Effects of preparing conditions on controllable one-step electrodeposition of ZnO nanotube arrays

By using a one-step electrodeposition method, well oriented single crystalline ZnO nanotube arrays (ZNTAs) with average diameter less than 200 nm were synthesized on FTO substrate under different conditions. The effects of preparing conditions such as pretreatment of substrate, pH value of electrolyte, electrodeposition potential, concentration of electrolyte, reaction temperature and growth time on the electrodeposition of ZNTAs were systematically investigated by scanning electron microscopy (SEM), and ultraviolet visible absorbance spectroscopy to make the formation mechanism clear. It is indicated that the electrodeposition parameters have significant influence on the morphology, average diameter and growth density of as-prepared ZNTAs. The aligned ZNTAs can be only obtained on the FTO substrate pre-treated with acid solution when the applied potential is controlled from -0.8 to -1.0 V and the pH value of electrolyte is from 3.10 to 3.90, simultaneously. The growth temperature and the electrolyte pH value have great impact on the morphology of as-prepared ZnO nanostructure. The tube diameters can be monitored to some extent only by changing the concentration of the zinc precursors or growth time, in addition, the growth time is closely related to the band gap energy (Eg) of as-prepared ZNTAs