structure started to be graphite-like structure and then gradually transformed into fullerene-like (FL) structure. The Si substrate-film structure began in FL structure and kept it through the thickness. The difference may be result from the competition between high starting substrate temperature after additional nitriding applied on the steel balls (its supply power is higher than that in the film deposition), and relaxation of compressive stress from energized ion bombardment in film deposition process. The FL structural film friction couples could achieve ultra-low friction in open air. In particular, the Si substrate-film with 3 h, against the steel ball-film with 2 h and 3 h, exhibited super-low friction (∼0.009) and superlong wear life (∼5.5 × 105 cycles). Our result could widen the superlubricity scope from previously high load and velocity, to middle load and velocity.

  3. Study of Amorphous Carbon Nitride Films Aiming at White Light Emitting Devices

    Science.gov (United States)

    Iwano, Yuta; Kittaka, Toshiaki; Tabuchi, Hidekazu; Soukawa, Masaya; Kunitsugu, Shinsuke; Takarabe, Kenichi; Itoh, Kunio

    2008-10-01

    The possibility for white light emitting devices using carbon nitride (CNx) thin films has been studied. Microwave electron cyclotron resonance (ECR)-plasma chemical vapor deposition (CVD) and RF-sputtering apparatuses have been used for the formation of CNx thin films. In both cases, CH4 was used as the source or sub-source of carbon in order to investigate the effect of hydrogenated carbon nitride for luminescence. The cathodoluminescence (CL) measurement of the film grown by ECR-plasma CVD method showed three peaks of red, green, and blue (R/G/B). The photoluminescence (PL) measurement of the film grown by RF-sputtering also showed the red peak, which could not be observed in the film without hydrogen. Together with the X-ray photoelectron spectroscopy (XPS) analysis data, we concluded that the red peak originates from the level relating to H atom and blue peak from C-N bonds.

  4. Amorphous carbon nanoparticles: a versatile label for rapid diagnostic (immuno)assays

    NARCIS (Netherlands)

    Posthuma-Trumpie, G.A.; Wichers, J.H.; Koets, M.; Berendsen, L.B.J.M.; Amerongen, van A.

    2012-01-01

    Carbon nanoparticles (CNPs) labeled with reporter molecules can serve as signaling labels in rapid diagnostic assays as an alternative to gold, colored latex, silica, quantum dots, or up-converting phosphor nanoparticles. Detailed here is the preparation of biomolecule-labeled CNPs and examples of

  5. Amorphous Ca-phosphate precursors for Ca-carbonate biominerals mediated by Chromohalobacter marismortui

    NARCIS (Netherlands)

    Rivadeneyra, María Angustias; Martín-Algarra, Agustín; Sánchez-Román, Mónica; Sánchez-Navas, Antonio; Martín-Ramos, José Daniel

    Although diverse microbial metabolisms are known to induce the precipitation of carbonate minerals, the mechanisms involved in the bacterial mediation, in particular nucleation, are still debated. The study of aragonite precipitation by Chromohalobacter marismortui during the early stages (3-7 days)

  6. Effects of substrate temperature on bonding structure and mechanical properties of amorphous carbon films

    Energy Technology Data Exchange (ETDEWEB)

    Chowdhury, S.; Laugier, M.T.; Rahman, I.Z

    2004-01-30

    Diamond-like carbon thin films were prepared at different substrate temperatures by RF magnetron sputtering of a graphite target. The chemical bonding of the carbon structure was characterised by Raman spectroscopy. Raman measurements showed that sp{sup 3} bonded carbon fraction increases from 50 to 80 deg. C temperatures and an increase in the substrate temperature after 80 deg. C results in an increase in the sp{sup 2}-bonded carbon atoms in DLC thin films. Mechanical properties, namely hardness and Young's modulus were determined by CSM{sup TM} nanohardness tester. The hardness (H) and Young's modulus (E) were found in the range of 11-22 and 110-160 GPa, respectively, at different substrate temperatures and increased with increase of substrate temperature up to 125 deg. C and decreased thereafter. These results indicate that substrate temperature has a strong influence on the bonding properties of the deposited films and the changes in bonding ratio (sp{sup 3}/sp{sup 2}) were correlated with changes in the mechanical properties.

  7. Chemical and physical controls on the transformation of amorphous calcium carbonate into crystalline CaCO3 polymorphs

    Science.gov (United States)

    Blue, C. R.; Giuffre, A.; Mergelsberg, S.; Han, N.; De Yoreo, J. J.; Dove, P. M.

    2017-01-01

    Calcite and other crystalline polymorphs of CaCO3 can form by pathways involving amorphous calcium carbonate (ACC). Apparent inconsistencies in the literature indicate the relationships between ACC composition, local conditions, and the subsequent crystalline polymorphs are not yet established. This experimental study quantifies the control of solution composition on the transformation of ACC into crystalline polymorphs in the presence of magnesium. Using a mixed flow reactor to control solution chemistry, ACC was synthesized with variable Mg contents by tuning input pH, Mg/Ca, and total carbonate concentration. ACC products were allowed to transform within the output suspension under stirred or quiescent conditions while characterizing the evolving solutions and solids. As the ACC transforms into a crystalline phase, the solutions record a polymorph-specific evolution of pH and Mg/Ca. The data provide a quantitative framework for predicting the initial polymorph that forms from ACC based upon the solution aMg2+/aCa2+ and aCO32-/aCa2+ and stirring versus quiescent conditions. This model reconciles discrepancies among previous studies that report on the nature of the polymorphs produced from ACC and supports the previous claim that monohydrocalcite may be an important, but overlooked, transient phase on the way to forming some aragonite and calcite deposits. By this construct, organic additives and extreme pH are not required to tune the composition and nature of the polymorph that forms. Our measurements show that the Mg content of ACC is recorded in the resulting calcite with a ≈1:1 dependence. By correlating composition of these calcite products with the Mgtot/Catot of the initial solutions, we find a ≈3:1 dependence that is approximately linear and general to whether calcite is formed via an ACC pathway or by the classical step-propagation process. Comparisons to calcite grown in synthetic seawater show a ≈1:1 dependence. The relationships suggest that the

  8. The Effect of Stress in the Density of States of Amorphous Carbon Films Determined by X-Ray Excited Auger Electron Spectroscopy

    Directory of Open Access Journals (Sweden)

    P. F. Barbieri

    2017-01-01

    Full Text Available Amorphous carbon films can be prepared with a large variety of structure and have been used in a number of technological applications. Many of their properties have been determined, but very little is known concerning the effect of pressure on their properties. In this work we investigate the influence of pressure of graphite-like amorphous carbon films on the density of states (DOS using X-ray Excited Auger Electron Spectroscopy (XAES and the second derivate method of the XAES. The films were deposited by ion beam deposition and simultaneously bombarded with argon, which is responsible for the variation of the film stress, reaching extremely high values (4.5 GPa. Marked variations of the density of states of the pπ, pσ, sp, and s components were observed with increasing stress.

  9. The hydrogen and oxygen content of self-supporting carbon foils prepared bydc glow discharge in ethylene

    Science.gov (United States)

    Tait, N. R. S.; Tolfree, D. W. L.; John, P.; Odeh, I. M.; Thomas, M. J. K.; Tricker, M. J.; Wilson, J. I. B.; England, J. B. A.; Newton, D.

    1980-10-01

    The hydrogen and oxygen content of self-supporting carbon films produced bydc glow discharge have been determined using a precise method involving the elastic scattering of 25 MeV α-particles. The number of carbon-hydrogen bonds has been determined for similar samples using infra-red spectroscopy. The results are compared with those for samples made by the carbon arc process. Assuming that the glow discharge carbon contains graphitic regions surrounded by amorphous tetrahedrally bonded material to which hydrogen can attach, a simple estimate is made of the relative numbers of carbon atoms in the two forms.

  10. The effect of postgrowth ion irradiation on the microstructure and the interface properties of amorphous carbon films on silicon

    Science.gov (United States)

    Patsalas, P.; Logothetidis, S.

    2000-12-01

    We studied the effect of postgrowth low energy (1.5 keV) Ar+ ion irradiation of various amorphous carbon (a-C) films with different microstructure and bonding. Detailed x-ray diffraction was used to identify the existing phases in thin (30-200 nm) a-C films, deposited on Si and subjected to Ar+ ion irradiation and to study the mechanisms of formation of diamond, lonsdaleite (diamond-2H), silicon carbide, and graphite grains. The relative content of each crystalline phase, the grain size, and distribution depend strongly on the microstructure of the as-grown films that is affected by the bias voltage applied during deposition of the films. Ion bombardment promoted the formation of graphite throughout the films and diamond and SiC grains close to the a-C/Si interface. Diamond and SiC nucleation at the a-C/Si interface area occurs beyond the penetration depth of the Ar+ ions and therefore is not attributed to a direct, ballistic ion-solid interaction but rather to a mechanism of charge transfer through conductivity channels. The latter is also considered and discussed in terms of other features of the as-grown a-C films such as density, voids content, electrical resistivity, and surface and interface morphology.

  11. Light emission in forward and reverse bias operation in OLED with amorphous silicon carbon nitride thin films

    Energy Technology Data Exchange (ETDEWEB)

    Reyes, R [Facultad de Ingenieria Quimica y Textil, Universidad Nacional de Ingenieria, Av. Tupac Amaru SN, Lima (Peru); Cremona, M [Departamento de Fisica, PontifIcia Universidade Catolica de Rio de Janeiro, PUC-Rio, Cx. Postal 38071, Rio de Janeiro, RJ, CEP 22453-970 (Brazil); Achete, C A, E-mail: rreyes@uni.edu.pe [Departamento de Engenheria Metalurgica e de Materiais, Universidade Federal do Rio de Janeiro, Cx. Postal 68505, Rio de Janeiro, RJ, CEP 21945-970 (Brazil)

    2011-01-01

    Amorphous silicon carbon nitride (a-SiC:N) thin films deposited by magnetron sputtering were used in the structure of an organic light emitting diode (OLED), obtaining an OLED operating in forward and reverse bias mode. The device consist of the heterojunction structure ITO/a-SiC:N/Hole Transport Layer (HTL)/ Electron Transport Layer (ETL)/a-SiC:N/Al. As hole transporting layer was used a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline - 6 - carboxyaldehyde - 1,1'- diphenylhydrazone (MTCD), while the tris(8-hydroxyquinoline aluminum) (Alq{sub 3}) is used as electron transport and emitting layer. A significant increase in the voltage operation compared to the conventional ITO/MTCD/Alq{sub 3}/Al structure was observed, so the onset of electroluminescence occurs at about 22 V in the forward and reverse bias mode of operation. The electroluminescence spectra is similar in both cases, only slightly shifted 0.14 eV to lower energies in relation to the conventional device.

  12. Multiwavelength Raman analysis of SiO{sub x} and N containing amorphous diamond like carbon films

    Energy Technology Data Exchange (ETDEWEB)

    Tamulevičienė, Asta, E-mail: asta.tamuleviciene@ktu.lt [Institute of Materials Science of Kaunas University of Technology, K. Baršausko St. 59, Kaunas LT-51423 (Lithuania); Kopustinskas, Vitoldas [Institute of Materials Science of Kaunas University of Technology, K. Baršausko St. 59, Kaunas LT-51423 (Lithuania); Niaura, Gediminas [Center for Physical Sciences and Technology, Institute of Chemistry, A. Goštauto 9, LT-01108 Vilnius (Lithuania); Meškinis, Šarūnas; Tamulevičius, Sigitas [Institute of Materials Science of Kaunas University of Technology, K. Baršausko St. 59, Kaunas LT-51423 (Lithuania)

    2015-04-30

    In the current research SiO{sub x} and N containing amorphous diamond like carbon (a-C:H) films were deposited on crystalline silicon from hexamethyldisiloxane and hexamethyldisilazane compounds respectively, using closed drift ion beam source and different ion beam energy in a range 300–800 eV. Hydrogen was used as a carrier gas of the precursors. Composition of the films was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The structure of these films was studied employing multiwavelength (325 nm–785 nm) Raman analysis. From the Raman spectra analysis, the characteristic parameters such as the position of G peak, D/G peak intensity ratio as well as dispersion of G (Disp(G)) peak showing topological disorder of sp{sup 2} phase in doped a-C:H films were determined. Analysis of Disp (G) and D/G intensity ratio revealed that in both types of films increase of ion beam energy gives higher sp{sup 3}/sp{sup 2} ratio in the films. - Highlights: • Siloxanes are used to incorporate Si, O and N into a-C:H films. • Closed drift ion beam source at varying ion beam energy was used. • Multiwavelength Raman spectroscopy analysis (325–785 nm) was performed. • Dispersion of G peak shows that sp{sup 3}/sp{sup 2} ratio rises with increasing ion beam energy.

  13. Ion Impact Energy Distributions and Properties of Amorphous Hydrogenated Carbon Thin Films Deposited in a Self-Biased RF Discharge

    Science.gov (United States)

    Tatsuta, Toshiaki; Tachibana, Kunihide; Tsuji, Osamu

    1994-11-01

    In a self-biased RF discharge in CH4 we have investigated the relationships between the properties of hydrogenated amorphous carbon (a-C:H) film and ion impact energy distributions (IIEDs) measured by retarding-type ion energy analyzer at both parallel-plate electrodes. On the RF electrode a high-energy peak (HEP) dur to the ion beam component was observed in IIED. The height of HEP decreased with increasing pressure at a given self-bias voltage (V dc) and the central energy of HEP increased linearly with V dc at a given pressure. The micro hardness of the film increased in proportion to the total incident ion current (TIIC) and central energy of HEP. The hydrogen content decreased and the surface morphology became fine as the central energy of HEP increased. From Raman and IR absorption spectra it turned out that there was an optimal energy of HEP to increase the content of the sp3 bonding structure in the film.

  14. Hard coating of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films on cemented tungsten carbide by coaxial arc plasma deposition

    Science.gov (United States)

    Naragino, Hiroshi; Egiza, Mohamed; Tominaga, Aki; Murasawa, Koki; Gonda, Hidenobu; Sakurai, Masatoshi; Yoshitake, Tsuyoshi

    2016-08-01

    Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were deposited on cemented carbide containing Co by coaxial arc plasma deposition. With decreasing substrate temperature, the hardness was enhanced accompanied by an enhancement in the sp3/(sp2 + sp3). Energy-dispersive X-ray and secondary ion mass spectrometry spectroscopic measurements exhibited that the diffusion of Co atoms from the substrates into the films hardly occurs. The film deposited at room temperature exhibited the maximum hardness of 51.3 GPa and Young's modulus of 520.2 GPa, which evidently indicates that graphitization induced by Co in the WC substrates, and thermal deformation from sp3 to sp2 bonding are suppressed. The hard UNCD/a-C films can be deposited at a thickness of approximately 3 μm, which is an order larger than that of comparably hard a-C films. The internal compressive stress of the 51.3-GPa film is 4.5 GPa, which is evidently smaller than that of comparably hard a-C films. This is a reason for the thick deposition. The presence of a large number of grain boundaries in the film, which is a structural specific to UNCD/a-C films, might play a role in releasing the internal stress of the films.

  15. Raman shift on n-doped amorphous carbon thin films grown by electron beam evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Rebollo P., B. [Departamento de Fisica, Pontificia Universidad Catolica de Rio de Janeiro (Brazil); Facultad de Ciencias Fisico-Matematicas, Benemerita Universidad Autonoma de Puebla (Mexico); Freire L., F. Jr. [Departamento de Fisica, Pontificia Universidad Catolica de Rio de Janeiro (Brazil); Lozada M., R.; Palomino M., R. [Facultad de Ciencias Fisico-Matematicas, Benemerita Universidad Autonoma de Puebla (Mexico); Jimenez S., S. [Centro de Investigacion y de Estudios Avanzados del IPN, Laboratorio de Investigacion en Materiales, Queretaro (Mexico); Zelaya A., O. [Centro de Investigacion y de Estudios Avanzados del IPN, Departamento de Fisica, CINVESTAV-IPN, P.O. Box 14-740, Mexico 07360 D.F. (Mexico)

    2007-04-15

    The structural properties of carbon thin films synthesized under an atmosphere of nitrogen by means of electron beam evaporation were studied by Raman scattering spectroscopy. The electron beam evaporation technique is an important alternative to grown layers of this material with interesting structural properties. The observed shift of the Raman G band shows that the structure of the films tends to become more graphitic upon the increase of the deposition time. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Physico-chemical studies of cuprous oxide (Cu{sub 2}O) nanoparticles coated on amorphous carbon nanotubes (α-CNTs)

    Energy Technology Data Exchange (ETDEWEB)

    Johan, Mohd Rafie, E-mail: mrafiej@um.edu.my; Meriam Suhaimy, Syazwan Hanani; Yusof, Yusliza, E-mail: yus_liza@siswa.um.edu.my

    2014-01-15

    Amorphous carbon nanotubes (α-CNTs) were synthesized by a chemical reaction between ferrocene and ammonium chloride at a temperature (∼250 °C) in an air furnace. As- synthesized α-CNTs were purified with deionized water and hydrochloric acid. A purified α-CNTs were hybridized with cuprous oxide nanoparticles (Cu{sub 2}O) through a simple chemical process. Morphology of the samples was analyzed with field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectra showed the attachment of acidic functional groups onto the surface of α-CNTs and the formation of hybridized α-CNTs-Cu{sub 2}O. Raman spectra reveal the amorphous nature of the carbon. X-ray diffraction (XRD) pattern confirmed the amorphous phase of the carbon and the formation of Cu{sub 2}O crystalline phase. The coating of Cu{sub 2}O was confirmed by FESEM, TEM, and XRD. Optical absorption of the samples has also been investigated and the quantum confinement effect was illustrated in the absorption spectra.

  17. Understanding phase-change behaviors of carbon-doped Ge₂Sb₂Te₅ for phase-change memory application.

    Science.gov (United States)

    Zhou, Xilin; Xia, Mengjiao; Rao, Feng; Wu, Liangcai; Li, Xianbin; Song, Zhitang; Feng, Songlin; Sun, Hongbo

    2014-08-27

    Phase-change materials are highly promising for next-generation nonvolatile data storage technology. The pronounced effects of C doping on structural and electrical phase-change behaviors of Ge2Sb2Te5 material are investigated at the atomic level by combining experiments and ab initio molecular dynamics. C dopants are found to fundamentally affect the amorphous structure of Ge2Sb2Te5 by altering the local environments of Ge-Te tetrahedral units with stable C-C chains. The incorporated C increases the amorphous stability due to the enhanced covalent nature of the material with larger tetrahedral Ge sites. The four-membered rings with alternating atoms are reduced greatly with carbon addition, leading to sluggish phase transition and confined crystal grains. The lower RESET power is presented in the PCM cells with carbon-doped material, benefiting from its high resistivity and low thermal conductivity.

  18. XPS and XAES studies of the amorphous hydrogenated carbon/silicon interface

    Science.gov (United States)

    Montero, I.; Galán, L.; Rueda, F.; Perrière, J.

    1993-12-01

    Low-pressure multipolar-plasma assisted deposition on c-Si substrates has been used to grow carbon films. Angle-resolved XPS and XAES were used to analyze the initial stages of the growth as a function of the ion deposition energy. A good signal-to-noise ratio allowed us to study simultaneously the film and the relatively deep inteface without any damage to the samples. Channeling RBS, NRA and ERDA were also used to complete the analysis. The same as in the a-C: H film, the physical and chemical nature of the film/substrate interface also varies with the ionic energy impinging on the substrate. After deposition, the original native silicon oxide, 10 Å thick, is either left practically unmodified for polymer-like films or an oxicarbide SiO 1.3C 0.3 + 20%SiC about 50 Å thick is formed for "diamond-like" films.

  19. Formation of carbon nanotubes on an amorphous Ni{sub 25}Ta{sub 58}N{sub 17} alloy film by chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Gromov, D. G.; Dubkov, S. V., E-mail: sv.dubkov@gmail.com [National Research University of Electronic Technology MIET (Russian Federation); Pavlov, A. A. [Russian Academy of Sciences, Institute of Nanotechnologies of Microelectronics (Russian Federation); Skorik, S. N. [Technological Center Research and Production Complex (Russian Federation); Trifonov, A. Yu. [Lukin Scientific Research Institute of Physical Problems (Russian Federation); Kirilenko, E. P.; Shulyat’ev, A. S. [National Research University of Electronic Technology MIET (Russian Federation); Shaman, Yu. P. [Technological Center Research and Production Complex (Russian Federation); Rygalin, B. N. [National Research University of Electronic Technology MIET (Russian Federation)

    2016-12-15

    It is shown that it is possible to grow carbon nanotubes on the surface of an amorphous Ni–Ta–N metal alloy film with a low Ni content (~25 at %) by chemical deposition from acetylene at temperature 400–800°C. It is established that the addition of nitrogen into the Ni–Ta alloy composition is favorable for the formation of tantalum nitride and the expulsion of Ni clusters, which act as a catalyst of the growth of carbon nanotubes, onto the surface. From Raman spectroscopy studies, it is found that, as the temperature of synthesis is raised, the quality of nanotubes is improved.

  20. Nonconforming tetrahedral mixed finite elements for elasticity

    OpenAIRE

    Arnold, Douglas N.; Awanou, Gerard; Winther, Ragnar

    2012-01-01

    This paper presents a nonconforming finite element approximation of the space of symmetric tensors with square integrable divergence, on tetrahedral meshes. Used for stress approximation together with the full space of piecewise linear vector fields for displacement, this gives a stable mixed finite element method which is shown to be linearly convergent for both the stress and displacement, and which is significantly simpler than any stable conforming mixed finite element method. The method ...

  1. Production and Characterization of Bulk MgB2 Material made by the Combination of Crystalline and Carbon Coated Amorphous Boron Powders

    Science.gov (United States)

    Hiroki, K.; Muralidhar, M.; Koblischka, M. R.; Murakami, M.

    2017-07-01

    The object of this investigation is to reduce the cost of bulk production and in the same time to increase the critical current performance of bulk MgB2 material. High-purity commercial powders of Mg metal (99.9% purity) and two types of crystalline (99% purity) and 16.5 wt% carbon-coated, nanometer-sized amorphous boron powders (98.5% purity) were mixed in a nominal composition of MgB2 to reduce the boron cost and to see the effect on the superconducting and magnetic properties. Several samples were produced mixing the crystalline boron and carbon-coated, nanometer-sized amorphous boron powders in varying ratios (50:50, 60:40, 70:30, 80:20, 90:10) and synthesized using a single-step process using the solid state reaction around 800 °C for 3 h in pure argon atmosphere. The magnetization measurements exhibited a sharp superconducting transition temperature with T c, onset around 38.6 K to 37.2 K for the bulk samples prepared utilizing the mixture of crystalline boron and 16.5% carbon-coated amorphous boron. The critical current density at higher magnetic field was improved with addition of carbon-coated boron to crystalline boron in a ratio of 80:20. The highest self-field Jc around 215,000 A/cm2 and 37,000 A/cm2 were recorded at 20 K, self-field and 2 T for the sample with a ratio of 80:10. The present results clearly demonstrate that the bulk MgB2 performance can be improved by adding carbon-coated nano boron to crystalline boron, which will be attractive to reduce the cost of bulk MgB2 material for several industrial applications.

  2. A facile solution combustion synthesis of nanosized amorphous iron oxide incorporated in a carbon matrix for use as a high-performance lithium ion battery anode material

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Chunyu, E-mail: chunyu6zhu@gmail.com; Saito, Genki; Akiyama, Tomohiro

    2015-06-05

    Highlights: • Iron oxide–carbon composite was fabricated by facile solution combustion synthesis. • Iron oxide nanoparticles of about 5 nm were uniformly embedded in dense carbon matrix. • The composite exhibited enhanced cyclability and rate capability. • A high capacity of 687 mA h g{sup −1} after 200 cycles at a current rate of 0.5 A g{sup −1} were obtained. - Abstract: An amorphous iron oxide–carbon composite has been fabricated through an effective, inexpensive, and scalable method employing solution combustion synthesis. Amorphous iron oxide nanoparticles with diameters of about 5 nm were synthesized and uniformly embedded in a dense carbon matrix. The synthesized composite exhibits enhanced cyclability and rate capability, showing a high reversible capacity of 687 mA h g{sup −1} after 200 discharge/charge cycles at a current rate of 0.5 A g{sup −1}, compared to the 400 mA h g{sup −1} observed for Fe{sub 2}O{sub 3} nanoparticles. This enhanced performance was retained despite more demanding conditions, delivering a high capacity of about 525 mA h g{sup −1} and a nearly perfect coulombic efficiency even after 400 cycles at 1 A g{sup −1}. The easy production and superior electrochemical properties of this composite suggest that it is a promising material for use as an anode material in high performance lithium ion batteries.

  3. The evolution of well-aligned amorphous carbon nanotubes and porous ZnO/C core-shell nanorod arrays for photosensor applications.

    Science.gov (United States)

    Wang, Ruey-Chi; Hsu, Chia-Chi; Chen, Shu-Jen

    2011-01-21

    Well-aligned amorphous carbon nanotube (a-CNT) and porous ZnO/C core-shell nanorod (NR) arrays were fabricated for the first time by a proposed deposition-etching-evaporation (DEE) route. The arrays were prepared by deposition of carbon on the surface of well-aligned ZnO NR arrays by thermal decomposition of acetone followed by spontaneous etching and evaporation of core-ZnO. By utilizing the decomposition of acetone as well as distinct degrees of interaction between intermediate products and ZnO, well-aligned nonporous ZnO/C core-shell NR, porous ZnO/C core-shell NR, and a-CNT arrays were separately prepared by varying the working temperature from 400 to 700 °C. Scanning electron microscopy and high-resolution transmission electron microscopy show that the thickness of carbon shells increases from 3 to 10 nm with the increase in working temperature. Raman spectra demonstrate slight sp(2) bonds of carbon, indicating small graphite regions embedded in amorphous carbon nanoshells. The E(2) peaks of ZnO reduce with the increase in substrate temperature. Photoresponse measurements of ZnO/C NR arrays shows enhancement of both photoresponsivity and response velocity, and the interference of humidity with regard to photosensing is effectively reduced by the capping of carbon nanoshells. The work not only provides an effective route to improve the photosensing of semiconductor nanomaterials for practical applications, but also sheds light on preparing various hollow carbon and porous ZnO/C core-shell nanostructures with distinct morphologies by employing the routes presented in the paper on diverse ZnO nanostructures for optoelectrochemical applications.

  4. Deposit of thin films of nitrided amorphous carbon using the laser ablation technique; Deposito de peliculas delgadas de carbono amorfo nitrurado utilizando la tecnica de ablacion laser

    Energy Technology Data Exchange (ETDEWEB)

    Rebollo, P.B.; Escobar A, L.; Camps C, E. [Departamento de Fisica, Instituto Nacional de Investigaciones Nucleares, C.P. 52045 Salazar, Estado de Mexico (Mexico); Haro P, E.; Camacho L, M.A. [Departamento de Fisica, Universidad Autonoma Metropolitana Iztapalapa (Mexico); Muhl S, S. [Instituto de Investigacion en Materiales, UNAM (Mexico)

    2000-07-01

    It is reported the synthesis and characterization of thin films of amorphous carbon (a-C) nitrided, deposited by laser ablation in a nitrogen atmosphere at pressures which are from 4.5 x 10 {sup -4} Torr until 7.5 x 10 {sup -2} Torr. The structural properties of the films are studied by Raman spectroscopy obtaining similar spectra at the reported for carbon films type diamond. The study of behavior of the energy gap and the ratio nitrogen/carbon (N/C) in the films, shows that the energy gap is reduced when the nitrogen incorporation is increased. It is showed that the refraction index of the thin films diminish as nitrogen pressure is increased, indicating the formation of graphitic material. (Author)

  5. Understanding API-polymer proximities in amorphous stabilized composite drug products using fluorine-carbon 2D HETCOR solid-state NMR.

    Science.gov (United States)

    Abraham, Anuji; Crull, George

    2014-10-06

    A simple and robust method for obtaining fluorine-carbon proximities was established using a (19)F-(13)C heteronuclear correlation (HETCOR) two-dimensional (2D) solid-state nuclear magnetic resonance (ssNMR) experiment under magic-angle spinning (MAS). The method was applied to study a crystalline active pharmaceutical ingredient (API), avagacestat, containing two types of fluorine atoms and its API-polymer composite drug product. These results provide insight into the molecular structure, aid with assigning the carbon resonances, and probe API-polymer proximities in amorphous spray dried dispersions (SDD). This method has an advantage over the commonly used (1)H-(13)C HETCOR because of the large chemical shift dispersion in the fluorine dimension. In the present study, fluorine-carbon distances up to 8 Å were probed, giving insight into the API structure, crystal packing, and assignments. Most importantly, the study demonstrates a method for probing an intimate molecular level contact between an amorphous API and a polymer in an SDD, giving insights into molecular association and understanding of the role of the polymer in API stability (such as recrystallization, degradation, etc.) in such novel composite drug products.

  6. Heavy-ion induced desorption yields of amorphous carbon films bombarded with 4.2 MeV/u lead ions

    CERN Document Server

    Mahner, E; Küchler, D; Scrivens, R; Costa Pinto, P; Yin Vallgren, C; Bender, M

    2011-01-01

    During the past decade, intense experimental studies on the heavy-ion induced molecular desorption were performed in several particle accelerator laboratories worldwide in order to understand and overcome large dynamic pressure rises caused by lost beam ions. Different target materials and various coatings were studied for desorption and mitigation techniques were applied to heavy-ion accelerators. For the upgrade of the CERN injector complex, a coating of the Super Proton Synchrotron (SPS) vacuum system with a thin film of amorphous carbon is under study to mitigate the electron cloud effect observed during SPS operation with the nominal proton beam for the Large Hadron Collider (LHC). Since the SPS is also part of the heavy-ion injector chain for LHC, dynamic vacuum studies of amorphous carbon films are important to determine their ion induced desorption yields. At the CERN Heavy Ion Accelerator (LINAC 3), carbon-coated accelerator-type stainless steel vacuum chambers were tested for desorption using 4.2 Me...

  7. Amorphous silicon-carbon nanospheres synthesized by chemical vapor deposition using cheap methyltrichlorosilane as improved anode materials for Li-ion batteries.

    Science.gov (United States)

    Zhang, Zailei; Zhang, Meiju; Wang, Yanhong; Tan, Qiangqiang; Lv, Xiao; Zhong, Ziyi; Li, Hong; Su, Fabing

    2013-06-21

    We report the preparation and characterization of amorphous silicon-carbon (Si-C) nanospheres as anode materials in Li-ion batteries. These nanospheres were synthesized by a chemical vapor deposition at 900 °C using methyltrichlorosilane (CH3SiCl3) as both the Si and C precursor, which is a cheap byproduct in the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that the synthesized Si-C nanospheres composed of amorphous C (about 60 wt%) and Si (about 40 wt%) had a diameter of 400-600 nm and a surface area of 43.8 m(2) g(-1). Their charge capacities were 483.6, 331.7, 298.6, 180.6, and 344.2 mA h g(-1) at 50, 200, 500, 1000, and 50 mA g(-1) after 50 cycles, higher than that of the commercial graphite anode. The Si-C amorphous structure could absorb a large volume change of Si during Li insertion and extraction reactions and hinder the cracking or crumbling of the electrode, thus resulting in the improved reversible capacity and cycling stability. The work opens a new way to fabricate low cost Si-C anode materials for Li-ion batteries.

  8. Sulfur-Doped Porphyrinic Carbon Nanostructures Synthesized with Amorphous MoS2 for the Oxygen Reduction Reaction in an Acidic Medium.

    Science.gov (United States)

    Park, Hyun-Suk; Han, Sang-Beom; Kwak, Da-Hee; Lee, Gyu-Ho; Choi, In-Ae; Kim, Do-Hyoung; Ma, Kyeng-Bae; Kim, Min-Cheol; Kwon, Hye-Jin; Park, Kyung-Won

    2017-05-22

    To develop doped carbon nanostructures as non-precious metal cathode catalysts, nanocomposites were synthesized by using SBA-15 and 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin-iron(III) chloride with different ratios of amorphous MoS2 precursor. From various analyses, it was found that, during pyrolysis at 900 °C under an N2 atmosphere, the amorphous MoS2 precursor decomposed into Mo and S, facilitating the formation of graphene sheet-like carbon with MoC and doping of sulfur in the carbon. In the nanocomposite formed from 10 wt % MoS2 precursor (denoted as Mo/S/PC-10), most of the MoS2 was decomposed, thus forming S-doped carbon, which was grown on the MoC phase without crystalline MoS2 . Furthermore, Mo/S/PC-10 exhibited better performance in the oxygen reduction reaction (specific activity of 1.23 mA cm(-2) at 0.9 V and half-wave potential of 0.864 V) than a commercial Pt catalyst, owing to a heteroatom-doped carbon nanostructure with a fairly high specific surface area. In the polarization curve of the unit-cell performance measured at 80 °C under ambient pressure, Mo/S/PC-10 as a cathode catalyst exhibited an optimal power density of 314 mW cm(-2) and a current density of 280 mA cm(-2) at 0.6 V. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Near-Edge X-Ray Absorption Fine Structure of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Films Prepared by Pulsed Laser Deposition

    Directory of Open Access Journals (Sweden)

    Shinya Ohmagari

    2009-01-01

    Full Text Available The atomic bonding configuration of ultrananocrystalline diamond (UNCD/hydrogenated amorphous carbon (a-C:H films prepared by pulsed laser ablation of graphite in a hydrogen atmosphere was examined by near-edge X-ray absorption fine structure spectroscopy. The measured spectra were decomposed with simple component spectra, and they were analyzed in detail. As compared to the a-C:H films deposited at room substrate-temperature, the UNCD/a-C:H and nonhydrogenated amorphous carbon (a-C films deposited at a substrate-temperature of 550∘C exhibited enhanced ∗ and ∗C≡C peaks. At the elevated substrate-temperature, the ∗ and ∗C≡C bonds formation is enhanced while the ∗C–H and ∗C–C bonds formation is suppressed. The UNCD/a-C:H film showed a larger ∗C–C peak than the a-C film deposited at the same elevated substrate-temperature in vacuum. We believe that the intense ∗C–C peak is evidently responsible for UNCD crystallites existence in the film.

  10. Synthesis and characterization of thin films of nitrided amorphous carbon deposited by laser ablation; Sintesis y caracterizacion de peliculas delgadas de carbono amorfo nitrurado, depositadas por ablacion laser

    Energy Technology Data Exchange (ETDEWEB)

    Rebollo P, B

    2001-07-01

    The objective of this work is the synthesis and characterization of thin films of amorphous carbon (a-C) and thin films of nitrided amorphous carbon (a-C-N) using the laser ablation technique for their deposit. For this purpose, the physical properties of the obtained films were studied as function of diverse parameters of deposit such as: nitrogen pressure, power density, substrate temperature and substrate-target distance. For the characterization of the properties of the deposited thin films the following techniques were used: a) Raman spectroscopy which has demonstrated being a sensitive technique to the sp{sup 2} and sp{sup 3} bonds content, b) Energy Dispersive Spectroscopy which allows to know semi-quantitatively way the presence of the elements which make up the deposited films, c) Spectrophotometry, for obtaining the absorption spectra and subsequently the optical energy gap of the deposited material, d) Ellipsometry for determining the refraction index, e) Scanning Electron Microscopy for studying the surface morphology of thin films and, f) Profilemetry, which allows the determination the thickness of the deposited thin films. (Author)

  11. Tetrahedrally coordinated half-metallic antiferromagnets

    Science.gov (United States)

    Nakao, Masao

    2006-11-01

    We explore the electronic structures of transition-metal-based chalcopyrites TMX2 ( X=S , Se, and Te) to establish a concept of half-metallic antiferromagnets (HM-AFM’s) within the class of tetrahedrally coordinated ternary systems. Using a full-potential muffin-tin approach and the spin-polarized density functional method, we find two series of HM-AFM’s: CrFeX2 and VCoX2 , where two constituent magnetic ions in a unit cell have antialigned local moments that cancel exactly by virtue of the integer filling of one spin channel. The bonding nature is interpreted in terms of the “ghost-bond-orbital model”; the T - X bonds are covalent while the M - X bonds are ionic, suggesting the magnetic interaction in each bond is due to ferromagnetic double exchange and antiferromagnetic superexchange, respectively, in the conventional scheme.

  12. Hierarchical Nanocomposite by the Integration of Reduced Graphene Oxide and Amorphous Carbon with Ultrafine MgO Nanocrystallites for Enhanced CO2Capture.

    Science.gov (United States)

    Li, Ping; Zeng, Hua Chun

    2017-11-07

    Exploring efficient and low-cost solid sorbents is essential for carbon capture and storage. Herein, a novel class of high-performance CO 2 adsorbent (rGO@MgO/C) is engineered based on the controllable integration of reduced graphene oxide (rGO), amorphous carbon, and MgO nanocrystallites. The optimized rGO@MgO/C nanocomposite exhibits remarkable CO 2 capture capacity (up to 31.5 wt % at 27 °C, 1 bar CO 2 , and 22.5 wt % under the simulated flue gas), fast sorption rate, and strong process durability. The enhanced capture capability of CO 2 is the best among all of the MgO-based sorbents reported so far. The high performance of rGO@MgO/C nanocomposite can be ascribed to the hierarchical architecture and special physicochemical features, including the sheet-on-sheet sandwich-like structure, ultrathin nanosheets with abundant nanopores, large surface area, and highly dispersed ultrafine MgO nanocrystallites (ca. 3 nm in size), together with the rGO sheets and in situ generated amorphous carbon that serve as a dual carbon support and protectant system with which to prevent MgO nanocrystallites from agglomeration. In addition, the CO 2 -uptake capacity at intermediate temperature (e.g., 350 °C) can be further improved threefold through alkali metal salt promotion treatment. This work provides a facile and effective strategy with which to engineer advanced graphene-based functional nanocomposites with rationally designed compositions and architectures for potential applications in the field of gas storage and separation.

  13. Structure, mechanical, and frictional properties of hydrogenated fullerene-like amorphous carbon film prepared by direct current plasma enhanced chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yongfu [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Gao, Kaixiong; Zhang, Junyan, E-mail: zhangjunyan@licp.cas.cn [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

    2016-07-28

    In this study, fullerene like carbon (FL-C) is introduced in hydrogenated amorphous carbon (a-C:H) film by employing a direct current plasma enhanced chemical vapor deposition. The film has a low friction and wear, such as 0.011 and 2.3 × 10{sup −9}mm{sup 3}/N m in the N{sub 2}, and 0.014 and 8.4 × 10{sup −8}mm{sup 3}/N m in the humid air, and high hardness and elasticity (25.8 GPa and 83.1%), to make further engineering applications in practice. It has several nanometers ordered domains consisting of less frequently cross-linked graphitic sheet stacks. We provide new evidences for understanding the reported Raman fit model involving four vibrational frequencies from five, six, and seven C-atom rings of FL-C structures, and discuss the structure evolution before or after friction according to the change in the 1200 cm{sup −1} Raman band intensity caused by five- and seven-carbon rings. Friction inevitably facilitates the transformation of carbon into FL-C nanostructures, namely, the ultra low friction comes from both such structures within the carbon film and the sliding induced at friction interface.

  14. Structure, mechanical, and frictional properties of hydrogenated fullerene-like amorphous carbon film prepared by direct current plasma enhanced chemical vapor deposition

    Science.gov (United States)

    Wang, Yongfu; Gao, Kaixiong; Zhang, Junyan

    2016-07-01

    In this study, fullerene like carbon (FL-C) is introduced in hydrogenated amorphous carbon (a-C:H) film by employing a direct current plasma enhanced chemical vapor deposition. The film has a low friction and wear, such as 0.011 and 2.3 × 10-9mm3/N m in the N2, and 0.014 and 8.4 × 10-8mm3/N m in the humid air, and high hardness and elasticity (25.8 GPa and 83.1%), to make further engineering applications in practice. It has several nanometers ordered domains consisting of less frequently cross-linked graphitic sheet stacks. We provide new evidences for understanding the reported Raman fit model involving four vibrational frequencies from five, six, and seven C-atom rings of FL-C structures, and discuss the structure evolution before or after friction according to the change in the 1200 cm-1 Raman band intensity caused by five- and seven-carbon rings. Friction inevitably facilitates the transformation of carbon into FL-C nanostructures, namely, the ultra low friction comes from both such structures within the carbon film and the sliding induced at friction interface.

  15. Edge effect enhanced electron field emission in top assembled reduced graphene oxide assisted by amorphous CNT-coated carbon cloth substrate

    Directory of Open Access Journals (Sweden)

    Rajarshi Roy

    2013-01-01

    Full Text Available In this work a hybrid structure assembly of amorphous carbon nanotubes (a-CNTs -reduced graphene oxide (RGO has been fabricated on carbon cloth/PET substrates for enhanced edge effect assisted flexible field emission device application. The carbon nanostructures prepared by chemical processes were finally deposited one over the other by a simple electrophoretic deposition (EPD method on carbon cloth (CC fabric. The thin films were then characterized by X-ray diffraction (XRD, Fourier transformed infrared spectroscopy (FTIR, field emission scanning electron microscopy (FESEM and high resolution transmission electron microscope (HRTEM. Field assisted electron emission measurement was performed on this hybrid structure. It was observed that the hybrid carbon nanostructure showed exceptional field emission properties with outstanding low turn-on and threshold field (Eto∼ 0.26 Vμm−1, Eth ∼ 0.55 Vμm1. These observed results are far better compared to standalone and plasma etched edge enhanced RGO systems due to the bottom layer a-CNTs bed which assisted in significant enhancement of edge effect in RGO sheets.

  16. The effect of deposition energy of energetic atoms on the growth and structure of ultrathin amorphous carbon films studied by molecular dynamics simulations

    KAUST Repository

    Wang, N

    2014-05-16

    The growth and structure of ultrathin amorphous carbon films was investigated by molecular dynamics simulations. The second-generation reactive-empirical-bond-order potential was used to model atomic interactions. Films with different structures were simulated by varying the deposition energy of carbon atoms in the range of 1-120 eV. Intrinsic film characteristics (e.g. density and internal stress) were determined after the system reached equilibrium. Short- and intermediate-range carbon atom ordering is examined in the context of atomic hybridization and ring connectivity simulation results. It is shown that relatively high deposition energy (i.e., 80 eV) yields a multilayer film structure consisting of an intermixing layer, bulk film and surface layer, consistent with the classical subplantation model. The highest film density (3.3 g cm-3), sp3 fraction (∼43%), and intermediate-range carbon atom ordering correspond to a deposition energy of ∼80 eV, which is in good agreement with experimental findings. © 2014 IOP Publishing Ltd.

  17. A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids : from Graphene to Amorphous Carbons

    NARCIS (Netherlands)

    Merlen, A.; Buijnsters, J.G.; Pardanaud, C.

    2017-01-01

    sp2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to

  18. A guide to and review of the use of Multiwavelength Raman Spectroscopy for characterizing defective aromatic carbon solids : From graphene to amorphous carbons

    NARCIS (Netherlands)

    Merlen, A.; Buijnsters, J.G.; Pardanaud, C.

    2017-01-01

    sp2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to

  19. More About the Tetrahedral Unstructured Software System

    Science.gov (United States)

    Abdol-Hamid, Khaled S.; Frink, Neal T.; Hunter, Craig A.; Parikh, Paresh C.; Pizadeh, Shalyar Z.; Samareh, Jamshid A.; Bhat, Maharaj K.; Pandya, Mohagna J.; Grismer, Matthew J.

    2006-01-01

    TetrUSS is a comprehensive suite of computational fluid dynamics (CFD) programs that won the Software of the Year award in 1996 and has found increasing use in government, academia, and industry for solving realistic flow problems (especially in aerodynamics and aeroelastics of aircraft having complex shapes). TetrUSS includes not only programs for solving basic equations of flow but also programs that afford capabilities for efficient generation and utilization of computational grids and for graphical representation of computed flows (see figure). The 2004 version of the Tetrahedral Unstructured Software System (TetrUSS), which is one of two software systems reported in "NASA s 2004 Software of the Year," NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 18, has been improved greatly since 1996. These improvements include (1) capabilities to simulate viscous flow by solving the Navier-Stokes equations on unstructured grids, (2) portability to personal computers from diverse manufacturers, (3) advanced models of turbulence, (4) a parallel-processing version of one of the unstructured-grid Navier-Stokes-equation-solving programs, and (5) advanced programs for generating unstructured grids.

  20. Polyvinylpyrrolidone surface modification with SiOx containing amorphous hydrogenated carbon (a-C:H/SiOx) and nitrogen-doped a-C:H/SiOx films using Hall-type closed drift ion beam source

    NARCIS (Netherlands)

    Lazauskas, A.; Grigaliunas, V.; Guobiene, A.; Puiso, J.; Prosycevas, I.; Baltrusaitis, Jonas

    2013-01-01

    In this study SiOx containing amorphous hydrogenated carbon (a-C:H/SiOx) and nitrogen-doped a-C:H/SiOx (a-C:H:N/SiOx) films were deposited on polyvinylpyrrolidone (PVP) templates of variable thickness using a Hall-type closed drift ion beam source with constant irradiation parameters. A detailed

  1. Track formation in two amorphous insulators, vitreous silica and diamond like carbon: Experimental observations and description by the inelastic thermal spike model

    Science.gov (United States)

    Rotaru, C.; Pawlak, F.; Khalfaoui, N.; Dufour, C.; Perrière, J.; Laurent, A.; Stoquert, J. P.; Lebius, H.; Toulemonde, M.

