Medium Energy Ion Scattering Spectrometry of Helium Ions Scattered from Rutile Titanium Dioxide Surfaces

Abstract

The charge state of medium energy He ions scattered from solid surfaces depends on emerging energy and angle as well as the surface materials. We measured He⁺ fractions for 54-140keV He⁺ ions incident on rutile TiO₂(110) and scattered from the top-layer Ti atoms at the [110]- and [001]-azimuth. The He+ fractions measured at both azimuths were decreased with increasing emerging angle (scaled from surface normal) and saturated at ~75 and ~85° at the [001]- and [110]-azimuth, respectively. The He⁺ fractions for the [110]-azimuth denoted by η₁₁₀ were considerably larger by 10-20% than those for the [001]-azimuth (η) at emerging angles below ~75° (non-equilibrated). The equilibrium He⁺ fraction is close to the semi-empirical data given by Marion-Young. It was also found that the η₁₁₀ values measured at emerging angle of ~80° were larger more than 20% compared with the η values in the emerging energy range from 50 to 130keV. Such a strong dependence on crystallographic orientation of scattering plane is simply explained by the atomic arrangements at the crystalline azimuths.