DIFFUSE REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION

A numerically manageable formalism for the dynamical calculation of di ffuse reflection high-energy electron diffraction (RHEED) is presented . The diffuse scattering arises from transitions between dynamically c alculated scattering states in the periodic part of the scattering pot ential and the nonperiodic part is treated as a perturbation. For atom s placed on equivalent lattice sites relative to the periodic-potentia l part, the formalism allows us to treat disorder scattering by kinema tical structure factors that have to be multiplied by dynamically calc ulated atomic-scattering amplitudes so that the statistics of the diso rder can be treated independently of the dynamical calculations. It is shown that azimuthal reflection profiles (parallel to the shadow edge ) can, in favorable cases, be interpreted kinematically whereas polar profiles (normal to the shadow edge) are strongly influenced dynamical ly. It is further demonstrated by model calculations for the diffuse R HEED from disordered adsorbate layers that the corresponding broad sca ttering distribution depends strongly on the position of the adsorbate relative to the substrate. This should enable the use of RHEED in the field of structure analysis of disordered adsorbate layers. Finally, our concept is applied to thermal diffuse scattering. We show that the main structures of a measured broad thermal-diffuse-scattering distri bution from Pt(110) can be explained with the Einstein model, i.e., in dependent atomic oscillations.