Transmission of low-energy (< 10 eV) O + ions through Au films on TiO 2(110)

Abstract

In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O + ions through discontinuous Au films adsorbed on TiO 2(110). A low energy (< 10 eV) O + ion beam is generated via electron stimulated desorption when an Au-dosed TiO 2(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at ∼ 300 K forms three-dimensional clusters on TiO 2(110). As the Au coverage increases, the formation of Au clusters on TiO 2(110) blocks a fraction of the TiO 2 surface and the O + yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O + signal decreases at a faster rate than the TiO 2 open area fraction. We attribute the attenuation of the O + yield for high Au coverages mainly to blocking of O + by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O + and neighboring Au clusters.