Forward electron emission in grazing ion-surface collisions

Abstract

Electrons emitted in grazing ion-surface collisions along the projectile outgoing trajectory carry information on the atomic and electronic structure of the surface, and its dynamic response to the external perturbation represented by the moving projectile. In the case of metal surfaces the shape of the spectra depends on the combined field of the moving ion and the charge polarization induced on the surface. In the case of insulator surfaces, the track of positive charges from ionization processes along the projectile path has a long enough lifetime to participate with the induced and projectile charges in shaping up the spectrum of emitted electrons. For both types of surfaces, imperfections in the form of terraces, steps and isolated impurity atoms and defects generate hard collisions with the projectile, producing emitted electrons typical of binary ion–atom collisions. In this work we first analyze recent measurement of electron emission from surfaces bombarded by keV/amu light ions, considering the dependence of the electron distribution on the type and quality of the surface. Both metal and insulator surfaces are considered. The description of the electron distribution on the final state long range Coulomb potentials of the projectile and surface charges is discussed. Finally, we present experimental results on H +–LiF grazing collisions taking into account the dependence of the emitted electron distribution on the topography of the surface and the conductivity of the crystal. The opposing actions on the electron distribution of the image charge and the track of positive charges left on the surface by previous ionizations by the projectile is analyzed.