Contribution of valence electrons to the electronic energy loss of hydrogen ions in oxides

Abstract

Based upon measured electronic stopping cross sections for protons of some solid oxygen compounds (H 2O-ice, SiO 2, Al 2O 3 and LiNbO 3) in the overall energy range 10–700 keV we investigate the contribution of valence electrons to the stopping process. We use first Born approximation calculations to subtract the core contribution of the constituents from the measured data. The result may be interpreted as that part of the electronic stopping cross section which is due to the valence electrons, ε val. It is proportional to the number of valence electrons but turns out to be quite insensitive to the detailed properties of the valence states like band gap, ionizity or band structure. This finding is corroborated by the fact that for energies above 100 keV, even ε val of the oxides coincides with ε val of oxygen gas, provided the different number of valence electrons is taken into account.