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 des orption, ESD, and using Auger electron spectroscopy, AES, as a complem entary technique. The clean surface shows thresholds of the O+-desorbe d ions at incident electron energies that can be assigned to ionisatio n 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 signifi cant increase and a new threshold at 290 eV identified with the C 1s e xcitation is observed. The CO coverage was 0.09 ML, the number of O va cancies 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+-de sorbed 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.