THE ENERGY AND ANGULAR DISTRIBUTIONS OF LOW-ENERGY He+ SCATTERED FROM Al(111)

Abstract

Measurements of 500 eV 4 He + scattered from Al(111) surfaces provide detailed information about the scattering process and surface crystallography. We report various observations concerning collision inelasticity, multiple scattering, and shadow-cone focusing effects. A large inelastic energy loss of the scattered He + is observed, which causes multiple-scattering events at oblique incidence angles to have energies below the elastic single-scattering energy. Inelastic He + scattering from clean, ordered Al(111) shows interesting intensity variations as a function of azimuthal orientation and incidence angle. At a critical incidence angle, where the top edge of a shadow cone intersects a nearest-neighbor Al surface atom, the scattered ion intensity exhibits 60° azimuthal periodicity. At a more glancing angle of incidence, a double-peaked structure appears. The scattered He + intensity varies as a function of incidence angle, as expected from classical shadow cone calculations.