Browsing by Author "Li, Y. C."

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Angular and energy dependences of the surface excitation parameter for electrons crossing a solid surface
(2006-09-15)
Kwei, C. M.
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Li, Y. C.
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Tung, C. J.
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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
When fast electrons cross a solid surface, surface plasmons may be generated. Surface plasmon excitations induced by electrons moving in the vacuum are generally characterized by the surface excitation parameter. This parameter was calculated for 200-1000 eV electrons crossing the surfaces of An, Cu, Ag, Fe, Si, Ni, Pd, MgO and SiO, with various crossing angles. Such calculations were performed based on the dielectric response theory for both incident (from vacuum to solid) and escaping (from solid to vacuum) electrons. Calculated results showed that the surface excitation parameter increased with crossing angle but decreased with electron energy. This was due to the longer time for electron-surface interaction by glancing incident or escaping electrons and by slow moving electrons. The results were fitted very well to a simple formula, i.e. P-s = aE(-b)/(cosx)(c), where P, is the surface excitation parameter, E is the electron energy, alpha is the angle between the electron trajectory and the surface normal, and a, b and c are material dependent constants. (c) 2006 Elsevier B.V. All rights reserved.
Dielectric response theory for electron energy loss in clad cylindrical systems
(2006-07-01)
Tu, Y. H.
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Kwei, C. M.
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Li, Y. C.
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Tung, C. J.
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電子工程學系及電子研究所
Inelastic interactions between an electron and a clad cylindrical system were investigated using the dielectric response theory. By solving the Poisson equation and applying the boundary conditions, these interactions were formulated in terms of the surface, interface and volume excitations. Formulas of the differential inverse inelastic mean free path (DIIMFP) were derived for electrons moving parallel to the axis of such a cylindrical structure. A sum-rule-constrained extended Drude dielectric function with spatial dispersion was applied to the calculations of the DIIMFP for a Si cylindrical tube or a Si cylinder clad in a SiO2 film. For the Si tube, it was found that surface excitations occurred as electrons moved near either the inner or outer surface of the tube and either inside or outside Si. Whereas, volume excitations arose only for electrons moving inside Si. Surface excitations increased, or volume excitations decreased, as electrons moved closer to the surface. For the Si cylinder clad in the SiO2 film, inelastic interactions were contributed from volume, surface, and interface excitations. Calculated results showed that the relative importance of these excitations depended on the electron distance from the surface or interface of the cylindrical system, the radius of the Si cylinder, and the thickness of the SiO2 film.