Density-controlled hydrothermal growth of well-aligned ZnO nanorod arrays

Density-controlled ZnO nanorod arrays (ZNAs) were prepared on pre-treatment substrates by a hydrothermal approach under different conditions. The effect of substrate pre-treatment conditions on controlling the density of ZNAs was systematically studied by scanning electron microscopy and x-ray diffraction. It is demonstrated that the substrate pre-treatment conditions such as the concentration of the ZnO colloid, spin coating times, and substrate annealing treatment have their respective influence on controlling the density of the ZNAs. The introduction of a ZnO nanoparticle layer on the substrate not only helps to control the nanorod density but also has a strong impact on the orientation of the nanorod arrays. Although controlling the spin coating process has a similar mechanism to controlling the concentration of colloid, it offers a convenient method to prepare a series of ZNAs with variable density. An annealing treatment of the substrate can influence the microstructure of the ZnO seed layer and then influence the density of the ZNAs.