LEED AND DLEED HOLOGRAPHY

The current status of reconstruction of real-space images from diffuse LEED (DLEED) intensity distributions is described. We show by reconstruction of images from measured data that reliable images cannot be obtained from single energy diffraction maps. This holds also when intensities 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 sampling the diffuse intensity distribution through conventional LEED spot intensities. In order to show the reasons for the failure of the holographic interpretation of single energy diffuse maps we break up the various dynamical diffraction processes in the surface into its relevant constituents. This allows the demonstration that multiple diffraction makes the reference wave generally ill defined and the weight of the object wave too large. However, by inclusion of multiple energy data and proper phased averaging of intensities the disturbing influence of multiple diffraction seems to degrade and much more reliable and sharp images can result. This gives LEED and DLEED holography a high potential for its use in surface crystallography.