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  • 1
    Electronic Resource
    Electronic Resource
    Numerical analysis of a step-coupled well: A novel quantum-confined Stark shift structure (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5329-5332 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new quantum-confined Stark shift structure, the step-coupled well, is introduced. The feature of the new structure is using a square well of only one quantum state to enhance the Stark shift of the step well. The design rule of 10-μm modulator is suggested. The transfer matrix technique is used for numerical calculation. Numerical results show that the new structure produces a larger Stark shift (13 meV) than the step well (7 meV) under the same bias (20 kV/cm). A lower electric field is thus needed for the step-coupled well to produce the same Stark shift, so that the leakage problem can be minimized and a high switching speed can be achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351967
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio calculation of band structure, x-ray emission, quantum yield, and electron-energy-loss spectra of hexagonal boron nitride (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7422-7426 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The band structure of hexagonal boron nitride (BN) has been calculated using an ab initio linear combination of pseudoatomic-orbitals method. The calculated band structure confirms a previous finding that this material is an indirect band-gap insulator and has two empty interlayer bands. Projected densities of states are compared with the experimental x-ray emission spectra of B and N K edges and the agreement is good. This good agreement between the present ground-state calculation and the experimental x-ray emission spectra supports our previous finding that there should be very little valence electron relaxation effect on x-ray emission spectra. A real-space Green's function technique and the Z+1 approximation have been used to calculate the exciton spectra of B and N K edges. The first peak at 192 eV in B K edge is found to be a bound exciton with a binding energy of 1.7±0.4 eV. Only resonance is found for the N K edge. The calculated exciton spectra agree very well with the experimental quantum-yield and electron-energy-loss spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353983
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical study of laser heating and dissociation reactions in solids using ultrafast time-resolved x-ray diffraction (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2174-2178 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of ultrafast time-resolved x-ray diffraction is presented. We show that for the case in which vibrational relaxation is fast, the x-ray diffraction intensities in pulse laser heating are determined by the Debye–Waller factor. We also show how the scattering intensities of the diffraction spots change with the position of the dissociating atoms in a time-resolved x-ray diffraction experiment studying dissociation reactions in solids. Our results show that the scattering intensities change in both the fully dissociated and the partially dissociated cases, and that time-resolved x-ray diffraction could be a useful tool in probing dissociation reactions in solids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351607
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  • 4
    Electronic Resource
    Electronic Resource
    Crystal growth and characterization of heavily MgO-doped LiNbO3 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7635-7639 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystals of LiNbO3 doped with up to 25 mol % of MgO were successfully grown. No precipitates were discovered. In studies of the change of the Curie temperatures and Raman spectra with composition, an abrupt change was observed near the composition of 10 mol % of MgO. From the model of Gallagher relating Tc and cation vacancies and the cation occupation calculated by x-ray data, it is proposed that the Mg atoms replace the Nb atoms at Li sites. When the Nb atoms are exhausted, the Mg atoms replace the Li sites and Li vacancies are created. The amount of Mg in the LiNbO3 structure could be predicted better from the 151 cm−1 peak shift in Raman spectra than from Tc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347533
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical comparison of electron energy-loss and x-ray absorption near-edge fine structure of the Si L2,3 edge (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 288-290 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Various approximations in the calculations of electron energy-loss cross section and x-ray absorption coefficient have been evaluated using the Si L2,3 edge as an example. It was found that the random phase approximation, for which the cross terms are neglected in the expressions of electron energy-loss cross section and x-ray absorption coefficient, is a very good approximation. The dipole approximation in the calculation of the electron energy-loss cross section was found to begin to break down even at small acceptance half angles, such as 12.5 mrad. For energy losses larger than that of the Si L2,3 edge the dipole approximation will break down faster. This approximation also fails for a large scattering angle even at a small energy loss. The electron energy-loss cross section and x-ray absorption coefficient of the Si L2,3 edge has been calculated and compared. The large difference in relative intensity reported experimentally between the two spectra is not confirmed in this study. More experimental comparisons between electron energy loss and x-ray absorption spectra are recommended for Si and other compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347129
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  • 6
    Electronic Resource
    Electronic Resource
    Critical behavior of amorphous Fe80−xMxB14Si6 alloys with M=Mo, V, Mn, and 2≤x≤14 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5439-5441 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Fe80−xMxB14Si6 alloys with M=Mo, V, Mn, and 2≤x≤14 have been made by the rapid quenching method. The critical exponents β, γ, δ, and Tc were determined by two independent methods: the method of Kouvel-Fisher and the scaling plot. With the addition of M, β, and γ deviate more from the values predicted by the three-dimensional Heisenberg model, and are closer to the values proposed by Sobotta and Wagner. δ remains less changed. The magnetic inhomogeneity of these alloys is evidenced by the specific heat, the forced magnetoresistance, and the Mössbauer measurements. By increasing x, the peak of specific heat becomes smeared and less divergent, and forced magnetoresistance changes from negative to positive around Tc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346103
