Atomic jumps during surface diffusion

Abstract

The characteristics of atomic displacements during surface diffusion of Cu on Cu͑111͒ are studied by means of molecular dynamics simulations. It is found that even at very low substrate temperatures, the majority of the jumps are correlated, i.e., the displacement directions are not randomly chosen but rather keep some sort of memory from the previous moves and are influenced by them. Long jumps, spanning several surface unit cells, are observed at all temperatures. From an analysis of their length probability distribution information can be obtained about the mechanisms of friction and energy transfer between the diffusing adatom and the substrate. Both long jumps and recrossings ͑displacements in which the adatom moves back and forth between two adjacent adsorption sites͒ appear with a higher activation energy than normal diffusion. Finally, the influence of the instantaneous atomic configuration of the substrate on the adatom's trajectory is also highlighted.

Ultrafast molecular transport on carbon surfaces: The diffusion of ammonia on graphite

“…energy dissipation via frictional coupling is likely to be responsible for the occurrence of the hopping motion. On the other hand with increasing thermal energy compared to the potential energy surface, more and more long jumps start to set in during jump diffusion [58][59][60][61] , which is evident from the experimental data, since the best fit Chudley-Elliott model gives an average jump length of 1.4 a gr . Note that a similar diffusive motion was observed for molecular hydrogen on graphite with jump diffusion and also a very low activation energy 33,50,62 .…”

Adsorption and dynamics of Si atoms at the monolayer Pb/Si(111) surface

“…Long hops of atoms or clusters have been reported in several previous studies using field ion microscope or STM [47][48][49][50][51]; some also show that short hops dominate at low temperatures but long hops dominate at high temperatures [51]. The behavior of long hops is an interesting phenomenon in surface diffusion.…”

Atomic mechanisms and diffusion anisotropy of Cu tetramers on Cu(111)

“…Since we intended to observe and compare diverse atomistic processes taking place at several temperatures and on different time scales, the same integration time step of 1 fs was used in all simulations. The atomic coordinates were stored at intervals of 40 fs to allow us to follow the atomic trajectories with sufficient precision [10]. These coordinates have been used to produce movies that graphically display all the different cluster motion events, facilitating their identification and description by simple inspection.…”

“…III D. For all types of events, a time threshold of 0.8 ps was established: all jumps or rotations resulting in shorter residence times at the new position were considered fluctuations and discarded. The choice of this value was initially motivated by our previous work on the diffusion of Cu monomers on Cu(111) [10], where we found that the fastest diffusion processes for single atoms took at least ≈0.4 ps. As it will be shown in Sec.…”

“…Many different examples can be found in the recent literature: besides the commonly assumed hopping mechanism for monomer diffusion, the atomic exchange was first predicted theoretically [4] and then observed in field ion microscopy (FIM) experiments [5,6]. Another of the basic postulates of classical diffusion theory, namely that the atomic trajectories are made up of individual nearest-neighbor hops, has also been proven too restrictive: longer jumps occur frequently [7][8][9][10][11] and have a sizable influence on nucleation and the growth mode of overlayers [12]. Finally, it has also been shown that in many cases the atomic jump directions are not statistically random, but rather result from complicated correlations involving the diffusing adatom(s) plus several neighbors, both within the overlayer and in the substrate [13,14].…”