Coverage dependence of the microscopic diffusion of Na atoms on the Cu(001) surface: A combined helium atom scattering experiment and molecular dynamics study - art. no. 195408

Previous quasielastic helium atom scattering studies of the low-coverage di ffusion of sodium (Theta (Na)less than or equal to0.05) on the Cu(001) surf ace have been extended up to coverages of Theta (Na)=0.18. These measuremen ts, at surface temperatures between T-s=180 and 390 K and parallel wave vec tor transfers up to DeltaK=3.34 Angstrom (-1), are compared with molecular dynamics simulations that include the dipole-dipole interactions between th e Na atoms. Whereas the simulations can explain the increase in the observe d activation energy and the change in the shape of the peak width with mome ntum transfer, they fail to reproduce the marked overall increases in peak widths observed as the coverage is increased. Several possible explanations are discussed and are shown to be unable to explain the results.