ENERGY-LOSS OF 0.7-MEV HE IONS DUE TO THE DYNAMIC-RESPONSE OF SURFACE ELECTRONS

The energy losses of 0.7-MeV He ions which have surface channeled along atomic rows on a clean (100) surface of SnTe are studied. An energy spectrum of the surface-channeled ions shows a few peaks whose energies and heights depend on the angle of incidence of He ions, theta(i). From the theta(i) dependence of the energy losses, position-dependent stopping powers of the (100) surface for the He ions are determined at the [001] and [011] surface channeling. The contribution of collective excitation of surface valence electrons to the stopping powers is extracted from the obtained position-dependent stopping powers. This agrees well with the theories where the dynamical response of valence electrons to the fast-moving ions is taken into account.