This paper describes a simple and convenient method that allows self-assembly of colloidal particles (50 nm-50 m in diameter) into cubic-close-packed (c.c.p.) lattices over areas larger than 1 cm2. These three-dimensional (3-D) lattices have a highly ordered structure similar to that of a natural opal, with a packing density of approximately 74%. They strongly diffract light, and each of them exhibits a stop band whose position is mainly determined by the size of the particles. These crystalline assemblies of particles have also been used as templates to fabricate inverse opals, that is, three-dimensionally porous membranes consisting of a c.c.p. lattice of interconnected air balls. Both types of periodic structures are potentially useful as 3-D photonic bandgap (PBG) crystals that can be used to control the emission and propagation of light in the spectral region ranging from ultraviolet (UV) to near infrared.
Younan Xia, Byron Gates, and Sang Hyun Park, "Fabrication of Three-Dimensional Photonic Crystals for Use in the Spectral Region from Ultraviolet to Near-Infrared," J. Lightwave Technol. 17, 1956- (1999)