The scattering of Ar from Ag(111): a molecular dynamics study

A static potential energy surface (PES) for Ar-Ag(lll), based upon the local density approximation, is tested in a molecular dynamics study. The PES is a pairwise additive potential and no potential parameters are optimized to fit experimental data. A large crystal with nearest neighbour interaction simulates the solid. Using this PES it is possible to describe the trends of the experimental data for thermal incidence energies (0.2-2.6 eV), including the transition from thermal to structure scattering. In addition we employ the potential for a broad range of incidence energies (0.01-100 eV) for a static surface and one with a surface temperature of 600 K. The high symmetry of a static surface results in the appearance of surface rainbows. At finite temperatures, all angular distributions are broadened and the rainbows disappear either due to the thermal vibrations of the surface (for low incidence energies), or due to their positional disorder (for high incidence energies). For low incidence energies, multiple collisions with the surface occur. The multiply colliding atoms do not grossly change the angular width. It is the effect of the thermal vibrations of the surface atoms that causes a large increase of the angular width for the low incidence energies. Sticking also occurs for low energies, an effect that strongly depends on the surface temperature. For high incidence energies scattering after penetration contributes to the distributions and sticking/implantation occurs.