FABRICATION OF HIGH REFRACTIVE INDEX, PERIODIC, COMPOSITE NANOSTRUCTURES FOR PHOTONIC AND SENSING APPLICATIONS

This dissertation examines methods of fabricating high refractive index, periodic structures and their applications. Structures with a refractive index periodicity in one-dimensionally are fabricated by stacking layers of (high-refractive index) nanoparticle-filled and unfilled layers. More complex two- and three-dimensional structures are fabricated by direct printing of nanoparticles via solvent-assisted soft nanoimprint lithography. Polymer-nanoparticle composites are an active area of research and development especially for photonic applications. We show use of two composite formulations, first for fabrication of one-dimensional photonic crystals, and second for scalable UV-nanoimprinting. One dimensional photonic crystals, which possess a periodicity in refractive index, result in a constructive interference-based reflectance peak, whose location, intensity, and bandwidth can be tuned by controlling the contrast in refractive index and the number of periods. Appropriate materials were selected to create a strain-tunable, one-dimensional photonic crystal-based mechanochromic sensor. The same material system and one-dimensional photonic crystal were used in conjunction with novel modulus-gradient elastomer substrates. When subjected to strain, the modulus gradient resulted in unique, bio-inspired photonic gradient effects. UV-nanoimprinting provides a convenient method for creating patterned surfaces. By incorporating high refractive index additives, ZrO2 and N-vinyl carbazole, we achieve an imprint-able, solvent-free, high refractive index UV-resin. For applications requiring even higher refractive indices and more harsh environments, polymer nanocomposites are not suitable. Direct patterning of nanoparticles via solvent-assisted soft nanoimprint lithography is used to fabricate periodic structures over large areas. Complex, three-dimensional woodpile structures were successfully fabricated through layer-by-layer imprinting of TiO2 nanoparticle-based dispersions. Similarly, imprinted TiO2 multidimensionalnanostructures were nitrided with high-temperature ammonia, resulting in multi-dimensional, nanostructured plasmonic materials. We examine the crystal structure, atomic concentration, optical properties as well as the resulting patterned structure after the nitridation process. Finally, a post-imprinting densification method is demonstrated, in which the refractive index TiO2 nanoparticle-based nanostructures can be tuned and dramatically increased. This fast, inexpensive, and scalable method could be attractive for production of dielectric metamaterials