The influence of hydroxide on the initial stages of anodic growth of TiO₂ nanotubular arrays

Understanding the mechanism for growing TiO2 nanotubes is important for controlling the nanostructures. The hydroxide nano-islands on the Ti surface play a significant role at the initial stage of anodization by forming the very first nano-pores at the interface between hydroxide islands and substrate and eliminating the H2O electrolysis. A quantitative time dependent SEM study has revealed a nanotube growth process with an initial linear increase of pore diameter, film thickness and number of pores. During the anodization of titanium, different current transient curves are observed for Ti samples with or without hydroxide on the surface. The transient current profile has been quantitatively analyzed by fitting several distinctive stages based on a growth mechanism supported by SEM observations. It is found that a saturated cubic dependent equation is appropriate to fit a short current upturn due to the increase of the surface area.