EVIDENCE FOR HOT-ELECTRON-INDUCED ANGULAR STRAGGLING OF NE BEAMS SCATTERED FROM CU(111)

We have measured, in two spatial dimensions, the energy and angular di stributions of neutral Ne atoms produced by scattering energetic Ne+ a t glancing angles of incidence from Cu(111). A comparison of the data with the results of an elastic scattering simulation shows that both t he translational energy loss and angular straggling of the beam are do minated by inelastic effects. We propose that the fast motion of the p rojectile in the vicinity of the surface causes electron-hole pair exc itation of the electron gas, and that the origin of the angular stragg ling is repeated resonant scattering of the resulting ''hot'' electron s through projectile resonances lying energetically above the Fermi le vel. Both quantum mechanical and semi-classical descriptions of the pr ocess are provided. The mechanism is similar to that invoked by Gadzuk et al. [Surf. Sci. 235 (1990) 317] and Misewich et al. [Phys. Rev. Le tt. 68 (1992) 3737] in the context of desorption of atoms or molecules from metals.