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 distributions of neutral Ne atoms produced by scattering energetic Ne+ at glancing angles of incidence from Cu(111). A comparison of the data with the results of an elastic scattering simulation shows that both the translational energy loss and angular straggling of the beam are dominated by inelastic effects. We propose that the fast motion of the projectile in the vicinity of the surface causes electron-hole pair excitation of the electron gas, and that the origin of the angular straggling is repeated resonant scattering of the resulting ''hot'' electrons through projectile resonances lying energetically above the Fermi level. Both quantum mechanical and semi-classical descriptions of the process are provided. The mechanism is similar to that invoked by Gadzuk et al. [Surf. Sci. 235 (1990) 317] and Misewich et al. [Phys. Rev. Lett. 68 (1992) 3737] in the context of desorption of atoms or molecules from metals.