Dielectric Photomasks for Nanopatterning Arbitrary Molecular Orientations

控制分子取向是制造液晶器件的重要步骤，例如液晶显示器，其中棒状分子需要在衬底表面以均匀方向排列。许多新兴的液晶应用，如平面光学元件，刺激响应材料和器件依赖于空间变化的分子取向。因此，对分子定向图的可扩展制造技术的需求很大。最近，一种利用铝膜上纳米大小的矩形孔制成的特殊设计的光掩膜的投影光模式技术被证明能够将分子取向光对准成复杂的模式，有望可扩展制造各种液晶器件。然而，这种金属掩膜的光传输效率较低，特别是对紫外线的传输效率较低。该奖项支持利用介电材料的纳米结构开发高效光掩膜的基础研究，并促进这种光模式技术在液晶器件制造中的实际应用。该项目利用紫外光和介电元掩膜研究具有有序分子取向的复杂结构的光图像化。该研究是跨学科的，涉及光掩模设计，数值模拟，液晶材料和器件，纳米制造和光学表征。PI将利用这项研究，向研究生和本科生传授多学科知识和技能，并通过让少数族裔和高中生参与，加强多样性和STEM教育。等离子体元掩膜可以产生光强和偏振方向的空间变化模式，最近被提出并用于分子取向的光定向成复杂的空间变化模式。等离子体元掩模的一个问题是，等离子体材料中的欧姆损耗使光传输降低。本项目旨在通过开发介电元掩膜来消除这一限制。本研究包括在紫外和近紫外波长范围内具有可设计偏振模式和高光透射的介电元掩模的模拟、制作和表征；光学光图系统的构建设计、制造和表征Pancharatnam-Berry微透镜阵列和反射镜作为测试平台。该研究促进了介电元掩模设计的基本认识和新知识，以及几何相位光学元件等液晶器件的可扩展制造能力。该项目的成功有望提高基于元掩模的光模式技术的空间分辨率和吞吐量。研究成果将丰富Pancharatnam-Berry平面光学元件的纳米制造工具箱，促进其实际应用。

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.