Self-consistent multiple-scattering approach to the interpretation of low-energy electron diffraction
The central problem in the theory of diffraction by crystals, as approached from the selfconsistent multiple-scattering viewpoint, is that of determining the effective wave field incident on each atom in the crystal. A derivation is given, in outline, of the effective field equations for a model crystal in which the individual atom layers are treated explicitly. It is shown that the properties of the effective field imply the existence of two specific dynamical effects in low-energy electron diffraction intensities, namely the occurrence of fractional order peaks in intensity curves and multiple scattering resonance effects. The underlying physical processes are discussed fully with reference to simplified model crystals. Experimental evidence for both types of dynamical effects is cited. Possible future applications of the multiple-scattering method to various topics in low-energy electron diffraction are described. The applications discussed are to the effects of adsorption on intensities, to thermal diffuse scattering, to Kikuchi effects and to effects of crystal size. Finally, a discussion is given of the prospect of developing the computational side of the theory to the stage at which it is possible to make realistic calculations of beam intensities.