Hydrothermal growth of well-aligned ZnO nanorod arrays: Dependence of morphology and alignment ordering upon preparing conditions

Well-aligned ZnO nanorod arrays were prepared on substrates by hydrothermal growth under different conditions. The effect of preparing conditions on the deposition of ZnO nanorods was systematically studied by scanning electron microscopy, X-ray diffraction and photoluminescence spectroscopy. It is demonstrated that the growth conditions such as pre-treatment of the substrates, growth temperature, deposition time and the concentration of the precursors have great influence on the morphology and the alignment ordering of ZnO nanorod arrays. Pre-treatment of substrates, including dispersion of ZnO nanoparticles and subsequent annealing, not only plays a main role in governing the rod diameter, but also greatly improves the rod orientation. Although the rod diameter and its distribution are mainly determined by pre-coated ZnO nanoparticles, they can also be monitored to some extent by changing the concentration of the precursors. The growth temperature has a little influence on the orientation of nanorods but it has great impact on their aspect ratio and the photoluminescent property. Kinetic studies show that the growth of ZnO nanorods contains two distinct step: a fast steps within the first hour, in which the nanorods tend to be short and wide, and a slow step, in which long rods with high aspect ratio are obtained.