Direct opal fabrication from silver-coated silica microspheres

Metallised photonic crystals offer possibilities to increase the effective refractive index of the opal and thus enhance the bandgap, to control the light propagation within the crystal. Such structures have a number of potential applications, for example substrates for surface enhanced Raman scattering, SERS. Since opal structures are easily disrupted and cracked by subsequent infiltration and annealing processes, it is difficult to realise uniform large-area crack-free photonic crystal domains. Here we directly fabricate the metallised opal by self-assembly of silver-coated silica microspheres, leading to a silica / silver opal incorporating silver particles uniformly throughout.