Glancing incidence scattering of hyperthermal He+, Xe+, and C60+ from graphite: Angular and velocity distributions of neutrals

In a comparative study of size and mass effects in the glancing incidence scattering of hyperthermal ions from a soft surface, He+, Xe+, and C60+ were scattered from highly oriented pyrolitic graphite (HOPG) over an energy range between 200 and 5000 eV. Predominantly neutral scattering products were observed for all projectiles. The corresponding angular and velocity distributions were recorded in the scattering plane. He+ gives rise to broad angular distributions conforming to the predictions of a simple binary collision model. With full widths at half maximum of less than 6 deg at typical collision energies, the angular distributions found for Xe+ and C60+ are very narrow. While Xe+ is always scattered near-specularly independent of collision energy, neutrals resulting from C60+ exit subspecularly—increasingly so the higher the collision energy. The experimental data are discussed in terms of dynamical simulations which indicate that Xe+ collides with a rigid ensemble of six carbon atoms while the fullerene scatters from a larger “moving target.”