Electron Spectroscopic Studies of the Electronic and Geometric Structure of, and Chemisorption on, Transition Metal Oxide Surfaces

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During the past few years the Surface Science Laboratory at Yale has become established as the world's foremost research center for the study of the fundamental properties of oxide surfaces. Professor Henrich's approach is to use single crystal samples, prepared and studied in an ultrahigh vacuum environment or under controlled chemisorption conditions, and to measure their geometric and electronic structure by using a wide range of surface sensitive electron spectroscopic techniques. Particular attention has been given to the transition metal oxides, whose cations can have any of several different valence states depending upon their ligand environment; these oxides are the most important ones in catalysis and surface chemistry. Measurements on nearly perfect, vacuum cleaved surfaces are a necessary starting point, particularly for comparison with theoretical calculations. However, his primary interest is in the properties of surface defects and their interaction with adsorbed molecules. Surface defects have been shown to be the active sites for chemisorption on almost all oxides that have been studied, with nearly perfect surfaces being relatively inert. Professor Henrich proposes here a three-year research program consisting both of a continuation of the most productive research areas that are currently being pursued and of several new directions that will address some of the important questions that research to date has left unanswered. Empty electronic states on oxide surfaces will be examined by using inverse photoelectron spectroscopy, and a newly acquired high resolution electron energy loss spectrometer will be used to study the subtleties of the interaction of molecules of catalytic interest with oxides. A collaborative effort with the IBM Watson Research Center will use scanning tunneling microscopy to determine the geometry of both perfect and defect oxide surfaces and to measure the spectra of their filled and empty electronic levels.