Inelastic energy loss of fast ions for direct scattering and skipping trajectories on metal surfaces

Abstract

Abstract We have measured the energy loss of 200–2000 eV silicon ions which have undergone both direct scattering and skipping motion on a Cu(111) surface. The inelastic energy losses associated with 1,2,…, 5 surface reflections for both positive and negative final charge states are identified. The energy loss is approximately proportional to the projectile energy and is independent of the crystal azimuth. A final charge state dependence is observed, as are extrapolated non-zero energy losses for Si− and Si+ production at zero beam energy. These latter losses agree quantitatively with the energy required to promote an electron from the Fermi level of Cu(111) to the affinity level of Si, and the energy required to reionize Si, respectively, thus providing direct information on the charge state during scattering. Comparison with theoretical calculations shows that energy loss theory must be extended to include charge redistributions characteristic of chemical bonding.