    2012-02-01

    Vitreous silica thin film (a-SiO 2) and mixed deuterated and hydrogenated amorphous carbon thin film (a-C:D,H), grown or deposited, respectively, on silicon, have been irradiated at GANIL in the MeV/u energy range with ions between C and U in order to reach electronic energy loss between 0.7 and 25 keV/nm. The evolution of Si-O bonds and C-D bonds contents was determined by infrared absorption spectroscopy. Complementary physico-chemical characterization was performed for a-C:D,H using Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). For a-SiO 2, the band at 1076 cm -1 decreases with the appearance of a band at 1046 cm -1. In the case of the diamond like amorphous carbon, the main effects due to MeV/u ion irradiations are the decrease of sp 3 bonding content and of deuterium relative concentration (D/C atomic ratio) as a function of fluence with the appearance of the sp 1 bond. The cylinder radii in which these physical phenomena are confined can be deduced from a statistical analysis. Using the inelastic thermal spike model (i-TS) these track radii can be described using the electron-phonon mean free path which takes values equal to 3 and 0.9 nm for a-SiO 2 and a-C:D, respectively. Extrapolation to low energy range (˜1 MeV in total or ˜0.02 MeV/u) will be made.

  2. Insight into the Capacity Fading Mechanism of Amorphous Se 2 S 5 Confined in Micro/Mesoporous Carbon Matrix in Ether-Based Electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Gui-Liang; Ma, Tianyuan; Sun, Cheng-Jun; Luo, Chao; Cheng, Lei; Ren, Yang; Heald, Steve M.; Wang, Chunsheng; Curtiss, Larry; Wen, Jianguo; Miller, Dean J.; Li, Tao; Zuo, Xiaobing; Petkov, Valeri; Chen, Zonghai; Amine, Khalil

    2016-04-13

    In contrast to the stable cycle performance of space confined Se-based cathodes for lithium batteries in carbonate-based electrolytes, their common capacity fading in ether-based electrolytes has been paid less attention and not yet well-addressed so far. In this work, the lithiation/delithiation of amorphous Se2S5 confined in micro/mesoporous carbon (Se2S5/MPC) cathode was investigated by in situ X-ray near edge absorption spectroscopy (XANES) and theoretical calculations. The Se2S5/MPC composite was synthesized by a modified vaporization-condensation method to ensure a good encapsulation of Se2S5 into the pores of MPC host. In situ XANES results illustrated that the lithiation/delithiation reversibility of Se component was gradually decreased in ether-based electrolytes, leading to an aggravated formation of long-chain polyselenides during cycling and further capacity decay. Moreover, ab initio calculations revealed that the binding energy of polyselenides (Li2Sen) with carbon host is in an order of Li2Se6 > Li2Se4 > Li2Se. The insights into the failure mechanism of Se-based cathode gain in this work are expected to serve as a guide for future design on high performance Se-based cathodes.

  3. From spent graphite to amorphous sp2+sp3 carbon-coated sp2 graphite for high-performance lithium ion batteries

    Science.gov (United States)

    Ma, Zhen; Zhuang, Yuchan; Deng, Yaoming; Song, Xiaona; Zuo, Xiaoxi; Xiao, Xin; Nan, Junmin

    2018-02-01

    Today, with the massive application of lithium ion batteries (LIBs) in the portable devices and electric vehicles, to supply the active materials with high-performances and then to recycle their wastes are two core issues for the development of LIBs. In this paper, the spent graphite (SG) in LIBs is used as raw materials to fabricate two comparative high-capacity graphite anode materials. Based on a microsurgery-like physical reconstruction, the reconstructed graphite (RG) with a sp2+sp3 carbon surface is prepared through a microwave exfoliation and subsequent spray drying process. In contrast, the neural-network-like amorphous sp2+sp3 carbon-coated graphite (AC@G) is synthesized using a self-reconfigurable chemical reaction strategy. Compared with SG and commercial graphite (CG), both RG and AC@G have enhanced specific capacities, from 311.2 mAh g-1 and 360.7 mAh g-1 to 409.7 mAh g-1 and 420.0 mAh g-1, at 0.1C after 100 cycles. In addition, they exhibit comparable cycling stability, rate capability, and voltage plateau with CG. Because the synthesis of RG and AC@G represents two typical physical and chemical methods for the recycling of SG, these results on the sp2+sp3 carbon layer coating bulk graphite also reveal an approach for the preparation of high-performance graphite anode materials derived from SG.

  4. Investigating the Basis of Biogenic Calcium Carbonate Formation from an Amorphous Precursor: Nature of the Transformation to Calcite on Hydroxyl Functionalized Surfaces

    Science.gov (United States)

    Wang, D.; Lee, J. R.; Talley, C. E.; Murphy, K. E.; Han, T. Y.; Deyoreo, J. J.; Dove, P. M.

    2006-12-01

    Calcium carbonate biominerals are particularly significant because of their direct role in regulating the global carbon cycle, as well as their ubiquitous occurrence across earth environments. Biogenic carbonates are further distinguished by their broad phlyogenetic distribution; hence it has been suggested that unrelated eukaryotes must have used similar biochemical strategies to control mineralization. Recent studies have shown that an amorphous calcium carbonate (ACC) phase potentially plays a key role in the initial formation of carbonate minerals and in "shaping" them into complex morphologies widely seen in biominerals. Echinoderms, mollusks, and possibly many other organisms use ACC as a precursor phase that is first nucleated in cellularly controlled environments such as vesicles and subsequently transforms into a fully crystalline material. Recent studies on sea urchin embryos have shown that during transformation ACC develops short range that resembles calcite before fully crystallizing and serve as inspiration for our studies in synthetic systems. Self-assembled monolayers (SAM) on gold and silver have been used as simple model systems that approximate biological surfaces. Many studies have shown that thiol monolayers with hydroxyl termination stabilize a transitory ACC film that with prolonged exposure to aqueous solution transforms into calcite nucleated on {104} faces. Using Near Edge X-ray Absorption Fine Structure (NEXAFS) we studied SAM/mineral interactions with well ordered mercaptophenol monolayers showed that when these films are first exposed to calcium carbonate solutions, they become disordered and remain so after subsequent deposition of an ACC over-layer. Yet calcite nucleates and grows from the surface bound ACC with predominantly {104} orientation, which suggests a dynamic structural relationship between the SAMs and the mineral phase. While the monolayer/mineral phase interaction has been characterized, the mechanism for nucleating

  5. Synthesis of amorphous hydrogenated carbon thin films by magnetized radio-frequency discharge in argon–acetylene mixture at very low gas pressure

    Energy Technology Data Exchange (ETDEWEB)

    Hamdan, Ahmad, E-mail: ahmad.ba.hamdan@gmail.com; Al Makdessi, Georges; Margot, Joëlle

    2016-01-29

    This paper presents a characterization study of carbon thin films grown on crystalline silicon substrates using a magnetized high-frequency discharge in argon–acetylene mixture at very low pressure. Thin films with different morphological structure are obtained. Depending on the gas pressure, acetylene percentage and process time, it is possible to categorize the surface film morphology into three categories: smooth, cracked or microstructured. Moreover, when applying external magnetic field, it has been observed that depending on the substrate direction (perpendicular or parallel) to the reactor axis, it is possible to obtain different film morphologies. For specific conditions, energetic argon ions are formed which lead to film surface damaging and to their inclusion when they impinge the film surface. Chemical pathways and most likely isomers that contribute to the growth are also identified and discussed. Synthesizing materials in such low pressure conditions is of particular interest for better understanding the complex phenomena taking place in the plasma such as instabilities induced by particles and infra-red spectra of carbonaceous interstellar dust. - Highlights: • Deposition of amorphous hydrogenated carbon by magnetized RF-discharge • Modifying the film morphology by changing the pressure and the C{sub 2}H{sub 2} percentage • Studying the effect of the magnetic field on the film structure.

  6. Acetic acid effects on enhancement of growth rate and reduction of amorphous carbon deposition on CNT arrays along a growth window in a floating catalyst reactor

    Science.gov (United States)

    Maghrebi, Morteza; Khodadadi, Abbas Ali; Mortazavi, Yadollah; Sane, Ali; Rahimi, Mohsen; Shirazi, Yaser; Tsakadze, Zviad; Mhaisalkar, Subodh

    2009-11-01

    The mm-long carbon nanotube (CNT) arrays were grown in a floating catalyst reactor, using xylene-ferrocene and a small amount of acetic acid as the feed. The CNT arrays deposited on a quartz substrate at several positions along the reactor were extensively characterized using Raman spectroscopy, scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, and optical microscopy. Various characterization methods consistently reveal that the acetic acid additive to the feed alleviates deposition of amorphous carbon layer, which gradually thickens CNTs along the reactor. The acetic acid also resulted in a higher growth rate along the so-called growth window, where CNT arrays are deposited on the quartz substrate. High-performance liquid chromatography of extracted byproducts (PAHs) confirmed the presence of some polycyclic aromatic hydrocarbons. The solid weight of PAHs decreased upon addition of ferrocene as the catalyst precursor, as well as of acetic acid to xylene feed. The results suggest that primary light products of xylene pyrolysis can be competitive reactants for both catalytic and subsequent pyrolytic reactions. They may also be more efficient feeds for CNT growth than xylene itself.

  7. Large-scale and patternable graphene: direct transformation of amorphous carbon film into graphene/graphite on insulators via Cu mediation engineering and its application to all-carbon based devices.

    Science.gov (United States)

    Chen, Yu-Ze; Medina, Henry; Lin, Hung-Chiao; Tsai, Hung-Wei; Su, Teng-Yu; Chueh, Yu-Lun

    2015-02-07

    Chemical vapour deposition of graphene was the preferred way to synthesize graphene for multiple applications. However, several problems related to transfer processes, such as wrinkles, cleanness and scratches, have limited its application at the industrial scale. Intense research was triggered into developing alternative synthesis methods to directly deposit graphene on insulators at low cost with high uniformity and large area. In this work, we demonstrate a new concept to directly achieve growth of graphene on non-metal substrates. By exposing an amorphous carbon (a-C) film in Cu gaseous molecules after annealing at 850 °C, the carbon (a-C) film surprisingly undergoes a noticeable transformation to crystalline graphene. Furthermore, the thickness of graphene could be controlled, depending on the thickness of the pre-deposited a-C film. The transformation mechanism was investigated and explained in detail. This approach enables development of a one-step process to fabricate electrical devices made of all carbon material, highlighting the uniqueness of the novel approach for developing graphene electronic devices. Interestingly, the carbon electrodes made directly on the graphene layer by our approach offer a good ohmic contact compared with the Schottky barriers usually observed on graphene devices using metals as electrodes.

  8. Corrosion resistant amorphous metals and methods of forming corrosion resistant amorphous metals

    Science.gov (United States)

    Farmer, Joseph C [Tracy, CA; Wong, Frank M. G. [Livermore, CA; Haslam, Jeffery J [Livermore, CA; Yang, Nancy [Lafayette, CA; Lavernia, Enrique J [Davis, CA; Blue, Craig A [Knoxville, TN; Graeve, Olivia A [Reno, NV; Bayles, Robert [Annandale, VA; Perepezko, John H [Madison, WI; Kaufman, Larry [Brookline, MA; Schoenung, Julie [Davis, CA; Ajdelsztajn, Leo [Walnut Creek, CA

    2009-11-17

    A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of composition: yttrium (.gtoreq.1 atomic %), chromium (14 to 18 atomic %), molybdenum (.gtoreq.7 atomic %), tungsten (.gtoreq.1 atomic %), boron (.ltoreq.5 atomic %), or carbon (.gtoreq.4 atomic %).

  9. Mechanisms of growth, properties and degradation of amorphous carbon films by closed field unbalanced magnetron sputtering on stainless steel bipolar plates for PEMFCs

    Science.gov (United States)

    Bi, Feifei; Hou, Kun; Yi, Peiyun; Peng, Linfa; Lai, Xinmin

    2017-11-01

    Stainless steel bipolar plates possess good manufacturability, low costs, but inadequate interfacial conductivity and corrosion resistance in proton exchange membrane fuel cells (PEMFCs). Amorphous carbon films have been deposited on stainless steel as a function of bias voltage through closed field unbalanced magnetron sputtering ion plating system (CFUMSIP) to enhance the interfacial conductivity and corrosion resistance. Surface and cross-section morphologies, hybridization, interfacial conductivity, corrosion resistance and degradation mechanisms of a-C films were systemically investigated and results are very sensitive to the substrate bias voltage. The compactness and hybridization sp2/sp3 ratio have parabolic relation with the substrate bias voltage and the a-C film deposited with 120 V has the densest cross structure and maximum sp3 percentage. Various electrochemical corrosion tests in the simulated PEMFCs cathode environment confirm the fact corrosion resistance is closely related to the film compactness and hybridization. Then a-C film prepared at bias voltage 120 V has the lowest corrosion current density. The initial interfacial contact resistance (ICR) of a-C is a combination result of sp2 percentage and film compactness and the samples deposited with bias voltage 60 V and 300 V have much lower ICR values than DOE target. Afterwards, the ICR increase mechanism of a-C film after electrochemical corrosion tests is illustrated through Raman and XPS detection, and the results reveal that increased oxygen content adsorbed on the film surface contributes to the increase of ICR value.

  10. High-pressure and high-temperature synthesis of rhenium carbide using rhenium and nanoscale amorphous two-dimensional carbon nitride

    Directory of Open Access Journals (Sweden)

    Nozomu Yasui

    2015-12-01

    Full Text Available Both Re2C and Re2N are ultra incompressible and have a bulk modulus of about 400 GPa. These materials are synthesized under high pressure and high temperature. The synthesis pressures are about 10 GPa or below for Re2C and 20–30 GPa for Re2N. If the synthesis pressure of Re2N was about 10 GPa or below, a large volume high-pressure cell like a multi-anvil apparatus can be used to synthesize Re2N. To realize this, a proper solid nitrogen source is needed instead of liquid or gas nitrogen. We used a precursor of a mixture of rhenium and home-made nanoscale amorphous two-dimensional carbon nitride as a solid nitrogen source. Consequently, the synthesis reaction produced Re2C but not Re2N. We characterized the synthesized Re2C by various techniques including high-pressure x-ray diffraction (XRD. The bulk modulus B0 of the synthesized Re2C under hydrostatic conditions was estimated to be 385.7 ± 18.0 GPa. This value is a little smaller than the previous data. When the pressure medium became non-hydrostatic, the peculiar compression behaviour occurred; the rate of broadening of XRD lines increased and the compression became negligible in the range of a few GPa. The reason for this peculiar behaviour is not known.

  11. Damage-free back channel wet-etch process in amorphous indium-zinc-oxide thin-film transistors using a carbon-nanofilm barrier layer.

    Science.gov (United States)

    Luo, Dongxiang; Zhao, Mingjie; Xu, Miao; Li, Min; Chen, Zikai; Wang, Lang; Zou, Jianhua; Tao, Hong; Wang, Lei; Peng, Junbiao

    2014-07-23

    Amorphous indium-zinc-oxide thin film transistors (IZO-TFTs) with damage-free back channel wet-etch (BCE) process were investigated. A carbon (C) nanofilm was inserted into the interface between IZO layer and source/drain (S/D) electrodes as a barrier layer. Transmittance electron microscope images revealed that the 3 nm-thick C nanofilm exhibited a good corrosion resistance to a commonly used H3PO4-based etchant and could be easily eliminated. The TFT device with a 3 nm-thick C barrier layer showed a saturated field effect mobility of 14.4 cm(2) V(-1) s(-1), a subthreshold swing of 0.21 V/decade, an on-to-off current ratio of 8.3 × 10(10), and a threshold voltage of 2.0 V. The favorable electrical performance of this kind of IZO-TFTs was due to the protection of the inserted C to IZO layer in the back-channel-etch process. Moreover, the low contact resistance of the devices was proved to be due to the graphitization of the C nanofilms after annealing. In addition, the hysteresis and thermal stress testing confirmed that the usage of C barrier nanofilms is an effective method to fabricate the damage-free BCE-type devices with high reliability.

  12. Study of electric properties of amorphous AgGe1+xAs1-xS3 with content of carbon nanotubes

    Science.gov (United States)

    Melnikova, Nina; Kurochka, Kirill; Volkova, Yana

    2013-06-01

    Multicomponent copper and silver chalcogenides have been known as promising materials for scientific and applied purposes. These materials are also under intense investigation for application in a phase-change random access memory. In order to obtain materials with a high ionic conductivity component, glassy silver chalcogenides AgGe1+xAs1-xS3 with the addition of nanotubes were synthesized. In this work the study of electrical properties of the amorphous chalcogenide AgGe1.4As0.6S3 (x = 0.4) with carbon nanotube content at a frequency of the alternating-current electric field varying from 1 Hz to 5 MHz and on direct current at ambient pressure and at pressure up to 30 GPa are presented. The ion transport was confirmed by means DC measurements in cells with blocking ion component of conductivity electrodes. An evaluation of the proportion of ionic conductivity can make a preliminary conclusion that the ionic component of the conductivity of at least 98%. Analyze of the baric dependences of AC properties have shown that the dielectric loss tangent and the real part of an admittance of the AgGe1.4As0.6S3 with carbon nanotube content compound exponentially increase with a pressure increase from 1 up to 30 GPa. The study was supported in part by the Ural Federal University development program with the financial support of young scientists; and by the Russian Foundation for Basic Research, project No. 12-02-31607.

  13. Relationship between Plasma Parameters and Carbon Atom Coordination in a-C:H Films Prepared by RF Glow Discharge Decomposition

    Science.gov (United States)

    Yamamoto, Kenji; Ichikawa, Yosuke; Nakayama, Takehisa; Tawada, Yoshihisa

    1988-08-01

    Amorphous C:H films were prepared by rf glow discharge decomposition from CH4 using a permanent magnet system to apply a static magnetic field perpendicular to the rf electric field. The structure and properties of a-C:H films have been investigated systematically with respect to the hydrogen content, hardness and coordination of carbon atoms as a function of rf power (self-bias voltage). The coordination of carbon atoms has been determined by solid-state 13C magic angle spinning nuclear magnetic resonance measurements. It is found that the fraction of graphitic (sp2) versus tetrahedral (sp3) bonding increases with increasing rf power (negative self-bias voltage). Film hardness is understood in terms of the balance between the incorporated hydrogen and the fraction of graphitic (sp2) versus tetrahedral (sp3) bonding. The production of ionic and neutral species from a glow discharge has also been monitored by mass spectroscopy and optical emission spectroscopy to investigate the relation between plasma parameters and carbon atom coordination. Using these measurements and negative self-bias measurements, it is shown that the coordination of carbon atoms is determined not only by the energy of impinging ions on the substrate but also by the type of active species. In addition, the neutral and ionic C2H2 related species are thought to be some of the species which increase the fraction of graphitic (sp2) versus tetrahedral (sp3) bonding.

  14. Determination of Initial Conditions for Tetrahedral Satellite Formation

    Directory of Open Access Journals (Sweden)

    Sung-Moon Yoo

    2011-12-01

    Full Text Available This paper presents an algorithm that can provide initial conditions for formation flying at the beginning of a region of interest to maximize scientific mission goals in the case of a tetrahedral satellite formation. The performance measure is to maximize the quality factor that affects scientific measurement performance. Several path constraints and periodicity conditions at the beginning of the region of interest are identified. The optimization problem is solved numerically using a direct transcription method. Our numerical results indicate that there exist an optimal configuration and states of a tetrahedral satellite formation. Furthermore, the initial states and algorithm presented here may be used for reconfiguration maneuvers and fuel balancing problems.

  15. Transient liquid phase bonding of carbon steel tubes using a Cu interlayer: Characterization and comparison with amorphous Fe–B–Si interlayer bonds

    Energy Technology Data Exchange (ETDEWEB)

    Di Luozzo, Nicolas, E-mail: nicolasdiluozzo@gmail.com [Laboratorio de Sólidos Amorfos, INTECIN, Facultad de Ingeniería, Universidad de Buenos Aires – CONICET, Paseo Colón 850, C1063ACV Buenos Aires (Argentina); Laboratoire des Matériaux et du Génie Physique (CNRS UMR 5628), Grenoble Institute of Technology, MINATEC, Grenoble Cedex 1 (France); Boudard, Michel; Doisneau, Béatrice [Laboratoire des Matériaux et du Génie Physique (CNRS UMR 5628), Grenoble Institute of Technology, MINATEC, Grenoble Cedex 1 (France); Fontana, Marcelo; Arcondo, Bibiana [Laboratorio de Sólidos Amorfos, INTECIN, Facultad de Ingeniería, Universidad de Buenos Aires – CONICET, Paseo Colón 850, C1063ACV Buenos Aires (Argentina)

    2014-12-05

    Highlights: • Cu and Fe–B–Si foils were used as interlayers to bond steel tubes by TLPB process. • The microstructure and mechanical properties were characterized. • In Cu bonded samples, the solidification process was not systematically completed. • When using Cu foils, evidences of epitaxial solidification were observed. • Tensile tests show that Cu and Fe–B–Si bonded samples failed away from the joint. - Abstract: In the present work the transient liquid phase bonding process was performed to join seamless carbon steel tubes using commercially pure Cu interlayers. The structural and mechanical characteristics of the resulting bonds are compared with those achieved using amorphous Fe–B–Si interlayers, under the same process parameters: a holding temperature of 1300 °C, a holding time of 7 min and an applied pressure of 5 MPa. The joined tubes microstructures were characterized by direct observations – scanning electron microscopy – and diffraction techniques – electron backscatter diffraction. Chemical analysis was performed using electron probe microanalysis. Whereas the amorphous Fe-B-Si interlayer leads to a completion of the bonding process over the whole bonding area, the bond performed using a Cu interlayer achieved the completion of the bonding process only partially. As the Cu is a cementite promoter, the amount of cementite coexisting with ferrite grains is higher in the joint region (JR) – corresponding to the higher concentration of Cu – as compared with the heat affected zone (HAZ) and the base metal (BM). An opposite effect is observed when using Fe-B-Si interlayers due to the fact that the cementite is unable to form in Si enriched zones – the microstructure at the JR presents only ferrite grains. Tensile tests show that the joined tubes using Cu or Fe–B–Si interlayers failed away from the bond, at the HAZ, attaining almost the same ultimate tensile strength of the BM, in the as-received condition. Hardness

  16. Properties of Erbium Doped Hydrogenated Amorphous Carbon Layers Fabricated by Sputtering and Plasma Assisted Chemical Vapor Deposition

    Directory of Open Access Journals (Sweden)

    V. Prajzler

    2008-01-01

    Full Text Available We report about properties of carbon layers doped with Er3+ ions fabricated by Plasma Assisted Chemical Vapor Deposition (PACVD and by sputtering on silicon or glass substrates. The structure of the samples was characterized by X-ray diffraction and their composition was determined by Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The Absorbance spectrum was taken in the spectral range from 400 nm to 600 nm. Photoluminescence spectra were obtained using two types of Ar laser (λex=514.5 nm, lex=488 nm and also using a semiconductor laser (λex=980 nm. Samples fabricated by magnetron sputtering exhibited typical emission at 1530 nm when pumped at 514.5 nm. 

  17. Tribological Performance of Hydrogenated Amorphous Carbon (a-C: H DLC Coating when Lubricated with Biodegradable Vegetal Canola Oil

    Directory of Open Access Journals (Sweden)

    H.M. Mobarak

    2014-06-01

    Full Text Available Increasing environmental awareness and demands for lowering energy consumptions are strong driving forces behind the development of the vehicles of tomorrow. Without the advances of lubricant chemistry and adequate lubricant formulation, expansion of modern engines would not have been possible. Considering environmental awareness factors as compared to mineral oils, vegetal oil based biolubricants are renewable, biodegradable, non-toxic and have a least amount of greenhouse gases. Furthermore, improvement in engine performance and transmission components, which were impossible to achieve by applying only lubricants design, is now possible through diamond like carbon (DLC coatings. DLC coatings exhibit brilliant tribological properties, such as good wear resistance and low friction. In this regard, tribological performance of a-C: H DLC coating when lubricated with Canola vegetal oil has been investigated by the help of a ball-on-flat geometry. Experimental results demonstrated that the a-C: H DLC coating exhibited better performance with Canola oil in terms of friction and wear as compared to the uncoated materials. Large amount of polar components in the Canola oil significantly improved the tribological properties of the a-C:H coating. Thus, usage of a-C: H DLC coating with Canola oil in the long run may have a positive impact on engine life.

  18. Superconvergence for tetrahedral quadratic finite element methods for elliptic equations

    NARCIS (Netherlands)

    Brandts, J.H.; Krizek, M.

    2005-01-01

    For a model elliptic boundary value problem we will prove that on strongly regular families of uniform tetrahedral partitions of the domain, the gradient of the quadratic finite element approximation is superclose to the gradient of the quadratic Lagrange interpolant of the exact solution. This

  19. Amorphous Computing

    Science.gov (United States)

    Sussman, Gerald

    2002-03-01

    agents constructed by engineered cells, but we have few ideas for programming them effectively: How can one engineer prespecified, coherent behavior from the cooperation of immense numbers of unreliable parts that are interconnected in unknown, irregular, and time-varying ways? This is the challenge of Amorphous Computing.

  20. Large-scale and patternable graphene: direct transformation of amorphous carbon film into graphene/graphite on insulators via Cu mediation engineering and its application to all-carbon based devices

    Science.gov (United States)

    Chen, Yu-Ze; Medina, Henry; Lin, Hung-Chiao; Tsai, Hung-Wei; Su, Teng-Yu; Chueh, Yu-Lun

    2015-01-01

    Chemical vapour deposition of graphene was the preferred way to synthesize graphene for multiple applications. However, several problems related to transfer processes, such as wrinkles, cleanness and scratches, have limited its application at the industrial scale. Intense research was triggered into developing alternative synthesis methods to directly deposit graphene on insulators at low cost with high uniformity and large area. In this work, we demonstrate a new concept to directly achieve growth of graphene on non-metal substrates. By exposing an amorphous carbon (a-C) film in Cu gaseous molecules after annealing at 850 °C, the carbon (a-C) film surprisingly undergoes a noticeable transformation to crystalline graphene. Furthermore, the thickness of graphene could be controlled, depending on the thickness of the pre-deposited a-C film. The transformation mechanism was investigated and explained in detail. This approach enables development of a one-step process to fabricate electrical devices made of all carbon material, highlighting the uniqueness of the novel approach for developing graphene electronic devices. Interestingly, the carbon electrodes made directly on the graphene layer by our approach offer a good ohmic contact compared with the Schottky barriers usually observed on graphene devices using metals as electrodes.Chemical vapour deposition of graphene was the preferred way to synthesize graphene for multiple applications. However, several problems related to transfer processes, such as wrinkles, cleanness and scratches, have limited its application at the industrial scale. Intense research was triggered into developing alternative synthesis methods to directly deposit graphene on insulators at low cost with high uniformity and large area. In this work, we demonstrate a new concept to directly achieve growth of graphene on non-metal substrates. By exposing an amorphous carbon (a-C) film in Cu gaseous molecules after annealing at 850 °C, the carbon (a

  1. Electron Cloud in Steel Beam Pipe vs Titanium Nitride Coated and Amorphous Carbon Coated Beam Pipes in Fermilab's Main Injector

    Energy Technology Data Exchange (ETDEWEB)

    Backfish, Michael

    2013-04-01

    This paper documents the use of four retarding field analyzers (RFAs) to measure electron cloud signals created in Fermilab’s Main Injector during 120 GeV operations. The first data set was taken from September 11, 2009 to July 4, 2010. This data set is used to compare two different types of beam pipe that were installed in the accelerator. Two RFAs were installed in a normal steel beam pipe like the rest of the Main Injector while another two were installed in a one meter section of beam pipe that was coated on the inside with titanium nitride (TiN). A second data run started on August 23, 2010 and ended on January 10, 2011 when Main Injector beam intensities were reduced thus eliminating the electron cloud. This second run uses the same RFA setup but the TiN coated beam pipe was replaced by a one meter section coated with amorphous carbon (aC). This section of beam pipe was provided by CERN in an effort to better understand how an aC coating will perform over time in an accelerator. The research consists of three basic parts: (a) continuously monitoring the conditioning of the three different types of beam pipe over both time and absorbed electrons (b) measurement of the characteristics of the surrounding magnetic fields in the Main Injector in order to better relate actual data observed in the Main Injector with that of simulations (c) measurement of the energy spectrum of the electron cloud signals using retarding field analyzers in all three types of beam pipe.

  2. Influence of source and drain contacts on the properties of indium-gallium-zinc-oxide thin-film transistors based on amorphous carbon nanofilm as barrier layer.

    Science.gov (United States)

    Luo, Dongxiang; Xu, Hua; Zhao, Mingjie; Li, Min; Xu, Miao; Zou, Jianhua; Tao, Hong; Wang, Lei; Peng, Junbiao

    2015-02-18

    Amorphous indium-gallium-zinc-oxide thin film transistors (α-IGZO TFTs) with damage-free back channel wet-etch (BCE) process were achieved by introducing a carbon nanofilm as a barrier layer. We investigate the effects of different source-and-drain (S/D) materials on TFT performance. We find the TFT with Ti/C S/D electrodes exhibits a superior performance with higher output current, lower threshold voltage, and higher effective electron mobility compared to that of Mo/C S/D electrodes. Transmittance electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) are employed to analysis the interfacial interaction between S/D metal/C/α-IGZO layers. The results indicate that the better performance of TFTs with Ti/C electrodes should be attributed to the formations of Ti-C and Ti-O at the Ti/C-contact regions, which lead to a lower contact resistance, whereas Mo film is relatively stable and does not react easily with C nanofilm, resulting in a nonohmic contact behavior between Mo/C and α-IGZO layer. However, both kinds of α-IGZO TFTs show good stability under thermal bias stress, indicating that the inserted C nanofilms could avoid the impact on the α-IGZO channel regions during S/D electrodes formation. Finally, we successfully fabricated a high-definition active-matrix organic lighting emitting diode prototype driven by α-IGZO TFTs with Ti/C electrodes in a pilot line.

  3. A comparison of amorphous calcium carbonate crystallization in aqueous solutions of MgCl2 and MgSO4: implications for paleo-ocean chemistry

    Science.gov (United States)

    Han, Mei; Zhao, Yanyang; Zhao, Hui; Han, Zuozhen; Yan, Huaxiao; Sun, Bin; Meng, Ruirui; Zhuang, Dingxiang; Li, Dan; Liu, Binwei

    2017-07-01

    Based on the terminology of "aragonite seas" and "calcite seas", whether different Mg sources could affect the mineralogy of carbonate sediments at the same Mg/Ca ratio was explored, which was expected to provide a qualitative assessment of the chemistry of the paleo-ocean. In this work, amorphous calcium carbonate (ACC) was prepared by direct precipitation in anhydrous ethanol and used as a precursor to study crystallization processes in MgSO4 and MgCl2 solutions having different concentrations at 60 °C (reaction times 240 and 2880 min). Based on the morphology of the aragonite crystals, as well as mineral saturation indices and kinetic analysis of geochemical processes, it was found that these crystals formed with a spherulitic texture in 4 steps. First, ACC crystallized into columnar Mg calcite by nearly oriented attachment. Second, the Mg calcite changed from columnar shapes into smooth dumbbell forms. Third, the Mg calcite transformed into rough dumbbell or cauliflower-shaped aragonite forms by local dissolution and precipitation. Finally, the aragonite transformed further into spherulitic radial and irregular aggregate forms. The increase in Ca2+ in the MgSO4 solutions compared with the MgCl2 solutions indicates the fast dissolution and slow precipitation of ACC in the former solutions. The phase transition was more complete in the 0.005 M MgCl2 solution, whereas Mg calcite crystallized from the 0.005 M MgSO4 solution, indicating that Mg calcite could be formed more easily in an MgSO4 solution. Based on these findings, aragonite and Mg calcite relative to ACC could be used to provide a qualitative assessment of the chemistry of the paleo-ocean. Therefore, calcite seas relative to high-Mg calcite could reflect a low concentration MgSO4 paleo-ocean, while aragonite seas could be related to an MgCl2 or high concentration of MgSO4 paleo-ocean.

  4. Pressure-induced transformations in amorphous Si-Ge alloy

    Energy Technology Data Exchange (ETDEWEB)

    Coppari, F.; Polian, A.; Menguy, N.; Trapananti, A.; Congeduti, A.; Newville, M.; Prakapenka, V.B.; Choi, Y.; Principi, E.; Di Cicco, A. (CNRS-UMR); (UC); (Camerino)

    2012-03-14

    The pressure behavior of an amorphous Si-rich SiGe alloy ({alpha}-Si{sub x}Ge{sub 1-x}, x = 0.75) has been investigated up to about 30 GPa, by a combination of Raman spectroscopy, x-ray absorption spectroscopy, and x-ray diffraction measurements. The trends of microscopic structural properties and of the Raman-active phonon modes are presented in the whole pressure range. Nucleation of nanocrystalline alloy particles and metallization have been observed above 12 GPa, with a range of about 2 GPa of coexistence of amorphous and crystalline phases. Transformations from the amorphous tetrahedral, to the crystalline tetragonal ({beta}-Sn) and to the simple hexagonal structures have been observed around 13.8 and 21.8 GPa. The recovered sample upon depressurization, below about 4 GPa, shows a local structure similar to the as-deposited one. Inhomogeneities of the amorphous texture at the nanometric scale, probed by high-resolution transmission electron microscopy, indicate that the recovered amorphous sample has a different ordering at this scale, and therefore the transformations can not be considered fully reversible. The role of disordered grain boundaries at high pressure and the possible presence of a high-density amorphous phase are discussed.

  5. Tetrahedral Mesh Improvement Using Multi-face Retriangulation

    DEFF Research Database (Denmark)

    Misztal, Marek Krzysztof; Bærentzen, Jakob Andreas; Anton, Francois

    2009-01-01

    the algorithm is completely general with regard to quality criterion, we target improvement of the dihedral angle. The central idea in our algorithm is the introduction of a new local operation called multi-face retriangulation (MFRT) which supplements other known local operations. Like in many previous papers......In this paper we propose a simple technique for tetrahedral mesh improvement without inserting Steiner vertices, concentrating mainly on boundary conforming meshes. The algorithm makes local changes to the mesh to remove tetrahedra which are poor according to some quality criterion. While...... on tetrahedral mesh improvement, our algorithm makes local changes to the mesh to reduce an energy measure which reflects the quality criterion. The addition of our new local operation allows us to advance the mesh to a lower energy state in cases where no other local change would lead to a reduction. We also...

  6. A computational study of nodal-based tetrahedral element behavior.

    Energy Technology Data Exchange (ETDEWEB)

    Gullerud, Arne S.

    2010-09-01

    This report explores the behavior of nodal-based tetrahedral elements on six sample problems, and compares their solution to that of a corresponding hexahedral mesh. The problems demonstrate that while certain aspects of the solution field for the nodal-based tetrahedrons provide good quality results, the pressure field tends to be of poor quality. Results appear to be strongly affected by the connectivity of the tetrahedral elements. Simulations that rely on the pressure field, such as those which use material models that are dependent on the pressure (e.g. equation-of-state models), can generate erroneous results. Remeshing can also be strongly affected by these issues. The nodal-based test elements as they currently stand need to be used with caution to ensure that their numerical deficiencies do not adversely affect critical values of interest.

  7. Ferromagnetism and electron pairing in tetrahedral Hubbard clusters

    Science.gov (United States)

    Kocharian, Armen; Fernando, Gayanath; Wang, Tun; Palandage, Kalum

    2007-03-01

    The canonical and grand canonical calculations in exactly solvable three dimensional tetrahedrons elucidate the origin of Mott-Hubbard-like transition, electron pairing and ferromagnetism in frustrated Hubbard clusters. The thermal properties of planar and tetrahedral clusters in magnetic field with one hole off half-filling provide a rigorous proof for the existence of Mott-Hubbard type insulators with spontaneous magnetization in the ground state and finite temperatures. Rigorous conditions for electron pairing instability and phase separation in frustrated tetrahedral cluster for all U>0 is also provided. We show that Nagaoka-type spin flip instability with ``unsaturated ferromagnetism'' is equivalent to electron charge and spin pairing instabilities with minimal, zero spin. The theory gives strong evidence for existence of charge- spin separation in three dimensional clusters and calculated phase diagram for condensation crossover temperatures at various instabilities encompass a number of phases recently discovered in clusters, small nanoparticles, transition metal oxides and high Tc cuprates.

  8. Motion Planning of Kinematically Redundant 12-tetrahedral Rolling Robot

    Directory of Open Access Journals (Sweden)

    Xingbo Wang

    2016-02-01

    Full Text Available The 12-tetrahedral robot is an addressable reconfigurable technology (ART-based variable geometry truss mechanism with 26 extensible struts and nine nodes arranged in a tetrahedral mesh. The robot has the capability of configuring its shape to adapt to environmental requirements, which makes it suitable for space exploration. This paper considers the motion planning problem for the robot in terms of gait planning and trajectory planning. First, a gait planning method is developed that limits the forward falling angles to only 25 degrees. Then, according to the given gait, the jerk-bounded method and inverse kinematics are utilized to calculate the trajectories of the nodes and the struts, respectively. A robot system model was built in ADAMS and simulations were conducted to demonstrate the feasibility of the motion planning method.

  9. Tetrahedral meshing via maximal Poisson-disk sampling

    KAUST Repository

    Guo, Jianwei

    2016-02-15

    In this paper, we propose a simple yet effective method to generate 3D-conforming tetrahedral meshes from closed 2-manifold surfaces. Our approach is inspired by recent work on maximal Poisson-disk sampling (MPS), which can generate well-distributed point sets in arbitrary domains. We first perform MPS on the boundary of the input domain, we then sample the interior of the domain, and we finally extract the tetrahedral mesh from the samples by using 3D Delaunay or regular triangulation for uniform or adaptive sampling, respectively. We also propose an efficient optimization strategy to protect the domain boundaries and to remove slivers to improve the meshing quality. We present various experimental results to illustrate the efficiency and the robustness of our proposed approach. We demonstrate that the performance and quality (e.g., minimal dihedral angle) of our approach are superior to current state-of-the-art optimization-based approaches.

  10. Crystallization Experiments in the MgO-CO2-H2O system: Role of Amorphous Magnesium Carbonate Precursors in Magnesium Carbonate Hydrated Phases and Morphologies in Low Temperature Hydrothermal Fluids

    Science.gov (United States)

    Giampouras, Manolis; Garcia-Ruiz, Juan Manuel; Garrido, Carlos J.

    2017-04-01

    Numerous forms of hydrated or basic magnesium carbonates occur in the complex MgO-CO2-H2O system. Mineral saturation states from low temperature hydrothermal fluids in Semail Ophiolite (Oman), Prony Bay (New Caledonia) and Lost City hydrothermal field (mid-Atlantic ridge) strongly indicate the presence of magnesium hydroxy-carbonate hydrates (e.g. hydromagnesite) and magnesium hydroxides (brucite). Study of formation mechanisms and morphological features of minerals forming in the MgO-CO2-H2O system could give insights into serpentinization-driven, hydrothermal, alkaline environments, which are related to early Earth conditions. Temperature, hydration degree, pH and fluid composition are crucial factors regarding the formation, coexistence and transformation of such mineral phases. The rate of supersaturation, on the other hand, is a fundamental parameter to understand nucleation and crystal growth processes. All these parameters can be examined in a solution using different crystallization techniques. In the present study, we applied different crystallization techniques to synthesize and monitor the crystallization of Mg-bearing carbonates and hydroxides under abiotic conditions. Various crystallization techniques (counter-diffusion, vapor diffusion and unseeded solution mixing) were used to screen the formation conditions of each phase, transformation processes and structural development. Mineral and textural characterization of the different synthesized phases were carried out by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy coupled to dispersive energy spectroscopy (FE-SEM-EDS). Experimental investigation of the effect of pH level and silica content under variable reactant concentrations revealed the importance of Amorphous Magnesium Carbonate (AMC) in the formation of hydroxy-carbonate phases (hydromagnesite and dypingite). Micro-structural resemblance between AMC precursors and later stage crystalline phases highlights the

  11. Tetrahedral gray code for visualization of genome information.

    Science.gov (United States)

    Ichinose, Natsuhiro; Yada, Tetsushi; Gotoh, Osamu

    2014-01-01

    We propose a tetrahedral Gray code that facilitates visualization of genome information on the surfaces of a tetrahedron, where the relative abundance of each [Formula: see text]-mer in the genomic sequence is represented by a color of the corresponding cell of a triangular lattice. For biological significance, the code is designed such that the [Formula: see text]-mers corresponding to any adjacent pair of cells differ from each other by only one nucleotide. We present a simple procedure to draw such a pattern on the development surfaces of a tetrahedron. The thus constructed tetrahedral Gray code can demonstrate evolutionary conservation and variation of the genome information of many organisms at a glance. We also apply the tetrahedral Gray code to the honey bee (Apis mellifera) genome to analyze its methylation structure. The results indicate that the honey bee genome exhibits CpG overrepresentation in spite of its methylation ability and that two conserved motifs, CTCGAG and CGCGCG, in the unmethylated regions are responsible for the overrepresentation of CpG.

  12. Tetrahedral gray code for visualization of genome information.

    Directory of Open Access Journals (Sweden)

    Natsuhiro Ichinose

    Full Text Available We propose a tetrahedral Gray code that facilitates visualization of genome information on the surfaces of a tetrahedron, where the relative abundance of each [Formula: see text]-mer in the genomic sequence is represented by a color of the corresponding cell of a triangular lattice. For biological significance, the code is designed such that the [Formula: see text]-mers corresponding to any adjacent pair of cells differ from each other by only one nucleotide. We present a simple procedure to draw such a pattern on the development surfaces of a tetrahedron. The thus constructed tetrahedral Gray code can demonstrate evolutionary conservation and variation of the genome information of many organisms at a glance. We also apply the tetrahedral Gray code to the honey bee (Apis mellifera genome to analyze its methylation structure. The results indicate that the honey bee genome exhibits CpG overrepresentation in spite of its methylation ability and that two conserved motifs, CTCGAG and CGCGCG, in the unmethylated regions are responsible for the overrepresentation of CpG.

  13. Pulsed-laser-deposited amorphous diamond and related materials: synthesis, characterization, and field emission properties

    Science.gov (United States)

    Merkulov, Vladimir I.; Lowndes, Douglas H.; Baylor, Larry R.; Jellison, Gerald E., Jr.; Puretzky, Alexander A.; Geohegan, David B.

    1999-07-01

    Amorphous carbon films with variable sp3 content were produced by ArF pulsed laser deposition. An in-situ ion probe was used to measure kinetic energy of C+ ions. In contrast to measurements made as a function of laser fluence, ion probe measurements of kinetic energy are a convenient as well as more accurate and fundamental method for monitoring deposition conditions, with the advantage of being readily transferable for inter-laboratory comparisons. Electron energy loss spectroscopy and spectroscopic ellipsometry measurement reveal that tetrahedral amorphous carbon films with the most diamond-like properties are obtained at the C ion kinetic energy of approximately 90 eV. Film properties are uniform within a 12-15 degrees angle from the plume centerline. Tapping-mode atomic force microscope measurements show that films deposited at near- optimum kinetic energy are extremely smooth, with rms roughness of only approximately 1 angstrom over distances of several hundred nm. Field emission (FE) measurements show that ta-C does not appear to be a good electron emitter. After conditioning of ta-C films deposited on n-type Si a rather high turn-on voltage of approximately 50 V/micrometers was required to draw current of approximately 1 nA to the probe. The emission was unstable and typically ceased after a few minutes of operation. The FE tests of ta-C and other materials strongly suggest that surface morphology plays a dominant role in the FE process, in agreement with conventional Fowler-Nordheim theory.

  14. A neutral cluster cage with a tetrahedral [Pd12(II)L6] framework: crystal structures and host–guest studies.

    Science.gov (United States)

    Gupta, Arvind K; Yadav, Ashok; Srivastava, Anant Kumar; Ramya, Kormathmadam Raghupathy; Paithankar, Harshad; Nandi, Shyamapada; Chugh, Jeetender; Boomishankar, Ramamoorthy

    2015-04-06

    A charge-neutral tetrahedral [(Pd3X)4L6] cage assembly built from a trinuclear polyhedral building unit (PBU), [Pd3X](3+), cis-blocked with an imido P(V) ligand, [(N(i)Pr)3PO](3-) (X(3-)), and oxalate dianions (L(2-)) is reported. Use of benzoate or ferrocene dicarboxylate anions, which do not offer wide-angle chelation as that of oxalate dianions, leads to smaller prismatic clusters instead of polyhedral cage assemblies. The porosity of the tetrahedral cage assembly was determined by gas adsorption studies, which show a higher uptake capacity for CO2 over N2 and H2. The tetrahedral cage was shown to encapsulate a wide range of neutral guest solvents from polar to nonpolar such as dimethyl sulfoxide, benzene, dichloromethane, chloroform, carbon tetrachloride, and cyclopentane as observed by mass spectral and single-crystal X-ray diffraction studies. The (1)H two-dimensional diffusion ordered spectroscopy NMR analysis shows that the host and guest molecules exhibit similar diffusion coefficients in all the studied host-guest systems. Further, the tetrahedral cage shows selective binding of benzene, CCl4, and cyclopentane among other solvents from their categories as evidenced from mass spectral analysis. A preliminary density functional theory analysis gave a highest binding energy for benzene among the other solvents that were structurally shown to be encapsulated at the intrinsic cavity of the tetrahedral cage.

  15. Resilient Amorphous Networks Prepared by Photo-Crosslinking High-Molecular-Weight D,L-Lactide and Trimethylene Carbonate Macromers : Mechanical Properties and Shape-Memory Behavior

    NARCIS (Netherlands)

    Sharifi, Shahriar; Grijpma, Dirk W.

    2012-01-01

    Tough networks are prepared by photo-crosslinking high-molecular-weight DLLA and TMC macromers. These amorphous networks exhibit tunable thermal and mechanical properties and have excellent shape-memory features. Variation of the monomer ratio allows adjustment of Tg between approximately -13 and

  16. Resilient Amorphous Networks Prepared by Photo-Crosslinking High-Molecular-Weight D,L-Lactide and Trimethylene Carbonate Macromers: Mechanical Properties and Shape-Memory Behavior

    NARCIS (Netherlands)

    Sharifi, Shahriar; Grijpma, Dirk W.

