Anodization fabrication of 3D TiO2 photonic crystals and their application for chemical sensors

Three-dimensional (3D) TiO2 photonic crystals (PCs) with multilayers films were prepared using a periodic pulse anodic oxidation method. Unlike the typical morphologies of bamboo-like tubes with the reinforced compact parts at the interface regions and also tube walls under constant anodization processes. The periodically concave structure was found outside of the TiO2 nanotubes under multipulsed anodization voltage condition, so that the periodic layered structure with different porosity was obtained along the longitudinal direction of tubes. The thickness of the tube and the size of pit could be tunable and controllable by modifying the duration of the high voltage and low voltage. The PCs have uniform narrow photonic band gap (PBG), steep band edge, which were applied successfully in chemical sensors. The formation mechanism of periodic structure was also discussed.