Helium scattering from solid surfaces

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Abstract
The quantum mechanical scattering of light atoms from well defined solid surfaces is studied via a simplified model of the gas surface system. The differential scattering cross section is calculated using a power series expansion with convergence properties similar to those of distorted wave perturbation theory. The cross section is averaged over the internal states of the system, and the temperature dependence of the one and two phonon contributions is calculated. It is concluded that at sufficiently low surface temperatures and beam energies, one phonon contributions dominate. Comparison of these results with perturbation theory indicates that, for these experimental conditions, a first order perturbation theory should be sufficient to interpret experiments. Arguments are given indicating that this first order calculation may yield direct information about the local density of states of the system. This suggests that He scattering may be developed into an analytical tool, similar to bulk neutron scattering, giving direct information about surface chemical bonding.