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  • 1
    Electronic Resource
    Electronic Resource
    Switching response of a polymer dispersed liquid-crystal composite (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3744-3748 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Control over the switching times of polymer dispersed liquid crystal (PDLC) displays is an area of technological importance. We found that the switching times of a PDLC cell can be effectively controlled by using a dual frequency addressable liquid crystal mixture and driving it with appropriate electric fields. The decay and rise times of such a PDLC cell can be reduced from a few thousand milliseconds to a few hundred milliseconds when driven by a low- and a high-frequency field, sequentially. We have also found that the decay and rise times of PDLC cells depend considerably on the frequency of the driving signal and on the initial light-scattering state of the film (which depends on the sample preparation conditions). Indeed, we found that a PDLC cell having an initial highly scattering state exhibits better switching response times than a PDLC cell with an initially transparent optical state. An attempt is made to elucidate the role of the confinement of the LC to the microdroplets on the switching response of a PDLC cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352906
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  • 2
    Electronic Resource
    Electronic Resource
    Optimization of the performance of a digital voltmeter for synchronous detection (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3209-3212 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A procedure for performing synchronous detection of signals using a digital voltmeter (DVM), beyond the frequency limit set by a straightforward consideration of the sampling theorem and the conversion time of the DVM, is presented. This is achieved by using an independent timer to produce a number of time series with appropriate phase relationships. These time series are then combined by a computer to give a single series with a smaller effective sampling time. A regular fast Fourier transform routine is used for the detection of signals. For a DVM with a minimum sampling time of 16 ms, the procedure has been implemented successfully up to 150 Hz. The limits on the applicability of the procedure for higher frequencies are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142580
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  • 3
    Electronic Resource
    Electronic Resource
    Plasma assisted two stage selenization process for the preparation of selenide semiconductor thin films using elemental selenium vapor (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3068-3071 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A plasma assisted two stage selenization process using elemental selenium vapor is demonstrated for the preparation of selenide semiconductor thin films. Vacuum evaporated copper films are selenized using the vapor of elemental selenium which has been ionized by a radio frequency plasma. This enhances the reaction kinetics by modifying the availability and ionization state of Sex species present in the gas phase. In contrast to the H2Se selenization, the availability of the Sex species in the gas phase is not dependent on the kinetics of its reaction with the precursor. Formation of highly crystalline CuSe films has been observed at low temperatures (250 °C) within 2–5 min. CuSe films show large (≈2–5 μm) rodlike crystallites, with a highly oriented microstructure in plasma assisted growth as different from the small (≤1 μm) coalescing grains in the polycrystalline films formed by the conventional selenization scheme. X-ray diffraction shows a threefold enhancement in the intensity of the (006) reflection of the hexagonal CuSe phase indicating the orientation of the c axis of the crystallites, normal to the plane of the film. The observed hexagonal CuSe growth phase is in agreement with the thermodynamics of copper selenium vapor reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357489
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  • 4
    Electronic Resource
    Electronic Resource
    Phase evolution in low-pressure Se vapor selenization of evaporated Cu/In bilayer precursors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3585-3591 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evolution of elemental binaries and single-phase copper indium diselenide, CuInSe2 (CIS) during Se vapor selenization of evaporated Cu/In bilayer metal precursors at pressures of 0.3–10 mbar and temperatures in the range of 260–400 °C has been investigated. At low pressures, the relative kinetics of selenization of Cu and In are changed resulting in the formation of single-phase CIS even at very low temperatures (260 °C). Optical, Auger, and x-ray photoelectron spectroscopy investigations are employed to characterize the chalcopyrite absorber layer. At higher pressures (≈7–10 mbar), simultaneous formation of the equilibrium binaries, CuSe and In2Se3 at low temperatures leads to the formation of CIS through a diffusion limited reaction of the binaries at higher temperatures. The availability of Se reacting species varies significantly in the pressure regime. At low reactor pressures and Se availability, the reaction CuSe+In(l)+Se→CIS, proceeds to completion even at low temperatures. The detailed study of the phase evolution is made by x-ray diffraction and scanning electron microscopy investigations and correlated with the Se availability in the reactor. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361411
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  • 5
    Electronic Resource
    Electronic Resource
