  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.
