We have conducted a theoretical study of atomic exchange processes occurring as Pt atoms are deposited on a Pt(111) surface. Using an embedded atom method type interaction potential, we have systematically sampled sites atop a heptamer and at straight A and B type steps to correlate incident atom energy and regions of impact with the probability of 'push-out' events, where deposited atoms displace peripheral island atoms. Push-out events lead to incorporation of the incident atom in the growing layer and, thereby, can contribute to layer-by-layer growth if islands are small enough. We find the probability of push-out events to be large for incident energy typical for sputter deposition, 10 and 20 eV. To some extent the 20 eV incident energy also results in detrimental effects, such as displacement of surface atoms (interface mixing), vacancy formation, and displacement of island atoms to positions atop the growing layer, promoting multilayer growth. We have evaluated the minimum energy paths and activation energy barriers for several representative exchange processes observed in the simulations. The calculated activation energy is surprisingly low, typically in the range of 0.6-0.8 eV, even for processes involving displacements of multiple atoms.
This work has been supported by NSF under Grant No. CHE-9217774. Support for M.V. was provided by the Ford Foundation. We gratefully acknowledge Daniel Faken for the GLMAN and TCON graphics programs.