Previous quasi-elastic He-atom scattering studies of the low-coverage (less than 0.05) diffusion of Na on the (001) Cu surface were extended to coverages of 0.18. These measurements, at surface temperatures of between 180 and 390K, were compared with molecular dynamics simulations that included dipole-dipole interactions between the Na atoms. The simulations could explain the increase in observed activation energy and the change in the shape of the peak-width with momentum transfer, but failed to reproduce the marked overall increases in peak-widths which were observed as the coverage was increased.

Coverage Dependence of the Microscopic Diffusion of Na Atoms on the Cu(001) Surface - a Combined Helium Atom Scattering Experiment and Molecular Dynamics Study. J.Ellis, A.P.Graham, F.Hofmann, J.P.Toennies: Physical Review B, 2001, 63[19], 195408 (9pp)