Nonequilibrium processes on TiV surface induced by activation and absorption of gases

X-ray photoelectron spectroscopy (XPS), high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the effects of thermal activation in the surface chemistry and morphology of a Ti70V30 gettering alloy. The samples were analysed as-received (after in-air exposure) and after different annealing treatments up to 600 degrees C. For temperatures greater than 270 degrees C a progressive reduction of the TiO2, initially found on the as-received samples, to TiOx (x < 2) occurs. The high concentration of vacancies in the TiOx (x < 2) lattice ensures that the surface oxide layer is transparent towards gas diffusion at relatively low temperatures. The activation process is accompanied by a roughening of the surface, probably induced by the condensation of vacancies in the non-stoichiometric TiOx lattice. Vanadium appears to exert some promoting effect on this mechanism. In the 300-500 degrees C temperature range a fraction of the carbon-based contamination on the surface forms carbides. These carbides start to decompose at temperatures above 550 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.