Theory of L.E.E.D.

Abstract

In Low Energy Electron Diffraction (LEED) experiments one studies the elastic scattering of a beam of electrons of well defined energy by a solid surface. Low energy in this context means less than about 500 eV. Since electrons of such energy penetrate only a short distance (of order 10 A) into the surface before inelastic scattering by valence electrons, the experimental data should yield information about the surface layers of the solid. In particular, the great hope was that LEED could be developed into a technique for the determination of surface structures. The main obstacle to the realisation of this hope was that the theory needed for the interpretation of the experimental data proved to be difficult to generate. The ion cores of the solid typically have cross-sections for elastic scattering of low energy electrons of the order of square angstroms, which means that simple approximations used for neutron and X-ray scattering are inapplicable. One had to face up to the full multiple scattering problem in LEED, and after all the reasonable simplifications had been made, it was still necessary to develop very elaborate computer programmes in order to make useful calculations. However, we have now reached the point where it is established beyond doubt that several non-trivial surface structure problems have been solved.