Fabrication and optical characterizations of gold nanoshell opal

We fabricated three-dimensional photonic crystals by self-assembling gold nanoshells via forced sedimentation method. Gold nanoshells with a diameter of 458 nm (418-nm silica core and 20-nm gold shell) were synthesized and self-assembled into a 5-mu m-thick opal structure. We observed reflection peaks at 710 and 1240 nm, which are believed to be from the complete three-dimensional photonic band gap and the (111) directional gap, respectively. Theses results were in good agreement with the photonic band-structurc calculations done by the finite-difference time-domain method. Angle-resolved reflectivity measurements were also performed to investigate the existence of the complete three-dimensional photonic band gap.