Facile hydrothermal epitaxial growth of vertical ZnO post arrays on sapphire substrates

In this paper we describe a facile approach for the epitaxial growth of ZnO posts on Al2O3 substrates using only solution-based processing. First, we prepared Al2O3 substrates buffered by ZnAl2O4 epilayers through solid state reactions (SSRs) between sol-gel-derived ZnO films and Al2O3 single crystals. To grow epitaxial ZnO post arrays with high coverage, it was critical for the epitaxial ZnAl2O4 buffer layers to have continuous structures-a feature that we realized through the presence of a ceramic ZnO box during the SSR. We used transmission electron microscopy to examine the microstructural evolution of both the ZnAl2O4 buffer layers formed through SSRs and the ZnO posts grown hydrothermally.