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  • 1
    Electronic Resource
    Electronic Resource
    Per-carrier nonlinear optical response of [111]-oriented piezoelectric InGaAs/GaAs multiple quantum wells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 417-423 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measure the per-carrier nonlinear responses caused by photoexcited carriers in two strained [111]-oriented InGaAs/GaAs multiple-quantum-well structures, and we compare them to that measured in a [100]-oriented structure. Without an external bias, we find that the absorption coefficient changes per photogenerated carrier for the [111]-oriented piezoelectric materials are smaller than for the [100]-oriented materials, not larger, as originally suggested. Subsequently, measurements of the per-carrier nonlinear responses as a function of reverse bias voltage demonstrate that the smaller per-carrier nonlinearities measured for the [111] structures are partially the result of a broadening of the excitons by the huge in-well fields, but can be primarily attributed to the quality of the [111]-grown materials. When corrected for differing in-well fields and for differing excitonic linewidths, the per-carrier responses are similar in magnitude, suggesting that the [111] response may eventually approach that of [100] material, but probably will not significantly exceed it. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360846
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison between disaccommodation and ferromagnetic resonance measurements in polycrystalline yttrium–iron–garnet samples : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5436-5438 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline yttrium–iron–garnet (YIG) samples were sintered in air at temperatures ranging from 1350 to 1450 °C. Ferromagnetic resonance measurements have been accomplished at 11 GHz from 77 to 350 K. The different contributions to the linewidth have been analyzed. These results are compared with previous measurements of magnetic disaccommodation in the same samples. A qualitative relationship between both kind of measurements for polycrystalline YIG samples by means of an induced anisotropy formalism is provided. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362331
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  • 3
    Electronic Resource
    Electronic Resource
    Light scattering in p-type GaAs:Ge (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2388-2395 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present in this work the results of a Raman spectroscopy study on the plasmon–phonon coupling in Ge-doped p-type gallium arsenide. A series of polarized Raman scattering experiments were carried out on epitaxial films grown by liquid-phase epitaxy on (100) GaAs substrates at 20, 100, and 300 K. The films were p type with free hole densities varying in the range of 5×1017–1×1020 cm−3. Under the scattering configurations employed, the longitudinal optical (LO) mode is forbidden for crossed polarization while the transverse optical (TO) mode is forbidden for both parallel and crossed polarizations. However, all the polarized Raman spectra showed two peaks with frequencies close to the TO and LO phonons of semi-insulating GaAs. The appearance of such forbidden modes was accounted for with a theoretical model which considers phonon–plasmon coupled modes with wave vectors much larger than those given by the regular q≈0 wave vector transferred by photons. Ionized acceptor impurities provide such additional wave vector transfer through elastic scattering of the photoexcited electrons and holes. It is demonstrated that the experimental values for position and linewidth of the peaks are well described by the theoretical calculations when Fröhlich-type and deformation potential mechanisms are considered as means of interaction. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363074
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  • 4
    Electronic Resource
    Electronic Resource
    Transport properties of amorphous CoZrNd thin films with very low Nd content (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6545-6545 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The composition and temperature dependence of electrical resistivity were studied for a series of amorphous (Co93Zr7)100−xNdx for x〈3.4 and for a temperature range between 77 and 300 K. The films were deposited by rf sputtering. Measurements of electrical resistivity were performed by the standard four probe technique with ac currents of 10 mA. The rate of heating and cooling was 1 K/min. The electrical resistivity is very sensitive to the presence of Nd ions, as the resistivity clearly increases with a very slight increase of Nd content. The temperature dependence of resistivity does not obey the T2 law predicted by the diffraction model as proposed by Meisel and Cote but follows very nicely the law ρ(T)=aT3/2−bT+c, a result also found for amorphous Gd–Co. The first term corresponds to the electron scattering from the magnetic spin and the second term to the electron scattering from the disordered configuration of atomic potentials. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361941
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  • 5
    Electronic Resource
    Electronic Resource
    The application of the photoacoustic transmittance oscillations for determining elastic constants in gallium and indium selenides (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3200-3204 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmittance periodic oscillations are observed in GaSe and InSe on excitation with optical pulses. Such oscillations are explained in terms of photoacoustic generation of dilatational waves, which become resonant within the crystal. Spectral analysis of those oscillations in samples of different thickness has led to an accurate determination of the longitudinal acoustic-wave velocity along the crystallographic axis c. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361219
