The present thesis includes contributions to the theory and methodology of Low Energy Electron Diffraction (LEED). These methods are applied to structure analyses of the clean and oxygen-covered (111) surface of aluminium; of the clean and cesium-covered (111) surface of copper; and of a sodium film evaporated onto a clean (111) surface of copper.

A general procedure is described by which to construct scattering potentials for an adsorbate. In this model the adsorbed overlayer of atoms or molecules is represented by a cluster and the potential is calculated by means of the discrete variation method. In order to account for the energy dependence of the exchange-correlation electron-electron interaction an excited state potential for use by LEED is designed. This potential is found to give excellent agreement when applied to Cu(lll). In connection with the multiple scattering process of the LEED electrons within the crystal a new model for the interlayer attenuation is proposed. The model introduces an anisotropy in the electron absorption and is found to reproduce details in LEED intensity spectra which are not resolved by conventional LEED calculations. Finally, for future use by LEED, two methods are deviced where the scattering of electrons by an axially symmetric ion core potential is treated.

By application of LEED to a site determination of the Al(111)p(1x1)0 structure it is shown that the adsorbed oxygen atoms are forming an ordered overlayer with chemisorption sites corresponding to a continuation of the (111) surface of aluminium. In a subsequent LEED study of this structure, where the cluster approach was used, the oxygen-aluminium interlayer spacing is found to be 0.7 Å. The cluster method is also applied to a LEED study of the Cu(111)p(2x2)Cs structure where the cesium atoms are proved to occupy on top positions. The cesium-copper interlayer spacing is found to be 3.02 Å. An interesting structural result indicated by LEED is that the stacking sequence of a sodium film, evaporated onto a clean Cu(lll) surface, is hexagonally close packed (hep) rather than body centered cubic (bcc), which is the natural crystal structure of sodium.