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Sample records for biaxially oriented cdse

  1. Biaxially Oriented CdSe Nanorod

    DEFF Research Database (Denmark)

    Breiby, Dag W.; Chin, Patrick T.K.; Andreasen, Jens Wenzel;

    2009-01-01

    The shape, structure, and orientation of rubbing-aligned cadmium selenide (CdSe) nanorods on polymer coated glass substrates have been studied using transmission electron microscopy (TEM) and grazing incidence X-ray scattering combined with computer simulations. The nanorods are found to be of...

  2. Biaxially oriented film on flexible polymeric substrate

    Science.gov (United States)

    Finkikoglu, Alp T.; Matias, Vladimir

    2009-10-13

    A flexible polymer-based template having a biaxially oriented film grown on the surface of a polymeric substrate. The template having the biaxially oriented film can be used for further epitaxial growth of films of interest for applications such as photovoltaic cells, light emitting diodes, and the like. Methods of forming such a flexible template and providing the polymeric substrate with a biaxially oriented film deposited thereon are also described.

  3. Analysis of Deformation Mechanisms Associated with Biaxially Oriented Polypropylene Films

    Science.gov (United States)

    Wang, Yong; Hsu, Shaw Ling

    1998-03-01

    Biaxially oriented samples can be prepared either by simultaneous or sequential deformation along two orthogonal directions. Generally speaking the orientation achieved in the plane of the film is independent of the method. In this study, we demonstrate that for sequential deformation, the degree of orientation achieved in the two orthogonal directions is dependent on initial sample morphology and deformation parameters. The achievable orientation is strongly dependent on the degree of crystallinity and initial crystallite dimensions. Samples containing small crystallites can achieve significantly higher orientation in the transverse direction (restretching step). The ultimate morphology is dictated by the temperature at which second drawing occurs. At lower deformation temperature, rotation of stacked crystalline lamellae can be accomplished to form biaxially oriented films. At higher temperatures, the dominant mechanism is unfolding of crystalline chain segments followed by recrystallization into units aligned with the restretching direction. X-ray diffraction, polarized infrared and Raman spectroscopy, and calorimetric techniques were employed to analyze these structural transformations.

  4. Conductive layer for biaxially oriented semiconductor film growth

    Science.gov (United States)

    Findikoglu, Alp T.; Matias, Vladimir

    2007-10-30

    A conductive layer for biaxially oriented semiconductor film growth and a thin film semiconductor structure such as, for example, a photodetector, a photovoltaic cell, or a light emitting diode (LED) that includes a crystallographically oriented semiconducting film disposed on the conductive layer. The thin film semiconductor structure includes: a substrate; a first electrode deposited on the substrate; and a semiconducting layer epitaxially deposited on the first electrode. The first electrode includes a template layer deposited on the substrate and a buffer layer epitaxially deposited on the template layer. The template layer includes a first metal nitride that is electrically conductive and has a rock salt crystal structure, and the buffer layer includes a second metal nitride that is electrically conductive. The semiconducting layer is epitaxially deposited on the buffer layer. A method of making such a thin film semiconductor structure is also described.

  5. Preparation of biaxially oriented TlCu-1234 thin films

    CERN Document Server

    Khan, N A; Tateai, F; Kojima, T; Ishida, K; Terada, N; Ihara, H

    1999-01-01

    The single phase of TlCu-1234 superconductor thin films is prepared for the first time by the amorphous phase epitaxy (APE) method, which is thallium treatment of sputtered amorphous phase at 900 degrees C for 1 h. The amorphous $9 phase is prepared by sputtering from the stoichiometric target composition CuBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 12-y/. The films on the SrTiO/sub 3/ substrate are aligned biaxially after the thallium treatment. Highly reproducible $9 TlCu-1234 films are prepared by this method. The XRD reflected a predominant single phase with the c-axis lattice constant of 18.74 AA. This lattice constant value is in between that of Cu-1234 (17.99 AA) and Tl-1234 (19.11 AA) . The $9 pole figure measurements of (103) reflection of the films showed a-axis-oriented crystals with Delta phi =0.8 degrees . The composition of the films after energy dispersive X-ray (EDX) measurements is Tl/sub 0.8/Cu/sub 0.2/Ba/sub $9 2/Ca/sub 3/Cu/sub 4/O /sub 12-y/. From the resistivity measurements, the T/sub c/ is 113 K...

  6. Atomic force microscopy study of biaxially oriented polypropylene films

    Science.gov (United States)

    Nie, H.-Y.; Walzak, M. J.; McIntyre, N. S.

    2004-08-01

    Atomic force microscopy (AFM) uses a very sharp pointed mechanical probe to collect real-space morphological information of solid surfaces. AFM was used in this study to image the surface morphology of a biaxially oriented polypropylene film. The polymer film is characterized by a nanometer-scale, fiberlike network structure, which reflects the drawing process used during the fabrication of the film. AFM was used to study polymer-surface treatment to improve wettability by exposing the polymer to ozone with or without ultraviolet (UV) irradiation. Surface-morphology changes observed by AFM are the result of the surface oxidation induced by the treatment. Due to the topographic features of the polymer film, the fiberlike structure has been used to check the performance of the AFM tip. An AFM image is a mixture of the surface morphology and the shape of the AFM tip. Therefore, it is important to check the performance of a tip to ensure that the AFM image collected reflects the true surface features of the sample, rather than contamination on the AFM tip.

  7. Scratch resistance anisotropy in biaxially oriented polypropylene and poly(ethylene terephthalate) films

    Science.gov (United States)

    Nie, H.-Y.; Walzak, M. J.; McIntyre, N. S.

    2006-12-01

    Using a diamond-tipped stylus, scratch tests were conducted on biaxially oriented polypropylene and poly(ethylene terephthalate) films in the two draw directions, i.e., the machine-direction (MD) and the transverse-direction (TD) along which the draw ratios are different. Atomic force microscopy study of those scratches revealed a significant anisotropy in the scratch resistance between the MD and TD for both of the polymer films. We confirmed that the scratch resistance of polymer strands is closely related to the draw ratios, which determine the mechanical strength and optical clarity of biaxially oriented polymer films.

  8. Band offsets for biaxially and uniaxially stressed silicon-germanium layers with arbitrary substrate and channel orientations

    Science.gov (United States)

    Eneman, Geert; Roussel, Philippe; Brunco, David Paul; Collaert, Nadine; Mocuta, Anda; Thean, Aaron

    2016-08-01

    The conduction and valence band offsets between a strained silicon-germanium layer and a silicon-germanium substrate are reported for arbitrary substrate and channel crystal orientations. The offsets are calculated both for the case of biaxial stress, corresponding approximately to the stress state of a thin strained channel in a planar field-effect transistor (FET), and for uniaxial stress, which is the approximate stress state for strained channels in a FinFET configuration. Significant orientation dependence is found for the conduction band offset, overall leading to the strongest electron quantum confinement in biaxial-tensile stressed channels on {100}-oriented substrates, and uniaxial-tensile stressed channels in the ⟨100⟩ and ⟨110⟩ directions. For biaxially stressed layers on {111} substrates, the conduction band offset is significantly smaller than for {100} or {110} directions. For the valence band offset, the dependence on crystal orientation is found to be small.

  9. Practical approach in surface modification of biaxially oriented polypropylene films for gravure printability

    Science.gov (United States)

    Nuntapichedkul, Boonchai; Tantayanon, Supawan; Laohhasurayotin, Kritapas

    2014-09-01

    Biaxially oriented polypropylene (BOPP) film is one of the most popularly used materials for the gravure printing process in flexible packaging industry. The skin layers of BOPP film were associated with 3-6 weight % of propylene-ethylene copolymer. These films were completely biaxial-oriented by sequential stretching process after which the film surfaces were subjected to corona treatment integrated in the production line. The FT-IR results exhibited that polar functional groups as carbonyl molecules were established on the corona-treated BOPP film. The contact angles of these BOPP films were measured; the surface free energies (SFE) were then calculated. AFM topographical images also agreed well with the SFE which increased as the contents of propylene-ethylene copolymer increased. An approximated 20% increased SFE was obtained for the BOPP film that was associated with 6% propylene-ethylene copolymer. The printing quality on BOPP films was tested by light microscope which confirmed that the chromatic resolution of the printed images improved down to even more smaller groove sizes, 10 or 5 dot%. This improvement was also examined and found to correspond well with the interfacial tensions and work of adhesion between the inks and the modified BOPP films.

  10. Abrasion resistance of biaxially oriented polypropylene films coated with nanocomposite hard coatings

    Science.gov (United States)

    Wang, Jing; Zhu, Yaofeng; Fu, Yaqin

    2013-11-01

    KMnO4-treated, functionalized, biaxially oriented polypropylene (BOPP) films coated with nano-silica hybrid material were synthesized. The abrasion resistance of the films was examined using a reciprocating fabric abrasion tester. Functional groups were confirmed by Fourier-transform infrared spectroscopy. Contact angle measurements were performed on the BOPP film surface to quantify the effectiveness of the functionalization. Results indicate that the abrasion resistance and roughness of the composite film were significantly affected by the modification of the BOPP film. Water surface contact angle of the modified BOPP films decreased from 90.1° to 71.4°,when KMnO4 concentration increased from 0 M to 0.25 M. Wettability of the BOPP films clearly improved after KMnO4 treatment. Abrasion resistance of the functionalized films coated with hybrid materials improved by 27.4% compared with that of the original film.

  11. UV protective zinc oxide coating for biaxially oriented polypropylene packaging film by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lahtinen, Kimmo, E-mail: kimmo.lahtinen@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Kääriäinen, Tommi, E-mail: tommi.kaariainen@colorado.edu [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Johansson, Petri, E-mail: petri.johansson@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Kotkamo, Sami, E-mail: sami.kotkamo@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Maydannik, Philipp, E-mail: philipp.maydannik@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Seppänen, Tarja, E-mail: tarja.seppanen@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Kuusipalo, Jurkka, E-mail: jurkka.kuusipalo@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Cameron, David C., E-mail: david.cameron@miktech.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland)

    2014-11-03

    Biaxially oriented polypropylene (BOPP) packaging film was coated with zinc oxide (ZnO) coatings by atomic layer deposition (ALD) in order to protect the film from UV degradation. The coatings were made at a process temperature of 100 °C using diethylzinc and water as zinc and oxygen precursors, respectively. The UV protective properties of the coatings were tested by using UV–VIS and infrared spectrometry, differential scanning calorimetry (DSC) and a mechanical strength tester, which characterised the tensile and elastic properties of the film. The results obtained with 36 and 67 nm ZnO coatings showed that the ZnO UV protective layer is able to provide a significant decrease in photodegradation of the BOPP film under UV exposure. While the uncoated BOPP film suffered a complete degradation after a 4-week UV exposure, the 67 nm ZnO coated BOPP film was able to preserve half of its original tensile strength and 1/3 of its elongation at break after a 6-week exposure period. The infrared analysis and DSC measurements further proved the UV protection of the ZnO coatings. The results show that a nanometre scale ZnO coating deposited by ALD is a promising option when a transparent UV protection layer is sought for polymer substrates. - Highlights: • Atomic layer deposited zinc oxide coatings were used as UV protection layers. • Biaxially oriented polypropylene (BOPP) film was well protected against UV light. • Formation of UV degradation products in BOPP was significantly reduced. • Mechanical properties of the UV exposed BOPP film were significantly improved.

  12. Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT-CdSe films grown by directional epitaxial crystallization.

    Science.gov (United States)

    Roiban, L; Hartmann, L; Fiore, A; Djurado, D; Chandezon, F; Reiss, P; Legrand, J-F; Doyle, S; Brinkmann, M; Ersen, O

    2012-11-21

    Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.

  13. Modeling of stored charge in metallized biaxially oriented polypropylene film capacitors based on charging current measurement.

    Science.gov (United States)

    Li, Hua; Wang, Bowen; Li, Zhiwei; Liu, De; Lin, Fuchang; Dai, Ling; Zhang, Qin; Chen, Yaohong

    2013-10-01

    Metallized biaxially oriented polypropylene film (BOPP) capacitors are widely used in pulsed power systems. When the capacitor is used as the energy storage equipment under high electric field, more charges should be provided to maintain the voltage of the capacitor. This should be ascribed to the completion of the slow polarization which may take several hours or even longer. This paper focuses on the stored charge in metallized BOPP film capacitors. The modeling of the stored charge by the equivalent conversion of circuits is conducted to analyse the slow polarization in the BOPP film. The 3-RC network is proposed to represent the time-dependent charge stored in the capacitor. A charging current measurement system is established to investigate the charge storage property of the capacitor. The measurement system can measure the long time charging current with a sampling rate of 300 Hz. The total charge calculated by the charging current indicates that the stored charge in the capacitor under the electric field of 400 V/μm is 13.5% larger than the product of the voltage and the capacitance measured by the AC bridge. The nonlinear effect of the electric field on the slow polarization charge is also demonstrated. And the simulation of charge storage based on the 3-RC network can match well with the trend of the stored charge increasing with the time. PMID:24182144

  14. Modeling of stored charge in metallized biaxially oriented polypropylene film capacitors based on charging current measurement

    Science.gov (United States)

    Li, Hua; Wang, Bowen; Li, Zhiwei; Liu, De; Lin, Fuchang; Dai, Ling; Zhang, Qin; Chen, Yaohong

    2013-10-01

    Metallized biaxially oriented polypropylene film (BOPP) capacitors are widely used in pulsed power systems. When the capacitor is used as the energy storage equipment under high electric field, more charges should be provided to maintain the voltage of the capacitor. This should be ascribed to the completion of the slow polarization which may take several hours or even longer. This paper focuses on the stored charge in metallized BOPP film capacitors. The modeling of the stored charge by the equivalent conversion of circuits is conducted to analyse the slow polarization in the BOPP film. The 3-RC network is proposed to represent the time-dependent charge stored in the capacitor. A charging current measurement system is established to investigate the charge storage property of the capacitor. The measurement system can measure the long time charging current with a sampling rate of 300Hz. The total charge calculated by the charging current indicates that the stored charge in the capacitor under the electric field of 400 V/μm is 13.5% larger than the product of the voltage and the capacitance measured by the AC bridge. The nonlinear effect of the electric field on the slow polarization charge is also demonstrated. And the simulation of charge storage based on the 3-RC network can match well with the trend of the stored charge increasing with the time.

  15. Biaxially oriented CdTe films on glass substrate through nanostructured Ge/CaF2 buffer layers

    Science.gov (United States)

    Lord, R. J.; Su, P.-Y.; Bhat, I.; Zhang, S. B.; Lu, T.-M.; Wang, G.-C.

    2015-09-01

    Heteroepitaxial CdTe films were grown by metal organic chemical vapor deposition on glass substrates through nanostructured Ge/CaF2 buffer layers which were biaxially oriented. It allows us to explore the structural properties of multilayer biaxial semiconductor films which possess small angle grain boundaries and to test the principle of a solar cell made of such low-cost, low-growth-temperature semiconductor films. Through the x-ray diffraction and x-ray pole figure analysis, the heteroepitaxial relationships of the mutilayered films are determined as [111] in the out-of-plane direction and CdTe//Ge//{ }{{{CaF}}2} in the in-plane direction. The I-V curves measured from an ITO/CdS/CdTe/Ge/CaF2/glass solar cell test structure shows a power conversion efficiency of ˜η = 1.26%, illustrating the initial success of such an approach. The observed non-ideal efficiency is believed to be due to a low shunt resistance and high series resistance as well as some residual large-angle grain boundary effects, leaving room for significant further improvement.

  16. Quantification of Coupled Stiffness and Fiber Orientation Remodeling in Hypertensive Rat Right-Ventricular Myocardium Using 3D Ultrasound Speckle Tracking with Biaxial Testing

    Science.gov (United States)

    Park, Dae Woo; Sebastiani, Andrea; Yap, Choon Hwai; Simon, Marc A.; Kim, Kang

    2016-01-01

    Mechanical and structural changes of right ventricular (RV) in response to pulmonary hypertension (PH) are inadequately understood. While current standard biaxial testing provides information on the mechanical behavior of RV tissues using surface markers, it is unable to fully assess structural and mechanical properties across the full tissue thickness. In this study, the mechanical and structural properties of normotensive and pulmonary hypertension right ventricular (PHRV) myocardium through its full thickness were examined using mechanical testing combined with 3D ultrasound speckle tracking (3D-UST). RV pressure overload was induced in Sprague–Dawley rats by pulmonary artery (PA) banding. The second Piola–Kirchhoff stress tensors and Green-Lagrangian strain tensors were computed in the RV myocardium using the biaxial testing combined with 3D-UST. A previously established non-linear curve-fitting algorithm was applied to fit experimental data to a Strain Energy Function (SEF) for computation of myofiber orientation. The fiber orientations obtained by the biaxial testing with 3D-UST compared well with the fiber orientations computed from the histology. In addition, the re-orientation of myofiber in the right ventricular free wall (RVFW) along longitudinal direction (apex-to-outflow-tract direction) was noticeable in response to PH. For normotensive RVFW samples, the average fiber orientation angles obtained by 3D-UST with biaxial test spiraled from 20° at the endo-cardium to -42° at the epi-cardium (Δ = 62°). For PHRV samples, the average fiber orientation angles obtained by 3D-UST with biaxial test had much less spiral across tissue thickness: 3° at endo-cardium to -7° at epi-cardium (Δ = 10°, P<0.005 compared to normotensive). PMID:27780271

  17. Effects of Interphase Modification and Biaxial Orientation on Dielectric Properties of Poly(ethylene terephthalate)/Poly(vinylidene fluoride-co-hexafluoropropylene) Multilayer Films.

    Science.gov (United States)

    Yin, Kezhen; Zhou, Zheng; Schuele, Donald E; Wolak, Mason; Zhu, Lei; Baer, Eric

    2016-06-01

    Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications. PMID:27163929

  18. Singular values, nematic disclinations, and emergent biaxiality

    OpenAIRE

    Dennis, Mark R.; Žumer, Slobodan; Kamien, Randall D.; Čopar, Simon

    2015-01-01

    Both uniaxial and biaxial nematic liquid crystals are defined by orientational ordering of their building blocks. While uniaxial nematics only orient the long molecular axis, biaxial order implies local order along three axes. As the natural degree of biaxiality and the associated frame that can be extracted from the tensorial description of the nematic order vanishes in the uniaxial phase, we extend the nematic director to a full biaxial frame by making use of a singular value decomposition ...

  19. Vector hysteresis measurements of not oriented grain SiFe steels by a biaxial hall sensors array

    Science.gov (United States)

    Cardelli, E.; Faba, A.

    2014-02-01

    This work discusses the vector measurement of the effective magnetic field inside a not oriented grain SiFe steel sample, taking into account the effect of the demagnetizing field. We propose an array of biaxial Hall sensors, placed up to the sample surface. The calibration of the system and a suitable extrapolation data strongly reduce the uncertainties of the direct measurement and provide an accurate evaluation of the magnetic field inside the material sample. Although the approach proposed can be also used for industrial frequencies, 50-60 Hz or more, the analysis is limited here to the static case, because we are mainly interested in static magnetic measurements. These measurements are especially useful for the vector characterization of soft magnetic materials and, in particular, for the identification and the experimental validation of vector hysteresis models. The experimental analysis presented in the paper deals with commercial not oriented grain SiFe steels. Experimental data about hysteresis loops and static power losses are given.

  20. High-performance poly-Si thin film transistors with highly biaxially oriented poly-Si thin films using double line beam continuous-wave laser lateral crystallization

    Science.gov (United States)

    Yamano, Masayuki; Kuroki, Shin-Ichiro; Sato, Tadashi; Kotani, Koji

    2014-01-01

    Highly biaxially oriented poly-Si thin films were formed by double-line beam continuous-wave laser lateral crystallization (DLB-CLC). The crystallinities of the DLB-CLC poly-Si thin films were (110), (111), and (211) for the laser scan, transverse, and surface directions, respectively, and an energetically stable Σ3 grain boundary was observed to be dominant. All silicon grains were elongated in the laser scan direction and one-dimensionally very large silicon grains with lengths of more than 100 µm were fabricated. Using these biaxially oriented polycrystalline silicon (poly-Si) films, low-temperature poly-Si TFTs (LTPS-TFTs) were fabricated at low temperatures (≦550 °C) by a metal gate self-aligned process. As a result, a TFT with a high electron field effect mobility of μFE = 450 cm2 V-1 s-1 in a linear region was realized.

  1. Partial hydrophilic modification of biaxially oriented polypropylene film by an atmospheric pressure plasma jet with the allylamine monomer

    Science.gov (United States)

    Chen, W. X.; Yu, J. S.; Hu, W.; Chen, G. L.

    2016-11-01

    In this paper, the partial modification of the biaxially oriented polypropylene (BOPP) film for potential biological and packaging applications was achieved via hydrophilic modification using atmospheric pressure plasma jet (APPJ). In the APPJ system, the allylamine (ALA) monomer was polymerized on the BOPP surface by either the Ar/O2 or the He/O2 plasma. The results showed that plasmatic modification created many micro/nano sized holes on the BOPP film, which increased the surface roughness dramatically and the increased roughness enhanced the combining intensity between the BOPP film and the ALA polymer. However, such a plasmatic modification increased the water vapor permeability. The FTIR and XPS characterizations showed that the amine groups were grafted onto the BOPP film, and the contact angle of the BOPP film decreases from 98.5° to 8°. Compared with the BOPP films treated by the Ar or He plasma, the barrier property of the modified BOPP film increased significantly when the ALA polymer was incorporated. The bio-affinity/toxicity of ALA polymer was illustrated by the attachment of the cultured SMMC-7721 hepatoma cells on the modified BOPP film. The significant enhancement in the cell density indicated that modified BOPP film was highly bio-compatible and non-toxic, especially treated with the Ar/O2/ALA plasma.

  2. Permeation of oxygen, water vapor, and limonene through printed and unprinted biaxially oriented polypropylene films.

    Science.gov (United States)

    Rubino, M; Tung, M A; Yada, S; Britt, I J

    2001-06-01

    Oriented polypropylene (OPP) and coated OPP (acrylic/OPP/PVDC) films were printed with two commercially available inks to investigate the influence of inks on water vapor and oxygen transmission rates. The permeation of an aroma compound (d-limonene) through coated OPP film printed with these inks was also evaluated at 35 degrees C and 100% relative humidity. The water vapor transmission rate increased significantly through OPP film printed with nitrocellulose-based ink. The oxygen transmission rate was significantly lower through both OPP and coated OPP films printed with the nitrocellulose ink. The effect of inks on limonene permeation was minor compared to the marked increase in permeation measured when the PVDC side of the coated film was exposed to the aroma, compared to the acrylic side. Scanning electron micrographs of coated film cross sections revealed changes in film structure upon exposure to limonene vapors, which were most pronounced when the PVDC side was exposed to limonene.

  3. Semicrystalline Structure-Dielectric Property Relationship and Electrical Conduction in a Biaxially Oriented Poly(vinylidene fluoride) Film under High Electric Fields and High Temperatures.

    Science.gov (United States)

    Yang, Lianyun; Ho, Janet; Allahyarov, Elshad; Mu, Richard; Zhu, Lei

    2015-09-16

    Poly(vinylidene fluoride) (PVDF)-based homopolymers and copolymers are attractive for a broad range of electroactive applications because of their high dielectric constants. Especially, biaxially oriented PVDF (BOPVDF) films exhibit a DC breakdown strength as high as that for biaxially oriented polypropylene films. In this work, we revealed the molecular origin of the high dielectric constant via study of a commercial BOPVDF film. By determination of the dielectric constant for the amorphous phase in BOPVDF, a high value of ca. 21-22 at 25 °C was obtained, and a three-phase (i.e., lamellar crystal/oriented interphase/amorphous region) semicrystalline model was proposed to explain this result. Meanwhile, electronic conduction mechanisms in BOPVDF under high electric fields and elevated temperatures were investigated by thermally stimulated depolarization current (TSDC) spectroscopy and leakage current studies. Space charge injection from metal electrodes was identified as a major factor for electronic conduction when BOPVDF was poled above 75 °C and 20 MV/m. In addition, when silver or aluminum were used as electrodes, new ions were generated from electrochemical reactions under high fields. Due to the electrochemical reactions between PVDF and the metal electrode, a question is raised for practical electrical applications using PVDF and its copolymers under high-field and high-temperature conditions. A potential method to prevent electrochemical degradation of PVDF is proposed in this study.

  4. Three-Dimensional Packing Structure and Electronic Properties of Biaxially Oriented Poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2- b ]thiophene) Films

    KAUST Repository

    Cho, Eunkyung

    2012-04-11

    We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl) thieno[3,2-b]thiophene) (PBTTT-C 14) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C 12 to C 14 and C 16 are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films. © 2012 American Chemical Society.

  5. Use of biaxially oriented polypropylene film for evaluating and cleaning contaminated atomic force microscopy probe tips: An application to blind tip reconstruction

    Science.gov (United States)

    Nie, H.-Y.; Walzak, M. J.; McIntyre, N. S.

    2002-11-01

    An atomic force microscopy (AFM) image of a surface is basically a convolution of the probe tip geometry and the surface features; it is important to know this tip effect to ensure that an image truly reflects the surface features. We have found that a biaxially oriented polypropylene (BOPP) film is suitable for checking tip performance and for cleaning contaminated tips, thus making it possible to collect images of the same area of a BOPP film surface before and after the tip was cleaned. Therefore, the difference between the two different images is solely due to the contamination of the tip. We took advantage of our ability to collect AFM images of the same area using the same tip, in one instance, contaminated and, in the other, after being cleaned. First we used blind reconstruction on the image collected using the contaminated tip. Blind tip reconstruction allows one to extract the geometry of the tip from a given image. Once we had estimated the geometry of the contaminated tip, we used it to simulate the tip effect using the image collected using the cleaned tip. By comparing the simulation result with the image collected using the contaminated tip we showed that the blind reconstruction routine works well. Prior to this, there was no de facto method for testing blind reconstruction algorithms.

  6. Effect of Low-Pressure Nitrogen DC Plasma Treatment on the Surface Properties of Biaxially Oriented Polypropylene, Poly (Methyl Methacrylate) and Polyvinyl Chloride Films

    Science.gov (United States)

    S. Hamideh, Mortazavi; Mahmood, Ghoranneviss; Soheil, Pilehvar; Sina, Esmaeili; Shamim, Zargham; S. Ebrahim, Hashemi; Hamzeh, Jodat

    2013-04-01

    In this study, commercial biaxially oriented polypropylene (BOPP), polyvinyl chloride (PVC) and poly (methyl methacrylate) (PMMA) films were treated with nitrogen plasma over different exposure times in a Pyrex tube surrounded by a DC variable magnetic field. The chemical changes that appeared on the surface of the samples were investigated using Fourier transform infrared (FT-IR) spectroscopy and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy after treatment for 2 min, 4 min and 6 min in a nitrogen plasma chamber. Effects of the plasma treatment on the surface topographies and contact angles of the untreated and plasma treated films were also analyzed by atomic force microscopy (AFM) and a contact angle measuring system. The results show that the plasma treated films become more hydrophilic with an enhanced wettability due to the formation of some new polar groups on the surface of the treated films. Moreover, at higher exposure times, the total surface energy in all treated films increased while a reduction in contact angle occurred. The behavior of surface roughness in each sample was completely different at higher exposure times.

  7. Growth of thin Al{sub 2}O{sub 3} films on biaxially oriented polymer films by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Vaehae-Nissi, Mika, E-mail: mika.vaha-nissi@vtt.fi [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland); Kauppi, Emilia, E-mail: emilia.kauppi@vti.fi [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland); Sahagian, Khoren, E-mail: khoren@anasysinstruments.com [Anasys Instruments, 121 Gray Avenue, Suite 100, Santa Barbara, CA 93101 (United States); Johansson, Leena-Sisko, E-mail: leena-sisko.johansson@aalto.fi [Aalto University, School of Chemical Technology, Department of Forest Products Technology, P.O. Box 16100, FI-00076 AALTO (Finland); Peresin, Maria Soledad; Sievaenen, Jenni; Harlin, Ali [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland)

    2012-11-01

    The effects of thin film nucleation and initial growth on roughness, chemistry and thermomechanical properties of polymer film surfaces were studied. Al{sub 2}O{sub 3} was deposited onto commercial biaxially oriented polypropylene and polylactic acid films at 80 Degree-Sign C by using atomic layer deposition technique. Both substrates, especially the more hydrophobic polypropylene, showed initial growth through Al{sub 2}O{sub 3} clusters. There was a faster deposition of Al{sub 2}O{sub 3} on polylactic acid film than on polypropylene at the early stages of the Al{sub 2}O{sub 3} deposition. There were also indications of chemical interactions between polylactic acid and trimethyl aluminum used as a precursor for Al{sub 2}O{sub 3}. Changes in the thermo-mechanical properties of the polymer surfaces with Al{sub 2}O{sub 3} also evidenced the differences between the substrate polymer films. The near surface interphase formed in polylactic acid probably contributed to the strong increase and scattering in the softening temperature during the early thin film growth. - Highlights: Black-Right-Pointing-Pointer Growth of atomic layer deposited Al{sub 2}O{sub 3} at 80 Degree-Sign C was studied on commercial films. Black-Right-Pointing-Pointer Both substrate films showed early Al{sub 2}O{sub 3} growth through clusters. Black-Right-Pointing-Pointer Initial growth rate depends on the nature of the substrate film surface. Black-Right-Pointing-Pointer There were indications of chemical interactions between substrate and precursor. Black-Right-Pointing-Pointer Film thickness and chemical interactions affect thermo-mechanical properties.

  8. Characterization Of Biaxial Strain Of Poly(L-Lactide) Tubes

    DEFF Research Database (Denmark)

    Løvdal, Alexandra Liv Vest; Andreasen, Jens Wenzel; Mikkelsen, Lars Pilgaard;

    2016-01-01

    . Through further WAXS analysis it was found that the SEQ biaxial strain yields larger interplanar spacing and distorted crystals and looser packing of chains. However, this does not influence the mechanical properties negatively. A loss of orientation in SEQ biaxial strained samples at high degrees...

  9. Novel mechanical behaviors of wurtzite CdSe nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Bing [Shanghai Normal University, Department of Physics (China); Chen, Li [MCPHS University, School of Arts and Sciences (United States); Xie, Yiqun; Feng, Jie; Ye, Xiang, E-mail: yexiang@shnu.edu.cn [Shanghai Normal University, Department of Physics (China)

    2015-09-15

    As an important semiconducting nanomaterial, CdSe nanowires have attracted much attention. Although many studies have been conducted in the electronic and optical properties of CdSe NWs, the mechanical properties of Wurtzite (WZ) CdSe nanowires remain unclear. Using molecular dynamics simulations, we have studied the tensile mechanical properties and behaviors of [0001]-oriented Wurtzite CdSe nanowires. By monitoring the stretching processes of CdSe nanowires, three distinct structures are found: the WZ wire, a body-centered tetragonal structure with four-atom rings (denoted as BCT-4), and a structure that consists of ten-atom rings with two four-atom rings (denoted as TAR-4) which is observed for the first time. Not only the elastic tensile characteristics are highly reversible under unloading, but a reverse transition between TAR-4 and BCT-4 is also observed. The stretching processes also have a strong dependence on temperature. A tubular structure similar to carbon nanotubes is observed at 150 K, a single-atom chain is formed at 300, 350 and 450 K, and a double-atom chain is found at 600 K. Our findings on tensile mechanical properties of WZ CdSe nanowires does not only provide inspiration to future study on other properties of CdSe nanomaterials but also help design and build efficient nanoscale devices.

  10. Vertically aligned biaxially textured molybdenum thin films

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan, Rahul [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Riley, Michael [Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Lee, Sabrina [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, New York 12189 (United States); Lu, Toh-Ming [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2011-09-15

    Vertically aligned, biaxially textured molybdenum nanorods were deposited using dc magnetron sputtering with glancing flux incidence (alpha = 85 degrees with respect to the substrate normal) and a two-step substrate-rotation mode. These nanorods were identified with a body-centered cubic crystal structure. The formation of a vertically aligned biaxial texture with a [110] out-of-plane orientation was combined with a [-110] in-plane orientation. The kinetics of the growth process was found to be highly sensitive to an optimum rest time of 35 seconds for the two-step substrate rotation mode. At all other rest times, the nanorods possessed two separate biaxial textures each tilted toward one flux direction. While the in-plane texture for the vertical nanorods maintains maximum flux capture area, inclined Mo nanorods deposited at alpha = 85 degrees without substrate rotation display a [-1-1-4] in-plane texture that does not comply with the maximum flux capture area argument. Finally, an in situ capping film was deposited with normal flux incidence over the biaxially textured vertical nanorods resulting in a thin film over the porous nanorods. This capping film possessed the same biaxial texture as the nanorods and could serve as an effective substrate for the epitaxial growth of other functional materials.

  11. Biaxial ferromagnetic liquid crystal colloids.

    Science.gov (United States)

    Liu, Qingkun; Ackerman, Paul J; Lubensky, Tom C; Smalyukh, Ivan I

    2016-09-20

    The design and practical realization of composite materials that combine fluidity and different forms of ordering at the mesoscopic scale are among the grand fundamental science challenges. These composites also hold a great potential for technological applications, ranging from information displays to metamaterials. Here we introduce a fluid with coexisting polar and biaxial ordering of organic molecular and magnetic colloidal building blocks exhibiting the lowest symmetry orientational order. Guided by interactions at different length scales, rod-like organic molecules of this fluid spontaneously orient along a direction dubbed "director," whereas magnetic colloidal nanoplates order with their dipole moments parallel to each other but pointing at an angle to the director, yielding macroscopic magnetization at no external fields. Facile magnetic switching of such fluids is consistent with predictions of a model based on competing actions of elastic and magnetic torques, enabling previously inaccessible control of light. PMID:27601668

  12. Anisotropy in CdSe quantum rods

    Energy Technology Data Exchange (ETDEWEB)

    Li, Liang-shi

    2003-09-01

    concentration. The preparation of the stable liquid crystalline solution of CdSe nanorods is described, as well as the large-scale alignment of the nanorods by taking advantage of the long-range orientational correlation in the liquid crystals. In addition, we investigated the phase diagram of the nanorod solution, as a step toward understanding the possible role of the long-range attractive interaction between the nanorods in the formation of lyotropic liquid crystals.

  13. Directional Differences in the Biaxial Material Properties of Fascia Lata and the Implications for Fascia Function

    OpenAIRE

    Eng, Carolyn M.; Pancheri, Francesco Q.; Lieberman, Daniel E.; Biewener, Andrew Austin; Dorfmann, Luis

    2014-01-01

    Fascia is a highly organized collagenous tissue that is ubiquitous in the body, but whose function is not well understood. Because fascia has a sheet-like structure attaching to muscles and bones at multiple sites, it is exposed to different states of multi- or biaxial strain. In order to measure how biaxial strain affects fascia material behavior, planar biaxial tests with strain control were performed on longitudinal and transversely oriented samples of goat fascia lata (FL). Cruciform samp...

  14. Biaxial Creep Specimen Fabrication

    Energy Technology Data Exchange (ETDEWEB)

    JL Bump; RF Luther

    2006-02-09

    This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.

  15. Biaxial Creep Specimen Fabrication

    International Nuclear Information System (INIS)

    This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments

  16. Biaxially textured articles formed by power metallurgy

    Science.gov (United States)

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2003-08-26

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of mixtures consisting of: at least 60 at % Ni powder and at least one of Cr powder, W powder, V powder, Mo powder, Cu powder, Al powder, Ce powder, YSZ powder, Y powder, Mg powder, and RE powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  17. Biaxially textured articles formed by powder metallurgy

    Science.gov (United States)

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2003-07-29

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of mixtures consisting of: at least 60 at % Ni powder and at least one of Cr powder, W powder, V powder, Mo powder, Cu powder, Al powder, Ce powder, YSZ powder, Y powder, Mg powder, and RE powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  18. Biaxially textured articles formed by powder metallurgy

    Science.gov (United States)

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2004-09-14

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of mixtures consisting of: at least 60 at % Ni powder and at least one of Cr powder, W powder, V powder, Mo powder, Cu powder, Al powder, Ce powder, YSZ powder, Y powder, Mg powder, and RE powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  19. Experimental realization of biaxial liquid crystal phases in colloidal dispersions of boardlike particles

    NARCIS (Netherlands)

    van den Pol, E; Petukhov, A.V.; Thies-Weesie, D.M.E.; Belov, D.V.; Vroege, G.J.

    2009-01-01

    Biaxial nematic and biaxial smectic phases were found in a colloidal model system of goethite ( -FeOOH) particles with a simple boardlike shape and short-range repulsive interaction. The macroscopic domains were oriented by a magnetic field and their structure was revealed by small angle x-ray scatt

  20. Composite enhancement technology of electrospun membrane with biaxial stretch and orientation%双向拉伸取向复合增强电纺膜技术

    Institute of Scientific and Technical Information of China (English)

    刘延波; 马素梅; 曹红; 石梦媛

    2016-01-01

    The orientation effect of nanofibers was achieved through heat stretch against blend-electrospun PVDF/PA12 membrane in MD, followed by cross-laying at 90° and then thermal calendering. The mechanical performance of the resultant composite electrospun membrane was elevated dramatically; meanwhile much more uniform web structure was obtained. It was found that the resulting electrospun membrane has smaller pore size, more uniform distribution of pore size and pore location, more regular fiber alignment, higher crystallinity, resulting in significant improvement of mechanical strength in both MD and CD.%对PVDF/PA12混纺电纺膜进行热牵伸取向处理,然后将2张取向电纺膜进行90°交叉铺叠,再进行热轧粘合,所得电纺膜在大幅提升机械性能的同时,获得了准各向同性电纺膜结构。研究发现:虽然热轧粘合后过滤效率和透气性会略有下降,但所得电纺膜具有更小的孔隙尺寸、更均匀的孔隙分布,纤维排列规整,结晶度增加,纵横向机械强度均得到大幅提升。

  1. Fragmentation in Biaxial Tension

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, G H; Archbold, G C; Hurricane, O A; Miller, P L

    2006-06-13

    We have carried out an experiment that places a ductile stainless steel in a state of biaxial tension at a high rate of strain. The loading of the ductile metal spherical cap is performed by the detonation of a high explosive layer with a conforming geometry to expand the metal radially outwards. Simulations of the loading and expansion of the metal predict strain rates that compare well with experimental observations. A high percentage of the HE loaded material was recovered through a soft capture process and characterization of the recovered fragments provided high quality data, including uniform strain prior to failure and fragment size. These data were used with a modified fragmentation model to determine a fragmentation energy.

  2. Biaxial fatigue behavior of a powder metallurgical TRIP steel

    Directory of Open Access Journals (Sweden)

    S. Ackermann

    2015-10-01

    had partially mode II orientation (tilted 45° to the loading axes and afterwards bifurcated into two pairs of mode I cracks. Another shear test revealed a major crack of mode I orientation (parallel to the loading axes. These results are in good agreement to the literature. Micro cracks after shear fatigue were longer than those after biaxial fatigue with strain ratios of 1 and 0.5. Major and minor cracks after equibiaxial and shear loading showed crack branching and crack coalescence. The results on fatigue crack behavior support the assumption that the period of stage I (mode II crack propagation is much longer under shear loading than under other biaxial conditions due to absence of tensile stress normal to the planes of maximum shear strain under shear loading

  3. Application of SSA analysis technique in biaxially oriented polypropylene specialty resin production%SSA 分析技术在双向拉伸聚丙烯专用料生产过程中的应用

    Institute of Scientific and Technical Information of China (English)

    刘兴旺; 朱宝兴; 赵爱利

    2012-01-01

    The isotacticity and its sequence distribution of several biaxially oriented polypropylene (BOPP) specialty resins were characterizated by successive self - nucleation annealing ( SSA ) method , and the relationship between crystallization and film forming performance was researched. On the basis of this,the cause for film breaking of BOPP resin manufactured in a 300 kt/a polypropylene unit of Lanzhou Petrochemical Company occurred during its extruding was analyzed, and the process parameters of the polymerization were optimized. The results showed that the film forming stability of BOPP resin was dependent on the isotacticity sequence distribution , that was the content of high isotacticity molecules needed to be decreased, and the content of low isotacticity molecules needed to be increased. The IPeakl/Peak2 ratio should be less than 1. With increasing the mass ratio of catalyst to external electron do-nor(T/D) ,the content of high isotacticity molecules decreased,the content of low and medium isotacticity molecules inceased,the lamellar became thinner, the isotacticity sequence distribution became broader , and the performance of film forming was improved.%采用连续自成核退火法(SSA)对几种不同双向拉伸聚丙烯(BOPP)树脂进行了等规度及等规序列分布表征,研究了其结晶行为与成膜稳定性之间的关系,据此分析了中国石油兰州石化公司30万t/a聚丙烯装置初期所产BOPP产品在使用过程中存在易破膜问题的原因,并进行了装置聚合工艺参数的优化.结果表明,BOPP树脂的成膜稳定性取决于其等规度分布情况,即高等规度组分含量应较低,低等规度组分含量应较高,峰高比值(Ipeak1/Ipeak2)以小于1为宜;随着催化剂与外给电子体质量比(T/D)的增大,BOPP树脂的高等规度组分含量逐渐降低,中、低等规度组分含量相对上升,晶片厚度变薄,分布加宽,成膜性能得以改善.

  4. Surface structure of CdSe Nanorods revealed by combined X-rayabsorption fine structure measurements and ab-initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Aruguete, Deborah A.; Marcus, Matthew A.; Li, Liang-shi; Williamson, Andrew; Fakra, Sirine; Gygi, Francois; Galli, Giulia; Alivisatos, A. Paul

    2006-01-27

    We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab-initio density functional theory calculations. Our measurements of crystallographically-aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.

  5. Colloidal Synthesis And Characterization Of Cdse Quantum Dots Role Of CdSe Molar Ratio And Temperature

    OpenAIRE

    Hakan Aydamp305n; M. R. Karim; Mesut Balaban; Hilmi Unlu

    2015-01-01

    Semiconductor Cadmium selenide CdSe Quantum Dots QDs were synthesized via colloidal chemistry method at moderately lower growth temperatures. Optical absorption and photoluminescence PL spectroscopy techniques were used to characterize the optical properties of CdSe QDs. Optical properties of colloidal CdSe QDs were successfully controlled by changing the initial CdSe molar ratios and temperature. Optical absorption and PL spectrum both showed gradual red shift with increasing CdSe molar rati...

  6. On the sensitivity of directions which support Voigt wave propagation in infiltrated biaxial dielectric materials

    CERN Document Server

    Mackay, Tom G

    2013-01-01

    Voigt wave propagation (VWP) was considered in a porous biaxial dielectric material which was infiltrated with a material of refractive index $n_a$. The infiltrated material was regarded as a homogenized composite material in the long-wavelength regime and its constitutive parameters were estimated using the extended Bruggeman homogenization formalism. In our numerical studies, the directions which support VWP were found to vary by as much as $300^\\circ$ per RIU as the refractive index $n_a$ was varied. The sensitivities achieved were acutely dependent upon the refractive index $n_a$ and the degrees of anisotropy and dissipation of the porous biaxial material. The orientations, shapes and sizes of the particles which constitute the infiltrating material and the porous biaxial material exerted only a secondary influence on the maximum sensitivities achieved. Also, for the parameter ranges considered, the degree of porosity of the biaxial material had little effect on the maximum sensitivities achieved. These n...

  7. Biaxially textured composite substrates

    Energy Technology Data Exchange (ETDEWEB)

    Groves, James R.; Foltyn, Stephen R.; Arendt, Paul N.

    2005-04-26

    An article including a substrate, a layer of a metal phosphate material such as an aluminum phosphate material upon the surface of the substrate, and a layer of an oriented cubic oxide material having a rock-salt-like structure upon the metal phosphate material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon a layer of a buffer material such as a SrTi.sub.x Ru.sub.1-x O.sub.3 layer.

  8. Amphoteric CdSe nanocrystalline quantum dots.

    Science.gov (United States)

    Islam, Mohammad A

    2008-06-25

    The nanocrystal quantum dot (NQD) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied a DC voltage across the pair, thin films of CdSe NQDs were deposited on both the positive and the negative electrodes. Extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: (1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, (2) there are equal numbers of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited dots is at least an order of magnitude higher than the number of initially charged dots, indicating regeneration. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of the CdSe NQDs.

  9. Electrodeposition of nanocrystalline CdSe thin films from dimethyl sulfoxide solution: Nucleation and growth mechanism, structural and optical studies

    Energy Technology Data Exchange (ETDEWEB)

    Henriquez, R., E-mail: rodrigo.henriquez@ucv.cl [Instituto de Quimica, Facultad de Ciencias, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Badan, A. [Instituto de Fisica, Facultad de Ingenieria, Herrera y Reissig 565, C.C. 30, 11000 Montevideo (Uruguay); Grez, P.; Munoz, E.; Vera, J. [Instituto de Quimica, Facultad de Ciencias, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Dalchiele, E.A.; Marotti, R.E. [Instituto de Fisica, Facultad de Ingenieria, Herrera y Reissig 565, C.C. 30, 11000 Montevideo (Uruguay); Gomez, H. [Instituto de Quimica, Facultad de Ciencias, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile)

    2011-05-01

    Highlights: > Electrodeposition of CdSe nanocrystalline semiconductor thin films. > Polycrystalline wurtzite structure with a slight (1010) preferred orientation. > Absorption edge shifts in the optical properties due to quantum confinement effects. - Abstract: Cadmium selenide (CdSe) nanocrystalline semiconductor thin films have been synthesized by electrodeposition at controlled potential based in the electrochemical reduction process of molecular selenium in dimethyl sulfoxide (DMSO) solution. The nucleation and growth mechanism of this process has been studied. The XRD pattern shows a characteristic polycrystalline hexagonal wurtzite structure with a slight (1 0 1 0) crystallographic preferred orientation. The crystallite size of nanocrystalline CdSe thin films can be simply controlled by the electrodeposition potential. A quantum size effect is deduced from the correlation between the band gap energy and the crystallite size.

  10. The elusive thermotropic biaxial nematic phase in rigid bent-core molecules

    Indian Academy of Sciences (India)

    Bharat R Acharya; Andrew Primak; Theo J Dingemans; Edward T Samulski; Satyendra Kumar

    2003-08-01

    The biaxial nematic liquid crystalline phase was predicted several decades ago. Several vigorous attempts to find it in various systems resulted in mis-identifications. The results of X-ray diffraction and optical texture studies of the phases exhibited by rigid bent-core molecules derived from 2,5-bis-(-hydroxyphenyl)-1,3,4-oxadiazole reveal that the biaxial nematic phase is formed by three compounds of this type. X-ray diffraction studies reveal that the nematic phase of these compounds has the achiral symmetry D2h, in which the overall long axes of the molecules are oriented parallel to each other to define the major axis of the biaxial phase. The apex of the bent-cores defines the minor axis of this phase along which the planes containing the bent-cores of neighboring molecules are oriented parallel to each other.

  11. Biaxial fatigue of metals the present understanding

    CERN Document Server

    Schijve, Jaap

    2016-01-01

    Problems of fatigue under multiaxial fatigue loads have been addressed in a very large number of research publications. The present publication is primarily a survey of biaxial fatigue under constant amplitude loading on metal specimens. It starts with the physical understanding of the fatigue phenomenon under biaxial fatigue loads. Various types of proportional and non-proportional biaxial fatigue loads and biaxial stress distributions in a material are specified. Attention is paid to the fatigue limit, crack nucleation, initial micro crack growth and subsequent macro-crack in different modes of crack growth. The interference between the upper and lower surfaces of a fatigue crack is discussed. Possibilities for predictions of biaxial fatigue properties are analysed with reference to the similarity concept. The significance of the present understanding for structural design problems is considered. The book is completed with a summary of major observations.

  12. Biaxial Stretch Improves Elastic Fiber Maturation, Collagen Arrangement, and Mechanical Properties in Engineered Arteries.

    Science.gov (United States)

    Huang, Angela H; Balestrini, Jenna L; Udelsman, Brooks V; Zhou, Kevin C; Zhao, Liping; Ferruzzi, Jacopo; Starcher, Barry C; Levene, Michael J; Humphrey, Jay D; Niklason, Laura E

    2016-06-01

    Tissue-engineered blood vessels (TEVs) are typically produced using the pulsatile, uniaxial circumferential stretch to mechanically condition and strengthen the arterial grafts. Despite improvements in the mechanical integrity of TEVs after uniaxial conditioning, these tissues fail to achieve critical properties of native arteries such as matrix content, collagen fiber orientation, and mechanical strength. As a result, uniaxially loaded TEVs can result in mechanical failure, thrombus, or stenosis on implantation. In planar tissue equivalents such as artificial skin, biaxial loading has been shown to improve matrix production and mechanical properties. To date however, multiaxial loading has not been examined as a means to improve mechanical and biochemical properties of TEVs during culture. Therefore, we developed a novel bioreactor that utilizes both circumferential and axial stretch that more closely simulates loading conditions in native arteries, and we examined the suture strength, matrix production, fiber orientation, and cell proliferation. After 3 months of biaxial loading, TEVs developed a formation of mature elastic fibers that consisted of elastin cores and microfibril sheaths. Furthermore, the distinctive features of collagen undulation and crimp in the biaxial TEVs were absent in both uniaxial and static TEVs. Relative to the uniaxially loaded TEVs, tissues that underwent biaxial loading remodeled and realigned collagen fibers toward a more physiologic, native-like organization. The biaxial TEVs also showed increased mechanical strength (suture retention load of 303 ± 14.53 g, with a wall thickness of 0.76 ± 0.028 mm) and increased compliance. The increase in compliance was due to combinatorial effects of mature elastic fibers, undulated collagen fibers, and collagen matrix orientation. In conclusion, biaxial stretching is a potential means to regenerate TEVs with improved matrix production, collagen organization, and mechanical

  13. Engineering piezoresistivity using biaxially strained silicon

    DEFF Research Database (Denmark)

    Pedersen, Jesper Goor; Richter, Jacob; Brandbyge, Mads;

    2008-01-01

    We calculate the shear piezocoefficient of p-type silicon with grown-in biaxial strain using a 66 k·p method. We find a significant increase in the value of the shear piezocoefficient for compressive grown-in biaxial strain, while tensile strain decreases the piezocoefficient. The dependence...... of the piezocoefficient on temperature and dopant density is altered qualitatively for strained silicon. In particular, we find that a vanishing temperature coefficient may result for silicon with grown-in biaxial tensile strain. These results suggest that strained silicon may be used to engineer the iezoresistivity...

  14. Liquid crystal display modes in a nontilted bent-core biaxial smectic liquid crystal

    Science.gov (United States)

    Nagaraj, Mamatha; Panarin, Y. P.; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-11-01

    Liquid crystal display (LCD) modes associated with the rotation of the secondary director in nontilted, biaxial smectic phase of an achiral bent-core compound are demonstrated. For LCDs, we find that at least four display modes are possible using SmAPA phase of the studied material, in which the minor directors in adjacent layers are aligned antiferroelectrically. The advantages of these modes include low driving field (1-2 V/μm), high contrast ratio 1000:1, relatively fast switching time of 0.5 ms and continuous gray scale. The molecular short axis or the polar axis in a negative dielectric, biaxial material is oriented by the in-plane electric field by a combination dielectric biaxiality and polarity at low electric fields and polarity at higher fields.

  15. A method to synthesize CdSe nanocrystals

    Institute of Scientific and Technical Information of China (English)

    XIE Chuang; CHEN Wei; WANG Jingkang

    2007-01-01

    CdSe nanocrystals (NCs) have great application prospects in various fields due to their novel properties.Some high-cost and toxic materials such as tri-n-octylphosphine oxide (TOPO) are used in the popular method to synthesize CdSe NCs.Based on this,a new low-cost,environment-friendly and safe solvent was introduced in the synthesis of CdSe NCs in this paper.The prepared CdSe NCs were characterized by ultraviolet-visible spectra (UV-Vis),photoluminescence (PL),transmission electron micrograph (TEM),energy disperse X-ray spectra (EDX) and X-ray diffraction (XRD).The CdSe NCs obtained which show a good PL properry are monodisperse,size-tunable and of high crystallinity.It indicates that the new solvent A is a good substitute for the solvent used in the classic route and achieves a greener synthesis of CdSe NCs.

  16. Colloidal Synthesis And Characterization Of Cdse Quantum Dots Role Of CdSe Molar Ratio And Temperature

    Directory of Open Access Journals (Sweden)

    Hakan Aydamp305n

    2015-08-01

    Full Text Available Semiconductor Cadmium selenide CdSe Quantum Dots QDs were synthesized via colloidal chemistry method at moderately lower growth temperatures. Optical absorption and photoluminescence PL spectroscopy techniques were used to characterize the optical properties of CdSe QDs. Optical properties of colloidal CdSe QDs were successfully controlled by changing the initial CdSe molar ratios and temperature. Optical absorption and PL spectrum both showed gradual red shift with increasing CdSe molar ratio and temperature. High-resolution transmission electron microscopy HRTEM technique were used to study the structural properties of CdSe QDs. Full width at half maximum FWHM values obtained from the emission spectrums were helped to prove the narrow size distribution which coincides with the matching results of HRTEM images and theoretical calculations.

  17. In situ biaxial texture analysis of MGO films during growth on amorphous substrates by ion beam-assisted deposition

    Energy Technology Data Exchange (ETDEWEB)

    Brewer, R. T. (Rhett T.); Arendt, P. N. (Paul N.); Atwater, H. A. (Harry A.); Groves, J. R. (James R.)

    2001-01-01

    We used a previously reported kinematical electron scattering model to develop a RHEED based method for performing quantitative analysis of mosaic polycrystalline thin film in-plane and out-of-plain grain orientation distributions. RHEED based biaxial texture measurements are compared to X-Ray and transmission electron microscopy measurements to establish the validity of the RHEED analysis method. In situ RHEED analysis reveals that the out of plane orientation distribution starts out very broad, and then decreases during IBAD MgO growth. Other results included evidence that the in-plane orientation distribution narrows, the grain size increases, and the film roughens as film thickness increases during IBAD MgO growth. Homoepitaxy of MgO improves the biaxial texture of the IBAD layer, making X-ray measurements of IBAD films with an additional homoepitaxial layer not quantitatively representative of the IBAD layer. Systematic offsets between RHEED analysis and X-ray measurements of biaxial texture, coupled with evidence that biaxial texture improves with increasing film thickness, indicate that RHEED is a superior technique for probing surface biaxial texture.

  18. Ultrasonic fatigue testing device under biaxial bending

    Directory of Open Access Journals (Sweden)

    C. Brugger

    2016-07-01

    Full Text Available A new fatigue testing device has been developed to test specimens under biaxial loading at 20 kHz. A flat smooth specimen with a disc geometry is placed on a torus frame and cyclically loaded at the center of its upper face. Disc bending generates a biaxial proportional stress state at the center of the lower face. Any positive loading ratio can be applied. A cast aluminum alloy (used to produce cylinder heads has been tested under biaxial bending using this device in order to determine its fatigue strength at 109 cycles under high hydrostatic pressure. Self-heating is moderate but macroscopic fatigue cracks after testing are very long. First results in VHCF regime are consistent with literature results obtained under similar stress state but in HCF regime and at 20 Hz.

  19. Biaxial tension on polymer in thermoforming range

    Directory of Open Access Journals (Sweden)

    Billon N.

    2010-06-01

    Full Text Available This paper presents an experimental characterization of mechanical properties of a polyethylene terephtalate (PET resin classically used in stretch blow moulding process. We have applied on such a material a well established experimental protocol at CEMEF, including new and relevant biaxial tensile tests. The experimental set-up relative to biaxial tension will be presented and described in a first part of the paper. Furthermore, we will focus on the experimental DMTA preliminary tests which are required to estimate the resin sensibility to temperature and strain rate in linear viscoelasticity domain. Finally, we will be interested in the material large strain behaviour: biaxial tensile results are presented and discussed. Finally, such an experimental approach should allow a relevant modelling of polymer physics and mechanics; this point will not be discussed here because of a lack of time.

  20. Biaxial tension on polymer in thermoforming range

    Science.gov (United States)

    Becker, S.; Combeaud, C.; Fournier, F.; Rodriguez, J.; Billon, N.

    2010-06-01

    This paper presents an experimental characterization of mechanical properties of a polyethylene terephtalate (PET) resin classically used in stretch blow moulding process. We have applied on such a material a well established experimental protocol at CEMEF, including new and relevant biaxial tensile tests. The experimental set-up relative to biaxial tension will be presented and described in a first part of the paper. Furthermore, we will focus on the experimental DMTA preliminary tests which are required to estimate the resin sensibility to temperature and strain rate in linear viscoelasticity domain. Finally, we will be interested in the material large strain behaviour: biaxial tensile results are presented and discussed. Finally, such an experimental approach should allow a relevant modelling of polymer physics and mechanics; this point will not be discussed here because of a lack of time.

  1. Structural and optical properties of electron beam evaporated CdSe thin films

    Indian Academy of Sciences (India)

    N J Suthan Kissinger; M Jayachandran; K Perumal; C Sanjeevi Raja

    2007-12-01

    Thin films of cadmium selenide (CdSe) as a semiconductor is well suited for opto-electronic applications such as photo detection or solar energy conversion, due to its optical and electrical properties, as well as its good chemical and mechanical stability. In order to explore the possibility of using this in optoelectronics, a preliminary and thorough study of optical and structural properties of the host material is an important step. Based on the above view, the structural and optical properties of CdSe films have been studied thoroughly in the present work. The host material, CdSe film, has been prepared by the physical vapour deposition method of electron beam evaporation (PVD: EBE) technique under a pressure of 5 × 10-5 mbar. The structural properties have been studied by XRD technique. The hexagonal structure with a preferred orientation along the (0 0 2) direction of films has been confirmed by the X-ray diffraction analysis. The films have been analysed for optical band gap and absorbed a direct intrinsic band gap of 1.92 eV.

  2. Towards the biaxial nematic phase via specific intermolecular interactions

    CERN Document Server

    Omnes, L

    2001-01-01

    The work described in this thesis has been focussed on the search of an elusive liquid crystal phase, known as the biaxial nematic phase. Indeed, despite nearly thirty years of intense research, no-one has been able to characterise unambiguously a biaxial nematic phase in a low-molar-mass thermotropic system. Our research is based on the concept of molecular biaxiality as distinct from shape biaxiality. Thus, we are seeking to design palladium complexes where specific intermolecular interactions could exist. Therefore, a few original synthetic strategies were developed to tackle the challenge of discovering the biaxial nematic phase

  3. On the sensitivity of directions that support Voigt wave propagation in infiltrated biaxial dielectric materials

    Science.gov (United States)

    Mackay, Tom G.

