Flexible Reflective Metasurface Displays

摘要：非技术：自然界的色彩和色调范围令人惊叹，但也许更令人惊讶的是某些物种主动模仿它们的能力。虽然具体的机制因物种而异，但每个物种都有一组可以跨越可见光谱的颜色产生细胞。在这一庞大的生物群中，头足类/章鱼作为冠军脱颖而出，它们擅长在几毫秒内覆盖大片的颜色。在自然界中，这些彩色显示器的关键方面是在薄、柔性和保形映射表面上生成颜色，而我们人造的最先进的显示器在自然界中仍然保持刚性、脆性和笨重。考虑到头足类动物，我们提出了一种灵活的反射超表面显示器，其中每个像素都可以在可见光谱中进行主动调节。这项工作对于开发低成本的柔性基板反射显示器具有重要意义。新开发的打印技术将使纳米结构超表面的大面积打印成为可能，从而降低制造成本。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良好的平台。这项研究将为学院的研究生和本科生教学提供令人兴奋的科学内容。该项目将整合自闭症学生、K-12学生和其他未被充分代表的少数族裔的外展活动。技术方面：本研究的重点是开发一种与液晶无关的反射超表面，以实现动态色彩调谐像素。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单元内独立调节颜色和灰度。利用纳米压印光刻技术生产大面积等离子体结构，可以绕过昂贵且繁琐的电子束或深紫外光刻技术，这些技术通常用于制造许多先前报道的等离子体器件。这与超快直接激光书写相结合，不同尺寸尺度的多种特征可以合并到主图案中。单个主器件可以包括任意像素化等离子体超表面、微观液晶单元间隔和纳米级液晶对准光栅。一个这样的大师可以生产100个聚合物印记邮票，一个这样的邮票可以生产1000个印记而没有任何明显的图案退化。纳米压印技术也被转化为卷对卷加工，这表明整个制造过程可以按工厂标准进行缩放。在主动可调谐等离子体领域还有很多需要理解和发展的地方。基于这一跨学科的研究，实现了一种快速响应、角度无关的液晶超表面显示，该显示可以主动改变其像素的颜色。对等离子体超表面、液晶取向及其相互影响进行了深入分析。该系统的一个关键目标是设计一个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超表面，该超表面不依赖于结构周期。虽然易于产生颜色，但由于固有的窄带吸收，这些等离子体表面不能产生显示所需的深黑色状态。本研究的目的是将等离子体颜色调谐和液晶灰态偏振技术整合到同一个液晶电池中。通过引入两组电极，颜色和亮度可以通过一种新颖的装置设计独立调节。所提出的装置可以容易地在柔性基板上制造，因为低温制造工艺与低玻璃化温度塑料兼容。特殊的超表面图案允许设备的灵活性，而不会损坏底层的纳米图案。这种方法不仅可以产生大面积的皮肤状全彩显示元件，而且可以提高一般等离子体超材料系统的主动可调性。

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.