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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5931-5931 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inelastic exchange scattering of electrons can result in spin-dependent mean free paths (MFP) for electrons in ferromagnetic transition metals and glasses. The MFP of electrons with spin in the majority-spin direction will be greater than those with spin in the minority direction due to the larger number of empty minority-spin d states into which minority-spin electrons can scatter. This difference in MFP can explain the increase in the spin polarization of secondary electrons in transition metals and glasses that is observed at low energies. In addition, it will be shown that the ratio of the majority to minority spin MFP as a function of energy can be determined directly from measurements of the energy dependence of the secondary electron-spin polarization. A different type of experiment in which exchange is important is the production of Ni Auger electrons by the scattering of metastable He atoms from a Ni surface. The number of Auger electrons produced is found to depend on the relative spin of the He and Ni, parallel or antiparallel. The normalized difference of these two cases is found to increase with increasing energy of the Auger electrons. It is found that this effect is directly related to exchange scattering of the Ni electrons that neutralize the He atoms and that the experimental results can be accounted for by a simple model.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 4063-4073 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the process of charged polymer translocation, driven by an external electric potential, through a narrow pore in a membrane. We assume that the number of polymer segments, m, having passed the entrance pore mouth, is a slow variable governing the translocation process. Outside the pore the probability that there is an end segment at the entrance pore mouth, is taken as the relevant parameter. In particular we derive an expression for the free energy as a function of m, F(m). F(m) is used in the Smoluchowski equation in order to obtain the flux of polymers through the pore. In the low voltage regime we find a thresholdlike behavior and exponential dependence on voltage. Above this regime the flux depends linearly on the applied voltage. At very high voltages the process is diffusion limited and the flux saturates to a constant value. The model accounts for all features of the recent experiments by Henrickson et al. [Phys. Rev. Lett. 85, 3057 (2000)] for the flux of DNA molecules through an α-hemolysin pore as a function of applied voltage. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3365-3372 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electromagnetic interaction energy of a molecular aggregate consisting of pointlike molecules in the presence of an electromagnetic field is derived. The corresponding Hamiltonian consists of three parts; H0 describes the aggregate in the absence of the electromagnetic field, H1 describes the interaction of the molecules with the external field, and H2 corresponds to the induced interaction between the molecules. Based on this Hamiltonian we derive a self-consistent equation of motion for a quasiparticle, which we refer to as a polarized exciton. The equation has the same form as the one in classical dipole theory. The polarized exciton model is based on a time-dependent perturbative treatment and corresponds to the assumption H0(very-much-greater-than)H1+H2. Our model is compared to standard exciton theory, which is based on the assumption H0(very-much-greater-than)H2(very-much-greater-than)H1. In particular the differences and similarities are illustrated for a direct example, a finite linear chain. We advocate the use of polarized excitons to fully account for the physics in these systems. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1175-1177 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theoretical basis for understanding photo-assisted resonant tunneling is generally taken to be the theory by Tien and Gordon [Phys. Rev. 129, 647 (1963)] in which the effect of a photon field on an energy state is to create sidebands at multiples of the photon energy. An alternative mechanism in which bulk photoabsorption is the photoexcitation mechanism is discussed. The two theories take the same form in the weak-field limit, and an expression is given for the relative size of tunneling currents.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stopping of energetic ions by ultrathin films is of interest, as such films are mesoscopic structures which comprise the delamination limit of crystals, and as they are of practical interest because of their connection to microelectronics. A matter of special interest is the effect of the number of target layers on the stopping. Here we show that the stopping cross-section, S(N, v), of a system of N layers for projectiles with velocity v is a linear function of N-1 for small N. Such behavior would be expected for N → ∞, in which case the constant term would be the bulk crystalline cross section at the specified projectile velocity and the coefficient of the linear term would be the lowest-order surface correction. Surprisingly, the constant coefficient from a small N fit is reasonably consistent (within limits of imprecision) with the crystalline cross section. This linear scaling of S with N-1 for small N tracks the scaling behavior of the cohesive energy of the films. We discuss the physics and provide some illustrations. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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