    2014-01-01

    Voigt wave propagation (VWP) was considered in a porous biaxial dielectric material that was infiltrated with a material of refractive index n. The infiltrated material was regarded as a homogenized composite material in the long wavelength regime, and its constitutive parameters were estimated using the extended Bruggeman homogenization formalism. In our numerical studies, the directions that support VWP were found to vary by as much as 300 deg per RIU as the refractive index n was varied. The sensitivities achieved were acutely dependent upon the refractive index n and the degrees of anisotropy and dissipation of the porous biaxial material. The orientations, shapes, and sizes of the particles that constitute the infiltrating material and the porous biaxial material exerted only a secondary influence on the maximum sensitivities achieved. Also, for the parameter ranges considered, the degree of porosity of the biaxial material had little effect on the maximum sensitivities achieved. These numerical findings bode well for the possible harnessing of VWP for optical sensing applications.

  4. Reversible ultrafast melting in bulk CdSe

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Wenzhi [School of Electronic Engineering, Heilongjiang University, Harbin 150080 (China); Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); He, Feng; Wang, Yaguo, E-mail: yaguo.wang@austin.utexas.edu [Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); The Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712 (United States)

    2016-02-07

    In this work, transient reflectivity changes in bulk CdSe have been measured with two-color femtosecond pump-probe spectroscopy under a wide range of pump fluences. Three regions of reflectivity change with pump fluences have been consistently revealed for excited carrier density, coherent phonon amplitude, and lattice temperature. For laser fluences from 13 to 19.3 mJ/cm{sup 2}, ultrafast melting happens in first several picoseconds. This melting process is purely thermal and reversible. A complete phase transformation in bulk CdSe may be reached when the absorbed laser energy is localized long enough, as observed in nanocrystalline CdSe.

  5. Biaxial testing for fabrics and foils optimizing devices and procedures

    CERN Document Server

    Beccarelli, Paolo

    2015-01-01

    This book offers a well-structured, critical review of current design practice for tensioned membrane structures, including a detailed analysis of the experimental data required and critical issues relating to the lack of a set of design codes and testing procedures. The technical requirements for biaxial testing equipment are analyzed in detail, and aspects that need to be considered when developing biaxial testing procedures are emphasized. The analysis is supported by the results of a round-robin exercise comparing biaxial testing machines that involved four of the main research laboratories in the field. The biaxial testing devices and procedures presently used in Europe are extensively discussed, and information is provided on the design and implementation of a biaxial testing rig for architectural fabrics at Politecnico di Milano, which represents a benchmark in the field. The significance of the most recent developments in biaxial testing is also explored.

  6. High pressure phase transitions for CdSe

    Indian Academy of Sciences (India)

    Bo Kong; Ti-Xian Zeng; Zhu-Wen Zhou; De-Liang Chen; Xiao-Wei Sun

    2014-05-01

    The structure and pressure-induced phase transitions for CdSe are investigated using first-principles calculations. The pressure-induced phase transition sequence WZ/ZB $\\to$ Rs $\\to$ $\\to$ CsCl for CdSe is drawn reasonably for the fist time, the corresponding transition pressures are 3.8, 29 and 107 GPa, respectively and the intermediate states between the structure and the CsCl structure should exist.

  7. Lasing with conical diffraction feature in the KGd(WO4)2:Nd biaxial crystal

    Science.gov (United States)

    Brenier, Alain

    2016-09-01

    With an experimental set-up designed to record simultaneously the far-field and the near-field patterns, we got lasing with feature of conical diffraction in the biaxial Nd3+-doped KGd(WO4)2 crystal. The key-point is that the lasing direction is not single and is constituted by an angular distribution including the optical axis. Very slight changes of crystal orientation leads to crescent shape 1068-nm light distributions in the near-field. The beam launched towards the biaxial crystal is mainly linear polarized with its intensity in agreement with the Nd fluorescence angular distribution. A theoretical background is provided, including the monoclinic and triclinic symmetries and laser amplification including elliptical modes and cavity round trip.

  8. MULTIPLE EXCITON GENERATIONSOLAR CELLS USING CdSe QUANTUM DOTS

    Directory of Open Access Journals (Sweden)

    HAFTOM MESFIN GEBRESLASSIE,

    2011-03-01

    Full Text Available Experimental and Simulation works of Nano structured Solar Cells Using CdSe Quantum Dots have been analyzed and investigated. CdSe quantum dots have been synthesized from non coordinating and highboiling solvent Octadecene and a series of increasing CdSe particle sizes are produced. The synthesized CdSe quantum dots are highly examined under a Transmission Electron Microscope and four images ofdifferent sizes of CdSe quantum dots (5.8 nm, 6.4 nm, 7.0 nm and 7.7 nm have been obtained. A 1.1x1.1cm2 TiO2 electrode is prepared using indium tin oxide conducting glass and TiO2 nanoparticles. The CdSe quantum dot (5.8nm was adsorbed on TiO2 photoelectrode and used as sensitizer. In this paper work, a sandwich type cell configuration which is made up of TiO2 photoelectrode, graphite coated counter electrode, an electrolyte of iodine and potassium iodide have been used. This sandwich type cell has been exposed to sun light and we have achieved 0.32 V and 0.2 mA

  9. Photoluminescence spectra and biaxial stress effects of yellow 1S excitons in Cu{sub 2}O thin films recrystallized epitaxially between paired MgO plates

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, S., E-mail: shingoauniv@gmail.com [Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami Chuo-ku, Kumamoto 860-8555 (Japan); Ota, A. [Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami Chuo-ku, Kumamoto 860-8555 (Japan); Iwamitsu, K. [Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami Chuo-ku, Kumamoto 860-8555 (Japan); Faculty of Science, Kumamoto University, 2-39-1, Kurokami Chuo-ku, Kumamoto 860-8555 (Japan); Ichikawa, F.; Isobe, H. [Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami Chuo-ku, Kumamoto 860-8555 (Japan); Shimamoto, T.; Akai, I. [Institute of Pulsed Power Science, Kumamoto University, 2-39-1, Kurokami Chuo-ku, Kumamoto 860-8555 (Japan)

    2015-11-15

    We investigated biaxial stress effects on the yellow 1S ortho excitons in Cu{sub 2}O thin films recrystallized between paired MgO plates by measuring photoluminescence spectra, X-ray diffraction and polarization microscope images. On the MgO (001) surface, we found two kinds of epitaxial growth modes of the Cu{sub 2}O thin films. In such thin films, the yellow 1S ortho exciton states split into two or three levels depending on the respective epitaxial growth modes due to the different biaxial stresses owing to the lattice mismatches between Cu{sub 2}O and MgO. By using effective Hamiltonians including such biaxial stress effects, we estimated the strengths of the biaxial stresses from the energy splittings of the 1S ortho excitons and confirmed the two kinds of epitaxial growth modes in our Cu{sub 2}O thin films. - Highlights: • Two different oriented Cu{sub 2}O thin films were epitaxially grown between paired MgO (001) plates. • The thin films were applied biaxial stresses due to lattice mismatch between Cu{sub 2}O and MgO. • The lattice mismatch stresses can change yellow 1S exciton states in Cu{sub 2}O thin films. • We report the biaxial stress strengths by analyzing splitting energies of the 1S ortho excitons.

  10. Composition-controlled optical properties of colloidal CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ayele, Delele Worku [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Department of Chemistry, Bahir Dar University, Bahir Dar (Ethiopia); Su, Wei-Nien, E-mail: wsu@mail.ntust.edu.tw [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Chou, Hung-Lung [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Pan, Chun-Jern [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Hwang, Bing-Joe, E-mail: bjh@mail.ntust.edu.tw [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China)

    2014-12-15

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.

  11. Biaxial crystal-based optical tweezers

    DEFF Research Database (Denmark)

    Angelsky, Oleg V.; Maksimyak, Andrew P.; Maksimyak, Peter P.;

    2010-01-01

    We suggest an optical tweezer setup based on an optically biaxial crystal. To control movements of opaque particles, we use shifts. The results of experimental studies are reported which are concerned with this laser tweezer setup. We demonstrate a movement of microparticles of toner using a sing...... a singular-optical trap, rotation of particles due to orbital angular momentum of the field, and converging or diverging of two different traps when changing transmission plane of polariser at the input of our polarisation interferometer....

  12. Biaxial CdTe/CaF{sub 2} films growth on amorphous surface

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, W., E-mail: yuanw@rpi.ed [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Tang, F.; Li, H.-F.; Parker, T. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); LiCausi, N. [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Lu, T.-M. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Bhat, I. [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Wang, G.-C. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Lee, S. [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, NY 12189 (United States)

    2009-10-30

    A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF{sub 2} nanorods as a buffer layer. The interface between the CdTe film and CaF{sub 2} nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {l_brace}111{r_brace}<121> biaxial texture of the CaF{sub 2} nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.

  13. Instability of a Biaxial Nematic Liquid Crystal Formed by Homeotropic Anchoring on Surface Grooves

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhi-Dong; XUAN Li

    2011-01-01

    A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition.Employing some approximations for the elastic constants,we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves,with a period of π/2.This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable.Our theoretical study explains why the homeotropic alignment method developed for uniaxial liquid crystals loses efficacy for biaxial nematics.In most liquid crystal devices,the liquid crystals are sandwiched between two substrates coated with alignment layers.In the absence of externally applied fields,the orientation of the liquid crystal in the cell is determined by the anchoring condition of the alignment layer.[1-3] One usually distinguishes three main types of liquid crystalline director alignment near solid walls:homeotropic,homogeneous (or planar) and tilted orientations.Here we study the first of these and consider the biaxial nematic phase,which was observed in lyotropic systems as early as 1980[4] and has been confirmed by deuterium NMR spectroscopy.%A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition. Employing some approximations for the elastic constants, we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves, with a period of π/2. This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable. Our

  14. Synthesis and characterization of CdSe colloidal quantum dots in organic solvent

    International Nuclear Information System (INIS)

    In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the range 2.28-2.92 nm which is in good agreement with PL measurements. (authors)

  15. SYNTHESIS AND CHARACTERIZATION OF CdSe COLLOIDAL QUANTUM DOTS IN ORGANIC SOLVENT

    OpenAIRE

    Ion Geru; Olga Bordian; Constantin Loshmansky; Ion Culeac; Constantin Turta

    2014-01-01

    In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the rang...

  16. SYNTHESIS AND CHARACTERIZATION OF CdSe COLLOIDAL QUANTUM DOTS IN ORGANIC SOLVENT

    Directory of Open Access Journals (Sweden)

    Ion Geru

    2014-06-01

    Full Text Available In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the range 2.28-2.92 nm which is in good agreement with PL measurements.

  17. Growth of Biaxially Textured Yttria-Stabilized Zirconia Thin Films on Si(111) Substrate by Ion Beam Assisted Deposition

    Institute of Scientific and Technical Information of China (English)

    MU Hai-Chuan; REN Cong-Xin; JIANG Bing-Yao; DING Xing-Zhao; YU Yue-Hui; WANG Xi; LIU Xiang-Huai; ZHOU Gui-En; JIA Yun-Bo

    2000-01-01

    The (001) oriented yttria-stabilized zirconia (YSZ) films with in-plane biaxial texture have been deposited on Si(lll ) substrates by ion beam assisted deposition at ambient temperature. The effects of ion/atom arrival rate ratio (R=(Ar+ +O2+)/ZrO2) and incident angle of bombarding ion beam on the film texture development were investigated. It was found that the in-plane biaxial texture of the films was improved gradually with increasing ion/atom arrival rate ratio R up to a critical value 1.9, but it was degraded with the further increase of R. The optimal in-plane biaxial texture, whose full width at half maximum of the (lll) φ-scan spectrum is 14°, can be obtained at R=1.9 and incident angle of 55°. For a fixed R, the optimal crystallinity and in-plane biaxial alignment of the YSZ films did not appear at the same incident angle and showed an opposite variation with the change of the incident angle from 51° to 55°. C-axis lignment (perpendicular to substrate surface) does not show any substantial variation with the change of incident angle within the range of 47° - 56°.

  18. Application of Bi-axial Warp Knitted Structures in Concrete Constructions

    Institute of Scientific and Technical Information of China (English)

    李炜; 陈南梁

    2001-01-01

    The warp knitted bi-axial directionally oriented structure (D. O. S. ) reinforcement substrates applied to building construction are discussed in comparison to woven fabrics. One of usage barriers of reinforced cement with gloss-grid is its sensitivity to alkali existed in the cement which will lead to the reduction of its service-life. The tests show that the treatment by sol-gel method to protect the composite from alkali corrosion is effective. Then two formulae of sol-gel solution are also recommended here for application.

  19. Piezo-phototronic effect of CdSe nanowires.

    Science.gov (United States)

    Dong, Lin; Niu, Simiao; Pan, Caofeng; Yu, Ruomeng; Zhang, Yan; Wang, Zhong Lin

    2012-10-23

    The piezo-phototronic effect on transport properties of flexible CdSe NW devices is investigated. An optimum sensitivity of the flexible CdSe NW devices can be achieved by adjusting the applied strain and illumination intensity. The piezo-phototronic effect under compressive strain increases the internal electric field of the Schottky barrier, and assists the separation of the photo-excited electron-hole pairs, resulting in the increase of photocurrent. A trap-mediated mechanism is responsible for the decreased hole separation when the strain is larger than the critical strain.

  20. Study on Surface Treatments on CdSe Wafers

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The surface treatments on CdSe wafers were studied by means of SEM, XPS and micro-current test instrument. The relations between electrical properties of CdSe wafers and surface topography, composition and structure were analyzed. The results show that the change of surface composition by etching is beneficial to decrease leakage current. Meanwhile, the increase of oxygen on surface caused by passivation can largely decrease leakage current. When passivating time is 40 min, the wafers surface appears smooth and compact, which will decrease the density of surface state, the optimal electrical property of the wafer is therefore obtained.

  1. Enhanced carrier mobility and direct tunneling probability of biaxially strained Ge{sub 1−x}Sn{sub x} alloys for field-effect transistors applications

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lei; Liang, Renrong, E-mail: liangrr@tsinghua.edu.cn, E-mail: junxu@tsinghua.edu.cn; Wang, Jing; Xu, Jun, E-mail: liangrr@tsinghua.edu.cn, E-mail: junxu@tsinghua.edu.cn [Tsinghua National Laboratory for Information Science and Technology, Institute of Microelectronics, Tsinghua University, Beijing 100084 (China)

    2015-05-14

    The carrier transport and tunneling capabilities of biaxially strained Ge{sub 1−x}Sn{sub x} alloys with (001), (110), and (111) orientations were comprehensively investigated and compared. The electron band structures of biaxially strained Ge{sub 1−x}Sn{sub x} alloys were calculated by the nonlocal empirical pseudopotential method and the modified virtual crystal approximation was adopted in the calculation. The electron and hole effective masses at the band edges were extracted using a parabolic line fit. It is shown that the applied biaxial strain and the high Sn composition are both helpful for the reduction of carrier effective masses, which leads to the enhanced carrier mobility and the boosted direct band-to-band-tunneling probability. Furthermore, the strain induced valance band splitting reduces the hole interband scattering, and the splitting also results in the significantly enhanced direct tunneling rate along the out-of-plane direction compared with that along the in-plane direction. The biaxially strained (111) Ge{sub 1−x}Sn{sub x} alloys exhibit the smallest band gaps compared with (001) and (110) orientations, leading to the highest in-plane and out-of-plane direct tunneling probabilities. The small effective masses on (110) and (111) planes in some strained conditions also contribute to the enhanced carrier mobility and tunneling probability. Therefore, the biaxially strained (110) and (111) Ge{sub 1−x}Sn{sub x} alloys have the potential to outperform the corresponding (001) Ge{sub 1−x}Sn{sub x} devices. It is important to optimize the applied biaxial strain, the Sn composition, and the substrate orientation for the design of high performance Ge{sub 1−x}Sn{sub x} field-effect transistors.

  2. Growth of inclined fatigue cracks using the biaxial CJP model

    Directory of Open Access Journals (Sweden)

    G. Laboviciute

    2015-07-01

    Full Text Available The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some longstanding controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model

  3. Tensile Property of Bi-axial Warp Knitted Structure

    Institute of Scientific and Technical Information of China (English)

    沈为

    2003-01-01

    The tensile property of bi-axial warp knitted fabrics is tested and compared with that of the plain weave fabric. The results show that there are obvious differences between the tensile property of a bi-axial warp knitted fabric and that of a plain weave fabric.The former can give fuller play to the property of a high modulus yarn than the latter. The tensile strength of a bi-axial warp knitted fabric is linear with the number of yarns in the direction of force.

  4. Conductive and robust nitride buffer layers on biaxially textured substrates

    Science.gov (United States)

    Sankar, Sambasivan [Chicago, IL; Goyal, Amit [Knoxville, TN; Barnett, Scott A [Evanston, IL; Kim, Ilwon [Skokie, IL; Kroeger, Donald M [Knoxville, TN

    2009-03-31

    The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metals and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layer. In some embodiments the article further comprises electromagnetic devices which may have superconducting properties.

  5. Selective Synthesis of Wurtzite CdSe Nanorods and Zinc Blend CdSe Nanocrystals through a Convenient Solvothermal Route

    Energy Technology Data Exchange (ETDEWEB)

    Liu Yong; Qiu Huayu [Hangzhou Teachers College, Key Laboratory of Organosilicon Chemistry and Material Technology of Education Ministry (China); Xu Yao; Wu Dong [Institute of Coal Chemistry, Chinese Academy of Science, State Key Lab of Coal Conversion (China); Li Meijiang; Jiang Jianxiong; Lai Guoqiao [Hangzhou Teachers College, Key Laboratory of Organosilicon Chemistry and Material Technology of Education Ministry (China)], E-mail: gqlai@hztc.edu.cn

    2007-10-15

    By simply changing the reactants' compositions, wurtzite CdSe nanorods and zinc blend CdSe nanoparticles were selectively synthesized through a convenient solvothermal route with the reaction of cadmium nitrate (Cd(NO{sub 3}){sub 2}. 4H{sub 2}O), hydrazine hydrate (N{sub 2}H{sub 4}. H{sub 2}O), and Se in ethylenediamine (en) at 140 deg. C. Effects of temperature and composition of the reactants were detected and the amount and gaining rate of Se{sup 2-} ions were found to determine the morphology and structure of the final product.

  6. Biaxial wheel/hub test facility. Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, G.; Grubisic, V. [eds.

    2000-07-01

    The 4{sup th} meeting aims to exchange the experience and knowledge of engineers during several presentations and discussions about new developments required for a reliable, time and cost reducing validation of the wheel/hub assembly. Tremendous development of the wheel performance, described by the ratio of the rated load (kg) versus the wheel weight (kg) had taken place during the last 5000 years. Starting from the ratio of 3 for wooden 2-piece-disc-wheels in Mesopotamia it needed nearly 1000 years to increase the ratio to approx 5 at light-weight spoke wheels for fighting carriages, found in the grave of king Tutenchamon in Egypt. Modern light alloy wheels of commercial vehicles reach values up to 160 kg/kg. Additionally the comlex design of the modern systems for cars and commercial vehicles comprising wheel, brake, hub, bearing, spindle and hub carrier, including different materials and their treatment, fasteners, press-fits, require an appropriate testing procedure. The variable loading conditions, caused by operational wheel forces, brake and torque moments including heating, may result in changing tolerances and press-fits during operation and consequently in different damage mechanisms. This can be simulated in the Biaxial Wheel Test Machine, whereby corresponding load programs are necessary. An overview about all biaxial test machines in usage at the end of 1999 is shown in the introduction. The total number is 17 for cars, 7 for commercial vehicles and 1 for trains. The six presentations of this meeting were consequently concentrated on: (a) recommendations for a standardization of load programs of the German Wheel Committee, (b) the simulation of brake and torque events and (c) the possibility for a numerical stress analyses and fatigue life assessment. (orig./AKF)

  7. Spin Selective Charge Transport through Cysteine Capped CdSe Quantum Dots.

    Science.gov (United States)

    Bloom, Brian P; Kiran, Vankayala; Varade, Vaibhav; Naaman, Ron; Waldeck, David H

    2016-07-13

    This work demonstrates that chiral imprinted CdSe quantum dots (QDs) can act as spin selective filters for charge transport. The spin filtering properties of chiral nanoparticles were investigated by magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements and magnetoresistance measurements. The mCP-AFM measurements show that the chirality of the quantum dots and the magnetic orientation of the tip affect the current-voltage curves. Similarly, magnetoresistance measurements demonstrate that the electrical transport through films of chiral quantum dots correlates with the chiroptical properties of the QD. The spin filtering properties of chiral quantum dots may prove useful in future applications, for example, photovoltaics, spintronics, and other spin-driven devices. PMID:27336320

  8. Ordered structures based on self-organized Au and CdSe nanoparticles

    International Nuclear Information System (INIS)

    Methods for obtaining cadmium selenide and gold nanoparticles have been developed. The sizes of the nanoparticles are determined and the morphology, structure, and chemical composition of these nanoparticles and their ensembles are studied by a complex of structural methods: electron diffraction, X-ray diffraction, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy, and small-angle X-ray scattering. Gold nanoparticles are mainly spherical and have an average size of 10 nm. They are single-phase and have an fcc crystal structure. Samples of synthesized CdSe nanoparticles contain monodisperse spherical particles 12 nm in size with a wurtzite structure. The deposition of nanoparticles on a carbon substrate is accompanied by their self-organization into a closely packed two-dimensional structure with a pronounced texture in which all nanoparticles are oriented in the [001] direction perpendicularly to the carbon substrate plane.

  9. Reverse loading tests of steel tube under biaxial stress states

    OpenAIRE

    Yanaga, Daisaku; Kuroda, Kouichi; Yaita, Satoshi; Kuwabara, Toshihiko

    2015-01-01

    Biaxial loading and reverse loading tests were performed using seamless carbon steel tubes. Biaxial stress components in the axial and circumferential directions were applied to the tubular specimens using a servo-controlled multiaxial tube expansion testing machine developed by Kuwabara and Sugawara (2013). The tubular specimens were loaded under linear tensile stress paths. Contours of plastic work were measured in the principal stress space, and the differential hardening (DH) behavior was...

  10. Photoinduced interaction of CdSe quantum dot with coumarins

    Energy Technology Data Exchange (ETDEWEB)

    El-Kemary, Maged, E-mail: elkemary@sci.kfs.edu.eg [Nanotechnology Center, Faculty of Science, Kafrelsheikh University, 33516 Kafrelsheikh (Egypt); Gaber, Mohamed; El-Sayed, Y.S. [Chemistry Department, Faculty of Science, University of Tanta, Tanta (Egypt); Gheat, Youssef [Nanotechnology Center, Faculty of Science, Kafrelsheikh University, 33516 Kafrelsheikh (Egypt); Chemistry Department, Faculty of Science, University of Tanta, Tanta (Egypt)

    2015-03-15

    Cadmium selenide (CdSe) quantum dots (QDs) were synthesized with a cubic shape having a diameter of ∼5.24 nm. The prepared CdSe QDs were characterized by using UV–visible, Fourier transform infrared (FTIR), powder X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The UV–visible absorption spectra indicate that the optical band gap of CdSe QDs is ∼622 nm and the peak shift can mainly be due to the quantum size effects. The fluorescence decay kinetics for the synthesized QDs was followed by time-resolved fluorescence spectroscopy, and the spectra were analyzed in regard to a bi-exponential model to identify two lifetime values, that is, shorter-lifetime 1.37 ns (55%) and longer-lifetime 6.58 ns (45%). The interaction of coumarin 152 (C152) and coumarin 153 (C153) with QDs surface brings about further considerable changes in the absorption and fluorescence patterns. The calculated binding constant from fluorescence quenching method matches well with that determined from the absorption spectral changes. The static quenching mechanism was confirmed by large magnitude of K{sub SV} and unaltered fluorescence lifetime. - Highlights: • CdSe QDs were synthesized with a cubic shape having a diameter of ∼5.24 nm. • The UV–visible absorption spectra indicate that the optical band gap of CdSe QDs is ∼622 nm. • Picosecond fluorescence measurements of the QDs suggest bi-exponential function. • The calculated binding constant from fluorescence quenching method matches well with that determined from the absorption spectral changes. • The static quenching mechanism was confirmed by large magnitude of K{sub SV} and unaltered fluorescence lifetime.

  11. CdSe quantum dot formation: alternative paths to relaxation of a strained CdSe layer and influence of the capping conditions.

    Science.gov (United States)

    Robin, I C; Aichele, T; Bougerol, C; André, R; Tatarenko, S; Bellet-Amalric, E; Van Daele, B; Van Tendeloo, G

    2007-07-01

    CdSe/ZnSe quantum dot formation is investigated by studying different steps of the growth. To precisely control the critical thickness of CdSe grown on a ZnSe buffer layer, the CdSe self-regulated growth rate in atomic layer epitaxy growth mode is determined by reflection high-energy electron diffraction (RHEED) measurements for a temperature range between 180 and 280 °C. Then, the two-dimensional-three-dimensional (2D-3D) transition of a strained CdSe layer on (001)-ZnSe induced by the use of amorphous selenium is studied. The formation of CdSe islands is found when 3 monolayers (ML) of CdSe are deposited. When only 2.5 ML of CdSe are deposited, another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. We also studied the evolution of the surface morphology when 2.7 ML are deposited, to study the boundary between those two phenomena. The influence of capping on quantum dot morphology is investigated. It is found that cadmium is redistributed within the layer during capping. Our results show that the cadmium distribution after capping depends on the capping temperature and on the strain of the CdSe layer. Cadmium incorporation after capping is also studied. It is found that the amount of incorporated cadmium depends on the strain of the CdSe layer before capping.

  12. CdSe quantum dot formation: alternative paths to relaxation of a strained CdSe layer and influence of the capping conditions

    Energy Technology Data Exchange (ETDEWEB)

    Robin, I C [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Aichele, T [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Bougerol, C [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Andre, R [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Tatarenko, S [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group Laboratoire de Spectrometrie Physique/CNRS UMR5588, Universite J. Fourier, Grenoble, BP87, 38402 St Martin d' Heres (France); Bellet-Amalric, E [CEA-CNRS-UJF ' Nanophysics and Semiconductors' Group, Departement de Recherche Fondamentale sur la Matiere Condensee/SP2M CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France); Daele, B Van [IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Tendeloo, G van [EMAT University of Antwerp (RUCA), Groenenborgerlaan 171, 2020 Antwerp (Belgium)

    2007-07-04

    CdSe/ZnSe quantum dot formation is investigated by studying different steps of the growth. To precisely control the critical thickness of CdSe grown on a ZnSe buffer layer, the CdSe self-regulated growth rate in atomic layer epitaxy growth mode is determined by reflection high-energy electron diffraction (RHEED) measurements for a temperature range between 180 and 280 deg. C. Then, the two-dimensional-three-dimensional (2D-3D) transition of a strained CdSe layer on (001)-ZnSe induced by the use of amorphous selenium is studied. The formation of CdSe islands is found when 3 monolayers (ML) of CdSe are deposited. When only 2.5 ML of CdSe are deposited, another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. We also studied the evolution of the surface morphology when 2.7 ML are deposited, to study the boundary between those two phenomena. The influence of capping on quantum dot morphology is investigated. It is found that cadmium is redistributed within the layer during capping. Our results show that the cadmium distribution after capping depends on the capping temperature and on the strain of the CdSe layer. Cadmium incorporation after capping is also studied. It is found that the amount of incorporated cadmium depends on the strain of the CdSe layer before capping.

  13. Influence of some crystal orientations in mechanical behaviour of zircaloy-4 tubes

    International Nuclear Information System (INIS)

    Zircaloy-4 tubing used in water cooled reactors work under biaxial loading due primarily to the circunferencial swelling of the fuel elements approximating a plane-strain behaviour. The tube is produced to have crystal orientations with high yield strengths under biaxial loading and principally in transverse plane strain. The contribution of individual crystal orientations to that specific yield strength is analysed based on crystallographic lower bound yield loci. (Author)

  14. Timely resolved measurements on CdSe nanoparticles; Zeitaufgeloeste Messungen an CdSe Nanopartikeln

    Energy Technology Data Exchange (ETDEWEB)

    Holt, B.E. von

    2006-06-06

    By means of infrared spectroscopy the influence of the organic cover on structure and dynamics of CdSe nanoparticles was studied. First a procedure was developed, which allows to get from the static infrared spectrum informations on the quality of the organic cover and the binding behaviour of the ligands. On qualitatively high-grade and well characterized samples thereafter the dynamics of the lowest-energy electron level 1S{sub e} was time-resolvedly meausred in thew visible range. As reference served CdSe TOPO, which was supplemented by samples with the ligands octanthiole, octanic acid, octylamine, naphthoquinone, benzoquinone, and pyridine. The studied nanoparticles had a diameter of 4.86 nm. By means of the excitation-scanning or pump=probe procedure first measurements in the picosecond range were performed. The excitation wavelengths were thereby spectrally confined and so chosen that selectively the transitions 1S{sub 3/2}-1S-e and 1P{sub 3/2}-1P{sub e} but not the intermediately lyingt transition 2S{sub 3/2}-1S{sub e} were excited. The excitation energies were kept so low that the excitation of several excitons in one crystal could be avoided. The scanning wavelength in the infrared corresponded to the energy difference between the electron levels 1S{sub e} and 1P{sub e}. The transients in the picosecond range are marked by a steep increasement of the signal, on which a multi-exponential decay follows. The increasement, which reproduces the popiulation of the excited state, isa inependent on the choice of the ligands. The influence of the organic cover is first visible in the different decay times of the excited electron levels. the decay of the measurement signal of CdSe TOPO can be approximatively described by three time constants: a decay constant in the early picosecond region, a time constant around hundert picoseconds, and a time constant of some nanoseconds. At increasing scanning wavelength the decay constants become longer. By directed excitation

  15. Synthesis and size dependent optical studies in CdSe quantum dots via inverse micelle technique

    International Nuclear Information System (INIS)

    Cadmium selenide quantum dots (CdSe QDs) were successfully synthesized without using trioctylphosphine (TOP). The XRD pattern showed zinc-blend phase of the CdSe QDs. The absorption and PL spectra exhibit a strong blue shift as the QDs size decreases due to the quantum confinement effect. In addition, the quantum efficiency of CdSe QDs with TOP capping is higher than CdSe QDs with oleic acid capping. TEM image shows a spherical shape, compact and dense structure of CdSe QDs. A good agreement between the Tauc's model and experimentally measured absorption spectra of CdSe QDs is achieved. The FTIR peak at ∼1712 cm-1 spectra confirms the influence of oleic acid as a capping agent.

  16. Graphene flakes under controlled biaxial deformation

    Science.gov (United States)

    Androulidakis, Charalampos; Koukaras, Emmanuel N.; Parthenios, John; Kalosakas, George; Papagelis, Konstantinos; Galiotis, Costas

    2015-12-01

    Thin membranes, such as monolayer graphene of monoatomic thickness, are bound to exhibit lateral buckling under uniaxial tensile loading that impairs its mechanical behaviour. In this work, we have developed an experimental device to subject 2D materials to controlled equibiaxial strain on supported beams that can be flexed up or down to subject the material to either compression or tension, respectively. Using strain gauges in tandem with Raman spectroscopy measurements, we monitor the G and 2D phonon properties of graphene under biaxial strain and thus extract important information about the uptake of stress under these conditions. The experimental shift over strain for the G and 2D Raman peaks were found to be in the range of 62.3 ± 5 cm-1/%, and 148.2 ± 6 cm-1/%, respectively, for monolayer but also bilayer graphenes. The corresponding Grüneisen parameters for the G and 2D peaks were found to be between 1.97 ± 0.15 and 2.86 ± 0.12, respectively. These values agree reasonably well with those obtained from small-strain bubble-type experiments. The results presented are also backed up by classical and ab initio molecular dynamics simulations and excellent agreement of Γ-E2g shifts with strains and the Grüneisen parameter was observed.

  17. Structure and optical properties of CdSe chalcogenide semiconductors

    Science.gov (United States)

    Ganaie, Mohsin; Prince, Zulfequar, M.

    2015-08-01

    CdSe bulk sample has been prepared by melt-quenching technique and were characterized with XRD, SEM, FTIR, and electrical measurements. Thin films were deposited by thermal evaporation technique on ultra clean glass substrates under a high vacuum of 10-6 Torr. An XRD measurement reveals the coexistence of glassy and crystalline phase in bulk sample. SEM studies shows single phase, porous, and granular surface morphology of powder CdSe alloy. Optical properties (optical gap, absorption coefficient, extinction coefficient, refractive index) are calculated in the range of 190-1100nm. Analysis of the optical measurement shows that the non-direct transition is predominant and the band gap come outs to be 1.751eV. Dc conductivity measurement is thermally activated process which shows the semiconducting nature of the sample having activation energy 0.31eV.

  18. Microscopic Theory of Cation Exchange in CdSe Nanocrystals

    OpenAIRE

    Ott, Florian D.; Spiegel, Leo L.; Norris, David J.; Erwin, Steven C.

    2014-01-01

    Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We used density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key...

  19. CdSe Quantum Dots for Solar Cell Devices

    Directory of Open Access Journals (Sweden)

    A. B. Kashyout

    2012-01-01

    Full Text Available CdSe quantum dots have been prepared with different sizes and exploited as inorganic dye to sensitize a wide bandgap TiO2 thin films for QDs solar cells. The synthesis is based on the pyrolysis of organometallic reagents by injection into a hot coordinating solvent. This provides temporally discrete nucleation and permits controlled growth of macroscopic quantities of nanocrystallites. XRD, HRTEM, UV-visible, and PL were used to characterize the synthesized quantum dots. The results showed CdSe quantum dots with sizes ranging from 3 nm to 6 nm which enabled the control of the optical properties and consequently the solar cell performance. Solar cell of 0.08% performance under solar irradiation with a light intensity of 100 mW/cm2 has been obtained. CdSe/TiO2 solar cells without and with using mercaptopropionic acid (MPA as a linker between CdSe and TiO2 particles despite a Voc of 428 mV, Jsc of 0.184 mAcm-2, FF of 0.57, and η of 0.05% but with linker despite a Voc of 543 mV, Jsc of 0.318 mAcm-2 , FF of 0.48, and η of 0.08%, respectively.

  20. Biaxial failure criteria and stress-strain response for concrete of containment structure

    International Nuclear Information System (INIS)

    Biaxial failure criteria and stress-strain response for plain concrete of containment structure on nuclear power plants are studied under uniaxial and biaxial stress(compression-compression, compression-tension, and tension-tension combined stress). The concrete specimens of a square plate type are used for uniaxial and biaxial loading. The experimental data indicate that the strength of concrete under biaxial compression, f2/f1=-1/-1, is 17 percent larger than under uniaxial compression and the poisson's ratio of concrete is 0.1745. On the base of the results, a biaxial failure envelope for plain concrete that the uniaxial strength is 5660 psi are provided, and the biaxial failure behaviors for three biaxial loading areas are plotted respectively. And, various analytical equations having the reliability are proposed for representations of the biaxial failure criteria and stress-strain response curves of concrete

  1. Laser Propagation in Biaxial Liquid Crystal Polymers

    OpenAIRE

    Choate, Eric P.; Zhou, Hong

    2011-01-01

    We examine the propagation of a laser beam through a liquid crystal polymer (LCP) layer using the finite-difference time-domain (FDTD) method. Anchoring conditions on supporting glass plates induce an orientational structure in the LCP between the plates. The orientation can deflect energy away from the direction of propagation of the incident beam when the optical axis or major director of a uniaxial medium is neither parallel nor orthogonal to the incident beam. The maximum e...

  2. Method for forming biaxially textured articles by powder metallurgy

    Science.gov (United States)

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2002-01-01

    A method of preparing a biaxially textured alloy article comprises the steps of preparing a mixture comprising Ni powder and at least one powder selected from the group consisting of Cr, W, V, Mo, Cu, Al, Ce, YSZ, Y, Rare Earths, (RE), MgO, CeO.sub.2, and Y.sub.2 O.sub.3 ; compacting the mixture, followed by heat treating and rapidly recrystallizing to produce a biaxial texture on the article. In some embodiments the alloy article further comprises electromagnetic or electro-optical devices and possesses superconducting properties.

  3. A shear stabilized biaxial texture in a lamellar block copolymer

    Energy Technology Data Exchange (ETDEWEB)

    Polis, D.L.; Pinheiro, B.S.; Winey, K.I.; Lakis, R.E. [Univ. of Pennsylvania, Philadelphia, PA (United States)

    1996-12-31

    Block copolymers spontaneously self-assemble into a variety of morphologies. Recent studies have produced a biaxial texture in poly(styrene-b-ethylene propylene), SEP, diblock copolymers by applying oscillatory shear. This biaxial texture consists of {open_quotes}parallel{close_quotes} lamellae (normal to lamellae aligned perpendicular to shearing surfaces) and {open_quotes}transverse{close_quotes} lamellae (normal to lamellae aligned parallel to shearing direction) according to small-angle X-ray scattering, SAXS. The present study has determined how these two populations of lamellae are arranged and how they relax upon quiescent annealing by examining the superstructure via FE-SEM.

  4. Irreversible magnetic processes under biaxial and uniaxial magnetic anisotropies

    Science.gov (United States)

    Pokharel, S.; Akioya, O.; Alqhtany, N. H.; Dickens, C.; Morgan, W.; Wuttig, M.; Lisfi, A.

    2016-05-01

    Irreversible magnetic processes have been investigated in magnetic systems with two different anisotropy symmetries (uniaxial and biaxial) through angular measurement of the switching field, the irreversible susceptibility and the magnetic viscosity. These two systems consist of two-dimensional cobalt ferrite hetero-structures epitaxially grown on (100) and (110) MgO substrate. It is found that for uniaxial anisotropy the irreversible characteristics of the magnetization are large and display a strong angular dependence, which exhibits its maximum at the easy axis and drops quickly to vanish at the hard axis. However, for biaxial anisotropy the magnetization irreversible characteristics are considerably reduced and are less sensitive to the field angle.

  5. Detection of an intermediate biaxial phase in the phase diagram of biaxial liquid crystals: entropic sampling study.

    Science.gov (United States)

    Kamala Latha, B; Jose, Regina; Murthy, K P N; Sastry, V S S

    2014-05-01

    We investigate the phase sequence of biaxial liquid crystals, based on a general quadratic model Hamiltonian over the relevant parameter space, with a Monte Carlo simulation which constructs equilibrium ensembles of microstates, overcoming possible (free) energy barriers (combining entropic and frontier sampling techniques). The resulting phase diagram qualitatively differs from the universal phase diagram predicted earlier from mean-field theory (MFT), as well as the Monte Carlo simulations with the Metropolis algorithm. The direct isotropic-to-biaxial transition predicted by the MFT is replaced in certain regions of the space by the onset of an additional intermediate biaxial phase of very low order, leading to the sequence N(B)-N(B1)-I. This is due to inherent barriers to fluctuations of the components comprising the total energy, and may explain the difficulties in the experimental realization of these phases.

  6. Detection of an intermediate biaxial phase in the phase diagram of biaxial liquid crystals: Entropic sampling study

    Science.gov (United States)

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2014-05-01

    We investigate the phase sequence of biaxial liquid crystals, based on a general quadratic model Hamiltonian over the relevant parameter space, with a Monte Carlo simulation which constructs equilibrium ensembles of microstates, overcoming possible (free) energy barriers (combining entropic and frontier sampling techniques). The resulting phase diagram qualitatively differs from the universal phase diagram predicted earlier from mean-field theory (MFT), as well as the Monte Carlo simulations with the Metropolis algorithm. The direct isotropic-to-biaxial transition predicted by the MFT is replaced in certain regions of the space by the onset of an additional intermediate biaxial phase of very low order, leading to the sequence NB-NB1-I. This is due to inherent barriers to fluctuations of the components comprising the total energy, and may explain the difficulties in the experimental realization of these phases.

  7. Reexamination of the mean-field phase diagram of biaxial nematic liquid crystals: Insights from Monte Carlo studies

    Science.gov (United States)

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2015-07-01

    Investigations of the phase diagram of biaxial liquid-crystal systems through analyses of general Hamiltonian models within the simplifications of mean-field theory (MFT), as well as by computer simulations based on microscopic models, are directed toward an appreciation of the role of the underlying molecular-level interactions to facilitate its spontaneous condensation into a nematic phase with biaxial symmetry. Continuing experimental challenges in realizing such a system unambiguously, despite encouraging predictions from MFT, for example, are requiring more versatile simulational methodologies capable of providing insights into possible hindering barriers within the system, typically gleaned through its free-energy dependences on relevant observables as the system is driven through the transitions. The recent paper from this group [Kamala Latha et al., Phys. Rev. E 89, 050501(R) (2014), 10.1103/PhysRevE.89.050501], summarizing the outcome of detailed Monte Carlo simulations carried out employing an entropic sampling technique, suggested a qualitative modification of the MFT phase diagram as the Hamiltonian is asymptotically driven toward the so-called partly repulsive regions. It was argued that the degree of (cross) coupling between the uniaxial and biaxial tensor components of neighboring molecules plays a crucial role in facilitating a ready condensation of the biaxial phase, suggesting that this could be a plausible factor in explaining the experimental difficulties. In this paper, we elaborate this point further, providing additional evidence from curious variations of free-energy profiles with respect to the relevant orientational order parameters, at different temperatures bracketing the phase transitions.

  8. Ligand induced circular dichroism and circularly polarized luminescence in CdSe quantum dots.

    Science.gov (United States)

    Tohgha, Urice; Deol, Kirandeep K; Porter, Ashlin G; Bartko, Samuel G; Choi, Jung Kyu; Leonard, Brian M; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2013-12-23

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by postsynthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Time Dependent Density Functional Theory (TDDFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The origin of the induced chirality is consistent with the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand.

  9. Self-Assembled Monolayers of CdSe Nanocrystals on Doped GaAs Substrates

    DEFF Research Database (Denmark)

    Marx, E.; Ginger, D.S.; Walzer, Karsten;

    2002-01-01

    This letter reports the self-assembly and analysis of CdSe nanocrystal monolayers on both p- and a-doped GaAs substrates. The self-assembly was performed using a 1,6-hexanedithiol self-assembled monolayer (SAM) to link CdSe nanocrystals to GaAs substrates. Attenuated total reflection Fourier tran...

  10. Multi-branched CdSe nanocrystals stabilized by weak ligand for hybrid solar cell application.

    Science.gov (United States)

    Liu, Jincheng; Tao, Hong; Cao, Yong; Ackermann, Jorg

    2014-04-01

    In this article, multi-branched CdSe nanocrystals were produced by a facile colloidal approach stabilized by oleylamine at a relative low temperature. The as-prepared multi-branched CdSe nanocrystals after simple washing process were used in the fabrication of poly(3-hexylthiophene)/CdSe bulk heterojunction photovoltaic device. The effective charge separation in the poly(3-hexylthiophene)/ CdSe nanocomposites have been confirmed by the strong photoluminescence quenching. The films of the blends of P3HT and simply-washed CdSe nanocrystals show more uniform morphology and flatter surface than the film of the bends of P3HT and pyridine-refluxed CdSe nanocrystals. The corresponding power conversion efficiency under 1 sun is about 0.66% for the P3HT/pyridine-washed CdSe hybrid device. Our work did a preliminary study in the hybrid solar cell application of branched blenze CdSe nanocrystals prepared by an easier way, and will be interesting and helpful for making the high-efficiency hybrid solar cells with branched CdSe acceptors.

  11. Exciton storage by Mn2+ in colloidal Mn2+-doped CdSe quantum dots

    NARCIS (Netherlands)

    Beaulac, R.; Archer, P.I.; van Rijssel, J.; Meijerink, A.; Gamelin, D.R.

    2008-01-01

    Colloidal Mn2+-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to τexc = 15 μs at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by ∼103 and are shown to arise from the creation of excitons by back energy transfer

  12. Effects of reaction temperature on size and optical properties of CdSe nanocrystals

    Indian Academy of Sciences (India)

    Shutang Chen; Xiaoling Zhang; Yanbing Zhao; Qiuhua Zhang

    2010-10-01

    We report experimental results on the reaction temperature dependence of luminescence properties in size-controlled CdSe nanocrystals. Such reaction temperature dependent property is also sizedependent. The diameter of the CdSe nanocrystals is tuned from 4–11.0 nm by varying the reaction temperatures. The growth process and characterization of CdSe nanocrystals are determined by photoluminescence (PL) spectroscopy, ultraviolet-visible (UV–Vis) spectroscopy, X-ray photoelectron spectrometry (XPS), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The influence of reaction conditions on the growth of CdSe nanocrystals demonstrates that low reaction temperature is favourable for the formation of high quality CdSe nanocrystals.

  13. HREM image simulation of CdSe quantum dots electrodeposited on [111] gold

    International Nuclear Information System (INIS)

    HREM images of CdSe nanocrystals on Au substrate were calculated for different relative shift of the Au and CdSe unit cells. The calculations proved that the added shift had significant influence on the images of the CdSe nanocrystals with thickness from 0.7 nm to 3.5 nm in the case of no tilt imaging condition. Experimental images exhibiting 1/3[422]Au and [10.0]CdSe patterns were simulated. A good fit between the experimental and calculated images were obtained in the tilted condition where the calculated images were very similar for different shifts. The thickness of the CdSe nanocrystals was estimated to be ca. 3 nm. (author)

  14. Biaxial mechanics and inter-lamellar shearing of stem-cell seeded electrospun angle-ply laminates for annulus fibrosus tissue engineering.

    Science.gov (United States)

    Driscoll, Tristan P; Nakasone, Ryan H; Szczesny, Spencer E; Elliott, Dawn M; Mauck, Robert L

    2013-06-01

    The annulus fibrosus (AF) of the intervertebral disk plays a critical role in vertebral load transmission that is heavily dependent on the microscale structure and composition of the tissue. With degeneration, both structure and composition are compromised, resulting in a loss of AF mechanical function. Numerous tissue engineering strategies have addressed the issue of AF degeneration, but few have focused on recapitulation of AF microstructure and function. One approach that allows for generation of engineered AF with appropriate (+/-)30° lamellar microstructure is the use of aligned electrospun scaffolds seeded with mesenchymal stem cells (MSCs) and assembled into angle-ply laminates (APL). Previous work indicates that opposing lamellar orientation is necessary for development of near native uniaxial tensile properties. However, most native AF tensile loads are applied biaxially, as the disk is subjected to multi-axial loads and is constrained by its attachments to the vertebral bodies. Thus, the objective of this study was to evaluate the biaxial mechanical response of engineered AF bilayers, and to determine the importance of opposing lamellar structure under this loading regime. Opposing bilayers, which replicate native AF structure, showed a significantly higher modulus in both testing directions compared to parallel bilayers, and reached ∼60% of native AF biaxial properties. Associated with this increase in biaxial properties, significantly less shear, and significantly higher stretch in the fiber direction, was observed. These results provide additional insight into native tissue structure-function relationships, as well as new benchmarks for engineering functional AF tissue constructs.

  15. Fabrication of YBCO Coated Conductors on Biaxial Textured Metal Substrate by All-Sputtering

    Institute of Scientific and Technical Information of China (English)

    Xiao Han; Jing-Tan He; Jie Xiong; Bo-Wan Tao

    2008-01-01

    CeO2/YSZ/CeO2 buffer layers were prepared on biaxial textured Ni-5at.%W substrate by direct-current magnetron reactive sputtering with the optimum process. YBCO thin films were deposited on CeO2/YSZ/CeO2 buffered Ni-5at.%W substrate at temperature ranging from 500°C to 700°C by diode dc sputtering. By optimizing substrate temperature, pure c-axis oriented YBCO films were obtained. The microstructures of CeO2/YSZ/CeO2 buffer layers were characterized by X-ray diffraction. A smooth, dense and crack-free surface morphology was observed with scanning electron microscopy. The critical current density Jc about 0.75 MA/cm2 at 77 K was obtained.

  16. BEGA-a biaxial excitation Generator for automobiles

    DEFF Research Database (Denmark)

    Scridon, S.; Boldea, Ion; Tutelea, L.;

    2005-01-01

    This paper presents the design and test results for a biaxial excitation generator/motor for automobiles (BEGA), which has a three-phase stator and a salient-pole excited heteropolar rotor with multiple flux barriers filled with low-cost permanent magnets (PMs). For this new generator, the low-vo...

  17. The effects of biaxial loading on the fracture characteristics of several engineering materials

    Science.gov (United States)

    Jones, D. L.; Poulose, P. K.; Liebowitz, H.

    1986-01-01

    Using the George Washington University biaxial test system, a static fracture toughness study of two polymers (PMMA and PVC) and three aluminum alloys was performed for several variations in specimen geometry. Photoelastic experiments indicate that the applied load biaxiality has a very strong influence on the size and shape of the crack-tip stress field, and fracture toughness values for both polymers were seen to decrease with increasing load biaxiality. The load biaxiality was also found to have a strong influence on the crack growth direction in PMMA and a negligible influence on the PVC. The 7075-T6 aluminum toughness values increased with biaxiality, while intermediate peak toughness values were noted at a 0.5 biaxiality ratio for the more ductile 2024-T3 and 6061-T4 alloys. Fracture toughnesses at the highest biaxiality ratios were found to be equal to the uniaxial results.

  18. Mobility activation in thermally deposited CdSe thin films

    Indian Academy of Sciences (India)

    Kangkan Sarmah; Ranjan Sarma

    2009-08-01

    Effect of illumination on mobility has been studied from the photocurrent decay characteristics of thermally evaporated CdSe thin films deposited on suitably cleaned glass substrate held at elevated substrate temperatures. The study indicates that the mobilities of the carriers of different trap levels are activated due to the energy of incident illumination, which results in the existence of two distinct trap levels. In each trap depth the energy of the trap increases linearly. It infers that there is a linear distribution of traps of different energies below the conduction band.

  19. Biaxial Behavior of Ultra-High Performance Concrete and Untreated UHPC Waffle Slab Bridge Deck Design and Testing

    Science.gov (United States)

    D'Alessandro, Kacie Caple

    Ultra-high performance concrete (UHPC) was evaluated as a potential material for future bridge deck designs. Material characterization tests took place to identify potential challenges in mixing, placing, and curing UHPC. Biaxial testing was performed to evaluate behavior of UHPC in combined tension and compression stress states. A UHPC bridge deck was designed to perform similarly to a conventional concrete bridge deck, and a single unit bridge deck section was tested to evaluate the design methods used for untreated UHPC. Material tests identified challenges with placing UHPC. A specified compressive strength was determined for structural design using untreated UHPC, which was identified as a cost-effective alternative to steam treated UHPC. UHPC was tested in biaxial tension-compression stress states. A biaxial test method was developed for UHPC to directly apply tension and compression. The influence of both curing method and fiber orientation were evaluated. The failure envelope developed for untreated UHPC with random fiber orientation was suggested as a conservative estimate for future analysis of UHPC. Digital image correlation was also evaluated as a means to estimate surface strains of UHPC, and recommendations are provided to improve consistency in future tests using DIC methods. A preliminary bridge deck design was completed for untreated UHPC and using established material models. Prestressing steel was used as primary reinforcement in the transverse direction. Preliminary testing was used to evaluate three different placement scenarios, and results showed that fiber settling was a potential placement problem resulting in reduced tensile strength. The UHPC bridge deck was redesigned to incorporate preliminary test results, and two single unit bridge deck sections were tested to evaluate the incorporated design methods for both upside down and right-side up placement techniques. Test results showed that the applied design methods would be conservative

  20. Spontaneous emission enhancement of colloidal CdSe nanoplatelets

    Science.gov (United States)

    Yang, Zhili; Pelton, Matthew; Waks, Edo

    Colloidal CdS /CdSe/CdS nanoplatelets synthesized recently are high efficient nano-emitters and gain media for nanoscale lasers and other nonlinear optical devices. They are characterized as quantum well structure due to energy gap difference between core CdSe and shell CdS, of which the luminescent wavelength could be tuned precisely by their thickness of growth. However, the influence of environment on the material's optical properties and further enhancement of the emission to implement nanoscale systems remains to be investigated. Here we demonstrate spontaneous emission rate enhancement of these CdSe nanoplatelets coupled to a photonic crystal cavity. We show clearly the photoluminescent spectrum modification of the nanoplatelets emission and an averaged Purcell enhancement factor of 3.1 is achieved when they are coupled to carefully-designed nanobeam photonic crystal cavities compared to the ones on unpatterned surface in our experiment of lifetime measurement. Also the phenomenon of cavity quality factor increasing is observed when increasing intensity of pumping, which attributes to saturable absorption of the nanoplatelets. Our success in enhancement of emission from these nanoplatelets here paves the road to realize actual nanoscale integrated systems such as ultra-low threshold micro-cavity lasers.

  1. Space charge limited conduction in CdSe thin films

    Indian Academy of Sciences (India)

    Pradip Kr Kalita; B K Sarma; H L Das

    2003-10-01

    The current ()–voltage () characteristics of thermally evaporated CdSe thin films having thickness in the range 850–3000 Å and deposited within the substrate temperature of 303–573 K show nearly linear dependence at low voltage and afterwards a non-linear behaviour at higher voltage range. A detailed study of – curves in dark and under illumination clearly reveals the mechanism as ohmic at low voltage and that of trap limited space charge limited conduction (SCLC) at higher voltage. The transition voltage () from ohmic to SCLC is found to be quite independent of ambient temperature as well as intensity of illumination. SCLC is explained on the basis of the exponential trap distribution in CdSe films. Trap depths estimated from the ln vs 103/T plots are found to be within 0.60–0.37 eV. Using the relevant SCLC theory, the carrier concentration, 0, total trap concentration, t, and the ratio of free charge to trapped charge, , have been calculated and correlated with ambient temperature and intensity of illumination.

  2. Stability studies of CdSe nanocrystals in an aqueous environment

    DEFF Research Database (Denmark)

    Xi, Lifei; Lek, Jun Yan; Liang, Yen Nan;

    2011-01-01

    In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH − ) while photo......-generated holes oxidize CdSe to Cd2 + and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH = 10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments...

  3. Synthesis of Monodisperse CdSe QDs using Controlled Growth Temperatures

    International Nuclear Information System (INIS)

    The effect of growth temperatures on size of CdSe quantum dots (QDs) has been investigated. CdSe QDs were synthesized using thermolysis of organometallics precursor route using wet chemical method. The growth temperature was varied from 260-310 degree Celsius with growth period fixed at 60 s. As the growth temperature increased, the monodispersed CdSe QDs with diameter in the range 3-7 nm were obtained. Both absorption and PL spectra of the QDs revealed a strong red-shift supporting the increment size of QDs with the rise of growth temperature. (author)

  4. Hydrothermal Routes for the Synthesis of CdSe Core Quantum Dots

    OpenAIRE

    Schneider, Raphaël; Balan, Lavinia

    2012-01-01

    The synthesis of QDs in aqueous solution is still pursued in hopes of providing a material that is easily fabricated and functionalized. During many years, the synthesis of CdSe in aqueous media has been investigated with limited success due to the low quantum yields and poor crystallinity of the nanoparticles produced. Moreover, the fluorescence of the CdSe QDs obtained by this approach cannot be controlled over a wide range. Direct synthesis of CdSe QDs in water is however a promising alter...

  5. Synthesis of Highly Emissive CdSe Quantum Dots by Aqueous Precipitation Method

    OpenAIRE

    Bing Gao; Chao Shen; Shuanglong Yuan; Yunxia Yang; Guorong Chen

    2013-01-01

    CdSe quantum dots (QDs) with high quantum yield (QY) up to 76.57% are synthesized using the aqueous precipitation method. With the control of SeSO32- concentration in Se precursor, the nucleation speed and concentration of CdSe QDs are increased. The mass of obtained Cd2+ and Se2+ in nanocrystal is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). XRD and HRTEM are used to identify the crystal phase and morphology of the products which are pure CdSe crystals in th...

  6. Quantum kinetic exciton-LO-phonon interaction in CdSe

    DEFF Research Database (Denmark)

    Woggon, Ulrike; Gindele, Frank; Langbein, Wolfgang;

    2000-01-01

    Oscillations with a period of similar to 150 fs are observed in the four-wave mixing (FWM) signal of bulk CdSe and interpreted in terms of non-Markovian exciton-LO-phonon scattering. The experiments show evidence of phonon quantum kinetics in semiconductors of strong polar coupling strength...... and high exciton binding energy. By comparison of the spectral and temporal response of the FWM signal in bulk CdSe and CdSe quantum dots, we demonstrate the influence of continuum states on the interference of electron-hole pair polarizations coupled via an LO phonon....

  7. Single-molecule detection of chaperonin dynamics through polarization rotation modulation of CdSe QD luminescence imaging

    International Nuclear Information System (INIS)

    We report our recent trials examining the single-molecule three-dimensional (3D) detection of protein conformational dynamics at room temperature. Using molecular chaperones as model proteins and cadmium selenide (CdSe) semiconductor quantum dots (QDs) as nanometer-scale probes, we monitored the temporal evolution of ATP-induced conformation changes with a total internal reflection fluorescence (TIRF) microscopy imaging technique in buffer solutions. The two-dimensional (2D) degenerate nature of the emission dipoles of the QDs, due to the uniaxial wurtzite crystal structure, made it possible to capture the 3D orientation using a polarization modulation technique in real time. The temporal resolution was half the period of analyzer rotation. Although still insufficient, the obtained signals suggest possible 3D detection of specific motions, which supports the two-step conformational changes triggered by ATP attachment. - Highlights: • We report our recent trials examining the single-molecule three-dimensional (3D) detection of protein conformational dynamics at room temperature. • Using molecular chaperones as model proteins and cadmium selenide (CdSe) semiconductor quantum dots (QDs) as nanometer-scale probes, we monitored the temporal evolution of ATP-induced conformation changes with a total internal reflection fluorescence (TIRF) microscopy imaging technique in buffer solutions. • The two-dimensional (2D) degenerate nature of the emission dipoles of the QDs, due to the uniaxial wurtzite crystal structure, made it possible to capture the 3D orientation using a polarization modulation technique in real time. • The temporal resolution was half the period of analyzer rotation. • Although still insufficient, the obtained signals suggest possible 3D detection of specific motions, which supports the two-step conformational changes triggered by ATP attachment

  8. CdSe纳米晶薄膜的制备与特性研究%Preparation and Characterization of CdSe Nanocrystalline Films

    Institute of Scientific and Technical Information of China (English)

    曾体贤; 刘其娅; 陈太红; 谌家军

    2013-01-01

    采用真空热蒸发技术,在光学玻璃基片上生长出排列整齐、高质量的CdSe纳米晶薄膜.通过X射线衍射(XRD)、X射线光电子能谱分析(XPS)、扫描电镜(SEM)、傅里叶红外光谱(IR)等进行表征.结果表明,薄膜结晶性能较好,纳米晶颗粒约为40 ~70 nm,呈半月状,排列整齐;化学元素配比为49.4∶50.6,稍微富Se;红外透过率高,禁带宽度为1.89 eV,高于块状的CdSe晶体(1.70 eV).%Good quality semiconducting nanocrystalline films of CdSe with regular arrangement and high quality were grown by thermal evaporation on glass substrate.The broad peaks are indexed as (002),(101),(102),(103) and (105) by XRD pattern,which confirmed that CdSe films exist in the hexagonal phase structure and orient with (001) crystalline direction perpendicular to their surface,and the crystallite size was estimated to be in the range 50 nm.SEM images show that the glass substrate is well covered with uniformly distributed lune-like grains and film surface is homogenous without cracks.The strong peaks for Cd and Se were found in the XPS spectrum,and the average atomic percentage ratio of Cd:Se was 49.4:50.6,which is close to the excellent composition ratio (1∶1).The as-deposited sample has high transparency at Mid-infrared region,and the band gap was found to be 1.89 eV,which slightly exceeds the reported value for bulk CdSe (1.70 eV).The preparation of high quality nanocrystalline thin film is a good foundation for the application of optoelectronic devices for CdSe.

