Simulations of energetic beam deposition: From picoseconds to seconds

We present a method for simulating crystal growth by energetic beam deposit ion. The method combines a kinetic Monte Carlo simulation for the thermal s urface diffusion with a small scale molecular-dynamics simulation of every single deposition event. We have implemented the method using the effective medium theory as a model potential for the atomic interactions, and presen t simulations for Ag/Ag(111) and Pt/Pt(111) for incoming energies up to 35 eV. The method is capable of following the growth of several monolayers at realistic growth rates of 1 ML per second, correctly accounting for both en ergy-induced atomic mobility and thermal surface diffusion. We find that th e energy influences island and step densities and can induce layer-by-layer growth. We find an optimal energy for layer-by-layer growth (25 eV for Ag) , which correlates with where the net impact-induced downward interlayer tr ansport is at a maximum. A high step density is needed for energy-induced l ayer-by-layer growth, hence the effect dies away at increased temperatures, where thermal surface diffusion reduces the step density. As part of the d evelopment of the method, we present molecular-dynamics simulations of sing le atom-surface collisions on flat parts of the surface and near straight s teps, we identify microscopic mechanisms by which the energy influences the growth, and we discuss the nature of the energy-induced atomic mobility. [ S0163-1829(98)04547-0].