2D and 3D periodic templates through holographic interference lithography : photonic and phononic crystals and biomimetic microlens arrays

Abstract

In this thesis a simple technique for controlling structure via holographic interference lithography was established and implemented. Access to various space groups including such important structures as the level set approximations to the Diamond, the Schwartz P structure, the FCC, and the non centrosymmetric Gyroid structures were demonstrated. The ability to make 3D structures over a large area, with low defect densities and periodicities on the sub/i scale opens a whole range of opportunities including such diverse areas as photonic crystals, phononic crystals, drug delivery, microtrusses, tissue scaffolds, microfluidics and colloidal crystallization. A correlation between structure and photonic band gap properties was established by systematically exploring the 11 FCC space groups. This resulted in a technique to search for photonic band gap structures. It was found that a fundamental connectivity caused by simple Fourier elements tended to support gaps. 2-3, 5-6 and 8-9 gaps were opened in the f.c.c lattices. The F-RD and 216 structures were newly shown to have complete band gaps. Two of the three previously established champion photonic crystal structures, viz. the Diamond and the Gyroid presented practical fabrication challenges, approximations to these structures were proposed.

(cont.) A scalable P structure and the 3-FCC structure were fabricated by single and multiple exposure techniques. Both negative and positive tone photoresist systems were demonstrated. Line defects were written into the negative tone system using two-photon lithography. The single crystalline, porous nature of the structures was exploited to examine the possibility for their use as hypersonic phononic crystals and microfluidic microlenses. Two dimensional single crystalline patterns were created using interference lithography. Their phononic band structure was probed by Brillioun light scattering to yield a phononic band diagram, which clearly demonstrates the effect of periodicity on the phononic density of states. The ability to control the density of states at these length scales holds the potential for control over thermal properties. The two dimensional structures fabricated in negative photoresist were also tested as microlenses with the integrated pores acting as microfluidic channels. This combination resulted in a structure reminiscent to that of the biological species ophiocoma wendtii.