Characterization of penetrating projectile trajectories in grazing-incidence ion-surface collisions

The study of fast ion-surface collisions requires that the projectile ions scatter from the topmost layer of surface atoms and avoid penetration into the bulk solid. This is often achieved by arranging for projectiles to interact with the surface at grazing angles of incidence. We present measurements of angular distributions of exiting carbon ions scattered from a silicon(100) surface at various incident angles between 0.1 and 0.8 degrees. Incident carbon ions with total kinetic energies between 3.0 and 6.0 MeV were produced by the EN Tandem Van de Graaff Accelerator Facility at Oak Ridge National Laboratory. Observation of the widths of the exiting projectile angular distributions vs. projectile incident angle indicate that there is a critical angle above which the width increases at a rate greater than for angles below this value. The existance of such a critical incidence angle is interpreted as an experimental signal of surface layer penetration.