LEED Investigation of Surface Processes

Abstract

LEED (Low Energy Electron Diffraction) provides a variety of information on surfaces. Although diffusion is not measured directly, many processes, which include diffusion at some intermediate step, are well studied with LEED. Information needed for evaluation of the processes is essentially given in the spot profiles. Therefore, an overview over the evaluation of the spot profiles with respect to lateral and vertical distribution, to defects like steps, facets, and point defects will be given. A well investigated non-equilibrium process is the epitaxial growth, especially under ultra high vacuum conditions where LEED study is possible during growth. The oscillation of the peak intensity has been used to determine the growth mode in homoepitaxy. Here the diffusion contributes to the nucleation and growth, so the barrier may be derived. A possible step edge barrier has a strong influence on the oscillation behaviour. Examples for Pt on Pt(111) and Ag on Ag(111) will demonstrate the possibilities. Other non-equilibrium processes, which include diffusion, are coarsening of islands or domain structures and faceting of surfaces due to adsorbates. At finite temperatures surface arrangements may be in thermal equilibrium, nevertheless the diffusion provides a steady fluctuation of the arrangement. LEED studies are especially informative, when all surface atoms are involved in the fluctuations. Two examples will be studied: the roughening transition at the Cu(311) surface and the melting of a monolayer of Pb on top of Cu(111).