    2012-01-01

    Tough networks are prepared by photo-crosslinking high-molecular-weight DLLA and TMC macromers. These amorphous networks exhibit tunable thermal and mechanical properties and have excellent shape-memory features. Variation of the monomer ratio allows adjustment of Tg between approximately −13 and

  17. Amorphous Insulator Films With Controllable Properties

    Science.gov (United States)

    Alterovitz, Samuel A.; Warner, Joseph D.; Liu, David C.; Pouch, John J.

    1987-01-01

    In experiments described in report, amorphous hydrogenated carbon films grown at room temperature by low-frequency plasma deposition, using methane or butane gas. Films have unique array of useful properties; (a) adhere to wide variety of materials; (b) contain only carbon and hydrogen; (c) smooth and free of pinholes; (d) resistant to attack by moisture and chemicals; and (e) have high electric-breakdown strength and electrical resistivity. Two of optical properties and hardness of this film controlled by deposition conditions. Amorphous a-C:H and BN films used for hermetic sealing and protection of optical, electronic, magnetic, or delicate mechanical systems, and for semiconductor field dielectrics.

  18. Stabilization of amorphous structure in silicon thin film by adding germanium

    Energy Technology Data Exchange (ETDEWEB)

    Makino, Nobuaki [Nanosystem Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027 (Japan); Toshiba Corporation, 33 Shin-Isogo-Cho, Isogo-ku, Yokohama 235-0017 (Japan); Shigeta, Yukichi [Nanosystem Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027 (Japan)

    2015-06-21

    The stabilization of the amorphous structure in amorphous silicon film by adding Ge atoms was studied using Raman spectroscopy. Amorphous Si{sub 1−x}Ge{sub x} (x = 0.0, 0.03, 0.14, and 0.27) films were deposited on glass substrates from electron beam evaporation sources and annealed in N{sub 2} atmosphere. The change in the amorphous states and the phase transition from amorphous to crystalline were characterized using the TO, LO, and LA phonons in the Raman spectra. The temperature of the transition from the amorphous phase to the crystalline phase was higher for the a-Si{sub 1−x}Ge{sub x} (x = 0.03, 0.14) films, and the crystallization was hindered. The reason why the addition of a suitable quantity of Ge atoms into the three-dimensional amorphous silicon network stabilizes its amorphous structure is discussed based on the changes in the Raman signals of the TO, LO, and LA phonons during annealing. The characteristic bond length of the Ge atoms allows them to stabilize the random network of the amorphous Si composed of quasi-tetrahedral Si units, and obstruct its rearrangement.

  19. Amorphous Solid Water:

    DEFF Research Database (Denmark)

    Wenzel, Jack; Linderstrøm-Lang, C. U.; Rice, Stuart A.

    1975-01-01

    -like structure factor. The Fourier-transformed structure e factor yields a real space pair distribution function consistent with local tetrahedral coordination and hydrogen bonding, as in other condensed phases of water. The intramolecular OD separation is 1.00 angstrom; the lack of data for very large wave...

  20. An aluminophosphate molecular sieve with 36 crystallographically distinct tetrahedral sites.

    Science.gov (United States)

    Lee, Jun Kyu; Turrina, Alessandro; Zhu, Liangkui; Seo, Seungwan; Zhang, Daliang; Cox, Paul A; Wright, Paul A; Qiu, Shilun; Hong, Suk Bong

    2014-07-14

    The structure of the new medium-pore aluminophosphate molecular sieve PST-6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X-ray powder diffraction, and computer modeling. PST-6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure-directing agent, which is thought to contain bridging hydroxy groups. PST-6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Amorphization within the tablet

    DEFF Research Database (Denmark)

    Doreth, Maria; Hussein, Murtadha Abdul; Priemel, Petra A.

    2017-01-01

    In situ amorphization is a concept that allows to amorphize a given drug in its final dosage form right before administration. Hence, this approach can potentially be used to circumvent recrystallization issues that other amorphous formulation approaches are facing during storage. In this study...... revealed that with increasing microwaving power and time, the fractions of crystalline IND and amorphous PVP reduced, whereas the amount of in situ formed IND-PVP glass solution increased. Intrinsic dissolution showed that the dissolution rate of the microwaved solid dispersion was similar...

  2. Creep in amorphous metals

    Directory of Open Access Journals (Sweden)

    Michael E. Kassner

    2015-01-01

    Full Text Available This paper reviews the work on creep behavior of amorphous metals. There have been, over the past several years, a few reviews of the mechanical behavior of amorphous metals. Of these, the review of the creep properties of amorphous metals by Schuh et al. though oldest of the three, is particularly noteworthy and the reader is referred to this article published in 2007. The current review of creep of amorphous metals particularly focuses on those works since that review and places the work prior to 2007 in a different context where new developments warrant.

  3. Effect of substrate temperature on the structure of amorphous oxygenated hydrocarbon films grown with a pulsed supersonic methane plasma flow

    Energy Technology Data Exchange (ETDEWEB)

    Fedoseeva, Yu. V., E-mail: fedoseeva@niic.nsc.ru [Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Pozdnyakov, G.A. [Khristianovich Institute of Theoretical and Applied Mechanics, SB RAS, Novosibirsk 630090 (Russian Federation); Okotrub, A.V.; Kanygin, M.A. [Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Nastaushev, Yu. V. [Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk 630090 (Russian Federation); Vilkov, O.Y. [St. Petersburg State University, St. Petersburg 198504 (Russian Federation); Bulusheva, L.G. [Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation)

    2016-11-01

    Highlights: • A deposition of supersonic methane plasma flow on silicon substrate produces amorphous oxygenated hydrocarbon (CO{sub x}H{sub y}) film. • The thickness, composition, and wettability of the film depend on the substrate temperature. • A rise of the substrate temperature from 500 to 700 °C promotes the sp{sup 3}-hybridization carbon formation. - Abstract: Since amorphous oxygenated hydrocarbon (CO{sub x}H{sub y}) films are promising engineering materials a study of the structure and composition of the films depending on the conditions of synthesis is important for controlling of their physicochemical properties. Here, we used the methods of scanning and transmission electron microscopy, X-ray photoelectron, near-edge X-ray absorption fine structure, Fourier transform infrared and Raman spectroscopy to reveal changes in the chemical connectivity of CO{sub x}H{sub y} films grown on silicon substrates heated to 300, 500, and 700 °C using a supersonic flow of methane plasma. It was found that the CO{sub x}H{sub y} films, deposited at 300 and 500 °C, were mainly composed of the sp{sup 2}-hybridized carbon areas with various oxygen species. A rise of the substrate temperature caused an increase of the portion of tetrahedral carbon atoms as well as carboxyl and hydroxyl groups. With growth of the substrate temperature, the film thickness reduced monotonically from 400 to 180 nm, while the film adhesion improved substantially. The films, deposited at lower temperatures, showed high hydrophilicity due to porosity and presence of oxygenated groups both at the surface and in the bulk.

  4. An Easy-Made, Economical and Efficient Carbon-Doped Amorphous TiO2 Photocatalyst Obtained by Microwave Assisted Synthesis for the Degradation of Rhodamine B

    Science.gov (United States)

    Luna-Flores, Adan; Morales-Sánchez, Marco Antonio; Agustín-Serrano, Ricardo

    2017-01-01

    The search for novel materials and the development of improved processes for water purification have attracted the interest of researchers worldwide and the use of titanium dioxide in photocatalytic processes for the degradation of organic pollutants contained in water has been one of the benchmarks. Compared to crystalline titanium dioxide (cTiO2), the amorphous material has the advantages of having a higher adsorption capacity and being easier to dope with metal and non-metal elements. In this work, we take advantage of these two features to improve its photocatalytic properties in the degradation of Rhodamine B. The structural characterization by XRD analysis gives evidence of its amorphous nature and the SEM micrographs portray the disc morphology of 300 nm in diameter with heterogeneous grain boundaries. The degradation of Rhodamine B tests with the amorphous TiO2 using visible light confirm its improved catalytic activity compared to that of a commercial product, Degussa P25, which is a well-known crystalline material. PMID:29261118

  5. An Easy-Made, Economical and Efficient Carbon-Doped Amorphous TiO2 Photocatalyst Obtained by Microwave Assisted Synthesis for the Degradation of Rhodamine B

    Directory of Open Access Journals (Sweden)

    Adan Luna-Flores

    2017-12-01

    Full Text Available The search for novel materials and the development of improved processes for water purification have attracted the interest of researchers worldwide and the use of titanium dioxide in photocatalytic processes for the degradation of organic pollutants contained in water has been one of the benchmarks. Compared to crystalline titanium dioxide (cTiO2, the amorphous material has the advantages of having a higher adsorption capacity and being easier to dope with metal and non-metal elements. In this work, we take advantage of these two features to improve its photocatalytic properties in the degradation of Rhodamine B. The structural characterization by XRD analysis gives evidence of its amorphous nature and the SEM micrographs portray the disc morphology of 300 nm in diameter with heterogeneous grain boundaries. The degradation of Rhodamine B tests with the amorphous TiO2 using visible light confirm its improved catalytic activity compared to that of a commercial product, Degussa P25, which is a well-known crystalline material.

  6. Analysis and modification of amorphous and partially-crystalline thin films

    Energy Technology Data Exchange (ETDEWEB)

    DiNardo, N.J.; Mercer, T.W. [Drexel Univ., Philadelphia, PA (United States). Dept. of Physics; Martinez-Miranda, L.J. [Univ. of Maryland, College Park, MD (United States). Dept. of Materials and Nuclear Engineering; Siegal, M.P.; Friedmann, T.A.; Sullivan, J.R. [Sandia National Labs., Albuquerque, NM (United States); Plank, R.V.; Vohs, J.M. [Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Chemical Engineering

    1997-12-01

    Thin films of light atomic weight elements in amorphous, partially-crystalline, or crystalline forms have applications in a broad range of technologies. For example, amorphous tetrahedral carbon (a-tC) and polymeric thin films impact electronic materials technology as electron- and light-emitting device elements, respectively. A lack of crystallinity introduces complexity in the experimental and theoretical characterization of these materials but is not necessarily a limiting factor in their performance. While the growth process is clearly a major factor governing the physical properties of a film, interactions with the substrate are also important, so surface and interface analysis provides an important complement to bulk measurements. This paper focuses on several approaches in the characterization and modification of thin films made possible by recent experimental advances. The structural and electronic properties of two model systems are considered as examples: a-tC thin films grown by pulsed laser deposition (PLD) and polyaniline thin films grown by vapor deposition. First, scanning probe microscopies and X-ray scattering are used to investigate the structural aspects of a-tC films as a function of PLD growth conditions. The possible connection of nanoscale surface modification and characterization with electron emission properties will be discussed. Second, the results of inelastic scattering spectroscopy and other surface techniques will be discussed to obtain information on both interfacial aspects of the growth of polyaniline thin films and microscopic and macroscopic aspects of electrical conductivity upon doping. Comparisons will be made with other studies that address properties of analogous crystalline systems as appropriate. A brief assessment of the broader problem of analyzing these systems will be given.

  7. Mechanisms of mineral membrane fouling growth modulated by pulsed modes of current during electrodialysis: evidences of water splitting implications in the appearance of the amorphous phases of magnesium hydroxide and calcium carbonate.

    Science.gov (United States)

    Cifuentes-Araya, Nicolás; Astudillo-Castro, Carolina; Bazinet, Laurent

    2014-07-15

    Experiments revealed the fouling nature evolutions along different electrodialysis (ED) trials, and how it disappears when current pulsation acts repetitively on the interfaces of ion-exchange membranes (IEMs). Fouling was totally controlled on the diluate side of cation-exchange membrane (CEM) by the repetitive pulsation frequency of the higher on-duty ratios applied. They created steady water splitting proton-barriers that neutralized OH(-) leakage through the membrane, decreasing the interfacial pH, and fouling of the concentrate side. The anion-exchange membrane (AEM) on the diluate side was similarly protected, but it was fouled once water splitting OH(-) generation became either intense enough or excessively weak. Interestingly, amorphous magnesium hydroxide (AMH) stemmed on the CEM-diluate side from brucite under intense water splitting OH(-) generation, and/or strong OH(-) leakage electromigration through the membrane. Water dissociation and overlimiting current regimes triggered drastic water molecule removal from crystal lattices through an accelerated cascade water splitting reaction. Also, amorphous calcium carbonate (ACC) appeared on CEM under intense water splitting reaction, and disappeared once intense OH(-) leakage was allowed by the water splitting proton-barrier dissipation. Our findings have implications for membrane fouling control, as well as for the understanding of the growth behavior of CaCO3 and Mg(OH)2 species on electromembrane interfaces. Copyright © 2014 Elsevier Inc. All rights reserved.

  8. New tetrahedral polymorphs of the group-14 elements

    Science.gov (United States)

    Mujica, A.; Pickard, C. J.; Needs, R. J.

    2017-10-01

    In this short communication we present the main results of an ab initio structural search for new polymorphs of the group-14 elements C, Si, and Ge, with a focus on low-density and energetically favorable sp 3-bonded tetrahedral polymorphs which could constitute candidate phases to be synthesized in the laboratory. We propose new orthorhombic and tetragonal polymorphs with enthalpies that are lower or comparable to those of other polymorphs of the group-14 elements that have either been experimentally synthesized or recently proposed as the structure of unknown phases obtained in experiments. The new phases have interesting structural and electronics properties. These include an orthorhombic phase that in Si is found to have a quasi-direct band gap at the zone center of about the right size for optimal photovoltaic applications, and a tetragonal phase with a chiral topology that displays an exotic pentagonal pattern and whose vibrational properties match those of an unknown phase of Si.

  9. Nuclear tetrahedral symmetry: possibly present throughout the periodic table.

    Science.gov (United States)

    Dudek, J; Goźdź, A; Schunck, N; Miśkiewicz, M

    2002-06-24

    More than half a century after the fundamental, spherical shell structure in nuclei had been established, theoretical predictions indicated that the shell gaps comparable or even stronger than those at spherical shapes may exist. Group-theoretical analysis supported by realistic mean-field calculations indicate that the corresponding nuclei are characterized by the TD(d) ("double-tetrahedral") symmetry group. Strong shell-gap structure is enhanced by the existence of the four-dimensional irreducible representations of TD(d); it can be seen as a geometrical effect that does not depend on a particular realization of the mean field. Possibilities of discovering the TD(d) symmetry in experiment are discussed.

  10. Physics of amorphous metals

    CERN Document Server

    Kovalenko, Nikolai P; Krey, Uwe

    2008-01-01

    The discovery of bulk metallic glasses has led to a large increase in the industrial importance of amorphous metals, and this is expected to continue. This book is the first to describe the theoretical physics of amorphous metals, including the important theoretical development of the last 20 years.The renowned authors stress the universal aspects in their description of the phonon or magnon low-energy excitations in the amorphous metals, e.g. concerning the remarkable consequences of the properties of these excitations for the thermodynamics at low and intermediate temperatures. Tunneling

  11. Thin films of hydrogenated amorphous carbon (a-C:H) obtained through chemical vapor deposition assisted by plasma; Peliculas delgadas de carbono amorfo hidrogenado (a-C:H) obtenidas mediante deposito quimico de vapores asistido por plasma

    Energy Technology Data Exchange (ETDEWEB)

    Mejia H, J.A.; Camps C, E.E.; Escobar A, L.; Romero H, S.; Chirino O, S. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Muhl S, S. [IIM-UNAM, 04510 Mexico D.F. (Mexico)

    2004-07-01

    Films of hydrogenated amorphous carbon (a-C:H) were deposited using one source of microwave plasma with magnetic field (type ECR), using mixtures of H{sub 2}/CH{sub 4} in relationship of 80/20 and 95/05 as precursory gases, with work pressures of 4X10{sup -4} to 6x10{sup -4} Torr and an incident power of the discharge of microwaves with a constant value of 400 W. It was analyzed the influence among the properties of the films, as the deposit rate, the composition and the bonding types, and the deposit conditions, such as the flow rates of the precursory gases and the polarization voltage of the sample holders. (Author)

  12. Atomic-scale study of the amorphous-to-crystalline phase transition mechanism in GeTe thin films.

    Science.gov (United States)

    Mantovan, R; Fallica, R; Mokhles Gerami, A; Mølholt, T E; Wiemer, C; Longo, M; Gunnlaugsson, H P; Johnston, K; Masenda, H; Naidoo, D; Ncube, M; Bharuth-Ram, K; Fanciulli, M; Gislason, H P; Langouche, G; Ólafsson, S; Weyer, G

    2017-08-15

    The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of 57Fe emission Mössbauer spectroscopy, following dilute implantation of 57Mn (T½ = 1.5 min) at ISOLDE/CERN, to study the electronic charge distribution in the immediate vicinity of the 57Fe probe substituting Ge (FeGe), and to interrogate the local environment of FeGe over the amorphous-crystalline phase transition in GeTe thin films. Our results show that the local structure of as-sputtered amorphous GeTe is a combination of tetrahedral and defect-octahedral sites. The main effect of the crystallization is the conversion from tetrahedral to defect-free octahedral sites. We discover that only the tetrahedral fraction in amorphous GeTe participates to the change of the FeGe-Te chemical bonds, with a net electronic charge density transfer of  ~ 1.6 e/a0 between FeGe and neighboring Te atoms. This charge transfer accounts for a lowering of the covalent character during crystallization. The results are corroborated by theoretical calculations within the framework of density functional theory. The observed atomic-scale chemical-structural changes are directly connected to the macroscopic phase transition and resistivity switch of GeTe thin films.

  13. An 8-node tetrahedral finite element suitable for explicit transient dynamic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Key, S.W.; Heinstein, M.W.; Stone, C.M. [Sandia National Labs., Albuquerque, NM (United States)

    1997-12-31

    Considerable effort has been expended in perfecting the algorithmic properties of 8-node hexahedral finite elements. Today the element is well understood and performs exceptionally well when used in modeling three-dimensional explicit transient dynamic events. However, the automatic generation of all-hexahedral meshes remains an elusive achievement. The alternative of automatic generation for all-tetrahedral finite element is a notoriously poor performer, and the 10-node quadratic tetrahedral finite element while a better performer numerically is computationally expensive. To use the all-tetrahedral mesh generation extant today, the authors have explored the creation of a quality 8-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four midface nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping and the element`s performance in applications are presented. In particular, they examine the 80node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element only samples constant strain states and, therefore, has 12 hourglass modes. In this regard, it bears similarities to the 8-node, mean-quadrature hexahedral finite element. Given automatic all-tetrahedral meshing, the 8-node, constant-strain tetrahedral finite element is a suitable replacement for the 8-node hexahedral finite element and handbuilt meshes.

  14. A Family of Uniform Strain Tetrahedral Elements and a Method for Connecting Dissimilar Finite Element Meshes

    Energy Technology Data Exchange (ETDEWEB)

    Dohrmann, C.R.; Heinstein, M.W.; Jung, J.; Key, S.W.

    1999-01-01

    This report documents a collection of papers on a family of uniform strain tetrahedral finite elements and their connection to different element types. Also included in the report are two papers which address the general problem of connecting dissimilar meshes in two and three dimensions. Much of the work presented here was motivated by the development of the tetrahedral element described in the report "A Suitable Low-Order, Eight-Node Tetrahedral Finite Element For Solids," by S. W. Key {ital et al.}, SAND98-0756, March 1998. Two basic issues addressed by the papers are: (1) the performance of alternative tetrahedral elements with uniform strain and enhanced uniform strain formulations, and (2) the proper connection of tetrahedral and other element types when two meshes are "tied" together to represent a single continuous domain.

  15. Slow dynamics in a primitive tetrahedral network model.

    Science.gov (United States)

    De Michele, Cristiano; Tartaglia, Piero; Sciortino, Francesco

    2006-11-28

    We report extensive Monte Carlo and event-driven molecular dynamics simulations of the fluid and liquid phase of a primitive model for silica recently introduced by Ford et al. [J. Chem. Phys. 121, 8415 (2004)]. We evaluate the isodiffusivity lines in the temperature-density plane to provide an indication of the shape of the glass transition line. Except for large densities, arrest is driven by the onset of the tetrahedral bonding pattern and the resulting dynamics is strong in Angell's classification scheme [J. Non-Cryst. Solids 131-133, 13 (1991)]. We compare structural and dynamic properties with corresponding results of two recently studied primitive models of network forming liquids-a primitive model for water and an angular-constraint-free model of four-coordinated particles-to pin down the role of the geometric constraints associated with bonding. Eventually we discuss the similarities between "glass" formation in network forming liquids and "gel" formation in colloidal dispersions of patchy particles.

  16. A suitable low-order, eight-node tetrahedral finite element for solids

    Energy Technology Data Exchange (ETDEWEB)

    Key, S.W.; Heinstein, M.S.; Stone, C.M.; Mello, F.J.; Blanford, M.L.; Budge, K.G.

    1998-03-01

    To use the all-tetrahedral mesh generation existing today, the authors have explored the creation of a computationally efficient eight-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four mid-face nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping, and the element`s performance in applications are presented. In particular they examine the eight-node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element samples only constant strain states and, therefore, has 12 hour-glass modes. In this regard it bears similarities to the eight-node, mean-quadrature hexahedral finite element. Comparisons with the results obtained from the mean-quadrature eight-node hexahedral finite element and the four-node tetrahedral finite element are included. Given automatic all-tetrahedral meshing, the eight-node, constant-strain tetrahedral finite element is a suitable replacement for the eight-node hexahedral finite element in those cases where mesh generation requires an inordinate amount of user intervention and direction to obtain acceptable mesh properties.

  17. Local order origin of thermal stability enhancement in amorphous Ag doping GeTe

    Science.gov (United States)

    Xu, L.; Li, Y.; Yu, N. N.; Zhong, Y. P.; Miao, X. S.

    2015-01-01

    We demonstrate the impacts of Ag doping on the local atomic structure of amorphous GeTe phase-change material. The variations of phonon vibrational modes, boding nature, and atomic structure are shown by Raman, X-ray photoelectron spectroscopy, and ab initio calculation. Combining the experiments and simulations, we observe that the number of Ge atoms in octahedral site decreases and that in tetrahedral site increases. This modification in local order of GeTe originating from the low valence element will affect the crystallization behavior of amorphous GeTe, which is verified by differential scanning calorimetry and transmission electron microscope results. This work not only gives the analysis on the structural change of GeTe with Ag dopants but also provides a method to enhance the thermal stability of amorphous phase-change materials for memory and brain-inspired computing applications.

  18. Dynamical Instability Causes the Demise of a Supercooled Tetrahedral Liquid

    Science.gov (United States)

    Gautam, Arvind Kumar; Pingua, Nandlal; Goyal, Aashish; Apte, Pankaj A.

    2017-09-01

    We investigate the relaxation mechanism of a supercooled tetrahedral liquid at its limit of stability using isothermal isobaric ( NPT) Monte Carlo simulations. In similarity with systems which are far from equilibrium but near the onset of jamming (O'Hern et al. in Phys Rev Lett 93:165702, 2004), we find that the relaxation is characterized by two time-scales: the decay of long-wavelength (slow) fluctuations of potential energy is controlled by the slope [partial (G/N)/partial φ ] of the Gibbs free energy ( G) at a unique value of per particle potential energy φ = φ _{mid}. The short-wavelength (fast) fluctuations are controlled by the bath temperature T. The relaxation of the supercooled liquid is initiated with a dynamical crossover after which the potential energy fluctuations are biased towards values progressively lesser than φ _{mid}. The dynamical crossover leads to the change of time-scale, i.e., the decay of long-wavelength potential energy fluctuations (intermediate stage of relaxation). Because of the condition [partial ^2 (G/N)/partial φ ^2 = 0] at φ = φ _{mid}, the slope [partial (G/N)/partial φ ] has a unique value and governs the intermediate stage of relaxation, which ends just after the crossover. In the subsequent stage, there is a relatively rapid crystallization due to lack of long-wavelength fluctuations and the instability at φ _{mid}, i.e., the condition that G decreases as configurations with potential energies lower than φ _{mid} are accessed. The dynamical crossover point and the associated change in the time-scale of fluctuations is found to be consistent with the previous studies.

  19. Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO{sub 2}: Bio-template assisted sol-gel synthesis and photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Mohamed Azuwa Mohamad [Advanced Membrane Technology Research Centre, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Wan Norharyati Wan Salleh, E-mail: hayati@petroleum.utm.my [Advanced Membrane Technology Research Centre, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Juhana Jaafar, E-mail: juhana@petroleum.utm.my [Advanced Membrane Technology Research Centre, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Mohamad Saufi Rosmi [Department of Chemistry, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900, Tanjung Malim, Perak (Malaysia); Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Zul Adlan Mohd Hir [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Muhazri Abd Mutalib; Ahmad Fauzi Ismail [Advanced Membrane Technology Research Centre, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru (Malaysia); Tanemura, Masaki [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

    2017-01-30

    Highlights: • RCM as bio-template and in-situ carbon shell and interstitial carbon doping. • Photo-sensitizers by carbonaceous layer grafted onto the surface of TiO{sub 2}. • Visible light response could be tailored depending on the annealing temperature. • Photocatalytic properties and charge carrier transfer mechanism was proposed. - Abstract: Regenerated cellulose membrane was used as bio-template nanoreactor for the formation of rutile TiO{sub 2} mesoporous, as well as in-situ carbon dopant in acidified sol-gel system. The effects of calcination temperature on the physicochemical characteristic of core-shell nanostructured of bio-templated C-doped mesoporous TiO{sub 2} are highlighted in this study. By varying the calcination temperature, the thickness of the carbon shell coating on TiO{sub 2}, crystallinity, surface area, and optical properties could be tuned as confirmed by HRTEM, nitrogen adsorption/desorption measurement, XRD and UV–vis-NIR spectroscopy. The results suggested that increment in the calcination temperature would lead to the band gap narrowing from 2.95 to 2.80 eV and the thickness of carbon shell increased from 0.40 to 1.20 nm. The x-ray photoelectron spectroscopy showed that the visible light absorption capability was mainly due to the incorporation of carbon dopant at interstitial position in the TiO{sub 2} to form O−Ti−C or Ti−O−C bond. In addition, the formation of the carbon core-shell nanostructured was due to carbonaceous layer grafted onto the surface of TiO{sub 2} via Ti−O−C and Ti−OCO bonds. The result indicated that bio-templated C-doped core-shell mesoporous TiO{sub 2} prepared at 300 °C exhibited the highest photocatalytic activity. It is worthy to note that, the calcination temperature provided a huge impact towards improving the physicochemical and photocatalytic properties of the prepared bio-templated C-doped core-shell mesoporous TiO{sub 2}.

  20. Magnetic Properties of Nanometer-sized Crystalline and Amorphous Particles

    DEFF Research Database (Denmark)

    Mørup, Steen; Bødker, Franz; Hansen, Mikkel Fougt

    1997-01-01

    are superparamagnetic at finite temperatures. The temperature dependence of the superparamagnetic relaxation time and the influence of inter-particle interactions is discussed. Finally, some examples of studies of surface magnetization of alpha-Fe particles are presented.......Amorphous transition metal-metalloid alloy particles can be prepared by chemical preparation techniques. We discuss the preparation of transition metal-boron and iron-carbon particles and their magnetic properties. Nanometer-sized particles of both crystalline and amorphous magnetic materials...

  1. Optical and magnetic properties of transition-metal ions in tetrahedral and octahedral compounds

    Science.gov (United States)

    Li, Huifang; Wang, Huaiqian; Kuang, Xiaoyu

    2011-10-01

    This paper presents the complete energy matrix of the 3d2 system containing the electron-electron interaction, the ligand-field interaction, the spin-orbit coupling interaction, and the Zeeman interaction, in which the optical spectra and g-factor of V3+and Ti2+ ions in the series of tetrahedral AIIBVI (AII=Zn, Cd, BVI=S, Se, Te) semiconductor materials are determined. In the investigation of the optical and magnetic properties of these transition-metal ions in the tetrahedral coordination complexes, we compared the data obtained from the transition-metal ions in the tetrahedral coordination complexes with those obtained from the corresponding ions in the octahedral ones, and found that the tetrahedral complexes have weaker crystal-field strength, inverse energy level ordering and stronger covalence effect.

  2. Comparison of hexahedral and tetrahedral elements in finite element analysis of the foot and footwear.

    Science.gov (United States)

    Tadepalli, Srinivas C; Erdemir, Ahmet; Cavanagh, Peter R

    2011-08-11

    Finite element analysis has been widely used in the field of foot and footwear biomechanics to determine plantar pressures as well as stresses and strains within soft tissue and footwear materials. When dealing with anatomical structures such as the foot, hexahedral mesh generation accounts for most of the model development time due to geometric complexities imposed by branching and embedded structures. Tetrahedral meshing, which can be more easily automated, has been the approach of choice to date in foot and footwear biomechanics. Here we use the nonlinear finite element program Abaqus (Simulia, Providence, RI) to examine the advantages and disadvantages of tetrahedral and hexahedral elements under compression and shear loading, material incompressibility, and frictional contact conditions, which are commonly seen in foot and footwear biomechanics. This study demonstrated that for a range of simulation conditions, hybrid hexahedral elements (Abaqus C3D8H) consistently performed well while hybrid linear tetrahedral elements (Abaqus C3D4H) performed poorly. On the other hand, enhanced quadratic tetrahedral elements with improved stress visualization (Abaqus C3D10I) performed as well as the hybrid hexahedral elements in terms of contact pressure and contact shear stress predictions. Although the enhanced quadratic tetrahedral element simulations were computationally expensive compared to hexahedral element simulations in both barefoot and footwear conditions, the enhanced quadratic tetrahedral element formulation seems to be very promising for foot and footwear applications as a result of decreased labor and expedited model development, all related to facilitated mesh generation. Copyright © 2011. Published by Elsevier Ltd.

  3. Study on the substrate-induced crystallisation of amorphous SiC-precursor ceramics. TIB/A; Untersuchungen zur substratinduzierten Kristallisation amorpher SiC-Precursorkeramiken

    Energy Technology Data Exchange (ETDEWEB)

    Rau, C.

    2000-12-01

    In the present thesis the crystallization behaviour of amorphous silicon-carbon materials (SiC{sub x}) was studied. The main topic of the experimental studies formed thereby the epitactical crystallization of thin silicon carbide layers on monocrystalline substrates of silicon carbides or silicon. Furthermore by thermolysis of the polymer amorphous SiC{sub x}-powder was obtained.

  4. Intermediate order in tetrahedrally coordinated silicon: evidence for chainlike objects

    Energy Technology Data Exchange (ETDEWEB)

    Tsu, D.V.; Chao, B.S.; Jones, S.J. [Energy Conversion Devices, Rochester Hills, MI (United States)

    2003-07-01

    In this report, we describe the nature of intermediate order in silicon as determined by recent measurements on thin films using transmission electron microscopy (TEM) and Raman scattering. The TEM images show in addition to the expected continuous random network (CRN), the presence of highly ordered quasi-one-dimensional ''chain-like objects'' (CLOs) that are 1-2 nm wide and tens of nm long that meander and show some evidence of cross-linking with each other. The presence of these objects correlate to a Raman feature centered at 490 cm{sup -1} whose width is 35-40 cm{sup -1}, and is used to quantify the heterogeneity in terms of the CLO and CRN (=475 cm{sup -1} scattering) concentrations. The 490 and 35 cm{sup -1} values are consistent with bond angle deviations approaching 0{sup o}, and thus reinforces an association with the CLOs. We find that in reference quality a-Si:H (made using pure SiH{sub 4}), the CLO concentration is about 5 vol%, while in state-of-the-art material using high H{sub 2} levels of dilution during processing, it increases to about 15%. Increased stability of such material to light-soaking is thus not mediated by a direct volumetric replacement of poor with high-quality components. Rather, an important characteristic of intermediate order in silicon is the low-dimensional aspect of its order, which allows it to influence more total volume than which it is itself composed. Consistent with these and other recent findings, we propose a tensegrity model of amorphous silicon. (author)

  5. Amorphous Phosphorus-Incorporated Cobalt Molybdenum Sulfide on Carbon Cloth: An Efficient and Stable Electrocatalyst for Enhanced Overall Water Splitting over Entire pH Values.

    Science.gov (United States)

    Ray, Chaiti; Lee, Su Chan; Sankar, Kalimuthu Vijaya; Jin, Bingjun; Lee, Jungpyo; Park, Jong Hyeok; Jun, Seong Chan

    2017-11-01

    The development of economical, proficient, and highly stable catalysts to substitute the expensive noble metal electrodes for electrocatalytic water-splitting applications is exceedingly desirable. In this context, the most fascinating and challenging approach is the rational design of a nanocomposite encompassing multiple components with unique functionalities. Herein, we describe the fabrication of a strongly catalytic and superb durable phosphorus-incorporated cobalt molybdenum sulfide electrocatalyst grown on carbon cloth (P-CoMoS/CC). The hybrid material exhibited excellent activity for hydrogen and oxygen evolution reactions over a wide range of pH (1-14) with extremely high stability (∼90% retention of the initial current density) after 24 h of electrolysis. Importantly, when P-CoMoS/CC was used as both cathode and anode for overall water splitting, a very low cell voltage of 1.54 V is required to attain the 10 mA cm -2 current density, and the hybrid material exhibited a long-term stability (89.8% activity retention after 100 h). The outstanding overall water-splitting performance compared to an electrolyzer consisting of the noble-metal-based catalysts Pt/C and RuO 2 makes P-CoMoS one of the most efficient earth-abundant water-splitting catalysts. Phosphorus incorporation was proved to be a vital aspect for the improved charge-transfer properties and catalytic durability of the P-CoMoS/CC catalyst.

  6. Implementation of tetrahedral-mesh geometry in Monte Carlo radiation transport code PHITS

    Science.gov (United States)

    Furuta, Takuya; Sato, Tatsuhiko; Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Brown, Justin L.; Bolch, Wesley E.

    2017-06-01

    A new function to treat tetrahedral-mesh geometry was implemented in the particle and heavy ion transport code systems. To accelerate the computational speed in the transport process, an original algorithm was introduced to initially prepare decomposition maps for the container box of the tetrahedral-mesh geometry. The computational performance was tested by conducting radiation transport simulations of 100 MeV protons and 1 MeV photons in a water phantom represented by tetrahedral mesh. The simulation was repeated with varying number of meshes and the required computational times were then compared with those of the conventional voxel representation. Our results show that the computational costs for each boundary crossing of the region mesh are essentially equivalent for both representations. This study suggests that the tetrahedral-mesh representation offers not only a flexible description of the transport geometry but also improvement of computational efficiency for the radiation transport. Due to the adaptability of tetrahedrons in both size and shape, dosimetrically equivalent objects can be represented by tetrahedrons with a much fewer number of meshes as compared its voxelized representation. Our study additionally included dosimetric calculations using a computational human phantom. A significant acceleration of the computational speed, about 4 times, was confirmed by the adoption of a tetrahedral mesh over the traditional voxel mesh geometry.

  7. Atomic-scale study of the amorphous-to-crystalline phase transition mechanism in GeTe thin films

    CERN Document Server

    Mantovan, R.; Mokhles Gerami, A.; Mølholt, T. E.; Wiemer, C.; Longo, M.; Gunnlaugsson, H. P.; Johnston, K.; Masenda, H.; Naidoo, D.; Ncube, M.; Bharuth-Ram, K.; Fanciulli, M.; Gislason, H. P.; Langouche, G.; Ólafsson, S.; Weyer, G.

    The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of 57Fe emission Mössbauer spectroscopy, following dilute implantation of 57Mn (T½ = 1.5 min) at ISOLDE/CERN, to study the electronic charge distribution in the immediate vicinity  of the 57Fe probe substituting Ge (FeGe), and to interrogate the local environment of FeGe over the amorphous-crystalline phase transition in GeTe thin films. Our results show that the local structure  of as-sputtered amorphous GeTe is a combination of tetrahedral and defect-octahedral sites. The main effect of the crystallization is the conversion from tetrahedral to defect-free octahedral sites.  We discover that only the tetrahedral fraction in amorphous GeTe participates to the change of the FeGe-Te chemical bond...

  8. Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)

    Energy Technology Data Exchange (ETDEWEB)

    Bertram, F.; Deiter, C. [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany); Schemme, T.; Jentsch, S.; Wollschlaeger, J. [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)

    2013-05-14

    Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

  9. Self-equilibrium and stability of regular truncated tetrahedral tensegrity structures

    Science.gov (United States)

    Zhang, J. Y.; Ohsaki, M.

    2012-10-01

    This paper presents analytical conditions of self-equilibrium and super-stability for the regular truncated tetrahedral tensegrity structures, nodes of which have one-to-one correspondence to the tetrahedral group. These conditions are presented in terms of force densities, by investigating the block-diagonalized force density matrix. The block-diagonalized force density matrix, with independent sub-matrices lying on its leading diagonal, is derived by making use of the tetrahedral symmetry via group representation theory. The condition for self-equilibrium is found by enforcing the force density matrix to have the necessary number of nullities, which is four for three-dimensional structures. The condition for super-stability is further presented by guaranteeing positive semi-definiteness of the force density matrix.

  10. Friction and wear performance of bearing ball sliding against diamond-like carbon coatings

    Science.gov (United States)

    Wu, Shenjiang; Kousaka, Hiroyuki; Kar, Satyananda; Li, Dangjuan; Su, Junhong

    2017-01-01

    We have studied the tribological properties of bearing steel ball (Japan standard, SUJ2) sliding against tetrahedral amorphous carbon (ta-C) coatings and amorphous hydrogenated carbon (a-C:H) coatings. The reciprocating sliding testes are performed with ball-on-plate friction tester in ambient air condition. Analysis of friction coefficient, wear volume and microstructure in wear scar are carried out using optical microscopy, atom force morphology (AFM) and Raman spectroscopy. The results show the SUJ2 on ta-C coating has low friction coefficient (around 0.15) but high wear loss. In contrast, the low wear loss of SUJ2 on a-C:H coating with high (around 0.4) and unsteady friction coefficient. Some Fe2O3, FeO and graphitization have been found on the wear scar of SUJ2 sliding against ta-C coating. Nearly no oxide materials exist on the wear scar of SUJ2 against a-C:H coating. The mechanism and hypothesis of the wear behavior have been investigated according to the measurement results. This study will contribute to proper selection and understand the tribological performance of bearing steels against DLC coatings.

  11. Physics of amorphous semiconductor devices

    Energy Technology Data Exchange (ETDEWEB)

    Adler, D.

    1987-01-01

    This book contains 19 papers. Some of the titles are: Self-consistent modeling of amorphous silicon devices; Numerical modeling of thin film Si:H solar cells; Submicron device physics for numerical simulations; and Applications of amorphous silicon thin film transistors to linear arrays.

  12. Amorphous Pt@PdCu/CNT Catalyst for Methanol Electrooxidation ...

    African Journals Online (AJOL)

    A multi-walled carbon nanotube-supported, Pt decorated nano-sized amorphous PdCu alloy cores (denoted as Pt@PdCu/CNT) catalyst with lower Pt loading is synthesized via a galvanic displacement reaction. The structure is examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM).

  13. Microstructure and debris fracture in amorphous Ni–P-CNT ...

    African Journals Online (AJOL)

    Amorphous nickel–phosphorus (Ni–P)-based Carbon Nanotubes (CNTs) composite coatings were prepared by brush electroplating technology. Wear tests for the coatings were conducted. The deformation of the microstructures in the coatings after wear was analyzed by transmission electron microscopy. The results ...

  14. Relationship between amorphous silica and precious metal in quartz veins

    Science.gov (United States)

    Harrichhausen, N.; Rowe, C. D.; Board, W. S.; Greig, C. J.

    2015-12-01

    Super-saturation of silica is common in fault fluids, due to pressure changes associated with fracture, fault slip, or temperature gradients in hydrothermal systems. These mechanisms lead to precipitation of amorphous silica, which will recrystallize to quartz under typical geologic conditions. These conditions may also promote the saturation of precious metals, such as gold, and the precipitation of nanoparticles. Previous experiments show that charged nanoparticles of gold can attach to the surface of amorphous silica nanoparticles. Thus, gold and silica may be transported as a colloid influencing mineralization textures during amorphous silica recrystallization to quartz. This may enrich quartz vein hosted gold deposits, but the instability of hydrous silica during subsequent deformation means that the microstructural record of precipitation of gold is lost. We investigate a recent, shallow auriferous hydrothermal system at Dixie Valley, Nevada to reveal the nano- to micro-scale relationships between gold and silica in fresh veins. Fault slip surfaces at Dixie Valley exhibit layers of amorphous silica with partial recrystallization to quartz. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) show amorphous silica can contain a few wt. % gold while areas recrystallized to quartz are barren. At the Jurassic Brucejack deposit in British Columbia, Canada we observe the cryptocrystalline quartz textures that may indicate recrystallization from amorphous silica within quartz-carbonate veins containing high grade gold. Comb quartz within syntaxial veins, vugs, and coating breccia clasts indicate structural dilation. Vein geometry is investigated to determine relative importance of fault slip in creating dilational sites. By comparing quartz-carbonate veins from the Dixie Valley to Brucejack, we can determine whether amorphous silica formed in different environments show similar potential to affect precious metal mineralization.

  15. Tetrahedral tetrazolate frameworks for high CO2 and H2 uptake.

    Science.gov (United States)

    Wang, Fei; Hou, Duan-Chuan; Yang, Hui; Kang, Yao; Zhang, Jian

    2014-02-28

    Three tetrahedral tetrazolate frameworks with two different 4-connected topologies including lonsdaleite (lon, for 1) and diamond (dia, for 2 and 3) have been synthesized, and the lon-type framework with high CO2 and H2 uptake capacity can irreversibly transform to the dia-type framework via solvent-exchange.

  16. A new third order finite volume weighted essentially non-oscillatory scheme on tetrahedral meshes

    Science.gov (United States)

    Zhu, Jun; Qiu, Jianxian

    2017-11-01

    In this paper a third order finite volume weighted essentially non-oscillatory scheme is designed for solving hyperbolic conservation laws on tetrahedral meshes. Comparing with other finite volume WENO schemes designed on tetrahedral meshes, the crucial advantages of such new WENO scheme are its simplicity and compactness with the application of only six unequal size spatial stencils for reconstructing unequal degree polynomials in the WENO type spatial procedures, and easy choice of the positive linear weights without considering the topology of the meshes. The original innovation of such scheme is to use a quadratic polynomial defined on a big central spatial stencil for obtaining third order numerical approximation at any points inside the target tetrahedral cell in smooth region and switch to at least one of five linear polynomials defined on small biased/central spatial stencils for sustaining sharp shock transitions and keeping essentially non-oscillatory property simultaneously. By performing such new procedures in spatial reconstructions and adopting a third order TVD Runge-Kutta time discretization method for solving the ordinary differential equation (ODE), the new scheme's memory occupancy is decreased and the computing efficiency is increased. So it is suitable for large scale engineering requirements on tetrahedral meshes. Some numerical results are provided to illustrate the good performance of such scheme.

  17. Spin-Crossover in a Pseudo-tetrahedral Bis(formazanate) Iron Complex

    NARCIS (Netherlands)

    Travieso-Puente, Raquel; Broekman, J.O.P.; Chang, Mu-Chieh; Demeshko, Serhiy; Meyer, Franc; Otten, Edwin

    2016-01-01

    Spin-crossover in a pseudo-tetrahedral bis(formazanate) iron(II) complex (1) is described. Structural, magnetic, and spectroscopic analyses indicate that this compound undergoes thermal switching between an S=0 and an S=2 state, which is very rare in four-coordinate complexes. The transition to the

  18. A review of defects and disorder in multinary tetrahedrally bonded semiconductors

    Science.gov (United States)

    Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; Toberer, Eric S.; Zakutayev, Andriy

    2016-12-01

    Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu2SnS3. We contrast our findings on Cu2SnS3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cu2ZnSnS4 and Cu(In,Ga)Se2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu2SnS3 and Cu2ZnSnS4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Overall, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.

  19. Enamel-like apatite crown covering amorphous mineral in a crayfish mandible

    Science.gov (United States)

    Bentov, Shmuel; Zaslansky, Paul; Al-Sawalmih, Ali; Masic, Admir; Fratzl, Peter; Sagi, Amir; Berman, Amir; Aichmayer, Barbara

    2012-01-01

    Carbonated hydroxyapatite is the mineral found in vertebrate bones and teeth, whereas invertebrates utilize calcium carbonate in their mineralized organs. In particular, stable amorphous calcium carbonate is found in many crustaceans. Here we report on an unusual, crystalline enamel-like apatite layer found in the mandibles of the arthropod Cherax quadricarinatus (freshwater crayfish). Despite their very different thermodynamic stabilities, amorphous calcium carbonate, amorphous calcium phosphate, calcite and fluorapatite coexist in well-defined functional layers in close proximity within the mandible. The softer amorphous minerals are found primarily in the bulk of the mandible whereas apatite, the harder and less soluble mineral, forms a wear-resistant, enamel-like coating of the molar tooth. Our findings suggest a unique case of convergent evolution, where similar functional challenges of mastication led to independent developments of structurally and mechanically similar, apatite-based layers in the teeth of genetically remote phyla: vertebrates and crustaceans. PMID:22588301

  20. Finite element simulation of articular contact mechanics with quadratic tetrahedral elements.

    Science.gov (United States)

    Maas, Steve A; Ellis, Benjamin J; Rawlins, David S; Weiss, Jeffrey A

    2016-03-21

    Although it is easier to generate finite element discretizations with tetrahedral elements, trilinear hexahedral (HEX8) elements are more often used in simulations of articular contact mechanics. This is due to numerical shortcomings of linear tetrahedral (TET4) elements, limited availability of quadratic tetrahedron elements in combination with effective contact algorithms, and the perceived increased computational expense of quadratic finite elements. In this study we implemented both ten-node (TET10) and fifteen-node (TET15) quadratic tetrahedral elements in FEBio (www.febio.org) and compared their accuracy, robustness in terms of convergence behavior and computational cost for simulations relevant to articular contact mechanics. Suitable volume integration and surface integration rules were determined by comparing the results of several benchmark contact problems. The results demonstrated that the surface integration rule used to evaluate the contact integrals for quadratic elements affected both convergence behavior and accuracy of predicted stresses. The computational expense and robustness of both quadratic tetrahedral formulations compared favorably to the HEX8 models. Of note, the TET15 element demonstrated superior convergence behavior and lower computational cost than both the TET10 and HEX8 elements for meshes with similar numbers of degrees of freedom in the contact problems that we examined. Finally, the excellent accuracy and relative efficiency of these quadratic tetrahedral elements was illustrated by comparing their predictions with those for a HEX8 mesh for simulation of articular contact in a fully validated model of the hip. These results demonstrate that TET10 and TET15 elements provide viable alternatives to HEX8 elements for simulation of articular contact mechanics. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Updates to Multi-Dimensional Flux Reconstruction for Hypersonic Simulations on Tetrahedral Grids

    Science.gov (United States)

    Gnoffo, Peter A.

