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  • 1
    Electronic Resource
    Electronic Resource
    Maximal entropy approach to reactivity and selectivity in elementary chemical reactions (1982)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 86 (1982), S. 4931-4937 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100222a020
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  • 2
    Electronic Resource
    Electronic Resource
    Electroreflectance study of a symmetrically coupled GaAs/Ga0.77Al0.23As double quantum well system (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3808-3814 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electroreflectance spectroscopy has been used to study a GaAs/Ga0.77Al0.23As symmetrically coupled double quantum well system as a function of externally applied electric field. Both intra- and inter-well exciton transitions were detected. The energy shifts of the coupled quantum confined levels are in good agreement with a theoretical calculation. Details of the lineshape fit yield important information about the modulation mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349184
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature dependence of the photoreflectance of a strained layer (001) In0.21Ga0.79As/GaAs single quantum well (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7537-7542 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the photoreflectance spectra of a strained layer (001) In0.21Ga0.79As/GaAs single quantum well as a function of temperature in the range 10 K〈T〈500 K. The details of the lineshape of the fundamental conduction to heavy-hole feature (11H) demonstrates its excitonic nature even up to 500 K. From the temperature dependence of the 11H linewidth we have obtained important information about the quality of the material and interface. The variation of the 11H energy gap with temperature agrees with that of bulk material. Comparison of the energies of 11H and higher lying transitions with an envelope function calculation yields a conduction band offset parameter Qc=0.65±0.07.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349706
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  • 4
    Electronic Resource
    Electronic Resource
    On the origin of Franz–Keldysh oscillations in AlGaAs/GaAs modulation-doped heterojunctions (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5577-5581 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed a series of photoreflectance measurements in a modulation-doped AlGaAs/GaAs heterojunction containing a high mobility two-dimensional electron gas. Measurements were performed as a function of temperature in the range 2 K≤T≤300 K. We studied the Franz–Keldysh oscillations associated with the E0 transition of both the GaAs and AlGaAs. The fields obtained from these oscillations for both sides of the heterojunction are quite different. Also, the temperature dependence of these fields are radically different. In fact, the temperature dependence of the field in the GaAs side of the modulation-doped heterojunction sample is very similar to that of the field in a single undoped GaAs film deposited on a GaAs substrate, where no two-dimensional electron gas is present. This shows that the field producing the observed oscillations on the GaAs side of the modulation-doped heterojunction sample is not related to the field that confines the two-dimensional electron gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350170
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  • 5
    Electronic Resource
    Electronic Resource
    Polish-induced damage in 〈100〉 GaAs: A comparison of transmission electron microscopy and Raman spectroscopy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4363-4365 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This communication presents a comparative study of polish-induced effects in 〈100〉 GaAs by Raman spectroscopy (strain) and cross-sectional transmission electron microscopy (dislocation density). It is found that the depth and polish-time dependence of both the strain and dislocation density obey the same relationship. However, the skin depth evaluated by Raman scattering is a factor of 10 smaller than that determined from transmission electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344928
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  • 6
    Electronic Resource
    Electronic Resource
    Optical and electrical characterization of an AlGaAs/GaAs heterostructure (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3426-3430 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance (PR) spectroscopy and Hall-effect measurements have been used for the analysis of a molecular beam epitaxially grown AlGaAs/GaAs heterostructure. The photoreflectance spectrum provided valuable information regarding the quality of the undoped GaAs, the aluminum composition of the AlGaAs layers, impurity diffusion, and the quantum well widths. Successive layer removal aided with the identification of some photoreflectance features and provided insight into the electrical transport properties of the heterostructure. Quantum well widths obtained from PR lineshape fits are compared with layer thicknesses measured from cross-sectional transmission electron micrographs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354541
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  • 7
    Electronic Resource
    Electronic Resource
    Canonical variational transition state theory for dissipative systems: Application to generalized Langevin equations (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8877-8888 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A numerical solution for the canonical variational dividing surface of two degree of freedom conservative systems is presented. The method is applied to reaction rates in dissipative systems whose dynamics is described by a generalized Langevin equation. Applications include a cubic and a quartic well using Ohmic and memory friction. For Ohmic friction, we find that in almost all cases, curvature of the optimal dividing surface may be neglected and the Kramers spatial diffusion limit for the rate is in practice an upper bound. For a Gaussian memory friction and a cubic oscillator, we compare the present theory with numerical simulations and other approximate theories presented by Tucker et al. [J. Chem. Phys. 95, 5809 (1991)]. For the quartic oscillator and exponential friction, we discover a strong suppression of the transmission coefficient and the reaction rate whenever the reduced static friction is of the same order of the reduced memory time. We also show that in this case, there is a strong suppression of the energy diffusion process in the reactants' well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462245
