Preparation of Photonic Crystals Made of Air Spheres in Titania

Abstract

Three-dimensional crystals of air spheres in titania (TiO2) with radii between 120 and 1000 nanometers were made by filling the voids in artificial opals by precipitation from a liquid-phase chemical reaction and subsequently removing the original opal material by calcination. These macroporous materials are a new class of photonic band gap crystals for the optical spectrum. Scanning electron microscopy, Raman spectroscopy, and optical microscopy confirm the quality of the samples, and optical reflectivity demonstrates that the crystals are strongly photonic and near that needed to exhibit band gap behavior.

Self-assembly of shape-controlled nanocrystals and their in-situ thermodynamic properties

“…The structure is ordered on the length-scale of the template spheres and the pore sizes are in submicron to micron range. Alternatively, ordered porous silica with much smaller pore sizes in nanosize range ( B 30 nm), produced deliberately by introducing surfactant, has also been processed [20,21], in which the porosity is created by surfactants. This is the so-called mesoporous structure.…”

“…The other is the ordered porous structures. Here the ordered hollow structure of titania is taken as an example [20,21]. The ordered hollow structure was made through a template-assisted technique, in which selfassembly of size selective polystyrene spheres creates an ordered template.…”

Evidence of the hexagonal columnar liquid-crystal phase of hard colloidal platelets by high-resolution SAXS

“…For instance, three-dimensional arrangements of spheres in colloidal crystals [1] might serve as photonic materials [2][3][4], intended to manipulate light. Colloidal particles with non-spherical shapes (such as rods and plates) are of particular interest because of their ability to form liquid crystals that might serve as templates for ordered porous materials.…”

Photonic crystals in the optical regime — past, present and future

“…Wijnhoven and Vos [70] describe a similar approach based on colloidal silica balls which are removed to form air spheres after in"lling with titania. It is worth remarking here that the microcrystalline nature of the material which forms the open-pore structure is such that it exhibits a high level of Rayleigh scattering, so that the out-of-stopband or o!-normal incidence transmission may also be negligible, thus masking true photonic band-gap behaviour.…”