Inelastic scattering of low-energy He+ from solid surfaces

Electronic excitation during impact scattering of He+ ions with a kinetic energy ranging from 0.1 to 1 keV from solid surfaces has been studied. The ionization probability of He0 is strongly dependent on the species of the target elements; the probability for Zn or Cd is estimated to be about three orders of magnitude smaller than that for Ca at a kinetic energy of 1 keV. The excitation of surface valence electrons in the course of He+ scattering also shows a remarkable target-material dependence, which has been confirmed at the surface of ionic compounds having a large band-gap energy: the excitation of surface p-electrons to the conduction band has been explicitly observed for a certain He- target combination which yields sufficient promotion of the He 1s orbital in the quasimolecular state. (author)