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  • 1
    Electronic Resource
    Electronic Resource
    Electron-impact ionization cross sections of atmospheric molecules (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1026-1033 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical model for electron-impact total ionization cross sections, which has been found to be reliable for a wide range of molecules, is applied to molecules of interest to atmospheric science. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical data for the ground state of the target molecule, which are readily available from molecular structure codes. Total ionization cross sections of 11 molecules, CS, CS2, COS, CH4, H2S, NH3, NO2, N2O, O3, S2, and SO2, are presented for incident electron energies from threshold to 1 keV with an average accuracy of 15% or better at the cross section peak. We also found that the use of vertical ionization potentials (IPs) rather than adiabatic IPs for the lowest IPs significantly improves BEB cross sections between the threshold and cross section peak for molecules whose adiabatic and vertical IPs are different by ∼1 eV or more (CH4 and NH3). The BEB cross sections are presented in a compact analytic form with a small number of constants, making the cross sections suitable for modeling applications. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473186
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  • 2
    Electronic Resource
    Electronic Resource
    New model for electron-impact ionization cross sections of molecules (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2956-2966 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical model for electron-impact ionization cross sections, which has been developed primarily for atoms and atomic ions, is applied to neutral molecules. The new model combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses minimal theoretical data for the ground state of the target molecule, which are readily available from public-domain molecular structure codes such as GAMESS. The theory is called the binary-encounter Bethe (BEB) model, and does not, in principle, involve any adjustable parameters. Applications to 19 molecules, including H2, NO, CH2, C6H6, and SF6, are presented, demonstrating that the BEB model provides total ionization cross sections by electron impact from threshold to several keV with an average accuracy of 15% or better at the cross section peak, except for SiF3. The BEB model can be applied to stable molecules as well as to transient radicals. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471116
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  • 3
    Electronic Resource
    Electronic Resource
    Photoelectric study of the Ni- and Ni-TeO2-electrodeposited n-type CdTe interfaces (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1245-1250 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The barrier heights of the electrodeposited n-type CdTe thin-film metal semiconductor (MS) and metal-thin insulating layer-semiconductor (MIS) devices have been measured by internal photoemission. The data for both MS and MIS devices can be fit with the square root of the photocurrent per absorbed photon dependence consistent with the Fowler theory. The barrier height of Ni-CdTe is 0.75 eV at room temperature, and its temperature dependence is about the same as that of the CdTe band gap. This suggests that the barrier height is pinned with respect to the CdTe valence band edge. Oxidation in air at 300 °C for an hour produces a layer of about 25 A(ring) or TeO2 on the CdTe surface. Thicker oxide can be grown for longer oxidation time. Negative oxide charges are found in some devices. At room temperature, the barrier height of Ni-TeO2-CdTe is 0.92 eV. As temperature is decreased, the barrier height increases and its rate of change with temperature is less than that of the CdTe band gap. Samples stored in room atmosphere show aging effects, one of which is the increase in surface-state density. The dips in the curve of the spectral dependence of the relative photon-induced current are caused by electrons which drift to the metal after being photoexcited from occupied surface states below the Fermi level. These dips correspond to peaks in the energy distribution of the surface state density. At zero bias and 170 °K, four peaks at 1.02, 1.06, 1.18, and 1.26 eV are observed for the MIS devices. For the MS devices zero biased at room temperature, four peaks at 0.85, 0.94, 1.02, and 1.05 eV are observed. The magnitudes of the dips at 0.85, 0.94, 1.18, and 1.26 eV vary with bulk-defect density and these levels shift towards higher energy as temperature is decreased. On the other hand, the levels at 1.02 and 1.05 eV for the MS devices and 1.02 and 1.06 eV for the MIS devices are independent of temperature and bulk defect density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336512
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of surface state density for GaAs and InAlAs by room temperature photoreflectance (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1765-1767 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room temperature photoreflectance (PR) was used to investigate the surface state densities of GaAs and In0.52Al0.48As surface intrinsic-n+ structures. The built-in electric field and thus the surface barrier height are evaluated using the observed Franz–Keldysh oscillations in the PR spectra. Based on the thermionic emission theory and current-transport theory, the surface state density as well as the pinning position of the Fermi level can be determined from the dependence of the surface barrier height on the pump beam intensity. Even though this method is significantly simpler, easier to perform, and time efficient compared with other approaches, the results obtained agree with the literature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370961
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  • 5
    Electronic Resource
    Electronic Resource