    2010-01-01

    The quality of simulated hypersonic stagnation region heating with tetrahedral meshes is investigated by using an updated three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. An earlier implementation of this algorithm provided improved symmetry characteristics on tetrahedral grids compared to conventional reconstruction methods. The original formulation however displayed quantitative differences in heating and shear that were as large as 25% compared to a benchmark, structured-grid solution. The primary cause of this discrepancy is found to be an inherent inconsistency in the formulation of the flux limiter. The inconsistency is removed by employing a Green-Gauss formulation of primitive gradients at nodes to replace the previous Gram-Schmidt algorithm. Current results are now in good agreement with benchmark solutions for two challenge problems: (1) hypersonic flow over a three-dimensional cylindrical section with special attention to the uniformity of the solution in the spanwise direction and (2) hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problems provide a sensitive indicator for algorithmic effects on heating. Additional simulations on a sharp, double cone and the shuttle orbiter are then presented to demonstrate the capabilities of the new algorithm on more geometrically complex flows with tetrahedral grids. These results provide the first indication that pure tetrahedral elements utilizing the updated, three-dimensional, upwind reconstruction algorithm may be used for the

  2. Characterization of amorphous hydrogenated carbon films ...

    Indian Academy of Sciences (India)

    sp3 fraction. References. Buijnsters J G, Camero M and Vazquez L 2006 Phys. Rev. B74. 155417. Chowdhury S, Laugier M T and Rahman I Z 2004 Thin Solid Films. 468 149. Clin M, Durand-Drouhin O, Zeinert A and Picot J C 1999 Dia. Relat. Mater. 8 527. Dai H Y, Wang L W, Jiang H and Huang N K 2007 Chin. Phys. Lett.

  3. Atmospheric Plasma Deposition of Diamond-like Carbon Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Ladwig, Angela

    2008-01-23

    There is great demand for thin functional coatings in the semiconductor, optics, electronics, medical, automotive and aerospace industries [1-13]. As fabricated components become smaller and more complex, the properties of the materials’ surface take on greater importance. Thin coatings play a key role in tailoring surfaces to give them the desired hardness, wear resistance, chemical inertness, and electrical characteristics. Diamond-like carbon (DLC) coatings possess an array of desirable properties, including outstanding abrasion and wear resistance, chemical inertness, hardness, a low coefficient of friction and exceptionally high dielectric strength [14-22]. Diamond-like carbon is considered to be an amorphous material, containing a mixture of sp2 and sp3 bonded carbon. Based on the percentage of sp3 carbon and the hydrogen content, four different types of DLC coatings have been identified: tetrahedral carbon (ta-C), hydrogenated amorphous carbon (a-C:H) hard, a-C:H soft, and hydrogenated tetrahedral carbon (ta-C:H) [20,24,25]. Possessing the highest hardness of 80 GPa, ta-C possesses an sp3 carbon content of 80 to 88u%, and no appreciable hydrogen content whereas a-C:H soft possesses a hardness of less than 10 GPa, contains an sp3 carbon content of 60% and a hydrogen content between 30 to 50%. Methods used to deposit DLC coatings include ion beam deposition, cathodic arc spray, pulsed laser ablation, argon ion sputtering, and plasma-enhanced chemical vapor deposition [73-83]. Researchers contend that several advantages exist when depositing DLC coatings in a low-pressure environment. For example, ion beam processes are widely utilized since the ion bombardment is thought to promote denser sp3-bonded carbon networks. Other processes, such as sputtering, are better suited for coating large parts [29,30,44]. However, the deposition of DLC in a vacuum system has several disadvantages, including high equipment cost and restrictions on the size and shape of

  4. Explosive transition in amorphous microwire

    Science.gov (United States)

    Borisenko, I. Yu.; Tulin, V. A.

    2017-11-01

    An amorphous microwire in a glass shell offers a quick thermal response and can be rapidly heated to the crystallization point. When heated by a current pulse with a small amplitude and duration, the wire passes from the amorphous to microcrystalline state. The crystallization of the amorphous state may represent a slow or explosive process depending on the parameters of the pulse. In the latter case, the emission of electromagnetic waves (flash of light) and a sharp rise in the resistance are observed. The rate of propagation of the crystallization front in our experiments has been found to be about 1 m/s.

  5. Kinetically Controlled Two-Step Amorphization and Amorphous-Amorphous Transition in Ice

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Chuanlong; Yong, Xue; Tse, John S.; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kenney-Benson, Curtis; Shen, Guoyin

    2017-09-01

    We report the results of in situ structural characterization of the amorphization of crystalline ice Ih under compression and the relaxation of high-density amorphous (HDA) ice under decompression at temperatures between 96 and 160 K by synchrotron x-ray diffraction. The results show that ice Ih transforms to an intermediate crystalline phase at 100 K prior to complete amorphization, which is supported by molecular dynamics calculations. The phase transition pathways show clear temperature dependence: direct amorphization without an intermediate phase is observed at 133 K, while at 145 K a direct Ih-to-IX transformation is observed; decompression of HDA shows a transition to low-density amorphous ice at 96 K and ~ 1 Pa , to ice Ic at 135 K and to ice IX at 145 K. These observations show that the amorphization of compressed ice Ih and the recrystallization of decompressed HDA are strongly dependent on temperature and controlled by kinetic barriers. Pressure-induced amorphous ice is an intermediate state in the phase transition from the connected H-bond water network in low pressure ices to the independent and interpenetrating H-bond network of high-pressure ices.

  6. Amorphous drugs and dosage forms

    DEFF Research Database (Denmark)

    Grohganz, Holger; Löbmann, K.; Priemel, P.

    2013-01-01

    The transformation to an amorphous form is one of the most promising approaches to address the low solubility of drug compounds, the latter being an increasing challenge in the development of new drug candidates. However, amorphous forms are high energy solids and tend to recry stallize. New...... formulation principles are needed to ensure the stability of amorphous drug forms. The formation of solid dispersions is still the most investigated approach, but additional approaches are desirable to overcome the shortcomings of solid dispersions. Spatial separation by either coating or the use of micro......-containers has shown potential to prevent or delay recrystallization. Another recent approach is the formation of co-amorphous mixtures between either two drugs or one drug and one low molecular weight excipient. Molecular interactions between the two molecules provide an energy barrier that has to be overcome...

  7. Synthesis, evaluation and defect compensation of tetrahedral glasses as possible solar cell materials. Final report, February 1, 1979-April 30, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Rauh, R.D.; Rose, T.L.; Scoville, A.N.

    1980-04-01

    The work reported was directed towards evaluation of new amorphous compounds for application in solar cells. The ternary A/sup II/B/sup IV/C/sub 2//sup V/ chalcopyrite systems were selected because of their inexpensive constituent elements and tetrahedral geometry. Polycrystalline samples of the ternary arsenides with Cd and Zn as the group II element and Ge, Si, Sn as the group IV element were synthesized. Thin films were deposited by vacuum evaporation of the bulk ternary arsenides. The stoichiometries of the films were irreproducible and were usually deficient in the lower vapor pressure group IV element. Films made by evaporating polycrystalline ZnAs/sub 2/, which also has a tetrahedral bonding structure, had stoichiometries generally in the range from Zn/sub 3/As/sub 2/ to ZnAs/sub 2/. The former compound is formed by the decomposition of ZnAs/sub 2/ to Zn/sub 3/As/sub 2/ and As/sub 4/. The intermediate stoichiometries are thought to be mixtures of the decomposition products. Preliminary results from annealing of the films indicate that heat treatment produces the stoichiometries expected for one of the two forms of zinc arsenide. The as-deposited films are amorphous when the substrate temperature is kept below 100/sup 0/C. The a-ZnAs/sub x/ films were characterized. EDAX and Auger analysis showed that films were homogeneous in the plane of the substrate, but that some variation occurred in the depth profile of the films. This change in composition is consistent with the sample decomposition which occurs during the evaporation. The as-prepared films were p-type with room temperature resistivities on the order of 10/sup 2/-10/sup 4/..cap omega..-cm. Optical absorption measurements gave optical band gap values of 1.2 eV for a-Zn/sub 3/As/sub 2/ and 1.5 eV for a-ZnAs/sub 2/. The ZnAs/sub x/ films were photoconductive.

  8. Structural modeling of amorphous graphene: a differential-mutation approach

    Science.gov (United States)

    Biswas, Katja

    A modified differential-mutation algorithm will be presented that can reliably produce low-lying energy structures of amorphous systems. The algorithm merges a genetic algorithm with a computational cooling procedure. This makes it possible to obtain low-lying energy minima with a very limited population size. The algorithm has been implemented for structural optimization of amorphous graphene, where the individual carbon atoms interact via a classical bond-order potential. It will be shown that the resulting minimum configurations are very close in energy and represent locally different topological structures of the material. The results for the coordination numbers, ring-size distribution and puckering of the amorphous surface will be discussed.

  9. In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation.

    Science.gov (United States)

    Gerbig, Y B; Michaels, C A; Bradby, J E; Haberl, B; Cook, R F

    2015-12-01

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline

  10. Transport of phase space densities through tetrahedral meshes using discrete flow mapping

    CERN Document Server

    Bajars, Janis; Sondergaard, Niels; Tanner, Gregor

    2016-01-01

    Discrete flow mapping was recently introduced as an efficient ray based method determining wave energy distributions in complex built up structures. Wave energy densities are transported along ray trajectories through polygonal mesh elements using a finite dimensional approximation of a ray transfer operator. In this way the method can be viewed as a smoothed ray tracing method defined over meshed surfaces. Many applications require the resolution of wave energy distributions in three-dimensional domains, such as in room acoustics, underwater acoustics and for electromagnetic cavity problems. In this work we extend discrete flow mapping to three-dimensional domains by propagating wave energy densities through tetrahedral meshes. The geometric simplicity of the tetrahedral mesh elements is utilised to efficiently compute the ray transfer operator using a mixture of analytic and spectrally accurate numerical integration. The important issue of how to choose a suitable basis approximation in phase space whilst m...

  11. Direct evidence for stability of tetrahedral interstitial Er in Si up to 900$^{\\circ}$C

    CERN Document Server

    Wahl, U; Langouche, G; Marques, J G; Vantomme, A

    1997-01-01

    Conversion electron emission channeling from the isotope $^{167m}$Er (2.28 s), which is the decay product of radioactive $^{167}$Tm (9.25 d), offers a means of monitoring the lattice sites of Er in single crystals. We have used this method to determine the lattice location of $^{167m}$Er in Si directly following room temperature implantation of $^{167}$Tm, after subsequent annealing steps, and also in situ during annealing up to 900°C. Following the recovery of implantation damage around 600°C, about 90% of Er occupies near-tetrahedral interstitial sites in both FZ and CZ Si. While in FZ Si $^{167m}$Er was found to be stable on these sites even at 900°C, the tetrahedral Er fraction in CZ Si decreased considerably after annealing for 10 min at 800°C and above.

  12. Atomic Scale Picture of the Ion Conduction Mechanism in Tetrahedral Network of Lanthanum Barium Gallate

    Energy Technology Data Exchange (ETDEWEB)

    Jalarvo, Niina H [ORNL; Gourdon, Olivier [ORNL; Bi, Zhonghe [ORNL; Gout, Delphine J [ORNL; Ohl, Michael E [ORNL; Paranthaman, Mariappan Parans [ORNL

    2013-01-01

    Combined experimental study of impedance spectroscopy, neutron powder diffraction and quasielastic neutron scattering was performed to shed light into the atomic scale ion migration processes in proton and oxide ion conductor; La0.8Ba1.2GaO3.9 . This material consist of tetrahedral GaO4 units, which are rather flexible and rocking motion of these units promotes the ionic migration process. The oxide ion (vacancy) conduction takes place on channels along c axis, involving a single elementary step, which occurs between adjacent tetrahedron (inter-tetrahedron jump). The proton conduction mechanism consists of intra-tetrahedron and inter-tetrahedron elementary processes. The intra-tetrahedron proton transport is the rate-limiting process, with activation energy of 0.44 eV. The rocking motion of the GaO4 tetrahedron aids the inter-tetrahedral proton transport, which has the activation energy of 0.068 eV.

  13. A rectangular tetrahedral adaptive mesh based corotated finite element model for interactive soft tissue simulation.

    Science.gov (United States)

    Tagawa, Kazuyoshi; Yamada, Takahiro; Tanaka, Hiromi T

    2013-01-01

    In this paper, we propose a rectangular tetrahedral adaptive mesh based corotated finite element model for interactive soft tissue simulation. Our approach consists of several computation reduction techniques. They are as follows: 1) an efficient calculation approach for computing internal forces of nodes of elastic objects to take advantage of the rectangularity of the tetrahedral adaptive mesh; 2) fast shape matching approach by using a new scaling of polar decomposition; 3) an approach for the reduction of the number of times of shape matching by using the hierarchical structure. We implemented the approach into our surgery simulator and compared the accuracy of the deformation and the computation time among 1) proposed approach, 2) L-FE), and 3) NL-FEM. Finally, we show the effectiveness of our proposed approach.

  14. Urea-functionalized crystalline capsules for recognition and separation of tetrahedral oxoanions

    Energy Technology Data Exchange (ETDEWEB)

    Custelcean, Radu [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division

    2012-12-21

    We reviewed the persistent ability of tripodal TREN-based tris-urea receptors (TREN = tris(2-aminoethyl)amine) to self-assemble with a variety of oxoanions into dimeric capsules upon crystallization. The capsule crystallization allows for charge-, shape-, and size-selective encapsulation of tetrahedral XO4n-anions (n = 2,3), and provides an effective way to separate these anions from competitive aqueous environments.

  15. Simulation of Stagnation Region Heating in Hypersonic Flow on Tetrahedral Grids

    Science.gov (United States)

    Gnoffo, Peter A.

    2007-01-01

    Hypersonic flow simulations using the node based, unstructured grid code FUN3D are presented. Applications include simple (cylinder) and complex (towed ballute) configurations. Emphasis throughout is on computation of stagnation region heating in hypersonic flow on tetrahedral grids. Hypersonic flow over a cylinder provides a simple test problem for exposing any flaws in a simulation algorithm with regard to its ability to compute accurate heating on such grids. Such flaws predominantly derive from the quality of the captured shock. The importance of pure tetrahedral formulations are discussed. Algorithm adjustments for the baseline Roe / Symmetric, Total-Variation-Diminishing (STVD) formulation to deal with simulation accuracy are presented. Formulations of surface normal gradients to compute heating and diffusion to the surface as needed for a radiative equilibrium wall boundary condition and finite catalytic wall boundary in the node-based unstructured environment are developed. A satisfactory resolution of the heating problem on tetrahedral grids is not realized here; however, a definition of a test problem, and discussion of observed algorithm behaviors to date are presented in order to promote further research on this important problem.

  16. Towards accurate models for amorphous GeTe: Crucial effect of dispersive van der Waals corrections on the structural properties involved in the phase-change mechanism

    Science.gov (United States)

    Micoulaut, M.; Piarristeguy, A.; Flores-Ruiz, H.; Pradel, A.

    2017-11-01

    The effect of van der Waals dispersion correction in combination with density functional theory is investigated on a canonical amorphous phase-change material. Density functional theory (DFT), using the generalized gradient approximation, usually fails to reproduce the structure of amorphous tellurides, which manifests by an overestimation of the interatomic bond distances, and particularly the Ge-Te one involved in local geometries (tetrahedral or defect octahedral). Here, we take into account dispersion forces in a semiempirical way and apply such DFT simulations to amorphous GeTe. We obtain a substantial improvement of the simulated structure factor and pair-correlation function, which now reproduce the experimental counterparts with an unprecedented accuracy, including on a recent partial contribution from anomalous x-ray scattering and from x-ray absorption. A detailed analysis of the corresponding structures indicates that the dispersion correction reduces the Ge-Te bond length, increases the fraction of tetrahedral germanium, and reduces the presence of heteropolar so-called fourfold ABAB rings. Given that these structural features have been stressed to be central for the understanding of the phase-change mechanism, the present results challenge our current understanding of the crystal to amorphous transformation at play.

  17. Deduced elasticity of sp3-bonded amorphous diamond

    Science.gov (United States)

    Ballato, J.; Ballato, A.

    2017-11-01

    Amorphous diamond was recently synthesized using high temperature and pressure techniques [Z. Zeng, L. Yang, Q. Zeng, H. Lou, H. Sheng, J. Wen, D. J. Miller, Y. Meng, W. Yang, W. L. Mao, and H. K. Mao, Nat. Commun. 8, 322 (2017)]. Here, selected physical properties of this new phase of carbon are deduced using an extension of the Voigt-Reuss-Hill (VRHx) methodology whereby single crystal values are averaged over all orientations to yield values for the amorphous analog. Specifically, the elastic constants were deduced to be c11 = 1156.5 GPa, c12 = 87.6 GPa, and c44 = 534.5 GPa, whereas the Young's modulus, bulk modulus, and Poisson's ratio were also estimated to be 1144.2 GPa, 443.9 GPa, and 0.0704, respectively. These numbers are compared with experimental and theoretical literature values for other allotropic forms, specifically, Lonsdaleite, and two forms each of graphite and amorphous carbon. It is unknown at this time how the high temperature and pressure synthesis approach employed influences the structure, hence properties, of amorphous diamond at room temperature. However, the values provided herein constitute a baseline against which future structure/property/processing analyses can be compared.

  18. Fundamentals of amorphous solids structure and properties

    CERN Document Server

    Stachurski, Zbigniew H

    2014-01-01

    Long awaited, this textbook fills the gap for convincing concepts to describe amorphous solids. Adopting a unique approach, the author develops a framework that lays the foundations for a theory of amorphousness. He unravels the scientific mysteries surrounding the topic, replacing rather vague notions of amorphous materials as disordered crystalline solids with the well-founded concept of ideal amorphous solids. A classification of amorphous materials into inorganic glasses, organic glasses, glassy metallic alloys, and thin films sets the scene for the development of the model of ideal amorph

  19. Hidden structure in amorphous solids

    Energy Technology Data Exchange (ETDEWEB)

    Inam, F. [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States); Lewis, James P. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Drabold, D.A. [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States); Trinity College, Cambridge CB2 1TQ (United Kingdom)

    2010-03-15

    Recent theoretical studies of amorphous silicon (a-Si) [Pan et al., Phys. Rev. Lett. 100, 206403 (2008)] have revealed subtle but significant structural correlations in network topology: the tendency for short (long) bonds to be spatially correlated with other short (long) bonds. These structures were linked to the electronic band tails in the optical gap. In this paper, we further examine these issues for a-Si, and demonstrate that analogous correlations exist in amorphous SiO{sub 2}, and in the organic molecule, {beta}-carotene. We conclude with a discussion of the origin of the effects and its possible generality. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  20. The Physics of Amorphous Solids

    CERN Document Server

    Zallen, Richard

    1998-01-01

    An in-depth study of non-crystalline solids in which the arrangement of the atoms do not have long-range order. Describes the way amorphous solids are formed, the phenomenology of the liquid-to-glass and glass- to-liquid transition, and the technological applications. Emphasizes modern approaches such as scaling, localization, and percolation. Includes extensive treatment of structural aspects of amorphous solids, ranging from metallic glasses, to chalcogenides, to organic polymers. Incorporates illustrations for the clarification of physics concepts.

  1. Amorphous titanium-oxide supercapacitors

    Science.gov (United States)

    Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko

    2016-10-01

    The electric capacitance of an amorphous TiO2-x surface increases proportionally to the negative sixth power of the convex diameter d. This occurs because of the van der Waals attraction on the amorphous surface of up to 7 mF/cm2, accompanied by extreme enhanced electron trapping resulting from both the quantum-size effect and an offset effect from positive charges at oxygen-vacancy sites. Here we show that a supercapacitor, constructed with a distributed constant-equipment circuit of large resistance and small capacitance on the amorphous TiO2-x surface, illuminated a red LED for 37 ms after it was charged with 1 mA at 10 V. The fabricated device showed no dielectric breakdown up to 1,100 V. Based on this approach, further advances in the development of amorphous titanium-dioxide supercapacitors might be attained by integrating oxide ribbons with a micro-electro mechanical system.

  2. Atomistic Models of Amorphous Semiconductors

    NARCIS (Netherlands)

    Jarolimek, K.

    2011-01-01

    Crystalline silicon is probably the best studied material, widely used by the semiconductor industry. The subject of this thesis is an intriguing form of this element namely amorphous silicon. It can contain a varying amount of hydrogen and is denoted as a-Si:H. It completely lacks the neat long

  3. Chemically Realistic Tetrahedral Lattice Models for Polymer Chains: Application to Polyethylene Oxide.

    Science.gov (United States)

    Dietschreit, Johannes C B; Diestler, Dennis J; Knapp, Ernst W

    2016-05-10

    To speed up the generation of an ensemble of poly(ethylene oxide) (PEO) polymer chains in solution, a tetrahedral lattice model possessing the appropriate bond angles is used. The distance between noncovalently bonded atoms is maintained at realistic values by generating chains with an enhanced degree of self-avoidance by a very efficient Monte Carlo (MC) algorithm. Potential energy parameters characterizing this lattice model are adjusted so as to mimic realistic PEO polymer chains in water simulated by molecular dynamics (MD), which serves as a benchmark. The MD data show that PEO chains have a fractal dimension of about two, in contrast to self-avoiding walk lattice models, which exhibit the fractal dimension of 1.7. The potential energy accounts for a mild hydrophobic effect (HYEF) of PEO and for a proper setting of the distribution between trans and gauche conformers. The potential energy parameters are determined by matching the Flory radius, the radius of gyration, and the fraction of trans torsion angles in the chain. A gratifying result is the excellent agreement of the pair distribution function and the angular correlation for the lattice model with the benchmark distribution. The lattice model allows for the precise computation of the torsional entropy of the chain. The generation of polymer conformations of the adjusted lattice model is at least 2 orders of magnitude more efficient than MD simulations of the PEO chain in explicit water. This method of generating chain conformations on a tetrahedral lattice can also be applied to other types of polymers with appropriate adjustment of the potential energy function. The efficient MC algorithm for generating chain conformations on a tetrahedral lattice is available for download at https://github.com/Roulattice/Roulattice .

  4. Shutdown dose rate analysis with CAD geometry, Cartesian/tetrahedral mesh, and advanced variance reduction

    Energy Technology Data Exchange (ETDEWEB)

    Biondo, Elliott D., E-mail: biondo@wisc.edu; Davis, Andrew, E-mail: davisa@engr.wisc.edu; Wilson, Paul P.H., E-mail: wilsonp@engr.wisc.edu

    2016-05-15

    Highlights: • A CAD-based shutdown dose rate analysis workflow has been implemented. • Cartesian and superimposed tetrahedral mesh are fully supported. • Biased and unbiased photon source sampling options are available. • Hybrid Monte Carlo/deterministic techniques accelerate photon transport. • The workflow has been validated with the FNG-ITER benchmark problem. - Abstract: In fusion energy systems (FES) high-energy neutrons born from burning plasma activate system components to form radionuclides. The biological dose rate that results from photons emitted by these radionuclides after shutdown—the shutdown dose rate (SDR)—must be quantified for maintenance planning. This can be done using the Rigorous Two-Step (R2S) method, which involves separate neutron and photon transport calculations, coupled by a nuclear inventory analysis code. The geometric complexity and highly attenuating configuration of FES motivates the use of CAD geometry and advanced variance reduction for this analysis. An R2S workflow has been created with the new capability of performing SDR analysis directly from CAD geometry with Cartesian or tetrahedral meshes and with biased photon source sampling, enabling the use of the Consistent Adjoint Driven Importance Sampling (CADIS) variance reduction technique. This workflow has been validated with the Frascati Neutron Generator (FNG)-ITER SDR benchmark using both Cartesian and tetrahedral meshes and both unbiased and biased photon source sampling. All results are within 20.4% of experimental values, which constitutes satisfactory agreement. Photon transport using CADIS is demonstrated to yield speedups as high as 8.5·10{sup 5} for problems using the FNG geometry.

  5. Spatial analysis and auralization of room acoustics using a tetrahedral microphone.

    Science.gov (United States)

    Amengual Garí, Sebastià V; Lachenmayr, Winfried; Mommertz, Eckard

    2017-04-01

    A compact tetrahedral microphone array is used to measure several controlled sound fields and compare the analysis of spatial room impulse responses with two methods: spatial decomposition method (SDM) and IRIS, a commercial system based on sound intensity vector analysis. Results suggest that the spatial accuracy of both methods is similar and in most cases the error is comparable to the localization uncertainty of human listeners. Furthermore, a listening test is conducted comparing three 3D-sound fields and their SDM auralizations. Results suggest that the similarity of the auralized and original sound fields depends on the target room and stimulus.

  6. Highly Parallel Demagnetization Field Calculation Using the Fast Multipole Method on Tetrahedral Meshes with Continuous Sources

    CERN Document Server

    Palmesi, Pietro; Bruckner, Florian; Abert, Claas; Suess, Dieter

    2016-01-01

    The long-range magnetic field is the most time-consuming part in micromagnetic simulations. Improvements both on a numerical and computational basis can relief problems related to this bottleneck. This work presents an efficient implementation of the Fast Multipole Method [FMM] for the magnetic scalar potential as used in micromagnetics. We assume linearly magnetized tetrahedral sources, treat the near field directly and use analytical integration on the multipole expansion in the far field. This approach tackles important issues like the vectorial and continuous nature of the magnetic field. By using FMM the calculations scale linearly in time and memory.

  7. A ROBUST ARBITRARILY HIGH ORDER TRANSPORT METHOD OF THE CHARACTERISTIC TYPE FOR UNSTRUCTURED TETRAHEDRAL GRIDS

    Energy Technology Data Exchange (ETDEWEB)

    R. M. Ferrer; Y. Y. Azmy

    2009-05-01

    We present a robust arbitrarily high order transport method of the characteristic type for unstructured tetrahedral grids. Previously encountered difficulties have been addressed through the reformulation of the method based on coordinate transformations, evaluation of the moments balance relation as a linear system of equations involving the expansion coefficients of the projected basis, and the asymptotic expansion of the integral kernels in the thin cell limit. The proper choice of basis functions for the high-order spatial expansion of the solution is discussed and its effect on problems involving scattering discussed. Numerical tests are presented to illustrate the beneficial effect of these improvements, and the improved robustness they yield.

  8. Highly parallel demagnetization field calculation using the fast multipole method on tetrahedral meshes with continuous sources

    Science.gov (United States)

    Palmesi, P.; Exl, L.; Bruckner, F.; Abert, C.; Suess, D.

    2017-11-01

    The long-range magnetic field is the most time-consuming part in micromagnetic simulations. Computational improvements can relieve problems related to this bottleneck. This work presents an efficient implementation of the Fast Multipole Method [FMM] for the magnetic scalar potential as used in micromagnetics. The novelty lies in extending FMM to linearly magnetized tetrahedral sources making it interesting also for other areas of computational physics. We treat the near field directly and in use (exact) numerical integration on the multipole expansion in the far field. This approach tackles important issues like the vectorial and continuous nature of the magnetic field. By using FMM the calculations scale linearly in time and memory.

  9. Tetrahedral-Mesh Simulation of Turbulent Flows with the Space-Time Conservative Schemes

    Science.gov (United States)

    Chang, Chau-Lyan; Venkatachari, Balaji; Cheng, Gary C.

    2015-01-01

    Direct numerical simulations of turbulent flows are predominantly carried out using structured, hexahedral meshes despite decades of development in unstructured mesh methods. Tetrahedral meshes offer ease of mesh generation around complex geometries and the potential of an orientation free grid that would provide un-biased small-scale dissipation and more accurate intermediate scale solutions. However, due to the lack of consistent multi-dimensional numerical formulations in conventional schemes for triangular and tetrahedral meshes at the cell interfaces, numerical issues exist when flow discontinuities or stagnation regions are present. The space-time conservative conservation element solution element (CESE) method - due to its Riemann-solver-free shock capturing capabilities, non-dissipative baseline schemes, and flux conservation in time as well as space - has the potential to more accurately simulate turbulent flows using unstructured tetrahedral meshes. To pave the way towards accurate simulation of shock/turbulent boundary-layer interaction, a series of wave and shock interaction benchmark problems that increase in complexity, are computed in this paper with triangular/tetrahedral meshes. Preliminary computations for the normal shock/turbulence interactions are carried out with a relatively coarse mesh, by direct numerical simulations standards, in order to assess other effects such as boundary conditions and the necessity of a buffer domain. The results indicate that qualitative agreement with previous studies can be obtained for flows where, strong shocks co-exist along with unsteady waves that display a broad range of scales, with a relatively compact computational domain and less stringent requirements for grid clustering near the shock. With the space-time conservation properties, stable solutions without any spurious wave reflections can be obtained without a need for buffer domains near the outflow/farfield boundaries. Computational results for the

  10. Interplay between spin frustration and thermal entanglement in the exactly solved Ising–Heisenberg tetrahedral chain

    Energy Technology Data Exchange (ETDEWEB)

    Rojas, Onofre, E-mail: ors@dex.ufla.br [Departamento de Ciencias Exatas, Universidade Federal de Lavras, 37200-000, Lavras-MG (Brazil); Strečka, Jozef [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Lyra, Marcelo L. [Instituto de Física, Universidade Federal de Alagoas, 57072-970, Maceio-AL (Brazil)

    2013-05-03

    The spin-1/2 Ising–Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry (the total spin of the Heisenberg bonds is locally conserved) and the transfer-matrix approach. Exact results derived for spin–spin correlation functions are employed to obtain the frustration temperature. In addition, we have exactly calculated a concurrence quantifying thermal entanglement. It is shown that the frustration and threshold temperature coincide at sufficiently low temperatures, while they exhibit a very different behavior in the high-temperature region when tending towards completely different asymptotic limits. The threshold temperature additionally shows a notable reentrant behavior when it extends over a narrow temperature region above the classical ground state without any quantum correlations. -- Highlights: ► Using local gauge symmetry we solved the spin-1/2 Ising–Heisenberg tetrahedral chain. ► The frustration temperature was calculated using the correlation functions. ► Thermal entanglement, concurrence and threshold temperature were analyzed. ► The zero-field specific heat was exactly calculated and discussed.

  11. Evolution of stacking fault tetrahedral and work hardening effect in copper single crystals

    Science.gov (United States)

    Liu, Hai Tao; Zhu, Xiu Fu; Sun, Ya Zhou; Xie, Wen Kun

    2017-11-01

    Stacking fault tetrahedral (SFT), generated in machining of copper single crystal as one type of subsurface defects, has significant influence on the performance of workpiece. In this study, molecular dynamics (MD) simulation is used to investigate the evolution of stacking fault tetrahedral in nano-cutting of copper single crystal. The result shows that SFT is nucleated at the intersection of differently oriented stacking fault (SF) planes and SFT evolves from the preform only containing incomplete surfaces into a solid defect. The evolution of SFT contains several stress fluctuations until the complete formation. Nano-indentation simulation is then employed on the machined workpiece from nano-cutting, through which the interaction between SFT and later-formed dislocations in subsurface is studied. In the meanwhile, force-depth curves obtained from nano-indentation on pristine and machined workpieces are compared to analyze the mechanical properties. By simulation of nano-cutting and nano-indentation, it is verified that SFT is a reason of the work hardening effect.

  12. A Reconstructed Discontinuous Galerkin Method for the Compressible Flows on Unstructured Tetrahedral Grids

    Energy Technology Data Exchange (ETDEWEB)

    Hong Luo; Yidong Xia; Robert Nourgaliev; Chunpei Cai

    2011-06-01

    A reconstruction-based discontinuous Galerkin (RDG) method is presented for the solution of the compressible Navier-Stokes equations on unstructured tetrahedral grids. The RDG method, originally developed for the compressible Euler equations, is extended to discretize viscous and heat fluxes in the Navier-Stokes equations using a so-called inter-cell reconstruction, where a smooth solution is locally reconstructed using a least-squares method from the underlying discontinuous DG solution. Similar to the recovery-based DG (rDG) methods, this reconstructed DG method eliminates the introduction of ad hoc penalty or coupling terms commonly found in traditional DG methods. Unlike rDG methods, this RDG method does not need to judiciously choose a proper form of a recovered polynomial, thus is simple, flexible, and robust, and can be used on unstructured grids. The preliminary results indicate that this RDG method is stable on unstructured tetrahedral grids, and provides a viable and attractive alternative for the discretization of the viscous and heat fluxes in the Navier-Stokes equations.

  13. Artificial intelligence approach to planning the robotic assembly of large tetrahedral truss structures

    Science.gov (United States)

    Homemdemello, Luiz S.

    1992-01-01

    An assembly planner for tetrahedral truss structures is presented. To overcome the difficulties due to the large number of parts, the planner exploits the simplicity and uniformity of the shapes of the parts and the regularity of their interconnection. The planning automation is based on the computational formalism known as production system. The global data base consists of a hexagonal grid representation of the truss structure. This representation captures the regularity of tetrahedral truss structures and their multiple hierarchies. It maps into quadratic grids and can be implemented in a computer by using a two-dimensional array data structure. By maintaining the multiple hierarchies explicitly in the model, the choice of a particular hierarchy is only made when needed, thus allowing a more informed decision. Furthermore, testing the preconditions of the production rules is simple because the patterned way in which the struts are interconnected is incorporated into the topology of the hexagonal grid. A directed graph representation of assembly sequences allows the use of both graph search and backtracking control strategies.

  14. Amorphous metal-organic frameworks.

    Science.gov (United States)

    Bennett, Thomas D; Cheetham, Anthony K

    2014-05-20

    Crystalline metal-organic frameworks (MOFs) are porous frameworks comprising an infinite array of metal nodes connected by organic linkers. The number of novel MOF structures reported per year is now in excess of 6000, despite significant increases in the complexity of both component units and molecular networks. Their regularly repeating structures give rise to chemically variable porous architectures, which have been studied extensively due to their sorption and separation potential. More recently, catalytic applications have been proposed that make use of their chemical tunability, while reports of negative linear compressibility and negative thermal expansion have further expanded interest in the field. Amorphous metal-organic frameworks (aMOFs) retain the basic building blocks and connectivity of their crystalline counterparts, though they lack any long-range periodic order. Aperiodic arrangements of atoms result in their X-ray diffraction patterns being dominated by broad "humps" caused by diffuse scattering and thus they are largely indistinguishable from one another. Amorphous MOFs offer many exciting opportunities for practical application, either as novel functional materials themselves or facilitating other processes, though the domain is largely unexplored (total aMOF reported structures amounting to under 30). Specifically, the use of crystalline MOFs to detect harmful guest species before subsequent stress-induced collapse and guest immobilization is of considerable interest, while functional luminescent and optically active glass-like materials may also be prepared in this manner. The ion transporting capacity of crystalline MOFs might be improved during partial structural collapse, while there are possibilities of preparing superstrong glasses and hybrid liquids during thermal amorphization. The tuning of release times of MOF drug delivery vehicles by partial structural collapse may be possible, and aMOFs are often more mechanically robust than

  15. Amorphous metal based nanoelectromechanical switch

    KAUST Repository

    Mayet, Abdulilah M.

    2013-04-01

    Nanoelectromechanical (NEM) switch is an interesting ultra-low power option which can operate in the harsh environment and can be a complementary element in complex digital circuitry. Although significant advancement is happening in this field, report on ultra-low voltage (pull-in) switch which offers high switching speed and area efficiency is yet to be made. One key challenge to achieve such characteristics is to fabricate nano-scale switches with amorphous metal so the shape and dimensional integrity are maintained to achieve the desired performance. Therefore, we report a tungsten alloy based amorphous metal with fabrication process development of laterally actuated dual gated NEM switches with 100 nm width and 200 nm air-gap to result in <5 volts of actuation voltage (Vpull-in). © 2013 IEEE.

  16. Topological Insulators in Amorphous Systems

    Science.gov (United States)

    Agarwala, Adhip; Shenoy, Vijay B.

    2017-06-01

    Much of the current understanding of topological insulators, which informs the experimental search for topological materials and systems, is based on crystalline band theory, where local electronic degrees of freedom at different crystal sites hybridize with each other in ways that produce nontrivial topology. Here we provide a novel theoretical demonstration of realizing topological phases in amorphous systems, as exemplified by a set of sites randomly located in space. We show this by constructing hopping models on such random lattices whose gapped ground states are shown to possess nontrivial topological nature (characterized by Bott indices) that manifests as quantized conductances in systems with a boundary. Our study adds a new dimension, beyond crystalline solids, to the search for topological systems by pointing to the promising possibilities in amorphous solids and other engineered random systems.

  17. Development of empirical potentials for amorphous silica

    Energy Technology Data Exchange (ETDEWEB)

    Carre, A.

    2007-09-15

    Amorphous silica (SiO{sub 2}) is of great importance in geoscience and mineralogy as well as a raw material in glass industry. Its structure is characterized as a disordered continuous network of SiO{sub 4} tetrahedra. Many efforts have been undertaken to understand the microscopic properties of silica by classical molecular dynamics (MD) simulations. In this method the interatomic interactions are modeled by an effective potential that does not take explicitely into account the electronic degrees of freedom. In this work, we propose a new methodology to parameterize such a potential for silica using ab initio simulations, namely Car-Parrinello (CP) method [Phys. Rev. Lett. 55, 2471 (1985)]. The new potential proposed is compared to the BKS potential [Phys. Rev. Lett. 64, 1955 (1990)] that is considered as the benchmark potential for silica. First, CP simulations have been performed on a liquid silica sample at 3600 K. The structural features so obtained have been compared to the ones predicted by the classical BKS potential. Regarding the bond lengths the BKS tends to underestimate the Si-O bond whereas the Si-Si bond is overestimated. The inter-tetrahedral angular distribution functions are also not well described by the BKS potential. The corresponding mean value of the SiOSi angle is found to be {approx_equal} 147 , while the CP yields to a SiOSi angle centered around 135 . Our aim is to fit a classical Born-Mayer/Coulomb pair potential using ab initio calculations. To this end, we use the force-matching method proposed by Ercolessi and Adams [Europhys. Lett. 26, 583 (1994)]. The CP configurations and their corresponding interatomic forces have been considered for a least square fitting procedure. The classical MD simulations with the resulting potential have lead to a structure that is very different from the CP one. Therefore, a different fitting criterion based on the CP partial pair correlation functions was applied. Using this approach the resulting

  18. Colloidal Photoluminescent Amorphous Porous Silicon, Methods Of Making Colloidal Photoluminescent Amorphous Porous Silicon, And Methods Of Using Colloidal Photoluminescent Amorphous Porous Silicon

    KAUST Repository

    Chaieb, Sahraoui

    2015-04-09

    Embodiments of the present disclosure provide for a colloidal photoluminescent amorphous porous silicon particle suspension, methods of making a colloidal photoluminescent amorphous porous silicon particle suspension, methods of using a colloidal photoluminescent amorphous porous silicon particle suspension, and the like.

  19. Carbonation of C–S–H and C–A–S–H samples studied by {sup 13}C, {sup 27}Al and {sup 29}Si MAS NMR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sevelsted, Tine F.; Skibsted, Jørgen, E-mail: jskib@chem.au.dk

    2015-05-15

    Synthesized calcium silicate hydrate (C–S–H) samples with Ca/Si ratios of 0.66, 1.0, and 1.5 have been exposed to atmospheric CO{sub 2} at room temperature and high relative humidity and studied after one to 12 weeks. {sup 29}Si NMR reveals that the decomposition of C–S–H caused by carbonation involves two steps and that the decomposition rate decreases with increasing Ca/Si ratio. The first step is a gradual decalcification of the C–S–H where calcium is removed from the interlayer and defect sites in the silicate chains until Ca/Si = 0.67 is reached, ideally corresponding to infinite silicate chains. In the seconds step, calcium from the principal layers is consumed, resulting in the final decomposition of the C–S–H and the formation of an amorphous silica phase composed of Q{sup 3} and Q{sup 4} silicate tetrahedra. The amount of solid carbonates and of carbonate ions in a hydrous environment increases with increasing Ca/Si ratio for the C–S–H, as shown by {sup 13}C NMR. For C–A–S–H samples with Ca/Si = 1.0 and 1.5, {sup 27}Al NMR demonstrates that all aluminium sites associated with the C–S–H are consumed during the carbonation reactions and incorporated mainly as tetrahedral Al(–OSi){sub 4} units in the amorphous silica phase. A small amount of penta-coordinated Al sites has also been identified in the silica phase.

  20. Interplay between spin frustration and thermal entanglement in the exactly solved Ising-Heisenberg tetrahedral chain

    Science.gov (United States)

    Rojas, Onofre; Strečka, Jozef; Lyra, Marcelo L.

    2013-05-01

    The spin-1/2 Ising-Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry (the total spin of the Heisenberg bonds is locally conserved) and the transfer-matrix approach. Exact results derived for spin-spin correlation functions are employed to obtain the frustration temperature. In addition, we have exactly calculated a concurrence quantifying thermal entanglement. It is shown that the frustration and threshold temperature coincide at sufficiently low temperatures, while they exhibit a very different behavior in the high-temperature region when tending towards completely different asymptotic limits. The threshold temperature additionally shows a notable reentrant behavior when it extends over a narrow temperature region above the classical ground state without any quantum correlations.

  1. An assessment of the adaptive unstructured tetrahedral grid, Euler Flow Solver Code FELISA

    Science.gov (United States)

    Djomehri, M. Jahed; Erickson, Larry L.

    1994-01-01

    A three-dimensional solution-adaptive Euler flow solver for unstructured tetrahedral meshes is assessed, and the accuracy and efficiency of the method for predicting sonic boom pressure signatures about simple generic models are demonstrated. Comparison of computational and wind tunnel data and enhancement of numerical solutions by means of grid adaptivity are discussed. The mesh generation is based on the advancing front technique. The FELISA code consists of two solvers, the Taylor-Galerkin and the Runge-Kutta-Galerkin schemes, both of which are spacially discretized by the usual Galerkin weighted residual finite-element methods but with different explicit time-marching schemes to steady state. The solution-adaptive grid procedure is based on either remeshing or mesh refinement techniques. An alternative geometry adaptive procedure is also incorporated.

  2. Relative Positioning Evaluation of a Tetrahedral Flight Formation’s Satellites

    Science.gov (United States)

    Mahler, W. F. C.; Rocco, E. M.; Santos, D. P. S.

    2017-10-01

    This paper presents a study about the tetrahedral layout of four satellites in a way that every half-orbital period this set groups together while flying in formation. The formation is calculated analyzing the problem from a geometrical perspective and disposed by precisely adjusting the orbital parameters of each satellite. The dynamic modelling considers the orbital motion equations. The results are analyzed, compared and discussed. A detection algorithm is used as flag to signal the regular tetrahedron’s exact moments of occurrence. To do so, the volume calculated during the simulation is compared to the real volume, based on the initial conditions of the exact moment of formation and respecting a tolerance. This tolerance value is stablished arbitrarily depending on the mission and the formation’s geometrical parameters. The simulations will run on a computational environment.

  3. Optical properties of the filled tetrahedral semiconductors LiMgX (X = N, P and As)

    Energy Technology Data Exchange (ETDEWEB)

    Kalarasse, F; Bennecer, B; Mellouki, A [Physics Laboratory at Guelma, Faculty of Science and Engineering, University of Guelma, PO Box 401 Guelma 24000 (Algeria)

    2006-08-09

    First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the electronic and optical properties of the filled tetrahedral compounds LiMgN, LiMgP and LiMgAs. The bandgap trend in the ternaries is found to be similar to the one encountered in the zinc-blende AlX. The assignment of the structures in the optical spectra and band structure transitions are investigated in detail. The predicted values of the dielectric constants for LiMgN, LiMgP and LiMgAs are close to those of the binary compounds AlN, AlP and AlAs.

  4. Geometrically nonlinear analysis of hyperelastic solids by high-order tetrahedral finite elements

    Science.gov (United States)

    Pascon, João P.; Coda, Humberto B.

