Calculation and fabrication of two-dimensional complete photonic bandgap structures composed of rutile TiO.sub.2 single crystals in air/liquid

Photoelectrochemical applications of photonic crystals are gathering great interests both from physicists and chemists. Here, we theoretically and experimentally present two-dimensional photonic bandgap (2D-PBG) structures based on rutile titanium dioxide (TiO.sub.2) single crystal that is a famous material because of the photoelectrochemical ability. The structures were the arrays of hollow hexagonal rutile TiO.sub.2 pillars in contact with air or a typical nonaqueous electrolyte solution, acetonitrile. Since the TiO.sub.2 refractive indices exhibit a strong dispersive behavior, the bandgap width was discussed from the viewpoint of the refractive index map that would be helpful for the real application of this structure. The 2D-PBG structures for both infrared light and visible light were fabricated by our established lithography technique for rutile TiO.sub.2 with and without Nb doping, i.e., photocatalytic TiO.sub.2 and high electron conductive TiO.sub.2, respectively. These structures show characteristic absorbance peaks or reflectance dips at wavelengths predicted by our theoretical calculations.