Interfacial and microstructural changes of the Al2O3/ZnO multilayer films induced by in-situ growth and post-annealing temperatures

Al2O3/ZnO nanolaminates are promising nanocomposites with special properties for the applications of oxide -based thin-film transistors, photoluminescence devices, and pitch grating references. In this study, Al2O3/ZnO nanolaminates were grown at 80 degrees C, 120 degrees C, 250 degrees C by atomic layer deposition, and then post-annealed by furnace annealing at 600 degrees C, 700 degrees C, 800 degrees C respectively. Both the in-situ growth temperature and post-annealing temperature-induced microstructures of Al2O3/ZnO nanolaminates were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). In addition, the interfacial diffusion and solid-state reaction were systematically studied by high-resolution transmission electron microscopy (HRTEM). The films grown at 80 degrees C and 250 degrees C show a typical polycrystalline structure, while the film grown at 120 degrees C possesses an obvious preferred orientation. After post-annealing at 700 degrees C, the spinel ZnAl2O4 grains are formed at the interface of the Al2O3/ZnO films grown at 80 degrees C and 250 degrees C, which indicates the solid-state re-action has occurred, but this phenomenon did not occur for the films grown at 120 degrees C. The results indicate that the growth temperature not only affects the crystallinity and preferred orientation of the ZnO interlayers, but also the interfacial diffusion and counter-diffusion of atoms, and thereby the solid-state reaction, in the post -annealing process. So, simultaneously controlling the effects of the growth and post-annealing temperatures has great significance for this kind of nanolaminates.