Voltage induced self-peeling of initiation layers on self-organized TiO₂-WO₃ nanotubes and formation of oxide nanosheet rolls

When anodic self-organized nanotube layers are formed on valve metals, often a disordered porous initiation layer is present on the tube tops. In the present work, we show that on the TiO₂-WO₃ nanotubes this layer can be triggered to self-peel and roll up in the nanosheets if the anodization is carried out at a sufficiently high voltage. An ultrasonic treatment allows to completely remove the nanosheet rolls and to obtain highly ordered nanotube layers. This finding is of high significance for any applications requiring defined tube tops.