NSF/DMR-BSF: Liquid Crystals as a Paradigm for Chirality and Topological Defects

非技术摘要：手性是指物体不能与其镜像重合，左手和右手可能是最著名的例子。当系统固有的“特征”--科学上称为其“序参数”--不能在点、线或面上唯一地描述时，就会出现拓扑缺陷。这两种现象在自然界中无处不在，往往是相互关联的，是科学和技术中核心问题的基础。一些例子包括量子光学、半导体二极管和生物材料中的手性-DNA是最广为人知的；手性转移，即如何在其他非手性材料中诱导手性；以及多个拓扑缺陷的相互作用。这个项目主要关注手性和拓扑缺陷，使用液晶作为范例。由于液晶的长尺度和新颖的光学性质，许多相关的现象可以被可视化和定量地测量。这使得人们能够对手性和拓扑缺陷有一个普遍的了解，这是通过研究其他材料所不可能的。技术摘要：由于液晶具有很大的光学、电学和磁性各向异性，因此是研究凝聚态和凝聚态以外的许多现象的理想试验台。这项工作的中心主题是利用液晶来探索可能影响更广泛的科学事业的手性和拓扑缺陷等开创性问题。PI利用他的纳米级技术来创造和成像表面受控的手性和缺陷--有时是组合在一起的。项目包括：在与生物相关的手性纳米胶囊中进行手性转移以实现圣杯，即手性诱导长度的测量；手性多极的创建；手性拓扑缺陷、诱导的双轴性和天米子；线缺陷的多稳态“重新布线”；用于纳米光子学和半导体的手性自组装单分子膜；以及高度复杂的油性和肥皂条纹液晶缺陷。Pi的团队使用了一系列实验工具，包括光学显微镜、共聚焦荧光显微镜、光学纳米断层扫描、原子力显微镜、AFM纳米光刻和椭偏测量。大部分工作是与耶路撒冷希伯来大学的化学家大卫·阿夫尼尔教授和他的同事合作完成的。通过利用PI的能力来创建精心定制的纳米级手性和拓扑缺陷易轴图案，并将液晶取向成像到50 x 50 x 2 nm的x、y、z维度，这项工作正在改变我们对手性、缺陷、如何在各向异性流体中耦合以及凝聚态中更广泛的问题的概念和方法。特别是，PI的工作有助于理解、量化和利用其他非手性材料中的诱导手性，以及对手性和非手性拓扑缺陷、它们的操纵以及在光学和电子学中的潜在应用的更深入的了解。所研究的问题跨越了多个学科，因为手性和缺陷的后果出现在生物、化学、物理、医学、药理学和材料科学中。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract:Chirality is the inability of an object to coincide with its mirror image, where the left and right hands are perhaps the best-known example. A topological defect occurs when the system's inherent "character", scientifically called its "order parameter", cannot be described uniquely at a point, line, or surface. Both phenomena are pervasive throughout nature, often are coupled, and are fundamental to central questions in science and technology. A few examples include chirality in quantum optics, semiconductor diodes, and biomaterials - DNA is the best known; chirality transfer, i.e., how chirality can be induced in an otherwise non-chiral materials; and interactions of multiple topological defects. This project focuses on chirality and topological defects using liquid crystals as a paradigm. Because of the long length scales and novel optical properties of liquid crystals, many of the associated phenomena can be visualized and measured quantitatively. This permits a general understanding of chirality and topological defects that would not be possible by studying other materials.Technical Abstract:Owing to their large optical, electrical, and magnetic anisotropies, liquid crystals are an ideal test bed for a multitude of phenomena in condensed matter and beyond. The central theme of this work is to exploit liquid crystals to explore seminal issues of chirality and topological defects that can impact the broader scientific enterprise. The PI utilizes his nanoscale techniques to create and image controlled chirality and defects at surfaces - sometimes in combination. Projects include: chirality transfer in biologically-relevant chiral nanocapsules to achieve the Holy Grail, viz., a measure of the chiral induction length; the creation of chiral multipoles; chiral topological defects, induced biaxiality, and skyrmions; multistable "rewiring" of line defects; chiral self-assembled monolayers for nanophotonics and semiconductors; and highly complex oily and soapy streak liquid crystalline defects. The PI's team employs a battery of experimental tools, including optical microscopy, confocal fluorescence microscopy, optical nanotomography, atomic force microscopy, AFM nanolithography, and ellipsometry. Much of the work is performed in collaboration with chemist Prof. David Avnir and his colleagues at the Hebrew University of Jerusalem. By exploiting the PI's ability to create exquisitely tailored nano-scale chiral and topological defect easy axis patterns, and to image liquid crystal orientation down to x,y,z dimensions of 50 x 50 x 2 nm, this work is transforming our conceptions about - and methodology toward - chirality, defects, how the two can be coupled in anisotropic fluids, and broader issues in condensed matter. In particular, the PI's work is leading to the understanding, quantification, and exploitation of induced chirality in otherwise achiral materials, as well as a deeper knowledge of chiral and achiral topological defects, their manipulation, and potential applications in optics and electronics. The issues studied cut across multiple disciplines, as consequences of chirality and defects appear throughout biology, chemistry, physics, medicine, pharmacology, and materials science.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.