ADDITIONAL IN-DEPTH INFORMATION OBTAINABLE FROM THE ENERGY-LOSS FEATURES OF PHOTOELECTRON PEAKS - THE OXIDATION AND REDUCTION OF AN FE/CR ALLOY IN OXYGEN AT LOW PARTIAL PRESSURES AND ULTRA HIGH-VACUUM

The oxidation and subsequent vacuum annealing of an Fe/Cr alloy has been studied by X-ray photo-electron spectroscopy (XPS). In addition to the conventional ways of extracting compositional depth information with this spectroscopy (i.e. by ion sputtering and angle resolved XPS), a special study has been made of the use of energy loss features within the XPS spectra to provide such information. There are three classes of energy losses that may prove useful: (i) the height of the inelastically scattered electron background immediately adjacent to the peak of interest which is defined by the term electron energy loss tail height (ELTH), (ii) the slope of the background some distance (e.g. 25 eV) from the photo-electron peak, the post-peak slope (P-PS), and (iii) the slope of the base line associated with the spectrum itself. The former categories provide definitive information concerning the hierarchy of discrete layers on the surface of a material, whilst the latter provides a means of identifying subtle concentration gradients that exist within the XPS sampling depth. The use of these methods in addition to the more conventional depth profiling studies have enabled a series of comprehensive models to be proposed for the formation of passivating layers on the Fe/Cr alloy in a variety of oxidation and reduction conditions at modest temperatures (200-300°C). The methods described have the added advantage that they provide the electron spectroscopist with the possibility of carrying out a retrospective depth profile long after the analysis has been completed. © 1990.