Microscopic characteristics of theAg(111)∕ZnO(0001)interface present in optical coatings

Abstract

A first-principles computational method is used to investigate the microscopic properties of the $\mathrm{Ag}\left(111\right)∕\mathrm{Zn}\mathrm{O}\left(0001\right)$ interface that is often present in optical coatings designed for solar-control windows. The mechanical stability of the interface is important and therefore the ideal work of separation has been calculated for several structural variants of the interface which have different lattice mismatches and in-plane orientations. The process by which silver atoms are deposited, cluster, and form layers on the ZnO(0001) surface has also been studied. It is found that interfaces with the O-terminated ZnO surface are stronger than those with the Zn-terminated surface. In addition, incoherent interfaces with small lattice mismatch and minimal strain are preferred. In particular, the large period $(9\times 8)$ $\mathrm{Ag}∕\mathrm{Zn}\mathrm{O}$ coincidence superstructure (0.1% mismatch) is found to have a significantly higher work of separation than the coherent $(1\times 1)$ interface (11% mismatch). A rotated variant of the interface $(2\times \surd 3)$ $R30$ (2.6% mismatch) has a work of separation that is comparable with the coincidence superstructure. Both the $(9\times 8)$ and $(2\times \surd 3)$ $R30$ $\mathrm{Ag}∕\mathrm{Zn}\mathrm{O}$ interfaces have been observed in deposition experiments and which one is seen depends on the ambient conditions and strain state of the interface. The calculated works of separation are consistent with measured works of adhesion obtained from cantilever beam experiments.