SusChEM: Synthesis and Structure-Property Elucidation of Direct-Bandgap Group IV Alloy Nanocrystals for Optoelectronic Applications

非技术描述：仅基于低成本、无毒和丰富的IV族元素(如硅)生产高效光电材料具有挑战性，因为IV族元素在电子-光子转换过程中的效率低于广泛使用的光电材料。该项目利用独特的纳米尺寸限制效应和与锡的合金化来生产具有优异光吸收和发射性能的硅-锡、锗-锡和硅-锗-锡纳米晶。合作团队支持合成工作以及先进的光学表征和理论计算，以获得对新兴材料属性的深入了解，并提高光电性能。跨学科研究为研究生和本科生提供了从智能材料设计到设备测试的有价值的培训。其他教育和外展活动包括K-12纳米科学外展努力以及让代表性不足的高中生和妇女参加暑期研究活动。技术说明：具有直接带隙的IV族半导体基合金是光电子材料领域长期追求的目标。然而，这一努力主要受到材料设计和合成方面的挑战，以及锡在硅和锗中的有限溶解度的阻碍。该项目利用量子限制效应和锡纳米合金化方法来制备纳米晶形式的直接带隙IV类合金。纳米晶体的尺寸和组成可调，这导致了更宽的有效禁带和优异的光物理性能。例如，通过一种创新的高温胶体合成方法，可以获得形貌和成分可控、远远超过锡在块状Si或Ge中的混溶极限的GeSn3、SiSn3和GeSiSn3种合金纳米晶。利用稳态和超快吸收发射光谱，在计算模拟的指导下，系统地研究了锡组分和量子限制效应对间接带隙到直接带隙跃迁的影响。电子结构计算被用来建立对限制诱导的准直接带隙行为、成分诱导到真正的直接带隙的转变以及与表面/缺陷相关的光物理性质的影响的基本理解。由分子金属硫化物连接的选定的合金纳米晶被用低成本的基于溶液的加工方法沉积在不同的衬底上，以展示它们在光电子学方面的潜力。

Non-technical Description: The production of high-efficiency optoelectronic materials based solely on low-cost, non-toxic, and abundant Group IV elements such as silicon is challenging as Group IV elements are less efficient in electron-photon conversion process compared to the widely used optoelectronic materials. This project utilizes the unique nanoscale size confinement effects and alloying with tin to produce silicon-tin, germanium-tin, and silicon-germanium-tin nanocrystals that exhibit superior light absorption and emission properties. The collaborative team supports the synthetic efforts along with advanced optical characterization and theoretical calculations to garner a deep understanding of the emerging materials properties and enhance the optoelectronic performance. The interdisciplinary research provides valuable training to the graduate and undergraduate students in the areas from smart material design to device testing. Other education and outreach activities include K-12 nanoscience outreach efforts and involving the under-represented high school students and women in summer research activities. Technical Description: Group IV semiconductor-based alloys with a direct bandgap are a long-sought goal in the field of optoelectronic materials. However this effort has been hindered primarily by the challenges in material design and synthesis, as well as the limited solubility of Sn in Si and Ge. This project utilizes both the quantum confinement effect and the Sn nano-alloying approach to produce direct bandgap Group IV alloys in nanocrystal form. The nanocrystals exhibit size and composition tunability that leads to wider effective bandgaps and superior photophysical properties. For example, GeSn, SiSn, and GeSiSn alloy nanocrystals with well controlled morphology and composition, far beyond the miscibility limit of Sn in bulk Si or Ge, are achieved via an innovative high-temperature colloidal synthesis method. Sn composition and quantum confinement effects on the indirect-to-direct bandgap transition are systematically investigated using steady-state and ultrafast absorption and emission spectroscopy, guided by computational simulations. The electronic structure calculations are used to establish a fundamental understanding of confinement-induced quasi direct bandgap behavior, composition-induced transition to true direct-gap, and surface/defect related effects on photophysical properties. Selected alloy nanocrystals linked by molecular metal chalcogenides are deposited on various substrates using low-cost, solution-based processing methods to demonstrate their potential for optoelectronics.