In low-energy electron microscopy (LEEM) we commonly encounter images which, beside amplitude contrast, also show signatures of phase contrast. The images are usually interpreted by following the evolution of the contrast during the experiment, and assigning gray levels to morphological changes. Through reconstruction of the exit wave, two aspects of LEEM can be addressed: (1) the resolution can be improved by exploiting the full information limit of the microscope and (2) electron phase shifts which contribute to the image contrast can be extracted. In this article, linear exit wave reconstruction from a through-focal series of LEEM images is demonstrated. As a model system we utilize a heteromolecular monolayer consisting of the organic molecules 3,4,9,10-perylene tetracarboxylic dianhydride and Cu-II-Phthalocyanine, adsorbed on a Ag(111) surface.

The following article is based on the MRS Medal talk by Norm Bartelt (Sandia National Laboratories, California), presented at the 2001 Materials Research Society Fall Meeting on November 29 in Boston. Bartelt received the Medal for his “contributions to the statistical mechanics of materials surfaces.” A long-standing goal of materials science research has been to predict the long-term evolution of the microstructure of materials from a knowledge of atomic processes. This is usually extremely difficult to do in any detail because of the large number of atomic processes to consider, many of which are poorly understood. On solid surfaces, however, progress in the prediction of microstructural evolution can now be made because of advances in real-time microscopy that allow the characterization of the time evolution of microstructure in unprecedented detail. These observations directly reveal the complex relationships between collective thermal fluctuations on atomic scales and deterministic behavior on macroscopic scales. In this presentation, attempts to construct models of these observations are discussed.