LEED AND DLEED HOLOGRAPHY

The current status of reconstruction of real-space images from diffuse LEED (DLEED) intensity distributions is described. We show by reconst ruction of images from measured data that reliable images cannot be ob tained from single energy diffraction maps. This holds also when inten sities for electron energies even up to the order of 1000 eV are used, and we propose a new method to measure such higher energy data by sam pling the diffuse intensity distribution through conventional LEED spo t intensities. In order to show the reasons for the failure of the hol ographic interpretation of single energy diffuse maps we break up the various dynamical diffraction processes in the surface into its releva nt constituents. This allows the demonstration that multiple diffracti on makes the reference wave generally ill defined and the weight of th e object wave too large. However, by inclusion of multiple energy data and proper phased averaging of intensities the disturbing influence o f multiple diffraction seems to degrade and much more reliable and sha rp images can result. This gives LEED and DLEED holography a high pote ntial for its use in surface crystallography.