Stopping of slow ions in the electron selvedge of a metal surface

From studies on the energy loss of fast atomic projectiles ( v = 0.5 v 0 ) ranging from protons to potassium ions in the scattering from a clean and flat Al(111)-surface under a grazing angle of incidence, we derive stopping powers as a function of distance from the surface plane. We observe that oscillations for the stopping powers with atomic number Z 1 show a pronounced dependence on the electron density as predicted by nonlinear density-functional calculations. For sufficiently low electron densities, those oscillations follow the intuitive picture in showing minima of stopping for projectiles with noble-gas configurations.