CHARGE-TRANSFER PROCESSES IN ATOM-SURFACE COLLISIONS AT LOW ENERGIES - A GREENS-FUNCTION APPROACH

A Green's functions analysis of the charge transfer probability is per formed within the one particle Anderson-Newns model and used to calcul ate the probabilities of the different charge-states of a scattered or sputtered atom by finite and semi-infinite linear chains. This formal ism has the advantage that it allows one to handle simultaneously cont inuous band states, localized surface states and core-like stares of t he substrate without a significative increase in the complexity of the numerical calculation. It also allows one to incorporate, at least wi thin a semi-classical level, the effects on the ionization probability of variations in the velocity of the projectile along the trajectory. As expected, these become important at low velocities, where velocity changes largely affect the phase interferences taking place within th e double transit of the projectile through the collision region in the scattering process.