  9. The fine structure of the vortex-beams in the biaxial and biaxially-induced birefringent media caused by the conical diffraction

    CERN Document Server

    Fadeyeva, Tatyana; Anischenko, Pavel; Volyar, Alexander

    2011-01-01

    We consider the paraxial propagation of nondiffracting singular beams inside natural biaxial and biaxially-induced birefringent media in vicinity of one of the optical axes in terms of eigenmode vortex-beams, whose angular momentum does not change upon propagation. We have predicted a series of new optical effects in the natural biaxial crystals such as the stable propagation of vector singular beams bearing the coupled optical vortices with fractional topological charges, the conversion of the zero-order Bessel beam with a uniformly distributed linear polarization into the radially-, azimuthally- and spirally-polarized beams and the conversion of the space-variant linear polarization in the combined beam with coupled vortices. We have revealed that the field structure of the vortex-beams in the biaxially-induced crystals resembles that in the natural biaxial crystals and form the vector structure inherent in the conical diffraction. However, the mode beams in this case do not change the propagation direction...

  10. Identification du comportement de composites en fatigue bi-axiale

    OpenAIRE

    Busca, Damien

    2014-01-01

    La connaissance du comportement de composites sous un état de contraintes multi-axial reste un enjeu majeur pour l’optimisation du dimensionnement des structures. La machine de fatigue bi-axiale présente au LGP permet de générer un état de contrainte bi-axial par l’utilisation d’éprouvettes cruciformes. La conception des éprouvettes reste un enjeu majeur pour les chercheurs pour répondre aux problèmes spécifiques liés aux matériaux composites. Un nouveau type d’éprouvette cruciforme en compos...

  11. Flexural rigidity of biaxially loaded reinforced concrete rectangular column sections

    Science.gov (United States)

    Resheidat, M.; Ghanma, M.; Sutton, C.; Chen, Wai-Fah

    1995-05-01

    An exact analysis is carried out utilizing the parabola-rectangle stress-strain curve for concrete and a typical idealized stress-strain curve for steel to develop the moment-curvature relationship for biaxially loaded reinforced concrete rectangular column sections. Based on that, the flexural rigidity EI of the section is determined at the yield curvature. A computer program is written by FORTRAN 77 to handle the required computations. The influence of material properties, the effect of steel ratios, and the impact of axial loads on the EI estimation were investigated. This study leads to the development of a new equation to estimate the flexural rigidity EI of reinforced concrete biaxially loaded rectangular columns in which these factors were considered. It is shown that the new equation stems from the actual behavior of the column. Therefore, it is recommended for general use in the design of slender columns.

  12. Theory of nine elastic constants of biaxial nematics

    Institute of Scientific and Technical Information of China (English)

    Liu Hong

    2008-01-01

    In this paper, a rotational invariant of interaction energy between two biaxial-shaped molecules is assumed and in the mean field approximation, nine elastic constants for simple distortion patterns in biaxial nematica are derived in terms of the thermal averagewhere D(l)mn is the Wigner rotation matrix.In the lowest order terms, the elastic constants depend on coefficients г,г',λ, order parameters Q0=Q0+Q2vj'j''j(r12) and probability function fk'k'' k (r12), where r12 is the distance between two molecules, andλis proportional to temperature. Q0 and Q2 are parameters related to multiple moments of molecules. Comparing these results with those obtained from Landau-de Gennes theory, we have obtained relationships between coefficients, order parameters used in both theories. In the special case of uniaxial nematics, both results are reduced to a degenerate case where K11=K33.

  13. Aspekte der Modellierung des Tragverhaltens von Textilbeton unter biaxialer Beanspruchung

    OpenAIRE

    Beyer, Frank R.; Zastrau, Bernd W.

    2011-01-01

    Zur Bemessung und Simulation von flächigen Textilbetonstrukturen werden Berechnungsmodelle benötigt, die das Materialverhalten unter biaxialer Beanspruchung abbilden können. Für eindimensionale Strukturen existieren einige Modelle, zu deren Weiterentwicklung eine Erweiterung zur Abbildung des biaxialen Materialverhaltens vorgeschlagen wird. In diesem Beitrag werden die notwendigen Erweiterungen und deren Umsetzbarkeit bei der Modellierung diskutiert und bewertet. For design and simulation...

  14. Design of a biaxial mechanical loading bioreactor for tissue engineering.

    Science.gov (United States)

    Bilgen, Bahar; Chu, Danielle; Stefani, Robert; Aaron, Roy K

    2013-04-25

    We designed a loading device that is capable of applying uniaxial or biaxial mechanical strain to a tissue engineered biocomposites fabricated for transplantation. While the device primarily functions as a bioreactor that mimics the native mechanical strains, it is also outfitted with a load cell for providing force feedback or mechanical testing of the constructs. The device subjects engineered cartilage constructs to biaxial mechanical loading with great precision of loading dose (amplitude and frequency) and is compact enough to fit inside a standard tissue culture incubator. It loads samples directly in a tissue culture plate, and multiple plate sizes are compatible with the system. The device has been designed using components manufactured for precision-guided laser applications. Bi-axial loading is accomplished by two orthogonal stages. The stages have a 50 mm travel range and are driven independently by stepper motor actuators, controlled by a closed-loop stepper motor driver that features micro-stepping capabilities, enabling step sizes of less than 50 nm. A polysulfone loading platen is coupled to the bi-axial moving platform. Movements of the stages are controlled by Thor-labs Advanced Positioning Technology (APT) software. The stepper motor driver is used with the software to adjust load parameters of frequency and amplitude of both shear and compression independently and simultaneously. Positional feedback is provided by linear optical encoders that have a bidirectional repeatability of 0.1 μm and a resolution of 20 nm, translating to a positional accuracy of less than 3 μm over the full 50 mm of travel. These encoders provide the necessary position feedback to the drive electronics to ensure true nanopositioning capabilities. In order to provide the force feedback to detect contact and evaluate loading responses, a precision miniature load cell is positioned between the loading platen and the moving platform. The load cell has high accuracies of 0

  15. Identification of material parameters using bi-axial machine

    OpenAIRE

    Flores, Paulo; de Montleau, P.; Mathonet, V.; Moureaux, P. (collab.); Habraken, Anne

    2004-01-01

    Experimental testing equipment is built in order to identify material parameters of complex phenomenological constitutive laws. This equipment consists in a bi-axial test machine able to perform plane strain and simple shear tests separately or simultaneously and a Miyauchi simple shear test device; an optical extensometer is used to identify the strain field. The article focus on the validation of the results of this new equipment by comparing with results obtained by standard machines and/o...

  16. Efficient Driving of Piezoelectric Transducers Using a Biaxial Driving Technique.

    Directory of Open Access Journals (Sweden)

    Samuel Pichardo

    Full Text Available Efficient driving of piezoelectric materials is desirable when operating transducers for biomedical applications such as high intensity focused ultrasound (HIFU or ultrasound imaging. More efficient operation reduces the electric power required to produce the desired bioeffect or contrast. Our preliminary work [Cole et al. Journal of Physics: Condensed Matter. 2014;26(13:135901.] suggested that driving transducers by applying orthogonal electric fields can significantly reduce the coercivity that opposes ferroelectric switching. We present here the experimental validation of this biaxial driving technique using piezoelectric ceramics typically used in HIFU. A set of narrow-band transducers was fabricated with two sets of electrodes placed in an orthogonal configuration (following the propagation and the lateral mode. The geometry of the ceramic was chosen to have a resonance frequency similar for the propagation and the lateral mode. The average (± s.d. resonance frequency of the samples was 465.1 (± 1.5 kHz. Experiments were conducted in which each pair of electrodes was driven independently and measurements of effective acoustic power were obtained using the radiation force method. The efficiency (acoustic/electric power of the biaxial driving method was compared to the results obtained when driving the ceramic using electrodes placed only in the pole direction. Our results indicate that the biaxial method increases efficiency from 50% to 125% relative to the using a single electric field.

  17. Photo-Corrosion of CdSe Film Electrode by Electrochemical Modulation Reflectance Spectrum

    Institute of Scientific and Technical Information of China (English)

    单忠强; 田建华; 刘义平; 田文娟

    2004-01-01

    The photo-corrosion of electrodeposited polycrystalline CdSe electrode was inhibited effectively by coating a thin layer of the conductive polyaniline (PAN) film. The relation between the performance and internal band structure of such film-covered PAN/CdSe electrode was studied by the electrochemical modulation reflectance spectrum (EMRS). EMRS of both CdSe and PAN/CdSe electrodes in K4Fe(CN)6/K3Fe(CN)6 solution exhibited typical France-Keidysh oscillations, by which the values of the energy gap and flat band potential were determined. The EMRS results indicated that the energy band structure of CdSe electrode was not changed after coated with PAN film, so that the photoelectrochemical characteristic of PAN/CdSe electrode was rather similar to that of CdSe electrode.

  18. Formation and spectroscopic characterization of mono-dispersed CdSe nanocrystals

    Institute of Scientific and Technical Information of China (English)

    Miao Yan-Ming; Li Chao-Rong; Cao Li; Liu Rui-Bin; He Yu-Ping; Xie Si-Shen; Zou Bing-Suo

    2005-01-01

    In this article, mono-dispersed hexagonal structure CdSe nanocrystals with polyhedron shape were prepared by an open solvent thermal reaction. They show a discrete excitonic transition structure in the absorption spectra and the minimal photoluminescence (PL) peak full-width at half-maximum of 19nm. The PL quantum yield is about 60%. Transmission electron micrographs, high-resolution transmission electron micrographs, x-ray powder diffraction patterns, UV-vis absorption spectra and PL spectra were obtained for the as-prepared CdSe nanocrystals. The size of the CdSe nanocrystals can be tuned by changing the reaction temperature or time. Due to the improved synthesis method, a different growth mechanism of the CdSe nanocrystals is discussed.

  19. Rapid synthesis of CdSe nanocrystals in aqueous solution at room temperature

    Indian Academy of Sciences (India)

    Yilin Wang; Jian Ping Lu; Zhang Fa Tong

    2010-10-01

    Water-soluble thioglycolic acid-capped CdSe nanocrystals (NCs) were prepared in aqueous solution at room temperature. We investigated the effects of pH values on the fluorescence intensity of the as-prepared CdSe NCs, and discussed the influence of the initial pH values on the fluorescence property. Their mean diameter was estimated to be 1.9 nm depending on the initial pH values in the preparation, the photoluminescence quantum yield could reach as high as 1.9%, almost comparable to the CdSe NCs prepared by an organometallic route. Finally, the products were characterized by Fourier transform infrared spectrometry (FTIR), atomic force microscope (AFM) and X-ray powder diffraction (XRD). AFM image showed that the NCs were ball-shaped with good dispersibility. XRD analysis disclosed that the CdSe NCs were of cubic zinc-blended structure.

  20. High critical current density superconducting tapes by epitaxial deposition of YBa2Cu3Ox thick films on biaxially textured metals

    International Nuclear Information System (INIS)

    A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high-temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high-Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures. copyright 1996 American Institute of Physics

  1. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Neetu, E-mail: singh.neetu1985@gmail.com; Kapoor, Avinashi [Department of Electronic Science, University of Delhi South Campus, New Delhi-110 021 (India); Kumar, Vinod [Department of Physics, University of the Free State, Bloemfontein, ZA9300 (South Africa); Mehra, R. M. [School of Engineering and Technology, Sharda University, Greater Noida-201 306, U.P. (India)

    2014-04-24

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5.

  2. Aqueous Synthesis and Characterization of TGA-capped CdSe Quantum Dots at Freezing Temperature

    OpenAIRE

    Qizhuang Sun; Chaobiao Huang; Tingmei Dong; Shuxian Liu; Shasha Fu

    2012-01-01

    CdSe quantum dots (QDs) have traditionally been synthesized in organic phase and then transferred to aqueous solution by functionalizing their surface with silica, polymers, short-chain thiol ligands, or phospholipid micelles. However, a drastic increase in the hydrodynamic size and biotoxicity of QDs may hinder their biomedical applications. In this paper, the TGA-capped CdSe QDs are directly synthesized in aqueous phase at freezing temperature, and they prove to possess high QY (up to 14%).

  3. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    International Nuclear Information System (INIS)

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5

  4. Ion-beam assisted deposition of MgO with in situ RHEED monitoring to control Bi-axial texture

    Energy Technology Data Exchange (ETDEWEB)

    Arendt, P. N. (Paul N.); Foltyn, S. R. (Stephen R.); Jia, Quanxi; DePaula, R. F. (Raymond Felix); Dowden, P. C. (Paul C.); Kung, H. (Harriett); Holesinger, T. G. (Terry G.); Stan, L. (Liliana); Emmert, L. A. (Luke A.); Peterson, E. J. (Eric J.); Groves, J. R. (James R.)

    2001-01-01

    We have studied the growth of magnesium oxide using ion-beam assisted deposition (IBAD) to achieve (100) oriented, bi-axially textured films with low mosaic spread, for film thicknesses of 10 nm on silicon substrates. We have refined the process by using reflected high-energy electron diffraction (RHEED) to monitor the growth of IBAD MgO films and found that the diffracted intensity can be used to determine (and ultimately control) final in-plane texture of the film. Here we present results on our work to develop the use of real-time RHEED monitoring to deposit well-oriented IBAD MgO films. The results have been corroborated with extensive grazing-incidence X-ray diffraction (GID). Results of these analyses have allowed us to deposit films on metallic substrates with in-plane mosaic spread less than 7{sup o}.

  5. Application of magnetomechanical hysteresis modeling of magnetic techniques for monitoring neutron embrittlement and biaxial stress

    International Nuclear Information System (INIS)

    Research was done on the biaxial stress problem accomplished in the first half of the second year. All of the work done was preparatory to magnetic measurements. Issues addressed were: construction of a model for extracting changes in the magnetic properties of a specimen from the readings of an indirect sensor; initial development of a model for how biaxial stress alters the intrinsic magnetic properties of thespecimen; use of finite element stress analysis modeling to determine a detailed shape for the cruciform biaxial stress specimen; and construction of the biaxial stress loading apparatus

  6. Structural and transport properties of CdSe nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Das, Sayantani, E-mail: sayantanidas22@yahoo.com; Banerjee, Sourish [Department of Physics, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata-700009 (India); Dutta, Alo; Ghosh, Binita; Sinha, T. P. [Department of Physics, Bose Institute, 93/1, Acharya Prafulla Chandra Road, Kolkata-700009 (India)

    2015-06-24

    The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route. The selected area electron diffraction pattern, high resolution TEM and X-ray diffraction pattern indicate the cubic structure of the sample. The band gap of the sample is obtained using Tauc relation to UV-visible spectrum and found to be 1.92 eV. 1{sup st} order and 2{sup nd} order Raman bands are followed to investigate the behaviour of the phonon modes of the materials which is considered to be important to predict the potential of the material to microwave applications. Thermal behaviour of the sample is investigated using differential scanning calorimeter. Kissinger equation is used to calculate the activation energy of the sample, which is found to be 1.67 eV.

  7. Assemblies composed of oligothiophene–ruthenium complexes bound to CdSe nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Bair, Nathan; Hancock, Jared M.; Simonson, Cameron J. [Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602 (United States); Thalman, Scott W.; Colton, John S. [Department of Physics and Astronomy,Brigham Young University, Provo, UT 84602 (United States); Asplund, Matthew C. [Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602 (United States); Harrison, Roger G., E-mail: roger_harrison@byu.edu [Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602 (United States)

    2015-02-15

    Molecular conjugates are important to link light sensitized materials to electron acceptors. We have synthesized oligothiophenes and oligothiophene–ruthenium complexes and bound them to CdSe nanoparticles. The absorption and fluorescence properties of the oligothiophenes bound to CdSe were measured. Steady-state luminescence and time correlated single photon counting were used to observe the effects on fluorescence and fluorescence lifetimes before and after binding. It was found that fluorescence of CdSe nanoparticles was quenched when they were bound to the oligothiophenes, and that the fluorescence of the oligothiophenes was also quenched. The fluorescence lifetimes of the quenched species were shortened and suggest electron transfer from oligothiophene to nanoparticle is on the order of one nanosecond. Orbital energy calculations predict that the Ru bound oligothiophenes have HOMO–LUMO energies of correct energy to allow electron and hole transfer. These experiments show that the oligothiophenes efficiently transfer optical energy between CdSe nanoparticles and could potentially be used as charge transfer junctions. - Highlights: • Ru bound thiophenes attached to CdSe nanoparticles. • Luminescence quenching of CdSe nanoparticles. • Molecular conjugates for photosensitized materials.

  8. Thermal conductivity of zinc blende and wurtzite CdSe nanostructures.

    Science.gov (United States)

    Yang, Juekuan; Tang, Hao; Zhao, Yang; Zhang, Yin; Li, Jiapeng; Ni, Zhonghua; Chen, Yunfei; Xu, Dongyan

    2015-10-14

    Many binary octet compounds including CdSe can be grown in either the wurtzite (WZ) or zinc blende (ZB) phase, which has aroused great interest among the research community in understanding the phase dependence of the thermal transport properties of these compounds. So far, it has been debatable whether the ZB phase possesses higher thermal conductivity than the WZ phase. In this work, we report on thermal conductivity measurements of CdSe nanowires/nanoribbons with both WZ and ZB phases via a suspended device method. At room temperature, the thermal conductivity of all the ZB CdSe nanostructures measured in this work is higher than the bulk thermal conductivity of the WZ CdSe reported in the literature, suggesting that the bulk thermal conductivity of the ZB CdSe is higher than that of the WZ phase. Our result is different from previous experimental results in the literature for InAs nanowires which suggest similar thermal conductivity values for the bulk ZB and WZ InAs crystals. The higher thermal conductivity of the ZB CdSe can be explained by its lower anharmonicity and a smaller number of atoms per unit cell compared to the WZ phase.

  9. In-situ material state monitoring using embedded CdSe quantum dots

    Science.gov (United States)

    Brubaker, Cole D.; Frecker, Talitha M.; Njoroge, Ian; Shane, Dylan O.; Smudde, Christine M.; Rosenthal, Sandra J.; Jennings, G. Kane; Adams, Douglas E.

    2016-04-01

    The development of new, smart materials capable of intrinsically detecting and communicating the occurrence of external loads and resultant damage present in a material will be crucial in the advancement of future structural health monitoring (SHM) and nondestructive evaluation (NDE) technologies. Traditionally, many SHM and NDE approaches have relied on the use of physical sensors to monitor a structure for damage, but are often hindered by their requirements for power consumption and large-scale data collection. In this work, we seek to evaluate the effectiveness of ultrasmall, white-light emitting Cadmium Selenide quantum dots (CdSe QDs) as an alternative to providing in-situ material state monitoring capabilities, while also aiming to reduce reliance on data collection and power consumption to effectively monitor a material and structure for damage. To achieve this goal, CdSe QDs are embedded in an optically clear epoxy composite matrix and exposed to external mechanical loadings. Initial results show a corresponding relationship between the shifts in observed emission spectra and external load for samples containing CdSe QDs. The effectiveness of CdSe QDs as a surface strain gauge on aluminum and fiberglass are also investigated in this paper. By monitoring changes in the emission spectra for materials containing CdSe QDs before, during and after the application of external loads, the effectiveness of CdSe QDs for communicating the occurrence of external loads acting on a material and detecting changes in material state is evaluated.

  10. High-conjugation-efficiency aqueous CdSe quantum dots.

    Science.gov (United States)

    Au, Giang H T; Shih, Wan Y; Shih, Wei-Heng

    2013-11-12

    Quantum dots (QDs) are photoluminescent nanoparticles that can be directly or indirectly coupled with a receptor such as an antibody to specifically image a target biomolecule such as an antigen. Recent studies have shown that QDs can be directly made at room temperature and in an aqueous environment (AQDs) with 3-mercaptopropionic acid (MPA) as the capping ligand without solvent and ligand exchange typically required by QDs made by the organic solvent routes (OQDs). In this study, we have synthesized CdSe AQDs and compared their conjugation efficiency and imaging efficacy with commercial carboxylated OQDs in HT29 colon cancer cells using a primary antibody-biotinylated secondary antibody-streptavidin (SA) sandwich. We showed that the best imaging condition for AQDs occurred when one AQD was bound with 3 ± 0.3 SA with a nominal SA/AQD ratio of 4 corresponding to an SA conjugation efficiency of 75 ± 7.5%. In comparison, for commercial CdSe-ZnS OQDs to achieve 2.7 ± 0.4 bound SAs per OQD for comparable imaging efficacy a nominal SA/OQD ratio of 80 was needed corresponding to an SA conjugation efficiency of 3.4 ± 0.5% for CdSe-ZnS OQDs. The more than 10 times better SA conjugation efficiency of the CdSe AQDs as compared to that of the CdSe-ZnS OQDs was attributed to more capping molecules on the AQD surface as a result of the direct aqueous synthesis. More capping molecules on the AQD surface also allowed the SA-AQD conjugate to be stable in cell culture medium for more than three days without losing their staining capability in a flowing cell culture medium. In contrast, SA-OQD conjugates aggregated in cell culture medium and in phosphate buffer saline solution over time. PMID:24151632

  11. Study on the Interaction between CdSe Quantum Dots and Bovine Serum Albumin with Ultraviolet Visible Absorption Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    He You HAN; De Hong HU; Jian Gong LIANG; Zong Hai SHENG

    2006-01-01

    The interaction of CdSe quantum dots (QDs) with bovine serum albumin (BSA) has been investigated with ultraviolet visible absorption spectroscopy (UVAS). It was found that the absorption intensity of CdSe QDs significantly decreased after adding BSA solution, showing that CdSe QDs were bonded to BSA. The binding molar ratio was 1:1 and the binding constant was 9.7 × 106 L mol-1.

  12. Charge separation in contact systems with CdSe quantum dot layers

    International Nuclear Information System (INIS)

    Quantum dot (QD) solar cells are a fast developing area in the field of solution processed photovoltaics. Central aspects for the application of QDs in solar cells are separation and transport of charge carriers in the QD layers and the formation of charge selective contacts. Even though efficiencies of up to 7% were reached in QD solar cells, these processes are not yet fully understood. In this thesis the mechanisms of charge separation, transport and recombination in CdSe QD layers and layer systems were studied. Charge separation was measured via surface photovoltage (SPV) at CdSe QD layers with thicknesses in the range of monolayers. To determine the influence of interparticle distance of QDs and trap states on the surface of QDs on charge separation, QDs with four different surfactant layers were studied. Layers of CdSe QDs were prepared on ITO, Si, SiO2 and CdS by dip coating under inert atmosphere. The layers were characterized by Rutherford backscattering spectrometry, UV-vis spectroscopy, step profilometry and scanning electron microscopy to determine the areal density, the absorption and thickness of CdSe QD monolayers. SPV measurements show that initial charge separation from the CdSe QDs on ITO only happened from the fi rst monolayer of QDs. Electrons, photo-excited in the fi rst monolayer of CdSe QDs, were trapped on the ITO surface. The remaining free holes were trapped in surface states and/or diffused into the neighboring QD layers. The thick surfactant layer (∼ 1.6 nm) of pristine QDs had to be reduced by washing and/or ligand exchange for separation of photo-excited charge carriers. Both, interparticle distance and trap density, influenced the processes of charge separation and recombination. SPV transients of CdSe monolayers could be described by a single QD approximation model, based on Miller-Abrahams hopping of holes between the delocalized excitonic state, traps on the surface of the QD and the filled trap on the ITO surface (recombination

  13. Charge separation in contact systems with CdSe quantum dot layers

    Energy Technology Data Exchange (ETDEWEB)

    Zillner, Elisabeth Franziska

    2013-03-06

    Quantum dot (QD) solar cells are a fast developing area in the field of solution processed photovoltaics. Central aspects for the application of QDs in solar cells are separation and transport of charge carriers in the QD layers and the formation of charge selective contacts. Even though efficiencies of up to 7% were reached in QD solar cells, these processes are not yet fully understood. In this thesis the mechanisms of charge separation, transport and recombination in CdSe QD layers and layer systems were studied. Charge separation was measured via surface photovoltage (SPV) at CdSe QD layers with thicknesses in the range of monolayers. To determine the influence of interparticle distance of QDs and trap states on the surface of QDs on charge separation, QDs with four different surfactant layers were studied. Layers of CdSe QDs were prepared on ITO, Si, SiO{sub 2} and CdS by dip coating under inert atmosphere. The layers were characterized by Rutherford backscattering spectrometry, UV-vis spectroscopy, step profilometry and scanning electron microscopy to determine the areal density, the absorption and thickness of CdSe QD monolayers. SPV measurements show that initial charge separation from the CdSe QDs on ITO only happened from the fi rst monolayer of QDs. Electrons, photo-excited in the fi rst monolayer of CdSe QDs, were trapped on the ITO surface. The remaining free holes were trapped in surface states and/or diffused into the neighboring QD layers. The thick surfactant layer ({approx} 1.6 nm) of pristine QDs had to be reduced by washing and/or ligand exchange for separation of photo-excited charge carriers. Both, interparticle distance and trap density, influenced the processes of charge separation and recombination. SPV transients of CdSe monolayers could be described by a single QD approximation model, based on Miller-Abrahams hopping of holes between the delocalized excitonic state, traps on the surface of the QD and the filled trap on the ITO surface

  14. Temperature-induced sign reversal of biaxiality observed by conoscopy in some ferroelectric Sm- C* liquid crystals

    OpenAIRE

    Fukuda, Atsuo; VIJ, JAGDISH KUMAR

    2007-01-01

    PUBLISHED Article number 011709 We have studied various ferroelectric liquid crystals to find the average molecular direction of the shortest axis in the perfectly unwound state by using tilted conoscopic measurements. We find that there exist two types of temperature dependencies of the biaxiality. Some materials exhibit increasing biaxiality while others show decreasing biaxiality with increasing temperature. The former shows a temperature-induced sign reversal of biaxiality. Three di...

  15. Lattice Spin Simulations of Topological Defects in Biaxial Nematic Films with Homeotropic Surface Alignment

    Science.gov (United States)

    Preeti, Gouripeddi Sai; Zannoni, Claudio; Chiccoli, Cesare; Pasini, Paolo; Sastry, Vanka S. S.

    2013-05-01

    We present a detailed Monte Carlo study of the effects of biaxiality on the textures of nematic films with specific homeotropic boundary conditions. We have used the Straley generalized Hamiltonian for a wide range of biaxial parameters and the differences obtained in the polarized microscopy images are analyzed for the various cases.

  16. Phase Matching of SHG in Arbitrary Directions of Biaxial Crystals

    Institute of Scientific and Technical Information of China (English)

    YANG Shengli; CHEN Mouzhi

    2002-01-01

    In this paper, propagation and polarization characteristics of optical waves in arbitrary directions in a biaxial crystal are analyzed, and universal relationships of refractive index dependence on their propagation directions and the principal refractive indices for two perpendicular polarization waves propagating in arbitrarily directions are derived from indicatrix equation. By using these relationships, methods of collinear phase matching (PM) of SHG are developed, and general expressions of the collinear PM angle dependent of the principal indices are given for SHG in arbitrarily directions. The expressions may be used to make optimization design of PM by computer for the SHG and to select optimum PM direction and to raise the SHG conversion efficiencies.

  17. Material Identification Using a Bi-Axial Test Machine

    OpenAIRE

    Flores, Paulo; Moureaux, Pierre; Habraken, Anne

    2005-01-01

    This paper shows the identification of material parameters for a DC06 IF steel sheet of 0.8 mm by mechanical tests. The experimental equipment used consists of a tensile test machine, a bi-axial test machine able to perform plane-strain and simple shear tests separately or simultaneously and an optical strain gauge. Tensile, plane-strain and simple shear tests were performed at 0°, 45° and 90° from the sheet rolling direction in order to identify Hill 1948 and Hosford 1979 yield criteria. ...

  18. Hole doped Dirac states in silicene by biaxial tensile strain

    KAUST Repository

    Kaloni, Thaneshwor P.

    2013-03-11

    The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doped Dirac states because of weakened Si–Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate a strain dependence similar to that of graphene.

  19. Molecular ordering in a biaxial smectic-A phase studied by scanning transmission X-ray microscopy (STXM).

    Science.gov (United States)

    Kaznacheev, Konstantin; Hegmann, Torsten

    2007-04-14

    Results of STXM investigations of a binary mixture (-TNF = 2 : 1; SmA(b) 140 M 180 Iso) known to form a SmA(b) phase [T. Hegmann, J. Kain, S. Diele, G. Pelzl and C. Tschierske, Angew. Chem. Int. Ed., 2001, 40, 887] are presented. Near edge X-ray absorption fine spectra (NEXAFS) of the -TNF board-like aggregates, in particular the intensity of the low energy peaks associated with aromatic ring pi* orbitals (284.5-286.5 eV), show that the molecular plane of these aggregates is very sensitive to the relative orientation of electric field vector E of linearly polarized light, which is used to determine the molecular orientation in the LC phase. The observed strong in-plane dichroic signal suggests the predominant orientation of the -TNF aggregates to be along the smectic layer normal as well as long-range ordering of the in-plane molecular orientation (biaxiality). Orientational maps derived from series of measurements at different sample rotation angles around the specimen normal clearly show a Schlieren-type texture, and permit a detailed examination of exclusive +/-(1/2) disclination theoretically predicted for the SmA(b) phase.

  20. Implementation of a Biaxial Resonant Fatigue Test Method on a Large Wind Turbine Blade

    Energy Technology Data Exchange (ETDEWEB)

    Snowberg, D.; Dana, S.; Hughes, S.; Berling, P.

    2014-09-01

    A biaxial resonant test method was utilized to simultaneously fatigue test a wind turbine blade in the flap and edge (lead-lag) direction. Biaxial resonant blade fatigue testing is an accelerated life test method utilizing oscillating masses on the blade; each mass is independently oscillated at the respective flap and edge blade resonant frequency. The flap and edge resonant frequency were not controlled, nor were they constant for this demonstrated test method. This biaxial resonant test method presented surmountable challenges in test setup simulation, control and data processing. Biaxial resonant testing has the potential to complete test projects faster than single-axis testing. The load modulation during a biaxial resonant test may necessitate periodic load application above targets or higher applied test cycles.

  1. Dynamic biaxial tissue properties of the human cadaver aorta.

    Science.gov (United States)

    Shah, Chirag S; Hardy, Warren N; Mason, Matthew J; Yang, King H; Van Ee, Chris A; Morgan, Richard; Digges, Kennerly

    2006-11-01

    This study focuses on the biaxial mechanical properties of planar aorta tissue at strain rates likely to be experienced during automotive crashes. It also examines the structural response of the whole aorta to longitudinal tension. Twenty-six tissue-level tests were conducted using twelve thoracic aortas harvested from human cadavers. Cruciate samples were excised from the ascending, peri-isthmic, and descending regions. The samples were subjected to equibiaxial stretch at two nominal speed levels using a new biaxial tissue-testing device. Inertia-compensated loads were measured to facilitate calculation of true stress. High-speed videography and regional correlation analysis were used to track ink dots marked on the center of each sample to obtain strain. In a series of component-level tests, the response of the intact thoracic aorta to longitudinal stretch was obtained using seven aorta specimens. The aorta fails within the peri-isthmic region. The aorta fails in the transverse direction, and the intima fails before the media or adventitia. The aorta tissue exhibits nonlinear behavior. The aorta as complete structure can transect completely from 92 N axial load and 0.221 axial strain. Complete transection can be accompanied by intimal tears. These results have application to finite element modeling and the better understanding of traumatic rupture of the aorta. PMID:17311166

  2. Biaxial tensile tests of the porcine ascending aorta.

    Science.gov (United States)

    Deplano, Valérie; Boufi, Mourad; Boiron, Olivier; Guivier-Curien, Carine; Alimi, Yves; Bertrand, Eric

    2016-07-01

    One of the aims of this work is to develop an original custom built biaxial set-up to assess mechanical behavior of soft tissues. Stretch controlled biaxial tensile tests are performed and stereoscopic digital image correlation (SDIC) is implemented to measure the 3D components of the generated displacements. Using this experimental device, the main goal is to investigate the mechanical behavior of porcine ascending aorta in the more general context of human ascending aorta pathologies. The results highlight that (i) SDIC arrangement allows accurate assessment of displacements and so stress strain curves, (ii) porcine ascending aorta has a nearly linear and anisotropic mechanical behavior until 30% of strain, (iii) porcine ascending aorta is stiffer in the circumferential direction than in the longitudinal one, (iv) the material coefficient representing the interaction between the two loading directions is thickness dependent, (v) taking into account the variability of the samples the stress values are independent of the stretch rate in the range of values from 10(-3) to 10(-1)s(-1) and finally, (vi) unlike other segments of the aorta, 4-month-old pigs ascending aorta is definitely not a relevant model to investigate the mechanical behavior of the human ascending aorta. PMID:27211783

  3. Resonant biaxial 7-mm MEMS mirror for omnidirectional scanning

    Science.gov (United States)

    Hofmann, U.; Aikio, M.; Janes, J.; Senger, F.; Stenchly, V.; Weiss, M.; Quenzer, H.-J.; Wagner, B.; Benecke, W.

    2013-03-01

    Low-cost automotive laser scanners for environment perception are needed to enable the integration of advanced driver assistant systems (ADAS) into all automotive vehicle segments, a key to reducing the number of traffic accidents on roads. An omnidirectional 360 degree laser scanning concept has been developed based on combination of an omnidirectional lens and a biaxial large aperture MEMS mirror. This omnidirectional scanning concept is the core of a small sized low-cost time-of-flight based range sensor development. This paper describes concept, design, fabrication and first measurement results of a resonant biaxial 7mm gimbal-less MEMS mirror that is electrostatically actuated by stacked vertical comb drives. Identical frequencies of the two resonant axes are necessary to enable the required circle scanning capability. A tripod suspension was chosen since it allows minimizing the frequency splitting of the two resonant axes. Low mirror curvature is achieved by a thickness of the mirror of more than 500 μm. Hermetic wafer level vacuum packaging of such large mirrors based on multiple wafer bonding has been developed to enable to achieve a large mechanical tilt angle of +/- 6.5 degrees in each axis. The 7mm-MEMS mirror demonstrates large angle circular scanning at 1.5kHz.

  4. CdSe Nanoparticles with Clean Surfaces: Gas Phase Synthesis and Optical Properties

    Directory of Open Access Journals (Sweden)

    Zhang Hongwei

    2015-01-01

    Full Text Available CdSe nanoparticles (NPs were generated in gas phase with a magnetron plasma gas aggregation cluster beam source. Coagulation-free CdSe nanocrystals with very clean particle surface and interface, as well as a fairly uniform spatial distribution were obtained. The deposited NPs have a good dispersity with a mean diameter of about 4.8nm. A strong photoluminescence band corresponding to the near- band-edge transition of the CdSe NPs was observed. The CdSe NP films show a significant photoconductance induced by laser irradiation. With an applied bias voltage of 10V, the photo- induced current can be as high as 0.4mA under 0.01mW/mm2 405nm laser illumination. Our approach offers an alternative method for CdSe NP synthesis, which has the advantages such as high purity, good process and product control, as well as mass production, as compared to the existing methods.

  5. Nanostructured TiO2 Films Attached CdSe QDs Toward Enhanced Photoelectrochemical Performance.

    Science.gov (United States)

    Du, Yingying; Yang, Ping; Liu, Yunshi; Zhao, Jie; He, Haiyan; Miao, Yanping

    2016-06-01

    TiO2 films consisted of small nanoparticles were fabricated via a spinning coating method on fluorine doped in tin oxide (FTO) slide glass. After calcination, the films were subsequently sensitized by CdSe quantum dots (QDs) using mercaptopropionic acid (MPA) as a bifunctional surface modifier. Upon UV light irradiation, CdSe QDs inject electrons into TiO2 nanoparticles, thus resulting in the generation of photocurrent in QD-sensitized solar cell. The results indicate that TiO2 films sensitized by CdSe QDs have achieved 1.5-fold enhancement in photocurrent compared with pure TiO2 films, indicating that CdSe QDs can improve the photocurrent by promoting the separation of photoinduced charge carriers. In addition, the photocurrent enhances as the thickness of TiO2 films increased. Such improved photoelectrochemical performance is ascribed to the basis of improved interfacial charge transport of the TiO2-CdSe composite films. Combining QDs on TiO2 thin films is a promising and effective way to enhance the photoelectrochemical performance, which is important in QD-sensitized solar cell application. PMID:27427714

  6. Size-dependent structure of CdSe nanoclusters formed after ion implantation in MgO

    NARCIS (Netherlands)

    van Huis, MA; van Veen, A; Schut, H; Eijt, SWH; Kooi, BJ; De Hosson, JTM

    2005-01-01

    The band gap as well as the optical and structural properties of semiconductor CdSe nanoclusters change as a function of the nanocluster size. Embedded CdSe nanoclusters in MgO were created by means of sequential Cd and Se ion implantation followed by thermal annealing. Changes during annealing were

  7. Flower-like CdSe ultrathin nanosheet assemblies for enhanced visible-light-driven photocatalytic H2 production.

    Science.gov (United States)

    Peng, Yong; Shang, Lu; Bian, Tong; Zhao, Yufei; Zhou, Chao; Yu, Huijun; Wu, Li-Zhu; Tung, Chen-Ho; Zhang, Tierui

    2015-03-18

    Flower-like CdSe architectures composed of ultrathin nanosheets were prepared via a facile solvothermal method. A relationship was established between the solvothermal temperature and the product structure, and thus the photocatalytic activity. When compared with well-studied CdSe quantum dots, the ultrathin nanosheet assemblies exhibited a better photocatalytic H2 evolution activity under visible light irradiation.

  8. Digital Doping in Magic-Sized CdSe Clusters.

    Science.gov (United States)

    Muckel, Franziska; Yang, Jiwoong; Lorenz, Severin; Baek, Woonhyuk; Chang, Hogeun; Hyeon, Taeghwan; Bacher, Gerd; Fainblat, Rachel

    2016-07-26

    Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms of the host crystal with individual dopants in a one-by-one fashion can lead to unique modifications of the material properties. Here, we demonstrate the dependence of the magneto-optical response of (CdSe)13 clusters on the discrete number of Mn(2+) ion dopants. Using time-of-flight mass spectrometry, we are able to distinguish undoped, monodoped, and bidoped cluster species, allowing for an extraction of the relative amount of each species for a specific average doping concentration. A giant magneto-optical response is observed up to room temperature with clear evidence that exclusively monodoped clusters are magneto-optically active, whereas the Mn(2+) ions in bidoped clusters couple antiferromagnetically and are magneto-optically passive. Mn(2+)-doped clusters therefore represent a system where magneto-optical functionality is caused by solitary dopants, which might be beneficial for future solotronic applications. PMID:27420556

  9. Morphological Manipulation of Solvothermal Prepared CdSe Nanostructures by Controlling the Growth Rate of Nanocrystals as a Kinetic Parameter

    Science.gov (United States)

    Zarghami, V.; Mohammadi, M. R.; Fray, D. J.

    2012-11-01

    The morphological manipulation, structural characterization, and optical properties of different cadmium selenide (CdSe) nanostructures are reported. Two different CdSe nanostructures, i.e., nanorods and nanoparticles, were grown by controlling the concentration of precursors (i.e., cadmium nitrate and selenium dioxide) in ethanolamine solvent. By manipulating the kinetic parameter of the process (i.e., growth rate) under constant growth driving force (i.e., degree of supersaturation), the morphology of CdSe nanostructures can be tailored from nanorods to nanoparticles. The optical properties of CdSe nanostructures were investigated using ultraviolet-visible (UV-vis) spectroscopy. The absorption edge of the samples showed a blue-shift. CdSe nanostructures prepared under optimized conditions showed good microstructural and optical properties for solar cell applications.

  10. Transverse-electric/transverse-magnetic polarization converter using 1D finite biaxial photonic crystal.

    Science.gov (United States)

    Ouchani, Noama; Bria, Driss; Djafari-Rouhani, Bahram; Nougaoui, Abdelkarim

    2007-09-01

    We show that by using a one-dimensional anisotropic photonic structure, it is possible to realize optical wave polarization conversion by reflection and transmission processes. Thus a single incident S(P) polarized plane wave can produce a single reflected P(S) polarized wave and a single transmitted P(S) polarized wave. This polarization conversion property can be fulfilled with a simple finite superlattice (SL) constituted of anisotropic dielectric materials. We discuss the appropriate choices of the material and geometrical properties to realize such structures. The transmission and reflection coefficients are calculated in the framework of the Green's function method. The amplitude and the polarization characteristics of reflected and transmitted waves are determined as functions of frequency, wave vector k(parallel) (parallel to the interface), and the orientations of the principal axes of the layers constituting the SL. Specific applications of these results are given for a SL consisting of alternating biaxial anisotropic layers NaNO(2)/SbSI sandwiched between two identical semi-infinite isotropic media. PMID:17767240

  11. Study on Growth Kinetics of CdSe Nanocrystals with a New Model

    Directory of Open Access Journals (Sweden)

    Dixon JohnDavid

    2010-01-01

    Full Text Available Abstract A model which involves both bulk diffusion process and surface reaction process has been developed for describing the growth behaviour of nanoparticles. When the model is employed, hypothesising that either of the processes alone dominates the overall growth process is unnecessary. Conversely, the relative magnitude of contributions from both processes could be obtained from the model. Using this model in our system, the growth process of CdSe QDs demonstrated two different growth stages. During the first stage, the growth of CdSe QDs was dominated by bulk diffusion, whereas, neither the bulk diffusion process nor the surface reaction process could be neglected during the later stage. At last, we successfully modelled the Ostwald ripening of CdSe QDs with LSW theories.

  12. Synthesis and characterization of monodisperse CdSe quantum dots in different organic solvents

    Institute of Scientific and Technical Information of China (English)

    He Rong; You Xiaogang; Tian Hongye; Gao Feng; Cui Daxiang; Gu Hongchen

    2006-01-01

    Nearly monodisperse CdSe quantum dots (QDs)have been prepared by a soft solution approach using air-stable reagents in different organic solvents.This scheme is a supplement to the conventional thermal decomposition of organometailic compounds at higher temperatures.CdSe nanocrystals of different sizes could be obtained by simply changing the solvent.This method is reproducible and simple and thus can be readily scaled up for industrial production.The reaction process was monitored by the temporal evolution of the UV-Vis absorption and room temperature photoluminensce spectra.The structures of the CdSe quantum dots were determined by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM).The phase-transfer of oleic acid-stabilized CdSe nanocrystals into PBS buffer solutions was also studied for their potentials in biological applications.

  13. The direct observation of charge separation dynamics in CdSe quantum dots/cobaloxime hybrids

    Energy Technology Data Exchange (ETDEWEB)

    Huang, J.; Tang, Y.; Mulfort, Karen L.; Zhang, Xiaoyi

    2016-02-14

    In this work, we investigated photoinduced charge separation dynamics in a CdSe quantum dot/cobaloxime molecular catalyst hybrid using the combination of transient optical (OTA) and X-ray absorption (XTA) spectroscopy. We show that ultrafast charge separation occurs through electron transfer (ET) from CdSe QDs to cobaloxime. In addition to the enhanced 1S exciton bleach recovery in CdSe QDs due to the presence of cobaloxime, the direct evidence for ET process, i.e. the formation of the transient charge separated state, is captured by XTA. These results not only demonstrate the capability of XTA to capture the transient species during the photoinduced reactions in hybrid nanostructures but also enhance our understanding of charge separation dynamics in semiconductor nanocrystal/molecular catalyst hybrid

  14. Cd And Se Atomic Environments During the Growth of CdSe Nanoparticles in Glass

    Energy Technology Data Exchange (ETDEWEB)

    Hayes, T.M.; Persans, P.D.; Filin, A.; Peng, C.; Huang, W.

    2006-10-27

    Thermal treatment of Cd and Se doped borosilicate glass yields CdSe nanoparticles that are interesting for applied and fundamental studies of quantum and size effects in semiconductors. Using x-ray absorption spectroscopy at both the Cd and Se K-edges, we have studied the local atomic structure for each of these reactants at several stages of particle growth. When the doped glass is quenched from 1050 C, the Cd neighbor is mostly oxygen and the Se neighbor is mostly Zn. With heat treatment at 600-750 C, the concentration of nearest neighbor Cd-Se bonds increases and becomes dominant while the optical spectrum evolves toward that of a composite containing CdSe.

  15. Synchronously pumped CdSe optical parametric oscillator in the 9-10 microm region.

    Science.gov (United States)

    Watson, M A; O'Connor, M V; Shepherd, D P; Hanna, D C

    2003-10-15

    Continuous mode-locked operation of a singly resonant, synchronously pumped optical parametric oscillator (SPOPO) based on CdSe has produced idler output tuned over the range of 9.1-9.7 microm, the longest wavelength generated so far to our knowledge from a SPOPO. Average idler powers as high as approximately 70 mW are generated in the crystal. Tandem pumping with a diffraction-grating-tuned parametric oscillator in periodically poled lithium niobate provides a convenient and agile means of tuning the noncritically phase-matched CdSe device. The absence of any detrimental thermal effects in the CdSe crystal suggests that significant further power scaling should be possible, with idler tuning ranges extendable to cover 8-12 microm.

  16. Photoluminescence of X-ray irradiated CdSe nanocrystals embedded in dielectric matrices

    Energy Technology Data Exchange (ETDEWEB)

    Prymak, M.V.; Azhniuk, Yu.M.; Zvenigorodsky, V.V.; Krasilinets, V.M.; Gomonnai, A.V. [Institute of Electron Physics, Ukrainian National Academy of Sciences, Universytetska Str. 21, Uzhhorod 88017 (Ukraine); Rayevska, O.E.; Stroyuk, O.L. [L.V. Pysarzhevsky Institute of Physical Chemistry, Ukrainian National Academy of Sciences, Prospect Nauky 31, Kyiv 03028 (Ukraine); Zahn, D.R.T. [Semiconductor Physics, Chemnitz University of Technology, 09107 Chemnitz (Germany)

    2013-06-15

    The effect of X-ray irradiation (up to 3200 Gy) on the photoluminescence (PL) of CdSe nanocrystals embedded in polyacrylamide and borosilicate glass matrices is studied. In both cases no PL quenching is observed: for the polyacrylamide-embedded CdSe nanocrystals the PL intensity remains stable, while for the borosilicate glass-embedded nanocrystals it increases somewhat. The obtained PL behavior correlates well with the optical absorption data. This testifies to the radiation stability of the optical characteristics of CdSe nanocrystals in polyacrylamide and irradiation-induced charge transfer between the nanocrystals and the borosilicate glass. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Molten-droplet synthesis of composite CdSe hollow nanoparticles

    KAUST Repository

    Gullapalli, Sravani

    2012-11-16

    Many colloidal synthesis routes are not scalable to high production rates, especially for nanoparticles of complex shape or composition, due to precursor expense and hazards, low yields, and the large number of processing steps. The present work describes a strategy to synthesize hollow nanoparticles (HNPs) out of metal chalcogenides, based on the slow heating of a low-melting-point metal salt, an elemental chalcogen, and an alkylammonium surfactant in octadecene solvent. The synthesis and characterization of CdSe HNPs with an outer diameter of 15.6 ± 3.5 nm and a shell thickness of 5.4 ± 0.9 nm are specifically detailed here. The HNP synthesis is proposed to proceed with the formation of alkylammonium-stabilized nano-sized droplets of molten cadmium salt, which then come into contact with dissolved selenium species to form a CdSe shell at the droplet surface. In a reaction-diffusion mechanism similar to the nanoscale Kirkendall effect it is speculated that the cadmium migrates outwardly through this shell to react with more selenium, causing the CdSe shell to thicken. The proposed CdSe HNP structure comprises a polycrystalline CdSe shell coated with a thin layer of amorphous selenium. Photovoltaic device characterization indicates that HNPs have improved electron transport characteristics compared to standard CdSe quantum dots, possibly due to this selenium layer. The HNPs are colloidally stable in organic solvents even though carboxylate, phosphine, and amine ligands are absent; stability is attributed to octadecene-selenide species bound to the particle surface. This scalable synthesis method presents opportunities to generate hollow nanoparticles with increased structural and compositional variety. © 2012 IOP Publishing Ltd.

  18. Optical absorption of CdSe quantum dots on electrodes with different morphology

    Directory of Open Access Journals (Sweden)

    Witoon Yindeesuk

    2013-10-01

    Full Text Available We have studied the optical absorption of CdSe quantum dots (QDs adsorbed on inverse opal TiO2 (IO-TiO2 and nanoparticulate TiO2 (NP-TiO2 electrodes using photoacoustic (PA measurements. The CdSe QDs were grown directly on IO-TiO2 and NP-TiO2 electrodes by a successive ionic layer adsorption and reaction (SILAR method with different numbers of cycles. The average diameter of the QDs was estimated by applying an effective mass approximation to the PA spectra. The increasing size of the QDs with increasing number of cycles was confirmed by a redshift in the optical absorption spectrum. The average diameter of the CdSe QDs on the IO-TiO2 electrodes was similar to that on the NP-TiO2 ones, indicating that growth is independent of morphology. However, there were more CdSe QDs on the NP-TiO2 electrodes than on the IO-TiO2 ones, indicating that there were different amounts of active sites on each type of electrode. In addition, the Urbach parameter of the exponential optical absorption tail was also estimated from the PA spectrum. The Urbach parameter of CdSe QDs on IO-TiO2 electrodes was higher than that on NP-TiO2 ones, indicating that CdSe QDs on IO-TiO2 electrodes are more disordered states than those on NP-TiO2 electrodes. The Urbach parameter decreases in both cases with the increase of SILAR cycles, and it tended to move toward a constant value.

  19. Design and Use of a Novel Bioreactor for Regeneration of Biaxially Stretched Tissue-Engineered Vessels.

    Science.gov (United States)

    Huang, Angela Hai; Lee, Yong-Ung; Calle, Elizabeth A; Boyle, Michael; Starcher, Barry C; Humphrey, Jay D; Niklason, Laura E

    2015-08-01

    Conventional bioreactors are used to enhance extracellular matrix (ECM) production and mechanical strength of tissue-engineered vessels (TEVs) by applying circumferential strain, which is uniaxial stretching. However, the resulting TEVs still suffer from inadequate mechanical properties, where rupture strengths and compliance values are still very different from native arteries. The biomechanical milieu of native arteries consists of both circumferential and axial loading. Therefore, to better simulate the physiological stresses acting on native arteries, we built a novel bioreactor system to enable biaxial stretching of engineered arteries during culture. This new bioreactor system allows for independent control of circumferential and axial stretching parameters, such as displacement and beat rate. The assembly and setup processes for this biaxial bioreactor system are reliable with a success rate greater than 75% for completion of long-term sterile culture. This bioreactor also supports side-by-side assessments of TEVs that are cultured under three types of mechanical conditions (static, uniaxial, and biaxial), all within the same biochemical environment. Using this bioreactor, we examined the impact of biaxial stretching on arterial wall remodeling of TEVs. Biaxial TEVs developed the greatest wall thickness compared with static and uniaxial TEVs. Unlike uniaxial loading, biaxial loading led to undulated collagen fibers that are commonly found in native arteries. More importantly, the biaxial TEVs developed the most mature elastin in the ECM, both qualitatively and quantitatively. The presence of mature extracellular elastin along with the undulated collagen fibers may contribute to the observed vascular compliance in the biaxial TEVs. The current work shows that biaxial stretching is a novel and promising means to improve TEV generation. Furthermore, this novel system allows us to optimize biomechanical conditioning by unraveling the interrelationships among the

  20. Surface-plasmon enhanced bright emission from CdSe quantum-dot nanocrystals

    OpenAIRE

    Okamoto, Koichi; Vyawahare, Saurabh; Scherer, Axel

    2006-01-01

    We obtained very bright light emission from CdSe quantum dots (QDs) by using the surface-plasmon (SP) coupling technique. 23-fold enhanced photoluminescence (PL) intensities and two-fold increased PL decay rates are observed when the QDs are located on evaporated gold films. This enhancement is not effective for CdSe cores with ZnS shells (ZnS/CdSe). The reason for this difference can be explained by using the SP dispersion diagram and by considering the SP coupling mechanism. We discuss the ...

  1. Aqueous Synthesis and Characterization of TGA-capped CdSe Quantum Dots at Freezing Temperature

    Directory of Open Access Journals (Sweden)

    Qizhuang Sun

    2012-07-01

    Full Text Available CdSe quantum dots (QDs have traditionally been synthesized in organic phase and then transferred to aqueous solution by functionalizing their surface with silica, polymers, short-chain thiol ligands, or phospholipid micelles. However, a drastic increase in the hydrodynamic size and biotoxicity of QDs may hinder their biomedical applications. In this paper, the TGA-capped CdSe QDs are directly synthesized in aqueous phase at freezing temperature, and they prove to possess high QY (up to 14%.

  2. Structural and optical characterization of Eu{sup 3+}/CdSe nanocrystal containing silica glass

    Energy Technology Data Exchange (ETDEWEB)

    Jose, Gijo [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686560 (India); Amrutha, K.A. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686560 (India); Toney, T.F. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686560 (India); Thomas, V. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686560 (India); Joseph, C. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686560 (India); Ittyachen, M.A. [Department of Instrumentation, Cochin University of Science and Technology, 7 Cochin-22 (India); Unnikrishnan, N.V. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686560 (India)]. E-mail: nvu50@yahoo.co.in

    2006-04-10

    The structural and optical properties of Eu{sup 3+}/CdSe nanocrystal in silica galss are presented. The presence of CdSe nanocrystals was confirmed using elctron diffraction studies. The nanocrystal size was determined from TEM micrographs. The phonon sideband spectrum (PSB) associated with the excitation transition {sup 7}F{sub 0}-{sup 5}D{sub 2} is used to determine the electron-phonon coupling constant and non-radiative de-excitation rate of the rare earth ions. The Si-O-Si vibrational energy obtained from the PSB spectrum is found to correlate with the FT-IR spectrum.

  3. Numerical and experimental study of cruciform specimens subjected to biaxial tensile test

    Science.gov (United States)

    Andrusca, L.; Goanta, V.; Barsanescu, P. D.; Steigmann, R.

    2016-08-01

    Multiaxial stress states are very common in engineering applications. To obtain a plane stress state in a material are used different experimental procedures. Biaxial tensile tests of cruciform specimens represent one of the most versatile techniques with accurate results for a wide range of materials. Specimen geometry and size must be adapted to biaxial experiments that use devices attached to universal testing machine. Biaxial tensile tests are performed using cruciform specimens optimized by a numerical study through finite element analysis and a custom built attachable device developed. The results obtained show that the method proposed in this paper can be used with good results to characterize the behaviour of ductile materials.

  4. Mastering the biaxial stress state in nanometric thin films on flexible substrates

    Energy Technology Data Exchange (ETDEWEB)

    Faurie, D., E-mail: faurie@univ-paris13.fr [LSPM-CNRS, UPR3407, Université Paris 13, Villetaneuse (France); Renault, P.-O.; Le Bourhis, E. [Institut Pprime UPR3346, CNRS – Université de Poitiers, Futuroscope (France); Geandier, G. [Institut Jean Lamour, CNRS UMR7198, Université de Lorraine, Nancy Cedex (France); Goudeau, P. [Institut Pprime UPR3346, CNRS – Université de Poitiers, Futuroscope (France); Thiaudière, D. [SOLEIL Synchrotron, Saint-Aubin, Gif-Sur-Yvette (France)

    2014-07-01

    Biaxial stress state of thin films deposited on flexible substrate can be mastered thanks to a new biaxial device. This tensile machine allows applying in-plane loads F{sub x} and F{sub y} in the two principal directions x and y of a cruciform-shaped polymer substrate. The transmission of the deformation at film/substrate interface allows controlling the stress and strain field in the thin films. We show in this paper a few illustrations dealing with strain measurements in polycrystalline thin films deposited on flexible substrate. The potentialities of the biaxial device located at Soleil synchrotron are also discussed.

  5. Spatial filtering efficiency of monostatic biaxial lidar: analysis and applications.

    Science.gov (United States)

    Agishev, Ravil R; Comeron, Adolfo

    2002-12-20

    Results of lidar modeling based on spatial-angular filtering efficiency criteria are presented. Their analysis shows that the low spatial-angular filtering efficiency of traditional visible and near-infrared systems is an important cause of low signal/background-radiation ratio (SBR) at the photodetector input The low SBR may be responsible for considerable measurement errors and ensuing the low accuracy of the retrieval of atmospheric optical parameters. As shown, the most effective protection against sky background radiation for groundbased biaxial lidars is the modifying of their angular field according to a spatial-angular filtering efficiency criterion. Some effective approaches to achieve a high filtering efficiency for the receiving system optimization are discussed. PMID:12510915

  6. Electromagnetic biaxial vector scanner using radial magnetic field.

    Science.gov (United States)

    Han, Aleum; Cho, Ah Ran; Ju, Suna; Ahn, Si-Hong; Bu, Jong-Uk; Ji, Chang-Hyeon

    2016-07-11

    We present an electromagnetic biaxial vector-graphic scanning micromirror. In contrast to conventional electromagnetic actuators using linear magnetic field, proposed device utilizes a radial magnetic field and uniquely designed current paths to enable the 2 degree-of-freedom scanning motion. As the radial field is generated by concentrically assembled magnets placed under the scanner die, large driving torque can be generated without the aid of hermetic packaging and relatively small device volume can be achieved. Mechanical half scan angle of 6.43° and 4.20° have been achieved at DC current of 250mA and 350mA for horizontal and vertical scans, respectively. Forced actuation along both scan axes has been realized by feedback control. PMID:27410851

  7. Characteristics of Plane Wave Propagation in Biaxially Anisotropic Gyrotropic Media

    Institute of Scientific and Technical Information of China (English)

    PAN Wei-Tao; LIU Song-Hua; QIU Zhi-Liang

    2012-01-01

    Propagation characteristics of electromagnetic waves at the interface between an isotropic regular medium and a biaxially anisotropic gyrotropic medium are investigated.The results indicate that the reflection and refract ionproperties of electromagnetic waves are closely dependent on the dispersion relation of the gyrotropic media,and that anomalous total reflection and negative refraction may occur.The existence conditions of total transmission are also considered.It is found that total transmission arises when the TE-polarized incident waves are normal to the interface and the physical parameters of the two media are chosen properly,which are quite different from the existence conditions of total transmission at the anisotropic left-handed material interface.Numerical resul tsare given to validate our theoretical analysis.

