Assembly of nanoparticles into opaline structures over large areas

A simple technique for crystallizing spherical nanoparticles into 3D opalin e structures, which can be of use as diffractive elements in the fabricatio n of optical or electro-optical devices, is presented. Both polystyrene bea ds and silica colloids within the size range 50-100 nm have been successful ly ordered and it is thought that the technique can also be applied to mono disperse particles of other materials and to particles of even smaller size .