Investigation of the controllable growth of the TiO₂ nanotube arrays fabricated by anodic oxidation method

The highly ordered and uniform TiO₂ nanotube arrays were fabricated by anodic oxidation of titanium foil in HF aqueous solution or ethylene glycol containing NH₄F and deionized water. The diameter, density, length and wall thickness of nanotube arrays can be controlled effectively by varying the anodization parameters including electrolyte composition, voltage, and time. The microstructures of the titania nanotube arrays were characterized by X-ray diffraction (XRD). The results showed that the as-anodized titania nanotubes were amorphous. And when annealed in vacuum or in oxygen ambient at 500°C, the samples prepared in HF aqueous solution showed only anatase phase, and the samples prepared in ethylene glycol containing NH₄F and deionized water showed both anatase and rutile phases. And the former and the latter batch of samples became better crystallized when annealed in oxygen and in vacuum, respectively. Furthermore, the controllable growth mechanism of nanotube arrays is discussed.