    Defect levels in electrodeposited n-type CdTe thin films (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2234-2243 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Admittance spectroscopy is used to measure electron traps near the conduction band of the n-type electrodeposited CdTe thin films. Several samples of Ni-CdTe Schottky-barrier and Ni-TeO2-CdTe devices are used in the measurement. Two donor levels with activation energies around 0.12 eV and between 0.19 and 0.26 eV are detected. In addition, there may be one or more shallow donor levels within 0.04 eV from the conduction band. Capacitance loops are observed in the capacitance-voltage measurements performed at different temperatures and bias sweep rates. The activation energies, densities, and electron-capture cross sections of the two slow electron-trap levels responding to the cyclical ramp bias are estimated. The rise and decay photocapacitance transient measurements at 295 K reveal two electron-trap levels with photoionization threshold energies of 0.8 and 1.3 eV. These two levels are suspected to correspond to the other two slow electron-trap levels estimated in the capacitance-voltage measurement and located around or above the midgap. The differences between thermal and optical ionization energies and the slow electron-capture rates of these two levels may be explained by the nonradiative, thermally activated capture processes with large lattice relaxation. Numerous defects around and below the midgap are detected by the steady-state photocapacitance measurement at 100 K. A band of seven defect levels spreading within 0.6 to 1.0 eV is observed. Large capacitance changes are recorded at 1.37, 1.41, and 1.45 eV. These three levels are speculated to be the major compensating acceptor levels. Based on both the photocurrent and photocapacitance measurements, electrons emitted from the 1.02-, 1.06-, 1.21-, and 1.28-eV levels are believed to arise from the defects at the TeO2-CdTe interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337985
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  • 6
    Electronic Resource
    Electronic Resource
    Photoconductance transient response in polycrystalline silicon (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 338-344 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoconductance transient response in polycrystalline silicon has been studied theoretically and experimentally. Shockley–Read–Hall statistics are used to describe the emission and capture processes at the grain-boundary traps. Under appropriate conditions, the minority carrier capture and emission time constants of the grain-boundary trap can be directly obtained from the photoconductance transient response. The photoconductance method is therefore useful for studying grain-boundary deep level states. The special case when a focused laser spot is employed is also discussed. From the experimental data obtained from large-grain Wacker polycrystalline silicon, we have discovered a donor-like level at 0.48 eV below the conduction band with a concentration of 2×1010 cm−2. The electron (minority carrier) lifetime is found to be about 6×10−10–10−9 s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334811
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  • 7
    Electronic Resource
    Electronic Resource
    Photoreflectance studies of surface state density of InAlAs (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1771-1776 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface barrier height and surface Fermi level of InAlAs were investigated via photoreflectance spectra. Surface state density was then determined from the surface barrier height as a function of temperature, illumination power intensity, and intrinsic layer thickness. Results obtained from these three independent approaches all give the same conclusion, that the surface states are distributed over two separate regions within the energy band gap. Closely examining the photovoltage induced by various incident beam intensities revealed that the photovoltage effect is negligible when the illumination power intensity is below 1.0 μW/cm2. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334926
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  • 8
    Electronic Resource
    Electronic Resource
    Photoreflectance study of the surface state density and distribution function of InAlAs (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 396-400 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance is used to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In0.52Al0.48As surface-intrinsic n+ structures having different undoped layer thicknesses. Experimental results indicate that, although the built-in electric field depends on the undoped layer thickness, there is a range of thickness within which the surface Fermi level is weakly pinned. From the dependence of electric field and surface Fermi level on the undoped layer thickness, we can determine that the surface states distribute over two separate regions within the energy band gap. The densities of the surface states are evaluated as well. Moreover, the dependence of the built-in electric field on undoped layer thickness is converted into the dependence of surface state density on the surface Fermi level in order to theoretically and exactly calculate the energy spectrum of the surface state density using a Guassian distribution function. The center and width of the distribution near the conduction band are obtained from the fitting parameters. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1324682
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of Fermi level pinning and surface state distribution in InAlAs heterostructures (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 3690-3695 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The band gaps, built-in electric field, and surface Fermi level of a series In1−xAlxAs surface-intrinsic-n+ (SIN+) structures have been studied by photoreflectance at room temperature. The samples were grown by molecular beam epitaxy with an undoped layer thickness of 1000 Å. Our study indicates that, in contrast to GaAs and AlGaAs, the surface Fermi level is not pinned at midgap over aluminum concentration of 0.42–0.57. The pinning position is composition dependent. The undoped layer was subsequently etched to 800, 600, 400, and 200 Å. Different chemical solutions were used in the etching process and the built-in electric field is found independent of the etching process. Although the surface Fermi level, in general, varies with the undoped layer thicknesses, there exists, for each Al concentration, a certain range of thicknesses within which the surface Fermi level is weakly pinned. From the dependence of electric field and surface Fermi level on the undoped layer thickness, we conclude that the surface states distribute over two separate regions within the energy band gap and the densities of surface states are as low as 1.36±0.05×1011 cm−2 eV−1 for the distribution near the conduction band and 4.38±0.05×1011 cm−2 eV−1 for the distribution near valence band. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366593
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  • 10
    Electronic Resource
    Electronic Resource
    An ab initio molecular fragment investigation of the inversion barrier and syn-anti isomerization mechanisms of formaldoxime (1978)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 82 (1978), S. 2126-2127 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100508a014
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