Study of natural photonic crystals in beetle scales and their conversion into inorganic structures via a sol-gel bio-templating route

The origin of the structural colors from several different examples of the weevil and longhorn families (Curculionidae and Cerambycidae, respectively) was investigated by structural and optical characterization techniques. A range of interesting three-dimensional photonic crystal structures operating at visible wavelengths was discovered, including both disordered and ordered non-close-packed lattices of cuticular spheres and bicontinuous diamond-based architectures. The discovered photonic structures display a large variation in lattice constants and dielectric filling fractions and thereby create optical reflectance colors spanning the entire visible range. To transform these bio-polymeric photonic crystals into heat and photo-stable inorganic structures, a low-temperature bio-templating method was developed. Using organic-inorganic hybrid silica sol-gel infiltration-templation chemistry combined with acid-etching template removal, stable inverse photonic structures were fabricated. The inverse structures display good structural quality and vivid reflection properties.