ESD STUDY OF CO REACTIVITY WITH TIO2(110)+TA DEFECTIVE SURFACE

CO reactivity with a defective (O vacancies, Ar+-sputtered) TiO2(110) surface evaporated with Ta has been studied by electron stimulated desorption, ESD, and using Auger electron spectroscopy, AES, as a complementary technique. The clean surface shows thresholds of the O+-desorbed ions at incident electron energies that can be assigned to ionisation of the Ti 3p, Ta 4f, 4d and 4p core levels. After CO exposure of the surface to saturation with 6 x 10(4) L, the ion yield shows a significant increase and a new threshold at 290 eV identified with the C 1s excitation is observed. The CO coverage was 0.09 ML, the number of O vacancies before the CO adsorption was 7% of the total number of O atoms of the nearly perfect surface (1.56 x 10(15) atoms/cm(2)) and the AES Ta(NVV)/Ti(LMM) ratio was 7%. The O+ ion yield follows quite well the secondary electron yield. Ion energy distribution curves of the O+-desorbed ions show structures that are identified with Of-desorbed ions from O species bonded to Ti and Ta atoms as well as from the CO. About 76% of the adsorbed CO is dissociated.