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

X-ray photoelectron spectroscopy (XPS), high-resolution scanning electron m icroscopy (SEM) and atomic force microscopy (AFM) were used to investigate the effects of thermal activation in the surface chemistry and morphology o f a Ti70V30 gettering alloy. The samples were analysed as-received (after i n-air exposure) and after different annealing treatments up to 600 degrees C. For temperatures greater than 270 degrees C a progressive reduction of t he 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 t hat the surface oxide layer is transparent towards gas diffusion at relativ ely low temperatures. The activation process is accompanied by a roughening of the surface, probably induced by the condensation of vacancies in the n on-stoichiometric TiOx lattice. Vanadium appears to exert some promoting ef fect on this mechanism. In the 300-500 degrees C temperature range a fracti on of the carbon-based contamination on the surface forms carbides. These c arbides start to decompose at temperatures above 550 degrees C. (C) 1999 El sevier Science Ltd. All rights reserved.