Colloidal Self-Assembly of Highly-Ordered Silica Inverse Opals for Deep Ultraviolet Diffraction

The fabrication of highly ordered similar to 2 mu m thick silica inverse opal (IO) photonic crystal (PhC) films is reported. These IO films diffract deep ultraviolet light (UV, <250 nm) and are prepared using the inward-growing self-assembly of similar to 143 nm diameter monodisperse polystyrene nanoparticles (PSNPs) suspended within a hydrolyzed silicate sol-gel precursor solution. Removal of the PSNPs results in solid, robust IOs that attenuate >70% of light meeting the Bragg condition at normal incidence. Structural and optical characterization of these silica IO films indicate that noncoherent scattering losses are low at deep UV wavelengths, even though substantial crack-type defects occur. The IO films exhibit a diffraction fwhm of similar to 12 nm with diffraction efficiencies of >30% for 213 nm laser light and possess nanoscale porosities of similar to 20 nm. Relative to reported silica IOs that diffract deep UV light, these new PhC materials show at least 28% narrower spectral bandwidths and 5-fold increased diffraction efficiencies. We postulate that increased ordering of the silica network is the principal factor that improves the optical performance. Furthermore, the relatively flat, homogeneous IO film surfaces produce narrow, symmetric diffraction beams suitable for optical imaging applications. Strategies to further improve the diffraction efficiencies of these silica IO materials and the implications for novel technological applications are discussed.