Diffusion of adatoms and vacancies on otherwise perfect surfaces: A molecular dynamics study

Abstract

Using computer simulation by the technique of molecular dynamics, we have investigated the influence of the terrace structure on the type and the dynamical aspects of atomic mechanisms for surface diffusion in fcc structure crystals. On the (100) terraces, vacancies are much more mobile than adatoms, while the opposite is true for (111) terraces. On the latter, vacancies migrate through the creation in their vicinity of paired, adatom-vacancy, defects. On the (100) face, the adatom jump length incrases with increasing temperature and reaches a value equal to several times the nearest neighbour distance. Adatoms are also fully delocalized on the (111) face and spend much more time in flight over the surface than by vibrations in the equilibrium sites. Large dynamical correlations are present in the vacancy movement on the (100) face and have been identified as new mechanisms of the defect migration by multiple jumps. On the (110) terrace, despite its anisotropic structure, two-dimensional diffusion takes place by an original atomic exchange mechanism. This mechanism has been identified to be the same as the one proposed by Halicioglu to explain two-dimensional diffusion on (110) Pt terraces, and recently corroborated by the FIM experiments of Wrigley and Ehrlich.