<title>Self-assembly of colloidal particles into three-dimensionally ordered arrays and its applications</title>

This paper describes a convenient method for self-assembling monodisperse colloidal spheres into 3D ordered arrays with domain sizes as large as several square-centimeters. These arrays have a cubic-close-packed structure or a face-center- cubic lattice similar to that of a natural opal. Each array exhibits a stop band whose position is mainly determined by the diameter of the colloidal particles. This type of structure can serve as a 3D photonic band-gap crystal, which is potentially useful in controlling the emission and propagation of light. The versatility of the present technique has allowed us to tailor the photonic properties of these arrays of colloidal particles. For example, the maximum attenuation of the photonic band-gap can be modulated by controlling the number of layers along the propagation direction of the light. The position of the mid- gap can be roughly changed by controlling the diameter of the particles and subsequently fine-tuned by sintering the sample at elevated temperatures.