Assembly of Nanoparticles into Opaline Structures over Large Areas

A simple technique for crystallizing spherical nanoparticles into 3D opaline structures, which can be of use as diffractive elements in the fabrication of optical or electro-optical devices, is presented. Both polystyrene beads and silica colloids within the size range 50–100 nm have been successfully ordered and it is thought that the technique can also be applied to monodisperse particles of other materials and to particles of even smaller size.