Photostimulated ion desorption from the TiO2(1 1 0) and ZnO surfaces

We used electron–ion coincidence spectroscopy to investigate the photostimulated ion desorption from clean and water-chemisorbed TiO2(1 1 0) and ZnO ( 1 0 1 ¯ 0 ) . Desorption of O+ from TiO2(1 1 0) and ZnO ( 1 0 1 ¯ 0 ) surfaces and that of H+ from water-chemisorbed TiO2(1 1 0) and ZnO ( 1 0 1 ¯ 0 ) 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(1 1 0) surfaces, but not observed from clean or water-chemisorbed ZnO ( 1 0 1 ¯ 0 ) surfaces. The ion desorption following the metal-core excitation cannot be fully explained by a similar mechanism to the KF model where the inter-atomic Auger decay provides the change of the charging state of the oxygen. We therefore propose a new mechanism in which the charge transfer from the O2p orbital to the Ti3d orbital is induced by the Ti3p-core hole potential and is responsible for the creation and desorption of the O+ ions.