    2010-06-01

    The purpose of this study is to develop a computer code for accurate prediction of the mechanical behavior of hyperelastic solids under large deformation and finite strains. It is used, in the present work, the Lagrangian positional version of the Finite Element Method, in which the degrees of freedom are current positions instead of displacements. The main mechanical variables are the Green-Lagrange strain and the second Piola-Kirchhoff stress tensors. Isoparametric tetrahedral solid finite element of any approximation degree is employed with full integration in order to obtain accuracy. In order to be general, it is developed a numerical strategy to determine the shape functions coefficients of any order, following tetrahedral basis. The solid equilibrium is achieved at the current position by means of the Minimal Potential Energy Principle regarding positions and is solved by the Newton-Raphson iterative scheme. It is important to mention that the adopted constitutive laws are nonlinear, isotropic and homogeneous hyperelastic, normally used in mechanical analysis of elastomers, with the near compressibility assumption. It is applied the Flory decomposition, i.e., the multiplicative split of the deformation gradient into a volumetric and an isochoric part. A parallel processing strategy is used to increase the simulation speed and memory capacity, justifying the use of high order elements for solid analysis. Results confirm that the developed computer code is capable of predicting the static behavior of complex problems, such as Cook's membrane and partially loaded block. The shape functions generator code exhibits simplicity and, thus, it may be easily implemented in other finite elements. The increase in the order of approximation and the mesh refinement improve accuracy and, therefore, the proposed methodology together with parallel computing indicate a safe way for further developments in plasticity and damage mechanics for large strain and deformations.

  5. On Structure and Properties of Amorphous Materials

    Directory of Open Access Journals (Sweden)

    Zbigniew H. Stachurski

    2011-09-01

    Full Text Available Mechanical, optical, magnetic and electronic properties of amorphous materials hold great promise towards current and emergent technologies. We distinguish at least four categories of amorphous (glassy materials: (i metallic; (ii thin films; (iii organic and inorganic thermoplastics; and (iv amorphous permanent networks. Some fundamental questions about the atomic arrangements remain unresolved. This paper focuses on the models of atomic arrangements in amorphous materials. The earliest ideas of Bernal on the structure of liquids were followed by experiments and computer models for the packing of spheres. Modern approach is to carry out computer simulations with prediction that can be tested by experiments. A geometrical concept of an ideal amorphous solid is presented as a novel contribution to the understanding of atomic arrangements in amorphous solids.

  6. On Structure and Properties of Amorphous Materials.

    Science.gov (United States)

    Stachurski, Zbigniew H

    2011-09-15

    Mechanical, optical, magnetic and electronic properties of amorphous materials hold great promise towards current and emergent technologies. We distinguish at least four categories of amorphous (glassy) materials: (i) metallic; (ii) thin films; (iii) organic and inorganic thermoplastics; and (iv) amorphous permanent networks. Some fundamental questions about the atomic arrangements remain unresolved. This paper focuses on the models of atomic arrangements in amorphous materials. The earliest ideas of Bernal on the structure of liquids were followed by experiments and computer models for the packing of spheres. Modern approach is to carry out computer simulations with prediction that can be tested by experiments. A geometrical concept of an ideal amorphous solid is presented as a novel contribution to the understanding of atomic arrangements in amorphous solids.

  7. The physics and applications of amorphous semiconductors

    CERN Document Server

    Madan, Arun

    1988-01-01

    This comprehensive, detailed treatise on the physics and applications of the new emerging technology of amorphous semiconductors focuses on specific device research problems such as the optimization of device performance. The first part of the book presents hydrogenated amorphous silicon type alloys, whose applications include inexpensive solar cells, thin film transistors, image scanners, electrophotography, optical recording and gas sensors. The second part of the book discusses amorphous chalcogenides, whose applications include electrophotography, switching, and memory elements. This boo

  8. Fracture Phenomena in Amorphous Selenium

    DEFF Research Database (Denmark)

    Lindegaard-Andersen, Asger; Dahle, Birgit

    1966-01-01

    Fracture surfaces of amorphous selenium broken in flexure at room temperature have been studied. The fracture velocity was found to vary in different regions of the fracture surface. Peculiar features were observed in a transition zone between fast and slower fracture. In this zone cleavage steps...... with a nearly constant spacing of approximately 1 µ were found. Occasionally long cleavage whiskers—up to some millimeters long—were observed. Within certain regions the cleavage steps were crossed and interrupted by two line systems. The maximum fracture velocity has been measured to 350 m/sec. Further...

  9. Application of valence-to-core X-ray emission spectroscopy for identification and estimation of amount of carbon covalently bonded to chromium in amorphous Cr-C coatings prepared by magnetron sputtering

    Science.gov (United States)

    Safonov, V. A.; Habazaki, H.; Glatzel, P.; Fishgoit, L. A.; Drozhzhin, O. A.; Lafuerza, S.; Safonova, O. V.

    2018-01-01

    Cr-C coatings containing different amount of carbon ranging from ∼5 to 50 at.% were prepared by the direct current (DC) magnetron sputtering on a polished substrate of polycrystalline silicon. The thickness of the samples was about 400 nm. We characterized the composition and the structure of the as-received coatings and those annealed at 500 °C by X-ray diffraction (XRD), Energy dispersion X-ray spectroscopy (EDX) and valence-to-core X-ray emission spectroscopy (vtc-XES) methods As follows from XRD measurements, the samples with the carbon content above 35 at.% do not demonstrate any sign of the long-range order and annealing at 500 °C does not change their crystallinity. The vtc-XES curves of the as-prepared and annealed samples can be fitted as a superposition of corresponding spectra of chromium metal and chromium carbide (Cr3C2) phases. After the annealing, the content of carbides in the samples (and, correspondingly, the content of covalently bonded carbon) somewhat increases. This suggests that the as-received coatings contain a certain amount of carbon that is not covalently bonded to chromium (most likely, elemental carbon) and their annealing at 500 °C transforms this carbon into the additional (of the order of 2-5 at.%) amount of chromium carbide compounds. It deserves mentioning that for Cr-C coatings prepared by the electrochemical deposition from Cr(III) electrolytes containing organic compounds we have not observed changes in the vtc-X-ray emission spectra after similar annealing. This suggests that electrochemical deposition method in contrast to magnetron sputtering technique even at low temperatures favors the formation of only covalently bonded carbon.

  10. Electronic Transitions as a Probe of Tetrahedral versus Octahedral Coordination in Nickel(II) Complexes: An Undergraduate Inorganic Chemistry Experiment.

    Science.gov (United States)

    Filgueiras, Carlos A. L.; Carazza, Fernando

    1980-01-01

    Discusses procedures, theoretical considerations, and results of an experiment involving the preparation of a tetrahedral nickel(II) complex and its transformation into an octahedral species. Suggests that fundamental aspects of coordination chemistry can be demonstrated by simple experiments performed in introductory level courses. (Author/JN)

  11. The asc trinodal platform: Two-step assembly of triangular, tetrahedral, and trigonal-prismatic molecular building blocks

    KAUST Repository

    Schoedel, Alexander

    2013-02-10

    The self-assembly of triangular, tetrahedral, and trigonal-prismatic molecular building blocks affords the first example of a trinodal family of metal-organic materials. Four examples of isoreticular expanded and functionalized frameworks are detailed. Gas adsorption experiments validated the permanent porosity of the parent structure. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Interacting spin-1/2 tetrahedral system Cu2Te2O5X2 (X = Cl, Br)

    DEFF Research Database (Denmark)

    Jensen, Jens

    2009-01-01

    Magnetic ordering and excitations of Cu2Te2O5Cl2 are analyzed in terms of a tetramerized spin model for the tetrahedral Cu clusters of spin 1/2. The mean-field model is able to account for the main properties of the incommensurable magnetic structure observed by Zaharko et al. [Phys. Rev. B 73, 0...

  13. Neutron diffraction and thermal studies of amorphous CS{sub 2} realised by low-temperature vapour deposition

    Energy Technology Data Exchange (ETDEWEB)

    Yamamuro, O.; Matsuo, T. [Osaka Univ., Dept. of Chemistry, Graduate School of Sciences (Japan); Onoda-Yamamuro, N. [Tokyo Denki Univ., College of Sciences and Technology (Japan); Takeda, K. [Naruto Univ., Dept. of Chemistry, Tokushima (Japan); Munemura, H.; Tanaka, S.; Misawa, M. [Niigata Univ. (Japan). Faculty of Science

    2003-08-01

    We have succeeded in preparing amorphous carbon disulphide (CS{sub 2}) by depositing its vapour on a cold substrate at 10 K. Complete formation of the amorphous state has been confirmed by neutron diffraction and differential thermal analysis (DTA). The amorphous sample crystallized at ca. 70 K, which is lower than the hypothetical glass transition temperature (92 K) estimated from the DTA data of the (CS{sub 2}){sub x}(S{sub 2}Cl{sub 2}){sub 1-x} binary mixture. CS{sub 2}, a symmetric linear tri-atomic molecule, is the simplest of the amorphized molecular substances whose structural and thermal information has been reported so far. Comparison of the static structure factors S(Q) has shown that the orientational correlation of CS{sub 2} molecules may be much stronger in the amorphous state than in the liquid state at higher temperature. (authors)

  14. Alternative catalytic materials: carbides, nitrides, phosphides and amorphous boron alloys.

    Science.gov (United States)

    Alexander, Anne-Marie; Hargreaves, Justin S J

    2010-11-01

    Catalysts generated by the addition of carbon, nitrogen or phosphorus to transition metals have interesting properties and potential applications. The addition of carbon, nitrogen or phosphorus can lead to substantial modification of the catalytic efficacy of the parent metal and some carbides and nitrides are claimed to be comparable to noble metals in their behaviour. Amorphous boron transition metal alloys are also a class of interesting catalyst, although their structures and phase composition are more difficult to define. In this critical review, the preparation of these catalysts is described and brief details of their application given. To date, attention has largely centred upon the application of these materials as alternatives for existing catalysts. However, novel approaches towards their utilisation can be envisaged. For example, the extent to which it is possible to utilise the "activated" carbon and nitrogen species within the host lattices of carbides and nitrides, respectively, as a reactant remains largely unexplored (195 references).

  15. Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy

    Energy Technology Data Exchange (ETDEWEB)

    McMullan, G., E-mail: gm2@mrc-lmb.cam.ac.uk; Vinothkumar, K.R.; Henderson, R.

    2015-11-15

    We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å{sup 2} for every incident 300 keV e{sup −}/Å{sup 2}. The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e{sup −}/Å{sup 2} per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. - Highlights: • Thon rings can be seen from amorphous ice. • Radiation damage to amorphous ice randomly displaces water molecules. • Each incident 300 keV e{sup −}/Å{sup 2} displaces water molecules on average by ∼1 Å. • Macromolecules embedded in amorphous ice undergo beam induced Brownian motion.

  16. Theoretical Considerations in Developing Amorphous Solid Dispersions

    DEFF Research Database (Denmark)

    Laitinen, Riikka; Priemel, Petra Alexandra; Surwase, Sachin

    2014-01-01

    Before pursuing the laborious route of amorphous solid dispersion formulation and development, which is the topic of many of the subsequent chapters in this book, the formulation scientist would benefit from a priori knowledge whether the amorphous route is a viable one for a given drug and how m...

  17. Neutron irradiation induced amorphization of silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Snead, L.L.; Hay, J.C. [Oak Ridge National Lab., TN (United States)

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  18. Locomotion of Amorphous Surface Robots

    Science.gov (United States)

    Bradley, Arthur T. (Inventor)

    2016-01-01

    An amorphous robot includes a compartmented bladder containing fluid, a valve assembly, and an outer layer encapsulating the bladder and valve assembly. The valve assembly draws fluid from a compartment(s) and discharges the drawn fluid into a designated compartment to displace the designated compartment with respect to the surface. Another embodiment includes elements each having a variable property, an outer layer that encapsulates the elements, and a control unit. The control unit energizes a designated element to change its variable property, thereby moving the designated element. The elements may be electromagnetic spheres with a variable polarity or shape memory polymers with changing shape and/or size. Yet another embodiment includes an elongated flexible tube filled with ferrofluid, a moveable electromagnet, an actuator, and a control unit. The control unit energizes the electromagnet and moves the electromagnet via the actuator to magnetize the ferrofluid and lengthen the flexible tube.

  19. Slow magnetic relaxation at zero field in the tetrahedral complex [Co(SPh)4]2-.

    Science.gov (United States)

    Zadrozny, Joseph M; Long, Jeffrey R

    2011-12-28

    The Ph(4)P(+) salt of the tetrahedral complex [Co(SPh)(4)](2-), possessing an S = (3)/(2) ground state with an axial zero-field splitting of D = -70 cm(-1), displays single-molecule magnet behavior in the absence of an applied magnetic field. At very low temperatures, ac magnetic susceptibility data show the magnetic relaxation time, τ, to be temperature-independent, while above 2.5 K thermally activated Arrhenius behavior is apparent with U(eff) = 21(1) cm(-1) and τ(0) = 1.0(3) × 10(-7) s. Under an applied field of 1 kOe, τ more closely approximates Arrhenius behavior over the entire temperature range. Upon dilution of the complex within a matrix of the isomorphous compound (Ph(4)P)(2)[Zn(SPh)(4)], ac susceptibility data reveal the molecular nature of the slow magnetic relaxation and indicate that the quantum tunneling pathway observed at low temperatures is likely mediated by intermolecular dipolar interactions. © 2011 American Chemical Society

  20. Tetrahedral node for Transmission-Line Modeling (TLM) applied to Bio-heat Transfer.

    Science.gov (United States)

    Milan, Hugo F M; Gebremedhin, Kifle G

    2016-12-01

    Transmission-Line Modeling (TLM) is a numerical method used to solve complex and time-domain bio-heat transfer problems. In TLM, parallelepipeds are used to discretize three-dimensional problems. The drawback in using parallelepiped shapes is that instead of refining only the domain of interest, a large additional domain would also have to be refined, which results in increased computational time and memory space. In this paper, we developed a tetrahedral node for TLM applied to bio-heat transfer that does not have the drawback associated with the parallelepiped node. The model includes heat source, blood perfusion, boundary conditions and initial conditions. The boundary conditions could be adiabatic, temperature, heat flux, or convection. The predicted temperature and heat flux were compared against results from an analytical solution and the results agreed within 2% for a mesh size of 69,941 nodes and a time step of 5ms. The method was further validated against published results of maximum skin-surface temperature difference in a breast with and without tumor and the results agreed within 6%. The published results were obtained from a model that used parallelepiped TLM node. An open source software, TLMBHT, was written using the theory developed herein and is available for download free-of-charge. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Intense turquoise colors of apatite-type compounds with Mn5+ in tetrahedral coordination

    Science.gov (United States)

    Medina, Elena A.; Li, Jun; Stalick, Judith K.; Subramanian, M. A.

    2016-02-01

    The solid solutions of chlorapatite compounds Ba5Mn3-xVxO12Cl (x = 0-3.0) and Ba5Mn3-xPxO12Cl (x = 0-3.0) have been synthesized through solid state reactions and Pechini or sol-gel method using citric acid. The colors of the samples change from white (x = 3.0) through turquoise (x = 1.5) to dark green (x = 0) with increasing amount of manganese. Optical measurements reveal that the origin of the color is presumably a combination of d-d transitions of Mn5+ and cation-anion charge transfer from transition metals to oxygens. Near IR reflectance measurements indicate that synthesized compounds are promising materials for ;cool pigments; applications. Magnetic measurements verify that manganese has two unpaired electrons and exhibits 5 + oxidation state. The IR spectra change systematically with sample compositions and the fingerprint region (700 cm-1 to 1100 cm-1) indicates characteristic bands belonging to (MnO4)3-, (VO4)3- and (PO4)3- functional groups. Structure refinements using neutron data confirm that Mn5+, V5+ and P5+ cations occupy the tetrahedral sites in the apatite structure.

  2. Aptamer-Modified Tetrahedral DNA Nanostructure for Tumor-Targeted Drug Delivery.

    Science.gov (United States)

    Li, Qianshun; Zhao, Dan; Shao, Xiaoru; Lin, Shiyu; Xie, Xueping; Liu, Mengting; Ma, Wenjuan; Shi, Sirong; Lin, Yunfeng

    2017-10-25

    Tetrahedral DNA nanostructures (TDNs) are considered promising drug delivery carriers because they are able to permeate cellular membrane and are biocompatible and biodegradable. Furthermore, they can be modified by functional groups. To improve the drug-delivering ability of TDNs, we chose anticancer aptamer AS1411 to modify TDNs for tumor-targeted drug delivery. AS1411 can specifically bind to nucleolin, which is overexpressed on the cell membrane of tumor cells. Furthermore, AS1411 can inhibit NF-κB signaling and reduce the expression of bcl-2. In this study, we compared the intracellular localization of AS1411-modified TDNs (Apt-TDNs) with that of TDNs in different cells under hypoxic condition. Furthermore, we compared the effects of Apt-TDNs and TDNs on cell growth and cell cycle under hypoxic condition. A substantial amount of Apt-TDNs entered and accumulated in the nucleus of MCF-7 cells; however, the amount of Apt-TDNs that entered L929 cells was comparatively less. TDNs entered in much lower quantity in MCF-7 cells than Apt-TDNs. Moreover, there was little difference in the amount of TDNs that entered L929 cells and MCF-7 cells. Apt-TDNs can inhibit MCF-7 cell growth and promote L929 cell growth, while TDNs can promote both MCF-7 and L929 cell growth. Thus, the results indicate that Apt-TDNs are more effective tumor-targeted drug delivery vehicles than TDNs, with the ability to specifically inhibit tumor cell growth.

  3. 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

  4. Crystalline to amorphous transformation in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Cheruvu, S.M.

    1982-09-01

    In the present investigation, an attempt was made to understand the fundamental mechanism of crystalline-to-amorphous transformation in arsenic implanted silicon using high resolution electron microscopy. A comparison of the gradual disappearance of simulated lattice fringes with increasing Frenkel pair concentration with the experimental observation of sharp interfaces between crystalline and amorphous regions was carried out leading to the conclusion that when the defect concentration reaches a critical value, the crystal does relax to an amorphous state. Optical diffraction experiments using atomic models also supported this hypothesis. Both crystalline and amorphous zones were found to co-exist with sharp interfaces at the atomic level. Growth of the amorphous fraction depends on the temperature, dose rate and the mass of the implanted ion. Preliminary results of high energy electron irradiation experiments at 1.2 MeV also suggested that clustering of point defects occurs near room temperature. An observation in a high resolution image of a small amorphous zone centered at the core of a dislocation is presented as evidence that the nucleation of an amorphous phase is heterogeneous in nature involving clustering or segregation of point defects near existing defects.

  5. Compositions of corrosion-resistant Fe-based amorphous metals suitable for producing thermal spray coatings

    Science.gov (United States)

    Farmer, Joseph C; Wong, Frank M.G.; Haslam, Jeffery J; Ji, Xiaoyan; Day, Sumner D; Blue, Craig A; Rivard, John D.K.; Aprigliano, Louis F; Kohler, Leslie K; Bayles, Robert; Lemieux, Edward J; Yang, Nancy; Perepezko, John H; Kaufman, Larry; Heuer, Arthur; Lavernia, Enrique J

    2013-09-03

    A method of coating a surface comprising providing a source of amorphous metal that contains manganese (1 to 3 atomic %), yttrium (0.1 to 10 atomic %), and silicon (0.3 to 3.1 atomic %) in the range of composition given in parentheses; and that contains the following elements in the specified range of composition given in parentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic %), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to 16 atomic %), and the balance iron; and applying said amorphous metal to the surface by a spray.

  6. Computing Normal Shock-Isotropic Turbulence Interaction With Tetrahedral Meshes and the Space-Time CESE Method

    Science.gov (United States)

    Venkatachari, Balaji Shankar; Chang, Chau-Lyan

    2016-11-01

    The focus of this study is scale-resolving simulations of the canonical normal shock- isotropic turbulence interaction using unstructured tetrahedral meshes and the space-time conservation element solution element (CESE) method. Despite decades of development in unstructured mesh methods and its potential benefits of ease of mesh generation around complex geometries and mesh adaptation, direct numerical or large-eddy simulations of turbulent flows are predominantly carried out using structured hexahedral meshes. This is due to the lack of consistent multi-dimensional numerical formulations in conventional schemes for unstructured meshes that can resolve multiple physical scales and flow discontinuities simultaneously. The CESE method - due to its Riemann-solver-free shock capturing capabilities, non-dissipative baseline schemes, and flux conservation in time as well as space - has the potential to accurately simulate turbulent flows using tetrahedral meshes. As part of the study, various regimes of the shock-turbulence interaction (wrinkled and broken shock regimes) will be investigated along with a study on how adaptive refinement of tetrahedral meshes benefits this problem. The research funding for this paper has been provided by Revolutionary Computational Aerosciences (RCA) subproject under the NASA Transformative Aeronautics Concepts Program (TACP).

  7. Simultaneous travel time tomography for updating both velocity and reflector geometry in triangular/tetrahedral cell model

    Science.gov (United States)

    Bai, Chao-ying; He, Lei-yu; Li, Xing-wang; Sun, Jia-yu

    2017-12-01

    To conduct forward and simultaneous inversion in a complex geological model, including an irregular topography (or irregular reflector or velocity anomaly), we in this paper combined our previous multiphase arrival tracking method (referred as triangular shortest-path method, TSPM) in triangular (2D) or tetrahedral (3D) cell model and a linearized inversion solver (referred to as damped minimum norms and constrained least squares problem solved using the conjugate gradient method, DMNCLS-CG) to formulate a simultaneous travel time inversion method for updating both velocity and reflector geometry by using multiphase arrival times. In the triangular/tetrahedral cells, we deduced the partial derivative of velocity variation with respective to the depth change of reflector. The numerical simulation results show that the computational accuracy can be tuned to a high precision in forward modeling and the irregular velocity anomaly and reflector geometry can be accurately captured in the simultaneous inversion, because the triangular/tetrahedral cell can be easily used to stitch the irregular topography or subsurface interface.

  8. Pressure-induced reversible amorphization and an amorphous-amorphous transition in Ge₂Sb₂Te₅ phase-change memory material.

    Science.gov (United States)

    Sun, Zhimei; Zhou, Jian; Pan, Yuanchun; Song, Zhitang; Mao, Ho-Kwang; Ahuja, Rajeev

    2011-06-28

    Ge(2)Sb(2)Te(5) (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te-Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST.

  9. Bulk amorphous Mg-based alloys

    DEFF Research Database (Denmark)

    Pryds, Nini

    2004-01-01

    and a low glass transition temperature. The alloys were prepared by using a relatively simple technique, i.e. rapid cooling of the melt in a copper wedge mould. The essential structural changes that are achieved by going from the amorphous to the crystalline state through the supercooled liquid state...... are discussed in this paper. On the basis of these measurements phase diagrams of the different systems were constructed. Finally, it is demonstrated that when pressing the bulk amorphous alloy onto a metallic dies at temperatures within the supercooled liquid region, the alloy faithfully replicates the surface......The present paper describes the preparation and properties of bulk amorphous quarternary Mg-based alloys and the influence of additional elements on the ability of the alloy to form bulk amorphous. The main goal is to find a Mg-based alloy system which shows both high strength to weight ratio...

  10. Surface magnetic structures in amorphous ferromagnetic microwires

    Energy Technology Data Exchange (ETDEWEB)

    Usov, N.A., E-mail: usov@obninsk.ru [National University of Science and Technology «MISIS», 119049 Moscow (Russian Federation); Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, IZMIRAN, 108840 Troitsk, Moscow (Russian Federation); Serebryakova, O.N.; Gudoshnikov, S.A. [National University of Science and Technology «MISIS», 119049 Moscow (Russian Federation); Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, IZMIRAN, 108840 Troitsk, Moscow (Russian Federation); Tarasov, V.P. [National University of Science and Technology «MISIS», 119049 Moscow (Russian Federation)

    2017-05-01

    The spatial period of magnetization perturbations that occur near the surface of magnetic nanotube or nanowire under the influence of surface magnetic anisotropy is determined by means of numerical simulation as a function of the sample geometry and material parameters. The surface magnetization distribution obtained is then used to estimate the period of the surface magnetic texture in amorphous microwire of several micrometers in diameter by means of appropriate variational procedure. The period of the surface magnetic texture in amorphous microwire is found to be significantly smaller than the wire diameter. - Highlights: • Magnetic structure may arise near the magnetic nanotube surface under the influence of surface magnetic anisotropy. • The period of the surface magnetization pattern is calculated as a function of the sample geometry. • Similar magnetic structure may exist in amorphous microwire of several micrometers in diameter. • The period of the surface magnetic structure in amorphous wire is found to be significantly smaller than the wire diameter.

  11. Pressure-Induced Amorphization and Phase Transformations in LiAlSiO4 β-eucryptite

    Science.gov (United States)

    Zelinskas, M. V.; Zhang, J.

    2002-12-01

    It has been well-established that β-eucryptite (LiAlSiO4), a structural derivative of β-quartz (SiO2), exhibits negative thermal expansion along the c axis and near-zero volume thermal expansion over a wide temperature range of 300-1400 K. This behavior makes this compound a good candidate for testing model predications of a connection between negative thermal expansion and pressure-induced amorphizaation. Such a connection, as already demonstrated in compounds such as ice, silicon, and ZrW2O8, may help extend our understanding of the underlying mechanisms. In this study, β-eucryptite has been investigated under static compression up to 25 GPa using in-situ x-ray diffraction and quenching techniques. High-pressure x-ray diffraction patterns revealed that β-eucryptite underwent progressive amorphization at pressures above 3 GPa and became complete amorphous at 19 GPa. Quench experiments showed that, at pressures of 7.5, 14, and 17 GPa, the original crystalline phase was retained after pressure release. A complete amorphous phase, however, was recovered in the experiment conducted at 25 GPa. The observed amorphization at relatively low pressures extends previous model predictions for tetrahedrally bonded networks, which are restricted to compounds exhibiting negative volume thermal expansion. In addition, β-eucryptite does not appear to have structural memory when it becomes complete amorphous. For comparison, there seems to exist some non-deformable units within the partially amorphous β-eucryptite samples that allow the reversion back to the ordered state. β-eucryptite has also been studied at high pressure and temperature. At 1173 K and 11 GPa, β-eucryptite was decomposed to a mixture of spodumene (LiAlSi2O6) and LiAlO2. At 14-16 GPa and 1273 K, the two phases were recombined into a single phase with a spinel structure. At 22 GPa and 1673 K, we observed a mixture of oxides, MgO, Al2O3, and a new phase of Li2O. These observations suggest that the pressure

  12. Amorphous Phases on the Surface of Mars

    Science.gov (United States)

    Rampe, E. B.; Morris, R. V.; Ruff, S. W.; Horgan, B.; Dehouck, E.; Achilles, C. N.; Ming, D. W.; Bish, D. L.; Chipera, S. J.

    2014-01-01

    Both primary (volcanic/impact glasses) and secondary (opal/silica, allophane, hisingerite, npOx, S-bearing) amorphous phases appear to be major components of martian surface materials based on orbital and in-situ measurements. A key observation is that whereas regional/global scale amorphous components include altered glass and npOx, local scale amorphous phases include hydrated silica/opal. This suggests widespread alteration at low water-to-rock ratios, perhaps due to snow/ice melt with variable pH, and localized alteration at high water-to-rock ratios. Orbital and in-situ measurements of the regional/global amorphous component on Mars suggests that it is made up of at least three phases: npOx, amorphous silicate (likely altered glass), and an amorphous S-bearing phase. Fundamental questions regarding the composition and the formation of the regional/global amorphous component(s) still remain: Do the phases form locally or have they been homogenized through aeolian activity and derived from the global dust? Is the parent glass volcanic, impact, or both? Are the phases separate or intimately mixed (e.g., as in palagonite)? When did the amorphous phases form? To address the question of source (local and/or global), we need to look for variations in the different phases within the amorphous component through continued modeling of the chemical composition of the amorphous phases in samples from Gale using CheMin and APXS data. If we find variations (e.g., a lack of or enrichment in amorphous silicate in some samples), this may imply a local source for some phases. Furthermore, the chemical composition of the weathering products may give insight into the formation mechanisms of the parent glass (e.g., impact glasses contain higher Al and lower Si [30], so we might expect allophane as a weathering product of impact glass). To address the question of whether these phases are separate or intimately mixed, we need to do laboratory studies of naturally altered samples made

  13. Amorphous chalcogenides as random octahedrally bonded solids: I. Implications for the first sharp diffraction peak, photodarkening, and Boson peak

    Science.gov (United States)

    Lukyanov, Alexey; Lubchenko, Vassiliy

    2017-09-01

    We develop a computationally efficient algorithm for generating high-quality structures for amorphous materials exhibiting distorted octahedral coordination. The computationally costly step of equilibrating the simulated melt is relegated to a much more efficient procedure, viz., generation of a random close-packed structure, which is subsequently used to generate parent structures for octahedrally bonded amorphous solids. The sites of the so-obtained lattice are populated by atoms and vacancies according to the desired stoichiometry while allowing one to control the number of homo-nuclear and hetero-nuclear bonds and, hence, effects of the mixing entropy. The resulting parent structure is geometrically optimized using quantum-chemical force fields; by varying the extent of geometric optimization of the parent structure, one can partially control the degree of octahedrality in local coordination and the strength of secondary bonding. The present methodology is applied to the archetypal chalcogenide alloys AsxSe1-x. We find that local coordination in these alloys interpolates between octahedral and tetrahedral bonding but in a non-obvious way; it exhibits bonding motifs that are not characteristic of either extreme. We consistently recover the first sharp diffraction peak (FSDP) in our structures and argue that the corresponding mid-range order stems from the charge density wave formed by regions housing covalent and weak, secondary interactions. The number of secondary interactions is determined by a delicate interplay between octahedrality and tetrahedrality in the covalent bonding; many of these interactions are homonuclear. The present results are consistent with the experimentally observed dependence of the FSDP on arsenic content, pressure, and temperature and its correlation with photodarkening and the Boson peak. They also suggest that the position of the FSDP can be used to infer the effective particle size relevant for the configurational equilibration in

  14. Amorphous Silicon Carbide for Photovoltaic Applications

    OpenAIRE

    Janz, Stefan

    2006-01-01

    Within this work amorphous SiC is investigated for its applicability in photovoltaic devices. The temperature stability and dopability of SiC makes this material very attractive for applications in this area. Physical basics of amorphous SiC networks and plasma processes are discussed and first measurements with FTIR of the different layer types show the complexity of the network. The special features of the plasma reactor such as high temperature deposition and two-source excitation are also...

  15. A Magnetic Sensor with Amorphous Wire

    Directory of Open Access Journals (Sweden)

    Dongfeng He

    2014-06-01

    Full Text Available Using a FeCoSiB amorphous wire and a coil wrapped around it, we have developed a sensitive magnetic sensor. When a 5 mm long amorphous wire with the diameter of 0.1 mm was used, the magnetic field noise spectrum of the sensor was about 30 pT/ÖHz above 30 Hz. To show the sensitivity and the spatial resolution, the magnetic field of a thousand Japanese yen was scanned with the magnetic sensor.

  16. Compaction of amorphous iron–boron powder

    DEFF Research Database (Denmark)

    Hendriksen, Peter Vang; Mørup, Steen; Koch, Christian

    1993-01-01

    Large scale practical use of bulk amorphous alloys requires the capability of molding the material to a desired design, for instance by compaction of an amorphous powder. This is a difficult task because the sintering temperature is limited by the crystallization temperature of the alloy.1 Here w...... of density and structure on compaction pressure and compaction temperature. Journal of Applied Physics is copyrighted by The American Institute of Physics....

  17. Using containerless methods to develop amorphous pharmaceuticals.

    Science.gov (United States)

    Weber, J K R; Benmore, C J; Suthar, K J; Tamalonis, A J; Alderman, O L G; Sendelbach, S; Kondev, V; Yarger, J; Rey, C A; Byrn, S R

    2017-01-01

    Many pipeline drugs have low solubility in their crystalline state and require compounding in special dosage forms to increase bioavailability for oral administration. The use of amorphous formulations increases solubility and uptake of active pharmaceutical ingredients. These forms are rapidly gaining commercial importance for both pre-clinical and clinical use. Synthesis of amorphous drugs was performed using an acoustic levitation containerless processing method and spray drying. The structure of the products was investigated using in-situ high energy X-ray diffraction. Selected solvents for processing drugs were investigated using acoustic levitation. The stability of amorphous samples was measured using X-ray diffraction. Samples processed using both spray drying and containerless synthesis were compared. We review methods for making amorphous pharmaceuticals and present data on materials made by containerless processing and spray drying. It was shown that containerless processing using acoustic levitation can be used to make phase-pure forms of drugs that are known to be difficult to amorphize. The stability and structure of the materials was investigated in the context of developing and making clinically useful formulations. Amorphous compounds are emerging as an important component of drug development and for the oral delivery of drugs with low solubility. Containerless techniques can be used to efficiently synthesize small quantities of pure amorphous forms that are potentially useful in pre-clinical trials and for use in the optimization of clinical products. Developing new pharmaceutical products is an essential enterprise to improve patient outcomes. The development and application of amorphous pharmaceuticals to increase absorption is rapidly gaining importance and it provides opportunities for breakthrough research on new drugs. There is an urgent need to solve problems associated with making formulations that are both stable and that provide high

  18. Carbon. Examples of Property Realization

    OpenAIRE

    I.A. Kossko; A.A. Onoprienko; T.G. Kossko

    2013-01-01

    Examples of realization of carbon properties in formation of section near-surface boundaries defining the mechanism of oxidizing (normal) wear are presented. Synthesis of strengt hening diamond- lonsdaleite -carbene «frame» and graphite with function of solid lubricant on a friction surface in high-desperse carbon environment is reviewed. Prospects of carbon ap placation in implementation of the concept of electronics on one element, and also use of thin-film structures of amorphous carbon – ...

  19. Radiation-Induced Amorphization of Crystalline Ice

    Science.gov (United States)

    Fama, M.; Loeffler, M. J.; Raut, U.; Baragiola, R. A.

    2009-01-01

    We study radiation-induced amorphization of crystalline ice, ana lyzing the resu lts of three decades of experiments with a variety of projectiles, irradiation energy, and ice temperature, finding a similar trend of increasing resistance of amorphization with temperature and inconsistencies in results from different laboratories. We discuss the temperature dependence of amorphization in terms of the 'thermal spike' model. We then discuss the common use of the 1.65 micrometer infrared absorption band of water as a measure of degree of crystallinity, an increasingly common procedure to analyze remote sensing data of astronomical icy bodies. The discussion is based on new, high quality near-infrared refl ectance absorption spectra measured between 1.4 and 2.2 micrometers for amorphous and crystalline ices irradiated with 225 keV protons at 80 K. We found that, after irradiation with 10(exp 15) protons per square centimeter, crystalline ice films thinner than the ion range become fully amorphous, and that the infrared absorption spectra show no significant changes upon further irradiation. The complete amorphization suggests that crystalline ice observed in the outer Solar System, including trans-neptunian objects, may results from heat from internal sources or from the impact of icy meteorites or comets.

  20. Neutron irradiation induced amorphization of silicon carbide

    Science.gov (United States)

    Snead, L. L.; Hay, J. C.

    1999-07-01

    This paper provides the properties of bulk stoichiometric silicon carbide which has been amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60°C to a total fast neutron fluence of 2.6 × 10 25 n/m 2. Amorphization was seen in both materials as evidenced by TEM, electron diffraction and X-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density (-10.8%), elastic modulus as measured using a nanoindentation technique (-45%), hardness as measured by nanoindentation (-45%), and standard Vickers hardness (-24%). Similar property changes are observed for the amorphized CVD SiC. Using measured thermal conductivity data for the CVD SiC sample, the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than ˜125°C.

  1. Tetra-hedral zinc in tetra-kis-(1-methyl-1H-imidazole-κN)zinc bis-(tetra-fluorido-borate).

    Science.gov (United States)

    Reedijk, Jan; van Albada, Gerard A; Limburg, Bart; Mutikainen, Ilpo; Turpeinen, Urho

    2012-01-01

    In the title compound, [Zn(C(4)H(6)N(2))(4)](BF(4))(2), the Zn(II) ion is in a slightly distorted tetra-hedral coordination geometry, with Zn-N distances in the range 1.980 (2)-1.991 (2) Å. The tetra-hedral angles are in the range 104.93 (9)-118.81 (9)°.

  2. Amorphous metallic alloys for oxygen reduction reaction in a polymer electrolyte membrane fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez-Huerta, R.; Guerra-Martinez, I.; Lopez, J.S. [Inst. Politecnico Nacional, ESIQIE, Mexico City (Mexico). Lab. de Electroquimica; Pierna, A.R. [Basque Country Univ., San Sebastian (Spain). Dept. of Chemical Engineering and Environment; Solorza-Feria, O. [Inst. Politenico Nacional, Centro de Investigacion y de Estudios Avanzados, Mexico City (Mexico). Dept. de Quimica

    2010-07-15

    Direct methanol fuel cells (DMFC) and polymer electrolyte membrane fuel cells (PEMFC) represent an important, environmentally clean energy source. This has motivated extensive research on the synthesis, characterization and evaluation of novel and stable oxygen reduction electrocatalysts for the direct four-electron transfer process to water formation. Studies have shown that amorphous alloyed compounds can be used as electrode materials in electrochemical energy conversion devices. Their use in PEMFCs can optimize the electrocatalyst loading in the membrane electrode assembly (MEA). In this study, amorphous metallic PtSn, PtRu and PtRuSn alloys were synthesized by mechanical milling and used as cathodes for the oxygen reduction reaction (ORR) in sulphuric acid and in a single PEM fuel cell. Two different powder morphologies were observed before and after the chemical activation in a hydrofluoric acid (HF) solution at 25 degrees C. The kinetics of the ORR on the amorphous catalysts were investigated. The study showed that the amorphous metallic PtSn electrocatalyst was the most active of the 3 electrodes for the cathodic reaction. Fuel cell experiments were conducted at various temperatures at 30 psi for hydrogen (H{sub 2}) and at 34 psi for oxygen (O{sub 2}). MEAs made of Nafion 115 and amorphous metallic PtSn dispersed on carbon powder in a PEMFC had a power density of 156 mW per cm{sup 2} at 0.43V and 80 degrees C. 12 refs., 1 tab., 5 figs.

  3. Formation and thermal stability of amorphous Ti-Si-C alloys

    Energy Technology Data Exchange (ETDEWEB)

    Naka, M. [Joining and Welding Research Inst., Osaka (Japan); Sakai, H. [Osaka University, Osaka 565 (Japan); Maeda, M. [Joining and Welding Research Inst., Osaka (Japan); Mori, H. [Research Center for Ultra-High Voltage Electronmicroscopy, Osaka University, Osaka 565 (Japan)

    1997-06-15

    The crystallization behavior of Ti-Si-C ternary amorphous alloys sputtered in low-pressure argon was investigated by measuring differential scanning calorimetry (DSC) curves. The crystallized microstructures of Ti-Si-C amorphous alloys were observed by in-situ heating in a hot stage of an electron microscope. Ti-46at.%Si-32at.%C amorphous alloy crystallizes to fine grains composed of {beta}-SiC and TiSi{sub 2}. Ti-14at.%Si-20at.%C amorphous alloy crystallizes to fine grains composed of TiC and Ti{sub 5}Si{sub 3}. Although the carbon improves the thermal stability of the Ti-Si-C ternary alloys, the silicon degrades the thermal stability of the alloys. The amorphous alloys containing compositions corresponding to carbosilicide or carbide such as Ti{sub 5}Si{sub 3}C{sub x}, Ti{sub 3}SiC{sub 2} or SiC possess high thermal stability and high hardness values. (orig.)

  4. Amorphous silicon detectors in positron emission tomography

    Energy Technology Data Exchange (ETDEWEB)

    Conti, M. (Istituto Nazionale di Fisica Nucleare, Pisa (Italy) Lawrence Berkeley Lab., CA (USA)); Perez-Mendez, V. (Lawrence Berkeley Lab., CA (USA))

    1989-12-01

    The physics of the detection process is studied and the performances of different Positron Emission Tomography (PET) system are evaluated by theoretical calculation and/or Monte Carlo Simulation (using the EGS code) in this paper, whose table of contents can be summarized as follows: a brief introduction to amorphous silicon detectors and some useful equation is presented; a Tantalum/Amorphous Silicon PET project is studied and the efficiency of the systems is studied by Monte Carlo Simulation; two similar CsI/Amorphous Silicon PET projects are presented and their efficiency and spatial resolution are studied by Monte Carlo Simulation, light yield and time characteristics of the scintillation light are discussed for different scintillators; some experimental result on light yield measurements are presented; a Xenon/Amorphous Silicon PET is presented, the physical mechanism of scintillation in Xenon is explained, a theoretical estimation of total light yield in Xenon and the resulting efficiency is discussed altogether with some consideration of the time resolution of the system; the amorphous silicon integrated electronics is presented, total noise and time resolution are evaluated in each of our applications; the merit parameters {epsilon}{sup 2}{tau}'s are evaluated and compared with other PET systems and conclusions are drawn; and a complete reference list for Xenon scintillation light physics and its applications is presented altogether with the listing of the developed simulation programs.

  5. Ta-based amorphous metal thin films

    Energy Technology Data Exchange (ETDEWEB)

    McGlone, John M., E-mail: mcglone@eecs.oregonstate.edu [School of Electrical Engineering and Computer Science, Oregon State University, Corvallis, OR 97331-5501 (United States); Olsen, Kristopher R. [Department of Chemistry, Oregon State University, Corvallis, OR 97331-4003 (United States); Stickle, William F.; Abbott, James E.; Pugliese, Roberto A.; Long, Greg S. [Hewlett-Packard Company, Corvallis, OR, 97333 (United States); Keszler, Douglas A. [Department of Chemistry, Oregon State University, Corvallis, OR 97331-4003 (United States); Wager, John F. [School of Electrical Engineering and Computer Science, Oregon State University, Corvallis, OR 97331-5501 (United States)

    2015-11-25

    With their lack of grains and grain boundaries, amorphous metals are known to possess advantageous mechanical properties and enhanced chemical stability relative to crystalline metals. Commonly, however, they exhibit poor high-temperature stability because of their metastable nature. Here, we describe two new Ta-based ternary metal thin films that retain thermal stability to 600 °C and above. The new thin-film compositions, Ta{sub 2}Ni{sub 2}Si{sub 1} and Ta{sub 2}Mo{sub 2}Si{sub 1}, are amorphous, exhibiting ultra-smooth surfaces (<0.4 nm) and resistivities typical of amorphous metals (224 and 177 μΩ cm, respectively). - Highlights: • New Ta-based amorphous metals were sputter deposited from individual targets. • As-deposited amorphous structure was confirmed through diffraction techniques. • Electrical and surface properties were characterized and possess smooth surfaces. • No evidence of crystallization up to 600 °C (TaNiSi) and 800 °C (TaMoSi). • Ultra-smooth surfaces remained unchanged up to crystallization temperature.

  6. The Structure of Liquid and Amorphous Hafnia.

    Science.gov (United States)

    Gallington, Leighanne C; Ghadar, Yasaman; Skinner, Lawrie B; Weber, J K Richard; Ushakov, Sergey V; Navrotsky, Alexandra; Vazquez-Mayagoitia, Alvaro; Neuefeind, Joerg C; Stan, Marius; Low, John J; Benmore, Chris J

    2017-11-10

    Understanding the atomic structure of amorphous solids is important in predicting and tuning their macroscopic behavior. Here, we use a combination of high-energy X-ray diffraction, neutron diffraction, and molecular dynamics simulations to benchmark the atomic interactions in the high temperature stable liquid and low-density amorphous solid states of hafnia. The diffraction results reveal an average Hf-O coordination number of ~7 exists in both the liquid and amorphous nanoparticle forms studied. The measured pair distribution functions are compared to those generated from several simulation models in the literature. We have also performed ab initio and classical molecular dynamics simulations that show density has a strong effect on the polyhedral connectivity. The liquid shows a broad distribution of Hf-Hf interactions, while the formation of low-density amorphous nanoclusters can reproduce the sharp split peak in the Hf-Hf partial pair distribution function observed in experiment. The agglomeration of amorphous nanoparticles condensed from the gas phase is associated with the formation of both edge-sharing and corner-sharing HfO6,7 polyhedra resembling that observed in the monoclinic phase.

  7. The Structure of Liquid and Amorphous Hafnia

    Directory of Open Access Journals (Sweden)

    Leighanne C. Gallington

    2017-11-01

    Full Text Available Understanding the atomic structure of amorphous solids is important in predicting and tuning their macroscopic behavior. Here, we use a combination of high-energy X-ray diffraction, neutron diffraction, and molecular dynamics simulations to benchmark the atomic interactions in the high temperature stable liquid and low-density amorphous solid states of hafnia. The diffraction results reveal an average Hf–O coordination number of ~7 exists in both the liquid and amorphous nanoparticle forms studied. The measured pair distribution functions are compared to those generated from several simulation models in the literature. We have also performed ab initio and classical molecular dynamics simulations that show density has a strong effect on the polyhedral connectivity. The liquid shows a broad distribution of Hf–Hf interactions, while the formation of low-density amorphous nanoclusters can reproduce the sharp split peak in the Hf–Hf partial pair distribution function observed in experiment. The agglomeration of amorphous nanoparticles condensed from the gas phase is associated with the formation of both edge-sharing and corner-sharing HfO6,7 polyhedra resembling that observed in the monoclinic phase.

  8. Structural survey of carbonate-containing antacids.

    Science.gov (United States)

    Serna, C J; White, J L; Hem, S L

    1978-03-01

    A series of carbonate-containing antacids was examined by IR and X-ray analysis to establish the role of carbonate and to compare the structure of the antacids to naturally occurring carbonate minerals. Based on IR analysis, the relative degree of perturbation of carbonate increases in the order calcium carbonate, carbonate-containing aluminum hydroxide gel, and dihydroxyaluminum sodium carbonate. The crystalline carbonate-containing antacids were poorly organized forms of the minerals calcite, CaCO3; dawsonite, NaAl(OH)2CO3; and hydrotalcite, Mg6Al2CO3(OH)16-4H2O. Amorphous carbonate-containing aluminum hydroxide gel can be classified mineralogically as amorphous aluminum hydroxycarbonate. IR and X-ray evidence indicates that magaldrate has a hydrotalcite-like structure with sulfate as the major interlayer anion and carbonate also present in the interlayer space.

