Investigation of Surface Topography of Oxygen on Nickel Single Crystals by Helium Ion Backscattering

Abstract

In an experiment which combines low energy noble gas ion backscattering with LEED the sorption of oxygen on the (110) face of a nickel single crystal is investigated. The energy of the backscattered He+ ions is governed by binary collisions whereas the intensity of the spectrum is given by the cross sections, the concentration of surface atoms, the neutralization probabilities and the geometry. The spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom. From a shadow effect observed at small angles of incidence it can be estimated that the adsorbed oxygen protrudes beyond the plane of the Ni atoms by about 0.4–0.8 Å.