Effects of The Ehrlich-Schwoebel Potential Barrier on the Wolf-Villain Model Simulations for Thin Film Growth

TL;DR

This study investigates how the Ehrlich-Schwoebel barrier influences thin film growth in the Wolf-Villain model, revealing that a strong barrier induces mound formation and surface roughness, with oscillating correlation functions indicating morphological changes.

Contribution

It introduces the effect of the Ehrlich-Schwoebel barrier into the Wolf-Villain model, demonstrating its role in surface morphology and mound formation during thin film growth.

Findings

ES barrier causes mound formation on the surface.

Correlation function oscillates with strong ES barrier.

Surface becomes kinetically rough with uphill current.

Abstract

\emph{Wolf-Villain (WV) model} is a simple model used to study \emph{ideal} molecular beam epitaxy (MBE) growth by using computer simulations. In this model, an adatom diffuses instantaneously within a finite diffusion length to maximize its coordination number. We study statistical properties of thin films grown by this model. The morphology of the WV model is found to be kinetically rough with a downhill particle diffusion current. In real MBE growth, however, there are additional factors such as the existence of a potential barrier that is known as the \emph{Ehrlich-Schwoebel (ES) barrier}. The ES barrier is an additional barrier for an adatom that diffuses over a step edge from the upper to a lower terrace which is known to induce an uphill particle current. We found that with the addition of the ES barrier, the WV-ES model morphology is rough with \emph{mound formation} on the surface when the barrier is strong enough. To confirm these results, the correlation function is also studied. We find no oscillation in the correlation function in the WV model. For the WV-ES model, the correlation function oscillates. These results confirm that a strong enough ES barrier can cause mound formation on the WV surface in our study.