  9. Vibrational spectroscopy and analysis of pseudo-tetrahedral complexes with metal imido bonds.

    Science.gov (United States)

    Mehn, Mark P; Brown, Steven D; Jenkins, David M; Peters, Jonas C; Que, Lawrence

    2006-09-04

    A number of assignments have been previously posited for the metal-nitrogen stretch (nu(M-NR)), the N-R stretch (nu(MN-R)), and possible ligand deformation modes associated with terminally bound imides. Here we examine mononuclear iron(III) and cobalt(III) imido complexes of the monoanionic tridentate ligand [PhBP3] ([PhBP3] = [PhB(CH2PPh2)3]-) to clarify the vibrational features for these trivalent metal imides. We report the structures of [PhBP3]FeNtBu and [PhBP3]CoNtBu. Pseudo-tetrahedral metal imides of these types exhibit short bond lengths (ca. 1.65 A) and nearly linear angles about the M-N-C linkages, indicative of multiple bond character. Furthermore, these compounds give rise to intense, low-energy visible absorptions. Both the position and the intensity of the optical bands in the [PhBP3]MNR complexes depend on whether the substituent is an alkyl or aryl group. Excitation into the low-energy bands of [PhBP3]FeNtBu gives rise to two Raman features at 1104 and 1233 cm(-1), both of which are sensitive to 15N and 2H labeling. The isotope labeling suggests the 1104 cm(-1) mode has the greatest Fe-N stretching character, while the 1233 cm(-1) mode is affected to a lesser extent by (15)N substitution. The spectra of the deuterium-labeled imides further support this assertion. The data demonstrate that the observed peaks are not simple diatomic stretching modes but are extensively coupled to the vibrations of the ancillary organic group. Therefore, describing these complexes as simple diatomic or even triatomic oscillators is an oversimplification. Analogous studies of the corresponding cobalt(III) complex lead to a similar set of isotopically sensitive resonances at 1103 and 1238 cm(-1), corroborating the assignments made in the iron imides. Very minimal changes in the vibrational frequencies are observed upon replacement of cobalt(III) for iron(III), suggesting similar force constants for the two compounds. This is consistent with the previously proposed

  10. Pressure and temperature variation of octahedral Na and tetrahedral Al in amphiboles in metamafic rocks

    Science.gov (United States)

    Jenkins, D. M.; Lei, J.

    2013-12-01

    The sodium content in the M4 site of amphibole (BNa) was calibrated by Brown (1977, J Petrol, 18, 53-72) in a study that continues to be highly cited to this day. This study, based on empirical observations of amphibole compositional changes in the presence of the buffering assemblage plagioclase, chlorite, epidote, iron oxide, and water, demonstrated a systematic variation in the BNa and tetrahedral Al (TAl) content with pressure. Recent experimental work in this lab aimed at defining the extent of miscibility along the tremolite-glaucophane and hornblende-glaucophane joins in the Na2O-CaO-MgO-Al2O3-SiO2-H2O system has provided some additional information on the cation mixing along these joins. These joins also serve as the chemically-simplified framework of the BNa versus TAl correlation reported by Brown (1977). There are now sufficient, though still a bare minimum, of experimentally-confirmed mixing data for sodium-rich amphiboles to test this correlation and for quantifying the pressure-temperature (P-T) dependence of amphibole compositions in metamafic rocks relevant to subduction zones. From experimental results obtained over the range of 500-800°C, 1.5-2.0 GPa, and using a variety of amphibole synthesis and re-equilibration methods, the following set of asymmetric formalism (ASF) macroscopic interaction and mixing parameters have been derived that can be used with THERMOCALC dataset 55: Wtrgl = 70 kJ, Wglts = Wtrts =20 kJ, α(tr) = 1.0, α(ts) = 1.2, and α(gl) = 0.52. Using a fixed MORB bulk composition, the composition of amphiboles within the P-T stability field of the buffering assemblage were calculated for the above chemical system with FeO added (i.e., NCFMASH) over the range of 0.2 - 2.0 GPa and 400 - 700°C. The following main observations can be made. First, the empirical amphibole compositions at low TAl and high BNa contents are well modeled by the miscibility gap in the amphibole ternary sub-system tremolite

  11. Amorphous Alloy: Promising Precursor to Form Nanoflowerpot

    Directory of Open Access Journals (Sweden)

    Guo Lan

    2014-01-01

    Full Text Available Nanoporous copper is fabricated by dealloying the amorphous Ti2Cu alloy in 0.03 M HF electrolyte. The pore and ligament sizes of the nanoporous copper can be readily tailored by controlling the dealloying time. The as-prepared nanoporous copper provides fine and uniform nanoflowerpots to grow highly dispersed Au nanoflowers. The blooming Au nanoflowers in the nanoporous copper flowerpots exhibit both high catalytic activity and stability towards the oxidation of glucose, indicating that the amorphous alloys are ideal precursors to form nanoflowerpot which can grow functional nanoflowers.

  12. Atomistic explanation of shear-induced amorphous band formation in boron carbide.

    Science.gov (United States)

    An, Qi; Goddard, William A; Cheng, Tao

    2014-08-29

    Boron carbide (B4C) is very hard, but its applications are hindered by stress-induced amorphous band formation. To explain this behavior, we used density function theory (Perdew-Burke-Ernzerhof flavor) to examine the response to shear along 11 plausible slip systems. We found that the (0111)/ slip system has the lowest shear strength (consistent with previous experimental studies) and that this slip leads to a unique plastic deformation before failure in which a boron-carbon bond between neighboring icosahedral clusters breaks to form a carbon lone pair (Lewis base) on the C within the icosahedron. Further shear then leads this Lewis base C to form a new bond with the Lewis acidic B in the middle of a CBC chain. This then initiates destruction of this icosahedron. The result is the amorphous structure observed experimentally. We suggest how this insight could be used to strengthen B4C.

  13. Amorphous material from the rapid evaporation of basalt weathering solutions: Implications for Amazonian alteration

    Science.gov (United States)

    Smith, R.; Horgan, B. H. N.; Christensen, P. R.

    2016-12-01

    Amorphous silicates of ambiguous origin are detected on the Martian surface through orbiter and rover measurements. Secondary amorphous silicates might precipitate from rapidly evaporating weathering solutions under Amazonian ( 3 BYA - present) surface conditions. Yet, such phases are poorly understood and are underrepresented in infrared spectral libraries. Amazonian weathering was simulated by dissolving two basaltic tephra compositions in DI water under two different atmospheres (1: oxidizing and 2: simulated Martian). The resulting weathering solutions were rapidly evaporated into sample cups. Precipitate mineralogy was studied using visible and near-infrared (VNIR) and thermal-infrared (TIR) spectroscopy and x-ray diffraction (XRD). Solution compositions were analyzed using Ion Chromatography (IC) and Inductively Coupled Plasma Mass-Spectroscopy (ICP-MS). All experiments formed hydrated amorphous silicates and nanophase iron-oxides, but precipitates from solutions formed under a simulated Martian atmosphere also contain crystalline carbonate and sulfate minerals. The oxidizing atmosphere precipitates are also S-bearing, based on solution chemistry, but no crystalline sulfates were unambiguously detected. The TIR spectra of all samples exhibit a spectral feature at 460 cm-1 that was previously only known to be present in the spectra of basaltic glass and some terrestrial palagonitized basalt samples, indicating that the precipitates are new to spectral libraries. Ongoing characterization will help determine the composition and structure of the amorphous phases. TIR spectral and XRD instruments on the Spirit and Mars Science Laboratory (MSL) rovers both indicate high abundances of basaltic glass in rock and soil samples, despite chemical evidence for aqueous alteration. Our results suggest that these measurements are consistent with secondary amorphous silicates formed through the rapid evaporation of basalt weathering solutions. Thus, transient water

  14. Atomistic and infrared study of CO-water amorphous ice onto olivine dust grain

    Science.gov (United States)

    Escamilla-Roa, Elizabeth; Moreno, Fernando; López-Moreno, J. Juan; Sainz-Díaz, C. Ignacio

    2017-01-01

    This work is a study of CO and H2O molecules as adsorbates that interact on the surface of olivine dust grains. Olivine (forsterite) is present on the Earth, planetary dust, in the interstellar medium (ISM) and in particular in comets. The composition of amorphous ice is very important for the interpretation of processes that occur in the solar system and the ISM. Dust particles in ISM are composed of a heterogeneous mixture of amorphous or crystalline silicates (e.g. olivine) organic material, carbon, and other minor constituents. These dust grains are embedded in a matrix of ices, such as H2O, CO, CO2, NH3, and CH4. We consider that any amorphous ice will interact and grow faster on dust grain surfaces. In this work we explore the adsorption of CO-H2O amorphous ice onto several (100) forsterite surfaces (dipolar and non-dipolar), by using first principle calculations based on density functional theory (DFT). These models are applied to two possible situations: i) adsorption of CO molecules mixed into an amorphous ice matrix (gas mixture) and adsorbed directly onto the forsterite surface. This interaction has lower adsorption energy than polar molecules (H2O and NH3) adsorbed on this surface; ii) adsorption of CO when the surface has previously been covered by amorphous water ice (onion model). In this case the calculations show that adsorption energy is low, indicating that this interaction is weak and therefore the CO can be desorbed with a small increase of temperature. Vibration spectroscopy for the most stable complex was also studied and the frequencies were in good agreement with experimental frequency values.

  15. The Case for Tetrahedral Oxy-subhydride (TOSH Structures in the Exclusion Zones of Anchored Polar Solvents Including Water

    Directory of Open Access Journals (Sweden)

    Klaus Oehr

    2014-11-01

    Full Text Available We hypothesize a mechanistic model of how negatively-charged exclusion zones (EZs are created. While the growth of EZs is known to be associated with the absorption of ambient photonic energy, the molecular dynamics giving rise to this process need greater elucidation. We believe they arise due to the formation of oxy-subhydride structures (OH−(H2O4 with a tetrahedral (sp3 (OH−(H2O3 core. Five experimental data sets derived by previous researchers were assessed in this regard: (1 water-derived EZ light absorbance at specific infrared wavelengths, (2 EZ negative potential in water and ethanol, (3 maximum EZ light absorbance at 270 nm ultraviolet wavelength, (4 ability of dimethyl sulphoxide but not ether to form an EZ, and (5 transitory nature of melting ice derived EZs. The proposed tetrahedral oxy-subhydride structures (TOSH appear to adequately account for all of the experimental evidence derived from water or other polar solvents.

  16. Design of Semiconducting Tetrahedral Mn_{1−x}Zn_{x}O Alloys and Their Application to Solar Water Splitting

    Directory of Open Access Journals (Sweden)

    Haowei Peng

    2015-05-01

    Full Text Available Transition metal oxides play important roles as contact and electrode materials, but their use as active layers in solar energy conversion requires achieving semiconducting properties akin to those of conventional semiconductors like Si or GaAs. In particular, efficient bipolar carrier transport is a challenge in these materials. Based on the prediction that a tetrahedral polymorph of MnO should have such desirable semiconducting properties, and the possibility to overcome thermodynamic solubility limits by nonequilibrium thin-film growth, we exploit both structure-property and composition-structure relationships to design and realize novel wurtzite-structure Mn_{1−x}Zn_{x}O alloys. At Zn compositions above x≈0.3, thin films of these alloys assume the tetrahedral wurtzite structure instead of the octahedral rocksalt structure of MnO, thereby enabling semiconductor properties that are unique among transition metal oxides, i.e., a band gap within the visible spectrum, a band-transport mechanism for both electron and hole carriers, electron doping, and a band lineup suitable for solar hydrogen generation. A proof of principle is provided by initial photo-electrocatalytic device measurements, corroborating, in particular, the predicted favorable hole-transport properties of these alloys.

  17. A novel coupled level set and volume of fluid method for sharp interface capturing on 3D tetrahedral grids

    Science.gov (United States)

    Lv, Xin; Zou, Qingping; Zhao, Yong; Reeve, Dominic

    2010-04-01

    We present a new three-dimensional hybrid level set (LS) and volume of fluid (VOF) method for free surface flow simulations on tetrahedral grids. At each time step, we evolve both the level set function and the volume fraction. The level set function is evolved by solving the level set advection equation using a second-order characteristic based finite volume method. The volume fraction advection is performed using a bounded compressive normalized variable diagram (NVD) based scheme. The interface is reconstructed based on both the level set and the volume fraction information. The novelty of the method lies in that we use an analytic method for finding the intercepts on tetrahedral grids, which makes interface reconstruction efficient and conserves volume of fluid exactly. Furthermore, the advection of volume fraction makes use of the NVD concept and switches between different high resolution differencing schemes to yield a bounded scalar field, and to preserve both smoothness and sharp definition of the interface. The method is coupled to a well validated finite volume based Navier-Stokes incompressible flow solver. The code validation shows that our method can be employed to resolve complex interface changes efficiently and accurately. In addition, the centroid and intercept data available as a by-product of the proposed interface reconstruction scheme can be used directly in near-interface sub-grid models in large eddy simulation.

  18. Influence of the exchange and correlation functional on the structure of amorphous InSb and In{sub 3}SbTe{sub 2} compounds

    Energy Technology Data Exchange (ETDEWEB)

    Gabardi, Silvia; Caravati, Sebastiano; Bernasconi, Marco, E-mail: marco.bernasconi@mater.unimib.it [Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 55, I-20125 Milano (Italy); Los, Jan H.; Kühne, Thomas D. [Institute of Physical Chemistry and Center for Computational Sciences, Johannes Gutenberg University Mainz, Staudinger Weg 7, D-55128 Mainz (Germany)

    2016-05-28

    We have investigated the structural, vibrational, and electronic properties of the amorphous phase of InSb and In{sub 3}SbTe{sub 2} compounds of interest for applications in phase change non-volatile memories. Models of the amorphous phase have been generated by quenching from the melt by molecular dynamics simulations based on density functional theory. In particular, we have studied the dependence of the structural properties on the choice of the exchange-correlation functional. It turns out that the use of the Becke-Lee-Yang-Parr functional provides models with a much larger fraction of In atoms in a tetrahedral bonding geometry with respect to previous results obtained with the most commonly used Perdew-Becke-Ernzerhof functional. This outcome is at odd with the properties of Ge{sub 2}Sb{sub 2}Te{sub 5} phase change compound for which the two exchange-correlation functionals yield very similar results on the structure of the amorphous phase.

  19. Excessively High Vapor Pressure of Al-based Amorphous Alloys

    OpenAIRE

    Jeong, Jae; Lee, Sung; Jeon, Je-Beom; Kim, Suk

    2015-01-01

    Aluminum-based amorphous alloys exhibited an abnormally high vapor pressure at their approximate glass transition temperatures. The vapor pressure was confirmed by the formation of Al nanocrystallites from condensation, which was attributed to weight loss of the amorphous alloys. The amount of weight loss varied with the amorphous alloy compositions and was inversely proportional to their glass-forming ability. The vapor pressure of the amorphous alloys around 573 K was close to the va...

  20. Amorphous track models: A numerical comparison study

    DEFF Research Database (Denmark)

    Greilich, Steffen; Grzanka, L.; Bassler, N.

    2010-01-01

    We present an open-source code library for amorphous track modelling which is suppose to faciliate the application and numerical comparability as well as serve as a frame-work for the implementation of new models. We show an example of using the library indicating the choice of submodels has...

  1. Amorphous silicon for thin-film transistors

    NARCIS (Netherlands)

    Schropp, Rudolf Emmanuel Isidore

    1987-01-01

    Hydrogenated amorphous silicon (a-Si:H) has considerable potential as a semiconducting material for large-area photoelectric and photovoltaic applications. Moreover, a-Si:H thin-film transistors (TFT’s) are very well suited as switching devices in addressable liquid crystal display panels and

  2. ANALYSIS AND STUDY OF AMORPHOUS ALLOYS PROPERTIES

    Directory of Open Access Journals (Sweden)

    T.P. Pavlenko

    2013-10-01

    Full Text Available The paper reviews and analyzes properties of amorphous alloys for the purpose of their application in magnetic systems of electrical apparatus instead of high-permeability electric steels. The studies have shown a possibility of utilizing these alloys in the magnetic structure of a current transformer in the pulsed voltage stabilizer of an automated circuit-breaker semiconductor release.

  3. Film adhesion in amorphous silicon solar cells

    Indian Academy of Sciences (India)

    A major issue encountered during fabrication of triple junction -Si solar cells on polyimide substrates is the adhesion of the solar cell thin films to the substrates. Here, we present our study of film adhesion in amorphous silicon solar cells made on different polyimide substrates (Kapton VN, Upilex-S and Gouldflex), and the ...

  4. Film adhesion in amorphous silicon solar cells

    Indian Academy of Sciences (India)

    TECS

    Abstract. A major issue encountered during fabrication of triple junction a-Si solar cells on polyimide sub- strates is the adhesion of the solar cell thin films to the substrates. Here, we present our study of film adhesion in amorphous silicon solar cells made on different polyimide substrates (Kapton VN, Upilex-S and ...

  5. Unusual photoanisotropic alignment in amorphous azobenzene polymers

    DEFF Research Database (Denmark)

    Ramanujam, P.S.

    2015-01-01

    It is well known that irradiation of azobenzene polymer films between 490 and 530nm results in alignment of molecules perpendicular to the polarization of the incident beam. I have recently found that irradiation of amorphous azobenzene polymers with linearly polarized light at wavelengths between...

  6. Trap level spectroscopy in amorphous semiconductors

    CERN Document Server

    Mikla, Victor V

    2010-01-01

    Although amorphous semiconductors have been studied for over four decades, many of their properties are not fully understood. This book discusses not only the most common spectroscopic techniques but also describes their advantages and disadvantages.Provides information on the most used spectroscopic techniquesDiscusses the advantages and disadvantages of each technique

  7. Indirect involvement of armorphous carbon layer on convective heat transfer enhancement using carbon nanofibers

    NARCIS (Netherlands)

    Taha, T.J.; Lefferts, Leonardus; van der Meer, Theodorus H.

    2015-01-01

    In this work, an experimental heat transfer investigation was carried out to investigate the combined influence of both amorphous carbon (a-C) layer thickness and carbon nanofibers (CNFs) on the convective heat transfer behavior. Synthesis of these carbon nanostructures was achieved using catalytic

  8. Characterization of Amorphous and Co-Amorphous Simvastatin Formulations Prepared by Spray Drying

    DEFF Research Database (Denmark)

    Craye, Goedele; Löbmann, Korbinian; Grohganz, Holger

    2015-01-01

    -amorphous mixture upon ball milling. In addition, a spray-dried formulation of SVS without LYS was prepared. Energy-dispersive X-ray spectroscopy (EDS) revealed that SLS coated the SVS and SVS-LYS particles upon spray drying. X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) showed......In this study, spray drying from aqueous solutions, using the surface-active agent sodium lauryl sulfate (SLS) as a solubilizer, was explored as a production method for co-amorphous simvastatin-lysine (SVS-LYS) at 1:1 molar mixtures, which previously have been observed to form a co...... the studied formulations were able to significantly extend the stability of amorphous SVS compared to previous co-amorphous formulations of SVS. The best stability (at least 12 months in dry conditions) was observed when SLS was spray-dried with SVS (and LYS). In conclusion, spray drying of SVS and LYS from...

  9. Molecular dynamics simulation of amorphous indomethacin.

    Science.gov (United States)

    Xiang, Tian-Xiang; Anderson, Bradley D

    2013-01-07

    Molecular dynamics (MD) simulations have been conducted using an assembly consisting of 105 indomethacin (IMC) molecules and 12 water molecules to investigate the underlying dynamic (e.g., rotational and translational diffusivities and conformation relaxation rates) and structural properties (e.g., conformation, hydrogen-bonding distributions, and interactions of water with IMC) of amorphous IMC. These properties may be important in predicting physical stability of this metastable material. The IMC model was constructed using X-ray diffraction data with the force-field parameters mostly assigned by analogy with similar groups in Amber-ff03 and atomic charges calculated with the B3LYP/ccpVTZ30, IEFPCM, and RESP models. The assemblies were initially equilibrated in their molten state and cooled through the glass transition temperature to form amorphous solids. Constant temperature dynamic runs were then carried out above and below the T(g) (i.e., at 600 K (10 ns), 400 K (350 ns), and 298 K (240 ns)). The density (1.312 ± 0.003 g/cm(3)) of the simulated amorphous solid at 298 K was close to the experimental value (1.32 g/cm(3)) while the estimated T(g) (384 K) was ~64 degrees higher than the experimental value (320 K) due to the faster cooling rate. Due to the hindered rotation of its amide bond, IMC can exist in different diastereomeric states. Different IMC conformations were sufficiently sampled in the IMC melt or vapor, but transitions occurred rarely in the glass. The hydrogen-bonding patterns in amorphous IMC are more complex in the amorphous state than in the crystalline polymorphs. Carboxylic dimers that are dominant in α- and γ-crystals were found to occur at a much lower probability in the simulated IMC glasses while hydrogen-bonded IMC chains were more easily identified patterns in the simulated amorphous solids. To determine molecular diffusivity, a novel analytical method is proposed to deal with the non-Einsteinian behavior, in which the temporal

  10. Experimental Investigation of Multipacting Suppression by amorphous Carbon Coatings

    CERN Document Server

    Holz, Michael

    The presence of electron cloud is considered as the most important limitation concerning the quality of the particle beam in the accelerators, especially with respect to the forthcoming LHC luminosity upgrade. The electron cloud can be mitigated by coating the vacuum beam chambers with thin films of low secondary electron yield (SEY). This technique is applied to two stand-alone main bending dipoles of the SPS, where the RF power is fed through a tungsten wire, stretched inside the vacuum chamber. A dipole with a bare stainless steel chamber shows a clear power threshold initiating an abrupt rise in reflected power and pressure. The effect is enhanced at RF frequencies corresponding to electron cyclotron resonances for given magnetic fields. The first results of a fully coated beam chamber do not exhibit any pressure rise or reflected RF power up to the maximum available input power. Here, reflected power has been observed only once and could not be reproduced. The results of a partially coated beam chamber s...

  11. First-Principles Prediction of Densities of Amorphous Materials: The Case of Amorphous Silicon

    Science.gov (United States)

    Furukawa, Yoritaka; Matsushita, Yu-ichiro

    2018-02-01

    A novel approach to predict the atomic densities of amorphous materials is explored on the basis of Car-Parrinello molecular dynamics (CPMD) in density functional theory. Despite the determination of the atomic density of matter being crucial in understanding its physical properties, no first-principles method has ever been proposed for amorphous materials until now. We have extended the conventional method for crystalline materials in a natural manner and pointed out the importance of the canonical ensemble of the total energy in the determination of the atomic densities of amorphous materials. To take into account the canonical distribution of the total energy, we generate multiple amorphous structures with several different volumes by CPMD simulations and average the total energies at each volume. The density is then determined as the one that minimizes the averaged total energy. In this study, this approach is implemented for amorphous silicon (a-Si) to demonstrate its validity, and we have determined the density of a-Si to be 4.1% lower and its bulk modulus to be 28 GPa smaller than those of the crystal, which are in good agreement with experiments. We have also confirmed that generating samples through classical molecular dynamics simulations produces a comparable result. The findings suggest that the presented method is applicable to other amorphous systems, including those for which experimental knowledge is lacking.

  12. Characterisation of reduced graphene oxides prepared from natural flaky, lump and amorphous graphites

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Weijun; Li, Hongqiang, E-mail: lhq-18@163.com; Hu, Yang; Liu, Yanyan; Song, Shaoxian

    2016-06-15

    Highlights: • Natural flaky, lumpy and amorphous graphites were used to synthesis rGO. • Investigation the effect of the crystal morphology on the oxidation process of GrO and characteristics of prepared rGO. • Low graphitisation degree, big specific surface area and small lateral size were beneficial to the oxidation of graphite. - Abstract: The characterisation of reduced graphene oxides (rGOs) prepared from natural flaky, lumpy, and amorphous graphites using Hummers method was investigated. The prepared graphite oxides (GrOs) and rGOs were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy, atomic force microscopy and electrochemical performance. The results showed that amorphous graphite was much easier to oxidise than lumpy and flaky graphites and was preferable for preparing single or double layer graphene because low graphitisation degree, high defect degree, high specific surface area and small crystal size were beneficial for (1) the oxidants to attack the exposed carbon atoms, (2) the intercalation of oxidants, and (3) the diffusion of oxidants between graphitic layers. In addition, rGO synthesised from amorphous graphite had the most defects and the smallest size of the in-plane sp{sup 2} domains compared to those obtained from the other two nature graphites.

  13. Thermal Conductivity and Wear Behavior of HVOF-Sprayed Fe-Based Amorphous Coatings

    Directory of Open Access Journals (Sweden)

    Haihua Yao

    2017-10-01

    Full Text Available To protect aluminum parts in vehicle engines, metal-based thermal barrier coatings in the form of Fe59Cr12Nb5B20Si4 amorphous coatings were prepared by high velocity oxygen fuel (HVOF spraying under two different conditions. The microstructure, thermal transport behavior, and wear behavior of the coatings were characterized simultaneously. As a result, this alloy shows high process robustness during spraying. Both Fe-based coatings present dense, layered structure with porosities below 0.9%. Due to higher amorphous phase content, the coating H-1 exhibits a relatively low thermal conductivity, reaching 2.66 W/(m·K, two times lower than the reference stainless steel coating (5.85 W/(m·K, indicating a good thermal barrier property. Meanwhile, the thermal diffusivity of amorphous coatings display a limited increase with temperature up to 500 °C, which guarantees a steady and wide usage on aluminum alloy. Furthermore, the amorphous coating shows better wear resistance compared to high carbon martensitic GCr15 steel at different temperatures. The increased temperature accelerating the tribological reaction, leads to the friction coefficient and wear rate of coating increasing at 200 °C and decreasing at 400 °C.

  14. Heat-Induced Agglomeration of Amorphous Silicon Nanoparticles Toward the Formation of Silicon Thin Film.

    Science.gov (United States)

    Jang, Bo Yun; Kim, Ja Young; Seo, Gyeongju; Shin, Chae-Ho; Ko, Chang Hyun

    2016-01-01

    The thermal behavior of silicon nanoparticles (Si NPs) was investigated for the preparation of silicon thin film using a solution process. TEM analysis of Si NPs, synthesized by inductively coupled plasma, revealed that the micro-structure of the Si NPs was amorphous and that the Si NPs had melted and merged at a comparatively low temperature (~750 °C) considering bulk melting temperature of silicon (1414 °C). A silicon ink solution was prepared by dispersing amorphous Si NPs in propylene glycol (PG). It was then coated onto a silicon wafer and a quartz plate to form a thin film. These films were annealed in a vacuum or in an N₂ environment to increase their film density. N2 annealing at 800 °C and 1000 °C induced the crystallization of the amorphous thin film. An elemental analysis by the SIMS depth profile showed that N₂annealing at 1000 °C for 180 min drastically reduced the concentrations of carbon and oxygen inside the silicon thin film. These results indicate that silicon ink prepared using amorphous Si NPs in PG can serve as a proper means of preparing silicon thin film via solution process.

  15. Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy.

    Science.gov (United States)

    McMullan, G; Vinothkumar, K R; Henderson, R

    2015-11-01

    We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å(2) for every incident 300 keV e(-)/Å(2). The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e(-)/Å(2) per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  16. Recent advances in co-amorphous drug formulations

    DEFF Research Database (Denmark)

    Dengale, Swapnil Jayant; Grohganz, Holger; Rades, Thomas

    2016-01-01

    Co-amorphous drug delivery systems have recently gained considerable interest in the pharmaceutical field because of their potential to improve oral bioavailability of poorly water-soluble drugs through drug dissolution enhancement as a result of the amorphous nature of the material. A co...... with other amorphous stabilization techniques. Because of this, several research groups started to investigate the co-amorphous formulation approach, resulting in an increasing amount of scientific publications over the last few years. This study provides an overview of the co-amorphous field and its recent...

  17. Preliminary study on a tetrahedral hohlraum with four half-cylindrical cavities for indirectly driven inertial confinement fusion

    Science.gov (United States)

    Jing, Longfei; Jiang, Shaoen; Kuang, Longyu; Zhang, Lu; Li, Liling; Lin, Zhiwei; Li, Hang; Zheng, Jianhua; Hu, Feng; Huang, Yunbao; Huang, Tianxuan; Ding, Yongkun

    2017-04-01

    A tetrahedral hohlraum with four half-cylindrical cavities (FHCH) is proposed to balance tradeoffs among the drive symmetry, coupling efficiency, and plasma filling of the hohlraum performance for indirectly driven inertial confinement fusion. The peak drive symmetry in the FHCH with a cavity-to-capsule ratio (CCR) of 2.2 is comparable to those in the spherical hohlraum of CCR  =  4.5 with six laser entrance holes (6LEHs-Sph.) ((Lan et al 2014 Phys. Plasmas 21 010704) and three-axis cylindrical hohlraum (6LEHs-Cyls.) of CCR  =  2.0 (Kuang et al 2016 Sci. Rep. 6 34636), and the filling time of plasma is close to the ones in the 6LEHs-Cyls. and the ignition target Rev5-CH of the national ignition campaign, and about half of that in the 6LEHs-Sph. In particular, the coupling efficiency is about 19% and 16% higher than those of the 6LEHs-Sph. and 6LEHs-Cyls., respectively. Besides, preliminary study indicates that the FHCH has a robust symmetry to uncertainties of power imbalance and pointing errors of laser beams. Furthermore, utilizing the FHCH, the feasibility of a tetrahedral indirect drive approach on the national ignition facility and hybrid indirect-direct drive approach with the laser arrangement designed specially for 6LEHs-Sph. or 6LEHs-Cyls., is also envisioned. Therefore, the proposed hohlraum configuration merits consideration as an alternative route to indirect-drive ignition.

  18. Self-Assembled DNA Tetrahedral Scaffolds for the Construction of Electrochemiluminescence Biosensor with Programmable DNA Cyclic Amplification.

    Science.gov (United States)

    Feng, Qiu-Mei; Guo, Yue-Hua; Xu, Jing-Juan; Chen, Hong-Yuan

    2017-05-24

    A novel DNA tetrahedron-structured electrochemiluminescence (ECL) platform for bioanalysis with programmable DNA cyclic amplification was developed. In this work, glucose oxidase (GOD) was labeled to a DNA sequence (S) as functional conjugation (GOD-S), which could hybridize with other DNA sequences (L and P) to form GOD-S:L:P probe. In the presence of target DNA and a help DNA (A), the programmable DNA cyclic amplification was activated and released GOD-S via toehold-mediated strand displacement. Then, the obtained GOD-S was further immobilized on the DNA tetrahedral scaffolds with a pendant capture DNA and Ru(bpy)32+-conjugated silica nanoparticles (RuSi NPs) decorated on the electrode surface. Thus, the amount of GOD-S assembled on the electrode surface depended on the concentration of target DNA and GOD could catalyze glucose to generate H2O2 in situ. The ECL signal of Ru(bpy)32+-TPrA system was quenched by the presence of H2O2. By integrating the programmable DNA cyclic amplification and in situ generating H2O2 as Ru(bpy)32+ ECL quencher, a sensitive DNA tetrahedron-structured ECL sensing platform was proposed for DNA detection. Under optimized conditions, this biosensor showed a wide linear range from 100 aM to 10 pM with a detection limit of 40 aM, indicating a promising application in DNA analysis. Furthermore, by labeling GOD to different recognition elements, the proposed strategy could be used for the detection of various targets. Thus, this programmable cascade amplification strategy not only retains the high selectivity and good capturing efficiency of tetrahedral-decorated electrode surface but also provides potential applications in the construction of ECL biosensor.

  19. Wear Resistant Amorphous and Nanocomposite Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Racek, O

    2008-03-26

    Glass forming materials (critical cooling rate <10{sup 4}K.s{sup -1}) are promising for their high corrosion and wear resistance. During rapid cooling, the materials form an amorphous structure that transforms to nanocrystalline during a process of devitrification. High hardness (HV 1690) can be achieved through a controlled crystallization. Thermal spray process has been used to apply coatings, which preserves the amorphous/nanocomposite structure due to a high cooling rate of the feedstock particles during the impact on a substrate. Wear properties have been studied with respect to process conditions and feedstock material properties. Application specific properties such as sliding wear resistance have been correlated with laboratory tests based on instrumented indentation and scratch tests.

  20. Modelling structure and properties of amorphous silicon boron nitride ceramics

    Directory of Open Access Journals (Sweden)

    Johann Christian Schön

    2011-06-01

    Full Text Available Silicon boron nitride is the parent compound of a new class of high-temperature stable amorphous ceramics constituted of silicon, boron, nitrogen, and carbon, featuring a set of properties that is without precedent, and represents a prototypical random network based on chemical bonds of predominantly covalent character. In contrast to many other amorphous materials of technological interest, a-Si3B3N7 is not produced via glass formation, i.e. by quenching from a melt, the reason being that the binary components, BN and Si3N4, melt incongruently under standard conditions. Neither has it been possible to employ sintering of μm-size powders consisting of binary nitrides BN and Si3N4. Instead, one employs the so-called sol-gel route starting from single component precursors such as TADB ((SiCl3NH(BCl2. In order to determine the atomic structure of this material, it has proven necessary to simulate the actual synthesis route.Many of the exciting properties of these ceramics are closely connected to the details of their amorphous structure. To clarify this structure, it is necessary to employ not only experimental probes on many length scales (X-ray, neutron- and electron scattering; complex NMR experiments; IR- and Raman scattering, but also theoretical approaches. These address the actual synthesis route to a-Si3B3N7, the structural properties, the elastic and vibrational properties, aging and coarsening behaviour, thermal conductivity and the metastable phase diagram both for a-Si3B3N7 and possible silicon boron nitride phases with compositions different from Si3N4: BN = 1 : 3. Here, we present a short comprehensive overview over the insights gained using molecular dynamics and Monte Carlo simulations to explore the energy landscape of a-Si3B3N7, model the actual synthesis route and compute static and transport properties of a-Si3BN7.

  1. Metastable states in amorphous chalcogenide semiconductors

    CERN Document Server

    Mikla, Victor I

    2009-01-01

    This book addresses an interesting and technologically important class of materials, the amorphous chalcogenide semiconductors. Experimental results on the structural and electronic metastable states in Se-rich chalcogenides are presented. Special attention is paid to the states in the mobility gap and their sensitivity to various factors such as irradiation, annealing and composition. Photoinduced changes of structure and physical properties are also considered and structural transformation at photocrystallization is studied in detail. Finally, the authors discuss potential applications of th

  2. Structure and dynamics of amorphous water ice

    Science.gov (United States)

    Laufer, D.; Kochavi, E.; Bar-Nun, A.; Owen, T. (Principal Investigator)

    1987-01-01

    Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.

  3. Fluctuation microscopy analysis of amorphous silicon models

    Energy Technology Data Exchange (ETDEWEB)

    Gibson, J.M., E-mail: jmgibson@fsu.edu [Northeastern University, Department of Physics, Boston MA 02115 (United States); FAMU/FSU Joint College of Engineering, 225 Pottsdamer Street, Tallahassee, FL 32310 (United States); Treacy, M.M.J. [Arizona State University, Department of Physics, Tempe AZ 85287 (United States)

    2017-05-15

    Highlights: • Studied competing computer models for amorphous silicon and simulated fluctuation microscopy data. • Show that only paracrystalline/random network composite can fit published data. • Specifically show that pure random network or random network with void models do not fit available data. • Identify a new means to measure volume fraction of ordered material. • Identify unreported limitations of the Debye model for simulating fluctuation microscopy data. - Abstract: Using computer-generated models we discuss the use of fluctuation electron microscopy (FEM) to identify the structure of amorphous silicon. We show that a combination of variable resolution FEM to measure the correlation length, with correlograph analysis to obtain the structural motif, can pin down structural correlations. We introduce the method of correlograph variance as a promising means of independently measuring the volume fraction of a paracrystalline composite. From comparisons with published data, we affirm that only a composite material of paracrystalline and continuous random network that is substantially paracrystalline could explain the existing experimental data, and point the way to more precise measurements on amorphous semiconductors. The results are of general interest for other classes of disordered materials.

  4. Amorphous self-lubricant MoS2-C sputtered coating with high hardness

    Science.gov (United States)

    Gu, Lei; Ke, Peiling; Zou, Yousheng; Li, Xiaowei; Wang, Aiying

    2015-03-01

    MoS2-C coatings with various carbon contents were deposited by direct current magnetron sputtering. Carbon concentration (from 40.9 at.% to 73.1 at.%) within the coatings was controlled by varying the number of MoS2 plates bonded to the carbon targets. Ti interlayer fabricated by a hybrid high power impulse magnetron sputtering was used to obtain excellent adhesion. By sputtering the composite target, the deposited coatings exhibited a typical amorphous structure feature which contributed to the high hardness of the coatings. Meanwhile, the friction coefficient of the composite coating was lower than 0.1 in the ambient air and exhibited high wear resistance. Furthermore, the composite coatings exhibited an increasing hardness (from 7.0 to 10.8 GPa) with increasing carbon content.

  5. Crystalline-amorphous core-shell silicon nanowires for high capacity and high current battery electrodes.

    Science.gov (United States)

    Cui, Li-Feng; Ruffo, Riccardo; Chan, Candace K; Peng, Hailin; Cui, Yi

    2009-01-01

    Silicon is an attractive alloy-type anode material for lithium ion batteries because of its highest known capacity (4200 mAh/g). However silicon's large volume change upon lithium insertion and extraction, which causes pulverization and capacity fading, has limited its applications. Designing nanoscale hierarchical structures is a novel approach to address the issues associated with the large volume changes. In this letter, we introduce a core-shell design of silicon nanowires for highpower and long-life lithium battery electrodes. Silicon crystalline-amorphous core-shell nanowires were grown directly on stainless steel current collectors by a simple one-step synthesis. Amorphous Si shells instead of crystalline Si cores can be selected to be electrochemically active due to the difference of their lithiation potentials. Therefore, crystalline Si cores function as a stable mechanical support and an efficient electrical conducting pathway while amorphous shells store Li(+) ions. We demonstrate here that these core-shell nanowires have high charge storage capacity ( approximately 1000 mAh/g, 3 times of carbon) with approximately 90% capacity retention over 100 cycles. They also show excellent electrochemical performance at high rate charging and discharging (6.8 A/g, approximately 20 times of carbon at 1 h rate).

  6. Crystalline-Amorphous Core−Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes

    KAUST Repository

    Cui, Li-Feng

    2009-01-14

    Silicon is an attractive alloy-type anode material for lithium ion batteries because of its highest known capacity (4200 mAh/g). However silicon\\'s large volume change upon lithium insertion and extraction, which causes pulverization and capacity fading, has limited its applications. Designing nanoscale hierarchical structures is a novel approach to address the issues associated with the large volume changes. In this letter, we introduce a core-shell design of silicon nanowires for highpower and long-life lithium battery electrodes. Silicon crystalline- amorphous core-shell nanowires were grown directly on stainless steel current collectors by a simple one-step synthesis. Amorphous Si shells instead of crystalline Si cores can be selected to be electrochemically active due to the difference of their lithiation potentials. Therefore, crystalline Si cores function as a stable mechanical support and an efficient electrical conducting pathway while amorphous shells store Li ions. We demonstrate here that these core-shell nanowires have high charge storage capacity (̃1000 mAh/g, 3 times of carbon) with ̃90% capacity retention over 100 cycles. They also show excellent electrochemical performance at high rate charging and discharging (6.8 A/g, ̃20 times of carbon at 1 h rate). © 2009 American Chemical Society.

  7. Solvent-mediated amorphous-to-crystalline transformation of nitrendipine in amorphous particle suspensions containing polymers

    DEFF Research Database (Denmark)

    Xia, Dengning; Wu, Jian-Xiong; Cui, Fude

    2012-01-01

    The amorphous-to-crystalline transformation of nitrendipine was investigated using Raman spectroscopy and X-ray powder diffraction (XRPD). The nucleation and growth rate of crystalline nitrendipine in a medium containing poly (vinyl alcohol) (PVA) and polyethylene glycol (PEG 200) were quantitati......The amorphous-to-crystalline transformation of nitrendipine was investigated using Raman spectroscopy and X-ray powder diffraction (XRPD). The nucleation and growth rate of crystalline nitrendipine in a medium containing poly (vinyl alcohol) (PVA) and polyethylene glycol (PEG 200) were...... quantitatively determined using image analysis based on polarized light microscopy. The findings from the image analysis revealed that the transformation process occurred through the dissolution of amorphous drug precipitate followed by the nucleation and growth of the crystalline phase with the amorphous....... However, a further increase in drug concentration to 100mg/ml decelerated the growth of nitrendipine crystals. Combining image analysis of polarized light micrographs together with Raman spectroscopy and XRPD provided an in-depth insight into solid state transformations in amorphous nitrendipine...

  8. Amorphous P2S5/C Composite as High-Performance Anode Materials for Sodium-Ion Batteries.

    Science.gov (United States)

    Li, Xiang; Guo, Shaohua; Jiang, Kezhu; Qiao, Yu; Ishida, Masayoshi; Zhou, Haoshen

    2018-01-10

    We show a general method for achieving high-performance sodium storage materials via transforming crystalline P2S5 to amorphous P2S5 adhered to carbon matrix. The amorphous P2S5/C composite shows unique structural characteristics differing from the crystalline, which is identified by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM) and so on. The amorphous P2S5/C composite exhibits a safe average potential of 0.82 V, a reversible capacity of 400 mA h g-1, a remarkable capacity retention of 89.4% over 4000 cycles as well as good rate capability. Our findings open up opportunities to design of advanced anodes for room-temperature sodium-ion batteries.

  9. Quantifying Macroscopic Friction of Diamond-like Carbon Films by Microscopic Adsorption and Removal of Water Molecules.

    Science.gov (United States)

    Wang, Jingjing; Shang, Lunlin; Li, Xia; Lu, Zhibin; Zhang, Guangan

    2017-12-29

    The adsorption and desorption of water molecules, which affect the physical and chemical properties of the sliding interface, are critical for the friction behaviors of two solid contacts in atmosphere environment. The amount of water adsorbed on the open surface is a function of gas pressure according to an adsorption equation. However, for a confined sliding interface, the variation of surface fraction covered by gas molecules with water vapor pressure and its induced effects on friction have not been figured out. In this work, the macroscopic friction of diamond-like carbon (DLC) films in a water vapor atmosphere is quantified on the basis of microscopic adsorption and removal of water molecules. The studies correlate the fraction of water molecules adsorbed on the interface of self-mated DLC films with water vapor pressure to illustrate the direct relationship between friction coefficient and gas pressure by first-principles calculations and model fitting. The calculated results revealed that chemisorption and physisorption of water molecules occur on the surfaces of hydrogen-free DLC films (ta-C) and hydrogenated DLC films (HCF). Then, the relation between friction and gas pressure was built by employing a fractional coverage model based on the linear adsorption equation and gas removal. The obtained model agrees well with the typical experimental results about the steady-state friction coefficient of both highly hydrogenated DLC film (HCF) and tetrahedral amorphous carbon (ta-C) film during sliding at various water vapor pressures. In addition, it gave the curves of fractional surface coverage as a function of water vapor pressure. These results show that the frictional coefficient of DLC films could be predicted on the basis of fractional surface coverage as well as the intrinsic characters on surface chemistry. We suggest that the model may be thus extended to understand and predict the friction of DLC films under a specific gas pressure at a low load and

  10. Magnetization process, bipartite entanglement, and enhanced magnetocaloric effect of the exactly solved spin-1/2 Ising-Heisenberg tetrahedral chain.

    Science.gov (United States)

    Strečka, Jozef; Rojas, Onofre; Verkholyak, Taras; Lyra, Marcelo L

    2014-02-01

    The frustrated spin-1/2 Ising-Heisenberg ladder with Heisenberg intra-rung and Ising inter-rung interactions is exactly solved in a longitudinal magnetic field by taking advantage of the local conservation of the total spin on each rung and the transfer-matrix method. We have rigorously calculated the ground-state phase diagram, magnetization process, magnetocaloric effect, and basic thermodynamic quantities for the model, which can be alternatively viewed as an Ising-Heisenberg tetrahedral chain. It is demonstrated that a stepwise magnetization curve with an intermediate plateau at half of the saturation magnetization is also reflected in respective stepwise changes of the concurrence serving as a measure of bipartite entanglement. The ground-state phase diagram and zero-temperature magnetization curves of the Ising-Heisenberg tetrahedral chain are contrasted with the analogous results of the purely quantum Heisenberg tetrahedral chain, which have been obtained through density-matrix renormalization group (DMRG) calculations. While both ground-state phase diagrams fully coincide in the regime of weak inter-rung interaction, the purely quantum Heisenberg tetrahedral chain develops Luttinger spin-liquid and Haldane phases for strongly coupled rungs, which are absent in the Ising-Heisenberg counterpart model.

  11. Crystallized and amorphous vortices in rotating atomic-molecular Bose-Einstein condensates

    Science.gov (United States)

    Liu, Chao-Fei; Fan, Heng; Gou, Shih-Chuan; Liu, Wu-Ming

    2014-02-01

    Vortex is a topological defect with a quantized winding number of the phase in superfluids and superconductors. Here, we investigate the crystallized (triangular, square, honeycomb) and amorphous vortices in rotating atomic-molecular Bose-Einstein condensates (BECs) by using the damped projected Gross-Pitaevskii equation. The amorphous vortices are the result of the considerable deviation induced by the interaction of atomic-molecular vortices. By changing the atom-molecule interaction from attractive to repulsive, the configuration of vortices can change from an overlapped atomic-molecular vortices to carbon-dioxide-type ones, then to atomic vortices with interstitial molecular vortices, and finally into independent separated ones. The Raman detuning can tune the ratio of the atomic vortex to the molecular vortex. We provide a phase diagram of vortices in rotating atomic-molecular BECs as a function of Raman detuning and the strength of atom-molecule interaction.

