Low-Temperature Fabrication of Mesoporous Titanium Dioxide Thin Films with Tunable Refractive Indices for One-Dimensional Photonic Crystals and Sensors on Rigid and Flexible Substrates

Highly transparent mesoporous titanium dioxide (TiO₂; anatase) thin films were prepared at room temperature via ultraviolet (UV) irradiation of hybrid polymer–TiO₂ nanoparticle thin films. This approach utilized a UV-curable polymer in conjunction with the photocatalytic activity of TiO₂ to form and degrade the organic component of the composite films in one step, producing films with well-controlled porosity and refractive index. By adjustment of the loading of TiO₂ nanoparticles in the host polymer, the refractive index was tuned between 1.53 and 1.73. Facile control of these properties and mild processing conditions was leveraged to fabricate robust one-dimensional photonic crystals (Bragg mirrors) consisting entirely of TiO₂ on silicon and flexible poly­(ethylene terephthalate) substrates. The mesoporous Bragg mirrors were shown to be effective chemical vapor sensors with strong optical responses