Angle Resolved XPS for Characterizing thin Oxide Films Formed on the Surface of Fe-10, 20 and 30 Mass% Cr Alloys Exposed to Air

Angle resolved X-ray photoelectron spectroscopy (AR-XPS) has been used for characterizing the surface of Fe-10, 20 and 30 mass% Cr alloys which were exposed to air at 298 K after applying the argon-ion sputtering in order to obtain the contamination free surface. The concentration of iron and chromium in AR-XPS are found to be independent of the take-off angle in specimens as cleaned by sputtering, whereas the concentration depends on the take-off angle in specimens exposed to air. These facts suggest that hydrocarbon and hydroxide cover the surface as an overlayer, and an oxide layer with the thickness in the nanometer order of magnitude forms beneath the overlayer. Effective thickness of the two layers for three iron-chromium alloys was estimated by coupling with a model. It would be interesting to note that the thickness of the oxidized layer on the surface decreases with the chromium concentration of the bulk. This estimation is in good agreement with the fact that the intensity of metallic peaks in Fe 2p and Cr 2p XPS spectra increases with the chromium concentration.