  12. Cutting applications of DLC, hard carbon and diamond films

    OpenAIRE

    Vandevelde, Thierry; VANDIERENDONCK, Kristine; VAN STAPPEN, M; Mong, W. D.; Perremans, P

    1999-01-01

    Due to their high hardness and low friction coefficient, diamond-like carbon (DLC), amorphous hard carbon (HC), and diamond coatings have great potential for dry cutting operations. The main differences between these coatings can be found in their hardness (respectively 2500, 5000-8000 and 10000 HV), morphology (DLC and HC: amorphous and diamond: crystalline) and their thermal stability (DLC, 250 degrees C, HC: 600 degrees C and diamond: 700 degrees C). DLC, HC and CVD diamond-coated hard ins...

  13. Emerging trends in the stabilization of amorphous drugs

    DEFF Research Database (Denmark)

    Laitinen, Riikka; Löbmann, Korbinian; Strachan, Clare J.

    2013-01-01

    The number of active pharmaceutical substances having high therapeutic potential but low water solubility is constantly increasing, making it difficult to formulate these compounds as oral dosage forms. The solubility and dissolution rate, and thus potentially the bioavailability, of these poorly...... water-soluble drugs can be increased by the formation of stabilized amorphous forms. Currently, formulation as solid polymer dispersions is the preferred method to enhance drug dissolution and to stabilize the amorphous form of a drug. The purpose of this review is to highlight emerging alternative...... methods to amorphous polymer dispersions for stabilizing the amorphous form of drugs. First, an overview of the properties and stabilization mechanisms of amorphous forms is provided. Subsequently, formulation approaches such as the preparation of co-amorphous small-molecule mixtures and the use...

  14. Research Progress on Laser Cladding Amorphous Coatings on Metallic Substrates

    Directory of Open Access Journals (Sweden)

    CHEN Ming-hui

    2017-01-01

    Full Text Available The microstructure and property of amorphous alloy as well as the limitations of the traditional manufacturing methods for the bulk amorphous alloy were briefly introduced in this paper.Combined with characteristics of the laser cladding technique,the research status of the laser cladding Fe-based,Zr-based,Ni-based,Cu-based and Al-based amorphous coatings on the metal substrates were mainly summarized.The effects of factors such as laser processing parameter,micro-alloying element type and content and reinforcing phase on the laser cladding amorphous coatings were also involved.Finally,the main problems and the future research directions of the composition design and control of the laser-cladded amorphous coating,the design and optimization of the laser cladding process,and the basic theory of the laser cladding amorphous coatings were also put forward finally.

  15. Photoelectron yield spectroscopy and inverse photoemission spectroscopy evaluations of p-type amorphous silicon carbide films prepared using liquid materials

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Tatsuya, E-mail: mtatsuya@jaist.ac.jp, E-mail: mtakashi@jaist.ac.jp [Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Masuda, Takashi, E-mail: mtatsuya@jaist.ac.jp, E-mail: mtakashi@jaist.ac.jp; Inoue, Satoshi; Shimoda, Tatsuya [Green Device Research Center, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1211 (Japan); Yano, Hiroshi; Iwamuro, Noriyuki [Graduate School of Pure and Applied Sciences, University of Tsukuba, Tennoudai, Tsukuba, Ibaraki 305-8573 (Japan)

    2016-05-15

    Phosphorus-doped amorphous silicon carbide films were prepared using a polymeric precursor solution. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage, providing semiconducting properties in the films. The valence and conduction states of resultant films were determined directly through the combination of inverse photoemission spectroscopy and photoelectron yield spectroscopy. The incorporated carbon widened energy gap and optical gap comparably in the films with lower carbon concentrations. In contrast, a large deviation between the energy gap and the optical gap was observed at higher carbon contents because of exponential widening of the band tail.

  16. Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces

    Science.gov (United States)

    Nelson, Joey; Wasylenki, Laura; Bargar, John R.; Brown, Gordon E.; Maher, Kate

    2017-10-01

    Metal ion-mineral surface interactions and the attendant isotopic fractionation depend on the properties of the mineral surface and the local atomic-level chemical environment. However, these factors have not been systematically examined for phases of the same composition with different levels of surface disorder. We present pH-dependent adsorption edges, X-ray absorption spectra, and isotopic measurements to illustrate the effects of surface structural disorder and surface coverage on zinc(II) (Zn(II)) surface complexation and isotope fractionation. Our results demonstrate that Zn(II) surface complexes on quartz and amorphous silica (SiO2(am)) transition from octahedral to tetrahedral coordination by oxygen as surface coverage increases. In low ionic strength solutions (I = 0.004 M) and at low surface loadings (Γ isotopic fractionation (Δ66/64Znaqueous-sorbed = -0.01 ± 0.06‰) from aqueous Zn(II). In contrast, under similar chemical conditions and surface loading, outer-sphere Zn(II) adsorption complexes are not observed on SiO2(am) surfaces. At high ionic strength (I = 0.1 M) and low surface loading (Γ isotope fractionation factors for inner-sphere octahedral and tetrahedral complexes versus dissolved Zn, under the same conditions and on the same silica substrate, are not distinguishable beyond uncertainties. However, there is a larger measured equilibrium isotope fractionation with preferential sorption of heavy Zn as inner-sphere complexes on SiO2(am) (Δ66/64Znaqueous-sorbed = -0.94 ± 0.11‰) than on quartz (Δ66/64Znaqueous-sorbed = -0.60 ± 0.11‰).The propensity for Zn(II) to occur in tetrahedral and octahedral coordination with oxygen may help explain these observations. We posit that the low energetic difference between octahedral and tetrahedral Zn(II) may be why changes in inner-sphere Zn(II) coordination numbers with increasing coverage do not manifest as distinguishable isotope fractionations or as an observable alteration to the macroscopic

  17. Topological signatures of medium range order in amorphous semiconductor models

    Energy Technology Data Exchange (ETDEWEB)

    Treacy, M. M. J.; Voyles, P. M.; Gibson, J. M.

    2000-05-23

    The topological local cluster (or Schlaefli cluster) concept of Marians and Hobbs is used to detect topologically crystalline regions in models of disordered tetrahedral semiconductors. The authors present simple algorithms for detecting both Wells-type shortest circuits and O'Keeffe-type rings, which can be used to delineate alternative forms of the Schlaefli cluster in models.

  18. Carbon. Examples of Property Realization

    Directory of Open Access Journals (Sweden)

    I.A. Kossko

    2013-11-01

    Full Text Available Examples of realization of carbon properties in formation of section near-surface boundaries defining the mechanism of oxidizing (normal wear are presented. Synthesis of strengt hening diamond- lonsdaleite -carbene «frame» and graphite with function of solid lubricant on a friction surface in high-desperse carbon environment is reviewed. Prospects of carbon ap placation in implementation of the concept of electronics on one element, and also use of thin-film structures of amorphous carbon – metal for data recording are discussed.

  19. CO2 capture in different carbon materials.

    Science.gov (United States)

    Jiménez, Vicente; Ramírez-Lucas, Ana; Díaz, José Antonio; Sánchez, Paula; Romero, Amaya

    2012-07-03

    In this work, the CO(2) capture capacity of different types of carbon nanofibers (platelet, fishbone, and ribbon) and amorphous carbon have been measured at 26 °C as at different pressures. The results showed that the more graphitic carbon materials adsorbed less CO(2) than more amorphous materials. Then, the aim was to improve the CO(2) adsorption capacity of the carbon materials by increasing the porosity during the chemical activation process. After chemical activation process, the amorphous carbon and platelet CNFs increased the CO(2) adsorption capacity 1.6 times, whereas fishbone and ribbon CNFs increased their CO(2) adsorption capacity 1.1 and 8.2 times, respectively. This increase of CO(2) adsorption capacity after chemical activation was due to an increase of BET surface area and pore volume in all carbon materials. Finally, the CO(2) adsorption isotherms showed that activated amorphous carbon exhibited the best CO(2) capture capacity with 72.0 wt % of CO(2) at 26 °C and 8 bar.

  20. Hydrogenation of Amorphous and Crystalline RE-Ni Alloys

    OpenAIRE

    AOKI, Kiyoshi; Shirakawa, Kiwamu; MASUMOTO, Tsuyoshi

    1985-01-01

    Amorphous alloys with the combination of a rare earth metal(RE=Y, La, Ce, Pr and Sm) and nickel were prepared around the composition at an eutectic point by the melt-quenching technique. Amorphous Y-Ni and Sm-Ni alloys absorbed a large amount of hydrogen even in the amorphous state, while the the other alloys in La-Ni, Ce-Ni and Pr-Ni systems were decomposed to a mixture of crystalline phase and hydride during hydrogenation at 323 K. An amorphous SmNi_2 phase was also synthesized by reaction ...

  1. Fast surface crystallization of amorphous griseofulvin below T g.

    Science.gov (United States)

    Zhu, Lei; Jona, Janan; Nagapudi, Karthik; Wu, Tian

    2010-08-01

    To study crystal growth rates of amorphous griseofulvin (GSF) below its glass transition temperature (T (g)) and the effect of surface crystallization on the overall crystallization kinetics of amorphous GSF. Amorphous GSF was generated by melt quenching. Surface and bulk crystal growth rates were determined using polarized light microscope. X-ray powder diffraction (XRPD) and Raman microscopy were used to identify the polymorph of the crystals. Crystallization kinetics of amorphous GSF powder stored at 40 degrees C (T (g)-48 degrees C) and room temperature (T (g)-66 degrees C) was monitored using XRPD. Crystal growth at the surface of amorphous GSF is 10- to 100-fold faster than that in the bulk. The surface crystal growth can be suppressed by an ultrathin gold coating. Below T (g), the crystallization of amorphous GSF powder was biphasic with a rapid initial crystallization stage dominated by the surface crystallization and a slow or suspended late stage controlled by the bulk crystallization. GSF exhibits the fastest surface crystallization kinetics among the known amorphous pharmaceutical solids. Well below T (g), surface crystallization dominated the overall crystallization kinetics of amorphous GSF powder. Thus, surface crystallization should be distinguished from bulk crystallization in studying, modeling and controlling the crystallization of amorphous solids.

  2. Excessively High Vapor Pressure of Al-based Amorphous Alloys

    Directory of Open Access Journals (Sweden)

    Jae Im Jeong

    2015-10-01

    Full Text Available Aluminum-based amorphous alloys exhibited an abnormally high vapor pressure at their approximate glass transition temperatures. The vapor pressure was confirmed by the formation of Al nanocrystallites from condensation, which was attributed to weight loss of the amorphous alloys. The amount of weight loss varied with the amorphous alloy compositions and was inversely proportional to their glass-forming ability. The vapor pressure of the amorphous alloys around 573 K was close to the vapor pressure of crystalline Al near its melting temperature, 873 K. Our results strongly suggest the possibility of fabricating nanocrystallites or thin films by evaporation at low temperatures.

  3. Delivery of poorly soluble compounds by amorphous solid dispersions.

    Science.gov (United States)

    Lee, Thomas W Y; Boersen, Nathan A; Hui, H W; Chow, S F; Wan, K Y; Chow, Albert H L

    2014-01-01

    Solid state manipulation by amorphous solid dispersion has been the subject of intensive research for decades due to their excellent potential for dissolution and bioavailability enhancement. The present review aims to highlight the latest advancement in this area, with focus on the fundamentals, characterization, formulation development and manufacturing of amorphous solid dispersions as well as the new generation amorphization technologies. Additionally, specific applications of amorphous solid dispersion in the formulation of herbal drugs or bioactive natural products are reviewed to reflect the growing interest in this relatively neglected area.

  4. Spectroscopie de vibration infrarouge du silicium amorphe ...

    African Journals Online (AJOL)

    Ce travail porte sur l'étude des configurations des liaisons Si-H des couches minces du silicium amorphe hydrogéné évaporé (a-Si:H) préparées dans un bâti ultra-vide (UHV). L'hydrogène atomique est obtenu à l'aide d'un plasma dans un tube à décharge dirigé vers le porte-substrat. Les fréquences de vibrations et la ...

  5. Modeling and Simulation of Amorphous Materials

    Science.gov (United States)

    Pandey, Anup

    The general and practical inversion of diffraction data - producing a computer model correctly representing the material explored - is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this dissertation, we introduce a robust method, Force-Enhanced Atomic Refinement (FEAR), which jointly exploits the power of ab initio atomistic simulation along with the information carried by diffraction data. As a preliminary trial, the method has been implemented using empirical potentials for amorphous silicon (a-Si) and silica ( SiO2). The models obtained are comparable to the ones prepared by the conventional approaches as well as the experiments. Using ab initio interactions, the method is applied to two very different systems: amorphous silicon (a-Si) and two compositions of a solid electrolyte memory material silver-doped GeSe3. It is shown that the method works well for both the materials. Besides that, the technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. It offers a means to add a priori information in first principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. Moreover, the method has also been used to create a computer model of a-Si, using highly precise X-ray diffraction data. The model predicts properties that are close to the continuous random network models but with no a priori assumptions. In addition, using the ab initio molecular dynamics simulations (AIMD) we explored the doping and transport in hydrogenated amorphous silicon a-Si:H with the most popular impurities: boron and phosphorous. We investigated doping for these impurities and the role of H in the doping process. We revealed the network motion and H hopping induced by

  6. Electronic and vibronic cluster models for the T24(G) level of d5 ions in tetrahedral symmetry

    Science.gov (United States)

    Parrot, R.; Boulanger, D.

    2006-08-01

    Electronic and vibronic cluster models are proposed to elaborate a general model for the T24(G) orbital triplet levels of d5 ions in tetrahedral symmetry. These models involve perturbation schemes and the diagonalization of the molecular electronic structure and vibronic Hamiltonian. First, the electronic fine structure is determined from the first- and second-order molecular spin-orbit (MSO) interaction. Then, Ham’s perturbation model for vibronic interactions is used in conjunction with the molecular model to analyze the vibronic interactions corresponding to a strong coupling to ɛ -vibrational modes. Then, a more general model is considered to account for the energy-level schemes and the strong intensity transfer observed, for example, on the fine structure lines of the T24(G) level of Mn2+ in ZnS and ZnSe. This model involves the diagonalization of the vibronic Hamiltonian for the T24(G) level and a perturbation model to account for vibronic interactions with all other multiplets of the d5 configuration. It is shown that the energy-level schemes as well as the strong intensity transfer of the fine structure lines of the T24(G) level of Mn2+ in ZnS and ZnSe are very well accounted for from the electronic molecular model involving the first- and second-order MSO interaction and from the proposed diagonalization and perturbation models for the coupling to ɛ -vibrational modes.

  7. Final Report - High-Order Spectral Volume Method for the Navier-Stokes Equations On Unstructured Tetrahedral Grids

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Z J

    2012-12-06

    The overriding objective for this project is to develop an efficient and accurate method for capturing strong discontinuities and fine smooth flow structures of disparate length scales with unstructured grids, and demonstrate its potentials for problems relevant to DOE. More specifically, we plan to achieve the following objectives: 1. Extend the SV method to three dimensions, and develop a fourth-order accurate SV scheme for tetrahedral grids. Optimize the SV partition by minimizing a form of the Lebesgue constant. Verify the order of accuracy using the scalar conservation laws with an analytical solution; 2. Extend the SV method to Navier-Stokes equations for the simulation of viscous flow problems. Two promising approaches to compute the viscous fluxes will be tested and analyzed; 3. Parallelize the 3D viscous SV flow solver using domain decomposition and message passing. Optimize the cache performance of the flow solver by designing data structures minimizing data access times; 4. Demonstrate the SV method with a wide range of flow problems including both discontinuities and complex smooth structures. The objectives remain the same as those outlines in the original proposal. We anticipate no technical obstacles in meeting these objectives.

  8. Thermo-Fluidic Comparison between Sandwich Panels with Tetrahedral Lattice Cores Fabricated by Casting and Metal Sheet Folding

    Directory of Open Access Journals (Sweden)

    Xiaoqing Zhang

    2017-07-01

    Full Text Available This numerical study compares single-phase forced convective heat transfer between two sandwich panels with tetrahedral metallic lattice cores separately fabricated by investment casting and the more cost-effective metal sheet folding method. The numerical model is validated against available experimental data. For a given Reynolds number and core porosity, the results reveal that the brazed sandwich outperforms the casted sandwich, exhibiting a 13% to 16% higher Nusselt number. Bigger vertexes and more evident blockage of mainstream by the ligaments are found to intensify the horseshoe vortex and the counter-rotating vortex pair upstream and downstream of each vertex. Relative to the casted sandwich panel, therefore, endwall heat transfer is enhanced by 22% to 27%, while similar heat transfer is achieved on the ligaments. It is also found that, for a given Reynolds number, the brazed sandwich induces a 1.6 to 1.7 times higher pressure drop relative to the casted sandwich due to more severe flow separation caused by the sharp edges of the rectangular ligaments. Finally, for a given pumping power, both sandwiches provide a similar heat transfer performance. Given that the brazed sandwich is more cost-effective and easier to fabricate than the casted one, the former may be superior from an engineering application point of view.

  9. 31P Differential Line Broadening in the Presence of the 59Co Quadrupolar-CSA Interference in Tetrahedral Clusters

    Science.gov (United States)

    Granger, Pierre; Elbayed, Karim; Raya, Jésus; Kempgens, Pierre; Rosé, Jacky

    The first investigation and analysis of the effects, theoretically predicted by Werbelow et al.[ J. Chem. Soc. Faraday Trans.83, 871 (1987)], of interference terms on the lineshape of a spin 1/2 coupled to a high-spin nucleus undergoing quadrupolar and chemical-shift anisotropy (CSA) relaxations are reported for three tetrahedral clusters HFeCo 3(CO) 11L with L = PPh 2H (1), L = PCy 2H (2), and L = PPh 3(3) (Cy = cyclohexyl). For these clusters in solution, an unusual asymmetric broad NMR multiplet of the 31P nucleus scalar-coupled to a 59Co nucleus is observed. It is shown that the 59Co CSA-quadrupolar interference term is the origin of the asymmetry of the 31P spectra. The analysis of the lineshape of the 1H-decoupled spectra gives the spin-coupling constants 1J( 31P- 59Co) and the CSA contribution to the 59Co relaxation. Experimental measurements of T1and of the linewidths for cobalt-59 are reported and support these findings.

  10. Ultrahard carbon nanocomposite films

    Energy Technology Data Exchange (ETDEWEB)

    SIEGAL,MICHAEL P.; TALLANT,DAVID R.; PROVENCIO,PAULA P.; OVERMYER,DONALD L.; SIMPSON,REGINA L.; MARTINEZ-MIRANDA,L.J.

    2000-01-27

    Modest thermal annealing to 600 C of diamondlike amorphous-carbon (a-C) films grown at room temperature results in the formation of carbon nanocomposites with hardness similar to diamond. These nanocomposite films consist of nanometer-sized regions of high density a-C embedded in an a-C matrix with a reduced density of 5--10%. The authors report on the evolution of density and bonding topologies as a function of annealing temperature. Despite a decrease in density, film hardness actually increases {approximately} 15% due to the development of the nanocomposite structure.

  11. Reducing the magnetic losses of amorphous ribbon

    Energy Technology Data Exchange (ETDEWEB)

    Raybould, D.; Das, S.K. [AlliedSignal Inc., Morristown, NJ (United States). Aerospace Technol. Team; Meola, M.; Bye, R. [AlliedSignal Inc., Amorphous Metals, Morristown, NJ 07962-1021 (United States)

    1998-01-30

    Amorphous alloys have lower magnetization losses than silicon steel and are therefore used as the cores of high-efficiency electrical transformers. Laser scribing the amorphous alloys using a very low power, so as not to melt the surface, results in an appreciable decrease in core loss with no decrease in measurable induction. A 2-5 mm line spacing appears optimum. Scribing prior to or after magnetic annealing results in similar properties, although the former requires a slightly higher laser power. Excimer and YAG lasers using optimized parameters both result in identical magnetic properties, but the optimum morphology of the scribed line is different for the two types of laser. For 25 {mu}m thick ribbon, a 29% decrease in core loss is obtained with no increase in exciting power. For thick, 50 {mu}m ribbon, properties superior to those of conventional 25 {mu}m ribbon are achievable, the core loss being decreased nearly 50% with no increase in exciting power. Thick ribbon with these properties could decrease the fabrication cost, while increasing the efficiency of power transformers. (orig.) 15 refs.

  12. High-harmonic generation in amorphous solids.

    Science.gov (United States)

    You, Yong Sing; Yin, Yanchun; Wu, Yi; Chew, Andrew; Ren, Xiaoming; Zhuang, Fengjiang; Gholam-Mirzaei, Shima; Chini, Michael; Chang, Zenghu; Ghimire, Shambhu

    2017-09-28

    High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We decouple the role of long-range periodicity by comparing harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. Our results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources.Although higher harmonic generation from solids has become of interest in many fields, its observation is typically limited to crystalline solids. Here, the authors demonstrate that higher harmonics can be generated from amorphous solids.

  13. The Local Physical Structure of Amorphous Boron Carbide Thin Films

    Science.gov (United States)

    Paquette, M. M.; Li, Wenjing; Driver, M. S.; Oyler, N. A.; Caruso, A. N.

    2011-03-01

    Thin-film amorphous hydrogenated boron carbide (a-B5 C:Hx) and technical boron carbide (B4 C:Cy) are important materials in next-generation solid-state neutron detectors and refractory electronics. Optimizing the electrical carrier transport and electronic structure of these films for the stated applications has been severely hindered by: (1) their lack of long-range periodicity; (2) the ability of boron-rich solids to form complex polyhedra; and, (3) the possibility that carbon atoms incorporate into the polyhedral structures in an intraicosahedral fashion or that they bridge polyhedral structures in an intericosahedral fashion. The use of traditional spectroscopies that are sensitive to local coordination environment have been inadequate in the determination of the local physical structure because of either poor resolution or very low interaction cross sections. However, magic spinning angle (MAS) solid-state nuclear magnetic resonance (SSNMR), does have the signal-to-noise and rigor to extract the local physical coordination structure of these materials, despite the challenges associated with deltahedra-based structures. This poster will describe the progress and challenges in structure determination through a comparison of unknown samples to known calibration standards using MAS techniques, in the context of furthering the general understanding of the electronic structure of a-B5 C:Hx and B4 C:Cy thin films.

  14. The chemical composition and band gap of amorphous Si:C:N:H layers

    Energy Technology Data Exchange (ETDEWEB)

    Swatowska, Barbara, E-mail: swatow@agh.edu.pl [AGH University of Science and Technology, Department of Electronics, Mickiewicza Av. 30, 30-059 Krakow (Poland); Kluska, Stanislawa; Jurzecka-Szymacha, Maria [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Mickiewicza Av. 30, 30-059 Krakow (Poland); Stapinski, Tomasz [AGH University of Science and Technology, Department of Electronics, Mickiewicza Av. 30, 30-059 Krakow (Poland); Tkacz-Smiech, Katarzyna [AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Mickiewicza Av. 30, 30-059 Krakow (Poland)

    2016-05-15

    Highlights: • Six type of amorphous hydrogenated films were obtained and analysed. • Investigated chemical bondings strongly influenced energy gap values. • Analysed layers could be applied as semiconductors and also as dielectrics. - Abstract: In this work we presented the correlation between the chemical composition of amorphous Si:C:N:H layers of various content of silicon, carbon and nitrogen, and their band gap. The series of amorphous Si:C:N:H layers were obtained by plasma assisted chemical vapour deposition method in which plasma was generated by RF (13.56 MHz, 300 W) and MW (2.45 GHz, 2 kW) onto monocrystalline silicon Si(001) and borosilicate glass. Structural studies were based on FTIR transmission spectrum registered within wavenumbers 400–4000 cm{sup −1}. The presence of Si−C, Si−N, C−N, C=N, C=C, C≡N, Si−H and C−H bonds was shown. The values band gap of the layers have been determined from spectrophotometric and ellipsometric measurements. The respective values are contained in the range between 1.64 eV – characteristic for typical semiconductor and 4.21 eV – for good dielectric, depending on the chemical composition and atomic structure of the layers.

  15. CO_2 Methanation Catalysts Prepared from Amorphous Ni-Valve Metal Alloys Containing Platinum Group Elements

    OpenAIRE

    Ken-ichiro, Wakuda; Hiroki, Habazaki; Asahi, Kawashima; Katsuhiko, Asami; Koji, Hashimoto; Institute for Materials Research

    1993-01-01

    The amorphous Ni-valve metal (Ti, Zr, Nb and Ta) alloys containing a few at% of platinum group elements were activated by immersion into hydrofluoric acid and used for hydrogenation of carbon dioxide at 100-300℃. This surface activation led to formation of nanocrystalline surface alloys with high surface area, and to surface enrichment of platinum group elements on the titanium-, niobium- and tantalum-containing alloys, but not on the zirconium-containing alloys. The surface of the latter all...

  16. Structure and electronic properties of amorphous WO3

    NARCIS (Netherlands)

    Wijs, G.A. de; Groot, R.A. de

    1999-01-01

    The structure and electronic structure of amorphous WO3 were studied with first-principles density-functional calculations. Upon amorphization, a large increase of the band gap is observed. The empty states exhibit a tendency towards localization. We studied the filling of these states as induced by

  17. Phase transformations of amorphous semiconductor alloys under high pressures

    CERN Document Server

    Antonov, V E; Fedotov, V K; Harkunov, A I; Ponyatovsky, E G

    2002-01-01

    The paper reviews the results of experimental studies and thermodynamical modelling of metastable T-P diagrams of initially amorphous GaSb-Ge and Zn-Sb alloys which provide a new insight into the problem of pressure-induced amorphization.

  18. Creep of FINEMET alloy at amorphous to nanocrystalline transition

    NARCIS (Netherlands)

    Csach, K.; Miškuf, J.; Juríková, A.; Ocelík, V.

    2009-01-01

    The application of FINEMET-type materials with specific magnetic properties prepared by the crystallization of amorphous alloys is often limited by their brittleness. The structure of these materials consists of nanosized Fe-based grains surrounded with amorphous phase. Then the final macroscopic

  19. Amorphization of SiC under ion and neutron irradiation

    Science.gov (United States)

    Snead, L. L.; Zinkle, S. J.; Hay, J. C.; Osborne, M. C.

    1998-05-01

    This paper presents results on the microstructure and physical properties of SiC amorphized by both ion and neutron irradiation. Specifically, 0.56 MeV Si ions have been implanted in single crystal 6H-SiC from ambient through >200°C and the critical threshold for amorphization was measured as a function of the irradiation temperature. From a high resolution transmission electron microscopy (HRTEM) study of the crystalline to amorphous transition region in these materials, elongated pockets of amorphous material oriented parallel to the free surface are observed. Single crystal 6H-SiC and hot pressed and sintered 6H and 3C SiC were neutron irradiated at approximately 70°C to a dose of ˜2.56 dpa causing complete amorphization. Property changes resulting from the crystal to amorphous transition in SiC include a density decrease of 10.8%, a hardness decrease from 38.7 to 21.0 GPa, and a decrease in elastic modulus from 528 to 292 GPa. Recrystallization of the amorphized, single crystal 6H-SiC appears to occur in two stages. In the temperature range of ˜800-1000°C, crystallites nucleate and slowly grow. In the temperature range of 1125-1150°C spontaneous nucleation and rapid growth of crystallites occur. It is further noted that amorphized 6H (alpha) SiC recrystallizes to highly faulted fcc (beta) SiC.

  20. Ductile fracture surface morphology of amorphous metallic alloys

    NARCIS (Netherlands)

    Miskuf, J; Csach, Kornel; Ocelik, [No Value; Bengus, VZ; Tabachnikova, ED; Duhaj, P; Ocelik, Vaclav

    2002-01-01

    Ductile shear failure of hulk amorphous metallic alloys was studied using a fractographic is analysis. Although the mechanisms of shear deformation and fracture are appeared the same as in conventional amorphous ribbons, some new fractographic features are observed in bulk alloys. Geometric

  1. Prenatal toxicity of synthetic amorphous silica nanomaterial in rats

    NARCIS (Netherlands)

    Hofmanna, T.; Schneider, S.; Wolterbeek, A.; Sandt, H. van de; Landsiedel, R.; Ravenzwaay, B. van

    2015-01-01

    Synthetic amorphous silica is a nanostructured material, which is produced and used in a wide variety of technological applications and consumer products. No regulatory prenatal toxicity studies with this substance were reported yet. Therefore, synthetic amorphous silica was tested for prenatal

  2. Amorphous and crystalline silicon based heterojunction solar cells

    NARCIS (Netherlands)

    Schuttauf, J.A.|info:eu-repo/dai/nl/314118039

    2011-01-01

    In this thesis, research on amorphous and crystalline silicon heterojunction (SHJ) solar cells is described. Probably the most important feature of SHJ solar cells is a thin intrinsic amorphous silicion (a‑Si:H) layer that is deposited before depositing the doped emitter and back surface field. The

  3. Spatial confinement can lead to increased stability of amorphous indomethacin

    DEFF Research Database (Denmark)

    Nielsen, Line Hagner; Keller, Stephan Sylvest; Gordon, Keith C.

    2012-01-01

    The aim of this study was to investigate whether the physical stability of amorphous indomethacin can be improved by separating the drug material into small units by the use of microcontainers. Crystallisation from the spatially confined amorphous indomethacin in the microcontainers was determined...

  4. Magnetic surface anisotropy of amorphous Fe-B ultrathin films

    Science.gov (United States)

    Zhang, L.; Rado, G. T.; Liou, S. H.; Chien, C. L.

    1986-02-01

    The magnetic surface anisotropy constants KS of amorphous Fe xB 100- x was determined by performing ferromagnetic resonance (FMR) measurements on ultrathin films and adapting a recent FMR theory to amorphous materials. For a given Fe content x the same value of KS is obtained at two frequencies and two FMR configurations.

  5. Tetrahedral connection of ε-Keggin-type polyoxometalates to form an all-inorganic octahedral molecular sieve with an intrinsic 3D pore system.

    Science.gov (United States)

    Zhang, Zhenxin; Sadakane, Masahiro; Murayama, Toru; Izumi, Shoko; Yasuda, Nobuhiro; Sakaguchi, Norihito; Ueda, Wataru

    2014-01-21

    A new type of polyoxometalate-based porous material was successfully synthesized. The new material is the first fully inorganic Keggin-type polyoxometalate-based microporous material with intrinsically ordered open micropores and is the third member of the small family of octahedral molecular sieves (OMSs). Twelve MoO6 or VO6 octahedra surround a central VO4 tetrahedron to form ε-Keggin polyoxometalate building blocks (ε-VMo9.4V2.6O40) that are linked by Bi(III) ions to form crystalline Mo-V-Bi oxide with a diamondoid topology. The presence of a tetrahedral shape of the ε-Keggin polyoxometalate building block results in arrangement of microporosity in a tetrahedral fashion which is new in OMSs. Owing to its microporosity, this Mo-V-Bi oxide shows zeolitic-like properties such as ion-exchange and molecule adsorption.

  6. A fully tetrahedral and highly corner-sharing network model of ZnCl2 glass and its comparison to SiO2 glass

    Science.gov (United States)

    Swansbury, Laura A.; Mountjoy, Gavin

    2017-07-01

    Zinc chloride, ZnCl2, is intermediate between a strong and a fragile glass former. During computational simulations, it is therefore important to account for ion polarizability. This, together with the lack of suitable interatomic potential parameters, is the likely cause for the lack of modeling studies on ZnCl2 glass which contain a high degree of ZnCl4 tetrahedral units. Through using accurate interatomic potential parameters and applying the adiabatic core-shell model, the first fully tetrahedral model of ZnCl2 glass was obtained. The Cl-Zn-Cl bond angle of 109° reproduced the ideal tetrahedral bond angle, and the calculated total neutron and x-ray structure factors closely replicated experimental findings. While 86% of the ZnCl4 tetrahedral units were corner-sharing, 14% were found to be edge-sharing. This led to two distinct contributions in both the Zn-Cl-Zn bond angle distribution and in the Zn⋯Zn nearest neighbour peaks being seen. These are not apparent in studies based on neutron diffraction. By comparing the intermediate glass former ZnCl2 to the strong glass former SiO2, marked differences in ring statistics became apparent. The Zn-Cl-Zn bond angle of around 110° enabled 3-membered rings to form in significant proportions. In contrast, 3-membered rings were only present in SiO2 glass as defects. By calculating the ZnCl2 and SiO2 partial structure factors, strong similarities became visible after scaling according to nearest neighbour distances. Although it was apparent that the main contributions to the first sharp diffraction peak (FSDP) came from cation-anion correlations, the relative scaling of the FSDP positions in ZnCl2 and SiO2 glass was not understood.

  7. 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.

  8. Charge transport in amorphous organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lukyanov, Alexander

    2011-03-15

    Organic semiconductors with the unique combination of electronic and mechanical properties may offer cost-effective ways of realizing many electronic applications, e. g. large-area flexible displays, printed integrated circuits and plastic solar cells. In order to facilitate the rational compound design of organic semiconductors, it is essential to understand relevant physical properties e. g. charge transport. This, however, is not straightforward, since physical models operating on different time and length scales need to be combined. First, the material morphology has to be known at an atomistic scale. For this atomistic molecular dynamics simulations can be employed, provided that an atomistic force field is available. Otherwise it has to be developed based on the existing force fields and first principle calculations. However, atomistic simulations are typically limited to the nanometer length- and nanosecond time-scales. To overcome these limitations, systematic coarse-graining techniques can be used. In the first part of this thesis, it is demonstrated how a force field can be parameterized for a typical organic molecule. Then different coarse-graining approaches are introduced together with the analysis of their advantages and problems. When atomistic morphology is available, charge transport can be studied by combining the high-temperature Marcus theory with kinetic Monte Carlo simulations. The approach is applied to the hole transport in amorphous films of tris(8- hydroxyquinoline)aluminium (Alq{sub 3}). First the influence of the force field parameters and the corresponding morphological changes on charge transport is studied. It is shown that the energetic disorder plays an important role for amorphous Alq{sub 3}, defining charge carrier dynamics. Its spatial correlations govern the Poole-Frenkel behavior of the charge carrier mobility. It is found that hole transport is dispersive for system sizes accessible to simulations, meaning that calculated

  9. Atomistic simulation of damage accumulation and amorphization in Ge

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Selles, Jose L., E-mail: joseluis.gomezselles@imdea.org; Martin-Bragado, Ignacio [IMDEA Materials Institute, Eric Kandel 2, 28906 Getafe, Madrid (Spain); Claverie, Alain [CEMES/CNRS, 29 rue J. Marvig, 31055 Toulouse Cedex (France); Sklenard, Benoit [CEA, LETI, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Benistant, Francis [GLOBALFOUNDRIES Singapore Pte Ltd., 60 Woodlands Industrial Park D Street 2, Singapore 738406 (Singapore)

    2015-02-07

    Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 10{sup 22} cm{sup −3} which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions. We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.

  10. Moringa coagulant as a stabilizer for amorphous solids: Part I.

    Science.gov (United States)

    Bhende, Santosh; Jadhav, Namdeo

    2012-06-01

    Stabilization of amorphous state is a focal area for formulators to reap benefits related with solubility and consequently bioavailability of poorly soluble drugs. In the present work, an attempt has been made to explore the potential of moringa coagulant as an amorphous state stabilizer by investigating its role in stabilization of spray-dried (amorphous) ibuprofen, meloxicam and felodipine. Thermal studies like glass forming ability, glass transition temperature, hot stage microscopy and DSC were carried out for understanding thermodynamic stabilization of drugs. PXRD and dissolution studies were performed to support contribution of moringa coagulant. Studies showed that hydrogen bonding and electrostatic interactions between drug and moringa coagulant are responsible for amorphous state stabilization as explored by ATR-FTIR and molecular docking. Especially, H-bonding was found to be predominant mechanism for drug stabilization. Therein, arginine (basic amino acid in coagulant) exhibited various interactions and played important role in stabilization of aforesaid amorphous drugs.

  11. A molecular dynamics study of the role of molecular water on the structure and mechanics of amorphous geopolymer binders

    Science.gov (United States)

    Sadat, Mohammad Rafat; Bringuier, Stefan; Asaduzzaman, Abu; Muralidharan, Krishna; Zhang, Lianyang

    2016-10-01

    In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.

  12. A Deep Penetration Problem Calculation Using AETIUS:An Easy Modeling Discrete Ordinates Transport Code UsIng Unstructured Tetrahedral Mesh, Shared Memory Parallel

    Science.gov (United States)

    KIM, Jong Woon; LEE, Young-Ouk

    2017-09-01

    As computing power gets better and better, computer codes that use a deterministic method seem to be less useful than those using the Monte Carlo method. In addition, users do not like to think about space, angles, and energy discretization for deterministic codes. However, a deterministic method is still powerful in that we can obtain a solution of the flux throughout the problem, particularly as when particles can barely penetrate, such as in a deep penetration problem with small detection volumes. Recently, a new state-of-the-art discrete-ordinates code, ATTILA, was developed and has been widely used in several applications. ATTILA provides the capabilities to solve geometrically complex 3-D transport problems by using an unstructured tetrahedral mesh. Since 2009, we have been developing our own code by benchmarking ATTILA. AETIUS is a discrete ordinates code that uses an unstructured tetrahedral mesh such as ATTILA. For pre- and post- processing, Gmsh is used to generate an unstructured tetrahedral mesh by importing a CAD file (*.step) and visualizing the calculation results of AETIUS. Using a CAD tool, the geometry can be modeled very easily. In this paper, we describe a brief overview of AETIUS and provide numerical results from both AETIUS and a Monte Carlo code, MCNP5, in a deep penetration problem with small detection volumes. The results demonstrate the effectiveness and efficiency of AETIUS for such calculations.

  13. Cryogenic grinding of indomethacin polymorphs and solvates: assessment of amorphous phase formation and amorphous phase physical stability.

    Science.gov (United States)

    Crowley, Kieran J; Zografi, George

    2002-02-01

    The effect of cryogenic grinding on five crystal forms of indomethacin (IMC) was investigated with particular interest in the formation of amorphous phase. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) demonstrated that amorphous phase formation took place for all three polymorphs (gamma, alpha, and delta) and one solvate (IMC methanolate). In the latter case, a postgrinding drying stage was needed to remove desolvated methanol from the ground amorphous product because methanol destabilized amorphous IMC presumably via a plasticizing effect. The crystal structure of another solvate, IMC t-butanolate, was unaffected by grinding, indicating that amorphous phase formation on grinding does not occur in all cases. Ground amorphous materials possessed similar glass transition temperatures but significant differences in physical stability as assessed by both isothermal and nonisothermal crystallization. It is argued that physical factors, namely residual crystal phase and specific surface area, determine the isothermal and nonisothermal crystallization behavior of ground amorphous samples as opposed to intrinsic differences in the structure of the amorphous phase. Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:492-507, 2002

  14. Amorphous silicon crystalline silicon heterojunction solar cells

    CERN Document Server

    Fahrner, Wolfgang Rainer

    2013-01-01

    Amorphous Silicon/Crystalline Silicon Solar Cells deals with some typical properties of heterojunction solar cells, such as their history, the properties and the challenges of the cells, some important measurement tools, some simulation programs and a brief survey of the state of the art, aiming to provide an initial framework in this field and serve as a ready reference for all those interested in the subject. This book helps to "fill in the blanks" on heterojunction solar cells. Readers will receive a comprehensive overview of the principles, structures, processing techniques and the current developmental states of the devices. Prof. Dr. Wolfgang R. Fahrner is a professor at the University of Hagen, Germany and Nanchang University, China.

  15. Computer simulation of amorphous MIS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Shousha, A.H.M.; El-Kosheiry, M.A. [Cairo University (Egypt). Electronics and Communications Engineering Dept.

    1997-10-01

    A computer model to simulate amorphous MIS solar cells is developed. The model is based on the self-consistent solution of the electron and hole continuity equations, together with the Poisson equation under proper boundary conditions. The program developed is used to investigate the cell performance characteristics in terms of its physical and structural parameters. The current-voltage characteristics of the solar cell are obtained under AMI solar illumination. The dependences of the short-circuit current, open-circuit voltage, fill factor and cell conversion efficiency on localized gap state density, carrier lifetime, cell thickness and surface recombination velocity are obtained and discussed. The results presented show how cell parameters can be varied to improve the cell performance characteristics. (Author)

  16. Spray drying formulation of amorphous solid dispersions.

    Science.gov (United States)

    Singh, Abhishek; Van den Mooter, Guy

    2016-05-01

    Spray drying is a well-established manufacturing technique which can be used to formulate amorphous solid dispersions (ASDs) which is an effective strategy to deliver poorly water soluble drugs (PWSDs). However, the inherently complex nature of the spray drying process coupled with specific characteristics of ASDs makes it an interesting area to explore. Numerous diverse factors interact in an inter-dependent manner to determine the final product properties. This review discusses the basic background of ASDs, various formulation and process variables influencing the critical quality attributes (CQAs) of the ASDs and aspects of downstream processing. Also various aspects of spray drying such as instrumentation, thermodynamics, drying kinetics, particle formation process and scale-up challenges are included. Recent advances in the spray-based drying techniques are mentioned along with some future avenues where major research thrust is needed. Copyright © 2015 Elsevier B.V. All rights reserved.

  17. A tissue-inspired amorphous photonic metamaterial

    Science.gov (United States)

    Bi, Dapeng

    Inspired by how cells pack in dense biological tissues, we design an amorphous material which possesses a complete photonic band gap. A physical parameter based by how cells adhere with one another and regulate their shapes can continuously tune the photonic band gap size as well as the bulk mechanical properties of the material. The material can be tuned through a solid-fluid phase transition characterized by a vanishing shear modulus. Remarkably, the photonic band gap persists in the fluid phase, giving rise to a photonic fluid that is robust to flow and rearrangements. Experimentally this design should lead to the engineering of self-assembled non-rigid photonic structures with photonic band gaps that can be controlled in real time.

  18. Three-Terminal Amorphous Silicon Solar Cells

    Directory of Open Access Journals (Sweden)

    Cheng-Hung Tai

    2011-01-01

    Full Text Available Many defects exist within amorphous silicon since it is not crystalline. This provides recombination centers, thus reducing the efficiency of a typical a-Si solar cell. A new structure is presented in this paper: a three-terminal a-Si solar cell. The new back-to-back p-i-n/n-i-p structure increased the average electric field in a solar cell. A typical a-Si p-i-n solar cell was also simulated for comparison using the same thickness and material parameters. The 0.28 μm-thick three-terminal a-Si solar cell achieved an efficiency of 11.4%, while the efficiency of a typical a-Si p-i-n solar cell was 9.0%. Furthermore, an efficiency of 11.7% was achieved by thickness optimization of the three-terminal solar cell.

  19. Three-dimensional dynamic rupture simulation with a high-order discontinuous Galerkin method on unstructured tetrahedral meshes

    KAUST Repository

    Pelties, Christian

    2012-02-18

    Accurate and efficient numerical methods to simulate dynamic earthquake rupture and wave propagation in complex media and complex fault geometries are needed to address fundamental questions in earthquake dynamics, to integrate seismic and geodetic data into emerging approaches for dynamic source inversion, and to generate realistic physics-based earthquake scenarios for hazard assessment. Modeling of spontaneous earthquake rupture and seismic wave propagation by a high-order discontinuous Galerkin (DG) method combined with an arbitrarily high-order derivatives (ADER) time integration method was introduced in two dimensions by de la Puente et al. (2009). The ADER-DG method enables high accuracy in space and time and discretization by unstructured meshes. Here we extend this method to three-dimensional dynamic rupture problems. The high geometrical flexibility provided by the usage of tetrahedral elements and the lack of spurious mesh reflections in the ADER-DG method allows the refinement of the mesh close to the fault to model the rupture dynamics adequately while concentrating computational resources only where needed. Moreover, ADER-DG does not generate spurious high-frequency perturbations on the fault and hence does not require artificial Kelvin-Voigt damping. We verify our three-dimensional implementation by comparing results of the SCEC TPV3 test problem with two well-established numerical methods, finite differences, and spectral boundary integral. Furthermore, a convergence study is presented to demonstrate the systematic consistency of the method. To illustrate the capabilities of the high-order accurate ADER-DG scheme on unstructured meshes, we simulate an earthquake scenario, inspired by the 1992 Landers earthquake, that includes curved faults, fault branches, and surface topography. Copyright 2012 by the American Geophysical Union.

  20. Ab initio van der waals interactions in simulations of water alter structure from mainly tetrahedral to high-density-like.

    Science.gov (United States)

    Møgelhøj, Andreas; Kelkkanen, André K; Wikfeldt, K Thor; Schiøtz, Jakob; Mortensen, Jens Jørgen; Pettersson, Lars G M; Lundqvist, Bengt I; Jacobsen, Karsten W; Nilsson, Anders; Nørskov, Jens K

    2011-12-08

    The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations in the NVE ensemble using van der Waals (vdW) density-functional theory, i.e., using the new exchange-correlation functionals optPBE-vdW and vdW-DF2, where the latter has softer nonlocal correlation terms. Inclusion of the more isotropic vdW interactions counteracts highly directional hydrogen bonds, which are enhanced by standard functionals. This brings about a softening of the microscopic structure of water, as seen from the broadening of angular distribution functions and, in particular, from the much lower and broader first peak in the oxygen-oxygen pair-correlation function (PCF) and loss of structure in the outer hydration shells. Inclusion of vdW interactions is shown to shift the balance of resulting structures from open tetrahedral to more close-packed. The resulting O-O PCF shows some resemblance with experiment for high-density water (Soper, A. K. and Ricci, M. A. Phys. Rev. Lett. 2000, 84, 2881), but not directly with experiment for ambient water. Considering the accuracy of the new functionals for interaction energies, we investigate whether the simulation protocol could cause the deviation. An O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from low-density liquid water, as extrapolated from experiments, reproduces near-quantitatively the experimental O-O PCF for ambient water. This suggests the possibility that the new functionals may be reliable and that instead larger-scale simulations in the NPT ensemble, where the density is allowed to fluctuate in accordance with proposals for supercooled water, could resolve the apparent discrepancy with the measured PCF. © 2011 American Chemical Society

  1. 3-D minimum-structure inversion of magnetotelluric data using the finite-element method and tetrahedral grids

    Science.gov (United States)

    Jahandari, H.; Farquharson, C. G.

