Photonic bandgap materials and structures by sol-gel processing

The sol-gel method is an inexpensive and flexible liquid phase processing technique that is suitable for the fabrication of 1-D PBG structures, such as multilayer dielectric mirrors. In the present work, we started by preparing highly reflecting quarter-wave multilayer stacks, composed of alternating films of high refractive index material (TiO2) and low refractive index material (SiO2 possessing well-defined stop bands. For example, for a 9-layer stack, a stop band was obtained with less than 5% transmittance (at normal incidence) between similar to 600-700 nm, with Deltalambda/lambda(min) = 0.35. Fabry-Perot microcavities, containing high or low index defects within the quarter-wave stack, were also prepared and tested. Such structures were optimized with the help of suitable modeling, using transfer matrix techniques. Various experimental techniques were also used to characterize these multilayers, including ellipsometry, UV-Vis spectroscopy, X-ray diffraction and Atomic Force Microscopy.