Rapid Sol–Gel Fabrication of High-Quality Thin-Film Stacks on Planar and Curved Substrates

A versatile and rapid sol–gel technique for the fabrication of high quality one-dimensional photonic bandgap materials was developed. Silica/titania multilayer materials are fabricated by a sol–gel chemistry route combined with dip-coating onto planar or curved substrates. A shock-cooling step immediately following the thin-film heat-treatment process is introduced. This step was found crucial in the prevention of film crack formationespecially in silica/titania alternating stack materials with a high number of layers. The versatility of this sol–gel method is demonstrated by the fabrication of various Bragg stack-type materials with fine-tuned optical properties by tailoring the number and sequence of alternating layers, the film thickness and the effective refractive index of the deposited thin films. Measured optical properties show good agreement with theoretical simulations, confirming the high quality of these sol–gel fabricated optical materials.