    2017-11-01

    Unstructured grids enable representing arbitrary structures more accurately and with fewer cells compared to regular structured grids. These grids also allow more efficient refinements compared to rectilinear meshes. In this study, tetrahedral grids are used for the inversion of magnetotelluric (MT) data, which allows for the direct inclusion of topography in the model, for constraining an inversion using a wireframe-based geological model and for local refinement at the observation stations. A minimum-structure method with an iterative model-space Gauss-Newton algorithm for optimization is used. An iterative solver is employed for solving the normal system of equations at each Gauss-Newton step and the sensitivity matrix-vector products that are required by this solver are calculated using pseudo-forward problems. This method alleviates the need to explicitly form the Hessian or Jacobian matrices which significantly reduces the required computation memory. Forward problems are formulated using an edge-based finite-element approach and a sparse direct solver is used for the solutions. This solver allows saving and re-using the factorization of matrices for similar pseudo-forward problems within a Gauss-Newton iteration which greatly minimizes the computation time. Two examples are presented to show the capability of the algorithm: the first example uses a benchmark model while the second example represents a realistic geological setting with topography and a sulphide deposit. The data that are inverted are the full-tensor impedance and the magnetic transfer function vector. The inversions sufficiently recovered the models and reproduced the data, which shows the effectiveness of unstructured grids for complex and realistic MT inversion scenarios. The first example is also used to demonstrate the computational efficiency of the presented model-space method by comparison with its data-space counterpart.

  2. Castable Amorphous Metal Mirrors and Mirror Assemblies

    Science.gov (United States)

    Hofmann, Douglas C.; Davis, Gregory L.; Agnes, Gregory S.; Shapiro, Andrew A.

    2013-01-01

    A revolutionary way to produce a mirror and mirror assembly is to cast the entire part at once from a metal alloy that combines all of the desired features into the final part: optical smoothness, curvature, flexures, tabs, isogrids, low CTE, and toughness. In this work, it has been demonstrated that castable mirrors are possible using bulk metallic glasses (BMGs, also called amorphous metals) and BMG matrix composites (BMGMCs). These novel alloys have all of the desired mechanical and thermal properties to fabricate an entire mirror assembly without machining, bonding, brazing, welding, or epoxy. BMGs are multi-component metal alloys that have been cooled in such a manner as to avoid crystallization leading to an amorphous (non-crystalline) microstructure. This lack of crystal structure and the fact that these alloys are glasses, leads to a wide assortment of mechanical and thermal properties that are unlike those observed in crystalline metals. Among these are high yield strength, carbide-like hardness, low melting temperatures (making them castable like aluminum), a thermoplastic processing region (for improving smoothness), low stiffness, high strength-to-weight ratios, relatively low CTE, density similar to titanium alloys, high elasticity and ultra-smooth cast parts (as low as 0.2-nm surface roughness has been demonstrated in cast BMGs). BMGMCs are composite alloys that consist of a BMG matrix with crystalline dendrites embedded throughout. BMGMCs are used to overcome the typically brittle failure observed in monolithic BMGs by adding a soft phase that arrests the formation of cracks in the BMG matrix. In some cases, BMGMCs offer superior castability, toughness, and fatigue resistance, if not as good a surface finish as BMGs. This work has demonstrated that BMGs and BMGMCs can be cast into prototype mirrors and mirror assemblies without difficulty.

  3. Phyllosilicates and Amorphous Gel in the Nakhlites

    Science.gov (United States)

    Hicks, L. J.; Bridges, J. C.; Gurman, S. J.

    2013-09-01

    Previous studies of the nakhlite martian meteorites have revealed hydrothermal minerals present within the fractures of the olivine minerals and the mesostasis. The olivine fractures of the Lafayette nakhlite reveal variations with initial deposits of siderite on the fracture walls, followed by crystalline phyllosilicates (smectite), and finishing with a rapidly cooled amorphous silicate gel within the central regions of the fractures. The mesostasis fractures of Lafayette also contain a crystalline phyllosilicate (serpentine). The amorphous gel is the most abundant secondary phase within the fractures of the other nakhlites [1, 2]. By studying nine nakhlite samples, including Lafayette, Governador Valadares, Nakhla, Y-000593, Y-000749, Miller-Range 03346, NWA 817, NWA 998, and NWA 5790, our aim is to constrain the identity of the phyllosilicate secondary phase minerals found throughout the nakhlite martian meteorites. This is achieved using methods including Electron Probe Micro-analysis (EPMA); X-ray Absorption Near-Edge Structure (Fe-K XANES) spectroscopy measured using Beamline I-18 at the Diamond Light Source synchrotron; and the use of Transmission Electron Microscopy (TEM) at the University of Leicester for High-Resolution (HR) imaging and Selected Area Electron Diffraction (SAED). BF studying nine nakhlite samples, including Lafayette, Governador Valadares, Nakhla, Y-000593, Y-000749, Miller-Range 03346, NWA 817, NWA 998, and NWA 5790, our aim is to constrain the identity of the phyllosilicate secondary phase minerals found throughout the nakhlite martian meteorites. This is achieved using methods including Electron Probe Micro-analysis (EPMA); X-ray Absorption Near-Edge Structure (Fe-K XANES) spectroscopy measured using Beamline I-18 at the Diamond Light Source synchrotron; and the use of Transmission Electron Microscopy (TEM) at the University of Leicester for High-Resolution (HR) imaging and Selected Area Electron Diffraction (SAED).

  4. Surface Complexation Model for Strontium Sorption to Amorphous Silica and Goethite

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, S; Robers, S; Criscenti, L; O' Day, P

    2007-11-30

    Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25 C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr{sup 2+} and SrOH{sup +} complexes on the {beta}-plane and a monodentate Sr{sup 2+} complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH{sup +} complexes and a tetradentate binuclear Sr{sup 2+} species on the {beta}-plane. The binuclear complex is needed to account for enhanced sorption at high strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr{sup 2+} and SrOH{sup +} carbonate surface complexes on the {beta}-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces. Strontium surface complexation equilibrium constants determined in this study combined with other alkaline earth surface complexation constants are used to recalibrate a predictive model based on Born solvation and crystal-chemistry theory. The model is accurate to about 0.7 log K units. More studies are needed to determine the dependence of alkaline earth sorption on ionic strength and dissolved carbonate and sulfate

  5. Surface complexation model for strontium sorption to amorphous silica and goethite

    Directory of Open Access Journals (Sweden)

    Criscenti Louise J

    2008-01-01

    Full Text Available Abstract Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25°C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr2+ and SrOH+ complexes on the β-plane and a monodentate Sr2+complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH+ complexes and a tetradentate binuclear Sr2+ species on the β-plane. The binuclear complex is needed to account for enhanced sorption at hgh strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr2+ and SrOH+ carbonate surface complexes on the β-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces. Strontium surface complexation equilibrium constants determined in this study combined with other alkaline earth surface complexation constants are used to recalibrate a predictive model based on Born solvation and crystal-chemistry theory. The model is accurate to about 0.7 log K units. More studies are needed to determine the dependence of alkaline earth sorption on ionic strength and dissolved carbonate and sulfate concentrations for the development of

  6. Preparation and characterization of polymer-derived amorphous silicon carbide with silicon-rich stoichiometry

    Energy Technology Data Exchange (ETDEWEB)

    Masuda, Takashi, E-mail: mtakashi@jaist.ac.jp [School of Material and Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Iwasaka, Akira [School of Material and Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Takagishi, Hideyuki [Faculty of Symbiotic System Science, Fukushima University, 1 Kanayagawa, Fukushima-shi, Fukushima 960-1296 (Japan); Shimoda, Tatsuya [School of Material and Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan)

    2016-08-01

    Polydihydrosilane with pendant hexyl groups was synthesized to obtain silicon-rich amorphous silicon carbide (a-SiC) films via the solution route. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage. Therefore, the polymer provides sufficient purity for the fabrication of semiconducting a-SiC. Here, we investigated the correlation of Si/C stoichiometry between the polymer and the resultant a-SiC film. The structural, optical, and electrical properties of the films with various carbon contents were also explored. Experimental results suggested that the excess carbon that did not participate in Si−C configurations was decomposed and was evaporated during polymer-to-SiC conversion. Consequently, the upper limit of the carbon in resultant a-SiC film was < 50 at.%; namely, the polymer provided silicon-rich a-SiC, whereas the conventionally used polycarbosilane inevitably provides carbon-rich one. These features of this unusual polymer open up a frontier of polymer-derived SiC and solution-processed SiC electronics. - Highlights: • Polymeric precursor solution for silicon carbide (SiC) is synthesized. • Semiconducting amorphous SiC is prepared via solution route. • The excess carbon is decomposed during cross-linking resulting in Si-rich SiC films. • The grown SiC films contain substantial amount of hydrogen atoms as SiH{sub n}/CH{sub n} entities. • Presence of CH{sub n} entities induces dangling bonds, causing poor electrical properties.

  7. Synthesizing carbon nanothreads from benzene

    Energy Technology Data Exchange (ETDEWEB)

    Badding, John V.; Crespi, Vincent H.

    2015-01-26

    Carbon nanomaterials—e.g., fullerenes, nanotubes, and graphene, with dimensionalities of 0, 1, and 2, respectively—possess beautiful chemical bonding arrangements and extraordinary physical and chemical properties:1–3 see Figure 1(a). As is the case with graphite, their carbon atoms are bonded to three neighbors. Diamondoid molecules and graphane (the fully hydrogenated form of graphene) have fourfold tetrahedral bonding (like diamond) and dimensionalities of 0 and 2, respectively: see Figure 1(b). The diamondoid molecule adamantane, which is capped by hydrogen atoms, comprises the smallest unit cage structure of the diamond crystal lattice. Similarly, graphane represents the thinnest possible sheet of diamond. In this context, queries arise regarding what form the thinnest possible 1D diamond thread would take.

  8. Solubility advantage of amorphous pharmaceuticals: I. A thermodynamic analysis.

    Science.gov (United States)

    Murdande, Sharad B; Pikal, Michael J; Shanker, Ravi M; Bogner, Robin H

    2010-03-01

    In recent years there has been growing interest in advancing amorphous pharmaceuticals as an approach for achieving adequate solubility. Due to difficulties in the experimental measurement of solubility, a reliable estimate of the solubility enhancement ratio of an amorphous form of a drug relative to its crystalline counterpart would be highly useful. We have developed a rigorous thermodynamic approach to estimate enhancement in solubility that can be achieved by conversion of a crystalline form to the amorphous form. We rigorously treat the three factors that contribute to differences in solubility between amorphous and crystalline forms. First, we calculate the free energy difference between amorphous and crystalline forms from thermal properties measured by modulated differential scanning calorimetry (MDSC). Secondly, since an amorphous solute can absorb significant amounts of water, which reduces its activity and solubility, a correction is made using water sorption isotherm data and the Gibbs-Duhem equation. Next, a correction is made for differences in the degree of ionization due to differences in solubilities of the two forms. Utilizing this approach the theoretically estimated solubility enhancement ratio of 7.0 for indomethacin (amorphous/gamma-crystal) was found to be in close agreement with the experimentally determined ratio of 4.9. 2009 Wiley-Liss, Inc. and the American Pharmacists Association

  9. Health hazards due to the inhalation of amorphous silica.

    Science.gov (United States)

    Merget, R; Bauer, T; Küpper, H U; Philippou, S; Bauer, H D; Breitstadt, R; Bruening, T

    2002-01-01

    Occupational exposure to crystalline silica dust is associated with an increased risk for pulmonary diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and lung cancer. This review summarizes the current knowledge about the health effects of amorphous (non-crystalline) forms of silica. The major problem in the assessment of health effects of amorphous silica is its contamination with crystalline silica. This applies particularly to well-documented pneumoconiosis among diatomaceous earth workers. Intentionally manufactured synthetic amorphous silicas are without contamination of crystalline silica. These synthetic forms may be classified as (1) wet process silica, (2) pyrogenic ("thermal" or "fumed") silica, and (3) chemically or physically modified silica. According to the different physicochemical properties, the major classes of synthetic amorphous silica are used in a variety of products, e.g. as fillers in the rubber industry, in tyre compounds, as free-flow and anti-caking agents in powder materials, and as liquid carriers, particularly in the manufacture of animal feed and agrochemicals; other uses are found in toothpaste additives, paints, silicon rubber, insulation material, liquid systems in coatings, adhesives, printing inks, plastisol car undercoats, and cosmetics. Animal inhalation studies with intentionally manufactured synthetic amorphous silica showed at least partially reversible inflammation, granuloma formation and emphysema, but no progressive fibrosis of the lungs. Epidemiological studies do not support the hypothesis that amorphous silicas have any relevant potential to induce fibrosis in workers with high occupational exposure to these substances, although one study disclosed four cases with silicosis among subjects exposed to apparently non-contaminated amorphous silica. Since the data have been limited, a risk of chronic bronchitis, COPD or emphysema cannot be excluded. There is no study

  10. On the Plasticity of Amorphous Solids

    Science.gov (United States)

    Lin, Jie

    Mechanical behaviors of amorphous materials under external stress are central to various phenomena including earthquakes and landslides. Most amorphous materials possess a well defined yield stress when thermal fluctuations are negligible. Only when the shear stress is above the yield stress, the material can flow as a fluid, otherwise it deforms as a solid. There are accumulating evidences that the yielding transition between the flowing and solid phase is a critical phenomenon, and one evidence is the long ranged correlations of plastic strain during adiabatic shear. In spite of this, we still have not fully understood the associated critical exponents and their scaling relations. In the last decade, it has been widely accepted that the elementary rearrangements in amorphous solids are not well-defined topological defects as crystals, instead they are local irreversible rearrangements of a few particles, denoted as shear transformations. Because a single shear transformation changes the local arrangement of particles, it therefore generates an elastic stress field propagating over the whole system. The resulting changes in the local stresses in other regions of the system may in turn trigger more shear transformations. A central feature that complicates the yielding transition is the long range and anisotropic stress field generated by shear transformations. This peculiar interaction between shear transformations leads to two important characteristics: 1.the mechanical noises generated by plastic deformation are broadly distributed 2.those regions that are undergoing plastic deformation has equal probability to make other parts of the material to be more stable or more unstable, depending on the direction between them. In this thesis, we show that these two important factors leads to a singular density of shear transformations, P( x) xtheta at small x, where x is a local measure of stability, namely, the extra stress one needs to add locally to reach the elastic

  11. Tammann paradox and amorphization of substances under pressure

    Science.gov (United States)

    Fedorov, P. P.

    2008-01-01

    It is shown that amorphization of substances under pressure can be related to the fundamental property of the isobaric-isothermal potential surface as a function of temperature and pressure: its convexity. Amorphization is cold melting. The peaks in the pressure dependences of the melting temperature are not anomalies but a manifestation of the general case, whose implementation is limited by polymorphism. A model of the amorphous state near the absolute zero of temperature is proposed: specifically, nanoceramics formed according to the mechanism of polysynthetic twinning.

  12. Picosecond amorphization of chalcogenides material: From scattering to ionization

    Science.gov (United States)

    Wang, P.; Ju, C.; Chen, W.; Huang, D. Q.; Guan, X. W.; Li, Z.; Cheng, X. M.; Miao, X. S.

    2013-03-01

    Phase change memory cells with chalcogenides material of different thicknesses were fabricated to study the picosecond amorphization process. The threshold voltage (Vth) and time (Tth) of the cells were characterized by the picoseconds electric pulses. The model of the impact ionization and carriers multiplication was proposed to describe the non-thermal amorphization process within picoseconds duration, compared with the inelastic scattering model for the thermal amorphization process within nanoseconds duration. First principle calculations based on density functional theory and Ridley luck-drift model confirmed the explanation and gave a quantitative expression for the origins of Vth and Tth.

  13. Amorphous Semiconductors: From Photocatalyst to Computer Memory

    Science.gov (United States)

    Sundararajan, Mayur

    Amorphous semiconductors are useful in many applications like solar cells, thin film displays, sensors, electrophotography, etc. The dissertation contains four projects. In the first three projects, semiconductor glasses which are a subset of amorphous semiconductors were studied. The last project is about exploring the strengths and constraints of two analysis programs which calculate the particle size information from experimental Small Angle X-ray Scattering data. By definition, glasses have a random atomic arrangement with no order beyond the nearest neighbor, but strangely there exists an Intermediate Range Order (IRO). The origin of IRO is still not clearly understood, but various models have been proposed. The signature of IRO is the First Sharp Diffraction Peak(FSDP) observed in x-ray and neutron scattering data. The FSDP of TiO 2 SiO2 glass photocatalyst with different Ti:Si ratio from SAXS data was measured to test the theoretical models. The experimental results along with its computer simulation results strongly supported one of two leading models. It was also found that the effect of doping IRO on TiO2 SiO2 is severe in mesoporous form than the bulk form. Glass semiconductors in mesoporous form are very useful photocatalysts due to their large specific surface area. Solar energy conversion of photocatalysts greatly depends on their bandgap, but very few photocatalysts have the optical bandgap covering the whole visible region of solar spectrum leading to poor efficiency. A physical method was developed to manipulate the bandgap of mesoporous photocatalysts, by using the anisotropic thermal expansion and stressed glass network properties of mesoporous glasses. The anisotropic thermal expansion was established by S/WAXS characterization of mesoporous silica (MCM-41). The residual stress in the glass network of mesoporous glasses was already known for an earlier work. The new method was initially applied on mesoporous TiPO4, and the results were

  14. Intense blue-white luminescence from amorphous silicon oxycarbide (a-SiCxOy) thin films

    Science.gov (United States)

    Nikas, Vasileios; Gallis, Spyros; Suhag, Himani; Huang, Mengbing; Kaloyeros, Alain E.

    2011-10-01

    We report on blue-white luminescence from amorphous silicon oxycarbide a-SiCxOy<=1.68 (0.25carbon concentration (8.4 at.% < C < 13.6 at.%) in the material and post-deposition annealing treatments (Ar and forming gas 5% of H2 ambient up to 1100°C) on the observed luminescence were studied. The emission intensity slightly decreased with increasing carbon content but was appreciably enhanced in the samples following post-deposition annealing treatment in forming gas 5% of H2 ambient.

  15. Frenkel defect process in amorphous silica

    Science.gov (United States)

    Kajihara, Koichi; Hirano, Masahiro; Skuja, Linards; Hosono, Hideo

    2011-06-01

    Point defects strongly influence optical properties of synthetic amorphous silica (synthetic a-SiO2) used in excimer laser photolithography and their properties are intensively studied. Decomposition of an Si-O-Si bond into a pair of oxygen vacancy and interstitial oxygen species is an intrinsic defect process in a-SiO2. It is similar to the creation of vacancy-interstitial pairs in crystalline materials and is regarded as "Frenkel defect process" in an amorphous material. Oxygens are also known to be emitted from a-SiO2 surfaces under irradiation with vacuumultraviolet (VUV) light or electron beam. However, the anion part of the Frenkel pair in a-SiO2, interstitial oxygen atom, lacks reliable spectroscopic signatures. Therefore, Frenkel process has been studied much less than another intrinsic defect process in a-SiO2, a simple cleavage of an Si-O bond, yielding a pair of silicon and oxygen dangling bonds. Interstitial oxygen molecule (O2), a common form of the interstitial oxygen species in a-SiO2, exhibits characteristic infrared photoluminescence (PL) at 1272 nm. This PL band allows interstitial O2 to be detected selectively with a high sensitivity, and is useful in studying Frenkel defect processes in both a-SiO2 and crystalline SiO2. The Frenkel process is dominant over the formation of the dangling bond pairs in highpurity synthetic a-SiO2. Both these processes are influenced by the degree of the structural disorder of a-SiO2characterized by distribution of Si-O-Si angles. Fluorine doping promotes the structural relaxation and is useful in decreasing the concentration of "strained" Si-O-Si bonds, which have Si-O-Si bond angles widely different from the relaxed angle and are vulnerable to radiation. Moderate fluorine doping is effective in improving both UV-VUV transparency and radiation hardness, whereas heavy fluorine doping tends to enhance defect processes involving the Frenkel mechanism and to degrade the radiation hardness.

  16. Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy.

    Science.gov (United States)

    Sibik, Juraj; Löbmann, Korbinian; Rades, Thomas; Zeitler, J Axel

    2015-08-03

    There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond-to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari-Goldstein (JG) secondary relaxation as a facilitator of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization in several chosen amorphous drugs. We believe that this technique has immediate applications to quantify the stability of amorphous drug materials.

  17. Hall Mobility of Amorphous Ge2Sb2Te5

    National Research Council Canada - National Science Library

    Baily, S. A; Emin, David; Li, Heng

    2006-01-01

    The electrical conductivity, Seebeck coefficient, and Hall coefficient of 3 micron thick films of amorphous Ge2Sb2Te5 have been measured as functions of temperature from room temperature down to as low as 200 K...

  18. Amorphous and nanocrystalline materials preparation, properties, and applications

    CERN Document Server

    Inoue, A

    2001-01-01

    Amorphous and nanocrystalline materials are a class of their own. Their properties are quite different to those of the corresponding crystalline materials. This book gives systematic insight into their physical properties, structure, behaviour, and design for special advanced applications.

  19. Directional amorphization of boron carbide subjected to laser shock compression

    Science.gov (United States)

    Zhao, Shiteng; Kad, Bimal; Remington, Bruce A.; LaSalvia, Jerry C.; Wehrenberg, Christopher E.; Behler, Kristopher D.; Meyers, Marc A.

    2016-10-01

    Solid-state shock-wave propagation is strongly nonequilibrium in nature and hence rate dependent. Using high-power pulsed-laser-driven shock compression, unprecedented high strain rates can be achieved; here we report the directional amorphization in boron carbide polycrystals. At a shock pressure of 45˜50 GPa, multiple planar faults, slightly deviated from maximum shear direction, occur a few hundred nanometers below the shock surface. High-resolution transmission electron microscopy reveals that these planar faults are precursors of directional amorphization. It is proposed that the shear stresses cause the amorphization and that pressure assists the process by ensuring the integrity of the specimen. Thermal energy conversion calculations including heat transfer suggest that amorphization is a solid-state process. Such a phenomenon has significant effect on the ballistic performance of B4C.

  20. Amorphous Alloy Surpasses Steel and Titanium

    Science.gov (United States)

    2004-01-01

    In the same way that the inventions of steel in the 1800s and plastic in the 1900s sparked revolutions for industry, a new class of amorphous alloys is poised to redefine materials science as we know it in the 21st century. Welcome to the 3rd Revolution, otherwise known as the era of Liquidmetal(R) alloys, where metals behave similar to plastics but possess more than twice the strength of high performance titanium. Liquidmetal alloys were conceived in 1992, as a result of a project funded by the California Institute of Technology (CalTech), NASA, and the U.S. Department of Energy, to study the fundamentals of metallic alloys in an undercooled liquid state, for the development of new aerospace materials. Furthermore, NASA's Marshall Space Flight Center contributed to the development of the alloys by subjecting the materials to testing in its Electrostatic Levitator, a special instrument that is capable of suspending an object in midair so that researchers can heat and cool it in a containerless environment free from contaminants that could otherwise spoil the experiment.

  1. Domain Wall Mobility in Co-Based Amorphous Wire

    Directory of Open Access Journals (Sweden)

    Maria Kladivova

    2007-01-01

    Full Text Available Dynamics of the domain wall between opposite circularly magnetized domains in amorphous cylindrical sample with circular easy direction is theoretically studied. The wall is driven by DC current. Various mechanisms which influence the wall velocity were taken into account: current magnitude, deformation of the mowing wall, Hall effect, axially magnetized domain in the middle of the wire. Theoretical results obtained are in a good agreement with experiments on Cobased amorphous ferromagnetic wires.

  2. Magnetic Properties of Amorphous Fe-Zr-B Alloys

    OpenAIRE

    Shigehiro, Ohnuma; Masateru, Nose; Kiwamu, Shirakawa; Tsuyoshi, Masumoto; The Research Institute of Electric and Magnetic Alloys; Sumitomo Special Metal Co. Ltd.; The Research Institute of Electric and Magnetic Alloys; The Research Institute for Iron, Steel and Other Metals

    1980-01-01

    The formation range, magnetic properties and thermal stability for Fe-Zr-B amorphous alloys have been examined. The combination of zirconium and boron as glass formation elements is extremely effective both in expanding the formation range and increasing stability against crystallization for Fe-based amorphous alloys. Both the Curie temperature and saturation magnetization at room temperature decrease with increasing Zr content. Magnetostriction for the present alloys is smaller than that of ...

  3. Influence of microenvironment pH, humidity, and temperature on the stability of polymorphic and amorphous forms of clopidogrel bisulfate

    DEFF Research Database (Denmark)

    Raijada, Dhara K; Singh, Saranjit; Bansal, Arvind K

    2010-01-01

    The effect of microenvironment pH, humidity, and temperature was evaluated on the stability of polymorphic and amorphous forms of clopidogrel bisulfate, when present alone or in combinations. Oxalic acid and sodium carbonate were used as solid stressors to create acidic and alkaline pH, respectiv......The effect of microenvironment pH, humidity, and temperature was evaluated on the stability of polymorphic and amorphous forms of clopidogrel bisulfate, when present alone or in combinations. Oxalic acid and sodium carbonate were used as solid stressors to create acidic and alkaline p......H, respectively. The samples without and with stressors were subjected for 3 months to (1) 0% RH, 25% RH, 75% RH, and 85% RH at 40 degrees C and also to (2) 60 degrees C, 80 degrees C, and 100 degrees C at 0% RH. In case of solid samples without stressors, the mixture of polymorphic and amorphous forms showed...... more degradation than the individual forms above critical relative humidity (85% RH). Similar higher degradation was observed between 75% RH and 85% RH in case of acid-stressed samples. In alkaline microenvironment, all the samples showed identical decomposition attributed to conversion of bisulfate...

  4. ACBC to Balcite: Bioinspired Synthesis of a Highly Substituted High-Temperature Phase from an Amorphous Precursor.

    Science.gov (United States)

    Whittaker, Michael L; Joester, Derk

    2017-07-01

    Energy-efficient synthesis of materials locked in compositional and structural states far from equilibrium remains a challenging goal, yet biomineralizing organisms routinely assemble such materials with sophisticated designs and advanced functional properties, often using amorphous precursors. However, incorporation of organics limits the useful temperature range of these materials. Herein, the bioinspired synthesis of a highly supersaturated calcite (Ca0.5 Ba0.5 CO3 ) called balcite is reported, at mild conditions and using an amorphous calcium-barium carbonate (ACBC) (Ca1-x Ba x CO3 ·1.2H2 O) precursor. Balcite not only contains 50 times more barium than the solubility limit in calcite but also displays the rotational disorder on carbonate sites that is typical for high-temperature calcite. It is significantly harder (30%) and less stiff than calcite, and retains these properties after heating to elevated temperatures. Analysis of balcite local order suggests that it may require the formation of the ACBC precursor and could therefore be an example of nonclassical nucleation. These findings demonstrate that amorphous precursor pathways are powerfully enabling and provide unprecedented access to materials far from equilibrium, including high-temperature modifications by room-temperature synthesis. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. ACBC to Balcite: Bioinspired Synthesis of a Highly Substituted High-Temperature Phase from an Amorphous Precursor

    Energy Technology Data Exchange (ETDEWEB)

    Whittaker, Michael L.; Joester, Derk (NWU)

    2017-04-28

    Energy-efficient synthesis of materials locked in compositional and structural states far from equilibrium remains a challenging goal, yet biomineralizing organisms routinely assemble such materials with sophisticated designs and advanced functional properties, often using amorphous precursors. However, incorporation of organics limits the useful temperature range of these materials. Herein, the bioinspired synthesis of a highly supersaturated calcite (Ca0.5Ba0.5CO3) called balcite is reported, at mild conditions and using an amorphous calcium–barium carbonate (ACBC) (Ca1- x Ba x CO3·1.2H2O) precursor. Balcite not only contains 50 times more barium than the solubility limit in calcite but also displays the rotational disorder on carbonate sites that is typical for high-temperature calcite. It is significantly harder (30%) and less stiff than calcite, and retains these properties after heating to elevated temperatures. Analysis of balcite local order suggests that it may require the formation of the ACBC precursor and could therefore be an example of nonclassical nucleation. These findings demonstrate that amorphous precursor pathways are powerfully enabling and provide unprecedented access to materials far from equilibrium, including high-temperature modifications by room-temperature synthesis.

  6. Synthesis of BiFeO3 by carbonate precipitation

    Indian Academy of Sciences (India)

    Abstract. Magnetoelectric multiferroic BiFeO3 (BFO) was synthesized by a simple carbonate precipitation tech- nique of metal nitrate solutions. X-ray powder diffraction and thermo-gravimetric analysis (TGA) revealed that the precipitate consists of an intimate mixture of crystalline bismuth carbonate and an amorphous ...

  7. Synthesis of BiFeO3 by carbonate precipitation

    Indian Academy of Sciences (India)

    Magnetoelectric multiferroic BiFeO3 (BFO) was synthesized by a simple carbonate precipitation technique of metal nitrate solutions. X-ray powder diffraction and thermo-gravimetric analysis (TGA) revealed that the precipitate consists of an intimate mixture of crystalline bismuth carbonate and an amorphous hydroxide of ...

  8. A new method of preparing single-walled carbon nanotubes

    Indian Academy of Sciences (India)

    A novel method of purification for single-walled carbon nanotubes, prepared by an arc-discharge method, is described. The method involves a combination of acid washing followed by high temperature hydrogen treatment to remove the metal nanoparticles and amorphous carbon present in the as-synthesized singlewalled ...

  9. Inhibiting surface crystallization of amorphous indomethacin by nanocoating.

    Science.gov (United States)

    Wu, Tian; Sun, Ye; Li, Ning; de Villiers, Melgardt M; Yu, Lian

    2007-04-24

    An amorphous solid (glass) may crystallize faster at the surface than through the bulk, making surface crystallization a mechanism of failure for amorphous pharmaceuticals and other materials. An ultrathin coating of gold or polyelectrolytes inhibited the surface crystallization of amorphous indomethacin (IMC), an anti-inflammatory drug and model organic glass. The gold coating (10 nm) was deposited by sputtering, and the polyelectrolyte coating (3-20 nm) was deposited by an electrostatic layer-by-layer assembly of cationic poly(dimethyldiallyl ammonium chloride) (PDDA) and anionic sodium poly(styrenesulfonate) (PSS) in aqueous solution. The coating also inhibited the growth of existing crystals. The inhibition was strong even with one layer of PDDA. The polyelectrolyte coating still permitted fast dissolution of amorphous IMC and improved its wetting and flow. The finding supports the view that the surface crystallization of amorphous IMC is enabled by the mobility of a thin layer of surface molecules, and this mobility can be suppressed by a coating of only a few nanometers. This technique may be used to stabilize amorphous drugs prone to surface crystallization, with the aqueous coating process especially suitable for drugs of low aqueous solubility.

  10. Anomalous electron transport in metal/carbon multijunction devices by engineering of the carbon thickness and selecting metal layer

    Science.gov (United States)

    Dwivedi, Neeraj; Dhand, Chetna; Rawal, Ishpal; Kumar, Sushil; Malik, Hitendra K.; Lakshminarayanan, Rajamani

    2017-06-01

    A longstanding concern in the research of amorphous carbon films is their poor electrical conductivity at room temperature which constitutes a major barrier for the development of cost effective electronic and optoelectronic devices. Here, we propose metal/carbon hybrid multijunction devices as a promising facile way to overcome room temperature electron transport issues in amorphous carbon films. By the tuning of carbon thickness and swapping metal layers, we observe giant (upto ˜7 orders) reduction of electrical resistance in metal/carbon multijunction devices with respect to monolithic amorphous carbon device. We engineer the maximum current (electrical resistance) from about 10-7 to 10-3 A (˜107 to 103 Ω) in metal (Cu or Ti)/carbon hybrid multijunction devices with a total number of 10 junctions. The introduction of thin metal layers breaks the continuity of relatively higher resistance carbon layer as well as promotes the nanostructuring of carbon. These contribute to low electrical resistance of metal/carbon hybrid multijunction devices, with respect to monolithic carbon device, which is further reduced by decreasing the thickness of carbon layers. We also propose and discuss equivalent circuit model to explain electrical resistance in monolithic carbon and metal/carbon multijunction devices. Cu/carbon multijunction devices display relatively better electrical transport than Ti/carbon devices owing to low affinity of Cu with carbon that restricts carbide formation. We also observe that in metal/carbon multijunction devices, the transport mechanism changes from Poole-Frenkel/Schottky model to the hopping model with a decrease in carbon thickness. Our approach opens a new route to develop carbon-based inexpensive electronic and optoelectronic devices.

  11. Amino acids as co-amorphous stabilizers for poorly water-soluble drugs - Part 2

    DEFF Research Database (Denmark)

    Löbmann, K.; Laitinen, R.; Strachan, C.

    2013-01-01

    The formation of co-amorphous drug-drug mixtures has proved to be a powerful approach to stabilize the amorphous form and at the same time increase the dissolution of poorly water-soluble drugs. Molecular interactions in these co-amorphous formulations can play a crucial role in stabilization...... as small molecular weight excipients in co-amorphous formulations to stabilize the amorphous form of a poorly water-soluble drug through strong and specific molecular interactions with the drug....

  12. Processing and characterization of amorphous magnesium based alloy for application in biomedical implants

    Directory of Open Access Journals (Sweden)

    Telma Blanco Matias

    2014-07-01

    Full Text Available Magnesium-based bulk metallic glasses are attractive due to their single-phase, chemically homogeneous alloy system and the absence of second-phase, which could impair the mechanical properties and corrosion resistance. However, one of the unsolved problems for the manufacturability and the applications of bulk metallic glasses is that their glass-forming ability is very sensitive to the preparation techniques and impurity of components since oxygen in the environment would markedly deteriorate the glass-forming ability. Therefore, the aim of this study was to establish proper processing conditions to obtain a magnesium-based amorphous ternary alloy and its characterization. The final composition was prepared using two binary master alloys by melting in an induction furnace. Carbon steel crucible was used in argon atmosphere with and without addition of SF6 gas in order to minimize the oxygen contamination. The microstructure, amorphous nature, thermal properties and chemical analysis of samples were investigated by scanning electron microscopy (SEM, X-ray diffraction (XRD, differential scanning calorimetry (DSC and inductively coupled plasma emission spectrometry, respectively. The oxygen content of the as-cast samples was chemically analyzed by using carrier gas hot extraction (O/N Analyzer TC-436/LECO and was kept bellow 25 ppm (without SF6 and 10 ppm (with SF6. Bulk samples were produced by rapid cooling in a cooper mold until 1.5 mm thickness, with amorphous structures being observed up to 2.5 mm.

  13. Structural characterization of rondorfite, calcium silica chlorine mineral containing magnesium in tetrahedral position [MgO4]6-, with the aid of the vibrational spectroscopies and fluorescence.

    Science.gov (United States)

    Dulski, M; Bulou, A; Marzec, K M; Galuskin, E V; Wrzalik, R

    2013-01-15

    Raman and infrared spectra of rondorfite Ca8Mg(SiO4)4Cl2, a calcium chlorosilica mineral containing magnesium in tetrahedral position, has been studied in terms of spectra-structure relations. Raman spectra have been measured at different excited laser lines: 780 nm, 532 nm, 488 nm and 457 nm. This mineral is characterized by a single sharp intense Raman band at 863 cm(-1) assigned to the ν1 [SiO4]4- (Ag) symmetric stretching mode in the magnesiosilicate pentamer. Due to symmetry restriction the other Raman bands have a small intensity. Two Raman bands observed at 564 cm(-1) and 526 cm(-1) are associated simultaneously with ν4 [MgO4]6- and ν4 [SiO4]4- symmetric and antisymmetric modes where magnesium occurs in the tetrahedral configuration. The weak bands at 422 cm(-1) and 386 cm(-1) are associated with the ν2 bending mode of CaO6 in octahedral configuration, respectively. Moreover the infrared spectrum shows very weak bands associated with the hydroxyl group and/or water molecule. Additionally, the strong fluorescence phenomenon was observed and related to the presence of chlorine atoms, magnesium Mg2+ ions in atypical configuration or point defects. Copyright © 2012 Elsevier B.V. All rights reserved.

  14. Decoration of the Truncated Tetrahedron—An Archimedean Polyhedron—To Produce a New Class of Convex Equilateral Polyhedra with Tetrahedral Symmetry

    Directory of Open Access Journals (Sweden)

    Stan Schein

    2016-08-01

    Full Text Available The Goldberg construction of symmetric cages involves pasting a patch cut out of a regular tiling onto the faces of a Platonic host polyhedron, resulting in a cage with the same symmetry as the host. For example, cutting equilateral triangular patches from a 6.6.6 tiling of hexagons and pasting them onto the full triangular faces of an icosahedron produces icosahedral fullerene cages. Here we show that pasting cutouts from a 6.6.6 tiling onto the full hexagonal and triangular faces of an Archimedean host polyhedron, the truncated tetrahedron, produces two series of tetrahedral (Td fullerene cages. Cages in the first series have 28n2 vertices (n ≥ 1. Cages in the second (leapfrog series have 3 × 28n2. We can transform all of the cages of the first series and the smallest cage of the second series into geometrically convex equilateral polyhedra. With tetrahedral (Td symmetry, these new polyhedra constitute a new class of “convex equilateral polyhedra with polyhedral symmetry”. We also show that none of the other Archimedean polyhedra, six with octahedral symmetry and six with icosahedral, can host full-face cutouts from regular tilings to produce cages with the host’s polyhedral symmetry.

  15. Caltech Center for Structural and Amorphous Metals

    Science.gov (United States)

    2005-05-10

    is an improvement on the method of pellet infiltration described above, wherein the pellets are replaced by hollow carbon spheres (i.e., ’ cenospheres ...8217). This approach solves the problems associated with that method; namely, the pore size is determined by the cenosphere diameter, which is much...smaller (on the order of 25-50 ptm) than the sample diameter, the use of fully- intact cenospheres prevents loss of porosity during infiltration, and no

  16. Health hazards due to the inhalation of amorphous silica

    Energy Technology Data Exchange (ETDEWEB)

    Merget, R.; Bruening, T. [Research Institute for Occupational Medicine (BGFA), Bochum (Germany); Bauer, T. [Bergmannsheil, University Hospital, Department of Internal Medicine, Division of Pneumonology, Allergology and Sleep Medicine, Bochum (Germany); Kuepper, H.U.; Breitstadt, R. [Degussa-Huels Corp., Wesseling (Germany); Philippou, S. [Department of Pathology, Augusta Krankenanstalten, Bochum (Germany); Bauer, H.D. [Research Institute for Hazardous Substances (IGF), Bochum (Germany)

    2002-01-01

    Occupational exposure to crystalline silica dust is associated with an increased risk for pulmonary diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and lung cancer. This review summarizes the current knowledge about the health effects of amorphous (non-crystalline) forms of silica. The major problem in the assessment of health effects of amorphous silica is its contamination with crystalline silica. This applies particularly to well-documented pneumoconiosis among diatomaceous earth workers. Intentionally manufactured synthetic amorphous silicas are without contamination of crystalline silica. These synthetic forms may be classified as (1) wet process silica, (2) pyrogenic (''thermal'' or ''fumed'') silica, and (3) chemically or physically modified silica. According to the different physico-chemical properties, the major classes of synthetic amorphous silica are used in a variety of products, e.g. as fillers in the rubber industry, in tyre compounds, as free-flow and anti-caking agents in powder materials, and as liquid carriers, particularly in the manufacture of animal feed and agrochemicals; other uses are found in toothpaste additives, paints, silicon rubber, insulation material, liquid systems in coatings, adhesives, printing inks, plastisol car undercoats, and cosmetics. Animal inhalation studies with intentionally manufactured synthetic amorphous silica showed at least partially reversible inflammation, granuloma formation and emphysema, but no progressive fibrosis of the lungs. Epidemiological studies do not support the hypothesis that amorphous silicas have any relevant potential to induce fibrosis in workers with high occupational exposure to these substances, although one study disclosed four cases with silicosis among subjects exposed to apparently non-contaminated amorphous silica. Since the data have been limited, a risk of chronic bronchitis, COPD or

  17. Thermodynamics, molecular mobility and crystallization kinetics of amorphous griseofulvin.

    Science.gov (United States)

    Zhou, Deliang; Zhang, Geoff G Z; Law, Devalina; Grant, David J W; Schmitt, Eric A

    2008-01-01

    Griseofulvin is a small rigid molecule that shows relatively high molecular mobility and small configurational entropy in the amorphous phase and tends to readily crystallize from both rubbery and glassy states. This work examines the crystallization kinetics and mechanism of amorphous griseofulvin and the quantitative correlation between the rate of crystallization and molecular mobility above and below Tg. Amorphous griseofulvin was prepared by rapidly quenching the melt in liquid N2. The thermodynamics and dynamics of amorphous phase were then characterized using a combination of thermal analysis techniques. After characterization of the amorphous phase, crystallization kinetics above Tg were monitored by isothermal differential scanning calorimetry (DSC). Transformation curves for crystallization fit a second-order John-Mehl-Avrami (JMA) model. Crystallization kinetics below Tg were monitored by powder X-ray diffraction and fit to the second-order JMA model. Activation energies for crystallization were markedly different above and below Tg suggesting a change in mechanism. In both cases molecular mobility appeared to be partially involved in the rate-limiting step for crystallization, but the extent of correlation between the rate of crystallization and molecular mobility was different above and below Tg. A lower extent of correlation below Tg was observed which does not appear to be explained by the molecular mobility alone and the diminishing activation energy for crystallization suggests a change in the mechanism of crystallization.

  18. Tailoring the optical and hydrophobic property of zinc oxide nanorod by coating with amorphous graphene

    Science.gov (United States)

    Pahari, D.; Das, N. S.; Das, B.; Chattopadhyay, K. K.; Banerjee, D.

    2016-09-01

    Zinc oxide (ZnO) nanorods were synthesized at room temperature on potassium permanganate activated silicon and glass substrate by simple chemical method using zinc acetate as precursor. To modify the surface energy of the as prepared ZnO thin films the samples were coated with amorphous graphene (a-G) synthesized by un-zipping of chemically synthesized amorphous carbon nanotubes (a-CNTs). All the pure and coated samples were characterized by x-ray diffraction, field emission scanning electron microscope, Raman spectroscopy, and Fourier transformed infrared spectroscopy. The roughness analysis of the as prepared samples was done by atomic force microscopic analysis. The detail optical properties of all the samples were studied with the help of a UV-Visible spectrophotometer. The surface energy of the as prepared pure and coated samples was calculated by measuring the contact angle of two different liquids. It is seen that the water repellence of ZnO nanorods got increased after they are being coated with a-Gs. Also even after UV irradiation the contact angle remain same unlike the case for the uncoated sample where the contact angle gets decreased significantly after UV irradiation. Existing Cassie-Wenzel model has been employed along with the Owen's approach to determine the different components of surface energy.

  19. Growth of Amorphous and Epitaxial ZnSiP2-Si Alloys on Si

    Energy Technology Data Exchange (ETDEWEB)

    Tamboli, Adele C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Martinez, Aaron [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Link, Elisa M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Norman, Andrew [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schnepf, Rekha [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Perkins, Craig [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Stradins, Paul [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Toberer, Eric [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Leick, Noemi [Formerly NREL

    2018-01-03

    ZnSiP2 is a wide band gap material that is lattice matched with Si, offering the potential for Si-based optoelectronic materials and devices, including multijunction photovoltaics. We present a carbon-free chemical vapor deposition process for the growth of both epitaxial and amorphous thin films of ZnSiP2-Si alloys with tunable Si content on Si substrates. Si alloy content is widely tunable across the full composition space in amorphous films. Optical absorption of these films reveals relatively little variation with Si content, despite the fact that ZnSiP2 has a much wider band gap of 2.1 eV. Post-growth crystallization of Si-rich films resulted in epitaxial alignment, as measured by X-ray diffraction and transmission electron microscopy. These films have an optical absorption onset near 1.1 eV, suggesting the possibility of band gap tuning with Si content in crystalline films. The optical absorption is comparably strong to pure ZnSiP2, suggesting a more direct transition than in pure Si.

  20. Modeling the Local Structure of Amorphous Materials: A Density Functional Theory Investigation

    Science.gov (United States)

    Gong, Kai; Ozcelik, Ongun; White, Claire

    Here, we present an iterative methodology alternating between density functional theory (DFT) calculations and pair distribution function (PDF) analysis to uncover the detailed atomic structure of highly amorphous materials. In this methodology, the DFT calculations are used to maintain chemical feasibility of the atomic structure, while the experimentally-driven refinements allow for exploration of the potential energy landscape. Through this iterative process, a final structure is obtained that is not only thermodynamically favorable but also in agreement with experiment data. Previously, we have demonstrated the applicability of similar DFT-PDF iterative methods in metakaolin and amorphous magnesium carbonate. Here, we have modified the methodology and applied it to resolve the atomic structure of ground granulated blast-furnace slag, a highly disordered calcium-magnesium aluminosilicate glassy material. Prior to applying the iterative process, a high temperature molecular dynamics (MD) simulation was used to generate a reasonable starting structure, which was found to be crucial. The iterative methodology outlined here is expected to be readily transferable to other disordered material systems where detailed atomic structures are currently not available. This material is based on work supported by the National Science Foundation under Grant No. 1362039.