Structure and Transmission Spectra for Colloidal Crystals with Silica Spheres

An ordered colloidal structure of SiO₂ spheres of 0.33μm diameter has been formed in distilled water. It is a face-centered cubic structure with a lattice constant of 0.54μm and a volume fraction of 0.48, as determined by the Kossel rings analysis. The light transmission in the 111 direction exhibited a dip located at 11600cm^-1. A plane wave expansion method is used to calculate the lowest gap at the L point. The gap center coincides quite well with the measured transmission dip.