DYNAMICAL RHEED FROM DISORDERED SURFACES - SHARP REFLECTIONS AND DIFFUSE-SCATTERING

A formalism for the dynamical calculation of RHEED from disordered surfaces, based on perturbation theory, is presented. The scattering into the sharp reflections is determined by the periodic part of the potential. The diffuse scattering arises from transitions between dynamically calculated scattering states in the periodic potential part and the non-periodic part is treated as a perturbation. For atoms being placed on equivalent lattice sites relative to the periodic potential part, a pseudo-kinematical treatment for the diffuse scattering is possible. Conventional structure factors have to be multiplied by. dynamically calculated atomic scattering amplitudes so that the statistics of the disorder can be treated independently from the dynamical calculations. Comparisons between theory and experiment are given for Pt(Ill) and Pt(110), including thermal diffuse scattering. Further model calculations for the diffuse RHEED from disordered adsorbate layers demonstrate that the corresponding scattering distribution depends strongly on the position of the adsorbate relative to the substrate. This may open the use of RHEED in the field of structure analysis of disordered adsorbate systems.