Crystallization of the anodic oxide on titanium in sulphuric acids solution at a very low potential

Anodic oxide films were formed on the deposited pure titanium in 0.1 M H2SO4 solution at 30 °C by using cyclic voltammetry (CV) anodization technique. Clear atomic images and step-terrace structure were observed on it by using STM, which gave a direct evidence for the local crystallinity of the anodic oxide films, even though the maximum anodization potential (Emax) was −50 mV, which was much lower than the lowest potential for crystallization in literatures. Moreover, the crystalline degree of the whole anodic oxide film was estimated from the refractive index (n), and the results showed that the crystalline degree increased with potentials. The analysis of XPS spectra revealed that high potentials were also beneficial for the formation of TiO2, which was the primary substance for the formation of stable crystals in the oxide films.