Fabrication and characterization of tunable photonic crystals by filling silica nanoparticles into the PS opals

Abstract

The self-assembly of monodispersed colloids into an ordered three-dimensional structure, i. e., an opal (colloidal crystal) structure, is routinely employed to fabricate photonic crystals. In this study, high-quality polystyrene (PS) colloidal crystals in large area were fabricated during 24 hours via the capillary-enhanced process. Then, the tunable photonic crystals were formed by incorporating silica nanoparticles of different concentration into the void space via a dipping process. According to Fick's Law, the interstitial space of opal could be completely filled. Thereby, the monodisperse spheres of opal will form core-shell structure. Moreover, increase of silica nanoparticle concentration will result in an increased refractive index of the opal film. The absorptive peak of pure opal is 445nm as measured in UV-Vis spectrum, and the absorptive peak of core-shell opal is 453nm, 463nm and 469nm for suspensions with different concentration of silica nanoparticles of 0.017, 0.122, and 0.244wt%, respectively. Therefore, by using this dipping process to fill the opal film with colloidal nanoparticles, the characteristic absorption wavelength for opal film can be fine-tuned more easily, efficiently and cost effectively than by traditional methods of constructing opal from monodispersed colloids of different diameter.