Dielectric Photomasks for Nanopatterning Arbitrary Molecular Orientations

Kent State University, Kent OH

Investigators

Abstract

Controlling molecular orientations is an essential step in manufacturing liquid crystal devices, such as liquid crystal displays where rod-shaped molecules need to be aligned in a uniform direction at substrate surfaces. Many emerging liquid crystal applications, such as flat optical elements, stimuli-responsive materials and devices rely on spatially varying molecular orientations. As a result, scalable manufacturing techniques for patterning molecular orientations are in high demand. Recently a projection photopatterning technique using specially designed photomasks made of nanometer-sized rectangular holes in aluminum films was shown capable of photo-aligning molecular orientations into complex patterns, promising scalable manufacturing of various liquid crystal devices. However, this kind of metallic photomask suffers from low efficiency in optical transmission, especially for ultra-violet light. This award supports fundamental research to develop high efficiency photomasks by using nanostructures of dielectric materials, and facilitates practical deployment of this photopatterning technique in liquid crystal device manufacturing. The project studies photo-patterning of complex structures with ordered molecular orientations using ultra-violet light and the dielectric metamasks. The research is interdisciplinary, involving photomask design, numerical simulations, liquid crystal materials and devices, nanomanufacturing and optical characterization. The PI will leverage the research to educate graduate and undergraduate students with multidisciplinary knowledge and skills, and to enhance diversity and STEM education by involving minority and high-school students. Plasmonic metamasks that can generate spatially-varying patterns of both light intensity and polarization direction have recently been suggested and utilized for photoaligning molecular orientations into complex spatially varying patterns. One issue with the plasmonic metamasks is that Ohmic losses in plasmonic materials make the optical transmission low. This project aims to eliminate this limit by developing dielectric metamasks. This research includes simulation, fabrication and characterization of dielectric metamasks with designable polarization patterns and high optical transmission in ultra-violet and near ultra-violet wavelength ranges; building of an optical photopatterning system; and designing, fabrication and characterization of Pancharatnam-Berry microlens arrays and mirrors as testbeds. The research advances basic understanding and new knowledge on designing dielectric metamasks and capabilities in scalable fabrication of liquid crystal devices such as geometric phase optical elements. Success of this project is expected to increase spatial resolution and throughput of the metamask-based photopatterning technique. The research outcomes should enrich the nanomanufacturing toolbox and facilitate practical applications of Pancharatnam-Berry flat optical elements.