Buffer-layer-assisted epitaxial growth of perfectly aligned oxide nanorod arrays in solution

Epitaxy between materials with good lattice match requires perfect staking on the atomic scale and is thus often considered to be challenging to achieve by low-temperature solution-based hydrothermal growth. Inspired by the concept of the buffer layer in vapor-phase epitaxial growth, we present herein a novel synthetic protocol of employing ZnAl₂O₄ epilayers to hydrothermally grow perfectly aligned ZnO nanorod arrays in solution. Remarkable tunability of the density and dimensions of the nanorods can be realized by adjusting the roughness of the ZnAl₂O₄ layer and the nutrient solution concentration, which is in line with the classical nucleation theory and also confirms that the nanorod growth is mass-transport-limited. Furthermore, through nanopatterning of the ZnAl₂O₄ layer by electron beam lithography, shape-controlled vertical ZnO nanostructures at predesigned positions can be achieved. Finally, taking advantage of the epitaxial relationships, we adjusted the tilting orientations of the aligned nanorods by selecting sapphire substrates with different surface planes.