  8. Surface polaritons in symmetry planes of biaxial crystals

    Energy Technology Data Exchange (ETDEWEB)

    Furs, A N; Galynsky, V M; Barkovsky, L M [Department of Theoretical Physics, Belarussian State University, Fr. Skarina Ave. 4, Minsk 220050 (Belarus)

    2005-09-16

    The problem of the surface polariton existence in symmetry planes of non-magnetic biaxial crystals is studied theoretically. The plane interface of such a crystal and a semi-infinite isotropic medium is considered. With the use of the integral formalism formulated in our earlier work, the dispersion equation is derived for the polaritons under consideration. The existence conditions for the dispersion equation solutions are obtained in the form of algebraic inequalities for principal values of inverse dielectric permittivity tensors. If these conditions are satisfied, then excitation of surface waves is possible along the allowed propagation directions, which constitute sectors in the interface plane. Exact expressions are obtained that determine location of these sectors with respect to the symmetry axes of the crystal.

  9. Dependence of electronic properties of germanium on the in-plane biaxial tensile strains

    International Nuclear Information System (INIS)

    The hybrid HSE06 functional with the spin–orbit coupling effects is used to calculate the habituation of the electronic properties of Ge on the (0 0 1), (1 1 1), (1 0 1) in-plane biaxial tensile strains (IPBTSs). Our motivation is to explore the nature of electronic properties of tensile-strained Ge on different substrate orientations. The calculated results demonstrate that one of the most effective and practical approaches for transforming Ge into a direct transition semiconductor is to introduce (0 0 1) IPBTS to Ge. At 2.3% (0 0 1) IPBTS, Ge becomes a direct bandgap semiconductor with 0.53 eV band gap, in good agreement with the previous theoretical and experimental results. We find that the (1 1 1) and (1 0 1) IPBTSs are not efficient since the shear strain and inner displacement of atoms introduced by them quickly decrease the indirect gap of Ge. By investigating the dependence of valence band spin–orbit splitting on strain, we prove that the dependency relationship and the coupled ways between the valence-band states of tensile-strained Ge are closely related to the symmetry of strain tensor, i.e., the symmetry of the substrate orientation. The first- and second-order coefficients describing the dependence of indirect gap, direct gap, the valence band spin–orbit coupling splitting, and heavy-hole–light-hole splitting of Ge on IPBTSs have been obtained by the least squares polynomial fitting. These coefficients are significant to quantitatively modulate the electronic properties of Ge by tensile strain and design tensile-strained Ge devices by semiconductor epitaxial technique

  10. Evaluation of micro fatigue crack growth under equi-biaxial stress by membranous pressure fatigue test

    International Nuclear Information System (INIS)

    For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)

  11. DYNAMIC STRAIN MAPPING AND REAL-TIME DAMAGE STATE ESTIMATION UNDER BIAXIAL RANDOM FATIGUE LOADING

    Data.gov (United States)

    National Aeronautics and Space Administration — DYNAMIC STRAIN MAPPING AND REAL-TIME DAMAGE STATE ESTIMATION UNDER BIAXIAL RANDOM FATIGUE LOADING SUBHASISH MOHANTY*, ADITI CHATTOPADHYAY, JOHN N. RAJADAS, AND...

  12. Maier-Saupe model for a mixture of uniaxial and biaxial molecules

    Science.gov (United States)

    Nascimento, E. S.; Henriques, E. F.; Vieira, A. P.; Salinas, S. R.

    2015-12-01

    We introduce shape variations in a liquid-crystalline system by considering an elementary Maier-Saupe lattice model for a mixture of uniaxial and biaxial molecules. Shape variables are treated in the annealed (thermalized) limit. We analyze the thermodynamic properties of this system in terms of temperature T , concentration c of intrinsically biaxial molecules, and a parameter Δ associated with the degree of biaxiality of the molecules. At the mean-field level, we use standard techniques of statistical mechanics to draw global phase diagrams, which are shown to display a rich structure, including uniaxial and biaxial nematic phases, a reentrant ordered region, and many distinct multicritical points. Also, we use the formalism to write an expansion of the free energy in order to make contact with the Landau-de Gennes theory of nematic phase transitions.

  13. Fatigue of Clip connectors for offshore drilling risers under biaxial tension

    Directory of Open Access Journals (Sweden)

    Gaur Vidit

    2014-06-01

    Full Text Available Drilling riser connectors designed by IFPEN undergo cyclic in-phase biaxial tension in their critical area. This type of loading was reproduced on steel tubular specimens loaded in cyclic tension and internal pressure. The fatigue lives were substantially reduced when the load biaxiality was increased from 0 to 0.4 and then further to 1, which was not captured by existing fatigue criteria. A deeper investigation is thus in progress. Emphasis is laid on the separate evaluation of mean stress and biaxiality effects, often treated in the same way in existing criteria. The influence of load biaxiality on the resistance of the steel to fatigue-corrosion in seawater will also be investigated.

  14. Suspended germanium cross-shaped microstructures for enhancing biaxial tensile strain

    Science.gov (United States)

    Ishida, Satomi; Kako, Satoshi; Oda, Katsuya; Ido, Tatemi; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2016-04-01

    We fabricate a suspended germanium cross-shaped microstructure to biaxially enhance residual tensile strain using a germanium epilayer directly grown on a silicon-on-insulator substrate. Such a suspended germanium system with enhanced biaxial tensile strain will be a promising platform for incorporating optical cavities toward the realization of germanium lasers. We demonstrate systematic control over biaxial tensile strain and photoluminescence peaks by changing structural geometry. The photoluminescence peaks corresponding to the direct recombination between the conduction Γ valley and two strain-induced separated valence bands have been clearly assigned. A maximum biaxial strain of 0.8% has been achieved, which is almost half of that required to transform germanium into a direct band-gap semiconductor.

  15. Phase- and morphology-controlled synthesis of CdSe microstructures through an effective mixed-solvothermal route

    International Nuclear Information System (INIS)

    Cubic-phase CdSe (C–CdSe) hollow microspheres and hexagonal-phase CdSe (H–CdSe) urchin-like microstructures have been controllably synthesized through an effective mixed solvothermal method in the absence of any surfactants. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–Vis absorption spectroscopy and photoluminescence spectroscopy. The volume ratio of ethylenediamine and ethanol of two solvents is a key factor that determines the phase and shape of CdSe crystals. When the volume ratio of ethylenediamine and ethanol is changed from 1:3, through 1:1 to 4:1, CdSe crystals can be changed from hollow spheres (cubic phase), through acanthosphere (mixed phase) to urchin-like architectures (hexagonal phase). Based on the investigation of the influence of solvent ratio on the phase and morphology of CdSe, an “in situ phase transformation and crystal growth” mechanism is proposed. Optical properties indicate that the as-obtained H–CdSe urchin-like microstructures have much stronger optical absorption and emission than C–CdSe hollow microspheres. - Highlights: • Cubic-phase CdSe hollow microspheres and hexagonal-phase CdSe urchin-like microstructures were controllably prepared. • The influence of solvent ratio on the phase and morphology of CdSe was investigated. • The optical properties of the obtained CdSe crystals were investigated. • An “in situ phase transformation and crystal growth” mechanism was proposed

  16. Air annealing induced transformation of cubic CdSe microspheres into hexagonal nanorods and micro-pyramids

    Energy Technology Data Exchange (ETDEWEB)

    Kale, Rohidas B., E-mail: rb_kale@yahoo.co.in [Department of Physics, Institute of Science, Mumbai 400032, M.S. (India); Lu, Shih-Yuan, E-mail: sylu@mx.nthu.edu.tw [Department of Chemical Engineering, National Tsing-Hua University, Hsin-Chu 30013, Taiwan (China)

    2015-08-15

    Highlights: • Nanocrystalline CdSe thin films were deposited using inexpensive CBD method. • Air annealing induced structural and interesting morphological transformation. • The as-deposited CdSe thin films showed a blue shift in its optical spectra. • The films showed a red shift in their optical spectra after annealing. - Abstract: CdSe thin films have been deposited onto glass substrates using a chemical bath deposition method at relatively low temperatures (40 °C). The precursors used for the deposition of the thin films are cadmium nitrate hexahydrate, freshly prepared sodium selenosulfate solution and aqueous ammonia solution as a complex as well as pH adjusting reagent. In order to study the influence of air annealing on their physicochemical properties, the as-deposited CdSe thin films were further annealed at 200 °C and 400 °C for 3 h in air atmosphere. Significant changes in the morphology and photonic properties were clearly observed after the thermal annealing of the CdSe thin films. The as-deposited CdSe films grow with the cubic phase that transforms into mixed cubic and hexagonal wurtzite phase with improved crystalline quality of the films after the air annealing. Morphological observation reveals that the as-deposited thin films grow with multilayer that consists of network or mesh like structure, uniformly deposited on the glass substrate over which microspheres are uniformly distributed. After air annealing, CdSe nanorods emerged from the microspheres along with conversion of few microspheres into micro-pyramids. The UV–visible study illustrates that the as-deposited thin film shows blue shifts in its optical spectrum and the spectrum was red-shifted after annealing the CdSe thin films. The band gap of the CdSe thin films were found to be decreased after the thermal treatment.

  17. Comparative efficiency analysis of different nonlinear modelling strategies to simulate the biaxial response of RC columns

    OpenAIRE

    Hugo Rodrigues; Humberto Varum; Antonio Arede; Anibal Costa

    2012-01-01

    The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified into two categories according to the nonlinearity distribution assumed in the elements: lumped-plasticity and distributed inelasticity. For this study, results of tests on 24 columns subjected to cyclic uniaxial and biaxial lateral displacements were numerically reproduced. The ...

  18. Two-Particle Cluster Theory for Biaxial Nematic Phase Based on a Recently Proposed Interaction Potential

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhi-Dong; ZHANG Yan-Jun; SUN Zong-Li

    2006-01-01

    @@ Two-particle cluster theory is applied to study the biaxial nematic phase formed by biaxial molecules interacting with a simplified model proposed by Sonnet et al. [Phys. Rev. E 67 (2003) 061701]. For the temperature dependences of the internal energy per particle and of the order parameters, the two-particle theory yields an improved result compared with mean field theory. Concerning the phase diagram, the two-particle theory gives the numerical result in qualitative agreement with the mean field theory.

  19. Fatigue Test Design: Scenarios for Biaxial Fatigue Testing of a 60-Meter Wind Turbine Blade

    Energy Technology Data Exchange (ETDEWEB)

    Post, Nathan [National Renewable Energy Lab. (NREL), Golden, CO (United States)

    2016-07-01

    Current practice in commercial certification of wind turbine blades is to perform separate flap and lead-lag fatigue tests. The National Renewable Energy Laboratory has been researching and evaluating biaxial fatigue testing techniques and demonstrating various options, typically on smaller-scale test articles at the National Wind Technology Center. This report evaluates some of these biaxial fatigue options in the context of application to a multimegawatt blade certification test program at the Wind Technology Testing Center in Charlestown, Massachusetts.

  20. Biaxial loading effects on fracture toughness of reactor pressure vessel steel

    International Nuclear Information System (INIS)

    The preliminary phases of a program to develop and evaluate fracture methodologies for assessing crack-tip constraint effects on fracture toughness of reactor pressure vessel (RPV) steels have been completed by the Heavy-Section Steel Technology (HSST) Program. Objectives were to investigate effect of biaxial loading on fracture toughness, quantify this effect through existing stress-based, dual-parameter, fracture-toughness correlations, or propose and verify alternate correlations. A cruciform beam specimen with 2-D, shallow, through-thickness flaw and a special loading fixture was designed and fabricated. Tests were performed using biaxial loading ratios of 0:1 (uniaxial), 0.6:1, and 1:1 (equi-biaxial). Critical fracture-toughness values were calculated for each test. Biaxial loading of 0.6:1 resulted in a reduction in the lower bound fracture toughness of ∼12% as compared to that from the uniaxial tests. The biaxial loading of 1:1 yielded two subsets of toughness values; one agreed well with the uniaxial data, while one was reduced by ∼43% when compared to the uniaxial data. Results were evaluated using J-Q theory and Dodds-Anderson (D-A) micromechanical scaling model. The D-A model predicted no biaxial effect, while the J-Q method gave inconclusive results. When applied to the 1:1 biaxial data, these constraint methodologies failed to predict the observed reduction in fracture toughness obtained in one experiment. A strain-based constraint methodology that considers the relationship between applied biaxial load, the plastic zone width in the crack plane, and fracture toughness was formulated and applied successfully to the data. Evaluation of this dual-parameter strain-based model led to the conclusion that it has the capability of representing fracture behavior of RPV steels in the transition region, including the effects of out-of-plane loading on fracture toughness. This report is designated as HSST Report No. 150

  1. Biaxial Testing of 2219-T87 Aluminum Alloy Using Cruciform Specimens

    Science.gov (United States)

    Dawicke, D. S.; Pollock, W. D.

    1997-01-01

    A cruciform biaxial test specimen was designed and seven biaxial tensile tests were conducted on 2219-T87 aluminum alloy. An elastic-plastic finite element analysis was used to simulate each tests and predict the yield stresses. The elastic-plastic finite analysis accurately simulated the measured load-strain behavior for each test. The yield stresses predicted by the finite element analyses indicated that the yield behavior of the 2219-T87 aluminum alloy agrees with the von Mises yield criterion.

  2. Biaxial-Type Concentrated Solar Tracking System with a Fresnel Lens for Solar-Thermal Applications

    OpenAIRE

    Tsung Chieh Cheng; Chao Kai Yang; Lin, I.

    2016-01-01

    In this paper, an electromechanical, biaxial-type concentrated solar tracking system was designed for solar-thermal applications. In our tracking system, the sunlight was concentrated by the microstructure of Fresnel lens to the heating head of the Stirling engine and two solar cells were installed to provide the power for tracking system operation. In order to obtain the maximum sun power, the tracking system traces the sun with the altitude-azimuth biaxial tracing method and accurately main...

  3. Femtosecond Cooling of Hot Electrons in CdSe Quantum-Well Platelets

    NARCIS (Netherlands)

    Sippel, Philipp; Albrecht, Wiebke; van der Bok, Johanna C.; Moes, Relinde; Hannappel, Thomas; Eichberger, Rainer; Vanmaekelbergh, Daniel

    2015-01-01

    Semiconductor quantum wells are ubiquitous in high-performance optoelectronic devices such as solar cells and lasers. Understanding and controlling of the (hot) carrier dynamics is essential to optimize their performance. Here, we study hot electron cooling in colloidal CdSe quantum-well nanoplatele

  4. Fabrication of CdSe quantum dots/permutite luminescent materials

    Indian Academy of Sciences (India)

    Meihua Yu; Yilin Wang

    2015-09-01

    Permutite incorporating CdSe in mesopores has been prepared with a simple route. Firstly, mercaptosuccinic acid-capped CdSe quantum dots (QDs) were prepared in aqueous solution by using SeO2 as selenium source and NaBH4 as reductant. Secondly, the commercial permutite was treated with acetic acid to induce a partial dealumnization, which can introduce a large number of intracrystal mesopores, and the CdSe QDs were successfully incorporated in the mesopores with the wet impregnation method. Photoluminescence spectra, X-ray diffraction and scanning electron microscopy were used for the characterization of samples. The spectra analyses results showed that the illuminant colour of QDs/permutite powder was similar to the corresponding QDs colloid. X-ray diffraction measurements indicated that the (1 0 1) diffraction peak at 2 = 27° for QDs/permutite powder was the same as the raw permutite, and the energy-dispersive X-ray spectra demonstrated that Cd and Se elements existed in the CdSe QDs/permutite powder.

  5. Photostability of CdSe quantum dots functionalized with aromatic dithiocarbamate ligands.

    Science.gov (United States)

    Tan, Yizheng; Jin, Song; Hamers, Robert J

    2013-12-26

    Organic ligands are widely used to enhance the ability of CdSe quantum dots (QDs) to resist photodegradation processes such as photo-oxidation. Because long alkyl chains may adversely affect the performance of QD devices that require fast and efficient charge transfer, shorter aromatic ligands are of increasing interest. In this work, we characterize the formation of phenyl dithiocarbamate (DTC) adducts on CdSe surfaces and the relative effectiveness of different para-substituted phenyl dithiocarbamates to enhance the aqueous photostability of CdSe QDs on TiO2. Optical absorption and photoluminescence measurements show that phenyl DTC ligands can be highly effective at reducing QD photocorrosion in water, and that ligands bearing electron-donating substituents are the most effective. A comparison of the QD photostability resulting from use of ligands bearing DTC versus thiol surface-binding groups shows that the DTC group provides greater QD photostability. Density functional calculations with natural bond order analysis show that the effectiveness of substituted phenyl DTC results from the ability of these ligands to remove positive charge away from the CdSe and to delocalize positive charge on the ligand. PMID:24256318

  6. Highly conjugated water soluble CdSe quantum dots to multiwalled carbon nanotubes

    Institute of Scientific and Technical Information of China (English)

    Gui Zheng Zou

    2009-01-01

    Highly conjugated multiwalled carbon nanotube-quantum dot heterojunctions were synthesized by ethylene carbodiimide coupling procedure. The functional multiwalled carbon nanotube with carboxylic groups on sidewall could react with the amino group of L-cysteine capped CdSe quantum dots and then resulted in nanotube-quantum dot heterojunctions. Scanning electron microscopy was used to characterize the heterojunctions.

  7. Coherent phonons in CdSe quantum dots triggered by ultrafast electron transfer

    Directory of Open Access Journals (Sweden)

    Wachtveitl J.

    2013-03-01

    Full Text Available The origin of coherent oscillations in CdSe quantum dots and in the CdSe/methylviologen electron transfer system is studied. In CdSe/methylviologen coherent phonons are triggered by the electron transfer from the quantum dot to methylviologen.

  8. Synthesis of Highly Emissive CdSe Quantum Dots by Aqueous Precipitation Method

    Directory of Open Access Journals (Sweden)

    Bing Gao

    2013-01-01

    Full Text Available CdSe quantum dots (QDs with high quantum yield (QY up to 76.57% are synthesized using the aqueous precipitation method. With the control of SeSO32- concentration in Se precursor, the nucleation speed and concentration of CdSe QDs are increased. The mass of obtained Cd2+ and Se2+ in nanocrystal is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES. XRD and HRTEM are used to identify the crystal phase and morphology of the products which are pure CdSe crystals in the cubic zinc blende phase and uniformly dispersed in the solution with the size between 2 nm and 2.3 nm. Results demonstrate that the emission wavelength of CdSe QDs is 500 nm~560 nm along with the increased temperature 50°C~90°C and prolonged time 5 min~25 min.

  9. A Biphasic Ligand Exchange Reaction on Cdse Nanoparticles: Introducing Undergraduates to Functionalizing Nanoparticles for Solar Cells

    Science.gov (United States)

    Zemke, Jennifer M.; Franz, Justin

    2016-01-01

    Semiconductor nanoparticles, including cadmium selenide (CdSe) particles, are attractive as light harvesting materials for solar cells. In the undergraduate laboratory, the size-tunable optical and electronic properties can be easily investigated; however, these nanoparticles (NPs) offer another platform for application-based tunability--the NP…

  10. Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

    DEFF Research Database (Denmark)

    Walzer, K.; Marx, E.; Greenham, N.C.;

    2003-01-01

    We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers...

  11. Oriented conductive oxide electrodes on SiO2/Si and glass

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Quanxi (Los Alamos, NM); Arendt, Paul N. (Los Alamos, NM)

    2001-01-01

    A thin film structure is provided including a silicon substrate with a layer of silicon dioxide on a surface thereof, and a layer of cubic oxide material deposited upon the layer of silicon dioxide by ion-beam-assisted-deposition, said layer of cubic oxide material characterized as biaxially oriented. Preferably, the cubic oxide material is yttria-stabilized zirconia. Additional thin layers of biaxially oriented ruthenium oxide or lanthanum strontium cobalt oxide are deposited upon the layer of yttria-stabilized zirconia. An intermediate layer of cerium oxide is employed between the yttria-stabilized zirconia layer and the lanthanum strontium cobalt oxide layer. Also, a layer of barium strontium titanium oxide can be upon the layer of biaxially oriented ruthenium oxide or lanthanum strontium cobalt oxide. Also, a method of forming such thin film structures, including a low temperature deposition of a layer of a biaxially oriented cubic oxide material upon the silicon dioxide surface of a silicon dioxide/silicon substrate is provided.

  12. Synthesis of high quality CdSe quantum dots through a mild solution-phase synthetic route

    International Nuclear Information System (INIS)

    High quality CdSe quantum dots are synthesized through a solution-phase synthesis technique with Cd(CH3COO)2.2H2O and Na2SeSO3 as precursors. In this synthesis approach, the participation of a novel terpyridine derivative provides much better control over growth dynamics of CdSe quantum dots, resulting in the suppression of the Ostwald ripening process of the particle size distribution during growth. The CdSe quantum dots meet the all requirements of high quality quantum dots.

  13. Studies on photoinduced effects in pulse-electrodeposited Ag/Hg-1212/CdSe hetero-nanostructures

    Indian Academy of Sciences (India)

    D D Shivagan; P M Shirage; S H Pawar

    2002-05-01

    Metal/superconductor/semiconductor (Ag/Hg-1212/CdSe) hetero-nanostructures have been fabricated using pulse-electrodeposition technique and are characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and Ag/Hg-1212/CdSe heterojunctions is measured in dark and under laser irradiation at room temperature. The nature of the junction formed and built-in-junction potentials were determined. The increase in carrier concentration across the junction due to photo-irradiation has been observed.

  14. Electronic structures and magnetism for carbon doped CdSe: Modified Becke-Johnson density functional calculations

    Science.gov (United States)

    Fan, S. W.; Song, T.; Huang, X. N.; Yang, L.; Ding, L. J.; Pan, L. Q.

    2016-09-01

    Utilizing the full potential linearized augment plane wave method, the electronic structures and magnetism for carbon doped CdSe are investigated. Calculations show carbon substituting selenium could induce CdSe to be a diluted magnetic semiconductor. Single carbon dopant could induce 2.00 μB magnetic moment. Electronic structures show the long-range ferromagnetic coupling mainly originates from the p-d exchange-like p-p coupling interaction. Positive chemical pair interactions indicate carbon dopants would form homogeneous distribution in CdSe host. The formation energy implies the non-equilibrium fabricated technology is necessary during the samples fabricated.

  15. An experimental study on the biaxial strength of the plain concrete for containment structures

    International Nuclear Information System (INIS)

    In this paper, an experimental study into the biaxial strength of plain concrete for containment structures is represented and technical difficulties encountered in the development of a suitable test setup are discussed. Prior to testing for a 1/8 model of cylindrical specimen(φ150x300) and four 1/4 models of plate specimens(200x200xT(=30, 50, 60, 70)mm) under uniaxial compression, the strength ratios between both specimens with different geometry shapes were found by nonlinear finite element analyses using ABAQUS. From the results three suitable type of considered plate specimens were selected for failure testing under biaxial stress. As initial approach to develop biaxial strength criteria of plain concrete, the various test data were obtained under uniaxial compression, uniaxial tension and biaxial compression. The test data indicate that the strength of concrete under biaxial compression, f1=f2, is 14.7 percent larger than under uniaxial compression and the Poisson's ratio of concrete is 0.155. Teflon employed to eliminate friction between test specimen and loading platens showed and excellent effect under biaxial compression, f1=f2

  16. Phase diagram of the uniaxial and biaxial soft-core Gay-Berne model

    Science.gov (United States)

    Berardi, Roberto; Lintuvuori, Juho S.; Wilson, Mark R.; Zannoni, Claudio

    2011-10-01

    Classical molecular dynamics simulations have been used to explore the phase diagrams for a family of attractive-repulsive soft-core Gay-Berne models [R. Berardi, C. Zannoni, J. S. Lintuvuori, and M. R. Wilson, J. Chem. Phys. 131, 174107 (2009)] and determine the effect of particle softness, i.e., of a moderately repulsive short-range interaction, on the order parameters and phase behaviour of model systems of uniaxial and biaxial ellipsoidal particles. We have found that isotropic, uniaxial, and biaxial nematic and smectic phases are obtained for the model. Extensive calculations of the nematic region of the phase diagram show that endowing mesogenic particles with such soft repulsive interactions affect the stability range of the nematic phases, and in the case of phase biaxiality it also shifts it to lower temperatures. For colloidal particles, stabilised by surface functionalisation, (e.g., with polymer chains), we suggest that it should be possible to tune liquid crystal behaviour to increase the range of stability of uniaxial and biaxial phases (by varying solvent quality). We calculate second virial coefficients and show that they are a useful means of characterising the change in effective softness for such systems. For thermotropic liquid crystals, the introduction of softness in the interactions between mesogens with overall biaxial shape (e.g., through appropriate conformational flexibility) could provide a pathway for the actual chemical synthesis of stable room-temperature biaxial nematics.

  17. An anisotropic hyperelastic constitutive model of brain white matter in biaxial tension and structural-mechanical relationships.

    Science.gov (United States)

    Labus, Kevin M; Puttlitz, Christian M

    2016-09-01

    Computational models of the brain require accurate and robust constitutive models to characterize the mechanical behavior of brain tissue. The anisotropy of white matter has been previously demonstrated; however, there is a lack of data describing the effects of multi-axial loading, even though brain tissue experiences multi-axial stress states. Therefore, a biaxial tensile experiment was designed to more fully characterize the anisotropic behavior of white matter in a quasi-static loading state, and the mechanical data were modeled with an anisotropic hyperelastic continuum model. A probabilistic analysis was used to quantify the uncertainty in model predictions because the mechanical data of brain tissue can show a high degree of variability, and computational studies can benefit from reporting the probability distribution of model responses. The axonal structure in white matter can be heterogeneous and regionally dependent, which can affect computational model predictions. Therefore, corona radiata and corpus callosum regions were tested, and histology and transmission electron microscopy were performed on tested specimens to relate the distribution of axon orientations and the axon volume fraction to the mechanical behavior. These measured properties were implemented into a structural constitutive model. Results demonstrated a significant, but relatively low anisotropic behavior, yet there were no conclusive mechanical differences between the two regions tested. The inclusion of both biaxial and uniaxial tests in model fits improved the accuracy of model predictions. The mechanical anisotropy of individual specimens positively correlated with the measured axon volume fraction, and, accordingly, the structural model exhibited slightly decreased uncertainty in model predictions compared to the model without structural properties. PMID:27214689

  18. An anisotropic hyperelastic constitutive model of brain white matter in biaxial tension and structural-mechanical relationships.

    Science.gov (United States)

    Labus, Kevin M; Puttlitz, Christian M

    2016-09-01

    Computational models of the brain require accurate and robust constitutive models to characterize the mechanical behavior of brain tissue. The anisotropy of white matter has been previously demonstrated; however, there is a lack of data describing the effects of multi-axial loading, even though brain tissue experiences multi-axial stress states. Therefore, a biaxial tensile experiment was designed to more fully characterize the anisotropic behavior of white matter in a quasi-static loading state, and the mechanical data were modeled with an anisotropic hyperelastic continuum model. A probabilistic analysis was used to quantify the uncertainty in model predictions because the mechanical data of brain tissue can show a high degree of variability, and computational studies can benefit from reporting the probability distribution of model responses. The axonal structure in white matter can be heterogeneous and regionally dependent, which can affect computational model predictions. Therefore, corona radiata and corpus callosum regions were tested, and histology and transmission electron microscopy were performed on tested specimens to relate the distribution of axon orientations and the axon volume fraction to the mechanical behavior. These measured properties were implemented into a structural constitutive model. Results demonstrated a significant, but relatively low anisotropic behavior, yet there were no conclusive mechanical differences between the two regions tested. The inclusion of both biaxial and uniaxial tests in model fits improved the accuracy of model predictions. The mechanical anisotropy of individual specimens positively correlated with the measured axon volume fraction, and, accordingly, the structural model exhibited slightly decreased uncertainty in model predictions compared to the model without structural properties.

  19. Study of optical and structural properties of CdSe quantum dot embedded in PVA polymer matrix

    Science.gov (United States)

    Tyagi, Chetna; Sharma, Ambika

    2015-08-01

    To enhance the properties and applicability of devices it is essential to incorporate semiconductor nanoparticles into polymer matrix. This introduces a new branch of science which includes device fabrications such as gas sensors, nonlinear optics, catalysis etc. Herein, we have synthesized CdSe/PVA nanocomposite (NC) material using wet chemical synthesis technique. The XRD studies revealed the formation of crystalline structure of CdSe nanoparticles (NP's) and PVA NC's with an average size of 100 nm and 5 nm respectively. Energy band gap is determined using UV-VIS Spectroscopy. A red shift in the absorption edge of CdSe/PVA NC is observed with respect to CdSe Np's, The photoluminescence spectra also show red shift for CdSe/PVA NC as compared to CdSe NP's Thus the use of CdSe/PVA for solar cell application would be more preferable than CdSe NP's.

  20. Photoelectrochemical (PEC) studies on CdSe thin films electrodeposited from non-aqueous bath on different substrates

    Indian Academy of Sciences (India)

    Y G Gudage; N G Deshpande; A A Sagade; R P Sharma; S M Pawar; C H Bhosale

    2007-08-01

    Thin films of CdSe were deposited by potentiostatic mode on different substrates such as stainless steel, titanium and fluorine tin–oxide (FTO) coated glass using non-aqueous bath. The preparative parameters were optimized to get good quality CdSe thin films. These films were characterized by X-ray diffraction (XRD), optical absorption and photoelectrochemical (PEC) techniques. XRD study revealed that the films were polycrystalline in nature with hexagonal phase. Optical absorption study showed that CdSe films were of direct band gap type semiconductor with a band gap energy of 1.8 eV. PEC study revealed that CdSe film deposited on FTO coated glass exhibited maximum values of fill factor (FF) and efficiency () as compared to the films deposited on stainless steel and titanium substrate.

  1. The Promotion of the Efficiency of Organic Photovoltaic Devices by Addition of Anisotropic CdSe Nanocrystals

    Directory of Open Access Journals (Sweden)

    Shu-Ru Chung

    2014-01-01

    Full Text Available CdSe nanocrystals (NCs with different morphologies have been synthesized and applied as the acceptor in the active layer of the organic photovoltaic (OPV devices. CdSe tetrapod (TP/nanorod (NR with zinc-blended seeds and wurtzite arms is prepared by seed growth method and mixed with poly(3-hexylthiophene (P3HT: [6,6]-phenyl-C61-butyric acid methyl ester (PCBM. When the concentrations of CdSe in P3HT: PCBM system are 50 wt% optimally, the efficiency can be promoted about 4.3%, suggesting that an enhancement of 13.2% can be obtained and the addition of anisotropic CdSe NCs content in the active layer can be beneficial for the transport of electrons and light absorption in the OPV devices.

  2. Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement

    Science.gov (United States)

    Valligatla, Sreeramulu; Haldar, Krishna Kanta; Patra, Amitava; Desai, Narayana Rao

    2016-10-01

    The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532 nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications.

  3. Electret properties of biaxially stretched polypropylene films containing various additives

    Energy Technology Data Exchange (ETDEWEB)

    Hillenbrand, J [Institute for Communications Technology, Darmstadt University of Technology, 64283 Darmstadt (Germany); Behrendt, N [Polymer Engineering, University of Bayreuth, 95447 Bayreuth (Germany); Altstaedt, V [Polymer Engineering, University of Bayreuth, 95447 Bayreuth (Germany); Schmidt, H-W [Macromolecular Chemistry I, University of Bayreuth, 95447 Bayreuth (Germany); Sessler, G M [Institute for Communications Technology, Darmstadt University of Technology, 64283 Darmstadt (Germany)

    2006-02-07

    Isotactic polypropylene (i-PP) films containing additives such as the commercial {alpha} -nucleation agent NA11 and the anorganic filler particles CaCO{sub 3} and Al{sub 2}O{sub 3} were biaxially stretched. As a result, the films assume a cellular morphology with oblong cavities extending in the direction of the film elongation. In the present study, stretched films of 50 {mu}m thickness with additive concentrations of 0.05-10 mass per cent were charged with a corona method to potentials of 400 or 500 V. The stability of the charges was tested isothermally at temperatures of 90 and 120 deg. C and by means of thermally stimulated discharge (TSD) experiments. The isothermal measurements show, for the above additives with concentrations higher than about 0.3%, a reduction of the charge decay with increasing additive concentrations. Compared with reference films of pure PP, the potential decay of the films containing additive concentrations of 10% is significantly reduced. Correspondingly, the TSD measurements indicate a shift of the main discharge peak to higher temperatures up to the melting temperature. Generally, the voiding and thus the stability also increases with the stretching ratio. These improvements of the charge stability are attributed to the barrier effect of the cavities. The results are of interest with respect to the various applications of PP electrets, such as ferroelectret devices and air filters.

  4. Electret properties of biaxially stretched polypropylene films containing various additives

    Science.gov (United States)

    Hillenbrand, J.; Behrendt, N.; Altstädt, V.; Schmidt, H.-W.; Sessler, G. M.

    2006-02-01

    Isotactic polypropylene (i-PP) films containing additives such as the commercial α -nucleation agent NA11 and the anorganic filler particles CaCO3 and Al2O3 were biaxially stretched. As a result, the films assume a cellular morphology with oblong cavities extending in the direction of the film elongation. In the present study, stretched films of 50 µm thickness with additive concentrations of 0.05-10 mass per cent were charged with a corona method to potentials of 400 or 500 V. The stability of the charges was tested isothermally at temperatures of 90 and 120 °C and by means of thermally stimulated discharge (TSD) experiments. The isothermal measurements show, for the above additives with concentrations higher than about 0.3%, a reduction of the charge decay with increasing additive concentrations. Compared with reference films of pure PP, the potential decay of the films containing additive concentrations of 10% is significantly reduced. Correspondingly, the TSD measurements indicate a shift of the main discharge peak to higher temperatures up to the melting temperature. Generally, the voiding and thus the stability also increases with the stretching ratio. These improvements of the charge stability are attributed to the barrier effect of the cavities. The results are of interest with respect to the various applications of PP electrets, such as ferroelectret devices and air filters.

  5. Studies on the interfacial charge transfer processes of nanocrystalline CdSe thin film electrodes by intensity modulated photocurrent spectroscopy

    Institute of Scientific and Technical Information of China (English)

    张敬波; 林原; 尹峰; 肖绪瑞

    2000-01-01

    Interfacial charge transfer kinetics of the nanocrystalline CdSe thin film electrodes have been studied in sodium polysulfide solutions by intensity modulated photocurrent spectroscopy (IMPS). The interfacial direct and indirect charge transfer and recombination processes were analyzed in terms of the parameters: normalized steady state photocurrents and surface state lifetimes obtained by measuring the IMPS responses under different applied potentials and different solution concentrations. IMPS responses of polycrystalline CdSe thin film electrodes were also presented for comparison.

  6. Effect of ligand self-assembly on nanostructure and carrier transport behaviour in CdSe quantum dots

    International Nuclear Information System (INIS)

    Adjustment of the nanostructure and carrier behaviour of CdSe quantum dots (QDs) by varying the ligands used during QD synthesis enables the design of specific quantum devices via a self-assembly process of the QD core–shell structure without additional technologies. Surface photovoltaic (SPV) technology supplemented by X-ray diffractometry and infrared absorption spectroscopy were used to probe the characteristics of these QDs. Our study reveals that while CdSe QDs synthesized in the presence of and capped by thioglycolic acid, 3-mercaptopropionic acid, mercaptoethanol or α-thioglycerol ligands display zinc blende nanocrystalline structures, CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures, because different end groups in these ligands induce distinctive nucleation and growth mechanisms. Carboxyl end groups in the ligand served to increase the SPV response of the QDs, when illuminated by hν ≥ Eg,nano-CdSe. Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit photo-generated free charge carrier (FCC) transfer transitions of CdSe QDs illuminated by photon energy of 4.13 to 2.14 eV. The terminal hydroxyl group might better accommodate energy released in the non-radiative de-excitation process of photo-generated FCCs in the ligand's lowest unoccupied molecular orbital in the 300–580 nm wavelength region, when compared with other ligand end groups. - Highlights: • CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures. • Carboxyl end groups in the ligand serve to increase the SPV response of CdSe QDs. • Terminal hydroxyl group in the ligand might accommodate non-radiative de-excitation process in CdSe QDs. • Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit carriers transport of CdSe QDs

  7. Synthesis and optical characterisation of triphenylamine-based hole extractor materials for CdSe quantum dots

    OpenAIRE

    Planells, Miquel; Reynolds, Luke X.; Bansode, Umesh; Chhatre, Shraddha; Ogale, Satishchandra; Robertson, Neil; Haque, Saif A

    2013-01-01

    We report the synthesis and optical characterisation of different triphenylamine-based hole capture materials able to anchor to CdSe quantum dots (QDs). Cyclic voltammetry studies indicate that these materials exhibit reversible electrochemical behaviour. Photoluminescence and transient absorption spectroscopy techniques are used to study interfacial charge transfer properties of the triphenylamine functionalized CdSe QDs. Specifically, we show that the functionalized QDs based on the most ea...

  8. Effect of ligand self-assembly on nanostructure and carrier transport behaviour in CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Li, Kuiying, E-mail: kuiyingli@ysu.edu.cn; Xue, Zhenjie

    2014-11-14

    Adjustment of the nanostructure and carrier behaviour of CdSe quantum dots (QDs) by varying the ligands used during QD synthesis enables the design of specific quantum devices via a self-assembly process of the QD core–shell structure without additional technologies. Surface photovoltaic (SPV) technology supplemented by X-ray diffractometry and infrared absorption spectroscopy were used to probe the characteristics of these QDs. Our study reveals that while CdSe QDs synthesized in the presence of and capped by thioglycolic acid, 3-mercaptopropionic acid, mercaptoethanol or α-thioglycerol ligands display zinc blende nanocrystalline structures, CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures, because different end groups in these ligands induce distinctive nucleation and growth mechanisms. Carboxyl end groups in the ligand served to increase the SPV response of the QDs, when illuminated by hν ≥ E{sub g,nano-CdSe}. Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit photo-generated free charge carrier (FCC) transfer transitions of CdSe QDs illuminated by photon energy of 4.13 to 2.14 eV. The terminal hydroxyl group might better accommodate energy released in the non-radiative de-excitation process of photo-generated FCCs in the ligand's lowest unoccupied molecular orbital in the 300–580 nm wavelength region, when compared with other ligand end groups. - Highlights: • CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures. • Carboxyl end groups in the ligand serve to increase the SPV response of CdSe QDs. • Terminal hydroxyl group in the ligand might accommodate non-radiative de-excitation process in CdSe QDs. • Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit carriers transport of CdSe QDs.

  9. Tailoring of morphology and crystal structure of CdSe nanostructures by controlling the ratio of triethylenetetraamine and water in their mixed solution

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadi, M.R.; Zarghami, V. [Sharif University of Technology, Department of Materials Science and Engineering, Tehran (Iran, Islamic Republic of); Fray, D.J. [University of Cambridge, Department of Materials Science and Metallurgy, Cambridge (United Kingdom)

    2012-05-15

    The morphological manipulation, structural characterization, and optical properties of different CdSe nanocrystals were reported. Several different CdSe nanostructures, including nanowires, tetrapod crystals, and nanoparticles were grown by varying the volume ratio of triethylenetetraamine (TETA) and water (WA) in their mixed solution. By manipulating the growth driving force (i.e., the degree of supersaturation) and kinetics of the process (i.e., growth rate), the morphology and crystal structure of CdSe nanocrystals can be tailored. Growth driving force changed their morphology from nanowires to tetrapod structures and from the latter structure to nanoparticles. Moreover, kinetics of the process altered their crystal structure from wurtzite to zinc blende. The optical property of CdSe nanocrystals was investigated using UV-vis spectroscopy. The absorption edge of CdSe nanostructures showed a blue shift. CdSe nanocrystals prepared under optimized conditions showed good microstructural and optical properties for solar cell application. (orig.)

  10. Development of pressurized disc type fatigue testing system for equi-biaxial fatigue

    International Nuclear Information System (INIS)

    A testing method for investigating fatigue strength under equi-biaxial stress/strain condition was developed. In this method, the equi-biaxial stress condition was achieved by applying pressure on the surfaces of a disc-type specimen, for which the disc edge was constrained by supporting jigs. Air pressure was used to apply the cyclic loading and the failure of the specimen was determined by detecting the crack penetration of the specimen thickness. This method allows application of the cyclic equi-biaxial stress without a complex testing apparatus or a complex controlling system such as the testing system using the cruciform or tubular specimens, conventionally used for the fatigue test under the equi-biaxial stress condition. After developing the testing system, the configuration of the disc-type specimen was designed by finite element analysis so that a crack would be initiated at the center of the specimen. Then, carbon steel (SS400 in JIS) specimens were subjected to the fatigue test. The developed system was demonstrated to be able to initiate a fatigue crack at the center of the specimen and to detect the specimen failure successfully. The test results showed that the fatigue lifetime under equi-biaxial stress was longer than that under uniaxial stress for the same Von Mises equivalent strain range. (author)

  11. Control of biaxial strain in single-layer molybdenite using local thermal expansion of the substrate

    Science.gov (United States)

    Plechinger, Gerd; Castellanos-Gomez, Andres; Buscema, Michele; van der Zant, Herre S. J.; Steele, Gary A.; Kuc, Agnieszka; Heine, Thomas; Schüller, Christian; Korn, Tobias

    2015-03-01

    Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllable biaxial tensile strain by heating the substrate with a focused laser. The effect of this biaxial strain is directly observable in optical spectroscopy as a redshift of the MoS2 photoluminescence. We also demonstrate the potential of this method to engineer more complex strain patterns by employing highly absorptive features on the substrate to achieve non-uniform heat profiles. By comparison of the observed redshift to strain-dependent band structure calculations, we estimate the biaxial strain applied by the silicone-based substrate to be up to 0.2%, corresponding to a band gap modulation of 105 meV per percentage of biaxial tensile strain.

  12. Photoluminescence waveguiding in CdSe and CdTe QDs-PMMA nanocomposite films

    Energy Technology Data Exchange (ETDEWEB)

    Suarez, I; Gordillo, H; Abargues, R; Albert, S; Martinez-Pastor, J, E-mail: isaac.suarez@uv.es [UMDO - Unidad Asociada al CSIC-IMM, Instituto de Ciencia de los Materiales, Universidad de Valencia, PO Box 22085, 46071 Valencia (Spain)

    2011-10-28

    In this paper, active planar waveguides based on the incorporation of CdSe and CdTe nanocrystal quantum dots in a polymer matrix are demonstrated. In the case of doping the polymer with both types of quantum dots, the nanocomposite film guides both emitted colors, green (550 nm, CdTe) and orange (600 nm, CdSe). The optical pumping laser can be coupled not only with a standard end-fire coupling system, but also directing the beam to the surface of the sample, indicating a good absorption cross-section and waveguide properties. To achieve these results, a study of the nanocomposite optical properties as a function of the nanocrystal concentration is presented and the optimum conditions are found for waveguiding.

  13. Electroluminescence from colloidal semiconductor CdSe nanoplatelets in hybrid organic-inorganic light emitting diode

    Science.gov (United States)

    Vitukhnovsky, A. G.; Lebedev, V. S.; Selyukov, A. S.; Vashchenko, A. A.; Vasiliev, R. B.; Sokolikova, M. S.

    2015-01-01

    We report on the fabrication of a hybrid light-emitting-diode based on colloidal semiconductor CdSe nanoplatelets as emitters and organic TAZ [3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole] and TPD [N, N‧-bis (3-methylphenyl)-N, N‧-bis (phenyl)-benzidine] materials as the electron and hole transporting layers. Electroluminescent and current-voltage characteristics of the developed hybrid device with the turn-on voltage of 5.5 V and the radiation wavelength of 515 nm have been obtained. Semiconductor nanoplatelets like CdSe are attractive for the fabrication of hybrid LEDs with low operating voltages, spectrally pure color and short-wavelength electroluminescence, which is required for RGB devices.

  14. Generation of fluorescent CdSe nanocrystals by short-pulse laser fragmentation

    Energy Technology Data Exchange (ETDEWEB)

    Zholudov, Yu. T., E-mail: yurets-z@rambler.ru [Kharkiv National University of Radioelectronics (Ukraine); Sajti, C. L., E-mail: l.sajti@lzh.de [Laser Zentrum Hannover e.V. (Germany); Slipchenko, N. N. [Kharkiv National University of Radioelectronics (Ukraine); Chichkov, B. N. [Laser Zentrum Hannover e.V. (Germany)

    2015-12-15

    A simple liquid-phase laser fragmentation approach, resulting in the rapid transformation of CdSe microcrystals into colloidal quantum dots (QDs), is presented. Laser fragmentation is achieved by irradiating a CdSe suspension in dimethylformamide with intense infrared, picosecond laser pulses followed by surface passivation with oleylamine or different types of phosphines. The generated QDs reveal perfect colloidal stability preventing agglomeration and precipitation, and show characteristic QD absorption and fluorescence characteristics, whereas their emission properties strongly depend on the surface states and applied capping ligands. These QDs show distinct photoemission under 405-nm single-photon and 800-nm multi-photon excitations in the 560- to 610-nm spectral region corresponding to the QDs size of about 1.5–2 nm in diameter which is confirmed by transmission electron microscopy.

  15. Electric field-induced emission enhancement and modulation in individual CdSe nanowires.

    Science.gov (United States)

    Vietmeyer, Felix; Tchelidze, Tamar; Tsou, Veronica; Janko, Boldizsar; Kuno, Masaru

    2012-10-23

    CdSe nanowires show reversible emission intensity enhancements when subjected to electric field strengths ranging from 5 to 22 MV/m. Under alternating positive and negative biases, emission intensity modulation depths of 14 ± 7% are observed. Individual wires are studied by placing them in parallel plate capacitor-like structures and monitoring their emission intensities via single nanostructure microscopy. Observed emission sensitivities are rationalized by the field-induced modulation of carrier detrapping rates from NW defect sites responsible for nonradiative relaxation processes. The exclusion of these states from subsequent photophysics leads to observed photoluminescence quantum yield enhancements. We quantitatively explain the phenomenon by developing a kinetic model to account for field-induced variations of carrier detrapping rates. The observed phenomenon allows direct visualization of trap state behavior in individual CdSe nanowires and represents a first step toward developing new optical techniques that can probe defects in low-dimensional materials.

  16. Light-gated single CdSe nanowire transistor: photocurrent saturation and band gap extraction

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yang, E-mail: yangzh08@gmail.com; Chakraborty, Ritun; Kudera, Stefan; Krahne, Roman, E-mail: roman.krahne@iit.it [Istituto Italiano di Tecnologia, Nanochemistry department (Italy)

    2015-11-15

    CdSe nanowires are popular building blocks for many optoelectronic devices mainly owing to their direct band gap in the visible range of the spectrum. Here we investigate the optoelectronic properties of single CdSe nanowires fabricated by colloidal synthesis, in terms of their photocurrent–voltage characteristics and photoconductivity spectra recorded at 300 and 18 K. The photocurrent is identified as the secondary photocurrent, which gives rise to a photoconductive gain of ∼35. We observe a saturation of the photocurrent beyond a certain voltage bias that can be related to the finite drift velocity of electrons. From the photoconductivity spectra, we determine the band gap energy of the nanowires as ∼1.728 eV, and we resolve low-energy peaks that can be associated with sub-bandgap states.Graphical Abstract.

  17. Inorganic solids of CdSe nanocrystals exhibiting high emission quantum yield

    Energy Technology Data Exchange (ETDEWEB)

    Khon, Elena; Khon, Dmitry; Moroz, Pavel; Zamkov, Mikhail [The Center for Photochemical Sciences and Department of Physics, Bowling Green State University, Bowling Green, OH 43403 (United States); Lambright, Scott; Smith, Bryan; O& #x27; Connor, Timothy; Diederich, Geoffrey [Department of Physics, Bowling Green State University, Bowling Green, OH 43403 (United States); Imboden, Martene [Department of Chemistry, Bowling Green State University, Bowling Green, OH 43403 (United States); Perez-Bolivar, Cesar; Anzenbacher, Pavel [The Center for Photochemical Sciences and Department of Chemistry, Bowling Green State University, Bowling Green, OH 43403 (United States)

    2012-09-11

    A general strategy for the assembly of all-inorganic light-emitting nanocrystal films with emission quantum yield in the 30-52% range is reported. The present methodology relies on solution-processing of CdSe nanocrystals into a crystalline matrix of a wide band gap semiconductor (CdS, ZnS), which replaces the original molecular ligands on nanocrystal surfaces with an inorganic medium. Such matrices efficiently protect nanoparticles from the surrounding environment and preserve the quantum confinement of electrical charges in embedded CdSe NCs. In addition to strong emission, fabricated films show excellent thermal and chemical stability, and a large refractive index, which avails their integration into emerging solid-state nanocrystal devices, including light-emitting diodes, solar concentrators, and quantum dot lasers. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. CdSe quantum dot internalization by Bacillus subtilis and Escherichia coli

    Science.gov (United States)

    Kloepfer, Jeremiah A.; Mielke, Randall E.; Nadeau, Jay L.

    2004-06-01

    Biological labeling has been demonstrated with CdSe quantum dots in a variety of animal cells, but bacteria are harder to label because of their cell walls. We discuss the challenges of using minimally coated, bare CdSe quantum dots as luminescent internal labels for bacteria. These quantum dots were solubilized with mercaptoacetic acid and conjugated to adenine. Significant evidence for the internal staining of Bacillus subtilis (Gram positive) and Escherichia coli (Gram negative) using these structures is presented via steady-state emission, epifluorescence microscopy, transmission electron microscopy, and energy dispersive spectroscopy. In particular, the E. coli adenine auxotroph, and not the wild type, took up adenine coated quantum dots, and this only occurred in adenine deficient growth media. Labeling strength was enhanced by performing the incubation under room light. This process was examined with steady-state emission spectra and time-resolved luminescence profiles obtained from time-correlated-single-photon counting.

  19. One pot synthesis of bi-linker stabilised CdSe quantum dots

    International Nuclear Information System (INIS)

    In this study we exploited the classic Murray's synthesis for generating a hydrophilic CdSe quantum dot system in a single step procedure, with the aim of directly obtaining a material responding to the characteristic of polarity required in many end applications. 6-phosphonohexanoic acid was used as both ligand for generating the active monomer during the synthesis of the quantum dots and final stabiliser. Diffraction measurements identified the cubic phase of cadmium selenide. Energy dispersive spectroscopy analysis revealed non-stoichiometric quantum dots, being the Cd/Se ratio 60/40. This feature suggests a configuration in which Cd2+ ions are present on the nanocrystal surface. Diffuse reflectance infrared Fourier transform analysis was applied in order to investigate the structure of the quantum dot system: the results indicate a configuration in which the carboxylic function of 6-phosphonohexanoic acid establishes only a partial interaction with the quantum dot surface, being set in a pseudo-ester configuration.

  20. Direct growth of CdSe semiconductor quantum dots in glass matrix by femtosecond laser beam

    Science.gov (United States)

    Bell, G.; Filin, A. I.; Romanov, D. A.; Levis, R. J.

    2016-02-01

    Controllable, spatially inhomogeneous distributions of CdSe nanocrystals smaller than the exciton Bohr radius are grown in a glass matrix under combined action of sample heating (below the transformation temperature) and focused high-repetition femtosecond (fs) laser beam. Selective quantum dot precipitation is evidenced by position-dependent absorption and Raman spectra. The particle size is estimated as r = 2.1 ± 0.3 nm by comparing the measured absorption and Raman spectra with those obtained from the samples grown in glass by traditional heat-treatment procedure. Direct growth of CdSe quantum dots in glass is enabled by nonlinear excitation using a focused fs duration laser beam (as differentiated from other methods), and this opens an avenue for adjustable selective growth patterns.

  1. Laser-induced fluorescence measurements on CdSe quantum dots

    Directory of Open Access Journals (Sweden)

    Zoltan Győri

    2010-03-01

    Full Text Available In this paper, we report on photoluminescence decay measurements on CdSe quantum dots (QDs as a function of size in the diameter range of 2.1 to 3.5 nm. The nanoparticles were synthesized by the kinetic growth method from CdO and elemental Se precursors. We studied the effects of growth time on the diameter, emission spectrum and the fluorescence lifetime of the synthesized QDs. The decay time measurements were performed using single shot time-resolved laser-induced fluorescence techniques using a Nd:YAG laser system. Two different decay times were measured on each CdSe sample, a fast one and a relatively slow one. The slow decay was found to be size dependent whereas the fast one was independent of the QD diameter.

  2. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

    Science.gov (United States)

    Aho, Johnathon M.; Qiang, Bo; Wigle, Dennis A.; Tschumperlin, Daniel J.; Urban, Matthew W.

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal

  3. Modeling of biaxial gimbal-less MEMS scanning mirrors

    Science.gov (United States)

    von Wantoch, Thomas; Gu-Stoppel, Shanshan; Senger, Frank; Mallas, Christian; Hofmann, Ulrich; Meurer, Thomas; Benecke, Wolfgang

    2016-03-01

    One- and two-dimensional MEMS scanning mirrors for resonant or quasi-stationary beam deflection are primarily known as tiny micromirror devices with aperture sizes up to a few Millimeters and usually address low power applications in high volume markets, e.g. laser beam scanning pico-projectors or gesture recognition systems. In contrast, recently reported vacuum packaged MEMS scanners feature mirror diameters up to 20 mm and integrated high-reflectivity dielectric coatings. These mirrors enable MEMS based scanning for applications that require large apertures due to optical constraints like 3D sensing or microscopy as well as for high power laser applications like laser phosphor displays, automotive lighting and displays, 3D printing and general laser material processing. This work presents modelling, control design and experimental characterization of gimbal-less MEMS mirrors with large aperture size. As an example a resonant biaxial Quadpod scanner with 7 mm mirror diameter and four integrated PZT (lead zirconate titanate) actuators is analyzed. The finite element method (FEM) model developed and computed in COMSOL Multiphysics is used for calculating the eigenmodes of the mirror as well as for extracting a high order (n < 10000) state space representation of the mirror dynamics with actuation voltages as system inputs and scanner displacement as system output. By applying model order reduction techniques using MATLABR a compact state space system approximation of order n = 6 is computed. Based on this reduced order model feedforward control inputs for different, properly chosen scanner displacement trajectories are derived and tested using the original FEM model as well as the micromirror.

  4. Tuning magnetism by biaxial strain in native ZnO.

    Science.gov (United States)

    Peng, Chengxiao; Wang, Yuanxu; Cheng, Zhenxiang; Zhang, Guangbiao; Wang, Chao; Yang, Gui

    2015-07-01

    Magnetic ZnO, one of the most important diluted magnetic semiconductors (DMS), has attracted great scientific interest because of its possible technological applications in optomagnetic devices. Magnetism in this material is usually delicately tuned by the doping level, dislocations, and local structures. The rational control of magnetism in ZnO is a highly attractive approach for practical applications. Here, the tuning effect of biaxial strain on the d(0) magnetism of native imperfect ZnO is demonstrated through first-principles calculations. Our calculation results show that strain conditions have little effect on the defect formation energy of Zn and O vacancies in ZnO, but they do affect the magnetism significantly. For a cation vacancy, increasing the compressive strain will obviously decrease its magnetic moment, while tensile strain cannot change the moment, which remains constant at 2 μB. For a singly charged anion vacancy, however, the dependence of the magnetic moment on strain is opposite to that of the Zn vacancy. Furthermore, the ferromagnetic state is always present, irrespective of the strain type, for ZnO with two zinc vacancies, 2VZns. A large tensile strain is favorable for improving the Curie temperature and realizing room temperature ferromagnetism for ZnO-based native semiconductors. For ZnO with two singly charged oxygen vacancies, 2Vs, no ferromagnetic ordering can be observed. Our work points the way to the rational design of materials beyond ZnO with novel non-intrinsic functionality by simply tuning the strain in a thin film form.

  5. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

    Science.gov (United States)

    Aho, Johnathon M.; Qiang, Bo; Wigle, Dennis A.; Tschumperlin, Daniel J.; Urban, Matthew W.

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal–submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa–submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered

  6. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry.

    Science.gov (United States)

    Aho, Johnathon M; Qiang, Bo; Wigle, Dennis A; Tschumperlin, Daniel J; Urban, Matthew W

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal

  7. A Suitable Polysulfide Electrolyte for CdSe Quantum Dot-Sensitized Solar Cells

    Directory of Open Access Journals (Sweden)

    H. K. Jun

    2013-01-01

    Full Text Available A polysulfide liquid electrolyte is developed for the application in CdSe quantum dot-sensitized solar cells (QDSSCs. A solvent consisting of ethanol and water in the ratio of 8 : 2 by volume has been found as the optimum solvent for preparing the liquid electrolytes. This solvent ratio appears to give higher cell efficiency compared to pure ethanol or water as a solvent. Na2S and S give rise to a good redox couple in the electrolyte for QDSSC operation, and the optimum concentrations required are 0.5 M and 0.1 M, respectively. Addition of guanidine thiocyanate (GuSCN to the electrolyte further enhances the performance. The QDSSC with CdSe sensitized electrode prepared using 7 cycles of successive ionic layer adsorption and reaction (SILAR produces an efficiency of 1.41% with a fill factor of 44% on using a polysulfide electrolyte of 0.5 M Na2S, 0.1 M S, and 0.05 M GuSCN in ethanol/water (8 : 2 by volume under the illumination of 100 mW/cm2 white light. Inclusion of small amount of TiO2 nanoparticles into the electrolyte helps to stabilize the polysulfide electrolyte and thereby improve the stability of the CdSe QDSSC. The CdSe QDs are also found to be stable in the optimized polysulfide liquid electrolyte.

  8. Energy relaxation in CdSe nanocrystals: the effects of morphology and film preparation

    OpenAIRE

    Spann, Bryan T.; Chen, Liangliang; Ruan, Xiulin; Xu, Xianfan

    2013-01-01

    Ultrafast time-resolved absorption spectroscopy is used to investigate exciton dynamics in CdSe nanocrystal films. The effects of morphology, quantum-dot versus quantum-rod, and preparation of nanocrystals in a thin film form are investigated. The measurements revealed longer intraband exciton relaxation in quantum-rods than in quantum-dots. The slowed relaxation in quantum-rods is due to mitigation of the Auger-relaxation mechanism from elongating the nanocrystal. In addition, the nanocrysta...

  9. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    OpenAIRE

    Denise Feder; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Santos-Mallet, Jacenir R.; Suzete A.O. Gomes; Cecilia Stahl Vieira; Almeida, Diogo B.

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellul...

  10. Green wet chemical route to synthesize capped CdSe quantum dots

    Indian Academy of Sciences (India)

    A Oudhia; P Bichpuria

    2014-02-01

    In the present work, we report green synthesis of tartaric acid (TA) and triethanolamine (TEA) capped cadmium selenide quantum dots (CdSe QDs) employing chemical bath deposition (CBD) method. The mechanism of capping using non-toxic binary capping agents is also discussed. Stable QDs of various sizes were obtained by varying pH of the bath. The structural, morphological and spectroscopic characterization of the as-prepared samples by XRD, SEM, optical absorption and photoluminescence (PL) is also reported.

