Composition dependence of the initial oxidation behaviour of Ti1-xAlxN (x=0.20, 0.45, 0.65) films studied by XAS and XPS

The difference in the initial oxidation behaviours of Ti1-xAlxN (x = 0.20, 0.45, 0.65) films was studied by x-ray absorption (XAS) and by x-ray photoe lectron spectroscopy (XPS) using synchrotron radiation (SR-XPS), The N It-e dge XAS results indicated rapid decreases in the relative ratio of AI-N rel ative to the total nitride with surface oxidation for all the Ti1-xAlxN fil ms, The SR-XPS analysis of O, Ti and Al species with different photon energ ies disclosed the formation of Al2O3 at an upper layer and TiO2 at a lower layer in oxidized Ti1-xAlxN films with x = 0.20 and 0.45. In contrast, a mi xed Al2O3 and TiO2 surface layer was formed in tie oxidized Ti1-xAlxN him w ith high aluminium content (x = 0.65), In addition, N-2 molecules, which we re formed as an intermediate species during the oxidation, were concentrate d in the interface of Al2O3 and TiO2 in the oxidized Ti0.55Al0.45N and Ti0. 80Al0.20N films, whereas they occurred near the surface in the oxidized Ti0 .35Al0.65N film. From these results, it was concluded that the high surface oxidation-resistant properties of Ti1-xAlxN film with low aluminium conten t originated from the rapid formation of a surface Al2O3 layer that prevent ed inward diffusion of oxygen as wed as outward diffusion of molecular nitr ogen. Copyright (C) 1999 John Wiley & Sons, Ltd.