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

Abstract

The surface diffusion of compact Cu tetramers on Cu (111) has been studied at the atomic scale by means of molecular dynamics simulations using embedded atom interatomic potentials. The Cu clusters diffuse by several different mechanisms; all of them have the common trait of involving concerted displacements of at least some of the atoms forming the island. The anisotropy in the rhombus shape of the Cu tetramers and the different activation energies of the translational and rotational jumps result in highly anisotropic diffusion, with a transition from practically one-dimensional motion at low temperature to nearly isotropical two-dimensional random walk at high temperature. The use of molecular dynamics allows us to also determine the preexponential factors for each jump mechanism, from which analysis we can obtain some insight into their basic nature and the relationships between them.

Self-learning kinetic Monte Carlo simulations of self-diffusion of small Ag islands on the Ag(111) surface

“…The frequency of occurrence of a diffusion process and the net displacement of CM it produces during an island diffusion affects not only the effective energy barrier but also the effective diffusion prefactor. Glancing through table 11, one can see that the effective energy barrier increases with island size, but there is no trend of how the effective diffusion prefactor varies with increasing island size. Nevertheless, the change in the diffusion prefactor from one island size to another can be explained based on the frequency of occurrence of the processes that do not contribute to the net displacement of CM of an island.…”

“…The primary role of dimer shearing is to rotate the long diagonal by °120 in either the clockwise or anti-clockwise direction. Note that, in the absence of the dimer-shearing process or at low temperatures, the tetramer will diffuse one-dimensionally [11]. The average activation barrier for fcc hcp off-longdiagonal translation is 0.192 eV and the effective activation barrier for tetramer diffusion is 0.202 eV.…”

Diffusion of Ga adatoms at the surface of GaAs(001) c(4x4) $α$ and $β$ reconstructions

“…When all these parameters are calculated, the next step is to describe particle diffusion process in this energy landscape. Development of ab-initio calculations in the last years resulted in very accurate description of the surface energy landscape at various systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14] . For many crystals, important because of their applications in nanotechnology or biotechnology, full energy map at the specific surface orientations and reconstructions were done.…”

“…To solve set of equations (5) we should find m eigenvalues and eigenvectors of matrix M . Each eigenvalue describes one dynamical mode responsible for the relaxation of the initial occupation probability towards equilibrium values.…”