Flexible Reflective Metasurface Displays

摘要：非技术性的：自然界中的各种颜色和色调令人惊叹，但也许更令人惊讶的是某些物种主动模仿它们的能力。虽然具体的机制和物种一样不同，但每个物种都有一组可以跨越可见光谱的颜色产生细胞。在这一庞大的生物集合中，头足类/章鱼脱颖而出，成为冠军，它们擅长在几毫秒内覆盖大片颜色。这些彩色显示器在自然界的关键方面是在薄薄、灵活和共形映射的表面上产生颜色，而我们的人造最先进的显示器本质上仍然僵硬、脆弱和笨重。正是考虑到头足类动物，人们提出了一种灵活的反射式超表面显示器，其中每个像素都可以在可见光谱内进行主动调谐。这项工作对于在柔性基板上开发低成本反射式显示器具有重要意义。新开发的打印技术将使大面积打印纳米结构的亚表面成为可能，以实现低成本制造。该项目为跨学科研究(包括集成光学、纳米制造和材料科学与工程)和研究生教育提供了一个很好的平台。这项研究将为丰富PI的研究生和本科教学提供令人振奋的科学内容。该计划将整合涵盖自闭症学生、K-12学生和其他代表性不足的少数族裔的外展活动。技术：本研究的主要目的是开发一种与角度无关的液晶反射亚表面，以实现像素的动态色彩调谐。动态像素的实现将减少对多个彩色子像素的需求，从而消除分层处理步骤，提高分辨率，并允许无与伦比的颜色控制。此外，该装置将通过新颖的液晶光学设计和多个电极，在单个液晶盒内独立调节颜色和灰度级。使用纳米压痕光刻技术在大面积上制造等离子体结构，可以绕过昂贵而繁琐的电子束或深紫外光光刻技术，用于制造许多先前报道的等离子体器件。这与超高速直接激光写入相结合，可以将不同尺寸的多个特征合并到母版图案中。单个器件母片可以包括任意像素化的等离子体亚表面、微观液晶单元间隔物和纳米尺度的液晶对准栅格。一张这样的母版可以制作100‘S聚合物印章，一张这样的邮票可以制作1000’S印花，而没有任何明显的图案退化。纳米压印光刻也被转化为卷到卷的处理，这表明整个制造过程可以按工厂标准进行规模。在主动可调谐等离子激元领域有许多需要理解和开发的地方。基于这一交叉学科的研究，实现了一种快速响应、角度无关的液晶超表面显示器，可以主动地改变其像素的颜色。深入分析了等离子体亚表面、液晶取向以及它们之间的相互影响。该系统的一个关键目标是设计一种基于特殊设计的金属-绝缘体-金属法布里-珀罗等离子体共振的广角亚表面，它不依赖于结构周期。虽然这些等离子体表面易于产生颜色，但由于固有的窄带吸收，无法产生显示器所需的深黑色状态。这项工作旨在将等离子体调色和液晶灰度态偏振光集成在同一液晶盒中。通过引入两组电极，通过一种新颖的器件设计，可以独立调节颜色和亮度。由于低温制造工艺与低玻璃化温度塑料兼容，所提出的器件可以很容易地在柔性衬底上制造。特殊的亚表面图案化允许设备的灵活性，而不会损害底层的纳米材料。这种方法不仅可以得到大面积的皮肤状全彩色显示元件，而且还可以提高一般等离子体超材料系统的有源可调谐能力。

Abstract:Non-technical: The range of colors and hues in the natural world are amazing, but perhaps even more astonishing is the ability of certain species to actively mimic them. Though the specific mechanisms are as varied as the species, each has a set of color producing cells which can span the visible spectrum. Within this vast set of creatures, cephalopods/octopi stand out as champions, who are adept to cover vast swaths of color within milliseconds. The key aspect of these color displays in nature is generation of color on a thin, flexible and conformally mapped surface whereas our manmade state-of-the art displays still remained rigid, brittle and bulky in nature. It's with cephalopods in mind that a flexible reflective metasurface display is proposed in which each pixel can be actively tuned across the visible spectrum. The proposed work is important for the development of low cost reflective displays on flexible substrates. The newly developed printing techniques will enable large area printing of nanostructured metasurfaces for low cost manufacturing. The program provides a good platform for interdisciplinary research (including integrated optics, nanofabrication and materials science and engineering) and graduate education. The research will generate exciting scientific content for enriching the PI's graduate and undergraduate teaching. The program will integrate outreach activities that span autistic students, K-12 students and other underrepresented minorities. Technical: The main focus of the proposed work is to develop an angle independent reflective metasurface with liquid crystals to achieve dynamic color tuning pixels. The implementation of dynamic pixels will reduce the need for multiple colored subpixels, thereby eliminating layered processing steps, increasing resolution, and allow unrivaled color control. Furthermore, the device will independently tune color and grey-scale within a singular liquid crystal cell through novel liquid crystal optics design and multiple electrodes. Using nanoimprint lithography to produce the plasmonic structure over large areas, one can bypass expensive and tedious electron-beam or deep-UV lithography techniques used in fabricating many previously reported plasmonic devices. This in combination with ultrafast direct laser writing, multiple features at varying size scales can be incorporated into the master patterns. A single device master can include arbitrarily pixelated plasmonic metasurface, microscopic liquid crystal cell spacers, and nanoscale liquid crystal alignment gratings. One such master can produce 100's of polymeric imprinting stamps, and one such stamp can produce 1000's of imprints without any noticeable pattern degradation. Nanoimprint lithography has also been translated to roll-to-roll processing which shows the entire fabrication process can be scaled to factory norms. There is much to understand and develop in the field of actively tunable plasmonics. A fast response, angle independent liquid crystal-metasurface based display which can actively shift the color of its pixels is achievable based on this interdisciplinary research. An in depth analysis of the plasmonic metasurface, liquid crystal orientation and how they influence each other will be studied. A key objective of the proposed system is to design a wide angle metasurface based on a specially engineered metal-insulator-metal Fabry-Perot plasmon resonance which doesn't depend on structure periodicity. While apt at producing color, these plasmonic surfaces cannot produce deep black states needed for displays due to intrinsic narrow band absorption. The proposed work intends to integrate plasmonic color tuning and liquid crystal grey state polarimetry within the same liquid crystal cell. By introducing two sets of electrodes, color and brightness can be independently tuned through a novel device design. The proposed device can readily be fabricated on flexible substrates as the low temperature fabrication process is compatible with low glassing temperature plastics. Special metasurface patterning allows device flexibility without damage to the underlying nanopatterns. Such an approach can not only lead to large area skin-like full color display elements, but can also improve the active tunability of general plasmonic metamaterial systems.