Binary contribution to the stopping in fast ion-surface collisions

The mechanism of the binary collision with the free-electron gas in the pro ximity of a surface is investigated by employing a semiclassical formalism. The surface dynamic screening of the projectile is described with two well -known models commonly used in the literature: the parallel-dispersion (PD) and specular-reflection (SR) models. The Mermin-Lindhard dielectric functi on is used to represent the dielectric response of the bulk material. The f ormalism is applied to the calculation of the energy loss by fast protons c olliding with an aluminum surface. Results are compared with those obtained with the dielectric formalism, and energy-loss distributions are analyzed. It is concluded that the models used to describe the dynamic screening pot ential do not seem to give a reliable description of the binary mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.