Integrated Research and Education on Metal Alloys with On-Demand Optical Response

由于需要提高计算速度，研究人员不断寻找超越当今微电子工业极限的方法。另一种选择是使用光而不是电子。因此，科学家和工程师一直在开发基于金属而不是半导体的设备，这种设备可以将光压缩到极小的结构中（不到人类头发厚度的千分之一，即纳米级）。这些所谓的等离子体器件的性能在很大程度上取决于金属的光学响应，例如，有多少光被传输、反射和吸收。迄今为止，金属构件是由硬币时代的金属制成的，如Au， Ag和Cu，具有明确的颜色，因此具有预先确定的光学性质。为了克服纯金属用于纳米级等离子体的现有限制，马里兰大学的Leite小组将研究混合金属或合金的光学响应。为此，他们将通过混合Au、Ag、Cu和Al来设计和制造合金薄膜和纳米级结构，并使用一套表征工具来模拟/测量它们在光照下的行为。控制合金金属的光学特性对纳米光子学、光伏和传感器等领域具有重要意义。该项目将涉及来自STEM中代表性不足群体的高中生和本科生，通过为他们提供在材料科学领域进行研究的机会，帮助他们在科学和技术领域获得领先的职业生涯。此计划的科学成果将以生动的插图广泛传播，向公众推广科学和工程。技术综述纳米光子器件的未来发展在很大程度上取决于组成结构的金属构件的介电功能。本提案的研究目标是开发和实现一类具有可调谐光学特性（即介电功能）的新型金属薄膜和纳米结构。为此，Leite团队将把计算材料科学与实验研究结合起来，设计和制造由Ag、Au、Cu和Al组成的合金薄膜和纳米结构。这些合金的光学响应将通过椭偏和近场光学显微镜来表征。合金纳米颗粒将应用于太阳能电池，通过增加半导体内的光吸收来改善器件性能。这项研究将通过结合两个几乎正交的领域，冶金学和等离子体动力学，推动基础材料科学的发展，使金属合金纳米结构的设计和制造具有在自然界中未发现的随需应变光学响应。这些光学材料的发展可能会对未来的纳米光子器件产生潜在的变革性影响，使其能够完全控制其介电功能，从而创造优越的光学性能。虽然多个实验已经证明了纯金属如何在太阳能电池中捕获光，但目前还没有使用合金的数值或实验演示。

NON-TECHNICAL SUMMARYMotivated by the need for improved computational speed, researchers are constantly searching for ways of surpassing the limit of today's microelectronics industry. One alternative is to use light instead of electrons. Thus, scientists and engineers have been developing devices based on metals instead of semiconductors, which can squeeze light into extremely small structures (less than one thousandth the thickness of a human hair, i.e. at the nanoscale). The performance of these so-called plasmonic devices heavily depends on the optical response of the metals, e.g., how much light is transmitted, reflected and absorbed. To date, the metallic building blocks are made of coin age metals, such as Au, Ag and Cu, with well defined color and, thus, pre-determined optical properties. In order to overcome the existing limitations of pure metals used in nanoscale plasmonics, the Leite group at the University of Maryland will investigate the optical response of mixed metals, or alloys. For that, they will design and fabricate alloyed thin films and nanoscale structures by mixing Au, Ag, Cu and Al, and model/measure their behavior upon illumination by using a set of characterization tools. Controlling the optical properties of alloyed metals can tremendously benefit the fields of nanoscale photonics, photovoltaics, and sensors. This project will involve high school and undergraduate students from under-represented groups in STEM to help them secure leading careers in science and technology by providing them with the opportunity to perform research in materials science. The scientific findings from this project will be widely disseminated through visually appealing illustrations, to promote science and engineering to the general public. TECHNICAL SUMMARYThe future development of nanophotonic devices critically depends on the dielectric function of the metallic building blocks composing the structures. The research objective of this proposal is to develop and implement a new class of metallic thin films and nanostructures with tunable optical properties, i.e., dielectric functions. For that, the Leite group will combine computational materials science with experimental research to design and fabricate alloyed thin films and nanostructures formed by Ag, Au, Cu and Al. The optical response of these alloys will be characterized by ellipsometry and near-field optical microscopy. Alloyed nanoparticles will be applied to solar cells to improve the device performance by increasing light absorption within the semiconductor. This research will advance fundamental materials science by combining two almost orthogonal fields, metallurgy and plasmonics, enabling the design and fabrication of metal-alloyed nanostructures with on-demand optical response not found in nature. The development of these optical materials may have a potentially transformative effect on future nanophotonic devices by enabling the complete control of their dielectric function and, therefore, creating superior optical performance. While multiple experiments have demonstrated how pure metals can be used to trap light inside solar cells, there are neither numerical nor experimental demonstrations using alloys.