Ab initio vacancy formation energies and kinetics at metal surfaces under high electric field

TL;DR

This study uses density functional theory to investigate vacancy formation and kinetics on electrified metal surfaces, demonstrating that high electric fields do not create vacancies but can hinder their annihilation, challenging previous assumptions.

Contribution

The paper provides the first ab initio analysis of vacancy formation energies and kinetics at metal surfaces under high electric fields, clarifying the effects of electric fields on surface defects.

Findings

Vacancy formation is more difficult under high electric fields than in field-free conditions.

Electric fields can introduce kinetic barriers to vacancy annihilation.

Results challenge previous suggestions that high fields create artefact vacancies.

Abstract

Recording field ion microscope images under field evaporating conditions and subsequently reconstructing the underlying atomic configuration, called three-dimensional field ion microscopy (3D-FIM) is one of the few techniques capable of resolving crystalline defects at an atomic scale. However, the quantification of the observed vacancies and their origins are still a matter of debate. It was suggested that high electric fields (1-5 V/\r{A}) used in 3D-FIM could introduce artefact vacancies. To investigate such effects, we used density functional theory (DFT) simulations. Stepped Ni and Pt surfaces with kinks were modelled in the repeated slab approach with a (971) surface orientation. An electrostatic field of up to 4 V/\r{A} was introduced on one side of the slab using the generalized dipole correction. Contrary to what was proposed, we show that the formation of vacancies on the electrified metal surface is more difficult compared to a field-free case. We also find that the electric field can introduce kinetic barriers to a potential vacancy-annihilation mechanism. We rationalize these findings by comparing to insights from field evaporation models.