X-ray photoelectron spectroscopic studies of metal oxides and related systems

Abstract

X-ray photoelectron spectroscopy (XPS) has been used to investigate the surfaces of some metals, metal oxides and related chemical systems, most of which are of technological importance or relevance. These substances were conductors or non-conductors, and a study was made concerning the correct binding energy referencing in the latter case. In some cases, a variation was found in the CIs binding energy with the surface coverage of adventitious carbon. This study revealed, however, that under sui table conditions this C Is binding energy can be used to obtain reproducible binding energies in insula tors. The surface of borided zirconium has been studied in collaboration with a colleague, with a view to evaluating its use in electrochemical applications. A number of oxides (of both boron and zirconium) have been observed on the substrate surface, and this must inhibit the use of this material for electrochemistry and in cases where the full boride surface properties are required. Studies of uranium metal and oxide systems were carried out with an emphasis on applications (especially the ammonium uranates) relevant to the nuclear power industry. The heating of uranium metal in vacuo has been studied and the presence of unusual species is reported. Some of the results are similar to those obtained by other workers in their studies of both uranium and plutonium. Two uranium species have been detected on the surface of the sample a t elevated temperatures. This corresponds to both uranium metal and one of its oxides; the stoichiometry of the latter species is uncertain. Two carbide species were also detected. Some aspects of the ammonium uranate system have been investigated. Problems associated with the use of XPS to analyse this material are discussed. Although conclusions as to the chemical nature of this material are limited, the results do show that XPS has considerable potential for the study of this system. Finally, the surface segregation of impurities in high purity samples of platinum and palladium has been observed on heating samples in vacuo and in oxygen. Such studies are important since these metals are used in many electrochemical and catalytic applications. Silver, gold and carbon were observed to segregate in platinum whereas silver and sulphur segregated in palladium. All species segregated in their elemental form. The core level binding energies of the silver and gold segregants were lower than those measured for the corresponding pure metal state.