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.