Effective chemical potential for non-equilibrium systems and its application to molecular beam epitaxy of Bi2Se3

TL;DR

This paper develops an effective chemical potential approach for non-equilibrium systems, applied to molecular beam epitaxy of Bi2Se3, revealing high supersaturation and agreement with experimental observations.

Contribution

It introduces a new method for defining chemical potential in non-equilibrium conditions, maintaining correct equilibrium limits and applying it to growth processes.

Findings

Effective chemical potential determined by most probable clusters.

Bi2Se3 exhibits high supersaturation during growth.

Results agree with experimental data.

Abstract

First-principles studies often rely on the assumption of equilibrium, which can be a poor approximation, e.g., for growth. Here, an effective chemical potential method for non-equilibrium systems is developed. A salient feature of the theory is that it maintains the equilibrium limits as the correct limit. In application to molecular beam epitaxy, rate equations are solved for the concentrations of small clusters, which serve as feedstock for growth. We find that the effective chemical potential is determined by the most probable, rather than by the lowest-energy, cluster. In the case of Bi2Se3, the chemical potential is found to be highly supersaturated, leading to a high nucleus concentration in agreement with experiment.