Glancing incidence scattering of hyperthermal He+, Xe+, and C-60(+) from graphite: Angular and velocity distributions of neutrals

In a comparative study of size and mass effects in the glancing incidence s cattering of hyperthermal ions from a soft surface, He+, Xe+, and C-60(+) w ere scattered from highly oriented pyrolitic graphite (HOPG) over an energy range between 200 and 5000 eV. Predominantly neutral scattering products w ere observed for all projectiles. The corresponding angular and velocity di stributions were recorded in the scattering plane. He+ gives rise to broad angular distributions conforming to the predictions of a simple binary coll ision model. With full widths at half maximum of less than 6 deg at typical collision energies, the angular distributions found for Xe+ and C-60(+) ar e very narrow. While Xe+ is always scattered near-specularly independent of collision energy, neutrals resulting from C-60(+) exit subspecularly-incre asingly so the higher the collision energy. The experimental data are discu ssed in terms of dynamical simulations which indicate that Xe+ collides wit h a rigid ensemble of six carbon atoms while the fullerene scatters from a larger "moving target." (C) 1999 American Institute of Physics. [S0021-9606 (99)70545-3].