The influence of oxygen on the neutralization of slow helium ions scattered from transition metals and aluminum surfaces

Low energy ion scattering (LEIS) was employed for the analysis of thin films of Mo, Ru, Hf, Al and their oxides. Measurements with different He+ energies showed that the characteristic velocities for neutralization of the transition metal atoms change when the metal binds with oxygen. However, such behavior was not observed for aluminum. We suggest that the increased neutralization in oxidized Ru, Hf and Mo originates from the presence of the O 2s band. This band is in resonance with the He 1s level, which allows for a quasi-resonant neutralization mechanism (qRN). On the other hand, a decrease of the strong Auger neutralization for metallic Al upon oxidation may compensate for the increase in neutralization by qRN, leading to similar neutralization behavior of Al in both states. We also demonstrate the dependence of characteristic velocity on oxygen content and discuss how this effect can be used to select proper reference samples for quantitative surface analysis by LEIS.