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

A formalism for the dynamical calculation of RHEED from disordered sur faces, based on perturbation theory, is presented. The scattering into the sharp reflections is determined by the periodic part of the poten tial. The diffuse scattering arises from transitions between dynamical ly calculated scattering states in the periodic potential part and the non-periodic part is treated as a perturbation. For atoms being place d 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 calculati ons for the diffuse RHEED from disordered adsorbate layers demonstrate that the corresponding scattering distribution depends strongly on th e position of the adsorbate relative to the substrate. This may open t he use of RHEED in the field of structure analysis of disordered adsor bate systems.