RESUMO
Three-dimensional photonic crystals (or photonic band gap materials) have been fabricated with oblate spheroids as the photonic building block. The nonspherical shape was realized by the blown film extrusion process of a prefabricated colloidal photonic crystal of spherical polystyrene particles, with its voids infiltrated by polyvinyl alcohol. The extrusion was applied on the composite film at a temperature above the glass transition temperature of both polymers. The uniformly applied two-dimensional stretching retains the positional order in the prefabricated colloidal crystal; transforms the spheres into oblate spheroids; and results in orientational order between the spheroids. The morphology of the particles can be predictably changed from a sphere into an oblate spheroid with a specified aspect ratio by the extent of the blown film extrusion. Therefore, the concomitant photonic band gap properties can be tuned in a convenient way.
RESUMO
A ternary system, consisting of air, an air-core/dense-silica-shell core-shell particle, and liquids has been used to fabricate an inverse opal structure with low fill factor, high refractive index contrast, and reversible tuning capabilities of the bandgap spectral position. The original close-packed opal structure is a ternary self-assembled photonic crystal from monodisperse and spherical polystyrene-core/silica-shell colloidal particles with air as the void material. Calcination removed the polystyrene and converted the core-shell particles to hollow spheres with a dense shell. In a final step, liquid is infiltrated only in the voids between the hollow spheres, but does not penetrate in the shell. This allows facile and reversible tuning of the bandgap properties in an inverse opal structure.
