DISCRETE ENERGY-LOSSES OF FAST PROTONS IN GRAZING SURFACE SCATTERING FROM AL(111)

The energy loss of fast protons scattered from a flat and clean Al(1 1 1)-surface under a grazing angle of incidence is investigated with high resolution with respect to angle of scattering and energy. We find two different kinds of multiple discrete energy losses in the spectra, which we attribute to hopping kind of trajectories at the surface ("skipping motion") and to subsurface channeling, respectively. By a variation of the charge state of the projectiles we show that charge exchange affects the image potential close to the surface in a decisive way and plays an important role for the understanding of the observed effects.