Photostimulated ion desorption from the TiO2(110) and ZnO(10(1)over-bar-0) surfaces

We used electron-ion coincidence spectroscopy to investigate the photostimulated ion-desorption from clean and water-chemisorbed TiO2 (110) and ZnO (10 (1) over bar0). Desorption of O+ from TiO2 ( 10) and ZnO (10 (1) over bar0) surfaces and that of H+ from water-chemisorbed TiO2 (110) and ZnO(10 (1) over bar0) surfaces were observed after O1s-excitaion. These are not due to the two-hole final state caused by the ordinal single-electron excitation and its normal Auger decay but mainly due to the n-hole (n > 2) final state which was provided by the multiple excitation/decay of the O1s electron. After metal-core excitation, meanwhile, ion (O+ and H+) desorption is observed from the clean and water-chemisorbed TiO2 (110) surfaces, but, not observed from clean or water-chemisorbed ZnO (10 (1) over bar0) surfaces. The ion desorption following the metal-core excitation cannot be fully explained by a similar mechanism to the KF model where the interatomic Auger decay prov'ides the change of the charging state of the oxygen. We therefore propose a new mechanism in which the charge trar sfer from the O2p orbital to the Ti3d orbital is induced by the Ti3d core hole potential and is responsible for the creation and desorption of the O+ ions. (C) 2004 Elsevier B.V. All rights reserved.