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∥[1 1 2̄ 0]_sapphire, [1 1 2̄ 0] _ZnO[0 0 0 1]_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∥[1 0 1̄ 4]_sapphire, [1 0 1̄ 0]_ZnO∥[1 2̄ 1 0]_sapphire epitaxy. A small fraction of the nanowires grow perpendicular to the substrate with [0 0 0 1]_ZnO∥[0 0 0 1] _sapphire.