    Thermally stable amorphous BaxTi2−xOy thin films (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 809-811 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reactive partially ionized beam deposition technique was used to deposit amorphous BaxTi2−xOy thin films with the Ba/Ti ratios from 1 for a stoichiometric BaTiO3 film to 0.2 for a Ti enriched film. A postdeposition annealing between 500 and 600 °C converted stoichiometric amorphous BaTiO3 into polycrystalline structure. This crystallization resulted in densification with a 9% decrease in film thickness. Off-stoichiometric thin films remained amorphous up to 700 °C. Annealed off-stoichiometric BaxTi2−xOy films, however, had lower leakage current and loss tangent than polycrystalline films due to their amorphous nature making them more suitable for electronic applications. At temperatures of 800 °C or higher, significant reaction occurred between the films and Si substrate as detected by Rutherford backscattered spectroscopy. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113428
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  • 6
    Electronic Resource
    Electronic Resource
    Critical influence of reactant pressure on the evolution of single phase CuInSe2 during selenization at low temperatures (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3128-3130 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single phase chalcopyrite CuInSe2 (CIS) phase formation at low temperatures (≈260 °C) is demonstrated by Se vapor selenization of evaporated metal precursors at a pressure of ≈0.3 mbar. The low pressure changes the relative kinetics of selenization of Cu and In due to the modification of the availability of Se reacting species. Consequently, the thermodynamically favorable reaction CuSe+In(1)+Se→CIS proceeds to completion at lower temperatures. This is confirmed by the absence of In2Se3 at intermediate pressures (0.5–1.0 mbar). At higher pressures (≈7–10 mbar) and Se flux, simultaneous formation of the equilibrium binaries, CuSe and In2Se3 at low temperatures, leads to the formation of CIS through a diffusion limited reaction of the binaries at higher (≥400 °C) temperatures. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113626
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  • 7
    Electronic Resource
    Electronic Resource
    Deposition of amorphous BaTiO3 optical films at low temperature (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 574-576 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A reactive partially ionized beam technique has been used to deposit amorphous BaTiO3 films at room temperature. The procedure employing independently controlled evaporation and ionization of Ba and TiO has been optimized to produce highly transparent films. Films deposited on quartz or glass show 100% optical transmission over the visible wavelengths with respect to the substrate. The refractive index can be varied over a range of 1.9–2.0 by varying the Ba/Ti ratio without effecting the optical transparency. Films with refractive indices up to 2.4 can be deposited but the optical transmission decreases. The best optical properties are obtained for films with near stoichiometric Ba/Ti ratio. Annealing at temperatures less than 500 °C leads to densification of the films with a 2%–3% decrease in film thickness. The anneal increases the refractive index marginally. The optical band gap of the films was calculated from the experimental transmission plots. The Eg value of 4.6±0.1 eV for stoichiometric films decreases to 4.3 eV for nonstoichiometric films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109981
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  • 8
    Electronic Resource
    Electronic Resource
    Nature of contact resistance in high-T c YBa2Cu3O7−δ Superconductors (1989)
    Springer
    Applied physics 48 (1989), S. 325-329 
    Details
    ISSN: 1432-0630
    Keywords: 74.70Ya ; 73.40N ; 73.90
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The contacts between various metals and the high-Tc superconductor YBa2Cu3O7−δ are characterized by contact resistance,R c, andI–V measurements from 300 K to 90 K. The contacts with bulk superconductor were made by vacuum deposition. Four metals, Au, Ag, Al, and Bi were investigated. The current transport across the contact is by carrier tunneling. All contacts were ohmic as theirI–V characteristics were symmetrical with respect to current direction.R c values range between 10−2 to 101 Ωcm2 and increase linearly as the temperature is lowered. The contact resistance originates from two distinct physical processes. One is the modification of the carrier concentration at the interface by the contact metal. The second is the nature of carrier injection at the free surface of the superconductor. TheR c values depend on the contact metal-oxygen interaction parameter signifying the need for oxygen passivation for obtaining low contact resistances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618893
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  • 9
    Electronic Resource
    Electronic Resource
    Ultrasonic velocities and thermal expansion coefficients of amorphous Se80Te20 and Se90Te10 alloys near glass transitions (1982)
    Springer
    Journal of materials science 17 (1982), S. 183-192 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Precise measurements of the ultrasonic velocities and thermal expansivities of amorphous Se80Te20 and Se90Te10 alloys are reported near the glass transition. The samples are produced by liquid quenching. The longitudinal and transverse velocities are measured at 10 MHz frequency using the McSkimin pulse superposition technique. The thermal expansivities,α, are measured using a three-terminal capacitance bridge. Theα-values show a sharp maximum near the glass transition temperature,T g. The ultrasonic velocities also show a large temperature derivative, dV/dT nearT g. The data are discussed in terms of existing theories of the glass transition. The continuous change inα shows that the glass transition is not a first-order transition, as suggested by some theories. The samples are found to be deformed by small loads nearT g. The ultrasonic velocities and dV/dT have contributions arising from this deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809050
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  • 10
    Electronic Resource
    Electronic Resource
    Structural study of annealed Ag-YBaCu3O7 interfaces (1989)
    Springer
    Journal of materials science 8 (1989), S. 977-978 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01729967
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