Resonant ion-stimulated desorption and low-energy proton-scattering study of interactions of hydrogen and oxygen with the SrTiO₃(100) surface

The mechanism of proton desorption by low-energy noble-gas ion bombardment of the SrTiO₃(100) surface was investigated, in comparison with scattering of hyperthermal energy H⁺ ions. The ionization of sputtered hydrogen occurs via both collisional and noncollisional electronic transitions as revealed from the energy distribution of the sputtered proton. The noncollisional sputtering is very efficient for He⁺ bombardment and decreases in order of He⁺, Ne⁺, and Ar⁺. The initiating event for the noncollisional sputtering of proton is found to be the formation of the O2s core hole via the quasiresonant charge exchange with the primary ion. The core-excited hydroxyl species have the antibonding character with a long lifetime from which the hydrogen desorbs. The ionization of hydrogen occurs due to the interatomic Auger decay of the O2s hole in the course of the O-H bond breaking. On the basis of these findings, we propose resonant ion stimulated desorption as a technique quite sensitive to the surface hydroxyl group and apply it to an analysis of interactions of oxygen and hydrogen with the SrTiO₃(100) surface. It is found that oxygen is adsorbed preferentially on the reduced Ti³⁺ site and that hydrogen or deuterium incorporated in the bulk tends to be segregated to the surface in the form of the hydroxyl group to occupy the oxygen vacancy of the reduced surface.