Matrix effect in transition metal oxide formation: neutralization by O 2s levels

Low energy ion scattering (LEIS) was employed in the analysis of Mo, Ru, Al and their oxides. Measurements with different He+ ion energies show that the characteristic neutralization velocities of the transition metals change when they bind to oxygen. However, such behavior was not observed for aluminum. We suggest that the existence of matrix effects in transition metal oxides is related to increase in neutralization by O 2s levels, which present are in (quasi-)resonance with He 1s. We further hypothesize that the matrix effect would not be observed in aluminum oxide due to changes in Auger neutralization from metal to oxidized form. This work provides a deeper understanding of the role of oxygen in low energy ion scattering analysis, granting tools for proper choice of reference samples and reliable quantification of surface elements by LEIS.