Observation of Skipping Motion in Small-Angle Ion-Surface Scattering

Abstract

We report the observation of skipping motion of 200-2000-eV ${\mathrm{Si}}^{+}$ beams on a smooth Cu(111) surface under grazing (1°-14°) angles of incidence. The kinetic-energy distributions of specularly scatered ${\mathrm{Si}}^{+}$ and ${\mathrm{Si}}^{-}$ ions exhibit discrete energy-loss features corresponding to an integral number of reflections. Energy losses up to 20% of the incident beam energy, associated with five reflections in a binding potential, are identified. Classical trajectory calculations imply that the beam is trapped following an energy loss, by substrate electron-hole pair or collective excitation, which exceeds the incident-beam-energy component normal to the surface.