Resonance reflections in RHEED

Electrons reflected from a crystal surface are generated by two scattering mechanisms. Bragg reflection, which is purely an elastic scattering process, is responsible for producing sharp peaks governed by Bragg's law. Inelastic scattering, which is dominated by valence-loss and thermal diffuse scattering (TDS), contributes a Kikuchi pattern background in the electron angular distribution and results in electron energy losses and momentum transfers. The excitation of Bragg reflections critically depends on the diffracting conditions, and the intensity distribution in a RHEED pattern is the result of dynamical scattering of electrons by the crystal surface. It is thus important to understand how electrons are reflected from the surface in order to illustrate the surface sensitivity of REM.