(Invited) Mechanism of Interlayer Transport on a Growing Metal Surface: 2D vs. 3D Growth

Abstract

The atomic scale transitions corresponding to diffusion and interlayer transport of metal adatoms on the low energy, close packed surfaces of several transition metals are studied using density functional theory calculations within the generalized gradient approximation. Minimum energy paths and estimates of activation energy are calculated for processes that influence whether the crystal grows layer-by-layer, i.e. 2D growth, or whether new islands nucleate on top of existing islands resulting in 3D growth. In some cases, the path of lowest activation energy for the descent of an adatom, i.e. interlayer transport, turns out to take place near, but not at, a kink site on a step. The energy barrier for the adatom to subsequently round the corner and enter the kink site is significantly higher. This near-kink-descent mechanism promotes the formation of a new row of step atoms and leads to the introduction of additional kink sites, thereby opening up new low activation energy paths for descent and promoting 2D growth. The sites adjacent and above the step edge can provide large binding energy for the adatom, and form a trough along which the adatom can migrate before descending, thereby increasing the probability that an adatom finds a kink site. These features of the energy landscape for an adatom point to the possibility of re-entrant layer-by-layer growth mode and have, for example, been found for Pt(111) and Au(111) surfaces.