Investigation of influence of electrolyte composition on formation of anodic titanium oxide nanotube films

We have studied titanium oxide (TiO₂) nanotube films formed by anodizing a metal titanium (Ti) film deposited on a silicon dioxide layer in an ethylene glycol solution of water and ammonium fluoride (NH₄F). We have systematically examined the influence of water and NH₄F contents on the nanotube formation and the morphology of formed nanotubes. We demonstrate the optimum anodization conditions (Ti film morphology and electrolyte composition) that lead to formation of well-ordered nanotube films. On the basis of the present experimental results, we suggest that a ratio of NH₄F concentration to water content in the electrolyte is a crucial parameter that affects the nanotube formation process as well as the structural properties of formed TiO₂ nanotube films. Furthermore, we propose a model of anodization that explains the observed dependence of the anodization rate of Ti on water and NH₄F contents in the electrolyte.