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  • American Institute of Physics (AIP)  (17)
  • Inter-Research
  • International Union of Crystallography
  • 1990-1994  (17)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Test of a model for reversible excimer kinetics: Pyrene in cyclohexanol (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8143-8149 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for reversible monomer–excimer kinetics that considers the time dependence of the excimer formation rate coefficient is proposed and tested for pyrene in cyclohexanol from 25 up to 85 °C. Simultaneous analysis of the monomer and excimer experimental decay curves allows the determination of all the relevant parameters for this reaction. The diffusion coefficient follows an Arrhenius plot with activation energy of 36±1 KJ mol−1, the encounter radius varies between 7.3 and 8.9 A(ring), and the intrinsic rate constant for excimer formation varies between 2.4×109 and 1.1×1010 M−1 s−1. The intrinsic reciprocal lifetime of the excimer follows an Arrhenius plot with activation energy of 12±1 KJ mol−1, and the rate constant for excimer dissociation, determined for high temperatures (T〉55 °C) when reversibility is important, has different values depending whether geminate pair effects are considered or not in the analysis. The binding energy of pyrene excimer obtained considering pair effects (ΔH=32±2 KJ mol−1) agrees with the published values for nonviscous solvents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462317
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  • 2
    Electronic Resource
    Electronic Resource
    Diffusion-influenced excimer formation kinetics (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1817-1824 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for reversible monomer–excimer kinetics is developed, taking into account that different distributions of monomers around the excited ones are created by light absorption and excimer dissociation. The excimer formation rate coefficient departs from the Collins–Kimball equation owing to reversibility, originating significant deviations to Birks' kinetics in the monomer and excimer decays. The contribution of the geminate pair created by excimer dissociation on the overall kinetics is significant for low monomer concentrations and high viscosities. Simultaneous analysis of the monomer and excimer decay curves according to the model developed should allow to extract all the relevant information concerning the excimer formation diffusion controlled process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461029
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  • 3
    Electronic Resource
    Electronic Resource
    Fluorescence depolarization by electronic energy transfer in donor–acceptor pairs of like and unlike chromophores (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8048-8055 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence depolarization by energy transfer resulting from dipole–dipole interaction (Förster type) is studied in donor–acceptor pairs of like and unlike chromophores at a fixed distance and with random and uncorrelated static orientations. For unlike chromophores, the acceptor anisotropy decay is shown to display three different extreme types of behavior. When the intrinsic decay rate of the acceptor is much faster than both the transfer rate and the donor intrinsic decay rate, the acceptor anisotropy decays from a positive value, then rises and passes through a maximum, and finally tends to a negative limiting value, yielding a zero steady-state value. The existence of a maximum is shown to be due to the peculiar relation between the orientation factor and the average angle formed by the donor and acceptor transition moments. For pairs of like chromophores, the exact anisotropy is calculated and compared with that given by an approximate treatment. It is also shown that the anisotropy of the indirectly excited partner varies with time, tending to zero, in contradiction to previous work, where it is reported to be 4% of that of the directly excited chromophore.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461285
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  • 4
    Electronic Resource
    Electronic Resource
    Mobility anisotropy of two-dimensional hole systems in (311)A GaAs/AlxGa1−xAs heterojunctions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1980-1982 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the low-temperature mobility of high-quality two-dimensional hole systems confined at the (311)A GaAs/AlxGa1−xAs interface. Variables were the thickness of the spacer layer separating the carriers from the Si dopants, and the carrier sheet density. A large anisotropy in mobility is found between the [2¯33] and [011¯] directions. While the high mobility [2¯33] direction yields results analogous to the two-dimensional electron case, we conclude that transport along [011¯] is almost entirely determined by anisotropic interface roughness scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358419
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  • 5
    Electronic Resource
    Electronic Resource
    Resonant tunneling in submicron double-barrier heterostructures (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 747-749 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated submicron resonant tunneling devices from double-barrier AlGaAs/GaAs heterostructures using electron beam lithography and wet chemical etching. These devices exhibit step-like features in the current-voltage curves. We interpret these steps as arising from additional size quantization of the electronic states in the well due to in-plane lithographic confinement. Magnetotunneling experiments on these devices are reported for the first time. A simple model calculation describes well the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104535
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  • 6
    Electronic Resource
    Electronic Resource
    Resonant tunneling of two-dimensional electrons into one-dimensional subbands of a quantum wire (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1440-1442 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Liquid phase epitaxy regrowth on the edge of in situ cleaved substrates is employed to create a vertical two-dimensional electron gas in a double-barrier tunneling potential. Resonant tunneling of two-dimensional electrons through one-dimensional quantum wire subbands is unambiguously identified by negative differential resistance features in the transport characteristics. The bias positions of these features agree with simple tunneling theory estimates based on conservation laws and the calculated band alignment in the structure under bias.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105192
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  • 7
    Electronic Resource
    Electronic Resource
    Novel superlattice in a selectively doped wide parabolic quantum well with a modulated potential (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2130-2132 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the realization of a novel superlattice which contains a high mobility ((approximately-equal-to) 1.1×105 cm2/V s at 4 K) degenerate electron system. The structure consists of a wide, undoped AlxGa1−xAs well bounded by undoped (spacer) and doped layers of AlyGa1−yAs (y(approximately-greater-than)x) on both sides. The alloy composition in the well (x) is graded in such a way as to result in a parabolic potential with an additional sinusoidal modulation superimposed on it. Once transferred into this well, the electrons screen the parabolic potential and an electron system with a modulated charge density is obtained. We present self-consistent quantum mechanical calculations of the electronic system, and report our characterization of the structure by secondary-ion mass spectrometry and magnetotransport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103920
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  • 8
    Electronic Resource
    Electronic Resource
    Surface resonant tunneling transistor: A new negative transconductance device (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 610-612 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new three-terminal device, the surface resonant tunneling transistor, is realized by the molecular beam epitaxial cleaved edge overgrowth technique in the GaAs/AlGaAs system. The device exhibits negative transconductance as well as negative differential resistance. Some possibilities for future applications of the device to low-power logic circuits are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111065
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  • 9
    Electronic Resource
    Electronic Resource
    Dimerization induced incorporation nonlinearities in GaAsP (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2418-2420 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We find that the incorporation of As and P into GaAs1−yPy, when using gas-source molecular beam epitaxy, does not depend linearly upon the atomic fluxes within the reactor. Rather, incorporation of As and P into GaAsP goes as the square of the atomic fluxes, i.e., y=fP2/(fP2+βfAs2),where fP(As) is the flux of P(As). β is a fitting parameter and that differs for relaxed and strained GaAsP. The deviation in y from a linear model [y=fP/(fP+fAs)] is as high as a factor of two, whereas our quadratic model is never more than a few percent off. We interpret this as due to surface pairing between two like species (dimerization) in order for them to incorporate into the crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111586
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  • 10
    Electronic Resource
    Electronic Resource
    Voltage-tunable multiple quantum well photodetector vertically integrated with voltage-tunable multiple quantum well filter (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3229-3231 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a n-i[multiple quantum well (MQW)]-p-i(MQW)-n device wherein the bottom MQW functions as a voltage-tunable photodetector and the top MQW functions as a voltage-tunable filter, allowing enhanced detectivity at the exciton wavelength compared to photon energies below or above the band gap. Thus this device more closely approximates a true single wavelength, voltage-tunable photodetector. We achieve about 2–1 selectivity over a tuning range of 14 nm with 12 V operation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109082
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