Gradient TiO2 Nanotube Arrays via Asymmetric Anodization

Gradient self-organized TiO2 nanotube arrays with the tube diameters and length gradually changing along the sample plane are conveniently fabricated. The fabrication method is based on asymmetric anodization with the point cathode placed close to the edge of the titanium foil anode. Mechanism study reveals that the drastic variance in the voltage drop over the tube bottom at different locations along the film is responsible for the formation of the gradient morphology. Experimentally, moderate electrolyte conductivitiesandsufficientlyhighanodizationvoltagesarenecessarytoenablethedesiredgradientTiO2 nanotubearrays.Moreover, the structural features of the fabricated gradient TiO2 nanotube arrays can be further adjusted by controlling the imperfection level of the titanium substrate.