Dielectric Photomasks for Nanopatterning Arbitrary Molecular Orientations

控制分子取向是制造液晶器件的关键步骤，例如液晶显示器，其中棒状分子需要在基板表面沿统一的方向排列。许多新兴的液晶应用，如平板光学元件、刺激响应材料和器件，都依赖于空间变化的分子取向。因此，对构图分子取向的可扩展制造技术的需求很高。最近，一种使用特殊设计的光掩模的投影光刻技术被证明能够将分子取向光对准成复杂的图案，这有望实现各种液晶器件的可规模化制造。然而，这种金属光掩模光传输效率较低，尤其是对紫外光的传输效率较低。该奖项支持利用介电材料的纳米结构开发高效率光掩模的基础研究，并促进了这种光刻蚀技术在液晶器件制造中的实际部署。该项目研究使用紫外光和介电掩模对具有有序分子取向的复杂结构进行光图案化。这项研究是跨学科的，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将利用这项研究来教育研究生和本科生掌握多学科的知识和技能，并通过让少数族裔和高中生参与来加强多样性和STEM教育。等离子体元任务可以产生光强度和偏振方向的空间变化图案，最近被提出并用于将分子取向光排列成复杂的空间变化图案。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变得很低。该项目旨在通过开发介电元掩模来消除这一限制。这项研究包括模拟、制作和表征在紫外光和近紫外光波长范围内具有可设计偏振图案和高透过率的介质掩模；建立光学光调制系统；以及作为试验台的Pancharatnam-Berry微透镜阵列和反射镜的设计、制造和表征。这项研究促进了对介电掩模设计的基本理解和新知识，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调制技术的空间分辨率和吞吐量。研究成果将丰富纳米制造工具箱，促进Pancharatnam-Berry平板光学元件的实际应用。

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.