Large-scale ZnO inverse opal films fabricated by a sol-gel technique

We demonstrate that high-quality large-scale ZnO inverse opals can be fabricated by a simple sol-gel technique, comprising infiltration of polystyrene colloidal crystal films with zinc nitrate solution, drying and annealing at 300 ^{{ring operator}}C. This simple method yields continuous films, which consist of inverse opal domains (up to several hundreds of μm² in size), separated by small cracks filled with zinc oxide. Microradian X-ray diffraction was employed to verify the crystalline quality of ZnO inverse opals on the macroscale, revealing that the samples have a predominant face-centered cubic structure, and that the majority of domains have the same crystallographic orientation. The samples exhibit bright iridescence and possess photonic stop-bands in the visible to near-infrared spectrum.