Domain mapping of inverse photonic crystals by laser diffraction

We report the first laser diffraction study of photonic crystals with an inverse opal structure. The samples were prepared by deposition of monodisperse polystyrene microspheres onto vertical glass substrates, infiltration of voids with WO3 sol followed by its gelation, and final removal of the polymer microspheres by annealing. Scanning electron micrographs revealed that the films consisted of 25–500 μm2 domains isolated by cracks. By using laser diffraction it was possible to calculate the period of photonic crystals and to examine their crystalline quality. We present for the first time the method for visualization of macroscale ordering of photonic crystals, termed as domain mapping. We constructed a domain map of a 2 mm2 area of the sample, demonstrating both large “single crystal” regions (up to 0.4×0.4 mm20.4×0.4 mm2), where all domains have the same crystallographic orientation, and disordered regions. The proposed method of quality control takes on special significance for inverse photonic crystals, for which average domain size is noticeably less than that of conventional opals.