Formation of a titanium dioxide nanotube array

Starting from the naturally occurring structure of porous aluminum oxide, a polymer mold suitable for the formation of titanium dioxide nanotubes was obtained. The tubular structure was formed by electrochemical deposition in the mold. After dissolution of the polymer, titanium dioxide nanotubes were obtained and characterized. The ''as deposited'' TiO2 tubes were amorphous, but polycrystalline anatase samples of the same structure were obtained after heat treatment. The inner diameter of the tubes decreased from about 100 to 70 nm during the crystallization. A mechanism for the electrochemical deposition is proposed. Furthermore, the preparation procedure could also be applied to other semiconducting materials.