Self-diffusion of adatoms, dimers, and vacancies on Cu(100)

TL;DR

This study combines ab initio and semi-empirical simulations to analyze the energetics and mechanisms of surface diffusion of adatoms, dimers, and vacancies on Cu(100), revealing that vacancy diffusion dominates and that static barriers approximate dynamic ones.

Contribution

It provides a detailed comparison of static and dynamic diffusion barriers and highlights the primary role of vacancy diffusion on Cu(100) surfaces.

Findings

Vacancy diffusion is the main surface diffusion mechanism.

Static barriers closely approximate dynamic energy barriers.

Adatoms and dimers primarily diffuse via jump mechanisms.

Abstract

We use ab initio static relaxation methods and semi-empirical molecular-dynamics simulations to investigate the energetics and dynamics of the diffusion of adatoms, dimers, and vacancies on Cu(100). It is found that the dynamical energy barriers for diffusion are well approximated by the static, 0 K barriers and that prefactors do not depend sensitively on the species undergoing diffusion. The ab initio barriers are observed to be significantly lower when calculated within the generalized-gradient approximation (GGA) rather than in the local-density approximation (LDA). Our calculations predict that surface diffusion should proceed primarily via the diffusion of vacancies. Adatoms are found to migrate most easily via a jump mechanism. This is the case, also, of dimers, even though the corresponding barrier is slightly larger than it is for adatoms. We observe, further, that dimers diffuse more readily than they can dissociate. Our results are discussed in the context of recent submonolayer growth experiments of Cu(100).