AN INVESTIGATION OF THE ENERGETICS AND DYNAMICS OF ADATOM MOTION TO DESCENDING-STEP EDGES IN PT/PT(111) HOMOEPITAXY

We have performed semi-empirical molecular-dynamics simulations and static potential-energy,oy calculations to study kinetic mechanisms in Pt/Pt(111) homoepitaxy. Energy barriers for adatom incorporation into and minimum-potential-energy profiles for adatoms approaching the descending-step edges of small islands have been investigated. Adatoms incorporate into descending-step edges via a concerted exchange mechanism. The effects of island size and step-edge type on the incorporation kinetics have been studied and are found to be consistent with a recently proposed explanation for reentrant growth in Pt/Pt(111) homoepitaxy. Adatoms near the step edge have a significantly higher energy than those in the center of the island, due to decreasing coordination with the island atoms. From static-energy calculations, we find that energy barriers for an adatom to approach the descending-step edges do not differ considerably from the clean-surface diffusion barrier.