CONTRIBUTION OF VALENCE-ELECTRONS TO THE ELECTRONIC-ENERGY LOSS OF HYDROGEN-IONS IN OXIDES

Based upon measured electronic stopping cross sections for protons of some solid oxygen compounds (H2O-ice, SiO2, Al2O3 and LiNbO3) in the o verall energy range 10-700 keV we investigate the contribution of vale nce electrons to the stopping process. We use first Born approximation calculations to subtract the core contribution of the constituents fr om the measured data. The result may be interpreted as that part of th e electronic stopping cross section which is due to the valence electr ons, epsilon(val). It is proportional to the number of valence electro ns but turns out to be quite insensitive to the detailed properties of the valence states like band gap, ionizity or band structure. This fi nding is corroborated by the fact that for energies above 100 keV, eve n epsilon(val) of the oxides coincides with epsilon(val) of oxygen gas , provided the different number of valence electrons is taken into acc ount.