  11. Formability and cavitation behavior of superplastic AA5083 aluminum alloy under biaxial tension

    Institute of Scientific and Technical Information of China (English)

    LUO Ying-bing; LI Da-yong; PENG Ying-hong

    2006-01-01

    The superplastic forming potential of two fine-grained 5083 aluminum alloys were studied under biaxial tension using a pneumatic bulge test. Experiments were performed at temperatures ranging from 475 to 525 ℃ with three different strain paths ranging from equi-biaxial to approaching plane strain. The shape of the forming limited diagram(FLD) is found to be significantly different from FLDs commonly used in room temperature stamping. The effects of temperature on final thickness distribution, dome height and cavitation were investigated for the case of equi-biaxial stretching. Increasing temperature in free bulge forming can improve the thickness distribution of final parts but have no significant effect on dome height. The results indicate that determination of forming limits in SPF cannot be represented with a simple FLD and additional metrics such as external thinning and internal cavitation needed to determine the SPF potential of a material.

  12. Formation of biaxially textured molybdenum thin films under the influence of recrystallization conditions

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan, Rahul, E-mail: krishr2@rpi.edu [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Riley, Michael [Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Lee, Sabrina [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, NY 12189 (United States); Lu, Toh-Ming [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)

    2011-06-01

    This article highlights the formation of biaxially textured body centered cubic Mo nanorods under recrystallization conditions using glancing angle deposition. The flux incidence angle has been changed ({alpha} = 0 deg., 70 deg. and 85 deg. away from the surface normal) to observe its effect on the formation of biaxial texture under a constant low Ar pressure environment (0.306 Pa). Only at a glancing flux incidence ({alpha} = 85 deg.), the directional diffusion overcomes the effect of recrystallization to yield a highly biaxial texture. In another study, a normal flux incidence ({alpha} = 0 deg.) was kept constant and the Ar pressure was changed (0.67, 1.33 and 2.67 Pa) to see its influence on the film morphology and the resulting texture. The Ar pressure variation was aimed at attempting a zone transformation in accordance with the structure zone model. While the morphology appeared to agree with the expected zone transformation, the texture did not.

  13. A confocal rheoscope to study bulk or thin-film material under uniaxial or biaxial shear

    CERN Document Server

    Lin, Neil Y C; Cheng, Xiang; Leahy, Brian; Cohen, Itai

    2016-01-01

    We present a new design of a confocal rheoscope that enables us to precisely impose a uniform uniaxial or biaxial shear. The design consists of two precisely-positioned parallel plates. Our design allows us to adjust the gap between the plates to be as small as 2$\\pm$0.1 $\\mu$m, allowing for the exploration of confinement effects. By using our shear cell in conjunction with a biaxial force measurement device and a high-speed confocal microscope, we are able to measure the real-time biaxial stress while simultaneously imaging the material 3D structure. We illustrate the importance of the instrument capabilities by discussing the applications of this instrument in current and future research topics in colloidal suspensions.

  14. STRAIN-CONTROLLED BIAXIAL TENSION OF NATURAL RUBBER: NEW EXPERIMENTAL DATA

    KAUST Repository

    Pancheri, Francesco Q.

    2014-03-01

    We present a new experimental method and provide data showing the response of 40A natural rubber in uniaxial, pure shear, and biaxial tension. Real-time biaxial strain control allows for independent and automatic variation of the velocity of extension and retraction of each actuator to maintain the preselected deformation rate within the gage area of the specimen. Wealso focus on the Valanis-Landel hypothesis that is used to verify and validate the consistency of the data.Weuse a threeterm Ogden model to derive stress-stretch relations to validate the experimental data. The material model parameters are determined using the primary loading path in uniaxial and equibiaxial tension. Excellent agreement is found when the model is used to predict the response in biaxial tension for different maximum in-plane stretches. The application of the Valanis-Landel hypothesis also results in excellent agreement with the theoretical prediction.

  15. Cytotoxicity and fluorescence studies of silica-coated CdSe quantum dots for bioimaging applications

    Energy Technology Data Exchange (ETDEWEB)

    Vibin, Muthunayagam [University of Kerala, Department of Biochemistry (India); Vinayakan, Ramachandran [National Institute for Interdisciplinary Science and Technology (CSIR), Photosciences and Photonics (India); John, Annie [Sree Chitra Tirunal Institute of Medical Sciences and Technology, Biomedical Technology Wing (India); Raji, Vijayamma; Rejiya, Chellappan S.; Vinesh, Naresh S.; Abraham, Annie, E-mail: annieab2@yahoo.co.in [University of Kerala, Department of Biochemistry (India)

    2011-06-15

    The toxicological effects of silica-coated CdSe quantum dots (QDs) were investigated systematically on human cervical cancer cell line. Trioctylphosphine oxide capped CdSe QDs were synthesized and rendered water soluble by overcoating with silica, using aminopropyl silane as silica precursor. The cytotoxicity studies were conducted by exposing cells to freshly synthesized QDs as a function of time (0-72 h) and concentration up to micromolar level by Lactate dehydrogenase assay, MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay, Neutral red cell viability assay, Trypan blue dye exclusion method and morphological examination of cells using phase contrast microscope. The in vitro analysis results showed that the silica-coated CdSe QDs were nontoxic even at higher loadings. Subsequently the in vivo fluorescence was also demonstrated by intravenous administration of the QDs in Swiss albino mice. The fluorescence images in the cryosections of tissues depicted strong luminescence property of silica-coated QDs under biological conditions. These results confirmed the role of these luminescent materials in biological labeling and imaging applications.

  16. Fingerprint detection and using intercalated CdSe nanoparticles on non-porous surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Algarra, Manuel, E-mail: malgarra67@gmail.com [Centro de Geología da Universidade do Porto, Departamento de Geociências, Ambiente e Ordenamemto do Territorio do Porto, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Radotić, Ksenija; Kalauzi, Aleksandar; Mutavdžić, Dragosav; Savić, Aleksandar [Institute for Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, 11000 Beograd (Serbia); Jiménez-Jiménez, José; Rodríguez-Castellón, Enrique [Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Málaga, Campus de Teatinos s/n, 29071Málaga (Spain); Silva, Joaquim C.G. Esteves da [Centro de Investigação em Química (CIQ-UP). Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Guerrero-González, Juan José [Policía Científica, Cuerpo Nacional de Policía, Málaga (Spain)

    2014-02-17

    Graphical abstract: -- Highlights: •Fluorescent nanocomposite based on the inclusion of CdSe quantum dots in porous phosphate heterostructures. •Characterized by FTIR, XRD and fluorescence spectroscopies. •Deconvolution of the emission spectra was confirmed by using multivariate curve resolution (MCR) method. •Application for fingerprint detection and analysis on different non-porous surfaces. -- Abstract: A fluorescent nanocomposite based on the inclusion of CdSe quantum dots in porous phosphate heterostructures, functionalized with amino groups (PPH-NH{sub 2}@CdSe), was synthesized, characterized and used for fingerprint detection. The main scopes of this work were first to develop a friendly chemical powder for detecting latent fingerprints, especially in non-porous surfaces; their further intercalation in PPH structure enables not to spread the fluorescent nanoparticles, for that reason very good fluorescent images can be obtained. The fingerprints, obtained on different non-porous surfaces such as iron tweezers, mobile telephone screen and magnetic band of a credit card, treated with this powder emit a pale orange luminescence under ultraviolet excitation. A further image processing consists of contrast enhancement that allows obtaining positive matches according to the information supplied from a police database, and showed to be more effective than that obtained with the non-processed images. Experimental results illustrate the effectiveness of proposed methods.

  17. Structural, optical and magnetic properties of cobalt-doped CdSe nanoparticles

    Indian Academy of Sciences (India)

    Jaspal Singh; N K Verma

    2014-05-01

    Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The synthesized nanoparticles have been characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Visible), photoluminescence spectroscopy (PL), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID), at room temperature. From XRD analysis, pure and cobalt-doped CdSe nanoparticles have been found to be polycrystalline in nature and possess zinc blende phase having cubic structure. In addition to this, some peaks related to secondary phase or impurities such as cobalt diselenide (CoSe2) have also been observed. The calculated average crystallite size of the nanoparticles lies in the range, 3–21 nm, which is consistent with the results obtained from TEM analysis. The decrease in average crystallite size and blue shift in the band gap has been observed with Co-doping into the host CdSe nanoparticles. The magnetic analysis shows the ferromagnetic behaviour up to 10% of Co-doping concentration. The increase of Co content beyond 10% doping concentration leads to antiferromagnetic interactions between the Co ions, which suppress the ferromagnetism.

  18. Analysis of the effects of surface chemistry on the XAS spectra of CdSe nanomaterials

    Science.gov (United States)

    Whitley, Heather; Prendergast, David; Ogitsu, Tadashi; Schwegler, Eric

    2010-03-01

    X-ray absorption spectroscopy (XAS) is an element-specific probe of local electronic structure, and is an ideal method to analyze chemical bonding. We investigate the consistency of theoretically predicted structures of CdSe nanomaterials with recently measured XAS via ab initio calculations. Using plane-wave DFT, the x-ray absorption cross-section for the Cd L3-edge of small CdSe clusters with a variety of surface ligands is calculated. We also highlight the importance of including excitonic effects in our simulations of core excitation spectra. We compare our simulations to existing experimental data on the ligand dependence of XAS for ligated quantum dots up to ˜3nm in diameter. Based on the favorable comparison of our theoretical spectra with experimental measurements, we infer the validity of our DFT-derived structure and surface passivation for these quantum dots and its relevance to understanding optoelectronic properties of solution-synthesized CdSe nanocrystals. Prepared by LLNL under Contract DE-AC52-07NA27344.

  19. Detection of CdSe quantum dot photoluminescence for security label on paper

    Energy Technology Data Exchange (ETDEWEB)

    Isnaeni,, E-mail: isnaeni@lipi.go.id; Sugiarto, Iyon Titok [Research Center for Physics, Indonesian Institute of Science, Building 442 Puspiptek Serpong, South Tangerang, Banten, Indonesia 15314 (Indonesia); Bilqis, Ratu; Suseno, Jatmiko Endro [Department of Physics, Diponegoro University, Jl. Prof. Soedarto, Tembalang, Semarang, Indonesia 50275 (Indonesia)

    2016-02-08

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word ’RAHASIA’. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.

  20. Detection of CdSe quantum dot photoluminescence for security label on paper

    International Nuclear Information System (INIS)

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word ’RAHASIA’. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns

  1. Preparation of sodium titanate nanotubes modified by CdSe quantum dots and their photovoltaic characteristics

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Sodium titanate nanotubes have been prepared and modified chemically with CdSe quantum dots (QDs) using bifunctional modifiers (HS-COOH). Their photovoltaic characteristics have also been studied. The results indicate that the surface photovoltage response of nanotubes extends to the visible light region, and the intensity of surface photovoltage is enhanced after modification with CdSe QDs. The field-induced surface photovoltage spectroscopy (FISPS) shows that sodium titanate nanotubes have different photovoltaic response before and after modification. That is, the surface photovoltaic re-sponse of pure sodium titanate nanotubes increases with the enhancement of positive applied bias and decreases with the enhancement of negative applied bias. Meanwhile, the surface photovoltaic re-sponse of CdSe modified sodium titanate nanotubes is different from that of the pure sodium titanate nanotubes. The whole spectrum increases with the enhancement of applied bias at the first stage. However, when the applied bias reaches a certain value, the surface photovoltage response keeps in-creasing in some spectrum regions, while decreasing in other spectrum regions. This novel phe-nomenon is explained by using an electric field induced dipole model.

  2. Inverted organic solar cells using a solution-processed TiO2/CdSe electron transport layer to improve performance

    Science.gov (United States)

    Ma, Xiaoxiao; Xiong, Zhicheng; Wang, Wen; Zhang, Luming; Wu, Sujuan; Lu, Xubing; Gao, Xingsen; Shui, Lingling; Liu, Jun-Ming

    2016-04-01

    In the present work, cadmium selenide (CdSe) nanoparticles are deposited directly on TiO2 film to fabricate the TiO2/CdSe interlayer by a chemical bath deposition method. The inverted organic solar cells using poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) bulk heterojunction as an active layer and TiO2/CdSe interlayer as an electron transport layer (ETL) are fabricated in air. A series of microstructural, photo-electronic, and electrochemical characterizations on these cells are performed. The TiO2/CdSe structure with respect to either the TiO2 layer or the CdSe layer as the ETL exhibits significantly enhanced external quantum efficiency (EQE) in the visible region. The photoluminescence (PL) measurement shows that the exciton dissociation in the TiO2/CdSe structure is more effective than that in either the TiO2 or CdSe structure. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) implies that the charge recombination in the TiO2/CdSe structure can be suppressed with respect to that in either the CdSe or TiO2 structure. The photovoltaic performances of the cells with the TiO2/CdSe ETL are clearly improved compared with the reference cells only with the TiO2 layer or CdSe layer as the ETL.

  3. Behavior of reinforced concrete slabs subjected to combined punching shear and biaxial tension

    International Nuclear Information System (INIS)

    This investigation was a continuing study of peripheral (punching) shear strength of precracked, biaxially tensioned, orthogonally reinforced concrete slabs. This research was motivated by the need to determie the strength of a reinforced concrete containment vessel wall when subjected to combined internal pressure and punching shear loads normal to the wall. The study served to determine the effect of three major variables (shear span, size of loaded area, and reinforcing steel ratio) on punching shear strength of slabs that were precracked in biaxial tension and then held at one of the two tension levels (0 or 0.8f/sub y/) during shear load application

  4. Long-term strength of Kh13M2S2 in biaxial stressed state

    International Nuclear Information System (INIS)

    Long-term strength of thin-walled tubular and plane samples of Kh13M2S2 steel at 650 deg C was studied. The tubular samples were loaded with internal gas pressure which resulted in a biaxial stressed state, the plane ones were loaded with uniaxial extension. Statistical processing of the experimental results was carried out, the straight lines of long-term strength with confidence intervals were plotted. Of four studied criteria of the complex stressed state the best coincidence of the experimental results under biaxial and uniaxial load is obtained using the Lebedev criterion

  5. Effective-Field Theory on High Spin Systems with Biaxial Crystal Field

    Institute of Scientific and Technical Information of China (English)

    JIANG Wei; GUO An-Bang; LI Xin; WANG Xi-Kun; BAI Bao-Dong

    2006-01-01

    Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found.

  6. CdSe quantum dots stabilized by carboxylic-functionalized PVA: Synthesis and UV-vis spectroscopy characterization

    International Nuclear Information System (INIS)

    Quantum dots (QDs) have drawn the attention of the research community in the last decade due to their potential use in the fast developing area of nanotechnology. In this study, it is reported the synthesis and characterization CdSe nanoparticles using acid-functionalized poly(vinyl alcohol) (PVA-COOH) polymer as capping ligands via aqueous route at room temperature by methods of colloidal chemistry. Different molar concentrations of PVA-COOH were investigated aiming at producing stable nanoparticles using cadmium perchlorate and synthesized sodium selenosulfate. UV-vis spectroscopy was used to evaluate the kinetics and the relative stability of CdSe nanocrystals considering their size as-prepared and subsequent growth. The QDs sizes were estimated by the 'absorbance onset' from UV-vis spectroscopy spectra, considering theoretical and empirical methods. The results have indicated that precursor solution of PVA-COOH at concentration of 1.0 mol L-1 was effective on stabilizing colloidal CdSe QDs in aqueous suspension. Moreover, ultra-small CdSe nanocrystals were produced with calculated average particles size under 2.0 nm, indicating they were in the so-called 'quantum-size confinement range'. Hence, it was developed a relatively simple colloidal route using a single-step method to produce CdSe QDs water soluble and commercially available polymers that offers a window of opportunities to explore these novel nanohybrid materials.

  7. Electronic and optical properties of kesterite Cu2ZnSnS4 under in-plane biaxial strains: First-principles calculations

    International Nuclear Information System (INIS)

    The electronic structures and optical properties of Cu2ZnSnS4 (CZTS) under in-plane biaxial strain were systematically investigated using first-principles calculations based on generalized gradient approximation and hybrid functional method, respectively. It is found that the fundamental bandgap at the Γ point decreases linearly with increasing tensile biaxial strain perpendicular to c-axis. However, a bandgap maximum occurs as the compressive biaxial strain is 1.5%. Further increase of compressive strain decreases the bandgap. In addition, the optical properties of CZTS under biaxial strain are also calculated, and the variation trend of optical bandgap with biaxial strain is consistent with the fundamental bandgap.

  8. Surface plasmon resonance enhanced photoluminescence from Au coated periodic arrays of CdSe quantum dots and polymer composite thin film

    International Nuclear Information System (INIS)

    We have fabricated an arrayed CdSe quantum dots composite thin film that can enhance the photoluminescence of CdSe under the 488 nm laser irradiation by tuning the gold surface plasmon resonance frequency. This thin film consists of a gold coated periodic array of hybrid material of CdSe and poly(methyl methacrylate) on indium tin oxide coated glass substrate. The main surface plasmon resonance was red shifted as we increased the column diameter of the array. By adjusting the column diameters and lattice constants of the array to coincide with the 488 nm excitation wavelength, an evident increase in luminescence intensity was obtained due to the surface plasmon resonance of gold. As a result of likely efficient energy transfer from gold surface plasmon resonance to CdSe, the photoluminescence intensity of CdSe has been increased to 248% at 570 nm. This composite film has many potential applications in high efficient optoelectronic devices

  9. The effect of biaxial strain on impurity diffusion in Si and SiGe

    DEFF Research Database (Denmark)

    Larsen, Arne Nylandsted; Zangenberg, Nikolaj; Fage-Pedersen, Jacob

    2005-01-01

    Results from diffusion studies of different impurities in biaxially strained Si and Si"1"-"xGe"x for low x-values will be presented. The structures are all molecular-beam epitaxy (MBE) grown on strain-relaxed Si"1"-"xGe"x layers, and the impurity profiles are introduced during growth. We have...

  10. Large-deformation properties of wheat dough in uni- and biaxial extension. Part I. Flour dough

    NARCIS (Netherlands)

    Sliwinski, E.L.; Kolster, P.; Vliet, van T.

    2004-01-01

    Rheological and fracture properties of optimally mixed flour doughs from three wheat cultivars which perform differently in cereal products were studied in uniaxial and biaxial extension. Doughs were also tested in small angle sinusoidal oscillation. In accordance with previously published results t

  11. Phase diagram of colloidal spheres in a biaxial electric or magnetic field

    NARCIS (Netherlands)

    Smallenburg, F.; Dijkstra, M.

    2010-01-01

    Colloidal particles with a dielectric constant mismatch with the surrounding solvent in an external biaxial magnetic or electric field experience an “inverted” dipolar interaction. We determine the phase behavior of such a system using Helmholtz free energy calculations in Monte Carlo simulations fo

  12. Failure Investigation for QP Steel Sheets under uniaxial and Equal-Biaxial Tension Conditions

    Science.gov (United States)

    Zou, Danqing; Li, Shuhui; He, Ji; Cui, Ronggao

    2016-08-01

    The Quenching and Partitioning (QP) steel sheet is new generation material to induce phase transformation for plasticity in forming vehicle parts. The phase transformation is strongly stress state dependent behavior in experiments, which should affect the failure timing and limit strain in forming processes. In this paper, Nakajima test with QP980 and DP1000 steel sheets under equal-biaxial loading condition is performed for failure behavior. X-ray diffraction (XRD) is adopted to obtain the volume fraction of retained austenite (fA). Digital Image Correlation (DIC) is used to record the surface strain field and its evolution during equal-biaxial tension deformation. The same level Dual Phase (DP) steel is also employed for the purpose of comparison. The results show that phase transformation in QP steel gives small impact on failure strain under equal biaxial tension condition which is contradicted with our understanding. It suggests that failure behavior under uniaxial tension of QP980 is strongly phase transformation dependent. But it shows almost independent under equal biaxial tension condition.

  13. 2D nonlocal versus 3D bifurcation studies for biaxially loaded plates

    DEFF Research Database (Denmark)

    Benallal, A.; Tvergaard, Viggo

    1998-01-01

    The main objective of this work is to analyse how a two-dimensional second gradient plasticity model is able to reproduce the three-dimensional bifurcation behaviour for a biaxially loaded flat plate. While it is found that the simple model used here is able to capture them qualitatively for the ...

  14. Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges

    Energy Technology Data Exchange (ETDEWEB)

    Clair, A. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Foucault, M.; Calonne, O. [Areva ANP, Centre Technique Departement Corrosion-Chimie, 30 Bd de l' industrie, BP 181, 71205 Le Creusot (France); Lacroute, Y.; Markey, L.; Salazar, M.; Vignal, V. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Finot, E., E-mail: Eric.Finot@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France)

    2011-05-15

    Research highlights: > Surface strains measured using nanogauge were compared to the texture obtained by EBSD. > Statistics of the principal strain discern the grains according to the Schmid factor. > Strain hotspots were localized near a triple junction of alloy 600 under tensile loading. > Asymetrical profile of the GB strains is a criterion for surface cracking initiation. - Abstract: A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then investigated both statistically for each grain and locally at the grain boundaries. The superimposition of microstructure and strain maps allows the high strain gradient (reaching 3-fold the applied strain) to be localized at preferential grain boundaries near the triple junction. The Schmid factors and the KAM were compared to the maximum principal strain and the in-plane shear strain respectively. The polycrystalline deformation was attributable first to the rotation of some grains, followed by the elongation of all grains along their preferential activated slip systems.

  15. Interference of wedge-shaped protrusions on the faces of a Griffith crack in biaxial stress. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Boulet, J.A.M. [Tennessee Univ., Knoxville, TN (United States)

    1992-04-01

    An initial investigation of the influence of protrusion interference on the fracture toughness required to prevent unstable propagation of a Griffith crack in a brittle material is described. The interference is caused by relative shear displacement of the crack faces when subjected to remote biaxial stress with neither principal stress parallel to the crack. It is shown that for room temperature cracks smaller than about one centimeter in silicon carbide, or about one millimeter in silicon nitride, the presence of interference changes the fracture stress. A mathematical model based on linear elasticity solutions and including multiple interference sites at arbitrarily specified positions on the crack is presented. Computations of the change in required fracture toughness and its dependence on wedge geometry (size and vertex angle), applied stresses (orientation and magnitude), and location of the interference site are discussed. Results indicate that a single interference site has only a slight effect on required toughness. However, the influence of interference increases monotonically with the number of interference sites. The two-dimensional model described herein is not accurate when the interference sites are closely spaced.

  16. Chemical role of amines in the colloidal synthesis of CdSe quantum dots and their luminescence properties

    International Nuclear Information System (INIS)

    The role of organic amines in the colloidal synthesis of CdSe quantum dots (QDs) has been studied. CdSe QDs were synthesized from the source solutions containing 5 vol% of amines having various alkyl chain lengths, stereochemical sizes and electron donation abilities. The role of the additional amines was evaluated on the basis of the photoluminescence (PL) properties such as PL wavelength and intensity of the obtained CdSe QDs. The observed PL spectra were explained by the fact that the amines behaved as capping ligands on the surface of the QDs in the product colloidal solution and complex ligands for cadmium in the source solutions. It was shown that the particle size was controlled by the diffusion process depending on the mass and stereochemical shape of the amines, and the luminescence intensity increased with the increasing electron donation ability and capping density of the amines

  17. Biaxial flexural strength of Turkom-Cera core compared to two other all-ceramic systems

    Directory of Open Access Journals (Sweden)

    Bandar Mohammed Abdullah Al-Makramani

    2010-12-01

    Full Text Available Advances in all-ceramic systems have established predictable means of providing metal-free aesthetic and biocompatible materials. These materials must have sufficient strength to be a practical treatment alternative for the fabrication of crowns and fixed partial dentures. OBJECTIVES: The aim of this study was to compare the biaxial flexural strength of three core ceramic materials. MATERIAL AND METHODS: Three groups of 10 disc-shaped specimens (16 mm diameter x 1.2 mm thickness - in accordance with ISO-6872, 1995 were made from the following ceramic materials: Turkom-Cera Fused Alumina [(Turkom-Ceramic (M Sdn Bhd, Puchong, Selangor, Malaysia], In-Ceram (Vita Zahnfabrik, Bad Säckingen, Baden-Württemberg, Germany and Vitadur-N (Vita Zahnfabrik, Bad Säckingen, Baden-Württemberg, Germany, which were sintered according to the manufacturer's recommendations. The specimens were subjected to biaxial flexural strength test in an universal testing machine at a crosshead speed of 0.5 mm/min. The definitive fracture load was recorded for each specimen and the biaxial flexural strength was calculated from an equation in accordance with ISO-6872. RESULTS: The mean biaxial flexural strength values were: Turkom-Cera: 506.8±87.01 MPa, In-Ceram: 347.4±28.83 MPa and Vitadur-N: 128.7±12.72 MPa. The results were analyzed by the Levene's test and Dunnett's T3 post-hoc test (SPSS software V11.5.0 for Windows, SPSS, Chicago, IL, USA at a preset significance level of 5% because of unequal group variances (P<0.001. There was statistically significant difference between the three core ceramics (P<0.05. Turkom-Cera showed the highest biaxial flexural strength, followed by In-Ceram and Vitadur-N. CONCLUSIONS: Turkom-Cera core had significantly higher flexural strength than In-Ceram and Vitadur-N ceramic core materials.

  18. Incidence of the core composition on the stability, the ROS production and the toxicity of CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Kauffer, Florence-Anaïs [Université de Lorraine, Laboratoire Réactions et Génie des Procédés (LRGP), UMR 7274, CNRS, 1 rue Grandville, BP 20451, 54001 Nancy Cedex (France); Université de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, CNRS, 15 Avenue du Charmois, 54500 Vandoeuvre-lès-Nancy (France); Merlin, Christophe [Université de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, CNRS, 15 Avenue du Charmois, 54500 Vandoeuvre-lès-Nancy (France); Balan, Lavinia [Institut de Science des Matériaux de Mulhouse (IS2M), LRC 7228, 15 rue Jean Starcky, 68093 Mulhouse (France); Schneider, Raphaël, E-mail: raphael.schneider@univ-lorraine.fr [Université de Lorraine, Laboratoire Réactions et Génie des Procédés (LRGP), UMR 7274, CNRS, 1 rue Grandville, BP 20451, 54001 Nancy Cedex (France)

    2014-03-01

    Graphical abstract: - Highlights: • Aqueous phase routes for the production of MSA-capped CdSe and alloyed CdSe(S) QDs were developed. • Despite their higher content in cadmium, CdSe(S) QDs are less toxic than CdSe ones. • Hydroxyl radical production is correlated to the photostability of the dots. • The surface chemistry and the reactivity of QDs play a crucial role on their phototoxicity. - Abstract: Mercaptosuccinic acid-capped CdSe and alloyed CdSe(S) QDs were prepared in aqueous solution at 100 and 170 °C, respectively. These dots were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV–vis and photoluminescence spectroscopies. The dots were found to be of similar size (ca. 2 nm) but differ in their composition and surface chemistry. The photostability of the QDs was found to correlate with their ability to produce reactive oxygen species (ROS) upon light activation. CdSe QDs produce hydroxyl radicals immediately after irradiation due to their modest photostability, while CdSe(S) QDs start to generate the hydroxyl radicals only once they start to be bleached (ca. 30 min). Cytotoxicity experiments conducted on Escherichia coli cells revealed that CdSe QDs were the more toxic despite being the least loaded in cadmium. In addition, consistent with ROS assays, the cytotoxicity of the CdSe QDs appeared light-dependent and is in accordance with a light-dependent oxidative stress observed with an oxyR-based whole cell biosensor. Our results demonstrate the crucial role played by nanoparticles synthesis process on their PL properties, their stability and their toxicity.

  19. Assessing potential harmful effects of CdSe quantum dots by using Drosophila melanogaster as in vivo model

    Energy Technology Data Exchange (ETDEWEB)

    Alaraby, Mohamed [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); Sohag University, Faculty of Sciences, Zoology Department, 82524-Campus, Sohag (Egypt); Demir, Esref [Akdeniz University, Faculty of Sciences, Department of Biology, 07058-Campus, Antalya (Turkey); Hernández, Alba [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); CIBER Epidemiología y Salud Pública, ISCIII, Madrid (Spain); Marcos, Ricard, E-mail: ricard.marcos@uab.es [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); CIBER Epidemiología y Salud Pública, ISCIII, Madrid (Spain)

    2015-10-15

    Since CdSe QDs are increasingly used in medical and pharmaceutical sciences careful and systematic studies to determine their biosafety are needed. Since in vivo studies produce relevant information complementing in vitro data, we promote the use of Drosophila melanogaster as a suitable in vivo model to detect toxic and genotoxic effects associated with CdSe QD exposure. Taking into account the potential release of cadmium ions, QD effects were compared with those obtained with CdCl{sub 2}. Results showed that CdSe QDs penetrate the intestinal barrier of the larvae reaching the hemolymph, interacting with hemocytes, and inducing dose/time dependent significant genotoxic effects, as determined by the comet assay. Elevated ROS production, QD biodegradation, and significant disturbance in the conserved Hsps, antioxidant and p53 genes were also observed. Overall, QD effects were milder than those induced by CdCl{sub 2} suggesting the role of Cd released ions in the observed harmful effects of Cd based QDs. To reduce the observed side-effects of Cd based QDs biocompatible coats would be required to avoid cadmium's undesirable effects. - Highlights: • CdSe QDs were able to cross the intestinal barrier of Drosophila. • Elevated ROS induction was detected in larval hemocytes. • Changes in the expression of Hsps and p53 genes were observed. • Primary DNA damage was induced by CdSe QDs in hemocytes. • Overall, CdSe QD effects were milder than those induced by CdCl{sub 2}.

  20. Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal

    Science.gov (United States)

    Nagaraj, Mamatha; Panarin, Y. P.; Manna, U.; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-01-01

    We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field.

  1. Incorporation of experimentally-derived fiber orientation into a structural constitutive model for planar collagenous tissues.

    Science.gov (United States)

    Sacks, Michael S

    2003-04-01

    Structural constitutive models integrate information on tissue composition and structure, avoiding ambiguities in material characterization. However, critical structural information (such as fiber orientation) must be modeled using assumed statistical distributions, with the distribution parameters estimated from fits to the mechanical test data. Thus, full realization of structural approaches continues to be limited without direct quantitative structural information for direct implementation or to validate model predictions. In the present study, fiber orientation information obtained using small angle light scattering (SALS) was directly incorporated into a structural constitutive model based on work by Lanir (J. Biomech., v. 16, pp. 1-12, 1983). Demonstration of the model was performed using existing biaxial mechanical and fiber orientation data for native bovine pericardium (Sacks and Chuong, ABME, v.26, pp. 892-902, 1998). The structural constitutive model accurately predicted the complete measured biaxial mechanical response. An important aspect of this approach is that only a single equibiaxial test to determine the effective fiber stress-strain response and the SALS-derived fiber orientation distribution were required to determine the complete planar biaxial mechanical response. Changes in collagen fiber crimp under equibiaxial strain suggest that, at the meso-scale, fiber deformations follow the global tissue strains. This result supports the assumption of affine strain to estimate the fiber strains. However, future evaluations will have to be performed for tissue subjected to a wider range of strain to more fully validate the current approach.

  2. In situ synthesis of P3HT-capped CdSe superstructures and their application in solar cells

    OpenAIRE

    Peng, Yanling; Song, Guosheng; Hu, Xianghua; He, Guanjie; CHEN, ZHIGANG; XU, XIAOFENG; Hu, Junqing

    2013-01-01

    Organic/inorganic hybrid solar cells have great potentials to revolutionize solar cells, but their use has been limited by inefficient electron/hole transfer due to the presence of long aliphatic ligands and unsatisfying continuous interpenetrating networks. To solve this problem, herein, we have developed a one-pot route for in situ synthesis of poly(3-hexylthiophene) (P3HT)-capped CdSe superstructures, in which P3HT acts directly as the ligands. These CdSe superstructures are in fact constr...

  3. Direct assembly of in situ templated CdSe quantum dots via crystalline lamellae structure of polyamide 66

    International Nuclear Information System (INIS)

    A simple concept is proposed for templating in situ synthesised CdSe quantum dots (QDs) into an organised nano-pattern using the crystalline lamellae structure of polyamide 66 (PA66). The morphology obtained for PA66 and the hybrid material on Si/SiOx solid substrate was characterised by means of atomic force microscope. Controlling the PA66 concentration in solution and the organic–inorganic interactions are found to be the keys factors to direct the assembly of CdSe QDs along the PA66 linear crystalline structure. This simple approach could be opened a new avenue for a large spectrum of innovative high-tech applications.

  4. Pyramid-Shaped Wurtzite CdSe Nanocrystals with Inverted Polarity.

    Science.gov (United States)

    Ghosh, Sandeep; Gaspari, Roberto; Bertoni, Giovanni; Spadaro, Maria Chiara; Prato, Mirko; Turner, Stuart; Cavalli, Andrea; Manna, Liberato; Brescia, Rosaria

    2015-08-25

    We report on pyramid-shaped wurtzite cadmium selenide (CdSe) nanocrystals (NCs), synthesized by hot injection in the presence of chloride ions as shape-directing agents, exhibiting reversed crystal polarity compared to former reports. Advanced transmission electron microscopy (TEM) techniques (image-corrected high-resolution TEM with exit wave reconstruction and probe-corrected high-angle annular dark field-scanning TEM) unequivocally indicate that the triangular base of the pyramids is the polar (0001̅) facet and their apex points toward the [0001] direction. Density functional theory calculations, based on a simple model of binding of Cl(-) ions to surface Cd atoms, support the experimentally evident higher thermodynamic stability of the (0001̅) facet over the (0001) one conferred by Cl(-) ions. The relative stability of the two polar facets of wurtzite CdSe is reversed compared to previous experimental and computational studies on Cd chalcogenide NCs, in which no Cl-based chemicals were deliberately used in the synthesis or no Cl(-) ions were considered in the binding models. Self-assembly of these pyramids in a peculiar clover-like geometry, triggered by the addition of oleic acid, suggests that the basal (polar) facet has a density and perhaps type of ligands significantly different from the other three facets, since the pyramids interact with each other exclusively via their lateral facets. A superstructure, however with no long-range order, is observed for clovers with their (0001̅) facets roughly facing each other. The CdSe pyramids were also exploited as seeds for CdS pods growth, and the peculiar shape of the derived branched nanostructures clearly arises from the inverted polarity of the seeds.

  5. Pyramid-Shaped Wurtzite CdSe Nanocrystals with Inverted Polarity.

    Science.gov (United States)

    Ghosh, Sandeep; Gaspari, Roberto; Bertoni, Giovanni; Spadaro, Maria Chiara; Prato, Mirko; Turner, Stuart; Cavalli, Andrea; Manna, Liberato; Brescia, Rosaria

    2015-08-25

    We report on pyramid-shaped wurtzite cadmium selenide (CdSe) nanocrystals (NCs), synthesized by hot injection in the presence of chloride ions as shape-directing agents, exhibiting reversed crystal polarity compared to former reports. Advanced transmission electron microscopy (TEM) techniques (image-corrected high-resolution TEM with exit wave reconstruction and probe-corrected high-angle annular dark field-scanning TEM) unequivocally indicate that the triangular base of the pyramids is the polar (0001̅) facet and their apex points toward the [0001] direction. Density functional theory calculations, based on a simple model of binding of Cl(-) ions to surface Cd atoms, support the experimentally evident higher thermodynamic stability of the (0001̅) facet over the (0001) one conferred by Cl(-) ions. The relative stability of the two polar facets of wurtzite CdSe is reversed compared to previous experimental and computational studies on Cd chalcogenide NCs, in which no Cl-based chemicals were deliberately used in the synthesis or no Cl(-) ions were considered in the binding models. Self-assembly of these pyramids in a peculiar clover-like geometry, triggered by the addition of oleic acid, suggests that the basal (polar) facet has a density and perhaps type of ligands significantly different from the other three facets, since the pyramids interact with each other exclusively via their lateral facets. A superstructure, however with no long-range order, is observed for clovers with their (0001̅) facets roughly facing each other. The CdSe pyramids were also exploited as seeds for CdS pods growth, and the peculiar shape of the derived branched nanostructures clearly arises from the inverted polarity of the seeds. PMID:26203791

  6. A novel strategy towards designing a CdSe quantum dot-metallohydrogel composite material.

    Science.gov (United States)

    Chatterjee, Sayantan; Maitra, Uday

    2016-08-11

    We have described here an efficient method to disperse hydrophobic CdSe quantum dots (QDs) in an aqueous phase using cetyltrimethylammonium bromide (CTAB) micelles without any surface ligand exchange. The water soluble QDs were then embedded in 3D self assembled fibrillar networks (SAFINs) of a hydrogel showing homogeneous dispersibility as evidenced from optical and electron microscopic techniques. The photophysical studies of the hydrogel-QD composite are reported for the first time. These composite materials may have potential applications in biology, optoelectronics, sensors, non-linear optics and materials science.

  7. Surface plasmon propelled high-performance CdSe nanoribbons photodetector.

    Science.gov (United States)

    Luo, Lin-Bao; Xie, Wei-Jie; Zou, Yi-Feng; Yu, Yong-Qiang; Liang, Feng-Xia; Huang, Zi-Jun; Zhou, Ke-Ya

    2015-05-18

    In this work, we present a plasmonic photodetector (PPD) with high sensitivity to red light illumination. The ultrasensitive PPD was composed of high-crystalline CdSe nanoribbons (NRs) decorated with plasmonic hollow gold nanoparticles (HGNs) on the surface, which were capable of coupling the incident light due to localized surface plasmon resonance (LSPR). Device analysis reveals that after modification of HGNs, both responsivity and detectivity were considerably improved. Further device performance analysis and theoretical simulation based on finite element method (FEM) find that the optimized performance is due to HGNs induced localized field enhancement and direct electron transfer. PMID:26074550

  8. Selenium Redox Reactivity on Colloidal CdSe Quantum Dot Surfaces.

    Science.gov (United States)

    Tsui, Emily Y; Hartstein, Kimberly H; Gamelin, Daniel R

    2016-09-01

    Understanding the structural and compositional origins of midgap states in semiconductor nanocrystals is a longstanding challenge in nanoscience. Here, we report a broad variety of reagents useful for photochemical reduction of colloidal CdSe quantum dots, and we establish that these reactions proceed via a dark surface prereduction step prior to photoexcitation. Mechanistic studies relying on the specific properties of various reductants lead to the proposal that this surface prereduction occurs at oxidized surface selenium sites. These results demonstrate the use of small-molecule inorganic chemistries to control the physical properties of colloidal QDs and provide microscopic insights into the identities and reactivities of their localized surface species. PMID:27518320

  9. Nanoparticle Concentration Effects on Kinetic Stability of CdSe Quantum Dots in Waters

    Science.gov (United States)

    Wan, J.; Kim, Y.; Tokunaga, T. K.

    2009-12-01

    Many recent laboratory studies on nanoparticle (NP) behavior used highly concentrated particle suspensions (up to several mM concentrations), largely to overcome instrument detection limits. In potentially engineered-NP impacted aquatic systems NP-concentrations can vary many orders of magnitude lower depending on the pathways of their release. We investigated NP concentration effects on kinetic stability of CdSe quantum dots (QDs), that have CdSe core diameter of 4.4 ±0.2 nm (by TEM), and the mercaptoundecanoic acid (MUA) coatings. The term stability is used to describe resistance to NP aggregation/coagulation and precipitation. We measured stability ratios of varied NP suspension concentrations, 10 to 0.1 mM (atom-based concentrations), under stability-favorable pH condition, and ionic strength (IS) from 1.0 mM to 2.0 M NaCl. In addition to determining short-term stability (10 seconds to 60 minute), we also measured long-term stability, up to 2 months (in order to observe precipitation). The results were compared with DLVO predictions using calculated Hamaker constants for MUA-coated CdSe QDs). Our data indicate that at the high concentrations (≥ 1.4 mM), CdSe QDs are extremely stable under low IS and favorable pH conditions, staying monodispersed for beyond the long experiment duration. Surprisingly, decreasing NP concentrations to coagulation (coagulation the aggregates were relatively stable in suspensions, with larger aggregate sizes in more diluted solutions, suspended in water for beyond the long experiment duration. Measured electrokinetic properties of NP suspensions at different concentrations are presented, and mechanisms are discussed. The phenomena observed in this study may be extended to some of other types of charge-stabilized engineered NPs, and their impacts on transport and bioavailability can be inferred. Funding for this study was provided by the U.S. Department of Energy, the joint BER-EPA-NSF nanoparticulate research program.

  10. Synthesis and analysis of ZnO and CdSe nanoparticles

    Indian Academy of Sciences (India)

    Shriwas S Ashtaputre; Aparna Deshpande; Sonali Marathe; M E Wankhede; Jayashree Chimanpure; Renu Pasricha; J Urban; S K Haram; S W Gosavi; S K Kulkarne

    2005-10-01

    Zinc oxide and cadmium selenide particles in the nanometer size regime have been synthesized using chemical routes. The particles were capped using thioglycerol in case of ZnO and 2-mercaptoethanol in case of CdSe to achieve the stability and avoid the coalescence. Zinc oxide nanoparticles were doped with europium to study their optical properties. A variety of techniques like UV-Vis absorption spectroscopy, X-ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles.

  11. Multicolored silica coated CdSe core/shell quantum dots

    Science.gov (United States)

    Goftman, Valentina V.; Markin, Alexey V.; De Saeger, Sarah; Goryacheva, Irina Y.

    2016-04-01

    Silanization is a convenient route to provide water-solubility to the quantum dots (QDs) with different structure. Green, orange and red emitting CdSe-based QDs were synthesized by varying of number and material of wider-band gap shells and fluorescent properties of QDs were characterized before and after silanization. It was shown that structure of the QD influences on the quantum yield of the silanized QDs: the better CdSe core is protected with wider-band gap semiconductor shells, the more fluorescence properties remain after silica coated QD possess. Hence silica coated QDs have a great perspectives for the multiplex analysis.

  12. Synthesis of CdSe quantum dots via paraffin liquid and oleic acid

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    This paper reported an efficient and rapid method to produce highly monodispersed CdSe quantum dots (QDs), in which the traditional tri10ylphosphine oxide (TOPO) was replaced by paraffin liquid as solvent and oleic acid as the reacting media. The experimental conditions and the properties of QDs had been studied in detail. The resulting samples were confirmed of uniform size distribution with transmission electronic microscopy (TEM), while UV-vis absorption and photoluminescence (PL) spectra clearly indicated that such synthesized QDs had good fluorescence properties.

  13. Physical and chemical analyses on single source precursor growth CdSe semiconductor nanomaterials

    International Nuclear Information System (INIS)

    CdSe nanocrystals (NCs) are synthesized by the single source precursor thermal method. The use of a temperature ramp allows to obtain faster elaboration and smaller nano-particles in size. A cross-disciplinary study between chemical analyses and physical techniques provides consistent data for these small size NCs. Joint mass spectroscopy, transmission electron microscopy and optical spectrometry techniques give a coherent picture about average size and size dispersion of the NCs, as well as their optical spectral response in correlation with their size via quantum confinement effects.

  14. Radiative parameters of Eu{sup 3+} ions in CdSe nanocrystal containing silica matrices

    Energy Technology Data Exchange (ETDEWEB)

    Jose, Gijo [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686 560 (India); Thomas, Vinoy [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686 560 (India); Fernandez, Toney T. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686 560 (India); Adiyodi, Amrutha K. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686 560 (India); Joseph, Cyriac [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686 560 (India); Ittyachen, M.A. [Department of Instrumentation, Cochin University of Science and Technology, Cochin 22 (India); Unnikrishnan, N.V. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam-686 560 (India)]. E-mail: nvu50@yahoo.co.in

    2005-03-15

    Optical absorption and emission spectra of Eu{sup 3+}/CdSe nanocrystallites and Eu{sup 3+} in sol-gel silica glass samples are being carried out. From the measured intensities of various absorption bands and applying thermal correction, the three Judd-Ofelt parameters {omega}{sub 2},{omega}{sub 4} and {omega}{sub 6} are evaluated for these glasses. From this theory, various radiative properties like transition probability A, branching ratio {beta}, the radiative lifetime {tau}{sub R}, absorption cross-section {sigma}{sub a} and the emission cross-section {sigma}{sup E} for various levels of these glasses are determined.

  15. Selenium Redox Reactivity on Colloidal CdSe Quantum Dot Surfaces

    Science.gov (United States)

    2016-01-01

    Understanding the structural and compositional origins of midgap states in semiconductor nanocrystals is a longstanding challenge in nanoscience. Here, we report a broad variety of reagents useful for photochemical reduction of colloidal CdSe quantum dots, and we establish that these reactions proceed via a dark surface prereduction step prior to photoexcitation. Mechanistic studies relying on the specific properties of various reductants lead to the proposal that this surface prereduction occurs at oxidized surface selenium sites. These results demonstrate the use of small-molecule inorganic chemistries to control the physical properties of colloidal QDs and provide microscopic insights into the identities and reactivities of their localized surface species. PMID:27518320

  16. Defects in CdSe thin films, induced by high energy electron irradiation

    International Nuclear Information System (INIS)

    Defects induced in CdSe thin films by high energy electron irradiation are investigated by means of thermally stimulated currents (TSC) spectroscopy. Films were obtained by vacuum deposition from a single source and irradiated with a 5 x 1013 electrons/cm2 s-1 beam of 6-MeV energy. It was found that electrical properties of the films are controlled by a deep donor state, located at 0.38 eV below the bottom edge of the conduction band. Parameters of the traps responsible for the recorded TSC peaks were determined. (authors)

  17. Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential

    Institute of Scientific and Technical Information of China (English)

    Zhang Zhi-Dong; Chang Chun-Rui; Ma Dong-Lai

    2009-01-01

    Hybrid nematic films have been studied by Monte Carlo simulations using a lattice spin model,in which the pair potential is spatially anisotropic and dependent on elastic constants of liquid crystals.We confirm in the thin hybrid nematic film the existence of a biaxially nonbent structure and the structarc transition from the biaxial to the bent-director structure,which is similar to the result obtained using the Lebwohl-Lasher model.However,the step-like director's profile,characteristic for the biaxial structure,is spatially asymmetric in the film because the pair potential leads to K1≠K3.We estimate the upper cell thickness to be 69 spin layers,in which the biaxial structure can be found.

  18. Room temperature growth of biaxially aligned yttria-stabilized zirconia films on glass substrates by pulsed-laser deposition

    CERN Document Server

    Li Peng; Mazumder, J

    2003-01-01

    Room temperature deposition of biaxially textured yttria-stabilized zirconia (YSZ) films on amorphous glass substrates was successfully achieved by conventional pulsed-laser deposition. The influence of the surrounding gases, their pressure and the deposition time on the structure of the films was studied. A columnar growth process was revealed based on the experimental results. The grown biaxial texture appears as a kind of substrate independence, which makes it possible to fabricate in-plane aligned YSZ films on various substrates.

  19. Discrete Element Simulations and Experiments on the Deformation of Cohesive Powders in a bi-axial Box

    OpenAIRE

    Imole, O.I.; Kumar, N; Magnanimo, V.; S. Luding

    2012-01-01

    We compare element test experiments and simulations on the deformation of frictional, cohesive particles in a bi-axial box. We show that computer simulations with the Discrete Element Method qualitatively reproduce a uniaxial compression element test in the true bi-axial tester. We highlight the effects of friction and polydispersity on our simulations and present the second stress response namely the deviatoric stress as a function of the deviatoric strain.

  20. Strength Behavior of High Strength R/C Columns under Biaxial Bending-Shear and Varying Axial Load

    OpenAIRE

    MIZOGUCHI, Mitsuo; Arakawa, Takashi; ARAI, Yasuyuki

    1991-01-01

    Twelve short square R/C columns using high-strength concrete were tested to examine the effects of biaxial bending-shear force and varying axial load on the shear and flexural strength behavior. The columns were cyclically deflected either along their transverse principal axis to produce uniaxial bending-shear or along their diagonal to produce biaxial bending-shear. For columns failing in flexure, the experimental results were found to be in close agreement with the computed values given by ...

  1. Fracture assessment of HSST Plate 14 shallow-flaw cruciform bend specimens tested under biaxial loading conditions

    Energy Technology Data Exchange (ETDEWEB)

    Bass, B.R.; McAfee, W.J.; Williams, P.T.; Pennell, W.E.

    1998-06-01

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow, surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies, namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states.

  2. Fracture assessment of HSST Plate 14 shallow-flaw cruciform bend specimens tested under biaxial loading conditions

    International Nuclear Information System (INIS)

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow, surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies, namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states

  3. Electrochemiluminescence biosensor based on CdSe quantum dots for the detection of thrombin

    International Nuclear Information System (INIS)

    A novel QDs electrochemiluminescence (ECL) biosensor for the determination of thrombin was described. The CdSe QDs solution was dripped onto the clear surface of the ITO and then immersed in PBS which contained EDC and NHS as a coupling agent to activate the carboxyl-terminated surface of the CdSe QDs. The ITO electrode was immersed in the PBS containing 0.4 μM aptamer, followed by rinsing with PBS and dried with N2 again, then dipped in the BSA solution for 30 min to decrease the non-specific binding. After that, the aptamer modified ITO was soaked in PBS to remove unbound aptamer. Under optimal conditions, the linear range was obtained from 0 to 64 μg mL−1 with a correlation coefficient of 0.9986 (n = 16). The control experiment was also carried out by using BSA, lysozyme and IgG in the absence of thrombin. The results showed that the aptasensor had good specificity, stability and reproducibility to the thrombin. Moreover, the aptasensor could be used for detection of real sample with consistent results in comparison with those obtained by electrochemical method which could provide a promising platform for fabrication of aptamer based biosensors.

  4. Optical properties of electrically pumped CdSe quantum dot structures

    International Nuclear Information System (INIS)

    CdSe quantum dots (QDs) embedded into MgS barriers possess a high potential as active material for single photon emitters working at room temperature in the green spectral region because of the enhanced confinement of the carriers leading to an improved luminescence stability. We will present micro-electroluminescence (μ-EL) measurements on a resonant-cavity light emitting diode (RCLED) which was grown by molecular beam epitaxy containing an active region consisting of self-assembled CdSe QDs in a cavity and a distributed Bragg reflector. In this presentation we will focus on integrated μ-EL intensity measurements of the QD ensemble and single-QD emission lines in dependence on the applied voltage and sample temperature. The comparison of the results achieved for single QDs leads to an estimate of the sample temperature at the position of the active region during LED operation. In addition, we will compare these results to micro-photoluminescence measurements which were performed at the same sample position including the discussion of the change of PL characteristic by the variation of the external electric field

  5. Single-step electrodeposition of polycrystalline CdSe microwire arrays: structural and optical properties

    Energy Technology Data Exchange (ETDEWEB)

    Riveros, G. [Universidad de Valparaiso, Facultad de Ciencias, Valparaiso (Chile); Vasquez, J. [Universidad Tecnologica Metropolitana, Departamento de Quimica, Facultad de Ciencias Naturales, Matematicas y del Medio ambiente, Santiago de Chile (Chile); Gomez, H. [Universidad Catolica de Valparaiso, Facultad de Ciencias, Valparaiso (Chile); Makarova, T. [Umeaa University, Department of Physics, Umeaa (Sweden); Silva, D.; Marotti, R.E.; Dalchiele, E.A. [Instituto de Fisica, Facultad de Ingenieria, Montevideo (Uruguay)

    2008-03-15

    In this work we report on the single-step synthesis of CdSe microwires with good crystalline characteristics by template-assisted electrochemical deposition from an electrolytic solution containing CdSO{sub 4}+SeO{sub 2} and sulfuric acid. Deposition was conducted at three different temperatures (25 C, 60 C and 80 C) under potentiostatic control using a commercial nanoporous alumina membrane as the working electrode. The best results were obtained when the electrodeposition was carried out at E=-0.610 V vs. Ag/AgCl and T=80 C. Under these experimental conditions, the microwires are uniform, well aligned, have a high packing density, and present a good crystalline character according to XRD analysis. TEM observations revealed that they are dense and continuous, with a mean diameter ranging from 360-380 nm, greater than the channel diameters of the alumina template used. A detailed study of the reflectance in the region close to CdSe bandgap energy allows the determination of a weak direct absorption edge at 1.65 eV, close to the bulk bandgap energy. The Raman spectra consist of a strong mode centered at 208 cm{sup -1} arising from the LO phonon and a somewhat weak, but still strong, mode arising from the second order LO(2LO) appearing at 415 cm{sup -1}. (orig.)

  6. Synthesis and characterization of CdSe semiconductor nanoparticles by ultrasonic irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Behboudnia, M. [Department of Physics, University of Mohaghegh Ardebily, P.O. Box 179, Ardebil (Iran, Islamic Republic of)]. E-mail: mbehboudnia@yahoo.com; Azizianekalandaragh, Y. [Department of Physics, Baku State University, Z. Khalilov Str. 23, Baku (Azerbaijan)

    2007-03-15

    Cubic CdSe nanoparticles have been prepared using cadmium acetate dihydrate (C{sub 4}H{sub 6}CdO{sub 4}.2H{sub 2}O) as a Cd{sup 2+} ion source and sodium selenosulfate (Na{sub 2}SeSO{sub 3}) as a Se{sup 2-} ion source with the aid of ultrasound irradiation in normal laboratory conditions at room temperature (27 deg. C). Scanning electron microscope (SEM) images display that the product consists of nanocrystallites of about 20 nm which aggregated in the form of polydispersive nanoclusters with dimensions in the range of 150-200 nm. X-ray diffraction analysis exhibits that the particles are excellently crystallized. Energy dispersive X-ray spectroscopy (EDX) measurements further confirms the formation of purely CdSe nanoparticles and average atomic percentage of Cd to Se is about 52:48; showing that the product is almost stoichiometric. UV-visible absorption spectroscopy of the as prepared nanoparticles shows the presence of direct transition with energy band gap of about 2.02 eV. Comparing to 1.74 eV, corresponding to its bulk value, a blue shift of about 0.28 eV is detected which is understood as a quantum size effect, due to confinement of electron and hole in a small volume.

  7. Comparison of three empirical force fields for phonon calculations in CdSe quantum dots

    Science.gov (United States)

    Kelley, Anne Myers

    2016-06-01

    Three empirical interatomic force fields are parametrized using structural, elastic, and phonon dispersion data for bulk CdSe and their predictions are then compared for the structures and phonons of CdSe quantum dots having average diameters of ˜2.8 and ˜5.2 nm (˜410 and ˜2630 atoms, respectively). The three force fields include one that contains only two-body interactions (Lennard-Jones plus Coulomb), a Tersoff-type force field that contains both two-body and three-body interactions but no Coulombic terms, and a Stillinger-Weber type force field that contains Coulombic interactions plus two-body and three-body terms. While all three force fields predict nearly identical peak frequencies for the strongly Raman-active "longitudinal optical" phonon in the quantum dots, the predictions for the width of the Raman peak, the peak frequency and width of the infrared absorption peak, and the degree of disorder in the structure are very different. The three force fields also give very different predictions for the variation in phonon frequency with radial position (core versus surface). The Stillinger-Weber plus Coulomb type force field gives the best overall agreement with available experimental data.

  8. High-Temperature Microfluidic Synthesis of CdSe Nanocrystals inNanoliter Droplets

    Energy Technology Data Exchange (ETDEWEB)

    Chan, Emory M.; Alivisatos, A. Paul; Mathies, Richard A.

    2005-06-09

    The high-temperature synthesis of CdSe nanocrystals innanoliter-volume droplets flowing in a perfluorinated carrier fluidthrough a microfabricated reactor is presented. A flow-focusing nanojetstructure with a step increase in channel height reproducibly generatedoctadecene droplets in Fomblin Y 06/6 perfluorinated polyether atcapillary numbers up to 0.81 and with a droplet:carrier fluid viscosityratio of 0.035. Cadmium and selenium precursors flowing in octadecenedroplets through a high-temperature (240-300 degrees C) glassmicroreactor produced high quality CdSe nanocrystals, as verified byoptical spectroscopy and transmission electron microscopy. Isolating thereaction solution in droplets prevented particle deposition andhydrodynamic dispersion, allowing the reproducible synthesis ofnanocrystals at three different temperatures and four different residencetimes in the span of four hours. Our synthesis of a wide range ofnanocrystals at high temperatures, high capillary numbers, and lowviscosity ratio illustrates the general utility of droplet-basedmicrofluidic reactors to encapsulate nanoliter volumes of organic oraqueous solutions and to precisely control chemical or biochemicalreactions.

  9. Templating growth of gold nanostructures with a CdSe quantum dot array

    Science.gov (United States)

    Paul, Neelima; Metwalli, Ezzeldin; Yao, Yuan; Schwartzkopf, Matthias; Yu, Shun; Roth, Stephan V.; Müller-Buschbaum, Peter; Paul, Amitesh

    2015-05-01

    In optoelectronic devices based on quantum dot arrays, thin nanolayers of gold are preferred as stable metal contacts and for connecting recombination centers. The optimal morphology requirements are uniform arrays with precisely controlled positions and sizes over a large area with long range ordering since this strongly affects device performance. To understand the development of gold layer nanomorphology, the detailed mechanism of structure formation are probed with time-resolved grazing incidence small-angle X-ray scattering (GISAXS) during gold sputter deposition. Gold is sputtered on a CdSe quantum dot array with a characteristic quantum dot spacing of ~7 nm. In the initial stages of gold nanostructure growth, a preferential deposition of gold on top of quantum dots occurs. Thus, the quantum dots act as nucleation sites for gold growth. In later stages, the gold nanoparticles surrounding the quantum dots undergo a coarsening to form a complete layer comprised of gold-dot clusters. Next, growth proceeds dominantly via vertical growth of gold on these gold-dot clusters to form an gold capping layer. In this capping layer, a shift of the cluster boundaries due to ripening is found. Thus, a templating of gold on a CdSe quantum dot array is feasible at low gold coverage.

  10. Photovoltaic devices from CdSe nanocrystals and conjugated polymer composites

    Institute of Scientific and Technical Information of China (English)

    LIU Yanshan; WANG Li; CAO Yong

    2007-01-01

    The preparation of CdSe nanospheres (ns-CdSe) and their application as electron acceptor in conjugated polymer photovoltaic devices are reported, ns-CdSe with diameters of 5 nm were prepared through an organometallic method. The transmission electron microscopy (TEM),ultraviolet-visible (UV-Vis) absorption and photolumines-cence (PL) spectra indicate that the CdSe nanocrystals (NCs) are monodispersed nanospheres with the first exciton absorption peak at around 625 nm and the emission peakat around 652 nm. The PL spectra of the ns-CdSe/polymer composite films show that the PL of the conjugated polymers is effectively quenched upon the addition of ns-CdSe.Photovoltaic devices were fabricated from the compositesof ns-CdSe and poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) or poly(3-hexylthiophene)(P3HT). Under AM 1.5 illumination (100 mW/cm2), the short circuit current (ISC), open circuit voltage (V), fill factor (FF)and energy conversion efficiency (η) reached 1.56 mA/cm2,0.75 V, 34.5% and 0.40%, respectively for device from the ns-CdSe/MEH-PPV (15:1 by weight) and 1.93 mA/cm2,0.65 V, 38.4% and 0.48%, respectively for device from the ns-CdSe/P3HT (10 : 1 by weight).

