Low-Dimensional Si-Sn and Si-Ge-Sn Nanoalloys as High-Efficiency, Direct-gap Nanostructures for Visible to Infrared Optoelectronics.

非技术描述：利用地球上丰富的元素开发高效的发光元件，以取代目前用于光学和电子技术的稀有和昂贵的材料是势在必行的。然而，潜在的低成本和无毒的候选材料，如硅，在其常规布置中显示出极低的电光转换效率。该项目整合了纳米级硅和锡合金化中独特的量子效应，以生产尺寸和成分可调的硅-锡和硅-锗-锡纳米粒子，具有优异的光吸收和发射性能，适用于可见光到红外应用。该研究小组将材料合成工作与计算计算以及先进的光学和结构表征相结合，以全面了解纳米级合金的物理和光学性质以及稳定性。这项研究的合作性质为研究生和本科生提供多学科的培训和指导，以发展材料设计和合成、计算化学、纳米科学和高级光学光谱学方面的技能。里士满公立学校的暑期活动让K-12年级的学生接触到尖端材料研究项目，并开发了适合年龄的材料科学课程模块，影响了数百名代表不足的少数族裔学生。技术描述：第四族半导体合金具有高效率的直接能隙发射，在实现硅基光电子技术方面获得了极大的兴趣。然而，锡在硅和锗中的窄能隙和极低的溶解度阻碍了它的制备和在可见光到红外光电子研究中的广泛应用。该项目利用量子限制效应、锡纳米合金化和溶液相合成的协同作用，制备出尺寸和成分可调的亚稳态硅锡和硅锗锡合金和量子点(量子点)，并在可见光到红外光谱范围内具有优异的吸收和发射性能。通过创新的胶体化学方法制备了一系列不同尺寸和成分的单分散合金。在第一性原理电子结构和热力学稳定性计算的指导下，通过稳态和时间分辨的光致发光和泵浦/探测的瞬时吸收光谱，深入系统地研究了锡的合金化和量子限制对光学性质的影响。实验的目的是探测硅的限制和成分诱导的直接禁带，暗激子态和亮激子态及其对纳米晶体尺寸和组成的依赖，以及涉及量子点核心、表面和它们的混合态的载流子弛豫机制，以优化辐射效率。这些后来的努力，加上纳米晶体合金的溶液处理和高热稳定性和光学稳定性，使未来能够设计高效率的硅基光电子产品。该奖项反映了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: Developing high-efficiency light emitters from earth abundant elements is imperative to replace rare and expensive materials currently used in optical and electronic technologies. The prospective low-cost and non-toxic candidates such as silicon, however, show extremely low electricity to light conversion efficiency in their conventional arrangement. This project integrates the unique quantum effects in nanoscale silicon and tin alloying to produce silicon-tin and silicon-germanium-tin nanoparticles with size and composition tunable superior light absorption and emission properties for visible to infrared applications. The research team combines the material synthesis efforts with computational calculations and advanced optical and structural characterizations to garner a comprehensive understanding of the physical and optical properties and stability of nanoscale alloys. The collaborative nature of this research provides multidisciplinary training and mentoring of graduate and undergraduate students, to develop skills in materials design and synthesis, computational chemistry, nanoscience, and advanced optical spectroscopy. The summer outreach to Richmond Public Schools exposes K-12 students to cutting-edge materials research projects and develops age-appropriate materials science curricular modules, impacting hundreds of underrepresented minority students. Technical Description: Group IV semiconductor alloys that show high efficiency direct-gap emission have gained exceptional interest for realizing Si-based optoelectronic technologies. However, the narrow energy gaps and the extremely low solubility of Sn in Si and Ge hindered their fabrication and widespread application in visible to infrared optoelectronic studies. This project exploits the concerted influences of quantum confinement effects, Sn nano-alloying, and solution-phase synthesis to produce metastable Si-Sn and Si-Ge-Sn alloys and quantum dots (QDs) with size and composition tunable direct energy gaps and superior absorption and emission properties across visible to infrared spectrum. A series of monodisperse alloys having various sizes and compositions are produced by innovative colloidal chemistry methods. The influences of Sn alloying and quantum confinement on optical properties are thoroughly and systematically probed via steady-state and time-resolved photoluminescence and pump/probe transient absorption spectroscopy, guided by first-principles electronic structure and thermodynamic stability calculations. Experiments are designed to probe confinement- and composition-induced direct-gaps of silicon, dark vs. bright excitonic states and their dependence on nanocrystal size and composition, and carrier relaxation mechanisms involving QD core, surface, and their hybrid states to optimize the radiative efficiency. These later efforts along with solution processing and high thermal and optical stability of nanocrystal alloys enable the future design of high-efficiency, silicon-based optoelectronics.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.