Current characterization and growth mechanism of anodic titania nanotube arrays

TiO2nanotube arrays were synthesized by anodic oxidation on a pure titanium substrate in solutions containing 0.175 M NH4F composed of mixtures with different volumetric ratios of DI water and glycerol. According to the results of the current curve recorded during anodization, the time of the first sharp current slope (corresponding to the initial oxide layer formation time) was found to vary from 8 to 171 s depending not only upon the water content in the electrolytes but also upon the voltage. The current curves exhibit oscillation with different amplitudes and periods. In combination with the scanning electron microscope (SEM) images, a growth mechanism, layer-by-layer model, of TiO2nanotube arrays was presented. Based on this mechanism, many phenomena that appeared during anodization can be reasonably explained. Our results would be helpful for the design of nanoarchitectures in related material systems.