  11. Efficient intranuclear gene delivery by CdSe aqueous quantum dots electrostatically-coated with polyethyleneimine

    International Nuclear Information System (INIS)

    Quantum dots (QDs) are semiconducting nanoparticles with photoluminescence properties that do not photobleach. Due to these advantages, using QDs for non-viral gene delivery has the additional benefit of being able to track the delivery of the genes in real time as it happens. We investigate the efficacy of mercaptopropionic acid (MPA)-capped CdSe aqueous quantum dots (AQDs) electrostatically complexed with branched polyethyleneimine (PEI) both as a non-viral gene delivery vector and as a fluorescent probe for tracking the delivery of genes into nuclei. The MPA-capped CdSe AQDs that were completely synthesized in water were the model AQDs. A nominal MPA:Cd:Se = 4:3:1 was chosen for optimal photoluminescence and zeta potential. The gene delivery study was carried out in vitro using a human colon cancer cell line, HT29 (ATCC). The model gene was a plasmid DNA (pDNA) that can express red fluorescent protein (RFP). Positively charged branched PEI was employed to provide a proton buffer to the AQDs to allow for endosomal escape. It is shown that by using a PEI-AQD complex with a PEI/AQD molar ratio of 300 and a nominal pDNA/PEI-AQD ratio of 6, we can achieve 75 ± 2.6% RFP expression efficiency with cell vitality remaining at 78 ± 4% of the control. (paper)

  12. Structure determination of the high-pressure phase of CdSe

    International Nuclear Information System (INIS)

    Structural phase transition sequence of CdSe has been investigated at pressures up to 60 GPa under quasi-hydrostatic conditions using synchrotron X-ray diffraction. A phase transition from the wurtzite type (B4) to the NaCl-type (B1) structure has been observed, followed by another phase transition to an orthorhombic structure at 27 GPa, in agreement with previous reports. We show that this high-pressure orthorhombic phase has a Pnma symmetry rather than being a Cmcm-symmetric structure as previously suggested. From our observations, the appearance of the new reflections and reflection splitting with increasing pressure is due to the change of atomic relative positions in crystal lattice and the difference in the compression ratio of lattice parameters for the Pnma structure, and we find no evidence for the third phase transition reported previously. The pressure-induced phase transition of CdSe has been further confirmed by the density-functional theory calculations.

  13. Evaluation of constraint methodologies applied to a shallow-flaw cruciform bend specimen tested under biaxial loading conditions

    International Nuclear Information System (INIS)

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a prototypic, far-field. out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for RPV materials. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies. namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness, the conventional maximum principal stress criterion indicated no effect

  14. White Light Electroluminescence by Organic-Inorganic Heterostructures with CdSe Quantum Dots as Red Light Emitters

    Directory of Open Access Journals (Sweden)

    Ilker Oner

    2011-01-01

    Full Text Available We have developed a white organic light-emitting diode featuring a double emission layer comprising a blue light-emitting conductive polymer as a host material for Cadmium Selenide (CdSe quantum dots as red light emitters and tris-(8-hydroxyquinoline aluminium thin layer for green light emission. The Commission Internationale de l'Eclairage coordinates of the emitting light of the device were found to be (0.32, 0.40 which were only slightly changed over a range of applied voltages between 5 and 10 volts. The use of CdSe nanocrystalline quantum dots (surface-stabilized with hexadecylamine/trioctylphosphine oxide ligands in the hybrid heterostructure with poly(9,9-di-n-octylfluorenyl-2,7-diyl conductive polymer was studied for a variety of CdSe concentrations developing the performance of the device in means of overcoming segregation problems in the blend. Besides, constituents' ratio was further examined for the exploration of possible energy transfer from polymer host material to the CdSe quantum dots as a key factor for well-balanced emission in the electroluminescent devices.

  15. Study of optical and structural properties of CdSe quantum dot embedded in PVA polymer matrix

    International Nuclear Information System (INIS)

    To enhance the properties and applicability of devices it is essential to incorporate semiconductor nanoparticles into polymer matrix. This introduces a new branch of science which includes device fabrications such as gas sensors, nonlinear optics, catalysis etc. Herein, we have synthesized CdSe/PVA nanocomposite (NC) material using wet chemical synthesis technique. The XRD studies revealed the formation of crystalline structure of CdSe nanoparticles (NP’s) and PVA NC’s with an average size of 100 nm and 5 nm respectively. Energy band gap is determined using UV-VIS Spectroscopy. A red shift in the absorption edge of CdSe/PVA NC is observed with respect to CdSe Np’s, The photoluminescence spectra also show red shift for CdSe/PVA NC as compared to CdSe NP’s Thus the use of CdSe/PVA for solar cell application would be more preferable than CdSe NP’s

  16. Adsorption behavior and current-voltage characteristics of CdSe nanocrystals on hydrogen-passivated silicon

    DEFF Research Database (Denmark)

    Walzer, Karsten; Quaade, Ulrich; Ginger, D.S.;

    2002-01-01

    Using scanning tunneling microscopy and spectroscopy we have studied both the geometric distribution and the conduction properties of organic shell capped CdSe nanocrystals adsorbed on hydrogen-passivated Si(100). At submonolayer concentrations, the nanocrystal distribution on the surface was fou...

  17. Study of the Spectral Properties of Nanocomposites with CdSe Quantum Dots in a Wide Range of Low Temperatures

    OpenAIRE

    Magaryan K.A.; Eremchev I.Y.; Karimullin K.R.; Knyazev M.V.; Mikhailov M.A.; Vasilieva I.A.; Klimusheva G.V.

    2015-01-01

    Luminescence spectra of the colloidal solution of CdSe quantum dots (in toluene) were studied in a wide range of low temperatures. Samples were synthesized in the liquid crystal matrix of cadmium octanoate (CdC8). A comparative analysis of the obtained data with previous results was performed.

  18. Study of the Spectral Properties of Nanocomposites with CdSe Quantum Dots in a Wide Range of Low Temperatures

    Directory of Open Access Journals (Sweden)

    Magaryan K.A.

    2015-01-01

    Full Text Available Luminescence spectra of the colloidal solution of CdSe quantum dots (in toluene were studied in a wide range of low temperatures. Samples were synthesized in the liquid crystal matrix of cadmium octanoate (CdC8. A comparative analysis of the obtained data with previous results was performed.

  19. Bio-templated CdSe quantum dots green synthesis in the functional protein, lysozyme, and biological activity investigation

    International Nuclear Information System (INIS)

    Bifunctional fluorescence (CdSe Quantum Dots) – protein (Lysozyme) nanocomposites were synthesized at room temperature by a protein-directed, solution-phase, green-synthetic method. Fluorescence (FL) and absorption spectra showed that CdSe QDs were prepared successfully with Lyz. The average particle size and crystalline structure of QDs were investigated by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively. With attenuated total reflection-fourier transform infrared (ATR-FTIR) spectra and thermogravimetric (TG) analysis, it was confirmed that there is interaction between QDs and amide I, amide II groups in Lyz. FL polarization was measured and FL imaging was done to monitor whether QDs could be responsible for possible changes in the conformation and activity of Lyz. Interestingly, the results showed Lyz still retain the biological activity after formation of QDs, but the secondary structure of the Lyz was changed. And the advantage of this synthesis method is producing excellent fluorescent QDs with specifically biological function. -- Highlights: ► Lysozyme-directed green synthesis of CdSe quantum dots. ► Lysozyme still retain the biological activity after formation of CdSe. ► The method is the production of fluorescent QDs with highly specific and functions.

  20. Green synthesis of highly efficient CdSe quantum dots for quantum-dots-sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn; Chen, Guorong, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Zhang, Bo [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China)

    2014-05-21

    Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30 nm, and absorption peak from 475 nm to 510 nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO{sub 2} electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO{sub 2}'s to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO{sub 2}. The resulting green synthesized CdSe QDSCs with Cu{sub 2}S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

  1. The synthesis of CdSe quantum dots with carboxyl group and study on their optical characteristics

    International Nuclear Information System (INIS)

    Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Green synthesis of highly efficient CdSe quantum dots for quantum-dots-sensitized solar cells

    International Nuclear Information System (INIS)

    Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30 nm, and absorption peak from 475 nm to 510 nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO2 electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO2's to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO2. The resulting green synthesized CdSe QDSCs with Cu2S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%

  3. Hyperbranched polyether hybrid nanospheres with CdSe quantum dots incorporated for selective detection of nitric oxide

    DEFF Research Database (Denmark)

    Liu, Shuiping; Jin, Lanming; Chronakis, Ioannis S.;

    2014-01-01

    In this work, hybrid nanosphere vehicles consisting of cadmium selenide quantum dots (CdSe QDs) were synthesized for nitric oxide (NO) donating and real-time detecting. The nanospheres with QDs being encapsulation have spherical outline with dimension of ~127 nm. The fluorescence properties...

  4. Controlled synthesis and optical properties of tunable CdSe quantum dots and effect of pH

    International Nuclear Information System (INIS)

    Cadmium selenide (CdSe) quantum dots (Q-dots) were prepared by using non-coordinating solvent octadecene instead of coordinating agent trioctylphosphine oxide (TOPO). Reaction processes were carried out at various temperatures of 240°, 260°, 280° and 300° C under nitrogen atmosphere. The prepared CdSe Q-dots which are highly stable show uniform size distribution and tunable optical absorption and photoluminescence (PL). The growth temperature significantly influenced the particle size; spectral behavior, energy band gap and PL intensity and the full width at half maxima (FWHM). Three different methods were employed to determine the particle size and the average particle size of the CdSe Q-dots is 3.2 - 4.3 nm, grown at different temperatures. In addition, stable and mono-dispersed water soluble CdSe Q-dots were prepared by the ligand exchange technique. Thus, the water soluble Q-dots, which are sensitive to the basic pH may be important for biological applications

  5. Study of optical and structural properties of CdSe quantum dot embedded in PVA polymer matrix

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, Chetna, E-mail: ctyagi05@gmail.com; Sharma, Ambika, E-mail: ambikasharma2004@yahoo.com [Department of Applied Sciences ITM University, HUDA Sector-23 A, Gurgaon, 122017 (Haryana) INDIA (India)

    2015-08-28

    To enhance the properties and applicability of devices it is essential to incorporate semiconductor nanoparticles into polymer matrix. This introduces a new branch of science which includes device fabrications such as gas sensors, nonlinear optics, catalysis etc. Herein, we have synthesized CdSe/PVA nanocomposite (NC) material using wet chemical synthesis technique. The XRD studies revealed the formation of crystalline structure of CdSe nanoparticles (NP’s) and PVA NC’s with an average size of 100 nm and 5 nm respectively. Energy band gap is determined using UV-VIS Spectroscopy. A red shift in the absorption edge of CdSe/PVA NC is observed with respect to CdSe Np’s, The photoluminescence spectra also show red shift for CdSe/PVA NC as compared to CdSe NP’s Thus the use of CdSe/PVA for solar cell application would be more preferable than CdSe NP’s.

  6. A sensitive electrochemical aptasensor based on water soluble CdSe quantum dots (QDs) for thrombin determination

    Energy Technology Data Exchange (ETDEWEB)

    Li Yanfen; Han Min [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); Bai Hongyan [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); College of Biological and Chemical Engineering, Jiaxing College, Jiaxing 314001 (China); Wu Yong [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); Dai Zhihui, E-mail: daizhihuii@njnu.edu.cn [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); Bao Jianchun, E-mail: baojianchun@njnu.edu.cn [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China)

    2011-08-01

    A novel aptamer biosensor with easy operation and good sensitivity, specificity, stability and reproducibility was developed by immobilizing the aptamer on water soluble CdSe quantum dots (QDs) modified on the top of the glassy carbon electrode (GCE). Methylene blue (MB) was intercalated into the aptamer sequence and used as an electrochemical marker. CdSe QDs improved the electrochemical signal because of their larger surface area and ion centers of CdSe QDs may also had a major role on amplifying the signal. The higher ion concentration caused more combination of aptamer which caused larger signal. The thrombin was detected by differential pulse voltammetry (DPV) quantitatively. Under optimal conditions, the two linear ranges were obtained from 3 to 13 {mu}g mL{sup -1} and from 14 to 31 {mu}g mL{sup -1}, respectively. The detection limit was 0.08 {mu}g mL{sup -1} at 3{sigma}. The constructed biosensor had better responses compared with that in the absence of the CdSe QDs immobilizing. The control experiment was also carried out by using BSA, casein and IgG in the absence of thrombin. The results showed that the aptasensor had good specificity, stability and reproducibility to the thrombin. Moreover, the aptasensor could be used for detection of real sample with consistent results in comparison with those obtained by fluorescence method which could provide a promising platform for fabrication of aptamer based biosensors.

  7. CdSe quantum dot in vertical ZnSe nanowire and photonic wire for efficient single-photon emission

    DEFF Research Database (Denmark)

    Cremel, Thibault; Bellet-Amalric, Edith; Cagnon, Laurent;

    conformal dielectric coating of Al2O3 on the NW-QDs using Atomic Layer Deposition so that a photonic wire is formed with the CdSe QD deterministically positioned on its axis. The collection enhancement effect is studied by measuring the emission (with pulse excitation, at saturation intensity) of single...

  8. Synthesis of Tapered CdS Nanobelts and CdSe Nanowires with Good Optical Property by Hydrogen-Assisted Thermal Evaporation

    Directory of Open Access Journals (Sweden)

    Wang Min

    2009-01-01

    Full Text Available Abstract The tapered CdS nanobelts and CdSe nanowires were prepared by hydrogen-assisted thermal evaporation method. Different supersaturation leads to two different kinds of 1D nanostructures. The PL measurements recorded from the as-prepared tapered CdS nanobelts and CdSe nanowires show only a bandgap emission with relatively narrow full-width half maximum, which means that they possess good optical property. The as-synthesized high-quality tapered CdS nanobelts and CdSe nanowires may be excellent building blocks for photonic devices.

  9. Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Mojumder, Satyajit [Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000 (Bangladesh); Amin, Abdullah Al [Department of Mechanical and Aerospace Engineering, Case western Reverse University, Cleveland, Ohio 44106 (United States); Islam, Md Mahbubul, E-mail: mmi122@psu.edu [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

    2015-09-28

    Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

  10. Structural stability and theoretical strength of Cu crystal under equal biaxial loading

    Indian Academy of Sciences (India)

    Jian-Min Zhang; Zhong-Liang Lin; Yan Zhang; Vincent Ji

    2010-02-01

    Cu has been used extensively to replace Al as interconnects in ULSI and MEMS devices. However, because of the difference in the thermal expansion coefficients between the Cu film and the Si substrate, large biaxial stresses will be generated in the Cu film. Thus, the Cu film becomes unstable and even changes its morphologies which affects the device manufacturing yield and ultimate reliability. The structural stability and theoretical strength of Cu crystal under equal biaxial loading have been investigated by combining the MAEAM with Milstein-modified Born stability criteria. The results indicate that, under sufficient tension, there exists a stress-free BCC phase which is unstable and slips spontaneously to a stress-free metastable BCT phase by consuming internal energy. The stable region ranges from −15.131 GPa to 2.803 GPa in the theoretical strength or from −5.801% to 4.972% in the strain respectively.

  11. Biaxial load effects on the crack border elastic strain energy and strain energy rate

    Science.gov (United States)

    Eftis, J.; Subramonian, N.; Liebowitz, H.

    1977-01-01

    The validity of the singular solution (first term of a series representation) is investigated for the crack tip stress and displacement field in an infinite sheet with a flat line crack with biaxial loads applied to the outer boundaries. It is shown that if one retains the second contribution to the series approximations for stress and displacement in the calculation of the local elastic strain energy density and elastic strain energy rate in the crack border region, both these quantities have significant biaxial load dependency. The value of the J-integral does not depend on the presence of the second term of the series expansion for stress and displacement. Thus J(I) is insensitive to the presence of loads applied parallel to the plane of the crack.

  12. Tunable biaxial in-plane compressive strain in a Si nanomembrane transferred on a polyimide film

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Munho; Mi, Hongyi; Cho, Minkyu; Seo, Jung-Hun; Ma, Zhenqiang, E-mail: mazq@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States); Zhou, Weidong [Department of Electrical Engineering, University of Texas at Arlington, Arlington, Texas 76019 (United States); Gong, Shaoqin [Department of Biomedical Engineering and Wisconsin Institute for Discovery, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States)

    2015-05-25

    A method of creating tunable and programmable biaxial compressive strain in silicon nanomembranes (Si NMs) transferred onto a Kapton{sup ®} HN polyimide film has been demonstrated. The programmable biaxial compressive strain (up to 0.54%) was generated utilizing a unique thermal property exhibited by the Kapton HN film, namely, it shrinks from its original size when exposed to elevated temperatures. The correlation between the strain and the annealing temperature was carefully investigated using Raman spectroscopy and high resolution X-ray diffraction. It was found that various amounts of compressive strains can be obtained by controlling the thermal annealing temperatures. In addition, a numerical model was used to evaluate the strain distribution in the Si NM. This technique provides a viable approach to forming in-plane compressive strain in NMs and offers a practical platform for further studies in strain engineering.

  13. New classes of bi-axially symmetric solutions to four-dimensional Vasiliev higher spin gravity

    CERN Document Server

    Sundell, Per

    2016-01-01

    We present new infinite-dimensional spaces of bi-axially symmetric asymptotically anti-de Sitter solutions to four-dimensional Vasiliev higher spin gravity, obtained by modifications of the Ansatz used in arXiv:1107.1217, which gave rise to a Type-D solution space. The current Ansatz is based on internal semigroup algebras (without identity) generated by exponentials formed out of the bi-axial symmetry generators. After having switched on the vacuum gauge function, the resulting generalized Weyl tensor is given by the sum of two generalized Petrov type-D tensors, and the twistor space connections are smooth in twistor space over finite regions of spacetime. We provide evidence for that the linearized twistor space connection can be brought to Vasiliev gauge.

  14. Genuine effectively biaxial left-handed metamaterials due to extreme coupling.

    Science.gov (United States)

    Menzel, Christoph; Alaee, Rasoul; Pshenay-Severin, Ekaterina; Helgert, Christian; Chipouline, Arkadi; Rockstuhl, Carsten; Pertsch, Thomas; Lederer, Falk

    2012-02-15

    Most left-handed metamaterials cannot be described by local effective permittivity or permeability tensors in the visible or near-infrared due to the mesoscopic size of the respective unit cells and the related strong spatial dispersion. We lift this problem and propose a metamaterial exhibiting artificial magnetism that does not suffer from this restriction. The artificial magnetism arises from the extreme coupling between both metallic films forming the unit cell. We show that its electromagnetic response can be properly described by biaxial local constitutive relations. A genuine biaxial left-handed fishnet metamaterial is suggested, which can be realized by atomic layer deposition to fabricate the nanoscaled spacing layers required for extreme coupling.

  15. A twist-bend nematic to an intercalated, anticlinic, biaxial phase transition in liquid crystal bimesogens.

    Science.gov (United States)

    Mandle, Richard J; Goodby, John W

    2016-02-01

    In this article we describe for bimesogens the first observed transition from a "heliconical" twist-bend nematic liquid crystal to a novel biaxial, anticlinic, intercalated lamellar phase. The phase behaviour and structures of both polymorphs is similar to that of polymers, confirming that bimesogens can act as model systems for main chain liquid crystal polymers, and in principle are separate soft-matter branches of self-organising systems. PMID:26626825

  16. Mechanical characterisation of porcine rectus sheath under uniaxial and biaxial tension.

    LENUS (Irish Health Repository)

    Lyons, Mathew

    2014-06-03

    Incisional hernia development is a significant complication after laparoscopic abdominal surgery. Intra-abdominal pressure (IAP) is known to initiate the extrusion of intestines through the abdominal wall, but there is limited data on the mechanics of IAP generation and the structural properties of rectus sheath. This paper presents an explanation of the mechanics of IAP development, a study of the uniaxial and biaxial tensile properties of porcine rectus sheath, and a simple computational investigation of the tissue. Analysis using Laplace׳s law showed a circumferential stress in the abdominal wall of approx. 1.1MPa due to an IAP of 11kPa, commonly seen during coughing. Uniaxial and biaxial tensile tests were conducted on samples of porcine rectus sheath to characterise the stress-stretch responses of the tissue. Under uniaxial tension, fibre direction samples failed on average at a stress of 4.5MPa at a stretch of 1.07 while cross-fibre samples failed at a stress of 1.6MPa under a stretch of 1.29. Under equi-biaxial tension, failure occurred at 1.6MPa with the fibre direction stretching to only 1.02 while the cross-fibre direction stretched to 1.13. Uniaxial and biaxial stress-stretch plots are presented allowing detailed modelling of the tissue either in silico or in a surrogate material. An FeBio computational model of the tissue is presented using a combination of an Ogden and an exponential power law model to represent the matrix and fibres respectively. The structural properties of porcine rectus sheath have been characterised and add to the small set of human data in the literature with which it may be possible to develop methods to reduce the incidence of incisional hernia development.

  17. Non-proportional tension-shear experiments in a biaxial test facility

    OpenAIRE

    Riel, van, A.C.M.J.; Boogaard, van den, F.E.; Huetink, J.

    2006-01-01

    This paper discusses the results obtained from experiments on DC06 mild steel with a biaxial test facility. The two presented tests are non-proportional tests consisting of a two stage strain path. First the samples are deformed in the tensile direction after which simple shear deformation is applied. In the one case elastic unloading is applied after the tensile deformation, while in the other case the tensile deformation is directly followed by the simple shear deformation. For the test wit...

  18. Measuring knife stab penetration into skin simulant using a novel biaxial tension device

    OpenAIRE

    Gilchrist, M. D.; Keenan, S.; Curtis, Michael; et al.,

    2008-01-01

    This paper describes the development and use of a biaxial measurement device to analyse the mechanics of knife stabbings. In medicolegal situations it is typical to describe the consequences of a stabbing incident in relative terms that are qualitative and descriptive without being numerically quantitative. Here, the mechanical variables involved in the possible range of knife-tissue penetration events are considered so as to determine the necessary parameters that would need to be controlled...

  19. Characterization of biaxial mechanical behavior of porcine aorta under gradual elastin degradation

    OpenAIRE

    Zeinali-Davarani, Shahrokh; Chow, Ming-Jay; Turcotte, Raphaël; Zhang, Yanhang

    2013-01-01

    Arteries are composed of multiple constituents that endow the wall with proper structure and function. Many vascular diseases are associated with prominent mechanical and biological alterations in the wall constituents. In this study, planar biaxial tensile test data of elastase-treated porcine aortic tissue (Chow et al. 2012) is re-examined to characterize the altered mechanical behavior at multiple stages of digestion through constitutive modeling. Exponential-based as well as recruitment-b...

  20. Novel biaxial tensile test for studying aortic failure phenomena at a microscopic level

    Directory of Open Access Journals (Sweden)

    Sugita Shukei

    2013-01-01

    Full Text Available Abstract Background An aortic aneurysm is a local dilation of the aorta, which tends to expand and often results in a fatal rupture. Although larger aneurysms have a greater risk of rupture, some small aneurysms also rupture. Since the mechanism of aortic rupture is not well understood, clarification of the microstructure influencing the failure to rupture is important. Since aortic tissues are stretched biaxially in vivo, we developed a technique to microscopically observe the failure of an aortic rupture during biaxial stretch. Methods A thinly sliced porcine thoracic aortic specimen was adhered to a circular frame and pushed onto a cylinder with a smaller diameter to stretch the specimen biaxially. To induce failure to rupture at the center, the specimen was thinned at the center of the hole as follows: the specimen was frozen while being compressed with metal plates having holes, which were 3 mm in diameter at their centers; the specimen was then sliced at 50-μm intervals and thawed. Results The ratio of the thickness at the center to the peripheral area was 99.5% for uncompressed specimens. The ratio decreased with an increase in the compression ratio εc and was 47.3% for specimens with εc = 40%. All specimens could be stretched until failure to rupture. The probability for crack initiation within the cylinder was εc εc >30%, respectively. Among specimens ruptured within the cylinder, 93% of those obtained from the mid-media showed crack initiation at the thin center area. Conclusions Aortic tissues were successfully stretched biaxially until failure, and their crack initiation points were successfully observed under a microscope. This could be a very useful and powerful method for clarifying the mechanism of aortic rupture. We are planning to use this technique for a detailed investigation of events occurring at the point of failure when the crack initiates in the aortic aneurysm wall.

  1. Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

    OpenAIRE

    Xue-wei Liu; Quan-sheng Liu; Shi-bing Huang; Lai Wei; Guang-feng Lei

    2016-01-01

    This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C). On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the...

  2. Biaxial Texture Evolution in MgO Films Fabricated Using Ion Beam-Assisted Deposition

    Science.gov (United States)

    Xue, Yan; Zhang, Ya-Hui; Zhao, Rui-Peng; Zhang, Fei; Lu, Yu-Ming; Cai, Chuan-Bing; Xiong, Jie; Tao, Bo-Wan

    2016-07-01

    The growth of multifunctional thin films on flexible substrates is important technologically, because flexible electronics require such a platform. In this study, we examined the evolution of biaxial texture in MgO films prepared using ion beam-assisted deposition (IBAD) on a Hastelloy substrate. Texture and microstructure developments were characterized through in situ reflection high-energy electron diffraction monitoring, x-ray diffraction, and atomic force microscopy, which demonstrated that biaxial texture was developed during the nucleation stage (~2.2 nm). The best biaxial texture was obtained with a thickness of approximately 12 nm. As MgO continued to grow, the influence of surface energy was reduced, and film growth was driven by the attempt to minimize volume free-energy density. Thus the MgO grains were subsequently rotated at the (002) direction toward the ion beam. In addition, an approach was developed for accelerating in-plane texture evolution by pre-depositing an amorphous MgO layer before IBAD.

  3. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    International Nuclear Information System (INIS)

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials’ life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman–Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures

  4. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    Energy Technology Data Exchange (ETDEWEB)

    Tung, Hsiao-Ming, E-mail: hmtung2@gmail.com [Institute of Nuclear Energy Research, Longtan, Taoyuan 32546, Taiwan, ROC (China); Mo, Kun; Stubbins, James F. [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)

    2014-04-01

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials’ life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman–Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

  5. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    Science.gov (United States)

    Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.

    2014-04-01

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials' life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman-Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

  6. The failure behavior of the cladding with outer surface pre-crack in biaxial stress test

    International Nuclear Information System (INIS)

    Biaxial stress tests using the unirradiated Cold Worked Stress Relieved (CWSR) Zircaloy-4 cladding with an outer surface pre-crack were conducted under room temperature condition. To reproduce the biaxial stress states assumed in RIA conditions, Expansion Due to Compression (EDC) test which induces uniaxial stress states was developed using a tensile test machine. Constant tensile loads, 0, 5.0 and 10.0 kN, were applied to specimens through each test, respectively. All specimens failed in the tests, and the failure morphology was similar to that observed in the PIEs conducted for the pulse irradiation experiments using a high burnup fuel. The longitudinal strain (εtz) at failure clearly increased with increasing tensile loads and the circumferential strain (εtθ) at failure decreased significantly in 5.0 and 10.0 kN tests compared to 0 kN tests. These data obtained in this study are considered as the fundamentals to quantify the failure criteria of claddings in a biaxial stress state. (author)

  7. On the correct interpretation of measured force and calculation of material stress in biaxial tests.

    Science.gov (United States)

    Nolan, D R; McGarry, J P

    2016-01-01

    Biaxial tests are commonly used to investigate the mechanical behaviour of soft biological tissues and polymers. In the current paper we uncover a fundamental problem associated with the calculation of material stress from measured force in standard biaxial tests. In addition to measured forces, localised unmeasured shear forces also occur at the clamps and the inability to quantify such forces has significant implications for the calculation of material stress from simplified force-equilibrium relationships. Unmeasured shear forces are shown to arise due to two distinct competing contributions: (1) negative shear force due to stretching of the orthogonal clamp, and (2) positive shear force as a result of material Poisson-effect. The clamp shear force is highly dependent on the specimen geometry and the clamp displacement ratio, as consequently, is the measured force-stress relationship. Additionally in this study we demonstrate that commonly accepted formulae for the estimation of material stress in the central region of a cruciform specimen are highly inaccurate. A reliable empirical correction factor for the general case of isotropic materials must be a function of specimen geometry and the biaxial clamp displacement ratio. Finally we demonstrate that a correction factor for the general case of non-linear anisotropic materials is not feasible and we suggest the use of inverse finite element analysis as a practical means of interpreting experimental data for such complex materials. PMID:26327453

  8. Fabrication and reliable implementation of an ionic polymer-metal composite (IPMC) biaxial bending actuator

    Science.gov (United States)

    Lee, Gil-Yong; Choi, Jung-Oh; Kim, Myeungseon; Ahn, Sung-Hoon

    2011-10-01

    Ionic polymer-metal composites (IPMCs) are one of the most popular types of electro-active polymer actuator, due to their low electric driving potential, large deformation range, and light weight. IPMCs have been used as actuators or sensors in many areas of biomedical and robotic engineering. In this research, IPMCs were studied as a biaxial bending actuator capable of smart and flexible motion. We designed and fabricated this bending actuator and implemented it to have a reliable actuating motion using a systematic approach. The resulting device was bar shaped with a square cross section and had four insulated electrodes on its surface. By applying different voltages to these four electrodes, a biaxial bending motion can be induced. To construct this actuator, several fabrication processes were considered. We modified the Nafion stacking method, and established a complete sequence of actuator fabrication processes. Using these processes, we were able to fabricate an IPMC biaxial bending actuator with both high actuating force and high flexibility. Several experiments were conducted to investigate and verify the performance of the actuator. The IPMC actuator system was modeled from experimentally measured data, and using this actuator model, a closed-loop proportional integral (PI) controller was designed. Reference position tracking performances of open-loop and closed-loop systems were compared. Finally, circular motion tracking performances of the actuator tip were tested under different rotation frequencies and radii of a reference trajectory circle.

  9. Loading system mechanism for dielectric elastomer generators with equi-biaxial state of deformation

    Science.gov (United States)

    Fontana, M.; Moretti, G.; Lenzo, B.; Vertechy, R.

    2014-03-01

    Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric Elastomer (DE) material. This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes and used for the experimental verification of the employed numerical models.

  10. Flexural strength of dental composite restoratives: comparison of biaxial and three-point bending test.

    Science.gov (United States)

    Chung, S M; Yap, A U J; Chandra, S P; Lim, C T

    2004-11-15

    This study compared two test methods used to evaluate the flexural strength of resin-based dental composites. The two test methods evaluated were the three-point bending test4 and the biaxial flexural test. Materials used in this investigation were from the same manufacturer (3M ESPE) and included microfill (A110), minifill (Z100 and Filtek Z250), polyacid modified (F2000), and flowable [Filtek Flowable (FF)] composites. Flexural strength was determined with the use of both test methods after 1 week of conditioning in water at 37 degrees C. Data were analyzed with the use of an ANOVA/Scheffe test and an independent-samples t test at significance level 0.05. Mean flexural strength (n = 7) ranged from 66.61 to 147.21 and 67.27 to 182.81 MPa for three-point bending and ball-on-three-ball biaxial test methods, respectively. In both test methods, Z100 was significantly stronger than all other composites evaluated. In the three-point bending test, flexural strength of Z250 was significantly higher than A110, F2000 and FF, and FF was significantly stronger than A110 and F2000. The biaxial test method arrived at the same conclusions except that there was no significant difference between Z250 and FF. Pearson's correlation revealed a significantly (p bending test. PMID:15386492

  11. Time-dependent biaxial mechanical behavior of the aortic heart valve leaflet.

    Science.gov (United States)

    Stella, John A; Liao, Jun; Sacks, Michael S

    2007-01-01

    Despite continued progress in the treatment of aortic valve (AV) disease, current treatments continue to be challenged to consistently restore AV function for extended durations. Improved approaches for AV repair and replacement rests upon our ability to more fully comprehend and simulate AV function. While the elastic behavior the AV leaflet (AVL) has been previously investigated, time-dependent behaviors under physiological biaxial loading states have yet to be quantified. In the current study, we performed strain rate, creep, and stress-relaxation experiments using porcine AVL under planar biaxial stretch and loaded to physiological levels (60 N/m equi-biaxial tension), with strain rates ranging from quasi-static to physiologic. The resulting stress-strain responses were found to be independent of strain rate, as was the observed low level of hysteresis ( approximately 17%). Stress relaxation and creep results indicated that while the AVL exhibited significant stress relaxation, it exhibited negligible creep over the 3h test duration. These results are all in accordance with our previous findings for the mitral valve anterior leaflet (MVAL) [Grashow, J.S., Sacks, M.S., Liao, J., Yoganathan, A.P., 2006a. Planar biaxial creep and stress relaxatin of the mitral valve anterior leaflet. Annals of Biomedical Engineering 34 (10), 1509-1518; Grashow, J.S., Yoganathan, A.P., Sacks, M.S., 2006b. Biaxial stress-stretch behavior of the mitral valve anterior leaflet at physiologic strain rates. Annals of Biomedical Engineering 34 (2), 315-325], and support our observations that valvular tissues are functionally anisotropic, quasi-elastic biological materials. These results appear to be unique to valvular tissues, and indicate an ability to withstand loading without time-dependent effects under physiologic loading conditions. Based on a recent study that suggested valvular collagen fibrils are not intrinsically viscoelastic [Liao, J., Yang, L., Grashow, J., Sacks, M.S., 2007

  12. Measuring photoluminescence spectra of self-assembly array nanowire of colloidal CdSe quantum dots using scanning near-field optics microscopy

    Science.gov (United States)

    Bai, Zhongchen; Hao, Licai; Zhang, Zhengping; Qin, Shuijie

    2016-05-01

    A novel periodic array CdSe nanowire is prepared on a substrate of the porous titanium dioxide by using a self-assembly method of the colloidal CdSe quantum dots (QDs). The experimental results show that the colloidal CdSe QDs have renewedly assembled on its space scale and direction in process of losing background solvent and form the periodic array nanowire. The main peak wavelength of Photoluminescence (PL) spectra, which is measured by using a 100-nm aperture laser beam spot on a scanning near-field optics microscopy, has shifted 60 nm with compared to the colloidal CdSe QDs. Furthermore, we have measured smaller ordered nanometer structure in thin QDs area as well, a 343-nm periodic nanowire in thick QDs area and the colloidal QDs in edge of well-ordered nanowire.

  13. Structural Investigations of Surfaces and Orientation-SpecificPhenomena in Nanocrystals and Their Assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Aruguete, Deborah Michiko

    2006-06-17

    Studies of colloidal nanocrystals and their assemblies are presented. Two of these studies concern the atomic-level structural characterization of the surfaces, interfaces, and interiors present in II-VI semiconductor nanorods. The third study investigates the crystallographic arrangement of cobalt nanocrystals in self-assembled aggregates. Crystallographically-aligned assemblies of colloidal CdSe nanorods are examined with linearly-polarized Se-EXAFS spectroscopy, which probes bonding along different directions in the nanorod. This orientation-specific probe is used, because it is expected that the presence of specific surfaces in a nanorod might cause bond relaxations specific to different crystallographic directions. Se-Se distances are found to be contracted along the long axis of the nanorod, while Cd-Se distances display no angular dependence, which is different from the bulk. Ab-initio density functional theory calculations upon CdSe nanowires indicate that relaxations on the rod surfaces cause these changes. ZnS/CdS-CdSe core-shell nanorods are studied with Se, Zn, Cd, and S X-ray absorption spectroscopy (XAS). It is hypothesized that there are two major factors influencing the core and shell structures of the nanorods: the large surface area-to-volume ratio, and epitaxial strain. The presence of the surface may induce bond rearrangements or relaxations to minimize surface energy; epitaxial strain might cause the core and shell lattices to contract or expand to minimize strain energy. A marked contraction of Zn-S bonds is observed in the core-shell nanorods, indicating that surface relaxations may dominate the structure of the nanorod (strain might otherwise drive the Zn-S lattice to accommodate the larger CdS or CdSe lattices via bond expansion). EXAFS and X-ray diffraction (XRD) indicate that Cd-Se bond relaxations might be anisotropic, an expected phenomenon for a rod-shaped nanocrystal. Ordered self-assembled aggregates of cobalt nanocrystals are

  14. Boosting the cell efficiency of CdSe quantum dot sensitized solar cell via a modified ZnS post-treatment

    International Nuclear Information System (INIS)

    Highlights: • Large improvement of the cell efficiency of CdSe QDSSC was achieved through a modified ZnS post-treatment by introducing a ZnSe in between CdSe QDs and ZnS • The introduction of ZnSe in post-treatment increased the cell stability. • The thickness of ZnSe was found to be crucial. • The role of ZnSe is ascribed to the suppression of defects at CdSe/ZnS interfaces and facilitating the growth of ZnS with higher quality. -- Abstract: We report here a large improvement of cell performance of CdSe quantum dot sensitized solar cell (QDSSC) by a modified ZnS post-treatment, being carried out by introducing a ZnSe thin layer before ZnS deposition through a successive ion layer adsorption reaction (SILAR) method. CdSe quantum dots were deposited onto TiO2 surface using a chemical bath deposition method. Photovoltaic measurements showed that the introduction of ZnSe layer can significantly increase the photocurrent of CdSe QDSSC, resulting in a large enhancement of the solar energy conversion efficiency of the cell. On variation of the numbers of ZnSe deposition cycle, the effect of the thickness of ZnSe was investigated. The maximum energy conversion efficiency of 3.46% was achieved for CdSe QDSSC with ZnSe/ZnS treatment, showing a 22% increment compared to that of with ZnS treatment. Moreover, it was found that the introduction of ZnSe improved the stability of CdSe QDSSC. The benefit role of ZnSe was ascribed to its intermediate lattice parameter to CdSe and ZnS, which leads to the suppression of defects at CdSe/ZnS interfaces and facilitating the growth of ZnS with higher quality

  15. Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

    Science.gov (United States)

    Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

    2016-06-15

    Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs.

  16. Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

    Science.gov (United States)

    Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

    2016-06-15

    Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs. PMID:27224958

  17. Photoconductivity of composites based on CdSe quantum dots and low-band-gap polymers

    Science.gov (United States)

    Dayneko, Sergey; Linkov, Pavel; Martynov, Igor; Tameev, Alexey; Tedoradze, Marine; Samokhvalov, Pavel; Nabiev, Igor; Chistyakov, Alexander

    2016-05-01

    Photoconductivity of thin layers prepared by spin coating of blends of CdSe quantum dots (QDs) and a low-band-gap polymer PCDTBT or PTB7 has been studied. It has been found that photocurrent in the composites containing QDs of 10-nm in size is significantly higher than in those of containing 5-nm QDs. Analysis of the results showed that the photoresponse of the thin layers is mainly determined by the relative positions of the frontier energy levels of the materials used, organic semiconductors and QDs. Therefore, the ability to tune the relative positions of these levels by varying the QD size is of special importance, thus allowing the optimization of photodetectors and photovoltaic cells.

  18. Facile and green route to highly luminescent ZnS-shelled CdSe nanocrystals

    Institute of Scientific and Technical Information of China (English)

    YE Xinyu; ZHUANG Weidong; HU Yunsheng; LUO Xinyu; ZHAO Chunlei; HUANG Xiaowei

    2009-01-01

    Highly luminescent CdSe/ZnS nanocrystals were obtained by adapting non-TOP-based synthesis and a subsequent two-phase ZnS shelling procedure: the core CdSe nanocrystals were synthesized in sole solvent paraffin liquid with cadmium oxide, elemental sele-nium, and oleic acid; the deposition of the ZnS shell was conducted by using zinc stearate in toluene and sodium sulfide in deionized water. The green and low-cost route was proved to be more efficient to constrain the size of core nanocrystals while tuning the growth of shell particles, which results in high quantum yields of CdSe/ZnS nanocrystals. The present route is accessible to laborato-ries with limited synthetic expertise to create CdSe/ZnS nanocrystals and easily scaled up to industrial applications.

  19. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    Science.gov (United States)

    Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

  20. Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

    Indian Academy of Sciences (India)

    P K Ghosh; A Ghosal; D Chattopadhyay

    2009-02-01

    Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

  1. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    Directory of Open Access Journals (Sweden)

    Denise Feder

    2011-12-01

    Full Text Available Quantum dots (QDs are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe or cadmium selenium (CdSe forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus.

  2. Photon echo studies of biexcitons and coherences in colloidal CdSe quantum dots

    Science.gov (United States)

    Colonna, Anne E.; Yang, Xiujuan; Scholes, Gregory D.

    2005-04-01

    The cover picture shows the size-dependent photoluminescence from CdSe colloidal quantum dots that were investigated in the work [1]. Ultrafast photon echo experiments were undertaken in conjunction with simulations based on a realistic many-body theory, shown in the picture, to ascertain the significance of many-body contributions to the third-order nonlinear response.The first author Anne E. Colonna undertook this research during a summer internship in the Department of Chemistry, University of Toronto. She is currently pursuing graduate studies at École Polytechnique, Saclay, in the Laboratoire d'Optique et Biosciences.The author Gregory D. Scholes is an Assistant Professor in the Department of Chemistry, University of Toronto. His research interests include synthesis and shape control of quantum dots, as well as the application of ultrafast laser spectroscopy to investigate the electronic structure of inorganic and organic semiconductors.

  3. Aqueous synthesis and characterization of Ni, Zn co-doped CdSe QDs

    Science.gov (United States)

    Thirugnanam, N.; Govindarajan, D.

    2016-01-01

    Ni, Zn co-doped CdSe quantum dots (QDs) were synthesized by chemical precipitation method through aqueous route. The prepared QDs were characterized by X-ray diffraction (XRD) technique, UV-Vis absorption spectroscopy, photoluminescence (PL) spectroscopy and high resolution transmission electron microscopy (HRTEM). XRD technique results indicate that the prepared samples have a zinc blende cubic phase. From UV-Vis absorption spectroscopy technique, the prepared samples were blue shifted with respect to their bulk counter part due to quantum confinement effect. Among different doping ratios examined, a maximum PL emission intensity was observed for CdSe:Ni(1 %):Zn(1 %) QDs. HRTEM pictures show that the prepared QDs were in spherical shape.

  4. Transient charge technique investigation of HgI/sub 2/ and CdSe nuclear detectors

    Energy Technology Data Exchange (ETDEWEB)

    Roth, M.; Burger, A.; Nissenbaum, J.; Schieber, M.

    1987-02-01

    The use of the Transient Charge Technique (TCT) for the evaluation of high resistivity Mercuric Iodide and Cadmium Selenide nuclear radiation detectors is suggested. It has been shown that the real values of mobilities and trapping times of electrons and holes in HgI/sub 2/ can be easily obtained from the analysis of the voltage transient response to drift of charge carriers created by alpha particles. This allows one to evaluate the bulk transport properties of the material and, additionally, to estimate accurately the surface recombination velocity of the carriers. Preliminary results on the shape of voltage transients in CdSe are also reported, and the limitations of the use of the TCT for characterization of both materials are discussed.

  5. Elastic and Thermodynamic Properties of CdSe from First-Principles Calculations

    Institute of Scientific and Technical Information of China (English)

    TAN Jia-Jin; CHENG Yan; ZHU Wen-Jun; GOU Qing-Quan

    2008-01-01

    The lattice parameters,bulk modulus,phase transition pressure,and temperature dependencies of the elastic constants Cij of CdSe are investigated by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of Density Functional Theory (DFT).It is found that the phase transitions from the ZB structure to the RS structure and from WZ structure to RS structure are 2.2 GPa and 2.8 GPa,respectively.Our results agree well with the available experimental data and other theoretical results.The aggregate elastic modulus (B,G,E,A),the Poisson's ratio (v),the Gruneisen parameter (γ),the Debye temperature θD on pressure and temperature are also successfully obtained.

  6. Broad spectral photocurrent enhancement in Au-decorated CdSe nanowires

    KAUST Repository

    Chakraborty, Ritun

    2013-01-01

    Metal-semiconductor hybrid nanostructures promise improved photoconductive performance due to plasmonic properties of the metal portions and intrinsic electric fields at the metal-semiconductor interface that possibly enhance charge separation. Here we report gold decorated CdSe nanowires as a novel functional material and investigate the influence of gold decoration on the lateral facets on the photoconductive properties. Gold decorated nanowires show typically an at least ten-fold higher photocurrent as compared to their bare counterparts. Interestingly, the photocurrent enhancement is wavelength independent, although the plasmon resonance related to the gold particles appears in the absorption spectra. Our experiments show that light scattering and Schottky fields associated with the metal-semiconductor interface are at the origin of the photocurrent enhancement. © 2013 The Royal Society of Chemistry.

  7. Radiative rate modification in CdSe quantum dot-coated microcavity

    Energy Technology Data Exchange (ETDEWEB)

    Veluthandath, Aneesh V.; Bisht, Prem B., E-mail: bisht@iitm.ac.in [Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India)

    2015-12-21

    Whispering gallery modes (WGMs) of the microparticles with spherical or cylindrical symmetry have exceptionally high quality factors and small mode volume. Quantum dots (QDs) are zero dimensional systems with variable band gap as well as luminescent properties with applications in photonics. In this paper, the WGMs have been observed in the luminescence spectra of CdSe QD-coated single silica microspheres. Theoretical estimations of variation of resonance frequency, electric field, and Q-values have been done for a multilayer coating of QDs on silica microspheres. Observed WGMs have been identified for their mode number and polarization using Mie theory. Broadening of modes due to material absorption has been observed. Splitting of WGMs has also been observed due to coherent coupling of counter propagating waves in the microcavity due to the presence of QDs. At room temperature, the time-resolved study indicates the modification of the radiative rate due to coupling of WGMs of the microcavity-QD hybrid system.

  8. Influence of acid and alkaline sources on optical, structural and photovoltaic properties of CdSe nanoparticles precipitated from aqueous solution

    Science.gov (United States)

    Coria-Monroy, C. Selene; Sotelo-Lerma, Mérida; Hu, Hailin

    2016-06-01

    CdSe is a widely researched material for photovoltaic applications. One of the most important parameters of the synthesis is the pH value, since it determines the kinetics and the mechanism of the reaction and in consequence, the optical and morphological properties of the products. We present the synthesis of CdSe in solution with strict control of pH and the comparison of ammonia and KOH as alkaline sources and diluted HCl as acid medium. CdSe formation was monitored with photoluminescence emission spectra (main peak in 490 nm, bandgap of CdSe nanoparticles). XRD patterns indicated that CdSe nanoparticles are mainly of cubic structure for ammonia and HCl, but the hexagonal planes appear with KOH. Product yield decreases with pH and also decreases with KOH at constant pH value since ammonia has a double function, as complexing agent and alkaline source. Changes in morphology were observed in SEM images as well with the different alkaline source. The effect of alkaline sources on photovoltaic performance of hybrid organic solar cells with CdSe and poly(3-hexylthiophene) as active layers was clearly observed, indicating the importance of synthesis conditions on optoelectronic properties of promising semiconductor nanomaterials for solar cell applications.

  9. Poly(3-hexylthiophene) - CdSe quantum dot bulk heterojunction solar cells: Influence of the functional end-group of the polymer

    KAUST Repository

    Palaniappan, Kumaranand

    2009-06-23

    The synthesis of H/thiol terminated P3HT from Br/allyl-terminated P3HT precursor was analyzed. The photovoltaic response of blends were prepared of H/thiol terminated P3HT with spherical CdSe quantum dots(QD) and compares the results with regioregular H/Br and Br/aryl-terminated P3HT. Phase segregation was carried by mixing relatively polar pyridine treated CdSe QD with nonpolar P3HT. The experiment revealed that a high loading of CdSe is necessary for an efficient charge transport and different loading ratios of CdSe has been investigated to correlate the photovoltaic response as a function of ration between donor H/thiol-P3ht polymer and acceptor Cdse QD. The results show that H/Br-P3HT, H/thiol- and Br/allyl-terminated P3HT exhibits better performance and Cdse quantum dots were used to obtain results.

  10. Transmission electron microscopy investigations of the CdSe based quantum structures

    International Nuclear Information System (INIS)

    In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)

  11. Transmission electron microscopy investigations of the CdSe based quantum structures

    Energy Technology Data Exchange (ETDEWEB)

    Roventa, E.

    2006-09-22

    In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)

  12. Study of the effect of an equi-biaxial loading on the fatigue lifetime of austenitic stainless steel

    International Nuclear Information System (INIS)

    Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures.In some nuclear power plant components, the fatigue loading may be equi-biaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equi-biaxial tension. The aim of this study is to present the experimental and numerical results obtained with a device 'FABIME2' developed in the LISN in collaboration with EDF and AREVA. The association of the experimental results, obtained on the new experimental fatigue device FABIME2, with the numerical analyses obtained by FEM simulation with Cast3M code, has enabled to define the aggravating effect of the equi-biaxial fatigue loading. However, this effect is covered by the Design fatigue curve defined from the nuclear industry. For the crack propagation, a first simplified approach enables to study the kinetic behavior of crack propagation in equi-biaxial fatigue. (author)

  13. Increased carrier mobility and lifetime in CdSe quantum dot thin films through surface trap passivation and doping.

    Science.gov (United States)

    Straus, Daniel B; Goodwin, E D; Gaulding, E Ashley; Muramoto, Shin; Murray, Christopher B; Kagan, Cherie R

    2015-11-19

    Passivating surface defects and controlling the carrier concentration and mobility in quantum dot (QD) thin films is prerequisite to designing electronic and optoelectronic devices. We investigate the effect of introducing indium in CdSe QD thin films on the dark mobility and the photogenerated carrier mobility and lifetime using field-effect transistor (FET) and time-resolved microwave conductivity (TRMC) measurements. We evaporate indium films ranging from 1 to 11 nm in thickness on top of approximately 40 nm thick thiocyanate-capped CdSe QD thin films and anneal the QD films at 300 °C to densify and drive diffusion of indium through the films. As the amount of indium increases, the FET and TRMC mobilities and the TRMC lifetime increase. The increase in mobility and lifetime is consistent with increased indium passivating midgap and band-tail trap states and doping the films, shifting the Fermi energy closer to and into the conduction band. PMID:26536065

  14. The heat capacity of zinc and cadmium chalcogenides (ZnTe, CdSe, and CdTe)

    International Nuclear Information System (INIS)

    Heat capacity of zinc telluride, cadmium selenide and telluride are measured by the calorimetry method at 370-640 K (ZnTe) and 500-760 K (CdSe, CdTe). Analysis of literature data on heat capacity of the above-mentioned solid solutions at temperatures in excess of 298 K is carried out. On the basis of the results obtained and most dependable literature data on heat capacity of the compounds for temperature ranges of 220-1500 K (ZnTe, CdSe) and 220-1300 K (CdTe) new equations of heat capacity temperature dependence are suggested and thermodynamic functions of the compounds are calculated

  15. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    International Nuclear Information System (INIS)

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at TG=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at TGD=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  16. Surface texture and percolation effects in microporous oriented films of polyolefins

    Science.gov (United States)

    Novikov, D. V.; Kuryndin, I. S.; Bukošek, V.; Elyashevich, G. K.

    2012-11-01

    The surface structure of polypropylene and polyethylene microporous films prepared by the extrusion of the polymer melt with the subsequent stages of annealing, uniaxial extension, and thermal fixation of the samples has been analyzed using scanning electron microscopy. It has been shown that percolation through pores corresponds to the axial texture of the surface with the channel structure described by the fractal cluster model. The transition from open pores (through-flow channels) to closed pores leads to the formation of surface regions with a biaxial texture. An increase in the density of the solid phase cluster is accompanied by the formation of a homogeneous biaxial texture with a period of alternation of the density in two mutually perpendicular directions, one of which coincides with the direction of orientation of the films.

  17. Magnetic response of FeNbCuBSi RQ ribbons to bi-axial strain

    International Nuclear Information System (INIS)

    Nanocrystalline strip samples of the FeNbCuBSi class that are macroscopically heterogeneous due to surface /volume differences have been investigated. This heterogeneity is found to be a general property of the class. It represents a base for mutual force influence between the surface and the majority volume beneath. The bi-axial in-plane stress exerted by the ribbon surfaces on the volume is demonstrated first of all by a magnetoelastic anisotropy. The contribution of the creep-induced anisotropy, which can build up under the surface stress at post-treatment temperature, is also found possible

  18. Collinear Acousto-Optical Transformation of Bessel Light Beams in Biaxial Gyrotropic Crystals

    Science.gov (United States)

    Belyi, V. N.; Kulak, G. V.; Krokh, G. V.; Shakin, O. V.

    2016-05-01

    The collinear acousto-optical transformation of Bessel light beams in biaxial gyrotropic crystals into two annular, internal conical refraction beams with orthogonal elliptical polarization is studied. It is found that the diffraction efficiency is maximal (~50-60%) for low ultrasound intensities and varies slightly with further increases in acoustic power. At high ultrasound intensities, the intensities of the transmitted and diffracted annular beams differ insignificantly. The possible use of this acousto-optical interaction for creating collinear tuneable narrow-band acousto-optical filters at low ultrasonic frequencies is demonstrated.

  19. Mechanism of biaxial pre-stress method on welding residual stress and hot cracks controlling

    Institute of Scientific and Technical Information of China (English)

    LIU Xuesong; ZHOU Guangtao; WANG Ping; LIU Haoyuan; FANG Hongyuan

    2009-01-01

    Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion as-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks

  20. Biaxially stretchable supercapacitors based on the buckled hybrid fiber electrode array

    Science.gov (United States)

    Zhang, Nan; Zhou, Weiya; Zhang, Qiang; Luan, Pingshan; Cai, Le; Yang, Feng; Zhang, Xiao; Fan, Qingxia; Zhou, Wenbin; Xiao, Zhuojian; Gu, Xiaogang; Chen, Huiliang; Li, Kewei; Xiao, Shiqi; Wang, Yanchun; Liu, Huaping; Xie, Sishen

    2015-07-01

    In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the fibers endow the supercapacitor with 100% stretchability along all directions. In addition, the supercapacitor exhibited good transparency, as well as excellent electrochemical properties and stability after being stretched 5000 times.In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the

  1. Biaxial high cycle fatigue: experimental investigation and two-scale damage model

    International Nuclear Information System (INIS)

    This research thesis first describes the multi-axial fatigue phenomenon in the cases of mechanical and complex loadings, discusses multi-axial fatigue criteria, and presents the approach of fatigue by incremental damage mechanics. Then, it reports an experimental investigation of fatigue crack initiation under biaxial polycyclic fatigue in 304L austenitic stainless steel and in titanium alloy. The author presents a probabilistic two-scale damage model, and then reports the assessment of multi-axial fatigue life by means of this model

  2. Behavior of High Water-cement Ratio Concrete under Biaxial Compression after Freeze-thaw Cycles

    Institute of Scientific and Technical Information of China (English)

    SHANG Huaishuai; SONG Yupu; OU Jinping

    2008-01-01

    The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied.Strength and deformations of plain concrete specimens after 0,25,50 cycles of freeze-thaw.Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed aecording to the experimental results.Based on the test data,the failure criterion expressed in terms of principal stress after difierent cycles of freeze-thaw,and the failure criterion with consideration of the influence of freeze-thaw cycle and sffess ratio were proposed respectively.

  3. Control of biaxial strain in single-layer Molybdenite using local thermal expansion of the substrate

    OpenAIRE

    Plechinger, G.; Castellanos-Gomez, A.; Buscema, M.; van der Zant, H. S. J.; Steele, G. A.; Kuc, A.; Heine, T.; Schüller, C; Korn, T.

    2015-01-01

    Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllabl...

  4. Transformation of vector beams with radial and azimuthal polarizations in biaxial crystals

    CERN Document Server

    Turpin, Alex; Lizana, Angel; Torres-Ruiz, Fabián; Estévez, Irene; Moreno, Ignacio; Campos, Juan; Mompart, Jordi

    2015-01-01

    We present both experimentally and theoretically the transformation of radially and azimuthally polarized vector beams when they propagate through a biaxial crystal and are transformed by the conical refraction phenomenon. We show that, at the focal plane, the transverse pattern is formed by a ring-like light structure with an azimuthal node, being this node found at diametrically opposite points of the ring for radial/azimuthal polarizations. We also prove that the state of polarization of the transformed beams is conical refraction-like, i.e. that every two diametrically opposite points of the light ring are linearly orthogonally polarized.

  5. Frequency-dependent spontaneous emission rate from CdSe and CdTe nanocrystals: Influence of dark states

    DEFF Research Database (Denmark)

    van Driel, A. F.; Allan, G.; Delerue, C.;

    2005-01-01

    We studied the rate of spontaneous emission from colloidal CdSe and CdTe nanocrystals at room temperature. The decay rate, obtained from luminescence decay curves, increases with the emission frequency in a supralinear way. This dependence is explained by the thermal occupation of dark exciton...... states at room temperature, giving rise to a strong attenuation of the rate of emission. The supralinear dependence is in agreement with the results of tight-binding calculations....

  6. Insertion of CdSe quantum dots in ZnSe nanowires: Correlation of structural and chemical characterization with photoluminescence

    OpenAIRE

    Den Hertog, Martien; Elouneg-Jamroz, Miryam; Bellet-Amalric, Edith; Bounouar, Samir; Bougerol, Catherine; André, Régis; Genuist, Yann; Poizat, Jean-Philippe; Kheng, Kuntheak; Tatarenko, Serge

    2011-01-01

    ZnSe nanowires with CdSe quantum dot insertions were grown by molecular beam epitaxy using gold as a catalyst. Structural, chemical, and optical properties of the wires and quantum dots were characterized using electron microscopy and photoluminescence spectroscopy. We determined the crystalline structure, the chemical composition, and the size of the quantum dot and established a correlation between quantum dot size and luminescence. As expected, a blueshift of the luminescence was observed ...

  7. CdSe quantum dot in a ZnSe nanowire as an efficient source of single photons

    Energy Technology Data Exchange (ETDEWEB)

    Tribu, A.; Aichele, T.; Kheng, K. [CEA/CNRS Group Nanophysique et Semi-Conducteurs, CEA/INAC/SP2M, Grenoble (France); Sallen, G.; Bougerol, C.; Andre, R.; Poizat, J.P.; Tatarenko, S. [CEA/CNRS Group Nanophysique et Semi-Conducteurs, Institut Neel CNRS, Universite J. Fourier Grenoble (France)

    2009-04-15

    We report on our development of fabrication of CdSe QD in ZnSe nanowire. We have been able to obtain high quality structures with very good optical properties. This has allowed us to measure photon emission from single quantum dots and to demonstrate photon antibunching. We show that this new type of II-VI quantum dot is very promising for high temperature operation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Reconstructing a solid-solid phase transformation pathway in CdSe nanosheets with associated soft ligands.

