Thin oxide film formation, metal physical

Thin oxide films formed by oxidation of metal surfaces have been center stage in semiconductor research since Walter Schottky formulated his ideas on electronic barriers in solids during the 1920s and 30s. In 1948, Nevill Mott and Nicolas Cabrera embraced these same ideas, in attempts to describe and explain the elementary processes involved in oxide layer formation. Scientists at the Department of Chemical Physics have made use of Schottky s ideas to approach a variety of seemingly disjunct problems, two of which will be outlined below. 

An unexpected result was the progressive apparent dechlorination of SiOTiCla. We have verified that this phenomenon was not related to the presence or absence of TiCU either physically adsorbed or in the gas phase. We could also observe the growth of the same IR bands between 1000 and 600 cm using a self-supporting disc. Therefore, the dechlorination of TiCU on silica and the eventual incorporation of Ti as a random mixed metal surface oxide is probably entropy driven. Although the initial chemisorption follows reaction (3) and (4), further dechlorination probably results in the formation of SiCl surface species. The vibrations of this near 7(X) cm would be impossible to detect with a thin film given the low extinction coefficient [15], and in any case, they would be masked by the much stronger SiOTi vibrations. Finally, the results have implications for mixed oxide catalysts which are prepared by chemical vapor deposition. Structural models which are based on the notion that only reactions like those depicted in schemes (3) and (4) occur are probably not valid. 

The analysis of the statistical or preferred orientation of the crystallites in solid polycrystaUine materials is commonly referred to as texture analysis. Again, the diffraction technique allows the definition of the relationship between a microscopic property, i.e. the orientation of the crystallites defined as coherent diffraction domains, and the macroscopic physical properties of the crystal aggregate. Texture studies are of course crucial in the characterization of oriented synthetic materials such as cold-rolled metals or oxide thin films, but they are also of great relevance in the study of the formation processes of mineral assemblages. As an example, the texture features of olivine or pyroxene minerals in meteoritic chondrules yield information on the early condensation sequence... 

---