Controlling anodization time to monitor film thickness, phase composition and crystal orientation during anodic growth of TiO₂ nanotubes

Anodic TiO₂ nanotube (TNT) films show promises for photon-driven catalytic, electricity storage and chemical processes. The film thickness of anodic TNT is known to affect its performance in optical and electronic applications. Also, factors affecting the morphology and dimensions of anodic TNT films are rather well-known. However, the knowledge on phase transition and composition in the growth of anodic TiO₂ from the titanium metal is very limited. In this work, the anodization time is controlled in intervals of 10, 60, 300, 1000, 2000 and 5000 s to investigate its effect on phase composition and transition, and the morphology of the anodic TNT during the growth process. Even though the mechanism of anodic TNT formation is still under debate, the scanning electron microscope results support bottom-up tube growth with evidence of a compact layer. It was also found that the Richards growth model is applicable to correlate growth time and film thickness. Finally, the phase transition, crystal orientation and pore formation during the anodic process are further discussed.