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0988-QQ05-08

3-D Photonic Band Structure Engineering in Self-Assembled Macroporous Photonic Crystals Jeremy W. Galusha, Kaycee Carter, and Michael H. Bartl Department of Chemistry, University of Utah, Salt Lake City, UT, 84112 *

Corresponding author: [email protected]

ABSTRACT By applying directional pressure along the (111) crystal axis of opaline photonic crystals under controlled temperatures, inverse opals with symmetry broken structures are fabricated. This selective deformation results in strongly modified photonic band structures and hence optical properties of the photonic crystals. Experimental data are accompanied by theoretical band structure calculations that confirm the experimental results and are used to predict new structures with optimized band gap properties. INTRODUCTION Periodically ordered macro- and mesoporous structures have become important materials for a broad range of applications, including catalysis, sensing, energy conversion, and photonics.[1] Especially, 3-dimensionally ordered structures with periodicities on the order of the wavelength of light have attracted great interest for use as photonic crystals. Photonic crystals (or photonic band gap structures) were originally proposed by Yablonovitch[2] and John[3] in 1987 and have since emerged as one of the most promising concepts for non-classical photon manipulation and are considered key components of next generation optical and optoelectronic devices.[4-6] Photonic crystals are artificial periodic electromagnetic structures for which the band structure concepts of solid-state physics are applied to electromagnetism, leading to fundamentally new optical principles such as localization of light in bulk materials and control of spontaneous emission over broad frequency ranges.[2-4] Among the various 3-dimensional photonic crystal structures operating in the visible range of the electromagnetic spectrum, so-called titania inverse opals – face-centeredcubic (fcc) arranged air-spheres in a high-dielectric titania matrix – are of particular interest due to their ease of fabrication based on colloidal sphere self-assembly/sol-gel chemistry and the unique optical properties of titania; combining a high refractive index with excellent optical transparency throughout the visible. Unfortunately, however, the structural properties of inverse opal photonic crystals (mainly their close-packed structure and high symmetry of the spherical building blocks) requires that the high-dielectric component possess a refractive index of 2.85 or higher in order to open an omnidirectional (“complete”) photonic band gap (PBG)[7] – a frequency range, for which light is classically forbidden to exist within the crystal.[4] Consequently, a photonic crystal with a complete band gap in the visible has not been experimentally realized so far due to the lack of appropriate dielectric materials that meet these requirements. In this paper we present first experimental results for selective post-assembly symmetry breaking in colloidal crystal-based photonic structur