By using numerical simulation a study was made of the diffusion of isolated lead atoms on Cu(110). The calculations rely on a phenomenological many-body potential derived in the framework of the second-moment approximation of the tight-binding method, with parameters fitted on the physical properties of the bulk crystals of copper and lead and to the copper-lead phase diagram. Static calculations, at T = 0K, provided the energy and relaxed atomic positions of the equilibrium and saddle-point configurations of various possible diffusion mechanisms. In spite of the large miscibility gap present in the lead-copper phase diagram, it was found that insertion of a lead adatom into the uppermost copper surface layer was a thermodynamically favored process. Molecular dynamics calculations showed that inserted lead atoms diffused via an exchange mechanism with copper adatoms and via jumps in adatom position along the open [1¯10] direction. These results confirmed previously published experimental observations. They also confirmed the validity of a statistical model that was developed to account for these observations. The quantity governing the variation of diffusion anisotropy with temperature was the difference Er-Ej between the activation energies for the insertion of a lead atom in the copper plane and for its jumps in adatom position. The value of this difference, as determined in the static simulations, compares very well with what could be deduced from experimental observations. The agreement was also very good concerning the value of the main diffusion barrier, which was the energy associated with the de-insertion of a lead atom. Simulations performed at 400 to 700K showed that multiple jumps occurred frequently. Their frequency increased with temperature, thus leading to lead diffusions that was more anisotropic and more steeply dependent upon temperature than could be expected from the static calculations.

Non-Isotropic Surface Diffusion of Lead on Cu(110): a Molecular Dynamics Study. Prévot, G., Cohen, C., Schmaus, D., Pontikis, V.: Surface Science, 2000, 459[1], 57-68