CONSTRUCTIVE INTERFERENCE EFFECTS IN ENERGY-LOSS SPECTRA OF ENERGETICNOBLE-GAS IONS AND ATOMS INCIDENT AT GLANCING INCIDENCE TO METAL-SURFACES

Scattering Of energetic noble gas ions and atoms at grazing incidence from smooth (111) surfaces of metals (Cu, Al) produces energy loss dis tributions with a no-loss contribution of low intensity (small Debye-W aller factor) and a broad inelastic sideband. At keV beam energies, th is sideband is typically peaked at a few to several tens of eV below t he no-loss contribution. We propose that electronic excitations in the metal are responsible for dissipation of the scattered particle kinet ic energy, and argue that the observed magnitude can only be explained by assuming a fluctuating effective charge or dipole on the moving pa rticle. Constructive interference between successive fluctuation steps gives rise to a high probability of translational energy loss and lea ds to the experimentally observed shape of the loss spectra.