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 Al2O3 (0 0 0 1) substrates in a temperature range of Tg = 180-330 deg. 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. Tg ≤ 240 deg. C) consisted of two domains with different in-plane orientations, while 30 deg.-twist ZnO domains became dominant for higher growth temperature (e.g. Tg ≥ 280 deg. 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 (0 1 1-bar 3)ZnO, (0 1 1-bar 2)ZnO and (0 1 1-bar 0)ZnO planes. A detailed discussion regarding the effects of growth temperature on the growth behaviour and evolution of ZnO layers is presented in this work.