Morphology of zinc oxide nanoparticles and nanowires: Role of surface and edge energies

Although zinc oxide (ZnO) is a widely studied nanomaterial and a useful photocatalyst, the structures predicted by traditional morphology models, such as the Wulff construction, are largely inconsistent with experimental observations. As well as being scientifically perplexing, this disparity hinders our ability to predict the conditions requires to produce specific ZnO nanostructures on demand. Using density functional theory calculations we compute and compare the surface and edge energies for surfaces of zinc oxide and their intersections, and use a nanomorphology model to predict the thermodynamically optimal shape of zinc oxide nanoparticles and nanowires as a function of size and aspect ratio. We find that edge energies play a significant role in determining the optimal morphology of small nanowires, with hexagonal cross sections preferred for cross sectional areas below 10 nm² and dodecagonal cross sections thermodynamically stable for larger nanostructures.