Self-consistent-field X-Alpha scattered-wave cluster molecular-orbital models have been constructe~ for transition and noble metals (Fe, Ni, Cu, and Ag) in contact with a sapphire (AI 2 0 3 ) surface. It lS found that a chemical bond is established between the metal d-orbital electrons and the non bonding ~p-orbital electr~ns of ~he ox~gen anions on the Al 2 0 3 surface. An increasing number of occupled metal-sapphlre anbbondlOg molecular orbitals explains qualitatively the observed decrease of contact shear strength through the series Fe, Ni, Cu, and Ag.

The effect of the x-ray flux in x-ray photoelectron spectroscopy (XPS) on the constitution of the polytetrafluoroethylene (PTFE) surface has been examined. The radiation dose rate for our specimen was ∠107 rad/s. We observed the structure, magnitude and binding energy of the C(1s) and F(1s) features of the XPS spectrum and the mass spectrum of gaseous species evolved during irradiation. The strong time dependence of these signals over a period of several hours indicated that the surface constitution of PTFE is greatly affected by this level of radiation dose. The results are consistent with the development of a heavily cross-linked or branched structure in the PTFE surface region and the evolution of short chain fragments into the gas phase.

Articles you may be interested inOxygen adsorption on Ag(111): X-ray photoelectron spectroscopy (XPS), angular dependent x-ray photoelectron spectroscopy (ADXPS) and temperature-programmed desorption (TPD) studies A thermal desorption and xray photoelectron spectroscopy study of the surface chemistry of iron pentacarbonylThe interfacial chemistry of Fomblin Z2S, a commercial perfluoropolyether used as lubricant for space applications, with different metallic surfaces-440 C steel, gold, and aluminum-was studied. Thin layers of Fomblin Z2S were evaporated onto the oxide-free substrates and the interfacial chemistry studied using x-ray photoelectron spectroscopy and temperature desorption spectroscopy. The reactions were induced by heating the substrate and by rubbing the substrate with a steel ball. Gold was found to be completely unreactive towards Fomblin at any temperature. Reaction at room temperature was observed only in the case of the aluminum substrate. the most reactive towards Fomblin Z25 of the substrates studied. It was necessary to heat the 440C steel substrate to 190·C to induce decomposition of the fluid. The degradation of the fluid was indicated by the formation of a debris layer at the interface. This debris layer, composed of inorganic and organic reaction products, when completely formed, passivated the surface from further attack to the Fomblin on top. The tribologically induced reactions on 440C steel fonned a debris layer of similar chemical characteristics to the thermally induced layer. In all cases, the degradation reaction resulted in preferential consumption of the difluoroformyl carbon (-OCF P-).