Forward electron emission produced in grazing ion-surface collisions: Dependence on the surface topography

We present measurements of electron emission produced in 64-keV H+ grazing bombardment of Si(111) surfaces prepared with different topographies. The surfaces were initially irradiated with several fluences of Ar+ at normal incidence, and their topographies characterized by an atomic-force microscope (AFM). The electron energy spectra, measured close to the direction of the projectile specular reflection, show two characteristic structures: a peak at an energy E-CE=35 eV, corresponding to electrons moving with the projectile velocity (convoy electrons), and a broad peak at an energy E-M>E-CE. Their relative intensities depend strongly on the surface roughness. A similar behavior was observed for GaAs(110) and Al(111) surfaces prepared with different in situ polishing methods. A code developed to process the AFM images allowed us to assign the electron structures at E-M and E-CE to specific topographic features.