Modelling the onset of oxide formation on metal surfaces from first principles

TL;DR

This study uses first-principles molecular dynamics to elucidate the spontaneous initial oxidation mechanisms of metal surfaces like Al(111) and TiN(001), revealing hot-atom dissociation and oxide formation at near-zero temperatures.

Contribution

It provides detailed mechanistic insights into ultrathin oxide formation on metals from first-principles simulations, highlighting the hot-atom dissociative process and surface-specific oxide structures.

Findings

Oxidation occurs via a hot-atom dissociative mechanism.

Ultrathin oxide forms on Al(111) and TiN(001) surfaces.

Different oxide structures develop on Al and TiN surfaces.

Abstract

The formation of ultrathin oxide layers on metal surfaces is a non-thermally-activated process which takes place spontaneously at very low temperatures within nanoseconds. This paper reports mechanistic details of the initial oxidation of bare metal surfaces, in particular Al(111) and TiN(001), as obtained by means of first-principles molecular dynamics modelling within the Density-Functional Theory. It is shown that the reactions of bare metal surfaces with O2 molecules take place according to a 'hot-atom' dissociative mechanism which is triggered by the filling of the sigma-star antibonding molecular orbital and is characterised by a sudden release of a large amount of kinetic energy. This released energy provides a driving force for metal/oxygen place-exchange processes which are responsible for the onset of oxide formation at virtually 0 K and at oxygen coverages well below 1 monolayer (ML). Further simulations of the oxidation reactions reveal that a disordered ultrathin oxide forms on Al(111), whereas a rather ordered structure develops on TiN(001) following a selective oxidation process which leaves clusters of Ti vacancies in the TiN lattice underneath the oxide layer.