Porous TiO ₂ photonic band gap materials by anodization

Self-organized TiO ₂ nanomaterials grown by anodic oxidation of Ti foils have attracted broad scientific interest due to their wide potential applications. The majority of anodic TiO ₂ nanostructures studied to date are in the form of self-ordered nanotube arrays. Here we report an exotic type of multilayered nanoporous TiO ₂ films that are conveniently fabricated by anodizing Ti foils of high imperfection levels using a novel multipulse anodization method. The fabricated TiO ₂ films feature tens of well-defined layers whose long-range structural periodicity leads to photonic band gaps in the visible wavelengths and vivid film colors. Moreover, the optical responses (or the film color) of the fabricated TiO ₂ multilayers not only are sensitive to environmental chemicals but also can be electrically switched on and off repeatedly, demonstrating their novel potential applications for, e.g., colored smart windows or electric display boards. © 2012 American Chemical Society.