Novel complex phenomena in atomic surface diffusion.

FERRÓN, J; GÓMEZ, L.; MIRANDA, R.; DE MIGUEL, J.J.

Paris, Francia

Conferencia; 24th European Conference on Surface Science.; 2006

Based on Molecular Dynamics simulations with EAM interatomic potentials it was recently demonstrated that in the surface self-diffusion of Cu on Cu(111) most of the atomic jumps take place in a non-random manner, thus contradicting the traditional view of atomic diffusion as a purely stochastic, thermally activated process [1]. At high temperatures the atomic displacements span several nearest-neighbor distances, whereas at low temperature the so-called “recrossings” dominate: these are double jumps in which the atom oscillates back-and-forth between two neighboring adsorption sites with zero net displacement. As a result of these observations, it is clear that the atomic movements cannot be correctly described in general in terms of a random walk model. Here we present new results giving additional insight into this suggestive subject. Firstly, the simulations have been extended to Au, demonstrating that the same basic behavior is found, i.e., these phenomena are not specific for Cu. From our simulations a complex picture emerges in which atomic diffusion seems to be a highly concerted process involving many substrate atoms. This view is supported by simulated experiments in which the correlations are destroyed by forced randomization of the substrate atoms (but not the diffusing adatom) during saddle-point crossing. Finally, we also demonstrate the influence of the substrate structure and geometry by comparing simulations on flat and stepped surfaces.