Diffuse LEED and local surface structure

Abstract

Low energy electron diffraction (LEED) widely is considered to apply only to surfaces exhibiting long-range order. It is demonstrated that this is a too simple view: Due to multiple scattering the diffraction intensities are formed within a local atomic cluster whose size is determined by the electron attenuation. In case of long-range order the interference of these cluster scattering amplitudes leads to the appearance of sharp diffraction spots. In the absence of long-range order and with all clusters being structurally identical the resulting diffraction pattern is diffuse (DLEED). Nevertheless it is not without spatial structure which reflects the real space structure of the cluster. The latter determines also the diffuse intensity versus energy spectra taken for constant momentum transfer parallel to the surface. So it turns out that such DI(E) and the usual I(E) spectra are equivalent. It is shown that diffuse intensity distributions can be interpreted in a holographic way with the local adsorbate atom acting as a microscopic beam splitter. By suitable energy averaging of data the reconstruction of real space atomic images with a resolution of about 0.1 nm becomes possible.