Atomistic details of oxide surfaces and surface oxidation: the example of copper and its oxides

TL;DR

This review summarizes recent atomic-level insights into copper oxide surfaces, their formation processes, and the challenges in understanding native oxidation and nucleation, highlighting advances in experimental and computational techniques.

Contribution

The paper provides a comprehensive overview of atomistic understanding of copper oxide surfaces and discusses recent progress and remaining challenges in the field.

Findings

Oxide growth occurs via nano-island formation and coalescence.

Electronic structure calculations aid in characterizing Cu oxide surfaces.

Challenges remain in understanding native oxidation and nucleation processes.

Abstract

The oxidation and corrosion of metals are fundamental problems in materials science and technology that have been studied using a large variety of experimental and computational techniques. Here we review some of the recent studies that have led to significant advances in our atomic-level understanding of copper oxide, one of the most studied and best understood metal oxides. We show that a good atomistic understanding of the physical characteristics of cuprous (Cu$_2$O) and cupric (CuO) oxide and of some key processes of their formation has been obtained. Indeed, the growth of the oxide has been shown to be epitaxial with the surface and to proceed, in most cases, through the formation of oxide nano-islands which, with continuous oxygen exposure, grow and eventually coalesce. We also show how electronic structure calculations have become increasingly useful in helping to characterise the structures and energetics of various Cu oxide surfaces. However a number of challenges remain. For example, it is not clear under which conditions the oxidation of copper in air at room temperature (known as native oxidation) leads to the formation of a cuprous oxide film only, or also of a cupric overlayer. Moreover, the atomistic details of the nucleation of the oxide islands are still unknown. We close our review with a brief perspective on future work and discuss how recent advances in experimental techniques, bringing greater temporal and spatial resolution, along with improvements in the accuracy, realism and timescales achievable with computational approaches make it possible for these questions to be answered in the near future.