Surface morphology and domain structure during the evolution of ZnO nanorods into films

We investigated the effects of growth temperature on the surface morphology and domain structure of ZnO nanorods and films grown on Al₂O ₃ (0 0 0 1) substrates in a temperature range of T_g = 180-330 °C by metal-organic chemical vapour deposition. As the growth temperature decreased, ZnO nanorods having a sharp tip changed into ZnO films with a faceted surface morphology. The ZnO films grown at a lower growth temperature (e.g. T_g ≤ 240 °C) consisted of two domains with different in-plane orientations, while 30°-twist ZnO domains became dominant for higher growth temperature (e.g. T_g ≥ 280 °C) to reduce the lattice mismatch. It was found that the inclination angle of the side facet observed in the surface of the ZnO layers was determined by the surface area of several facets such as, and planes. A detailed discussion regarding the effects of growth temperature on the growth behaviour and evolution of ZnO layers is presented in this work.