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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2018

Month Degree Awarded

September

First Advisor

James Watkins

Second Advisor

Kenneth Carter

Third Advisor

Jae-Hwang Lee

Subject Categories

Ceramic Materials | Materials Science and Engineering | Polymer and Organic Materials | Semiconductor and Optical Materials

Abstract

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.

Available for download on Sunday, September 01, 2019

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