Surface Science and LEEM
Soon after his arrival at the Michelson Laboratory in California, surface science was born. He was involved early in it in order to understand thin film phenomena. In this period he started in situ thin film growth studies by conventional electron microscopy, UHV reflection electron diffraction, LEED and Auger electron spectroscopy. He was one of the first to recognize the importance of exchange, polarization, multiple scattering, and of the energy dependence of inelastic scattering of very slow electrons in LEED studies of surfaces, and he took them into account theoretically. The importance of adsorption on the initial growth of thin films led him also to adsorption studies. In these early years of UHV technique and surface science much of the work went into technological and methodological development. The invention in 1962 of the Low Energy Electron Microscope (LEEM) was stimulated by a scientific dispute with Lester Germer about the difficulties in the interpretation of low energy electron diffraction (LEED) patterns. Ernst Bauer realized that electron microscopy using the diffracted electrons for imaging would be extremely important for the future of the surface science. He constructed the first LEEM prototype and reported it at the Fifth International Congress for Electron Microscopy in 1962.
At the Technical University Clausthal Ernst Bauer built up a broadly based surface science group encompassing a large variety of electron and ion beam techniques as well as optical methods. The quantitative interpretation of thermal desorption spectra was developed with the goal to obtain information on the interactions in adsorption layers. Work function measurements were developed and used for the determination of the thermodynamic properties of two-dimensional systems with attractive lateral interactions. For the study of two-dimensional systems with repulsive or oscillatory interactions, his group developed LEED-diffractometry that allows the determination of critical exponents in chemisorbed layers with accuracy comparable to that achieved with x-rays in physisorbed layers. He developed electron stimulated desorption (ESD) and static SIMS for the study of adsorbed layers and ultrathin films on single crystal surfaces; alkali ion scattering (ISS) for structural analysis of surfaces; field ion microscopy (FIM) of single atoms and clusters; UHV-SEM studies of surface melting. In this period (in 1985) the LEEM came also to fruition. In the late 1980s/ 1990s Ernst Bauer extended the LEEM technique in two directions by developing two new surface microscopy methods: Spin-Polarized Low Energy Electron Microscopy (SPLEEM) and Spectroscopic Photo Emission and Low Energy Electron Microscopy (SPELEEM).
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