Programs in Physics & Physical Chemistry
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|Manuscript Title: Computation of the surface electron-energy-loss spectrum in specular geometry for an arbitrary plane-stratified medium.|
|Authors: Ph. Lambin, J.-P. Vigneron, A.A. Lucas|
|Program title: HREELS of multilayers|
|Catalogue identifier: ABTI_v1_0|
Distribution format: gz
|Journal reference: Comput. Phys. Commun. 60(1990)351|
|Programming language: Fortran.|
|Computer: IBM 9377/90.|
|Operating system: VL/SP REL 5.|
|RAM: 65K words|
|Word size: 32|
|Keywords: Solid state physics, Surface analysis, Surface and interface Phonons, Electron-energy-loss Spectroscopy, Hreels, Thin films, Heterostructure, Superlattice.|
Nature of problem:
The computer program allows to calculate the electron-energy-loss spectrum of an arbitrary plane-stratified medium for low-energy electrons specularly reflected at the surface of the target. A dielectric approximation is used to characterize the response of the target material to the long-ranged coulomb field of the impinging electrons. Periodic superlattices can be considered as well as any arbitrary stacking of layers onto a thick substrate. In the later case, the substrate is allowed to be a anisotropic, uniaxial crystal having its axis perpendicular to the free surface of the system. Temperature effects are included according to Bose-Einstein statistics for the long- wavelength vibrations excited at the surface or interfaces by the electrons.
The EELS spectrum is computed in two sequential steps performed by two programs called EELS and BOSON. The single-scattering, classical loss spectrum of the target is first computed (program EELS) for an electron travelling along a specularly-reflected trajectory, with the possibility of taking into account the acceleration of the electron by the image force. The full EELS spectrum, which includes multiple-scattering events for an arbitrary temperature of the target, is next obtained through a suitable thermodynamic average of the quantized surface excitations (program BOSON), while keeping the classical nature of the impinging electrons. The computed EELS spectrum is convoluted with a model of instrumental response of the spectrometer so as to simulate limitations in the experimental energy resolution.
Only dipolar inelastic-scattering of the reflected electrons are considered. Possible variations of the surface reflection coefficient with the electron energy are not considered here as all inelastic spectra are normalized to unity. All the layers that compose the target are assumed to be made of materials having isotropic dielectric functions, except for a possible thick substrate on which the layer are stacked, which can be a uniaxial crystal.
The time for the test run on IBM 9377 is 40s.
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