Simulations of energetic beam deposition: from picoseconds to seconds

TL;DR

This paper introduces a hybrid simulation method combining kinetic Monte Carlo and molecular dynamics to model crystal growth via energetic beam deposition, capturing atomic mobility effects at realistic growth rates.

Contribution

The paper develops a novel multi-scale simulation approach that accurately models energetic beam deposition, integrating atomic-scale dynamics with surface diffusion over extended timescales.

Findings

Energy influences island and step densities.

Optimal energy for layer-by-layer growth identified (25 eV for Ag).

Energy-induced atomic mobility affects growth modes.

Abstract

We present a new method for simulating crystal growth by energetic beam deposition. The method combines a Kinetic Monte-Carlo simulation for the thermal surface 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 present 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 monolayer per second, correctly accounting for both energy-induced atomic mobility and thermal surface diffusion. We find that the 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 transport is at a maximum. A high step density is needed for energy induced layer-by-layer growth, hence the effect dies away at increased temperatures, where thermal surface diffusion reduces the step density. As part of the development of the method, we present molecular dynamics simulations of single atom-surface collisions on flat parts of the surface and near straight steps, we identify microscopic mechanisms by which the energy influences the growth, and we discuss the nature of the energy-induced atomic mobility.