Interaction of Charged Particles and Atoms with Surfaces · 6.1.1.4.2 VLEED

This chapter provides information on very low-energy electron diffraction (VLEED) method. Peaks can be reproduced in the standard LEED theory at low energy, including relativistic effects and also taking into account the non-sphericity of the potential. The effect due to a surface barrier is more important. This is also called “threshold” effect, because it is connected with the emergence of diffracted beams. The basic mechanism arises from the interference of the components of the wave fields which can propagate in a crystal, without having sufficient energy to escape, and which are thus reflected between the bulk and the surface barrier. Scattering by the surface barrier can be determined by numerical integration of a Schrodinger equation, and the reflection and transmission coefficients can also be calculated. The agreement between theory and experiment leads to the evaluation of the parameters, among which are the inner potential, the image plane location, a point at which the inner potential is reached.