Capabilities of LEED for defect analysis

A diffraction pattern using low or high energy electron diffraction may be employed via the (integral) intensity of the spots to derive the atomic positions within a unit of a periodic arrangement. Spot profile analysis (SPA) provides information on periodic and nonperiodic arrangements of units as superstructure domains, terraces or facets, strained regions and so on. The first point will be the instrumentation suited for that type of analysis (SPA-LEED, SPA-RHEED and ELS-LEED, the latter using high resolution electron energy loss spectroscopy simultaneously with SPA). It will be discussed how a simple, reliable and quantitative analysis is possible within the kinematic approximation. All deviations from simple structures via defects like strain, roughness, facets or dislocations produce characteristic modifications of the spot profile, so that a specific and quantitative evaluation is possible. Finally, examples of defect analysis of heteroepitaxial films with a thickness of one to many monolayers show that many defects are necessary and therefore unavoidable for misfit accommodation. Depending on growth conditions, many other defects may appear additionally; they, however, may be reduced or avoided by appropriate growth parameters. Examples are taken from films of metals, semiconductors and insulators on quite different substrates.