On atomic jumps during surface diffusion

JULIO FERRÓN; RODOLFO MIRANDA; JUAN JOSE DE MIGUEL

Groningen

Conferencia; European confererence on surface science. ECOSS 27; 2010

The characteristics of atomic displacements during surface diffusion of Cu on Cu(111) arestudied by means of Molecular Dynamics simulations using Embedded Atom interatomicpotentials [1]. It is found that even at very low substrate temperatures, only a smallfraction of the atomic jumps, namely those taking place with the lowest adatom kineticenergy, can be considered truly random. On the contrary, the great majority of the jumpsare correlated, i.e., the displacement directions are not randomly chosen but rather keepsome sort of memory from the previous moves and are influenced by them [2].Long jumps, spanning several surface unit cells, are observed at all temperatures. Ananalysis of the kinetic energy of the adatoms performing these long displacementsconfirms that these are distinct events, with a higher activation energy than thelow-energy, nearest-neighbour hops. Their length probability distribution follows adecreasing exponential dependence with jump length, consistent with a discretemechanism of atomic friction in which the diffusing adatoms transfer their excess kineticenergy to the substrate in a single scattering event, instead of gradually losing it alongtheir entire path.Recrossings (displacements in which the adatom moves back and forth between twoadjacent adsorption sites) show the same energetic characteristics of the long jumps;both types of events can thus be considered manifestations of one and the same physicalprocess.Finally, the influence of the instantaneous atomic configuration of the substrate on theadatom's trajectories will also be discussed.