Probing a cold surface with slow heavy-atom scattering: Experimental results and theoretical calculations

Slow heavy atoms scattering from cold surfaces excite many phonons, but still have a finite elastic scattering fraction. We have measured the coherent elastic intensity of low-energy Ne, Ar, and Kr beams scattered from a Cu(111) surface, and compared the results to accurate semiclassical calculations. Earlier experiments have been extended to a range of incident beam energies, while earlier calculations have been improved by using state-of-the-art atom-surface potentials and surface phonon densities of states. All inputs to the calculations are taken from the literature. so they involve no adjustable parameters. We compare both the zero-temperature limit and the thermal attenuation of the elastic scattering at elevated temperatures. Our comparisons confirm that the probability for elastic scattering is (i) independent of particle mass in at low surface temperatures and (ii) depends on rootm at elevated temperatures, Corresponding experimental observations for the comparatively light, Particles H-2, D-2 and He show clear deviations from the semiclassical predictions. Our analysis, shows that this regime provides new and complementary information about both surface phonons and atom-surface potentials.