Probing inelastic interactions of ions moving in solids by electron spectroscopy

Abstract

We have measured energy distributions of electrons emitted from clean aluminum surfaces by 20 keV/amu H+, He+ and He0 projectiles. Ratios of energy distributions obtained from two types of projectiles carry information on differences in the electron excitation collisions. We discuss these differences in terms of screening of the projectile by valence electrons, Auger capture and projectile ionization, with the aid of linear response theory. We find the shapes of secondary electron energy spectra are dominated by the energy dependence of the electron escape depth and of the binary ion–electron interaction. The latter must be determined by considering the screened potential of the projectile and its changing charge state as it penetrates the solid.