Cu/ZnO(0001) under oxidating and reducing conditions: A first-principles survey of surface structures

Abstract

We investigate the stability of Cu-exposed ZnO(0001) surface structures in an oxygen environment using density functional theory and the method of ab initio atomistic thermodynamics. A two-dimensional phase diagram is constructed which identifies stable surface structures as a function of the copper and oxygen chemical potentials. Two structures with a $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$R30${}^{\ensuremath{\circ}}$ unit cell are found to be prominently stable at intermediate oxygen and copper chemical potentials. These phases are characterized by a single adlayer of Cu${}_{4}$O${}_{3}$ and Cu${}_{12}$O${}_{13}$ stoichiometry on ZnO(0001). We rationalize recent experimental observations in the literature in terms of our results.