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  • 6
    Electronic Resource
    Electronic Resource
    High-resolution x-ray diffraction study of piezoelectric InGaAs/GaAs multiquantum well p-i-n photodiodes grown on (111)B GaAs (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1574-1576 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution x-ray diffractometry has been applied to the structural characterization of piezoelectric strained InGaAs/GaAs multiquantum well p-i-n diodes grown by molecular beam epitaxy on (111)B GaAs substrates. Reference samples simultaneously grown on (001) GaAs have been also characterized. Diodes with 3, 7, and 10 periods and different well to barrier thickness ratio have been studied. Symmetric and asymmetric reflections at various azimuths were measured and the scans were fitted with theoretical curves obtained through a dynamical simulation program developed in our lab. The comparison between experimental and simulated profiles has enabled us to determine the main structural parameters of the samples. High-resolution x-ray diffractometry provided accurate data about period and capping layer thicknesses, indium content in the wells and state of relaxation, information which cannot be always obtained in (111)B samples from other characterization techniques such as photoluminescence or photocurrent spectroscopies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117034
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic disaccommodation in single yttrium iron garnet crystal (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 564-565 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of magnetic disaccommodation in single yttrium iron garnet (YIG) crystals are presented. Two peaks of 0.2%–0.3% are observed in the isochronal spectrum around 130 and 250 K. Comparison of our results with those on polycrystalline YIG samples and with similar data on illuminated and gamma ray irradiated single YIG crystal samples is provided. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116401
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  • 8
    Electronic Resource
    Electronic Resource
    Extraordinary thermopower in magnetoresistive (La1−xYx)0.67Ca0.33MnO3 oxides (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2288-2290 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report that the thermopower Q(T) of the (La1−xYx)0.67Ca0.33MnO3 (x=0–0.25) magnetoresistive oxides, displays a pronounced peak at temperatures Ts close to the ferromagnetic ordering temperature. The temperature Ts decreases monotonously when increasing x whereas the maximal Q(Ts) is found to increase with the Y contents. The huge enhancement of Q at Ts is found to be as high as 460% for x=0.25. It is shown that the extraordinary thermopower observed at Ts results from the reduced charge carrier mobility when approaching Ts and the variation of Q(T) with the Y contents reflects the accompanying band narrowing. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116166
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  • 9
    Electronic Resource
    Electronic Resource
    The T1(nπ*)←S0 laser induced phosphorescence excitation spectrum of acetaldehyde in a supersonic free jet: Torsion and wagging potentials in the lowest triplet state (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2547-2552 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser induced T1(nπ*)←S0 phosphorescence excitation spectrum of jet-cooled acetaldehyde has been observed for the first time with a rotating slit nozzle excitation system. The vibronic origins were fitted to a set of levels that were obtained from a Hamiltonian that employed flexible torsion-wagging large amplitude coordinates. The potential surface extracted from the fitting procedure yielded barriers to torsion and inversion of 609.68 and 869.02 cm−1, respectively. Minima in the potential hypersurface at θ=61.7° and α=42.2° defined the equilibrium positions for the torsion and wagging coordinates. A comparison to the corresponding S1-state parameters showed that the torsion barrier (in cm−1) does not greatly change, S1/T1=710.8/609.7, whereas the barrier height for the wagging-inversion barrier increases dramatically, 574.4/869.0. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472120
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  • 10
    Electronic Resource
    Electronic Resource
    Poly(α-isobutyl-β-D,L-aspartate)s: Polymerization effects on configuration and crystal structure of the stereocopolymers (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1959-1968 
    Details
    ISSN: 0887-624X
    Keywords: optically active polyamides ; helical nylons ; nylon-3 ; poly(β-amide)s ; poly(β-aspartate)s ; poly(α-isobutyl-β-L-aspartate) ; stereoselective polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different polymerization methods were used for the preparation of poly(α-isobutyl-β-D,L-aspartate)s containing variable ratios of D- to L-aspartic units and the microstructure of the resulting stereocopolymers was examined by NMR spectroscopy. Anionic ring-opening polymerization in solution of enantiomeric mixtures of α-isobutyl-β-D- and L-aspartalactams was found to proceed stereoselectively rendering block copolymers composed of right- and left-handed helical sequences. Configurationally statistical copolymers were obtained instead when the enantiomeric lactam mixtures were polymerized in the bulk. Random stereocopolymers could be prepared also by polycondensation in solution of mixtures of pentachlorophenyl α-isobutyl-β-D and -L-aspartates. The conformation in solution and the crystal structure of the resulting copolymers were investigated in connection with their stereochemical configuration and these features compared with those displayed by optically pure poly(α-isobutyl-β-L-aspartate). © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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