A Multiple Scattering Theory of Thermal-diffuse Scattering for Low-Energy Electrons

A perturbation theory of thermal diffuse scattering of low-energy electrons is developed along the lines of von Laue's "reciprocity theorem" approach successfully used by Kainuma in the consideration of diffuse scattering in high-energy electron diffraction. This theory takes into account the multiple scattering of the electrons within the crystal, and is so formulated that it may be used in conjunction with present LEED calculations for the elastic scattering from a perfect crystal. It is shown that by a pseudokinematical approximation for the perfect crystal wave functions, the normal pseudokinematical result for the diffuse intensity is obtained. Under certain conditions differences between the multiple scattering theory and the pseudokinematical theory are expected to occur. These deviations have their origin in resonance processes. Some numerical results comparing the two theories are presented.