FORMATION AND DIFFUSION PROPERTIES OF OXIDE-FILMS ON METALS AND ON NITRIDE COATINGS STUDIED WITH AUGER-ELECTRON SPECTROSCOPY AND X-RAY PHOTOELECTRON-SPECTROSCOPY

An understanding of the mechanisms which govern the formation and growth kinetics of oxides requires an appropriate chemical characterization at different stages. This can be achieved by surface analysis methods with an information depth of a few atomic layers. In particular, Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) are frequently used to extract both the elemental composition and the chemical binding state. The initial stages of oxide formation can be studies in situ by AES and XPS at low oxygen pressures, while the in-depth composition of the generated oxide layer is obtained by sputter depth profiling. Application of factor analysis and least-squares fitting methods to spectra involving valence band transitions in AES has shown its capability to differentiate quantitatively between the chemical states of the metallic elements. Comparative studies of low temperature oxidation of pure metals such as tantalum and nickel and of NiCrFe alloys reveal the role of thermodynamic stability and transport mechanisms which govern the establishment of layered structures. The high temperature oxidation behaviour of nitride coatings of titanium and chromium with addition of the ternary component aluminium as studied by AES depth profiling allows the evaluation of diffusion properties and layer compositions which are responsible for the high oxidation resistance of these coatings.