    Science.gov (United States)

    Wang, Zhongwu; Wen, Xiao-Dong; Hoffmann, Roald; Son, Jae Sung; Li, Ruipeng; Fang, Chia-Chen; Smilgies, Detlef-M; Hyeon, Taeghwan

    2010-10-01

    Integrated single-crystal-like small and wide-angle X-ray diffraction images of a CdSe nanosheet under pressure provide direct experimental evidence for the detailed pathway of transformation of the CdSe from a wurtzite to a rock-salt structure. Two consecutive planar atomic slips [(001) {110} in parallel and (102) {101}with a distortion angle of ∼40°] convert the wurtzite-based nanosheet into a saw-like rock-salt nanolayer. The transformation pressure is three times that in the bulk CdSe crystal. Theoretical calculations are in accord with the mechanism and the change in transformation pressure, and point to the critical role of the coordinated amines. Soft ligands not only increase the stability of the wurtzite structure, but also improve its elastic strength and fracture toughness. A ligand extension of 2.3 nm appears to be the critical dimension for a turning point in stress distribution, leading to the formation of wurtzite (001)/zinc-blende (111) stacking faults before rock-salt nucleation.

  9. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Dieter Konrad Michael

    2013-11-08

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  10. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Dieter Konrad Michael

    2013-11-08

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  11. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    International Nuclear Information System (INIS)

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  12. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films

    Science.gov (United States)

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates.

  13. Electroluminescence from isolated CdSe /ZnS quantum dots in multilayered light-emitting diodes

    Science.gov (United States)

    Zhao, Jialong; Zhang, Jingying; Jiang, Chaoyang; Bohnenberger, Jolanta; Basché, Thomas; Mews, Alf

    2004-09-01

    Electro- and photoluminescence spectra of the CdSe /ZnS core-shell quantum dots (QDs) covered by various organic ligands and incorporated into multilayered light-emitting diodes (LEDs) were recorded by a confocal optical microscope. The QDs were dispersed in a hole transporting material, N,N'-Diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), to investigate the LED performance at different QD concentrations and the effect of different surface modifications on the isolated QDs. No wavelength shift was observed in the electroluminescence spectra from the QD LEDs with or without the TPD. The peak energies of the electro- and photoluminescence showed only small spectral shifts (several nanometer) for the diluted QDs and no dependence on the QD-concentration, surface ligands, or conductive polymers that were used. This suggests that the relative peak shifts are related to the different filling processes in the CdSe QDs under photo excitation and electric injection, rather than to the "chemical" effects on the surface of the CdSe /ZnS QDs.

  14. Preparation, characterization and application of polyelectrolytes/TiO{sub 2}/CdSe self-assembled films

    Energy Technology Data Exchange (ETDEWEB)

    Faria, Ana Claudia R. [Centro de Ciências Exatas e Tecnologia, Universidade de Caxias do Sul – UCS, Rua Francisco Getúlio Vargas, 1130, Caxias do Sul 95070-560, RS (Brazil); Menezes, Frederico D.; Milani, Raquel [Universidade Federal de Pernambuco – UFPE, Av. Prof. Moraes Rego, 1235, Recife 50740-560, PE (Brazil); Pereira, Marcelo B.; Gonçalves, Renato V.; Horowitz, Flavio [Instituto de Física, Universidade Federal do Rio Grande do Sul – UFRGS, Av. Bento Gonçalves, 9500, Porto Alegre 91501-970, RS (Brazil); Giovanela, Marcelo [Centro de Ciências Exatas e Tecnologia, Universidade de Caxias do Sul – UCS, Rua Francisco Getúlio Vargas, 1130, Caxias do Sul 95070-560, RS (Brazil); Machado, Giovanna [Universidade Federal de Pernambuco – UFPE, Av. Prof. Moraes Rego, 1235, Recife 50740-560, PE (Brazil); Centro de Tecnologias Estratégicas do Nordeste – CETENE, Av. Prof. Luiz Freire, 01, Recife 50740-540, PE (Brazil); Crespo, Janaina S., E-mail: jscrespo@ucs.br [Centro de Ciências Exatas e Tecnologia, Universidade de Caxias do Sul – UCS, Rua Francisco Getúlio Vargas, 1130, Caxias do Sul 95070-560, RS (Brazil)

    2014-01-31

    The aim of this work was to prepare self-assembled films (SAF) via a layer-by-layer technique and to characterize the films by applying several instrumental techniques. The cationic system was composed of the organic polyelectrolyte poly(diallyldimethylammonium chloride) and the inorganic semiconductor cadmium selenide (CdSe), whereas the anionic system was composed of poly(acrylic acid) and nanoparticles of the photoactive semiconductor titanium dioxide (TiO{sub 2}). Through measurements of the diffuse reflectance spectrum, absorption bands were observed in the near ultraviolet region for TiO{sub 2} and in the visible region for CdSe. The thicknesses of the SAF were determined through profilometry and scanning electron microscopy techniques, and the obtained values were on the order of microns. Finally, the SAF were irradiated with a Xe/Hg lamp, and the results indicated their potential for solar hydrogen production. - Highlights: • Development of polyelectrolytes/TiO{sub 2}/CdSe self-assembled films • Films characterization applying several instrumental techniques • Potential application in the solar hydrogen production.

  15. Biomimetic Synthesis of CdSe Quantum Dots through Emulsion Liquid Membrane System of Gas-Liquid Transport

    Institute of Scientific and Technical Information of China (English)

    LIU,LU(刘璐); WU,Qing-Sheng,(吴庆生); DING,Ya-Ping(丁亚平); LIU,Hua-Jie(柳华杰); ZHANG,Bao-Quan(张保权)

    2004-01-01

    The cadmium selenide quantum dots (QD) have been synthesized by template-control in an emulsion liquid membrane system.The system consisted of kerosene as solvent,L152 (dialkylene succinimide) as surfactant,N7301 (trialiphatic amine,R3N,R=Cs-C10) as carrier,0.1 mol/L CdC12 solution as internal-aqueous phase and H2Se gas as external phase.Additive organic template agent in internal-aqueous phase was necessary to form CdSe QD.The influence of the nature of template and its concentration on sizes of the formed CdSe QD has also been studied.Transmission electron microscopy showed that the sizes of the products could be controlled down to 3-4nm.X-ray diffraction analysis revealed that the crystals had cubic structure.The formation process and the optical properties of CdSe QD have also been presented.

  16. Optical and photoelectric properties of nanocrystalline SnO{sub 2} - CdSe quantum dot structures

    Energy Technology Data Exchange (ETDEWEB)

    Dobrovolsky, Alexandr; Drozdov, Konstantin; Khokhlov, Dmitry [Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation); Vasiliev, Roman; Maslova, Olga [Faculty of Material Science, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation); Rumyantseva, Marina; Gaskov, Alexander; Ryabova, Ludmila [Faculty of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation)

    2010-04-15

    Microstructure, optical and photoelectric properties of nanocrystalline porous SnO{sub 2} films on an insulating substrate with colloidal CdSe quantum dots as a sensitizer have been studied. SnO{sub 2} films consist of nanocrystallites with the average size of {proportional_to}20 nm combined into agglomerates as large as {proportional_to}1 {mu}m. CdSe quantum dots with the mean size of {proportional_to}3.5 nm were incorporated into porous SnO{sub 2} films by dipping the substrates into a colloidal solution of CdSe quantum dots. Transport and photoelectric properties of the structures were studied in the temperature interval 77 - 300 K. Optical properties were investigated in the visible spectral range. Persistent photoconductivity at the room temperature has been observed. Possible mechanisms of the persistent photoconductivity for this composite system are discussed. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Annealing Effect on Photovoltaic Performance of CdSe Quantum-Dots-Sensitized TiO2 Nanorod Solar Cells

    Directory of Open Access Journals (Sweden)

    Yitan Li

    2012-01-01

    Full Text Available Large area rutile TiO2 nanorod arrays were grown on F:SnO2 (FTO conductive glass using a hydrothermal method at low temperature. CdSe quantum dots (QDs were deposited onto single-crystalline TiO2 nanorod arrays by a chemical bath deposition (CBD method to make a photoelectrode. The solar cell was assembled using a CdSe-TiO2 nanostructure as the photoanode and polysulfide solution as the electrolyte. The annealing effect on optical and photovoltaic properties of CdSe quantum-dots-sensitized TiO2 nanorod solar cells was studied systematically. A significant change of the morphology and a regular red shift of band gap of CdSe nanoparticles were observed after annealing treatment. At the same time, an improved photovoltaic performance was obtained for quantum-dots-sensitized solar cell using the annealed CdSe-TiO2 nanostructure electrode. The power conversion efficiency improved from 0.59% to 1.45% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by annealing treatment.

  18. Preparation, characterization and application of polyelectrolytes/TiO2/CdSe self-assembled films

    International Nuclear Information System (INIS)

    The aim of this work was to prepare self-assembled films (SAF) via a layer-by-layer technique and to characterize the films by applying several instrumental techniques. The cationic system was composed of the organic polyelectrolyte poly(diallyldimethylammonium chloride) and the inorganic semiconductor cadmium selenide (CdSe), whereas the anionic system was composed of poly(acrylic acid) and nanoparticles of the photoactive semiconductor titanium dioxide (TiO2). Through measurements of the diffuse reflectance spectrum, absorption bands were observed in the near ultraviolet region for TiO2 and in the visible region for CdSe. The thicknesses of the SAF were determined through profilometry and scanning electron microscopy techniques, and the obtained values were on the order of microns. Finally, the SAF were irradiated with a Xe/Hg lamp, and the results indicated their potential for solar hydrogen production. - Highlights: • Development of polyelectrolytes/TiO2/CdSe self-assembled films • Films characterization applying several instrumental techniques • Potential application in the solar hydrogen production

  19. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    Energy Technology Data Exchange (ETDEWEB)

    Mahapatra, Suddhasatta

    2008-01-16

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at T{sub G}=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at T{sub G}<{proportional_to}240 C. In the second variant technique, formation of large and distinct islands is demonstrated by deposition of amorphous selenium (a-Se) onto a 2D CdSe epilayer at room temperature and its subsequent desorption at a higher temperature (T{sub D}=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  20. Surface-enhanced Raman scattering by colloidal CdSe nanocrystal submonolayers fabricated by the Langmuir–Blodgett technique

    Directory of Open Access Journals (Sweden)

    Alexander G. Milekhin

    2015-12-01

    Full Text Available We present the results of an investigation of surface-enhanced Raman scattering (SERS by optical phonons in colloidal CdSe nanocrystals (NCs homogeneously deposited on both arrays of Au nanoclusters and Au dimers using the Langmuir–Blodgett technique. The coverage of the deposited NCs was less than one monolayer, as determined by transmission and scanning electron microscopy. SERS by optical phonons in CdSe nanocrystals showed a significant enhancement that depends resonantly on the Au nanocluster and dimer size, and thus on the localized surface plasmon resonance (LSPR energy. The deposition of CdSe nanocrystals on the Au dimer nanocluster arrays enabled us to study the polarization dependence of SERS. The maximal SERS signal was observed for light polarization parallel to the dimer axis. The polarization ratio of the SERS signal parallel and perpendicular to the dimer axis was 20. The SERS signal intensity was also investigated as a function of the distance between nanoclusters in a dimer. Here the maximal SERS enhancement was observed for the minimal distance studied (about 10 nm, confirming the formation of SERS “hot spots”.

  1. The Investigation of 6mu Biaxially Oriented Polyethylene 2, 6, -Naphthalate As a Possible Dielectric For Pulse Power Capacitors

    Science.gov (United States)

    Yen, S. P. S.; Lowry, L.; Cygan, P. J.; Jow, T. R.

    1993-01-01

    The introduction of polythylene -2, 6-Naphthalate (PEN) semicrystalline film with thicknesses of 0.9mu, 1.5mu, 4.0Mu and community. Its unique chemical and high temparterure stability, as well as superior thermo-mechanical properties allow ultra thin ( 2mu) PEN film to be processed into miniature multilayer chip capacitors for surface mount technology (SMT) application that can be used with standard soldering techniques.

  2. Electronic and optical properties of kesterite Cu{sub 2}ZnSnS{sub 4} under in-plane biaxial strains: First-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chun-Ran [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); College of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); Li, Yong-Feng, E-mail: liyongfeng@jlu.edu.cn [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Yao, Bin, E-mail: binyao@jlu.edu.cn [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Yang, Gang [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Ding, Zhan-Hui [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); Deng, Rui [School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022 (China); Liu, Lei [State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun 130033 (China)

    2013-11-08

    The electronic structures and optical properties of Cu{sub 2}ZnSnS{sub 4} (CZTS) under in-plane biaxial strain were systematically investigated using first-principles calculations based on generalized gradient approximation and hybrid functional method, respectively. It is found that the fundamental bandgap at the Γ point decreases linearly with increasing tensile biaxial strain perpendicular to c-axis. However, a bandgap maximum occurs as the compressive biaxial strain is 1.5%. Further increase of compressive strain decreases the bandgap. In addition, the optical properties of CZTS under biaxial strain are also calculated, and the variation trend of optical bandgap with biaxial strain is consistent with the fundamental bandgap.

  3. Orienteering club

    CERN Document Server

    Club d'orientation

    2015-01-01

    Course d'orientation La reprise des courses d’orientation était attendue dans la région puisque près de 150 coureurs ont participé à la première épreuve automnale organisée par le club d’orientation du CERN sur le site de La Faucille. Les circuits ont été remportés par Yann Locatelli du club d’Orientation Coeur de Savoie avec 56 secondes d’avance sur Damien Berguerre du club SOS Sallanches pour le parcours technique long, Marie Vuitton du club CO CERN (membre également de l’Equipe de France Jeune) pour le parcours technique moyen avec presque 4 minutes d’avance sur Jeremy Wichoud du club Lausanne-Jorat, Victor Dannecker pour le circuit technique court devant Alina Niggli, Elliot Dannecker pour le facile moyen et Alice Merat sur le facile court, tous membres du club O’Jura. Les résultats comp...

  4. Effects of the biaxial transverse crystal-field on the phase diagrams of a spin-1 nanowire

    Science.gov (United States)

    Magoussi, H.; Zaim, A.; Boughrara, M.; Kerouad, M.

    2016-09-01

    By using the effective field theory based on a probability distribution method, the phase diagrams and the magnetic properties of an Ising nanowire in the presence of the biaxial transverse crystal-field are investigated. The effects of the biaxial transverse crystal field, the interfacial coupling and the exchange interaction in the surface on the phase diagram, the magnetization and the internal energy are examined. Some characteristic phenomena are found such as the tricritical behavior, the critical end point and the re-entrant phenomenon.

  5. Biaxial-Type Concentrated Solar Tracking System with a Fresnel Lens for Solar-Thermal Applications

    Directory of Open Access Journals (Sweden)

    Tsung Chieh Cheng

    2016-04-01

    Full Text Available In this paper, an electromechanical, biaxial-type concentrated solar tracking system was designed for solar-thermal applications. In our tracking system, the sunlight was concentrated by the microstructure of Fresnel lens to the heating head of the Stirling engine and two solar cells were installed to provide the power for tracking system operation. In order to obtain the maximum sun power, the tracking system traces the sun with the altitude-azimuth biaxial tracing method and accurately maintains the sun’s radiation perpendicular to the plane of the heating head. The results indicated that the position of heating head is an important factor for power collection. If the sunlight can be concentrated to completely cover the heating head with small heat loss, we can obtain the maximum temperature of the heating head of the Stirling engine. Therefore, the temperature of heating head can be higher than 1000 °C in our experiment on a sunny day. Moreover, the results also revealed that the temperature decrease of the heating head is less than the power decrease of solar irradiation because of the latent heat of copper and the small heat loss from the heating head.

  6. Time-evolving collagen-like structural fibers in soft tissues: biaxial loading and spherical inflation

    Science.gov (United States)

    Topol, Heiko; Demirkoparan, Hasan; Pence, Thomas J.; Wineman, Alan

    2016-05-01

    This work considers a previously developed constitutive theory for the time dependent mechanical response of fibrous soft tissue resulting from the time dependent remodeling of a collagen fiber network that is embedded in a ground substance matrix. The matrix is taken to be an incompressible nonlinear elastic solid. The remodeling process consists of the continual dissolution of existing fibers and the creation of new fibers. Motivated by experimental reports on the enzyme degradation of collagen fibers, the remodeling is governed by first order chemical kinetics such that the dissolution rate is dependent upon the fiber stretch. The resulting time dependent mechanical response is sensitive to the natural configuration of the fibers when they are created, and different assumptions on the nature of the fiber's stress free state are considered here. The response under biaxial loading, a type of loading that has particular significance for the characterization of biological materials, is studied. The inflation of a spherical membrane is then analyzed in terms of the equal biaxial stretch that occurs in the membrane approximation. Different assumptions on the natural configuration of the fibers, combined with their time dependent dissolution and reforming, are shown to emulate alternative forms of creep and relaxation response. This formal similarity to viscoelastic phenomena occurs even though the underlying mechanisms are fundamentally different from the mechanism of macromolecular reconfiguration that one typically associates with viscoelastic response.

  7. Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

    Directory of Open Access Journals (Sweden)

    Xue-wei Liu

    2016-01-01

    Full Text Available This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C. On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the propagation paths are affected by the loading condition obviously. Then, by adopting acoustic emission (AE location technique, AE event localization characteristics in the process of loading are investigated. The locations of AE events are in good agreement with the macroscopic fracture propagation path. Finally, the micromechanism of macroscopic fracture propagation under uniaxial and biaxial compression conditions is analyzed, and the fracture propagation can be concluded as a result of microdamage accumulation inside the material. The results of this paper are helpful for theory and engineering design of the fractured rock mass.

  8. Measurement and material modeling of biaxial work-hardening behavior for pure titanium sheet

    Science.gov (United States)

    Sumita, Takeshi; Kuwabara, Toshihiko

    2013-12-01

    Biaxial tensile tests of a commercial pure titanium sheet (JIS ♯1) were performed using a servo-controlled multiaxial tube expansion testing machine developed by one of the authors [Kuwabara, T. and Sugawara, F., Multiaxial tube expansion test method for measurement of sheet metal deformation behavior under biaxial tension for a large strain range, Int. J. Plasticity, 45 (2013), 103-118]. Tubular specimens with an inner diameter of 54 mm were fabricated by roller bending and TIG welding the as-received test material with a thickness of 0.5 mm. Several linear stress paths in the first quadrant of the stress space were applied to the tubular specimens to measure the contours of plastic work and the directions of the plastic strain rates for an equivalent plastic strain range of 0.05 ≤ ɛ0p ≤ 0.30. It was found that the shapes of the work contours significantly changed with an increase in ɛ0p and that the Yld2000-2d yield function could reproduce the differential work hardening behavior of the test material by changing the material parameters and the exponent as functions of ɛ0p.

  9. Effects of Arbitrarily Directed Field on Spin Phase Oscillations in Biaxial Molecular Magnets

    Institute of Scientific and Technical Information of China (English)

    HU Hui; ZHU JiaLin; LU Rong; XIONG JiaJiong

    2001-01-01

    Quantum phase interference and spin-parity effects are studied in biaxial molecular magnets in a magnetic field at an arbitrarily directed angle. The calculations of the ground-state tunnel splitting are performed on the basis of the instanton technique in the spin-coherent-state path-integral representation, and complemented by exactly numerical diagonalization. Both the Wentzel-Kramers-Brillouin exponent and the pre-exponential factor are obtained for the entire region of the direction of the field. Our results show that the tunnel splitting oscillates with the field for the small field angle, while for the large field angle the oscillation is completely suppressed. This distinct angular dependence, together with the dependence of the tunnel splitting on the field strength, provides an independent test for spin-parity effects in biaxial molecular magnets. The analytical results for the molecular Fes magnet are found to be in good agreement with the numerical simulations, which suggests that even the molecular magnet with total spin S = 10 is large enough to be treated as a giant spin system.``

  10. Upregulation of matrix synthesis in chondrocyte-seeded agarose following sustained bi-axial cyclic loading

    Directory of Open Access Journals (Sweden)

    Belinda Pingguan-Murphy

    2012-08-01

    Full Text Available OBJECTIVES: The promotion of extracellular matrix synthesis by chondrocytes is a requisite part of an effective cartilage tissue engineering strategy. The aim of this in vitro study was to determine the effect of bi-axial cyclic mechanical loading on cell proliferation and the synthesis of glycosaminoglycans by chondrocytes in threedimensional cultures. METHOD: A strain comprising 10% direct compression and 1% compressive shear was applied to bovine chondrocytes seeded in an agarose gel during two 12-hour conditioning periods separated by a 12-hour resting period. RESULTS: The bi-axial-loaded chondrocytes demonstrated a significant increase in glycosaminoglycan synthesis compared with samples exposed to uni-axial or no loading over the same period (p<0.05. The use of a free-swelling recovery period prior to the loading regime resulted in additional glycosaminoglycan production and a significant increase in DNA content (p<0.05, indicating cell proliferation. CONCLUSIONS: These results demonstrate that the use of a bi-axial loading regime results in increased matrix production compared with uni-axial loading.

  11. Characterization of Biaxial and Triaxial Braids: Fiber Architecture and Mechanical Properties

    Science.gov (United States)

    Birkefeld, Karin; Röder, Mirko; von Reden, Tjark; Bulat, Martina; Drechsler, Klaus

    2012-06-01

    Biaxial and triaxial carbon fiber braids with off-axis braiding angles of 30°, 45° and 55° are characterized with respect to their fiber architecture. All braids are produced on a round mandrel with constant cross section. Detailed geometric information on the different braids, like roving dimensions, roving shapes and the degree of nesting is given. The findings from measurements in photomicrographs are used to construct meso-model yarn architectures at the unit cell level which are then analyzed with the WiseTex software (Lomov et al. Compos. Sci. Technol. 60:2083-2095, 2000). The results of the models' analysis with TexComp and comparison of mechanical properties with tests are consistent and essential for further steps in predictive modeling. Predictive modeling was also performed for biaxial braids based on the packing density in the material and parameters of the braiding process. The good conformance of the predictive models gives a validated starting point for development of braided structures concerning stiffness behavior. In addition, the information about the fiber architecture can be used for failure analysis on unit cell level.

  12. Fatigue life prediction of magnetorheological elastomers subjected to dynamic equi-biaxial cyclic loading

    International Nuclear Information System (INIS)

    Prediction of fatigue life is of great significance in ensuring that dynamically loaded rubber components exhibit safety and reliability in service. In this text, the dynamic equi-biaxial fatigue behaviour of magnetorheological elastomer (MREs) using a bubble inflation method is described. Wöhler (S–N) curves for both isotropic and anisotropic MREs were produced by subjecting the compounds to cycling over a range of stress amplitudes (σa) between 0.75 MPa and 1.4 MPa. Changes in physical properties, including variation in stress–strain relations and complex modulus (E*) during the fatigue process were analysed. It was found that the complex modulus of MRE samples decreased throughout the entire fatigue test and failure took place at a limiting value of approximately 1.228MPa ± 4.38% for isotropic MREs and 1.295 ± 10.33% for anisotropic MREs. It was also determined that a dynamic stored energy criterion can be used as a plausible predictor in determining the fatigue life of MREs. - Highlights: • The first Wöhler curves for MREs subjected to equi-biaxial loading were presented. • Anisotropic MREs exhibited higher fatigue resistance than isotropic MREs. • There is a limiting value of complex modulus (E*) at which fatigue failure will occur. • The dynamic stored energy criterion can be used as a fatigue life predictor

  13. Optical and Surface Characterization Studies of CdSe Quantum Dots Undergoing Photooxidation

    Science.gov (United States)

    Powell, Lauren C. J.

    Realization of the potential of Quantum Dots (QDs) for biological, energy-efficient lighting and energy harvesting applications requires that their long-term photostability be improved, especially with regards to protection from photooxidation. The overarching objective of this project was the determination of the chemical and physical mechanisms of photooxidation of CdSe QDs. Pittsburgh-based Crystalplex, Inc. provided CdSe QDs with different organic ligands for this research. Three integrated in situ and ex situ characterization techniques were used to observe changes in optical behavior, QD morphology, and surface chemistry during photooxidation conditions. Single-molecule fluorescence microscopy experiments were used to observe real-time changes in the photoluminescence (PL) behavior of single QDs with oleic and lauric acid ligands. The QDs are exposed to 1 atm of pure O2, dry Ar, Ar bubbled through DI water, or air in an environmental chamber and excited with a 488 nm light. Changes in PL intensities were analyzed with respect to the periods of exposure to controlled atmospheres and light. Samples illuminated continuously exhibited strong photoenhancement effects, while those kept in the dark showed atmospheric-dependent PL loss. Microstructural and chemical identification was performed with aberration-corrected transmission electron microscopy (TEM). Ex situ exposures of QD samples to air, dry O2, and dry Ar revealed changes in surface oxide growth with respect to exposure length, illumination, and column vacuum pressure. Samples exposed to air and light exhibited the most extensive photooxidation. Quantum dots with oleic acid ligands were treated with UV/ozone plasma, and extensive degradation of QDs was observed. X-ray photoemission spectroscopy (XPS) measurements at CMU were used to identify the chemical and bonding states of the surface species before and after photooxidation. Analysis of the acquired spectra showed that exposure to below-bandgap light

  14. Orienteering Club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Courses d’orientation Une bonne dizaine de clubs étaient représentés samedi dernier à La Faucille pour participer à la  2e manche de la coupe genevoise organisée par le club du CERN. Les 120 coureurs ont pu découvrir des parcours classés "technique". Ceux du Haut-Jura familiarisés à ce type de terrain ont pu sortir leur épingle du jeu et se sont octroyé la victoire sur 4 des 5 circuits. Samedi 21 septembre, la montagne du Haut-Jura était encore plébiscitée puisque les coureurs étaient attendus à Saint Cergue sur la carte des Pralies. Pour les résultats complets de La Faucille et les informations sur la prochaine étape, consultez le site du club http://cern.ch/club-orientation.

  15. Orientation Club

    CERN Multimedia

    Club d'orientation

    2014-01-01

    COURSE ORIENTATION Résultats de samedi 10 mai    C’est sur une carte entièrement réactualisée dans les bois de Versoix, que plus de 100 coureurs sont venus participer à la course d’orientation, type longue distance, préparée par des membres du club du CERN. Le terrain plutôt plat nécessitait une orientation à grande vitesse, ce qui a donné les podiums suivants :  Technique long avec 17 postes : 1er Jurg Niggli, O’Jura en 52:48, 2e Beat Muller, COLJ Lausanne-Jorat en 58:02, 3e Christophe Vuitton, CO CERN en 58:19 Technique moyen avec 13 postes : 1er Jean-Bernard Zosso, CO CERN, en 46:05 ; 2e Yves Rousselot, Balise 25 Besançon, en 55:11 ; 3e Laurent Merat, O'Jura, en 55:13 Technique court avec 13 postes : 1er Julien Vuitton, CO CERN en 40:59, 2e Marc Baumgartner, CO CERN en 43:18, 3e Yaelle Mathieu en 51:42 Su...

  16. Orienteering Club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Courses d’orientation ce printemps Le Club d’orientation du CERN vous invite à venir découvrir la course d’orientation et vous propose, en partenariat avec d’autres clubs de la région, une dizaine de courses populaires. Celles-ci ont lieu les samedis après-midi, elles sont ouvertes à tous, quel que soit le niveau, du débutant au sportif confirmé, en famille ou en individuel, en promenade ou en course. Si vous êtes débutant vous pouvez profiter d’une petite initiation offerte par l’organisateur avant de vous lancer sur un parcours. Divers types de parcours sont à votre choix lors de chaque épreuve : facile court (2-3 km), facile moyen (3-5 km), technique court (3-4 km), technique moyen (4-5 km) et technique long (5-7 km). Les dates à retenir sont les suivantes : Samedi 23 mars: Pully (Vd) Samedi 13 avril: Pougny...

  17. Effects of morphology, diameter and periodic distance of the Ag nanoparticle periodic arrays on the enhancement of the plasmonic field absorption in the CdSe quantum dots

    Science.gov (United States)

    Kohnehpoushi, Saman; Eskandari, Mehdi; Ahmadi, Vahid; Yousefirad, Mansooreh; Nabavi, Elham

    2016-09-01

    In this work, the numerical calculations of plasmonic field absorption of Ag nanoparticles (Ag NPs) periodic arrays in the CdSe quantum dot (QD) film are investigated by the three-dimensional finite difference time domain (FDTD). Diameter (D), periodic distance (P), and morphology effects of Ag NPs are investigated on the improvement of the plasmonic field absorption in CdSe QD film. Results show that plasmonic field absorption in CdSe QD film is enhanced with reduction of D of Ag NPs until 5 nm and reduces thereafter. It is observed that with raising D of Ag NPs, optimum plasmonic field absorption in CdSe QD film is shifted toward the higher P. Moreover, with varying morphology of Ag NPs from spherical to cylindrical, cubic, ringing and pyramid, the plasmonic field absorption is considerably enhanced in CdSe QD film and position of quadrupole plasmon mode (QPPM) is shifted toward further wavelength. For cylindrical Ag NPs, the QPPM intensity increased with raising height (H) until 15 nm and reduces thereafter.

  18. Investigation on the influence of pH on structure and photoelectrochemical properties of CdSe electrolytically deposited into TiO2 nanotube arrays

    International Nuclear Information System (INIS)

    Highlights: • There-dimensional CdSe-TiO2 multijunction was fabricated by electrochemical method. • CdSe nanoparticles had a good bonding with the walls of TiO2 nanotube. • pH value played an important role in the quality of CdSe-TiO2 interfaces. - Abstract: In this work, we fabricated CdSe/TiO2 nanotube arrays (NTAs) by electrochemical method. In electrodeposition, the pH value of the electrolyte played an important role in formation of CdSe nanoparticles. As the pH value decreased, more CdSe deposited on TiO2 NTAs. Scanning electron microscopy and transmission electron microscopy characterization shows that the CdSe nanoparticles were uniformly deposited on and into TiO2 nanotubes when the pH value was 3, and this structure fully utilized the three-dimensional (3D) space of TiO2 nanotubes to form 3D multijunction heterostructures. According to the photoelectrochemical test, the CdSe/TiO2 NTAs sample prepared at pH = 3 exhibited maximum photocurrent and open circuit potential. This is because that the deposited CdSe nanoparticles had better bond with the walls of TiO2 nanotube than the samples deposited at other pH values, which facilitated the propagation and kinetic separation of photogenerated charges

  19. A Novel Approach to the Fabrication of CdSe Quantum Dots in Aqueous Solution: Procedures for Controlling Size, Fluorescence Intensity, and Stability over Time

    Directory of Open Access Journals (Sweden)

    M. J. Almendral-Parra

    2014-01-01

    Full Text Available This paper report a straightforward approach for the synthesis of CdSe quantum dots (CdSe QDs in aqueous solution. This method, performed in homogeneous phase, affords optimal sizes and high quantum yields for each application desired. It is an a la carte procedure for the synthesis of nanoparticles aimed at their later application. By controlling the experimental conditions, CdSe QDs of sizes ranging between 2 and 6 nm can be obtained. The best results were achieved in an ice-bath thermostated at 4°C, using mercaptoacetic acid as dispersant. Under these conditions, a slow growth of quantum nanocrystals was generated and this was controlled kinetically by the hydrolysis of SeSO32- to generate Se2-   in situ, one of the forming species of the nanocrystal. The organic dispersant mercaptoacetate covalently binds to the Cd2+ ion, modifying the diffusion rate of the cation, and plays a key role in the stabilization of CdSe QDs. In optimum conditions, when kept in their own solution CdSe QDs remain dispersed over 4 months. The NPs obtained under optimal conditions show high fluorescence, which is a great advantage as regards their applications. The quantum efficiency is also high, owing to the formation under certain conditions of a nanoshell of Cd(OH2, values of 60% being reached.

  20. An orientation competition in yttria-stabilized zirconia thin films fabricated by ion beam assisted sputtering deposition

    International Nuclear Information System (INIS)

    A previously found orientation competition in ion beam sputtered yttria-stabilized zirconia thin films was studied in detail. The effects of sputtering energy and deposition angle were analyzed in ion sputtered films without assisting ions bombardment. It is found that for normally deposited films, (001) and (011) orientations are favored at low and high sputtering energy respectively. For inclined substrate deposited films, as deposition angle increases, (001), (011) and (111) orientations are advantaged in turn. The results can be attributed to the in-plane energy exchange of deposition atom and adatoms. In ion beam assisting deposited YSZ films of low assisting ions energy and current, a (001) oriented biaxial texture is gradually induced as ion energy increased. In the case of ion beam assisted inclined deposition of 45°, (001) orientation is enhanced and two preferential in-plane orientations are found coexist.

  1. Biaxial flexural strength of high-viscosity glass-ionomer cements heat-cured with an LED lamp during setting

    NARCIS (Netherlands)

    Molina, G. Fabian; Cabral, R.J.; Mazzola, I.; Lascano, L. Brain; Frencken, J.E.F.M.

    2013-01-01

    Adding heat to glass ionomers during setting might improve mechanical properties. The aim was to compare the biaxial flexural strength (BFS) between and within four glass ionomers, by time of exposure to a high-intensity LED light-curing unit. Materials and methods. Samples of Fuji 9 Gold Label, Ket

  2. Highly reinforced, low magnetic and biaxially textured Ni-7 at.%W/Ni-12 at.%W multi-layer substrates developed for coated conductors

    International Nuclear Information System (INIS)

    Mechanically strengthened, highly cube textured Ni-7 at.%W/Ni-12 at.%W multi-layer substrates developed for coated conductors have been prepared by the advanced spark plasma sintering technique. The key innovation for developing this weakly magnetic and reinforced substrate was to use a new powder metallurgy and sintering route to bond multi-layers of Ni7W/Ni12W/Ni7W together in order to get an initial ingot, followed by the optimized cold working and annealing. Particular efforts were made in view of the optimization of the design, pressing as well as the heat treatment processes of the starting ingots to obtain a chemically gradient composite bulk, thus ensuring the subsequent cold deformation. The produced composite substrates have a strong {100} texture on Ni7W outer layers. The percentage of the biaxially orientated grains within a misorientation angle of 10 deg. is as high as 97.5%, while the length percentage of low-angle grain boundaries ranging from 2 deg. to 10 deg. in the composite substrate reaches 87.2%. Moreover, the yield strength σ0.2 of the tape approaches 333 MPa, and the saturation magnetization is substantially reduced by 81.6% at 77 K when compared to that of a commercial used Ni5W substrate

  3. Comparison of photovoltaic parameters of CdSe QD and Safranin Dye based solar cell

    International Nuclear Information System (INIS)

    In the present investigation, comparison between photovoltaic parameters of FTO/TiO2 /CdSe.QDs/Pt/FTO and FTO/TiO2 /Safaranin Dye/Pt/FTO are presented. Photo electrodes are prepared on FTO coated glass with three layers; titanium isopropoxide with spin coating, TiO2 nano- crystalline paste using doctor-blade technique, and a thin layer of titanium chloride with spin coating. Counter electrodes are prepared with sputtering on FTO. CdSe quantum dots are synthesized in three neck flask using trioctylphosphine oxide. Higher photovoltage V∞ in QDSSC has been observed whereas higher photocurrents have been measured in DSSC solar cell. At 100 mW/cm-2 power density, maximum power is achieved in Safranin dye based solar cell. The capacitance -voltage characteristics of the cell were measured in a wide range of frequencies. It shows a behavior from positive to negative capacitance due to injection of electrons from FTO electrode into TiO2 . Key words: Quantum dots, Solar cells, Photo electrode, Electrolyte, Impedance spectroscopy

  4. Effect of electric field on the photoluminescence intensity of single CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Park, So-Jung; Link, Stephan; Miller, William L.; Gesquiere, Andre [Department of Chemistry and Biochemistry and the Center for Nano- and Molecular Science and Technology, University of Texas, Austin, TX 78712 (United States); Barbara, Paul F. [Department of Chemistry and Biochemistry and the Center for Nano- and Molecular Science and Technology, University of Texas, Austin, TX 78712 (United States)], E-mail: p.barbara@mail.utexas.edu

    2007-11-15

    An investigation of the effect of an applied electric field on the photoluminescence (PL) intensity of single CdSe nanocrystals has revealed a measurable field induced PL modulation for a large fraction of the nanocrystals studied. The field induced intensity modulation characteristics (i.e. modulation sign and depth) were observed to vary from particle to particle, and even for different time periods for the same particle in many cases. Simultaneous intensity and frequency resolved PL measurement show that the PL intensity modulation is in fact due to an electric field effect on the PL quantum yield. The results are consistent with a model in which the energies of surface charge trapping sites are modulated by the applied electric field, causing in turn a modulation of the rates of exciton quenching by these sites. The complex observed field effects can be explained by the superposition of the applied and internal electric fields due to deeply trapped charges on the surface of the nanoparticle.

  5. Directed energy transfer in films of CdSe quantum dots: beyond the point dipole approximation.

    Science.gov (United States)

    Zheng, Kaibo; Žídek, Karel; Abdellah, Mohamed; Zhu, Nan; Chábera, Pavel; Lenngren, Nils; Chi, Qijin; Pullerits, Tõnu

    2014-04-30

    Understanding of Förster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size of QDs, so that the simple point-dipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using ultrafast transient absorption spectroscopy and theoretical modeling. Pairwise interdot transfer time was determined in the range of 1.5 to 2 ns by spectral analyses which enable separation of the FRET contribution from intrinsic exciton decay. A rational model is suggested by taking into account the distribution of the electronic transition densities in the dots and using the film morphology revealed by AFM images. The FRET dynamics predicted by the model are in good quantitative agreement with experimental observations without adjustable parameters. Finally, we use our theoretical model to calculate dynamics of directed energy transfer in ordered multilayer QD films, which we also observe experimentally. The Monte Carlo simulations reveal that three ideal QD monolayers can provide exciton funneling efficiency above 80% from the most distant layer. Thereby, utilization of directed energy transfer can significantly improve light harvesting efficiency of QD devices.

  6. Growth technology, X-ray and optical properties of CdSe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Esparza-Ponce, H.E. [CINVESTAV-IPN Unidad Queretaro, Queretaro 76230, Qro (Mexico); CIMAV, Miguel de Cervantes 120, Chihuahua 31109, Chih. (Mexico)], E-mail: hilda.esparza@cimav.edu.mx; Hernandez-Borja, J. [CINVESTAV-IPN Unidad Queretaro, Queretaro 76230, Qro (Mexico); Reyes-Rojas, A. [CIMAV, Miguel de Cervantes 120, Chihuahua 31109, Chih. (Mexico); Cervantes-Sanchez, M. [CINVESTAV-IPN Unidad Queretaro, Queretaro 76230, Qro (Mexico); Instituto Tecnologico de Morelia, Morelia 58120, Michoacan (Mexico); Vorobiev, Y.V.; Ramirez-Bon, R.; Perez-Robles, J.F. [CINVESTAV-IPN Unidad Queretaro, Queretaro 76230, Qro (Mexico); Gonzalez-Hernandez, J. [CIMAV, Miguel de Cervantes 120, Chihuahua 31109, Chih. (Mexico)

    2009-02-15

    An ammonia-free chemical-bath deposition was used to obtain CdSe thin films on glass substrate. The materials used in the chemical bath were cadmium chloride complexed with sodium citrate and sodium selenosulphate. The preparation conditions, especially the starting solution characteristics, such as concentration of dissolved materials, temperature, pH value as well as deposition time and immersion cycles were optimized to obtain homogeneous stoichiometric films with good adherence to the glass substrate. The films thickness was in the range of 400-500 nm with a growing time of 4 h. The material obtained was characterized by optical absorption, SEM with the energy dispersive X-ray analysis (EDS) and X-ray diffraction. The films obtained at bath temperatures of 70 and 80 deg. C had the hexagonal structure (of wurtzite type), with crystallite size of about 20 nm. Room temperature deposition results in films with the cubic structure and crystallite size of about 4 nm. From optical transmission data, an energy gap equal to 1.88 eV was found. The material is interesting for applications in hybrid systems for solar energy conversion.

  7. Exciton-phonon complexes and optical properties in CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Menendez-Proupin, E [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile (Chile); Cabo-Bizet, N G [Facultad de Fisica, Universidad de La Habana, Vedado 10400, La Habana (Cuba); Trallero-Giner, C [Facultad de Fisica, Universidad de La Habana, Vedado 10400, La Habana (Cuba)

    2006-08-09

    A method to calculate the quantum states of exciton-phonon complexes in semiconductor nanocrystals is presented. The exciton-phonon complexes are built from a basis set made of products of phonon states and electron-hole pairs, which are coupled through the electron-phonon Froehlich interaction, and the electron-hole Coulomb and exchange interactions. In CdSe nanocrystals, the conduction band electrons are described by the effective mass equation, while the holes are represented by the spherical 4 x 4 Baldereschi-Lipari Hamiltonian. It is shown that a flexible and complete electron-hole basis, not limited to the 1s-1S{sub 3/2} octet, is essential to obtain converged eigenvalues and the correct polaron shift to the exciton energy. A study of the spectral properties is presented; in particular, the spectral region which involves the lowest exciton-phonon complex eigenstates is analysed in details. Specifically, the non-adiabatic nature of the exciton-phonon dynamics in the nanocrystals examined is clearly shown by the vibron eigenstates that were obtained.

  8. Enhancement in the photorefractive performance of organic composites photosensitized with functionalized CdSe quantum dots

    Science.gov (United States)

    Liang, Yichen; Wang, Wei; Moon, Jong-Sik; Winiarz, Jeffrey G.

    2016-08-01

    Enhancement in the photorefractive (PR) performance of organic composites photosensitized by CdSe quantum dots (QCdSe) passivated with the charge-transport ligands, sulfonated triphenyldiamine (STPD), is reported. This enhancement is primarily attributed to the ability of the passivating ligand, STPD, to facilitate the charge-transfer process between the QCdSe and the triphenyldiamine (TPD) charge-transport matrix. The PR composites exhibited a maximum photocharge-generation efficiency of 0.9% and two-beam coupling gain coefficient of 110 cm-1. These figures of merit represent a significant improvement over similar composites photosensitized with more conventional trioctylphosphine oxide-passivated QCdSe (TQCdSe). Moreover, composites photosensitized with SQCdSe had a faster response time of τ = 128 ms at an electric field of 60 V/μm compared with τ = 982 ms for those containing TQCdSe. Because of the molecular similarity between the STPD passivating groups and the TPD-based charge-transport matrix, concentrations of up to 1.4 wt% of SQCdSe are achieved in PR composites without any detectable phase separation, a considerable improvement over the 0.7 wt% for TQCdSe.

  9. EFFECT OF DIELECTRIC CONSTANT ON THE EXCITON GROUND STATE ENERGY OF CdSe QUANTUM DOTS

    Institute of Scientific and Technical Information of China (English)

    HUI PING

    2000-01-01

    The B-spline technique is used in the calculation of the exciton ground state energy based on the effective mass approximation (EMA) model.The exciton is confined in CdSe microspherical crystallites with a finite-height potential wall (dots).In this approach,(a) the wave function is allowed to penetrate to the outside of the dots; (b) the dielectric constants of the quantum dot and the surrounding material are considered to be different; and (c) the dielectric constant of the dots are size-dependent.The exciton energies as functions of radii of the dots in the range 0.5-3.5nm are calculated and compared with experimental and previous theoretical data.The results show that: (1) The exciton energy is convergent as the radius of the dot becomes very small.(2) A good agreement with the experimental data better than other theoretical results is achieved.(3) The penetration (or leaking) of the wave function and the difference of the dielectric constants in different regions are necessary for correcting the Coulomb interaction energy and reproducing experimental data.(4) The EMA model with B-spline technique can describe the status of excition confined in quantum dot very well.

  10. Selective Synthesis and Advanced Characteristic of CdSe Semiconductor Quantum Dots by Aqueous Phase

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This work mainly investigated the influences of some factors, such as, synthesis methods, pre cursor alternatives, and vacuum heat-treating process, etc, on the fluorescent characteristics of the semiconductor quantum dots synthesized by aqueous phase.The research results indicate that the fluorescent characteristic of water-solution sample prepared from Na2 SO3 precursor was sensitive to water bath heating time, and specially, its photoluminescence spectrum shows the unique phenomenon of double excitation and emission peaks.Meanwhile,the fluorescent characteristic of water- solution sample prepared from NaBH4 precursor is slightly influenced by water bath heating time, and the surface of CdSe quantum dots could be passivated by the excessive amount of NaBH4precursor, which results in the effective decrease of surface traps and great enhancement of quantum yield.Furthermore, the fluorescent emission peaks of samples could be sharpeued by vacuum heat-treating process, with its spectral full width at half of maximum (FWHM) around 30-40 nm, so the emission peaks become redshift, ofwhich the intensity greatly increases.

  11. Morphology of CdSe films prepared by chemical bath deposition: The role of substrate

    Energy Technology Data Exchange (ETDEWEB)

    Simurda, M. [Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Nemec, P. [Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic)]. E-mail: nemec@karlov.mff.cuni.cz; Formanek, P. [Institut fuer Strukturphysik, Technische Universitaet Dresden, Zellescher Weg 16, D-01062 Dresden (Germany); Nemec, I. [Charles University in Prague, Faculty of Science, Albertov 6, 128 43 Prague 2 (Czech Republic); Nemcova, Y. [Charles University in Prague, Faculty of Science, Albertov 6, 128 43 Prague 2 (Czech Republic); Maly, P. [Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic)

    2006-07-26

    We combine optical spectroscopy and transmission electron microscopy to study the growth and the structural morphology of CdSe films prepared by chemical bath deposition (CBD) on two considerably different substrates. The films grown on glass are compact and strongly adherent to the substrate. On the contrary, the films deposited on carbon-coated glass (with approx. 20 nm thick amorphous carbon layer) are only loosely adherent to the substrate. Using transmission electron microscopy we revealed that even though the films grown on both substrates are assembled from closely spaced nanocrystals with diameter of about 5 nm, the films morphology on the sub-micrometer scale is considerably different in the two cases. While the films deposited on glass are rather compact, the films prepared on carbon layer have high porosity and are formed by interconnected spheres which size is dependent on the duration of deposition (e.g. 155 nm for 6 h and 350 nm for 24 h). This shows that the choice of the substrate for CBD has a stronger influence on the sub-micrometer film morphology than on the properties of individual nanocrystals forming the film.

  12. Morphology of CdSe films prepared by chemical bath deposition: The role of substrate

    International Nuclear Information System (INIS)

    We combine optical spectroscopy and transmission electron microscopy to study the growth and the structural morphology of CdSe films prepared by chemical bath deposition (CBD) on two considerably different substrates. The films grown on glass are compact and strongly adherent to the substrate. On the contrary, the films deposited on carbon-coated glass (with approx. 20 nm thick amorphous carbon layer) are only loosely adherent to the substrate. Using transmission electron microscopy we revealed that even though the films grown on both substrates are assembled from closely spaced nanocrystals with diameter of about 5 nm, the films morphology on the sub-micrometer scale is considerably different in the two cases. While the films deposited on glass are rather compact, the films prepared on carbon layer have high porosity and are formed by interconnected spheres which size is dependent on the duration of deposition (e.g. 155 nm for 6 h and 350 nm for 24 h). This shows that the choice of the substrate for CBD has a stronger influence on the sub-micrometer film morphology than on the properties of individual nanocrystals forming the film

  13. The influence of pyridine ligand onto the structure and phonon spectra of CdSe nanocrystals

    Science.gov (United States)

    Dzhagan, V. M.; Lokteva, I.; Himcinschi, C.; Kolny-Olesiak, J.; Valakh, M. Ya.; Schulze, S.; Zahn, D. R. T.

    2011-04-01

    The influence of ligand exchange for pyridine onto the structure and phonon spectra of oleic acid-stabilized CdSe nanocrystals (NCs) is studied by resonant Raman and optical absorption spectroscopy, nuclear magnetic resonance and transmission electron microscopy. The removal of oleic acid ligand by pyridine treatment results in change of intensity ratio of the longitudinal optical (LO) phonon peak to its overtones. The latter effect is attributed to a changed electron-phonon coupling in NCs upon introduction of the hole-capturing ligand (pyridine). The upward shift and broadening of the LO phonon peak are also observed and supposed to be the result of interplay between partial oxidation of the NC and strain induced by surface reconstruction. The relative contribution of these two effects is found to be dependent on the NC size. The activation of two additional Raman features, in the low-frequency range and above the LO band, for pyridine-treated NCs is supposed to be related with induced disorder or reconstruction on the NC surface. No noticeable effect of the surface treatment and concomitant NC aggregation onto the surface optical phonon mode was observed.

  14. Direct Observation of Photoexcited Hole Localization in CdSe Nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ye; Wu, Kaifeng; Shabaev, Andrew; Efros, Alexander L.; Lian, Tianquan; Beard, Matthew C.

    2016-07-08

    Quantum-confined 1D semiconductor nanostructures are being investigated for hydrogen generation photocatalysts. In the photoreaction, after fast electron transfer, holes that remain in the nanostructure play an important role in the total quantum yield of hydrogen production. Unfortunately, knowledge of hole dynamics is limited due to lack of convenient spectroscopic signatures. Here, we directly probe hole localization dynamics within CdSe nanorods (NRs) by combining transient absorption (TA) and time-resolved terahertz (TRTS) spectroscopy. We show that when methylene blue is used as an electron acceptor, the resulting electron transfer occurs with a time constant of 3.5 +/- 0.1 ps and leaves behind a delocalized hole. However, the hole quickly localizes in the Coulomb potential well generated by the reduced electron acceptor near the NR surface with time constant of 11.7 +/- 0.2 ps. Our theoretical investigation suggests that the hole becomes confined to a ~ +/-0.8 nm region near the reduced electron acceptor and the activation energy to detrap the hole from the potential well can be as large as 235 meV.

  15. Phase transition of CdSe nanocrystallines with controlled morphologies induced by ratios of ethanolamine and water in their mixed solution

    Science.gov (United States)

    Fan, Hai; Liang, Jianbo; Zhang, Yuanguang; Zhang, Maofeng; Xi, Baojuan; Wang, Xuyang; Qian, Yitai

    2008-07-01

    The phase transition of CdSe nanocrystallines from zinc blende to wurtzite phase can be controlled by varying the volume ratio of ethanolamine (EA) and water (WA) in their mixed solution and the morphologies of the CdSe nanocrystals are controlled simultaneously. The phase transition has been demonstrated by XRD patterns and HRTEM images. The samples are investigated by Raman spectrum. The Raman shifts of the samples show a gradual blue shift with the gradual transformation from zinc blende to wurtzite CdSe phase. This method is convenient and controllable which can provide a strategy way to control the phase and morphology of the nanomaterials and study their phase transitions in nanoscale field.

  16. CdSe Quantum Dots Sensitized Mesoporous TiO2 Solar Cells with CuSCN as Solid-State Electrolyte

    Directory of Open Access Journals (Sweden)

    Guanbi Chen

    2011-01-01

    Full Text Available Mesoporous TiO2 is functionalized by 3-mercaptopropyl trimethyoxysilane (MPTMS to anchor CdSe quantum dots (QDs. The resulting TiO2/CdSe is combined with solid-state electrolyte (CuSCN to form solar cells. It is found that the efficiency of electron injection from QDs to TiO2 can be improved owing to the substitution of the long chains of organic capping agents at the surface of QDs with MPTMS. The hydrolyzate of MPTMS forms an insulating barrier layer to reduce the recombination at the TiO2/CdSe interface, leading to the increase of open-circuit voltage (Voc.

  17. Optically enhanced SnO{sub 2}/CdSe core/shell nanostructures grown by sol-gel spin coating method

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Vijay, E-mail: vijaynadda83@gmail.com; Goswami, Y. C. [School of Physical Sciences, ITM University, Turari, Gwalior, MP 474001 (India); Rajaram, P. [School of Studies in Physics, Jiwaji University, Gwalior MP 474011 (India)

    2015-08-28

    Synthesis of SnO{sub 2}/CdSe metal oxide/ chalcogenide nanostructures on glass micro slides using ultrasonic sol-gel process followed by spin coating has been reported. Stannous chloride, cadmium chloride and selenium dioxide compounds were used for Sn, Cd and Se precursors respectively. Ethylene glycol was used as complexing agent. The samples were characterized by XRD, SEM, AFM and UV-spectrophotometer. All the peaks shown in diffractograms are identified for SnO{sub 2}. Peak broadening observed in core shell due to stress behavior of CdSe lattice. Scanning electron microscope and AFM exhibits the conversion of cluster in to nanorods structures forms. Atomic force microscope shows the structures in nanorods form and a roughness reduced 1.5194 nm by the deposition of CdSe. Uv Visible spectra shows a new absorption edge in the visible region make them useful for optoelectronic applications.

  18. Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

    Science.gov (United States)

    Panarin, Y. P.; Nagaraj, Mamatha; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-10-01

    The structural and electro-optic investigations of an achiral bent-core molecule in SmAPA phase, in which the polar directors in the neighboring layers are arranged anti-ferroelectrically, show that it undergoes transformation from one biaxial to another biaxial structure via a quasi-stable uniaxial structure on the application of the electric field. The non-continuous change in biaxiality is explained by an intermediate state in which the secondary directors in the neighboring layers are perpendicular to each other.

  19. Orienteering Club

    CERN Multimedia

    Club d'Orientation

    2013-01-01

    Course d’orientation Face aux Championnats de France des Clubs à Poitiers, et à une météo hivernale (vent glaciale et pluie), il ne restait qu’une cinquantaine d’orienteurs pour participer à l’épreuve organisée le samedi 25 mai à Grange-Malval. Les participants ont tout de même bien apprécié les 5 circuits proposés par le Satus Genève. Les résultats sont disponibles sur notre site http://cern.ch/club-orientation. En plus des résultats, vous pourrez noter des informations sur la nouvelle école de CO encadrée par B. Barge, Prof. EPS à Ferney-Voltaire pour les jeunes à partir de 6 ans. La prochaine étape de la coupe genevoise se déroulera samedi 1er juin à Morez (39). Epreuve organisée par le club O’Jura&nb...

  20. Orienteering club

    CERN Multimedia

    Club d’Orientation du CERN

    2015-01-01

    Courses d’orientation Nouvelle saison nouveau programme Le Club d’orientation du CERN, en partenariat avec d’autres clubs de la région, vous propose une dizaine de courses populaires comptant pour la coupe Genevoise de printemps: samedi 28 mars: Vernand Dessus samedi 18 avril: Pougny/Challex samedi 25 avril: Chancy/Valleiry samedi 2 mai: Mauvernay samedi 9 mai: Longchaumois samedi 16 mai: Genolier samedi 30 mai: Prevondavaux samedi 6 juin: Biere-Ballens samedi 13 juin: Haut-Jura samedi 20 juin: Bonmont - Finale Ces courses sont ouvertes à tous, quel que soit le niveau, du débutant au sportif confirmé, en famille ou en individuel, en promenade ou en course. Les inscriptions se font sur place le jour de l’épreuve. Si vous êtes débutant, vous pouvez profiter d’une initiation offerte par l’organisateur avant de vous lancer sur un parcours. Le club propose aussi...

  1. Orienteering Club

    CERN Multimedia

    Club d'orientation

    2010-01-01

    COURSE D’ORIENTATION La finale de la coupe de printemps Après avoir remporté le challenge club, samedi 29 juin lors du relais inter-club à Lausanne, le Club d’orientation du CERN organisait la dernière étape de la coupe genevoise de printemps samedi 5 juin à Saint-Cergue dans les bois de Monteret (Canton de Vaud). Plus de 100 participants se sont déplacés pour venir participer à la finale et découvrir une toute nouvelle carte dans une forêt vallonnée. Les résultats pour chaque circuit de cette étape sont : Technique long : 1. Jurg Niggli du club O’Jura, 2. Clément Poncet, 3. Oystein Midttun. Technique moyen : 1. Zoltan Trocsanyi CO CERN, 2. Christophe Ingold, 3. Christina Falga. Technique court : 1. Pierre-Andre Baum, CARE Vevey, 2. Emese Szunyog, 3. Solène Balay. Facile moyen : 1. Elisa P...

  2. Orienteering club

    CERN Multimedia

    Orienteering Club

    2016-01-01

    Course d'orientation Calendrier des courses d’orientation Coupe genevoise d’automne 2016 Samedi 3 septembre : La Faucille (01) Samedi 10 septembre : Prémanon (39) Samedi 17 septembre : Saint-Cergue (VD) Samedi 24 septembre : Jorat / Corcelles (VD) Samedi 1 octobre: Bière - Ballens (VD) -relais Vendredi 14 octobre : Parc Mon Repos (GE) - nocturne Samedi 15 octobre : Terrasse de Genève (74) Samedi 29 octobre : Bonmont (VD) Samedi 5 novembre : Pomier (74) – one-man-relay - Finale   Courses ouvertes à toutes et à tous, sportifs, familles, débutants ou confirmés, du CERN ou d’ailleurs. Cinq circuits disponibles, ceci va du facile court (2 km) adapté aux débutants et aux enfants jusqu’au parcours technique long de 6 km pour les chevronnés en passant par les parcours facile moyen (4&am...

  3. COURSE ORIENTATION

    CERN Multimedia

    Club d'orientation du CERN

    2015-01-01

      Les coureurs d’orientation de la région se sont donné rendez-vous samedi dernier dans les bois de Pougny/Challex lors de l’épreuve organisée par le club d’orientation du CERN. La carte proposée pour les 5 circuits offrait aussi bien un coté très technique avec un relief pentu qu’un coté avec de grandes zones plates à forêt claire. Le parcours technique long comportant 20 postes a été remporté par Beat Muller du COLJ Lausanne en 56:26 devançant Denis Komarov, CO CERN en 57:30 et Yvan Balliot, ASO Annecy en 57:46. Pour les autres circuits les résultats sont les suivants: Technique moyen (13 postes): 1er Joël Mathieu en 52:32 à une seconde du 2e Vladimir Kuznetsov, COLJ Lausanne-Jorat, 3e Jean-Bernard Zosso, CO CERN, en 54:01 Technique court (12 postes): 1er Lennart Jirden, ...

  4. Orienteering Club

    CERN Document Server

    Club d'Orientation

    2012-01-01

     Course d’orientation C’est sous un magnifique soleil que s’est tenue la 7e épreuve de la coupe genevoise organisée par le club d’orientation du CERN. Les organisateurs avaient concocté des parcours assez techniques sur le site de La Faucille. Sur le parcours technique long, beau podium avec la victoire de Domenico Lepori (double médaillés aux championnats du monde en 2010 en vétéran) du club Care Vevey en 1:00:23, juste devant Jürg Niggli du club O’Jura en 1:00:56 puis Beat Mueller du club Lausanne-Jorat en 1:04:28. Sur le parcours technique moyen, Franck Longchampt s’est octroyé la première place, sur le parcours technique court, le jeune Julien Vuitton, qui n’a pas tout à fait 11 ans, a remporté son circuit. Coté parcours facile moyen, Victor Kuznetsov a une fois de plus gagn&eacut...

