Collaborative Research: Atomic-Scale Hybrids, Tuning the IR Dielectric Function through Superlattice Design

非技术描述：红外光谱范围提供了大量的技术机会，包括热成像、透过尘埃或云层的能力、用于医疗诊断的化学识别和危险识别，仅举几例。与玻璃等材料以极低的成本提供极高性能的可见光谱范围不同，红外光学元件通常对水敏感，在可见光下不透明，昂贵和/或易碎。因此，寻找能够为下一代红外光学和光源提供基础的替代材料或材料平台是非常必要的。在红外线内，许多极性材料，如碳化硅，表现出可以用光激发的晶体振动。这提供了将长波长红外光压缩到纳米级长度的机会，从而有可能显著减小红外光学元件的尺寸。然而，这些晶体振动是特定于材料的，因此，在所需的红外频率范围内找到合适的材料是具有挑战性的。该项目研究由改变堆积的薄层组成的新型杂化材料，该材料具有改变其晶体振动的潜力，以努力改变其相应的红外特性。这项合作研究试图了解当薄膜厚度减少到原子级别的厚度时，这些振动是如何受到影响的，并涉及一个由材料科学家、物理学家和机械工程师组成的多学科团队，以帮助实现被认为是“晶体杂化”的设计者红外材料。该项目培训研究生和本科生半导体生长、红外光谱以及复杂固体的表征和理论描述。技术描述：该项目寻求开发一种名为晶体杂化(XHs)的新材料类别，该材料有望实现用户定义的红外(IR)光学材料。这些新材料可以作为下一代红外光学元件、光源和探测器元件的基础。这个协作项目的一个主要研究目标是发现合理设计XH以满足给定应用空间的理论指导原则。XH方法试图在组成多层超晶格的原子薄层内修正极性光学声子。在这些结构中，层的厚度将小于声子平均自由程，从而导致振动态的量子限制和频率调谐。此外，超晶格结构中多个界面处的修饰键引入了新的界面声子。这些修改的声子性质直接影响材料的红外响应，因为光学声子主导着极性晶体的红外行为。这项研究的重点是由近晶格匹配的III-V半导体InAs、GaSb和AlSb组成的超晶格，它消除了应变等外部效应，并允许进行良好控制的实验。该项目涉及一群不同的研究生和本科生，他们接受过半导体生长基础知识、红外光谱、纳米材料的理论和第一性原理计算方面的培训，使他们能够在纳米光子学研究的前沿工作。材料科学家、物理学家和工程师之间的合作扩大了这项工作的影响。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。

Non-Technical Description: The infrared spectral range offers a wealth of technological opportunities, including thermal imaging, ability to see through dust or clouds, chemical identification for medical diagnostics and hazard identification, to name a few. Unlike the visible spectral range where materials such as glass provide exceptionally high performance at extremely low cost, the infrared optical components are typically sensitive to water, opaque in the visible, expensive and/or brittle. Thus, identifying alternative materials or material platforms that can provide the basis of next generation infrared optics and light sources is highly desired. Within the infrared, many polar materials, such as silicon carbide, exhibit crystal vibrations that can be excited using light. This provides opportunities to compress long-wavelength infrared light to nanometer scale lengths, offering the potential to significantly reduce the size of infrared optics. However, these crystal vibrations are material specific and thus, finding the right material in the desired infrared frequency range is challenging. This project investigates novel hybrid materials composed of altering stacking thin layers with potential to modify their crystal vibrations in an effort to change its corresponding infrared properties. The collaborative research seeks to understand how these vibrations are influenced when the layer thickness is reduced to atom-scale thicknesses, and involves a multidisciplinary team of a material scientist, physicist and mechanical engineer to aid in realizing designer infrared materials deemed 'crystalline hybrids'. The project trains graduate and undergraduate students in semiconductor growth, infrared spectroscopy and characterization and theoretical descriptions of complex solids.Technical Description: This project seeks to develop a new class of materials called Crystalline Hybrids (XHs) that offers the promise for realizing user-defined infrared (IR) optical materials. These novel materials can serve as the basis of next generation IR optical components, sources and detector elements. A primary research goal of this collaborative program is to discover theory-guided principles for the rational design of XHs to meet a given application space. The XH approach seeks to modify polar optic phonons within atomically thin layers comprising a multilayered superlattice. Within these structures, the layer thicknesses will be less than the phonon mean-free-path, resulting in quantum confinement and frequency tuning of the vibrational state. Furthermore, the modified bonding at the multiple interfaces within the superlattice structures introduce new interfacial phonons. These modified phonon properties directly influence the infrared response of the material, as it is optic phonons that dominate the IR behavior of polar crystals. The research is focused on superlattices comprised of the near-lattice matched III-V semiconductors InAs, GaSb and AlSb, which eliminate external effects like strain and allow well-controlled experiments to be performed. The project involves a diverse group of graduate and undergraduate students who are trained in the basics of semiconductor growth, IR spectroscopy, theory and first-principles calculations of nanomaterials, enabling them to work at the frontiers of nanophotonics research. The collaboration between material scientists, physicists and engineers broadens the impact of this work.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.