Origins of Unique Optical Properties in Intermediate Band Nanocrystals

第一部分：当金属缩小到纳米尺寸时，它可以获得更大的块状材料所不存在的新的光学吸收特性。这些被称为等离子体激元的新特性改变了金属的颜色，使通常预期的颜色变得不同，就像纳米级的金胶体显示为红色。有趣的是，有一些非金属（半导体）在纳米尺度上表现出同样的效果，但这些效果的起源和尺寸依赖性还没有得到很好的理解。该项目由材料研究部的固态和材料化学项目支持，采用最先进的X射线表征方法来阐明半导体纳米晶体的未回答的结构-性质问题。该项目正在研究几种假设，以了解半导体等离子体的性质，包括激发的电子电荷如何在材料中移动以及这些电荷如何受到纳米尺寸的影响。为了实现这些目标，PI正在合成纳米晶体，并通过量子限制尺寸机制用包括X射线共振非弹性X射线散射（RIXS）测量在内的方法对其进行表征。这项工作的产品将有利于社会，因为这些纳米晶体具有光伏应用的潜力，或者它们可能导致其他人，如激光照射后肿瘤细胞湮灭的光热治疗。这些纳米晶体还可以导致光的高频、全光调制和开关。伴随的推广计划通过借阅等离子体演示套件激发了公众对有趣材料化学的兴奋。此外，PI通过康奈尔大学的一个项目指导学生的颜色。第2部分：技术总结某些金属硫族化物纳米晶体具有维持吸收特征的能力，这种吸收特征类似于通常在金属纳米晶体中看到的局部表面等离子体共振（LSPR）。然而，这些材料中这些特征的电子起源并不完全清楚。一种理论认为，带间电子跃迁导致的功能。该项目由材料研究部的固态和材料化学项目支持，采用最先进的X射线表征方法来确定量子限制对半导体纳米晶体的电子能带和光学吸收曲线的影响。中心假设是带之间的跃迁控制吸收特征，并且可以受到量子限制的影响。为了验证这些假设，该项目正在使用同步加速器X射线光谱学，包括硬X射线共振非弹性X射线散射（RIXS）测量和分析，通过量子限制范围的半导体。该团队正在合成一系列尺寸的单分散纳米晶体，用X射线光谱和光吸收对其进行表征，并将信息与电子结构模型相关联，以阐明基本的结构-性质关系。这项工作的产品将有利于社会，因为这些纳米晶体具有光伏应用的潜力，或者它们可能导致其他人，如激光照射后肿瘤细胞湮灭的光热治疗。这些纳米晶体可能导致光的高频、全光调制和开关。伴随的推广计划通过借阅等离子体演示套件激发了公众对有趣材料化学的兴奋。此外，PI通过康奈尔大学的一个项目指导有色人种学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYWhen a metal is shrunk down to nanometer sizes, it can obtain new optical absorption features that don’t exist in bigger, bulk materials. These new features, called plasmons, change the color of the metal, so that the commonly expected color becomes something different, like nanoscale gold colloids appearing red. Interestingly, there are some non-metals (semiconductors) that show this same effect at the nanoscale, but the origin and size-dependence of these effects is not well-understood. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, employs state-of-the-art x-ray characterization methods to elucidate unanswered structure-property questions of semiconducting nanocrystals. This project is examining several hypotheses to understand the nature of the semiconductor plasmons, including how excited electronic charges move in the materials and how these are affected by nano-sizing. To accomplish the goals, the PI is synthesizing nanocrystals, and characterizing them with methods including x-ray resonant inelastic x-ray scattering (RIXS) measurements through the quantum confinement size regime. The products of this work will benefit society because these nanocrystals have the potential for photovoltaic applications or they could lead to others such as photothermal therapy of tumor cell annihilation upon laser irradiation. These nanocrystals could also lead to high-frequency, all-optical modulation and switching of light. The accompanying outreach programs invigorate the public excitement about interesting Materials Chemistry through Lending Library demonstration kits on plasmonics. Furthermore, the PI mentors students of color through a program at Cornell.PART 2: TECHNICAL SUMMARYCertain metal chalcogenide nanocrystals have the ability to sustain absorption features that resemble localized surface plasmon resonances (LSPRs) typically seen in metal nanocrystals. The electronic origin of these features in these materials, however, is not completely understood. One theory is that interband electronic transitions lead to the features. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, employs state-of-the-art x-ray characterization methods to determine the influence of quantum confinement on the electronic bands and optical absorption profile of semiconducting nanocrystals. The central hypotheses are that transitions between bands control the absorption features and can be affected by quantum confinement. To test these hypotheses, this project is using synchrotron x-ray spectroscopy, including hard x-ray resonant inelastic x-ray scattering (RIXS) measurements and analysis, of nanocrystal semiconductors through the quantum confinement range. The team is synthesizing a size series of monodisperse nanocrystals, characterizing them with x-ray spectroscopy and optical absorption, and correlating the information with electronic structure models, to elucidate fundamental structure-property relationships. The products of this work will benefit society because these nanocrystals have the potential for photovoltaic applications or they could lead to others such as photothermal therapy of tumor cell annihilation upon laser irradiation. These nanocrystals could lead to high-frequency, all-optical modulation and switching of light. The accompanying outreach programs invigorate the public excitement about interesting Materials Chemistry through Lending Library demonstration kits on plasmonics. Furthermore, the PI mentors students of color through a program at Cornell.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.