Synthesis and self-assembly of metal-coated nanoparticles

We report theoretical and experimental studies on the metal-dielectric photonic crystal structure, which is constructed by the self-assembly of metal-coated nanoparticles. The finite-difference time-domain (FDTD) simulations were carried out to predict the width and position of the 3D photonic bandgap. For fabrication, we first prepared gold-embedded silica nanoparticles containing extremely small gold nanoparticles. The core particles are then immersed in a gold-containing solution in which the gold shells were formed by subsequent reduction. Formation of continuous shells was confirmed by scanning electron microscope (SEM) and the optical response due to the surface plasmons. We also performed self-assembly of both the gold-embedded core particles and metal-coated particles. SEM micrographs showed the formation highly ordered structures. The optical reflectance spectra exhibited shifts of the Bragg reflection peak due to the change in refractive index produced by gold nanoparticles.