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

摘要：本项目的目标是合成、表征和表面化学的明确，超薄（小于10纳米）氧化膜。超薄氧化膜将在难熔单晶衬底上制备，并使用一系列表面科学技术进行表征，包括低能电子衍射、俄歇电子能谱、x射线和紫外光电子能谱、离子散射能谱、反射吸收傅立叶变换红外能谱、高分辨率电子能量损失能谱、扫描隧道显微镜/原子力显微镜、温度程序解吸。有序的，薄膜形式的氧化物表面将在单晶，折射金属衬底上制备。这种方法将扩展到包括各种氧化物和混合氧化物类型。利用这些高度有序的化学计量氧化物薄膜的方法为研究这些材料的表面化学提供了一种有前途的新策略，这种方法无法利用大块材料和传统技术。这项研究影响了氧化物的基础科学和各种实用技术，如环境废物修复，设备制造和催化。由于许多氧化物材料的高度绝缘性，它们的表面几何和电子特性，一般来说，受到的关注要比金属表面少得多。迄今为止，人们已经对氧化物材料的化学吸附和催化性能进行了大量的研究，然而，发生在氧化物表面的微观反应机制仍然没有得到很好的理解。这样做的主要原因是这些研究主要是在粉末样品上进行的。因此，除了粉末样品中不可避免地存在的各种缺陷外，该信息还代表了暴露的各种晶面的平均值。另一方面，许多氧化物材料的高纯度单晶一直难以获得，并且这些绝缘材料的研究经常遇到与表面充电、样品加热和清洗有关的困难。因此，显然需要合成高质量、薄的氧化膜。氧化材料的结构和化学吸附性能可以通过制备定义良好的氧化薄膜来获得，其性能与单晶体相同，从而促进了这些材料在受控条件下的表面化学研究。

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.