Epitaxial growth of ZnO nanowires on a- and c-plane sapphire

Epitaxial ZnO nanowires were grown on a- and c-plane sapphire substrates by metalorganic chemical vapor deposition without metal catalysts or templates. Nanowires with monodisperse diameters grow in dense arrays perpendicular to a-plane sapphire and with in-plane rotational alignment due to [0 0 0 1]ZnO∥[ 112¯0]sapphire, [112¯0]ZnO[0001]sapphire epitaxy. On c-plane sapphire, multiple possible epitaxial relations give a mixture of nanowire orientations. The majority of the nanowires grow in one of the three directions all at an angle of 51.8° off the substrate plane with [0 0 0 1]ZnO∥[ 101¯4]sapphire, [101¯0]ZnO∥[ 12¯10]sapphire epitaxy. A small fraction of the nanowires grow perpendicular to the substrate with [0 0 0 1]ZnO∥[0 0 0 1]sapphire.