Novel Colloidal Routes to Photonic Band Gap Materials

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This research project will develop patternable, 3-D photonic band gap (PBG) materials. Such systems will be templated from hard-sphere colloidal crystals assembled epitaxially from depletion-stabilized silica suspensions of varying chemistry, functionality, and size. Through photopolymerization of functional groups grafted onto the silica particle surfaces or of the surrounding aqueous matrix, the assemblies will be patterned to embed critical features (e.g., waveguides) needed for device applications. Formation of PBG structures with the desired optical contrast will be created by infilling as-grown colloidal crystals with a high refractive index material followed by removal of the colloidal template. Finally, the photonic properties of these novel PBG materials will be measured experimentally and compared to theoretically predicted behavior. Engineering patternable 3-D PBG structures requires an interdisciplinary effort that brings together researchers in the fields of colloid science, materials synthesis, PBG fabrication, and photonic properties. Hard-sphere colloidal crystals that serve as templates for PBG structures will be assembled from depletion-stabilized suspensions of bare, uncharged silica spheres of varying functionality. Colloidal epitaxy will be implemented to achieve the desired fcc crystal structure. The assemblies will then be gelled in situ by a photopolymerization process induced via confocal lithography. The patterned assemblies will be infitrated with rare earth doped chalcogenide glasses. The photonic properties of the resulting inverse fcc structures will be characterized with respect to their PBG structure, wave guiding nature, and luminescence. Successful implementation of this multidisciplinary research project will lead to new scientific understanding in several key areas. Fundamental knowledge of depletion-enhanced colloidal crystallization, the mechanical and rheological properties of colloidal assemblies, and important discoveries in the patterning, drying, and infiltration behavior of colloidal crystals, and their photonic properties are expected. These results should have broad impact on colloidal processing of ceramics, fabrication of porous materials for related applications including catalysts, membranes and biostructures, and on the technologically significant area of photonic band gap materials needed for the next generation of information technology.