Acta Physica Academiae Scientiarum Hungaricae 51. (1981)

1981 / 3. szám - Condensed Matter - A. Stachulec: Temperature Dependence of Low Energy Electron Diffraction in Pseudoharmonic Approximation

Acta Physica Academiae Scientiarum Hungaricae, Tomus 51 (3), pp. 243—258 (1981) TEMPERATURE DEPENDENCE OF LOW ENERGY ELECTRON DIFFRACTION IN PSEUDOHARMONIC APPROXIMATION By A. Stachulec DEPARTMENT OF PHYSICS, TECHNICAL UNIVERSITY, KIELCE, POLAND (Received 12. У. 1981) The intensity of electrons scattered by a metallic surface is considered in terms of the surface electron density modulated by lattice vibrations of atoms at the surface. The tempera­ture dependence of thermal vibrations is determined on the basis of the pseudoharmonic approxi­mation for the interatomic interaction. The pseudoharmonic method brings an essential correc­tion to the temperature behaviour of the low energy electron intensity and it seems to be a very useful approach to the description of diffraction phenomena. I. Introduction The surface effects considered in the low energy electron diffraction LEED method are usually described by means of the Debye—Waller para­meter which appears in the structural factor given for a crystallographic structure of investigated samples (e.g. [1]). The electron density at the surface as well as the force constants are calculated in an approximation where they do not depend on temperature, so that the temperature dependence of the LEED intensity is included only by the Debye—Waller parameter occurring in the sum over atomic positions in a sample. The aim of the present paper is to give a modified approach to the LEED description in order to explain the temperature dependence of the cross­­section for the low energy electron scattering in a more appropriate way. First of all we assume that the electron density at the surface can change its shape as a function of temperature, which implies the temperature-dependent behaviour of the scattering potential. Next, we take into account that the phonon properties depend on temperature and influence the Debey—Waller parameter. The force constants as well as the scattering potential are considered by means of the pseudoharmonic approximation [2, 3], also applied with a great success in many approaches to the description of thermal properties [e.g. 4]. It seems to us that the pseudoharmonic model is very useful for the explana­tion of the electron motion in the effective field averaged over all atomic contributions following from their dynamical behaviour. Acta Physica Academiae Scientiarum Hungaricae 51, 1981

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