Fabrication and Characterization of Large Macroporous Photonic Crystals in Titania

We made large, highly ordered structures consisting of crystals of macropores in titania (TiO2), by template-assisted growth. The crystals were characterized by synchrotron small-angle X-ray diffraction, X-ray absorption, wide-angle X-ray diffraction, scanning electron microscopy, optical microscopy, optical reflectivity, and Raman spectroscopy. Care was taken to make well-ordered templates, by slowly growing colloidal crystals from lightly charged polystyrene latex particles and carefully drying them to form opals. Solid material was deposited in the opal template by precipitation from an alkoxide hydrolysis. Subsequently, the samples were heated to 450 °C to form anatase TiO2 and to remove the latex template, which resulted in a macroporous crystal, inverse opal, or air-sphere crystal. The macropores were close-packed and interconnected by windows, and small additional voids were located at interstices between the pores. The macropores were arranged on a face-centered cubic lattice with domains of more ...