Annealing study of titanium oxide nanotube arrays

Titanium dioxide nanotube arrays fabricated by anodization of titanium foil and annealed at different temperatures were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and positron annihilation spectroscopy (PAS). The crystallization process and morphological changes of the nanotubes have been discussed. It was found that anatase (1 0 1) only appeared on the walls of the nanotubes. The atomic concentration of fluoride and the ratio of Ti/O decreased when the annealing temperature increased. Vacancy type defects were found to diffuse toward the surface when the samples were annealed at 200 °C and 400 °C and healing of vacancies occurred at 600 °C. In addition, fluoride may form some complexes with vacancies on the surface hence lowering the value of S parameter.