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  • 8
    Electronic Resource
    Electronic Resource
    Variational transition state theory for reactions in condensed phases (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 533-539 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A generalization of the Kramers–Grote–Hynes theory for reaction rates in the spatial diffusion limit is derived for a general class of Hamiltonians. Previous restrictions to harmonic baths and bilinear system bath couplings are removed. The key ingredient is the systematic use of variational transition state theory (VTST) to identify the optimal dividing surface. A pair of collective modes are defined as a linear combination of all system and bath modes. A free energy surface is defined in the two degree of freedom collective mode phase space. The VTST estimate for the rate of reaction on this surface is shown to be an upper bound to the exact rate. The optimal definition of the collective modes is obtained by minimizing the rate. The resulting rate expression is formally identical to the Kramers–Grote–Hynes theory. However, the minimization procedure leads to a new definition of the time dependent friction. In consistence with transition state theory, this time dependent friction is constructed from equilibrium properties of the composite system and does not call for any dynamical computations. The friction parameters are determined from equilibrium centroid averages of partial derivatives of the full potential at the barrier of the potential of mean force. This removes previous ambiguities as to the definition of time dependent friction in condensed matter systems. A procedure is presented for finding collective modes along which the friction exerted by the bath is minimized. This result may be of substantial interest in the study of complex dynamical systems in biology, chemistry, and physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461453
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  • 9
    Electronic Resource
    Electronic Resource
    Activated rate processes: Generalization of the Kramers–Grote–Hynes and Langer theories (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2422-2437 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The variational transition state theory approach for dissipative systems is extended in a new direction. An explicit solution is provided for the optimal planar dividing surface for multidimensional dissipative systems whose equations of motion are given in terms of coupled generalized Langevin equations. In addition to the usual dependence on friction, the optimal planar dividing surface is temperature dependent. This temperature dependence leads to a temperature dependent barrier frequency whose zero temperature limit in the one dimensional case is just the usual Kramers–Grote–Hynes reactive frequency. In this way, the Kramers–Grote–Hynes equation for the barrier frequency is generalized to include the effect of nonlinearities in the system potential. Consideration of the optimal planar dividing surface leads to a unified treatment of a variety of problems. These are (a) extension of the Kramers–Grote–Hynes theory for the transmission coefficient to include finite barrier heights, (b) generalization of Langer's theory for multidimensional systems to include both memory friction and finite barrier height corrections, (c) Langer's equation for the reactive frequency in the multidimensional case is generalized to include the dependence on friction and the nonlinearity of the multidimensional potential, (d) derivation of the non-Kramers limit for the transmission coefficient in the case of anisotropic friction, (e) the generalized theory allows for the possibility of a shift of the optimal planar dividing surface away from the saddle point, this shift is friction and temperature dependent, (f) a perturbative solution of the generalized equations is presented for the one and two dimensional cases and applied to cubic and quartic potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463081
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  • 10
    Electronic Resource
    Electronic Resource
    Comparison of rate theories for generalized Langevin dynamics (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5809-5826 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rate constants evaluated from (1) the energy-loss turnover theory of Pollak, Grabert, and Hänggi (PGH), (2) the Grote–Hynes extension of Kramers theory (GH), and (3) the microcanonical variational transition state theory for dissipative systems of Tucker and Pollak (μVTST) are compared with rate constants determined from direct computer simulations of generalized Langevin dynamics. The comparisons are made for a cubic oscillator under the influence of a slow bath characterized by a Gaussian friction kernel. In the μVTST calculations, which are based on an effective two degree of freedom Hamiltonian, barrier crossing due to energy transfer from the bath to the effective Hamiltonian is neglected. This neglect is significant only at very strong coupling, where it causes the μVTST results to drop below the simulation results. Both GH and μVTST theories fail (as expected) in the energy diffusion regime, while PGH theory is only moderately successful. The μVTST results agree extremely well with the simulation results in the spatial diffusion regime, providing a significant improvement over the GH results at intermediate coupling strengths and over the PGH results at strong coupling strengths. This improvement is a result of nonlinear effects which are included in the μVTST approach but neglected in the PGH and GH theories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461603
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