The Synthesis, Characterization, and Surface Chemistry of Ultra-thin Oxide Films

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Abstract 9423707 The goal of this project is the synthesis, characterization, and surface chemistry of well defined, ultra-thin (less than 10 nm) oxide films. Ultra-thin oxide films will be prepared on refractory single crystal substrates and characterized using an array of surface science techniques, including low energy electron diffraction, Auger electron spectroscopy, X-ray and ultraviolet photoelectron spectroscopy and, ion scattering spectroscopy, reflection absorption Fourier transform infrared spectroscopy, high resolution electron energy loss spectroscopy, scanning tunneling microscopy/atomic force microscopy, and temperature programmed desorption. Ordered, oxide surfaces in thin film form will be prepared on single-crystal, refractor metal substrates. This approach will be extended to include a variety of oxide and mixed-oxide types. A methodology utilizing these highly ordered, stoichiometric oxide thin films offers a promising new strategy for studying the surface chemistry of these materials in ways precluded utilizing the bulk materials and traditional techniques. %%% This study impacts the basic science of oxides and various practical technologies such as environmental waste remediation, device fabrication, and catalysis. Because of the highly insulating nature of many oxide materials, their surface geometrical and electronic properties, in general, have received much less attention than, for example, metal surfaces. To date, extensive work on the chemisorption and catalytic properties of oxide materials have been conducted, however, the microscopic reaction mechanisms occurring on oxide surfaces are still not well understood. The principle reason for this is that these studies have been performed primarily on powder samples. Therefore, the information represents an average of the various crystal faces exposed in addition to a variety of defects which are inevitably present in the powdered samples. On the other hand, high-purity single cr ystals of many oxide materials have been difficult to obtain and studies of these insulating materials have often encountered the difficulties associated with surface charging, sample heating and cleaning. Therefore, there is a clear need for the synthesis of high quality, thin oxide films. Structural and chemisorptive properties of oxide materials can be obtained by preparing well-defined, thin oxide films whose properties are identical to their single-crystal bulk counterparts, thereby facilitating surface chemical studies of these materials under controlled conditions.