Browsing by Author "Tu, YH"

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Inelastic interactions of electrons with cylindrical interfaces
(2006-02-15)
Tu, YH
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Kwei, CM
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Tung, CJ
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A theory was developed to deal with inelastic interactions for an electron moving parallel to the axis of a cylindrical structure. Formulas for the differential inverse inelastic mean free path (DIIMFP) and the total inverse inelastic mean free path (IIMFP) were derived using dielectric response theory. A sum-rule-constrained extended Drude dielectric function with spatial dispersion was applied to calculate DIIMFPs and IIMFPs for a solid wire and a cavity in solid. The calculated results showed that surface excitations occurred as the electron moved near the boundary either inside or outside the solid, whereas volume excitations arose only for electron moving inside the solid. It was found that the probability for surface excitations increases and that for volume excitations decreases for an electron moving close to the surface. Near the surface, the decrease in volume excitations is compensated by the increase in surface excitations. For a cavity in solid, the IIMFP inside the solid can be approximated by a constant value equal to the IIMFP for the infinite solid, except in the immediate vicinity of the cavity boundary. (c) 2005 Elsevier B.V. All rights reserved.
Influence of the direction of motion on the inelastic interaction between electrons and solid surfaces
(2005-09-01)
Li, YC
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Tu, YH
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Kwei, CM
;
Tung, CJ
;
電子工程學系及電子研究所
Theoretical derivations of the inelastic differential inverse mean free path (DIMFP) and inelastic mean free path (IMFP) for electrons crossing solid surfaces were made for different crossing angles and electron distances relative to the crossing point at the surface. Individual contributions from volume and surface excitations were separated and analyzed for electrons traveling inside and outside the solid. Extended Drude dielectric functions were employed to calculate the DIMFP and inverse IMFP for electrons incident into and escaping from Cu. It was found that the DIMFP and inverse IMFP for electrons moving inside the solid were approximately independent of crossing angle and position of electrons due to the compensation of volume and surface excitations. For electrons moving deep inside the solid, the DIMFP and inverse IMFP reduced to the values for electrons moving in an infinite solid. As electrons traveling in the vacuum, the DIMFP and inverse IMFP became greater for glancing incident and escaping angles since surface excitations were more probable. The surface excitation parameter (SEP) for electrons traveling in vacuum showed an angular dependence. The SEP of escaping electrons was found larger than that of incident electrons due to the attractive force exerted by the induced surface charges. The calculated SEP was found to follow a simple expression. (c) 2005 Elsevier B.V. All rights reserved.
Memory effect on energy losses of charged particles moving parallel to solid surface
(2006-02-01)
Kwei, CM
;
Tu, YH
;
Hsu, YH
;
Tung, CJ
;
電子工程學系及電子研究所
Theoretical derivations were made for the induced potential and the stopping power of a charged particle moving close and parallel to the surface of a solid. It was illustrated that the induced potential produced by the interaction of particle and solid depended not only on the velocity but also on the previous velocity of the particle before its last inelastic interaction. Another words, the particle kept a memory on its previous velocity, v(0), in determining the stopping power for the particle of velocity v. Based on the dielectric response theory, formulas were derived for the induced potential and the stopping power with memory effect. An extended Drude dielectric function with spatial dispersion was used in the application of these formulas for a proton moving parallel to Si surface. It was found that the induced potential with memory effect lay between induced potentials without memory effect for constant velocities v(0) and v. The memory effect was manifest as the proton changes its velocity in the previous inelastic interaction. This memory effect also reduced the stopping power of the proton. The formulas derived in the present work can be applied to any solid surface and charged particle moving with arbitrary parallel trajectory either inside or outside the solid. (c) 2005 Elsevier B.V. All rights reserved.
Memory effect on the inelastic interaction of electrons moving parallel to a solid surface
(2006-02-01)
Kwei, CM
;
Hsu, YH
;
Tu, YH
;
Tung, CJ
;
電子工程學系及電子研究所
It is generally assumed that two successive inelastic interactions between an electron and a solid are independent of each other. In other words, the electron has no memory of its previous interaction. However, the previous interaction of the electron generates a potential that should influence its succeeding inelastic interaction. The aim of this work is to establish a model to account for the memory effect of an electron between two successive inelastic interactions. On the basis of the dielectric response theory, formulae for differential inverse inelastic mean free paths (DIIMFPs) and inelastic mean free paths (IMFPs) considering the memory effect were derived for electrons moving parallel to a solid surface by solving the Poisson equation and applying suitable boundary conditions. These mean free paths were then calculated with the extended Drude dielectric function for a Cu surface. It was found that the DIIMFP and the IMFP with the memory effect for electron energy E lay between the corresponding values without the memory effect for electron energy E and previous energy Eo. The memory effect increased with increasing electron energy loss, E-0 - E-1 in the previous inelastic interaction. Copyright (c) 2005 John Wiley & Sons, Ltd.
Surface excitation parameter for semiconducting III-V compounds
(2005-04-01)
Kwei, CM
;
Tu, YH
;
Tung, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In the rapid development of mesoscopic science, the study of surface excitations in solids and overlayer systems plays a crucial role. The surface excitation parameter which describes the total probability of surface plasmon excitations by an electron traveling in vacuum before impinging on or after escaping from a semiconducting III-V compound has been calculated for 200-2000 eV electrons crossing the compound surface. These calculations were performed using the dielectric response theory with sum-rule -constrained extended Drude dielectric functions established by the fits of these functions to optical data. Surface excitation parameters calculated for InSb, InAs, Gap, GaSb or GaAs III-V compounds were found to follow to a simple formula, i.e. P-s = aE(-b), where Ps is the surface excitation parameter and E is the electron energy. These surface excitation parameters were then applied to determine the elastic reflection coefficient for electrons elastically backscattered from III-V compounds using the Monte Carlo simulations. Good agreement was found for the electron elastic reflection coefficient between calculated results and experimental data. (c) 2004 Elsevier B.V. All rights reserved.