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical study of memory kernel and velocity correlation function for condensed phase isomerization. I. Memory kernel (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6335-6339 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A unified memory kernel function is proposed on the basis of molecular dynamics simulations and comparison with experimental data. A frozen-solvent-like friction arises from the near-neighbor solvent cage effect, while the interaction between the system and the disordered heat bath or "broken cage'' gives rise to a white-noise friction. On short time scales, the apparent friction is a "series addition'' of these two limits, each solute molecule experiencing either an intact cage or a broken cage environment. For longer time scale behavior, the solvent is able to evolve, and some system molecules can experience both types of environments during the course of their own dynamics: the effective friction for these molecules then appears as a "parallel addition'' of the same two contributions. This leads to a memory kernel having a simple exponential behavior. As the time scale for the system dynamics becomes still longer, the cage becomes indistinguishable from the heat bath, and a purely Markoffian relaxation with delta-function memory kernel ensues. This unified memory kernel model has been found to be applicable to ultrafast chemical reaction rates and diffusion properties both in molecular dynamics simulations and laboratory experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456350
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  • 8
    Electronic Resource
    Electronic Resource
    Extraction of ground state properties by discretized path integral formulations (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3233-3239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We offer a way of determining the temperature range in which a path integral (PI) formulation of the quantum partition function works well and a way of calculating the ground state properties without employing extremely low temperatures (in order to elude the awkward problem that the quantities calculated by the PI formulation become inaccurate with decreasing temperature owing to unavoidable truncation of an infinite number of path integral variables). The fact that the PI energy, specific heat, etc. behave in a low temperature range against physical laws makes it possible to locate the "marginal'' temperature at which the PI specific heat begins to grow infinitely and to estimate the lowest temperature at which the PI formulation functions well (the "threshold temperature''). Whether or not the threshold temperature is low enough to extract only the ground state properties can be answered by either checking if the PI energy and free energy are equal at the threshold temperature or checking if the PI specific heat is relatively small thereat. If the system is in the ground state at the threshold temperature obtained, it is recommended to calculate the ground state properties at this temperature. This scheme can be executed by Monte Carlo methods, being open to many-particle systems. Using the discretized PI formulations, we apply the above procedure to a harmonic oscillator and a double-well potential. It is concluded that this scheme is successful at least as long as the potential is a slowly varying function of coordinates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454980
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  • 9
    Electronic Resource
    Electronic Resource
    Resonances in molecular photoionization. IV. Theory of one-color and two-color near-threshold photoionization of molecules (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6209-6219 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A relatively comprehensive theoretical description of one-color and two-color photoionization of molecules by strong laser fields is developed. The molecular system is modeled by a number of discrete electronic configurations and a number of electronic ionization continua in a diabatic representation, allowing for intramolecular coupling of the discrete states and the continua. The vibrational degrees of freedom are included in compact operator notation without invoking the Born–Oppenheimer approximation. The relevant radiative dipole couplings are treated nonperturbatively on an equal footing with the intramolecular couplings. The important Coulomb threshold effects (accumulating Rydberg series at the electronic–vibrational ionization thresholds) are included via a threshold expansion of the complex level-shift operators representing intramolecular and radiative couplings. The weak-field, long-time ionization rate (golden-rule formula) is rederived from the general theory both in the one-color and the two-color case. In the two-color case, strong-field effects caused by either one of the two lasers are briefly discussed. We derive a simplified multichannel-quantum-defect model from the general two-color formalism which nicely reproduces a number of characteristic features of vibronic autoionization recently observed in several polyatomic molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455438
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of multiphoton processes by the Fourier-expansion density matrix method (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2910-2916 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Fourier-expansion density matrix method is developed to describe the multiphoton processes of molecules interacting with the heat bath under the strong laser light. This method is applied to deriving expressions for the absorption spectra in the case in which a single-mode laser interacts with the molecular system of a three-level taking into account the dynamic Stark effect. Model calculations are performed to demonstrate the dynamic Stark effects on the absorption ability in the three-level system, and compared with the results of the weak laser light case. The calculated band shapes of the two-photon absorption are analyzed in terms of the simultaneous and sequential mechanisms. The sequential mechanism is characterized by bath-induced intramolecular transitions. As the laser intensity is increased the simultaneous mechanism makes a dominant contribution with increased dynamic Stark effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457938
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