Number Density and Diameter Control of Chemical Bath Deposition of ZnO Nanorods on FTO by Forced Hydrolysis of Seed Crystals

ZnO nanorods have been studied extensively due to facile synthesis and useful optoelectronic properties for applications in nanoscale devices. In a common two-step procedure, an ethanolic Zn2+ precursor solution is used to deposit ZnO seed crystals on a substrate, which is then immersed in an aqueous Zn2+ precursor solution to grow the nanorods. Here, a forced hydrolysis technique was employed based on additions of water and heat to the seed precursor solution before depositing the seeds on commercial fluorine-doped tin oxide (FTO)/glass substrates. ZnO nanorods were then grown from these seeds by chemical bath deposition. Analyses showed that the forced hydrolysis resulted in an increase in seed crystallite size and a decrease in the number of seeds deposited. With increasing seed size, the number density of nanorods decreased, while the length and diameter of each rod increased. These findings offer a simple method for exerting control over the number density of ZnO nanorods that is compatible with the rough FTO surface, unlike other methods that require smoother substrates.