  5. Club Orientation

    CERN Multimedia

    Club d'orientation

    2014-01-01

      COURSE ORIENTATION   Pas moins de 100 concurrents sont venus s’affronter sur les parcours proposés par le club d’orientation du CERN ce samedi 26 avril lors de la 4e étape de la coupe genevoise de printemps. Les podiums ont été attribués à :  Technique long avec 19 postes : 1er Yvan Balliot, ASO Annecy en 1:01:39 ; 2e Dominique Fleurent, ASO Annecy, en 1:05:12 ; 3e Rémi Fournier, SOS Sallanches, en 1:05:40. Technique moyen avec 14 postes : 1er Jean-Bernard Zosso, CO CERN, en 46:42 ; 2e Céline Zosso, CO CERN, en 50:51 ; 3e Clément Poncet, O’Jura Prémanon, en 51:27. Technique court avec 13 postes : 1er Jaakko Murtomaki, YKV Seinaejoki, en 36:04 ; 2e Marc Baumgartner en 41:27 ; 3e Natalia Niggli, O’Jura Prémanon, en 52:43. Sur les parcours facile moyen et facile court, victoire respectivement de Stéphanie...

  6. Orienteering club

    CERN Multimedia

    Club d'orientation

    2010-01-01

    Course d’orientation : Coupe Genevoise de printemps 2010 Et c’est reparti pour une nouvelle saison! Pour cette coupe de printemps 2010, le Club d’Orientation du CERN, en partenariat avec d’autres clubs de la région, vous propose le calendrier suivant: – samedi 20 mars : Cossonay (Vd) – samedi 10 avril : Echallens (Vd) – samedi 17 avril : Trélex (Vd) – samedi 24 avril : Genolier (Vd) – samedi 1 mai : Vulbens/Valleiry (74) – samedi 8 mai : Bois de la Rippe (Vd) – samedi 29 mai : Sauvabellin (Vd) : relais – samedi 5 juin: St Cergue (Vd) : grande finale Les courses populaires ont lieu en général le samedi après-midi, elles sont ouvertes à tous, quel que soit le niveau, du débutant au sportif confirmé, en famille ou en individuel, en promenade ou en course. Pour cela, divers types de parcours sont &agr...

  7. Orienteering club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Courses d’orientation Le soleil enfin de retour a incité nombre de sportifs et promeneurs à nous rejoindre dans la belle forêt de Challex /Pougny pour la deuxième étape de notre coupe de printemps 2013. Certains sont revenus crottés et fourbus alors que d’autres avaient les joues bien roses après un grand bol d’air frais. Mais tous avaient passé un agréable moment dans la nature. Nous rappelons que nos activités sont ouvertes à tous, jeunes, moins jeunes, sportifs, familles, du CERN ou d’ailleurs, et que le seul inconvénient est que si vous goûtez à la course d’orientation, il vous sera difficile de ne pas y revenir ! Samedi 20 avril 2013, nous serons sur le Mont Mourex (entre Gex et Divonne) pour notre prochaine épreuve et vous y serez les bienvenus. Les inscriptions et les départ...

  8. Orienteering Club

    CERN Multimedia

    Club d'Orientation

    2015-01-01

    Course orientation C’est au pied du Salève, proche du Golf de Bosset, que le club d’orientation du CERN (CO CERN) a organisé samedi 19 septembre une nouvelle épreuve comptant pour la Coupe Genevoise d’automne. La zone « des Terrasses de Genève » avait été cartographiée et mise en service l’année dernière. Les participants ont pu apprécier un terrain ludique avec beaucoup de microreliefs, de points d’eau et de gros rochers, le tout au milieu d’une forêt assez claire et agréable à courir. Sur le parcours technique long, le résultat a été très serré puisque Pierrick Merino du club d’Annecy a gagné avec seulement 9 secondes d’avance sur Gaëtan Vuitton (CO CERN) qui confiait avoir perdu beaucoup du te...

  9. Comparison of calculation methods for the tunnel splitting at excited states of biaxial spin models

    Institute of Scientific and Technical Information of China (English)

    Cui Xiao-Bo; Chen Zhi-De

    2004-01-01

    We present the calculation and comparison of tunnel splitting at excited levels of biaxial spin models by various methods, including the generalized instanton method, the generalized path integral method for coherent spin states,the perturbation method, and the exact method by numerical diagonalization of the Hamiltonian. It is found that,for integer spin with spin number around 10, tunnel splitting predicted by the generalized path integral for coherent spin states is about 10-n times of the exact numerical result for the nth excited level, while the ratio of the results of the perturbation method and the exact numerical method diverges in the large spin limit. We thus conclude that the generalized instanton method is the best approximate way for calculating tunnel splitting in spin models.

  10. Biaxial lidar efficiency rising based on improving of spatial selectivity and stability against background radiation

    Energy Technology Data Exchange (ETDEWEB)

    Agishev, R.R.; Bajazitov, R.A.; Galeyev, M.M. [Kazan State Technical Univ., Tatarstan (Russian Federation). Dept. of Radioelectronic and Quantum Systems

    1996-12-31

    A criterion of spatial-angular efficiency (SAE) of remote electro-optical systems for atmosphere monitoring is formulated. The dependencies of the SAE from normalized range and minimal operating range for different optical receiving schemes of ground-based biaxial lidar are analyzed. It is shown that low SAE of traditional VIS and NIR systems are a main cause of a low signal-to-background-noise ratio at the photodetector input, the considerable measurements errors. and the following low accuracy of atmospheric optical parameters reconstruction. The most effective protection against sky background radiation in such systems consists in forming an angular field according to the introduced SAE criterion. Some approaches to achieve high value of the SAE-parameter for receiving system optimization are discussed.

  11. Measurement of refractive index of biaxial potassium titanyl phosphate crystal plate using reflection spectroscopic ellipsometry technique

    Indian Academy of Sciences (India)

    A K Chaudhary; A Molla; A Asfaw

    2009-10-01

    The paper reports the measurement of refractive indices and anisotropic absorption coefficients of biaxial potassium titanyl phosphate (KTP) crystal in the form of thin plate using reflection ellipsometry technique. This experiment is designed in the Graduate Optics Laboratory of the Addis Ababa University and He–Ne laser ( = 632.8 nm), diode laser ( = 670.0 nm) and temperature-tuned diode laser ( = 804.4 and 808.4 nm), respectively have been employed as source. The experimental data for , are fitted to the Marquardt–Levenberg theoretical model of curve fitting. The obtained experimental data of refractive indices are compared with different existing theoretical and experimental values of KTP crystals and found to be in good agreement with them.

  12. A novel biaxial specimen for inducing residual stresses in thermoset polymers and fibre composite material

    DEFF Research Database (Denmark)

    Jakobsen, Johnny; Andreasen, Jens Henrik; Jensen, Martin

    2015-01-01

    A new type of specimen configuration with the purpose of introducing a well-defined biaxial residual (axisymmetric) stress field in a neat thermoset or a fibre composite material is presented. The ability to experimentally validate residual stress predictions is an increasing need for design...... engineers when they challenge the material limits in present and future thermoset and composite component. In addition to the new specimen configuration, this paper presents an analytical solution for the residual stress state in the specimen. The analytical solution assumes linear elastic and isotropic...... material behaviour. Experimental strain release measurements and the analytical solution determine the residual stress state present in the material. A demonstration on neat epoxy is conducted and residual stress predictions of high accuracy and repeatability have been achieved. The precise determination...

  13. Numerical simulations of biaxial experiments on damage and fracture in sheet metal forming

    Science.gov (United States)

    Gerke, Steffen; Schmidt, Marco; Brünig, Michael

    2016-08-01

    The damage and failure process of ductile metals is characterized by different mechanisms acting on the micro-scale as well as on the macro-level. These deterioration processes essentially depend on the material type and on the loading conditions. To describe these phenomena in an appropriate way a phenomenological continuum damage and fracture model has been proposed. To detect the effects of stress-state-dependent damage mechanisms, numerical simulations of tests with new biaxial specimen geometries for sheet metals have been performed. The experimental results including digital image correlation (DIC) show good agreement with the corresponding numerical analysis. The presented approach based on both experiments and numerical simulation provides several new aspects in the simulation of sheet metal forming processes.

  14. Voigt wave investigation in the KGd(WO4)2:Nd biaxial laser crystal

    Science.gov (United States)

    Brenier, Alain

    2015-07-01

    We have investigated the Nd3+-doped KGd(WO4)2 biaxial laser crystal for wave propagation directions in the vicinity of the optical axis at wavelengths tunable around 800 nm. The angular absorption distribution was found to be strongly anisotropic. Increasing absorption, the optical axis splits in two new ones able to propagate unchanged a left or a right circularly polarized light and able to propagate a circularly polarized Voigt wave with a linear spatial dependence. The intensities of the transmitted light in different configurations of polarizations were investigated. The angular displacement of the two optical axes versus the absorbed wavelengths was measured and explained with a single oscillator model. The light energy propagation was found distributed inside a crescent-shaped area.

  15. Development of a synchrotron biaxial tensile device for in situ characterization of thin films mechanical response

    International Nuclear Information System (INIS)

    We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine working in the synchrotron environment for in situ diffraction characterization of thin polycrystalline films mechanical response. The machine has been designed to test compliant substrates coated by the studied films under controlled, applied strain field. Technological challenges comprise the sample design including fixation of the substrate ends, the related generation of a uniform strain field in the studied (central) volume, and the operations from the beamline pilot. Preliminary tests on 150 nm thick W films deposited onto polyimide cruciform substrates are presented. The obtained results for applied strains using x-ray diffraction and digital image correlation methods clearly show the full potentialities of this new setup.

  16. Impacts of virtual substrate doping on high frequency characteristics of biaxially strained Si PMOSFET

    Science.gov (United States)

    Khatami, Mohammad Mahdi; Shalchian, Majid; Kolahdouz, Mohammadreza

    2015-09-01

    Formation of a parasitic channel in biaxially strained Si channel p-MOSFET, degrades performance of the device. In this paper the effect of SiGe (virtual substrate) doping on formation of parasitic channel and high frequency characteristics of the strained MOSFET has been studied. Simulation results, indicate that increasing virtual substrate's doping from e.g. 4 × 1015 cm-3 to 4 × 1017 cm-3 effectively eliminates parasitic channel by reducing hole concentration from 1 × 1017 cm-3 to 1 × 1011 cm-3 in the parasitic channel. This improves MOSFET's characteristics including parasitic capacitances and channel length modulation. Also it has been demonstrated that the highest unity-gain bandwidth might be achieved at doping level of 4 × 1017 cm-3.

  17. The Landau-de Gennes theory of nematic liquid crystals: Uniaxiality versus Biaxiality

    KAUST Repository

    Majumdar, Apala

    2011-12-01

    We study small energy solutions within the Landau-de Gennes theory for nematic liquid crystals, subject to Dirichlet boundary conditions. We consider two-dimensional and three-dimensional domains separately. In the two-dimensional case, we establish the equivalence of the Landau-de Gennes and Ginzburg-Landau theory. In the three-dimensional case, we give a new definition of the defect set based on the normalized energy. In the threedimensional uniaxial case, we demonstrate the equivalence between the defect set and the isotropic set and prove the C 1,α-convergence of uniaxial small energy solutions to a limiting harmonic map, away from the defect set, for some 0 < a < 1, in the vanishing core limit. Generalizations for biaxial small energy solutions are also discussed, which include physically relevant estimates for the solution and its scalar order parameters. This work is motivated by the study of defects in liquid crystalline systems and their applications.

  18. Numerical and experimental analysis of the directional stability on crack propagation under biaxial stresses

    Energy Technology Data Exchange (ETDEWEB)

    RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME), Edificio 5. 2do Piso, Unidad Profesional Adolfo Lopez Mateos ' Zacatenco' Col. Lindavista, C.P. 07738, Mexico, D.F. (Mexico); Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M, E-mail: rrodriguezm@ipn.m, E-mail: urrio332@hotmail.co, E-mail: guiurri@hotmail.co, E-mail: luishector56@hotmail.co, E-mail: eamerchan@gmail.co, E-mail: ricname@hotmail.co, E-mail: jsandovalp@ipn.m [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME). Unidad profesional, AZCAPOTZALCO, Av. de las Granjas No. 682, Col. Sta. Catarina Azcapotzalco, C.P. 02550, Mexico D.F. (Mexico)

    2009-08-01

    In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K{sub 1} values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.

  19. ANALYTICAL SOLUTIONS TO STRESS CONCENTRATION PROBLEM IN PLATES CONTAINING RECTANGULAR HOLE UNDER BIAXIAL TENSIONS

    Institute of Scientific and Technical Information of China (English)

    Yi Yang; Jike Liu; Chengwu Cai

    2008-01-01

    The stress concentration problem in structures with a circular or elliptic hole can be investigated by analytical methods.For the problem with a rectangular hole,only approximate results are derived.This paper deduces the analytical solutions to the stress concentration problem in plates with a rectangular hole under biaxial tensions.By using the U-transformation technique and the finite element method,the analytical displacement solutions of the finite element equations are derived in the series form.Therefore,the stress concentration can then be discussed easily and conveniently.For plate problem the bilinear rectangular element with four nodes is taken as an example to demonstrate the applicability of the proposed method.The stress concentration factors for various ratios of height to width of the hole are obtained.

  20. Powder metallurgy for the fabrication of bi-axially textured Ni tapes for YBCO coated conductors

    International Nuclear Information System (INIS)

    Bi-axially textured Ni tapes for YBCO coated conductors were fabricated by forming, sintering, cold rolling and heat treatment of Ni powder compacts. The powder metallurgy process consists of filling of fine Ni powders in a rubber mold, cold isostatical pressing in a water chamber and sintering of the powder compacts. The sintered compacts were cold-rolled and made into tapes with a thickness of 100 micron and then heat-treated at 1000 deg. C for various time periods for the development of the (2 0 0) texture. The (2 0 0) texture of Ni tape was successfully formed through the optimization of the recrystallization heat treatment condition for the cold rolled Ni tapes. The full width half maximum of the Ni tapes was 8-10 deg. and the atomic force microscopy surface roughness was 3-5 nm

  1. Application of magnetomechanical hysteresis modeling to magnetic techniques for monitoring neutron embrittlement and biaxial stress

    International Nuclear Information System (INIS)

    The objective is to investigate experimentally and theoretically the effects of neutron embrittlement and biaxial stress on magnetic properties in steels, using various magnetic measurement techniques. Interaction between experiment and modeling should suggest efficient magnetic measurement procedures for determining neutron embrittlement biaxial stress. This should ultimately assist in safety monitoring of nuclear power plants and of gas and oil pipelines. In the first six months of this first year study, magnetic measurements were made on steel surveillance specimens from the Indian Point 2 and D.C. Cook 2 reactors. The specimens previously had been characterized by Charpy tests after specified neutron fluences. Measurements now included: (1) hysteresis loop measurement of coercive force, permeability and remanence, (2) Barkhausen noise amplitude; and (3) higher order nonlinear harmonic analysis of a 1 Hz magnetic excitation. Very good correlation of magnetic parameters with fluence and embrittlement was found for specimens from the Indian Point 2 reactor. The D.C. Cook 2 specimens, however showed poor correlation. Possible contributing factors to this are: (1) metallurgical differences between D.C. Cook 2 and Indian Point 2 specimens; (2) statistical variations in embrittlement parameters for individual samples away from the stated men values; and (3) conversion of the D.C. Cook 2 reactor to a low leakage core configuration in the middle of the period of surveillance. Modeling using a magnetomechanical hysteresis model has begun. The modeling will first focus on why Barkhausen noise and nonlinear harmonic amplitudes appear to be better indicators of embrittlement than the hysteresis loop parameters

  2. Controlled growth of catalyst assisted and catalyst free CdSe micro cactuses with sharply pointed nanorods, their Photoluminescence (PL) and Photo electrochemical (PEC) properties

    International Nuclear Information System (INIS)

    Highlights: ► Catalyst assisted (CA) and catalyst free (CF) growth of CdSe microcactuses with sharply pointed nanorods. ► VLS growth mechanism is proposed for CA and solid state chemical reaction for CF growth of CdSe Microcactus. ► Fabrication of PEC solar cell with 0.47% efficiency and 0.35 fill factor. ► PL studies exhibit peaks at 672 nm for CA and 596 nm for CF growth of CdSe cactuses respectively. ► CF growth is concluded to be better option as compared to CA growth for nanostructured materials. - Abstract: We report here a thermochemical approach for controlling the catalyst assisted and catalyst free growth of CdSe cactus like structures with sharply pointed nanorods (SPNR). The cactuses were simultaneously obtained on the silicon substrate and in semicircular alumina boat using cadmium and selenium powders as precursors under ammonia gas flow. The aqueous ammonia helps to control the growth of 1D structure and the formation of CdSe. Vapor–liquid–solid (VLS) growth mechanism is proposed for the catalyst assisted while solid state chemical reaction is suggested for the catalyst free growth of microcactuses. The microcactuses obtained in the boat as powder form are hollow whereas solid on the silicon substrate. Room temperature photoluminescence (PL) studies exhibit sharp peak at 672 nm for catalyst assisted CdSe microcactuses. A broad peak at 596 nm was observed for catalyst free growth of CdSe SPNR. In this work we have demonstrated that PL emission from the catalyst free growth of nanostructured CdSe is broad and intense. These two peaks are blue shifted from the bulk. Nanorods emerging from exterior surface of cactus like structures are observed to have decreasing diameter along vertical-axis and end up in SPNR. Average diameter in the middle of nanorods is estimated in the range of 250–450 nm. Photo electrochemical (PEC) solar cell is fabricated on ITO coated glass substrate with the help of PVDF in NMP solution. The efficiency and fill

  3. A DFT/TDDFT study on the optoelectronic properties of the amine-capped magic (CdSe)13 nanocluster.

    Science.gov (United States)

    Azpiroz, Jon M; Matxain, Jon M; Infante, Ivan; Lopez, Xabier; Ugalde, Jesus M

    2013-07-14

    Motivated by the recent experiments by Wang et al. (Angew. Chem., Int. Ed. 2012, 51, 6154-6157), in which the alkylamine-capped magic-size (CdSe)13 has been isolated for the first time, we report on the computational modeling of the putative low-lying isomers of (CdSe)13, both bare and ligand-protected. According to Density Functional Theory (DFT) calculations, the core@cage configuration Se@Cd13Se12, consisting of a Se atom incarcerated in the center of a puckered Cd13Se12 cage, lies lower in energy than fullerene- and wurtzite-like structures. Methylamine-capped nanoclusters present average bond energies per ligand of about 20 kcal mol(-1), while bond energy decomposition schemes show this interaction to be mostly electrostatically-driven. The computed Time-Dependent-DFT (TDDFT) spectrum of the lowest-lying methylamine-protected (CdSe)13 isomer essentially coincides with the experiment, with a notable blueshift of the absorption features induced by the ligands. The LUMO has been found to be the acceptor orbital for all the lowest-lying electronic excitations, in both the bare and methylamine-capped clusters, which could explain the narrow emission profiles inherent in semiconductor nanostructures. In addition, the attachment of pyridine and aniline molecules has been evaluated. Interestingly, the molecular orbitals of these aromatic amines located on the edges of the valence and conduction bands may act as trap states, in agreement with experimental evidences. In the particular case of pyridine molecules, unoccupied orbitals intrude into the HOMO-LUMO gap of the cluster. PMID:23712668

  4. Orientation games in kindergarten

    OpenAIRE

    Pišek, Anja

    2012-01-01

    The thesis presents the area of general orientation and orientation of the child. The focus is placed on orientation games for preschool children. The first part outlines different definitions of orientation, types of orientation, accessories for orientation and major errors in orientation. It also presents the development of spatial orientation of preschool children, the development of the concept of space according to the level of cognitive development in line with the theory by Piaget,...

  5. Orienting hypnosis.

    Science.gov (United States)

    Hope, Anna E; Sugarman, Laurence I

    2015-01-01

    This article presents a new frame for understanding hypnosis and its clinical applications. Despite great potential to transform health and care, hypnosis research and clinical integration is impaired in part by centuries of misrepresentation and ignorance about its demonstrated efficacy. The authors contend that advances in the field are primarily encumbered by the lack of distinct boundaries and definitions. Here, hypnosis, trance, and mind are all redefined and grounded in biological, neurological, and psychological phenomena. Solutions are proposed for boundary and language problems associated with hypnosis. The biological role of novelty stimulating an orienting response that, in turn, potentiates systemic plasticity forms the basis for trance. Hypnosis is merely the skill set that perpetuates and influences trance. This formulation meshes with many aspects of Milton Erickson's legacy and Ernest Rossi's recent theory of mind and health. Implications of this hypothesis for clinical skills, professional training, and research are discussed.

  6. Orienteering club

    CERN Multimedia

    Club d'orientation

    2011-01-01

    Reprise fin août Le Club d’orientation, en partenariat avec d’autres clubs de la région, vous propose une nouvelle série de courses pour cet automne. Le calendrier à retenir est le suivant : Samedi 27 août : Granges Malval (GE) – type classique Samedi 10 septembre : Lamoura (39) – type classique Samedi 17 septembre : La Dôle (F/VD) – type classique Samedi 24 septembre : Monteret (VD) – relais Samedi 8 octobre : Saint Cergue (VD) – type classique Vendredi 14 octobre : Les Evaux (GE) – nocturne Samedi 15 octobre : Grand Jorat (VD) – type classique Samedi 22 octobre : Pomier (74) – type classique Samedi 5 novembre : Echallens (VD) – type classique Samedi 12 novembre : CERN (GE) - sprint - Finale Généralement cinq circuits sont disponibles : ceci va du facile court (2 km) adapt&eacu...

  7. SINTEZA IN KARAKTERIZACIJA NANODELCEV CdS IN CdSe S SONOKEMIJSKO METODO V VODNEM MEDIJU

    OpenAIRE

    Danč, Valerija

    2010-01-01

    Sonokemija je področje kemije, kjer na potek kemijskih reakcij odločilno vpliva zvočna energija v obliki ultrazvoka. Ultrazvok in z njimi povezani pojavi so že znani več kot sto let, njegova uporaba v kemiji pa dosega razcvet v današnjem času. Naše raziskave so temeljile na sintezah nanodelcev kadmijevih sulfidov (CdS) in kadmijevih selenidov (CdSe) s sonokemijsko metodo. Ta metoda se je pri sintezah pokazala kot zelo uporabna, saj so končni produkti nanokristalinični materiali. Namen ra...

  8. Temperature-dependent photovoltaic behavior of CdSe quantum dots/P3HT hybrid thinfilm

    Science.gov (United States)

    Zhang, Hui-chao; Du, Xiao-wei; Wang, Yu-qiao; Guan, Qiu-mei; Sun, Yue-ming; Cui, Yi-ping; Zhang, Jia-yu

    2013-03-01

    An organic-inorganic hybrid solar cell based on CdSe quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) was fabricated. Its temperature-dependent photovoltaic behaviors, such as I-V characteristic curves and open circuit voltage (Voc) transient response, were measured. The photovoltaic behavior of this hybrid thin film device was similar with that of organic thin film solar cells, according to analysis results based on the equivalent circuit method. The exact carrier lifetime was remarkably different between under low-temperature region and under temperature above 197 K.

  9. Synthesis of CdSe nanoparticles and their effect on the antioxidant activity of Spirulina platensis and Porphyridium cruentum cells

    International Nuclear Information System (INIS)

    Single-crystalline cadmium selenide nanoparticles were obtained using high-temperature solution phase synthesis (HTSPS) synthesis. X-Ray powder diffraction and transmission electron microscopy were used to confirm the crystallinity and morphology of the resulting nanoparticles. To study the action of CdSe on antioxidant activity, we selected two biotechnological important strains of microalgae: cyanobacteria Spirulina platensis and red microalgae Porphyridium cruentum. In the case of Porphyridium cruentum, the obtained results demonstrated an increase in the productivity. For Spirulina platensis, the presence of the compound in the cultivating medium decreased the productivity of cyanobacteria.

  10. Enhanced growth of highly lattice-mismatched CdSe on GaAs substrates by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jyh-Shyang, E-mail: jswang@cycu.edu.tw [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Tsai, Yu-Hsuan; Wang, Hsiao-Hua; Ke, Han-Xiang; Tong, Shih-Chang [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Yang, Chu-Shou [Graduate institute of Electro-Optical Engineering, Tatung University, Taipei 10452, Taiwan (China); Wu, Chih-Hung [Institute of Nuclear Energy Research, Longtan 32546, Taiwan (China); Shen, Ji-Lin [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China)

    2013-04-01

    This work demonstrates the improvement of the molecular beam epitaxial growth of zinc-blende CdSe on (0 0 1) GaAs substrate with a large lattice mismatch by introducing a small amount of Te atoms. Exposing the growing surface to Te atoms changes the reflection high-energy electron diffraction pattern from spotty to streaky together with (2 × 1) surface reconstruction, and greatly reduces the full width at half maximum of the X-ray rocking curve and increases the integral intensity of room-temperature photoluminescence by a factor of about nine.

  11. Quenching of coumarin emission by CdSe and CdSe/ZnS quantum dots: Implications for fluorescence reporting

    Energy Technology Data Exchange (ETDEWEB)

    Baride, Aravind [Department of Chemistry, University of South Dakota, Vermillion, SD 57069 (United States); Engebretson, Daniel [Biomedical Engineering, University of South Dakota, Vermillion, SD 57069 (United States); Berry, Mary T. [Department of Chemistry, University of South Dakota, Vermillion, SD 57069 (United States); Stanley May, P., E-mail: smay@usd.edu [Department of Chemistry, University of South Dakota, Vermillion, SD 57069 (United States)

    2013-09-15

    The photoinduced release of highly fluorescent 7-diethylamino coumarin (7DEAC) from CdSe quantum dots (QD) modified with a thiocinnamate ligand (11-mercapto undecyl-E-3-(4-(N,N-diethylamino)-2-hydroxy phenyl) propenoate, [4DEATC]) has been previously described. Coumarin fluorescence was used to ‘report’ the photochemical reaction. The current study quantifies the quenching effect of the QDs on the coumarin emission in this system. A systematic study is presented on the quenching of 7DEAC by CdSe and CdSe/ZnS quantum dots capped with 2-[2-(2-methoxyethoxy)ethoxy] ethanethiol (PEG-thiol). A new method for the functionalization of CdSe and CdSe/ZnS QDs with PEG-thiol was developed, which does not require isolation of the as-synthesized QDs. Stern–Volmer analysis was applied to quantify the effect of the PEG-CdSe and PEG-CdSe/ZnS on 7DEAC emission. The Stern–Volmer constant, K{sub SV}, was shown to be inversely proportional to temperature for quenching by PEG-CdSe, and the fluorescence lifetime of 7DEAC was shown to be independent of PEG-CdSe concentration. Room-temperature K{sub SV} values were similar for the PEG-CdSe and PEG-CdSe/ZnS quenchers. The large magnitude of K{sub SV}, the temperature dependence of K{sub SV}, the lifetime data, and the similarity of K{sub SV} values for the core and core–shell QD quenchers are all consistent with a static quenching mechanism. Assuming a static quenching mechanism, the temperature dependence of the coumarin-QD binding constant, K{sub b}, was used to estimate the ΔH and ΔS for the binding process. -- Highlights: • Quenching of a coumarin derivative by CdSe and CdSe/ZnS quantum dots is demonstrated • Stern–Volmer analysis is performed as a function of temperature • Fluorescence lifetime analysis was used to support Stern–Volmer analysis • Data overwhelmingly support quenching via a Static Mechanism • Quenching of coumarin by quantum dots is significant and must be considered in any release and report

  12. Properties of electrospun CdS and CdSe filled poly(methyl methacrylate) (PMMA) nanofibres

    Energy Technology Data Exchange (ETDEWEB)

    Mthethwa, T.P. [University of Johannesburg, Department of Chemical Technology, P.O. Box 17011, Doornfontein 2028 (South Africa); Moloto, M.J., E-mail: mmoloto@uj.ac.za [University of Johannesburg, Department of Chemical Technology, P.O. Box 17011, Doornfontein 2028 (South Africa); De Vries, A.; Matabola, K.P. [CSIR Materials Science and Manufacturing, 4 Gomery avenue, Summerstrand, Port Elizabeth 6000 (South Africa)

    2011-04-15

    Graphical abstract: SEM images of CdS/PMMA showing coiling as loading of CdS nanoparticles is increased. Thermal stability is increased with increase in %loading of both CdS and CdSe nanoparticles. Research highlights: {yields} TOPO-capped CdS and HDA-capped CdSe nanoparticles were synthesized and fully characterized. {yields} The nanoparticles were mixed with the polymer, PMMA using electrospinning technique using 2, 5 and 10% weight loadings. {yields} The mixture was spun to produce fibres with optical and thermal properties showing significant change and also the increase in loading causing bending or spiraling. {yields} Both TEM images for nanoparticles and SEM for fibres shows the morphology and sizes of the particles. -- Abstract: Electrospinning technique was used to fabricate poly(methyl methacrylate) (PMMA) fibres incorporating CdS and CdSe quantum dots (nanoparticles). Different nanoparticle loadings (2, 5 and 10 wt% with respect to PMMA) were used and the effect of the quantum dots on the properties of the fibres was studied. The optical properties of the hybrid composite fibres were investigated by photoluminescence and UV-vis spectrophotometry. Scanning electron microscopy (SEM), X-ray diffraction and FTIR spectrophotometry were also used to investigate the morphology and structure of the fibres. The optical studies showed that the size-tunable optical properties can be achieved in the polymer fibres by addition of quantum dots. SEM images showed that the morphologies of the fibres were dependent on the added amounts of quantum dots. A spiral type of morphology was observed with an increase in the concentration of CdS and CdSe nanoparticles. Less beaded structures and bigger diameter fibres were obtained at higher quantum dot concentrations. X-ray diffractometry detected the amorphous peaks of the polymer and even after the quantum dots were added and the FTIR analysis shows that there was no considerable interaction between the quantum dots and the

  13. EDITORIAL: Optical orientation Optical orientation

    Science.gov (United States)

    SAME ADDRESS *, Yuri; Landwehr, Gottfried

    2008-11-01

    priority of the discovery in the literature, which was partly caused by the existence of the Iron Curtain. I had already enjoyed contact with Boris in the 1980s when the two volumes of Landau Level Spectroscopy were being prepared [2]. He was one of the pioneers of magneto-optics in semiconductors. In the 1950s the band structure of germanium and silicon was investigated by magneto-optical methods, mainly in the United States. No excitonic effects were observed and the band structure parameters were determined without taking account of excitons. However, working with cuprous oxide, which is a direct semiconductor with a relative large energy gap, Zakharchenya and his co-worker Seysan showed that in order to obtain correct band structure parameters, it is necessary to take excitons into account [3]. About 1970 Boris started work on optical orientation. Early work by Hanle in Germany in the 1920s on the depolarization of luminescence in mercury vapour by a transverse magnetic field was not appreciated for a long time. Only in the late 1940s did Kastler and co-workers in Paris begin a systematic study of optical pumping, which led to the award of a Nobel prize. The ideas of optical pumping were first applied by Georges Lampel to solid state physics in 1968. He demonstrated optical orientation of free carriers in silicon. The detection method was nuclear magnetic resonance; optically oriented free electrons dynamically polarized the 29Si nuclei of the host lattice. The first optical detection of spin orientation was demonstrated by with the III-V semiconductor GaSb by Parsons. Due to the various interaction mechanisms of spins with their environment, the effects occurring in semiconductors are naturally more complex than those in atoms. Optical detection is now the preferred method to detect spin alignment in semiconductors. The orientation of spins in crystals pumped with circularly polarized light is deduced from the degree of circular polarization of the recombination

  14. Cytotoxic effect of CdSe quantum dots on mouse embryonic development

    Institute of Scientific and Technical Information of China (English)

    Wen-hsiung CHAN; Nion-heng SHIAO

    2008-01-01

    Aim: The aim of this study was to examine the cytotoxic effect of quantum dots (QD), a novel luminescent material, on early post-implantation embryonic development. Methods: Mouse blastocysts were incubated in medium with or without CdSe-core QD (250 or 500 nmol/L) for 24 h. Cell apoptosis was analyzed by terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling assay and Annexin V/propidium iodide staining, and proliferation was investigated by dual differential staining. Pre-implantation and post-implantation development was assessed by in vitro and in vivo analyses, respectively. Results: The apoptotic staining analysis showed that CdSe-core QD induced apoptosis in mouse blastocysts in a dose-dependent manner. Pretreatment of blastocysts with CdSe-core QD inhibited cell proliferation, primarily in the inner cell mass. CdSe-core QD also inhibited post-implantation embryonic development; fewer CdSe-core QD-pretreated blastocysts reached the later stages of development com-pared to the controls. The pre-implantation development of morulas into blasto-cysts was also inhibited by CdSe-core QD. Furthermore, CdSe-core QD at 500 nmol/L were associated with resorption of post-implantation blastocysts and a decrease in fetal weight. The cytotoxicity of CdSe QD in embryonic development was significantly reduced by the addition of a ZnS coating. Conclusion: Our results show that CdSe-core QD induce apoptosis in mouse blastocysts, inhibit cell proliferation, retard early post-implantation blastocyst development, and in-crease early-stage blastocyst death in vitro and in vivo.

  15. Orienteering club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Course d'orientation Finale de la coupe genevoise Rapide et méthodique, voilà les qualités dont il fallait faire preuve pour remporter la dernière étape de la coupe organisée par le club du CERN dans les bois de Monteret. Il s’agissait d’une course au score où chaque concurrent disposait d’un temps imparti pour poinçonner le maximum de balises. Le parcours technique a été remporté par Tomas Shellman et le parcours facile par Victor Dannecker. Cette dernière étape était aussi décisive pour la désignation des lauréats de la coupe genevoise de printemps. Les résultats officiels étaient donnés par le président du club, L. Jirden : Circuit Technique Long : Berni Wehrle, Bruno Barge, Edvins Reisons Circuit Technique Moyen : J.-Bernard Zosso, ...

  16. Orienteering Club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    De jour comme de nuit Les amateurs de course d’orientation ont pu s’en donner à cœur joie ce week-end puisqu’ils avaient la possibilité de courir sur deux épreuves en moins de 24 heures. En effet, le club du CERN organisait une course de nuit aux Evaux et la 7e étape de la coupe genevoise se tenait samedi après-midi dans les bois du Grand Jorat à Savigny. Les vainqueurs pour chaque course sont : Technique long CO de nuit: Julien Charlemagne, SOS Sallanches CO samedi: Philipp Khlebnikov, ANCO   Technique moyen CO de nuit: Céline Zosso, CO CERN CO samedi: Pavel Khlebnikov, ANCO Technique court CO de nuit: Colas Ginztburger, SOS Sallanches CO samedi: Victor Kuznetsov, COLJ Lausannne Facile moyen CO de nuit: Gaëtan Rickenbacher, CO CERN CO samedi: Tamas Szoke   Facile court CO de nuit:Oriane Rickenbacher, CO CERN CO samedi: Katya Kuznetsov...

  17. Orienteering Club

    CERN Multimedia

    Club d'orientation

    2011-01-01

    Coupe genevoise, suite Résultats de la course de Saint-Cergue, sur la carte Les Pralies, samedi 17 septembre. Nouvelle victoire du finlandais Ville Keskisaari, du club COLJ sur le parcours technique long avec une belle avance sur le deuxième concurrent Christophe Vuitton du CO CERN. David Cuenin a remporté le parcours technique moyen, Franck Lonchampt du club O’Jura a, lui aussi, remporté à nouveau le parcours technique court, tout comme Julien Vuitton du club CO CERN sur le facile moyen. Pour finir, Stéphane Clément devance Victor Dannecker sur le parcours facile court. Les résultats complets sont disponibles sur le site du club du CERN http://cern.ch/club-orientation. Un abonnement est pris sur le secteur de Saint-Cergue, puisque le club organise les deux prochaines étapes de la coupe genevoise dans le Haut-Jura suisse. Tout d’abord le samedi 24 septembre, un relais inter-club se courr...

  18. Orienteering club

    CERN Multimedia

    Club d'orientation

    2010-01-01

    COURSE D’ORIENTATION  De La Rippe à Sauvabellin, la coupe genevoise continue ! Le rendez-vous était donné samedi 8 mai aux amateurs de course d’orientation dans les bois de La Rippe (Canton de Vaud). Cette 6e épreuve était organisée par le Club Satus Grutli de Genève. Il est dommage que les participants n’aient pas été aussi nombreux que lors des dernières courses, les Championnats de France des clubs à Dijon ayant certainement retenus plus d’un compétiteur. La première place est revenue à : – Technique long : Berni Wehrle – Technique moyen : Jean-Bernard Zosso – Technique court : Berni Wehrle – Facile moyen : Peter Troscanyi – Facile court : Claire Droz. Il ne restera plus que deux épreuves ...

  19. Orienteering Club

    CERN Multimedia

    Club d'Orientation

    2015-01-01

    Course orientation Finale de la coupe genevoise La série des courses de printemps s’est achevée samedi dernier dans les bois de Bonmont (Vaud) avec une épreuve «one-man-relay» organisée par le club. Le vainqueur du parcours technique  long, Yann Locatelli (Club de Chambéry Savoie) a réalisé les deux boucles comportant 24 balises avec presque 6 minutes d’avance sur le second concurrent Domenico Lepori (Club CARE Vevey). Cette dernière étape était aussi décisive pour la désignation des lauréats de la coupe genevoise de printemps, en comptabilisant les 6 meilleurs résultats sur les 10 épreuves. Le podium officiel était donné par le président du club, L. Jirden, qui profitait de l’occasion pour remercier tous les participants et également tous les...

  20. Orienteering Club

    CERN Document Server

    Club d'Orientation

    2012-01-01

    Course d'orientation Ces deux dernières semaines, le club a organisé la troisième puis la quatrième étape de la coupe de printemps, une dans la forêt de Collogny/Moissey près de Vulbens, l’autre vers le parcours vita de Trélex. Les résultats sont: Facile court Vulbens : 1er Léo Lonchampt, O’Jura (16:04), 2e Timothée Bazin (23:07), 3e Francesco Pieri (26:57) Trélex : 1er Noora Maurent (23:11), 2e Sarah Stuber, COLJ (26:51), 3e T. Bazin (28:17) Facile moyen Vulbens : 1er Victor Kuznetsov, CO CERN (25:36), 2e Didier Descourvières (28:03), 3e Konstantinos Haider, CO CERN (36:53) Trélex : 1er V. Kuznetsov, COLJ (38:01), 2e K. Haider, CO CERN (43:15), 3e ex aequo Olivia Nguyen et Sven Vietmeier (58:11) Technique court Vulbens : 1er Benoit Bazin (41:21), 2e Colas Gintzburger (55:12), 3e Nathan Freydoz (55:48) Trélex : 1...

  1. Orienteering Club

    CERN Document Server

    Club d'orientation

    2013-01-01

    Finale de la coupe d’automne La dernière épreuve de la coupe d’automne organisée par le club d’orientation du CERN s’est déroulée ce samedi 2 novembre avec une course au score dans le bois Tollot (GE). Les concurrents disposaient d’un temps imparti pour poinçonner le maximum de balises différemment placées selon le circuit choisi. Juerg Niggli (club O’Jura) a remporté le parcours technique long. A l’issue de cette course, le classement général de la coupe d’automne, basé sur les 6 meilleurs résultats de la saison, est le suivant : Circuit technique long : 1er Juerg Niggli (O’Jura), 2e Bruno Barge, 3e Beat Mueller. Circuit technique moyen : 1er Laurent Merat (O’Jura), 2e Jirden Lennart, 3e Daria Niggli. Circuit technique court : 1er Victor Kuznetsov (COLJ), 2e N...

  2. Orienteering club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Course d'orientation Vers les dernières courses de printemps Une centaine de coureurs se sont déplacés sur le site de la Roche Fendue prés de Morez pour gouter à un des 5 parcours proposés par le club du O’Jura. Le terrain était gras mais que peut-on trouver d’autre avec cette météo! Les vainqueurs de chaque circuit sont : Alina Niggli (O’Jura) facile court, Natalja Niggli (O’Jura) facile moyen, Victor Kuznetsov (COLJ) technique court, Yves Rousselot (Balise 25) technique moyen et pour finir François Gonon (O’Jura) avec une victoire haut la main sur le technique long. Il ne reste plus que deux épreuves pour la coupe genevoise de printemps : à savoir samedi 8 juin, course de type longue distance organisée par le club de Lausanne Jorat (COLJ) dans le bois de Seyte sur Mutrux/Concise, inscription de 12h &...

  3. Orienteering Club

    CERN Document Server

    Club d'Orientation

    2012-01-01

     Finale de la coupe de printemps   La dernière course d’orientation comptant pour la Coupe de printemps a eu lieu samedi dernier dans le village des Rousses et vers le Fort. Il s’agissait d’un sprint organisé par le club O’Jura. Les temps de course ont avoisiné les 20 minutes que ce soit pour le parcours technique moyen ou technique long. Tous les habitués étaient au rendez-vous pour venir consolider ou améliorer leur place au classement. A l’issue de cette course, le classement général de la Coupe de printemps prenant en compte les 6 meilleurs résultats des 9 courses était établi et les lauréats de chaque catégorie sont les suivants: Circuit technique long : 1er Berni Wehrle, 2e Bruno Barge, 3e Edvins Reisons. Circuit technique moyen : 1er Jean-Bernard Zosso, 2e Cédric Wehrl&...

  4. Orienteering Club

    CERN Document Server

    Club d'orientation

    2012-01-01

    Finale de la coupe d’automne   La coupe d’automne organisée par le club d’orientation du CERN s’est terminée ce samedi 10 novembre avec une course sprint à Prévessins. C’était la 12e épreuve de la saison. En stage dans la région, Tanya Ryabkina, championne d’Europe en titre et médaillée de bronze en moyenne distance lors des championnats du monde à La Givrine cet été, a fait l’honneur de sa présence et termine 2e à 8 secondes de Trygve Buanes, norvégien du club de Bergen. A l’issue de cette dernière épreuve, le classement général de la coupe d’automne, basé sur les 8 meilleurs résultats de la saison, est ainsi le suivant : Circuit technique long : 1er Jurg Niggli (O&rsqu...

  5. Orienteering club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Courses d’orientation Samedi 20 avril, les organisateurs du Club de CO du CERN ont accueilli au Mont Mourex 70 participants qui n’ont pas hésité à venir malgré la forte bise. Berni Wehrle du CO CERN s’est octroyé la première place en 1:04:49 sur le parcours technique long devant Pyry Kettunen du Saynso Juankoski en 1:06:52, la 3e place revenant à Bruno Barge, CO CERN, à 7 secondes. Les autres parcours ont été remportés par : Technique moyen : 1er Jacques Moisset, Chamonix (47:44), 2e Yves Rousselot, Balise 25 Besançon (57:16), 3e Jean-Bernard Zosso, CO CERN (59:28). Technique court : 1er Victor Kuznetsov, COLJ (51:53), 2e Pierrick Collet, CO CERN (1:12:52), 3e Dominique Balay, CO CERN (1:16:04). Pour les parcours facile moyen et facile court, Ralf Nardini et Léa Nicolas, tous deux du CO CERN, terminaient respectivement premier. Voi...

  6. Orienteering Club

    CERN Multimedia

    CLUB D'ORIENTATION

    2013-01-01

    Calendrier de la coupe d’automne Le Club d’orientation du CERN, en partenariat avec d’autres clubs de la région, vous propose, pour cette nouvelle coupe d’automne genevoise, une série de 10 courses. Le club du O’Jura donnera le coup d’envoi le samedi 31 août. Les courses s’enchaîneront selon le calendrier suivant : Samedi 31 août : Prémanon (39) - longue distance Samedi 14 septembre : La Faucille (01) - longue distance Samedi 21 septembre : Saint Cergue (VD) - longue distance Samedi 28 septembre : Ballens (VD) - relais Samedi 5 octobre : La Pile (VD) - longue distance Vendredi 11 octobre : Les Evaux (GE) - nocturne Samedi 12 octobre : Grand Jorat, Savigny (VD) - longue distance Samedi 19 octobre : Terrasses de Genève (74) - longue distance Samedi 26 octobre : Prémanon (39) - longue distance Samedi 2 novembre : Bois Tollot (GE) - score - Finale Les &a...

  7. Orienteering Club

    CERN Multimedia

    Club d'Orientation

    2011-01-01

    Course d'orientation Avec la CO en nocturne organisée par le club du CERN vendredi 14 octobre au stade des Eveaux (Ge), et la CO à Savigny (Vd) proposée par le club de Lausanne-Jorat le lendemain, les étapes de la coupe genevoise d’automne s’enchainent rapidement. Il ne reste plus que 3 rendez-vous pour boucler la saison. Les premières places devraient certainement se jouer entre des membres du club du CERN, du O’Jura ou de Lausanne-Jorat. La prochaine course du club est programmée pour samedi 22 octobre à Pomier, près de Cruseilles. L’accueil se fera à partir de 12h30 et les départs s’échelonneront de 13h à 15h. * * * * * * * Nouvelle belle victoire samedi 8 octobre à Saint Cergue du jeune finlandais Ville Keskisaari (COLJ) en 50:56 devant Jürg Niggli (O’Jura) en 1:03:32, et Alexandre...

  8. Orienteering club

    CERN Multimedia

    Club d'orientation

    2014-01-01

    Course d'orientation C’est sous un beau soleil samedi 4 octobre que s’est déroulée la 6e étape de la Coupe genevoise d’automne organisée par le club. Plus d’une centaine de concurrents provenant de 7 clubs de CO avaient fait le déplacement pour courir sur un des cinq parcours proposés dans les bois de Trélex-Génolier (VD). Le podium est le suivant : Technique long (5,9 km, 19 postes) : 1er Jurg Niggli, O’Jura (1:00:02); 2e Berni Wehrle, CO CERN (1:06:44); 3e Konrad Ehrbar, COLJ (1:07:08) Technique moyen (4,8 km, 18 postes) : 1er Christophe Vuitton, CO CERN (54:25); 2e J.B. Zosso, CO CERN (1:01:19); 3e Jeremy Wichoud, COLJ (1:06:21) Technique court (3,8 km, 14 postes) : 1er Julien Vuitton, CO CERN (36:19); 2e Vladimir Kuznetsov, COLJ (48:47); 3e Natalia Niggli, O’Jura (50:38) Facile moyen (3,2 km, 11 postes) : 1ère Alina Niggli, O&...

  9. Orienteering Club

    CERN Multimedia

    Club d'Orientation

    2012-01-01

    Relais inter-club/Challenge Carlo Milan Samedi dernier, lors de l’épreuve de course d’orientation organisée par le club du O’Jura, le moteur de la discipline était l’esprit d’équipe, puisqu’il était question d’un relais inter-club avec le Challenge Carlo Milan. Les clubs avaient aligné leurs coureurs soit sur le relais technique (trois participants) soit sur le relais facile (deux participants). Côté O’Jura, il fallait noter la participation de François Gonon, champion du monde 2011, côté club du CERN, Marie et Gaëtan Vuitton, jeunes espoirs du club, devaient préparer la piste pour lancer le dernier relayeur. Côté Lausanne-Jorat, il fallait compter sur le très jeune Viktor Kuznetsov. Les 31 équipes engagées n’ont pas m&ea...

  10. Orienteering club

    CERN Multimedia

    Club d'orientation

    2014-01-01

    Course d'orientation Finale de la coupe d’automne La dernière épreuve de la coupe d’automne organisée par le club s’est déroulée ce samedi 1er novembre avec une course type «one-man-relay» dans la forêt de Trelex (Vd). Les concurrents des circuits techniques devaient parcourir trois boucles et ceux des circuits «faciles» deux boucles, avec changements de carte. Le parcours technique long a été remporté par un membre du club, Berni Wehrle. A l’issue de cette course, le Président du club, L. Jirden annonçait le classement général de la coupe d’automne, basé sur les 6 meilleurs résultats de la saison : Circuit technique long : 1er Juerg Niggli (O’Jura), 2e Berni Wehrle, 3e Beat Mueller. Circuit technique moyen : 1er Laurent Merat (O&r...

  11. Orienteering Club

    CERN Multimedia

    Club d'orientation

    2013-01-01

    Course d'orientation Le coup d’envoi de la coupe genevoise a été donné samedi 31 août dans les bois de Combe Froide à Prémanon. Plus de 150 coureurs avaient fait le déplacement. Les parcours facile court, facile moyen et technique court ont été remportés par des coureurs du club O’Jura - Ulysse Dannecker, Léo Lonchampt, Franck Lonchampt, le technique moyen par Pekka Marti du club Ol Biel Seeland et le technique long par Térence Risse du CA Rosé – également membre de l’équipe nationale suisse des moins de 20 ans. Pour le club du CERN, les meilleures résultats ont été obtenus pas Emese Szunyog sur technique court et Marie Vuitton sur technique moyen avec une 4e place. La prochaine course aura lieu samedi 14 septembre à La Faucille. Le club propose aussi...

  12. Effect of Biaxial Stretching at Temperatures and Strain Histories Comparable to Injection Stretch Blow Moulding on Tensile Modulus for Polyethylene Terephthalate (PET)

    Science.gov (United States)

    Tan, C. W.; Menary, G. H.; Harkin-Jones, E. M. A.; Armstrong, C. G.; Martin, P. J.

    2007-04-01

    This study is particularly relevant to the injection stretch blow moulding (ISBM) process where PET material is typically biaxially stretched to form bottles for the water and carbonated soft drinks industry. The aim of this paper is to investigate the effect of biaxial stretching on the mechanical properties of Polyethylene Terephthalate (PET) using a custom built biaxial testing machine. An initially amorphous PET sample was prepared via injection moulding to form a square sample (76mm × 76mm) suitable for stretching on the machine. This sample was then subjected to a series of biaxial tests (simultaneous and sequential) within a temperature range between 85°C and 110 °C, strain rates in the range of 1s-1 to 32s-1 and stretch ratios in the range of 1.5 to 3. Specimens were subsequently cut from the biaxial stretched sheets and used to measure the tensile modulus. Results showed that there is almost no effect found for strain rate and temperature on modulus development whilst stretch ratio and mode of deformation played the most important role on modulus development on PET under biaxial deformation.

  13. Se EXAFS study of the elevated wurtzite to rock salt structural phase transition in CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Tolbert, S.H.; Alivisatos, A.P. [Lawrence Berkeley Lab., CA (United States)]|[California Univ., Berkeley, CA (United States). Dept. of Chemistry

    1993-09-01

    High pressure Se EXAFS data has been obtained on 2.7 nm radius CdSe semiconductor nanocrystals. This system is observed to undergo a solid-solid phase transition at 6.5 GPa which is approximately twice the reported value for bulk CdSe. In combination with high pressure optical absorption experiments, EXAFS data can be used to identify the high-pressure phase structure as rock salt. EXAFS data can be fit with equations of state to yield pressure volume curves. Resultant values of bulk modulus and its derivative with respect to pressure are B{sub o} = 37 {plus_minus} 5 GPa and B{sub o}{prime} = 11 {plus_minus} 3. A thermodynamic model for the data is presented in which the internal energy in each phase is modified by a surface energy term. Differences in surface energy are used to explain the elevation in phase transition pressure. The model can be used to estimate a value for the surface energy in the rock salt phase; 1.9 {plus_minus} 0.3 N/m is obtained in comparison to 0.9 {plus_minus} 0. 1 N/m for the wurtzite phase.

  14. Fabrication of fluorescence-based biosensors from functionalized CdSe and CdTe quantum dots for pesticide detection

    Science.gov (United States)

    Tran, Thi Kim Chi; Chinh Vu, Duc; Dieu Thuy Ung, Thi; Yen Nguyen, Hai; Hai Nguyen, Ngoc; Cao Dao, Tran; Nga Pham, Thu; Liem Nguyen, Quang

    2012-09-01

    This paper presents the results on the fabrication of highly sensitive fluorescence biosensors for pesticide detection. The biosensors are actually constructed from the complex of quantum dots (QDs), acetylcholinesterase (AChE) and acetylthiocholine (ATCh). The biosensor activity is based on the change of luminescence from CdSe and CdTe QDs with pH, while the pH is changed with the hydrolysis rate of ATCh catalyzed by the enzyme AChE, whose activity is specifically inhibited by pesticides. Two kinds of QDs were used to fabricate our biosensors: (i) CdSe QDs synthesized in high-boiling non-polar organic solvent and then functionalized by shelling with two monolayers (2-ML) of ZnSe and eight monolayers (8-ML) of ZnS and finally capped with 3-mercaptopropionic acid (MPA) to become water soluble; and (ii) CdTe QDs synthesized in aqueous phase then shelled with CdS. For normal checks the fabricated biosensors could detect parathion methyl (PM) pesticide at very low contents of ppm with the threshold as low as 0.05 ppm. The dynamic range from 0.05 ppm to 1 ppm for the pesticide detection could be expandable by increasing the AChE amount in the biosensor.

  15. Linear and nonlinear optical properties of functionalized CdSe quantum dots prepared by plasma sputtering and wet chemistry.

    Science.gov (United States)

    Humbert, Christophe; Dahi, Abdellatif; Dalstein, Laetitia; Busson, Bertrand; Lismont, Marjorie; Colson, Pierre; Dreesen, Laurent

    2015-05-01

    We develop an innovative manufacturing process, based on radio-frequency magnetron sputtering (RFMS), to prepare neat CdSe quantum dots (QDs) on glass and silicon substrates and further chemically functionalize them. In order to validate the fabrication protocol, their optical properties are compared with those of QDs obtained from commercial solutions and deposited by wet chemistry on the substrates. Firstly, AFM measurements attest that nano-objects with a mean diameter around 13 nm are located on the substrate after RFMS treatment. Secondly, the UV-Vis absorption study of this deposited layer shows a specific optical absorption band, located at 550 nm, which is related to a discrete energy level of QDs. Thirdly, by using two-color sum-frequency generation (2C-SFG) nonlinear optical spectroscopy, we show experimentally the functionalization efficiency of the RFMS CdSe QDs layer with thiol derived molecules, which is not possible on the QDs layer prepared by wet chemistry due to the surfactant molecules from the native solution. Finally, 2C-SFG spectroscopy, performed at different visible wavelengths, highlights modifications of the vibration mode shape whatever the QDs deposition method, which is correlated to the discrete energy level of the QDs.

  16. Fabrication of fluorescence-based biosensors from functionalized CdSe and CdTe quantum dots for pesticide detection

    International Nuclear Information System (INIS)

    This paper presents the results on the fabrication of highly sensitive fluorescence biosensors for pesticide detection. The biosensors are actually constructed from the complex of quantum dots (QDs), acetylcholinesterase (AChE) and acetylthiocholine (ATCh). The biosensor activity is based on the change of luminescence from CdSe and CdTe QDs with pH, while the pH is changed with the hydrolysis rate of ATCh catalyzed by the enzyme AChE, whose activity is specifically inhibited by pesticides. Two kinds of QDs were used to fabricate our biosensors: (i) CdSe QDs synthesized in high-boiling non-polar organic solvent and then functionalized by shelling with two monolayers (2-ML) of ZnSe and eight monolayers (8-ML) of ZnS and finally capped with 3-mercaptopropionic acid (MPA) to become water soluble; and (ii) CdTe QDs synthesized in aqueous phase then shelled with CdS. For normal checks the fabricated biosensors could detect parathion methyl (PM) pesticide at very low contents of ppm with the threshold as low as 0.05 ppm. The dynamic range from 0.05 ppm to 1 ppm for the pesticide detection could be expandable by increasing the AChE amount in the biosensor. (paper)

  17. Effect of annealing temperature on the crystalline quality and phase transformation of chemically deposited CdSe films

    International Nuclear Information System (INIS)

    Polycrystalline CdSe thin films were grown on glass substrates by chemical bath deposition at 50 C. The samples were annealed in air atmosphere at different temperatures and characterized by X-ray diffraction and Raman spectroscopy. It was found that the as-grown films have cubic structure. These samples maintain their cubic structure for annealing temperatures between 60 C and 300 C. For annealing temperatures higher than 300 C we obtain a mixture of cubic and hexagonal phases. The analysis made by X-ray diffraction and Raman dispersion show that the samples annealed at temperatures under the phase-transition temperature increase their crystalline quality. In order to determinate the temperature for the complete transition of the cubic phase, we used the precipitated material obtained during the grown of the CdSe films. This material was annealed on air atmosphere between 300 C and 500 C with 50 intervals. The samples were measured by X-ray diffraction. The samples maintained the cubic structure if the annealing temperature is under 300 C. For temperatures between 300 C and 450 C we found a mixture of cubic and hexagonal phase. For an annealing temperature of 500 C we obtain only the hexagonal phase. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Au-assisted growth of anisotropic and epitaxial cdse colloidal nanocrystals via in situ dismantling of quantum dots

    KAUST Repository

    Fernàndez-Altable, Víctor

    2015-03-10

    Metallic nanocrystals have been revealed in the past years as valuable materials for the catalytic growth of semiconductor nanowires. Yet, only low melting point metals like Bi have been reported to successfully assist the growth of elongated CdX (X = S, Se, Te) systems in solution, and the possibility to use plasmonic noble metals has become a challenging task. In this work we show that the growth of anisotropic CdSe nanostructures in solution can also be efficiently catalyzed by colloidal Au nanoparticles, following a preferential crystallographic alignment between the metallic and semiconductor domains. Noteworthy, we report the heterodox use of semiconductor quantum dots as a homogeneous and tunable source of reactive monomer species to the solution. The mechanistic studies reveal that the in situ delivery of these cadmium and chalcogen monomer species and the formation of AuxCdy alloy seeds are both key factors for the epitaxial growth of elongated CdSe domains. The implementation of this method suggests an alternative synthetic approach for the assembly of different semiconductor domains into more complex heterostructures.

  19. Statics and field-driven dynamics of transverse domain walls in biaxial nanowires under uniform transverse magnetic fields

    Science.gov (United States)

    Lu, Jie

    2016-06-01

    In this work, we report analytical results on transverse domain wall (TDW) statics and field-driven dynamics in quasi-one-dimensional biaxial nanowires under arbitrary uniform transverse magnetic fields (TMFs) based on the Landau-Lifshitz-Gilbert equation. Without axial driving fields, the static TDW should be symmetric about its center while twisted in its azimuthal angle distribution. By decoupling polar and azimuthal degrees of freedom, an approximate solution is provided which reproduces these features to a great extent. When an axial driving field is applied, the dynamical behavior of a TDW is viewed as the response of its static profile to external excitations. By means of the asymptotic expansion method, the TDW velocity in the traveling-wave mode is obtained, which provides the extent and boundary of the "velocity-enhancement" effect of TMFs on TDWs in biaxial nanowires. Finally, numerical simulations are performed and strongly support our analytics.

  20. Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

    Science.gov (United States)

    Garcia, V.; Sidis, Y.; Marangolo, M.; Vidal, F.; Eddrief, M.; Bourges, P.; Maccherozzi, F.; Ott, F.; Panaccione, G.; Etgens, V. H.

    2007-09-01

    The α-β magnetostructural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an α-β phase coexistence and, more importantly, for the stabilization of the ferromagnetic α phase at a higher temperature than in the bulk. We explain the premature appearance of the β phase at 275 K and the persistence of the ferromagnetic α phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.