Equilibrium thermodynamics of semiconductor nanocrystal ligand and ion exchange via calorimetry

通过量热法研究半导体纳米晶体配体和离子交换的平衡热力学这项资助支持南卡罗来纳大学的Andrew Greytak博士通过使用等温滴定量热法（ITC）来提高对胶体量子点化学的理解。纳米晶体量子点（QDs）是由半导体材料组成的可溶的纳米级粒子。量子点可以具有明亮和大小可调的荧光，目前在平板显示器和生物成像中有应用。量子点对于解决方案可处理的太阳能电池也很有兴趣，可以持续缩放以满足全球能源需求。然而，量子点太阳能电池的性能仍然远远低于理论极限。由于QD表面的结构差异，在大小和组成相似的QD样品中，荧光性能存在相当大的差异。将新兴的分析方法和理论模型与具有理想表面性质的稳定量子点的设计联系起来是很重要的。该项目采用了一种新的方法，通过测量量子点发生化学转化时释放或吸收的热量，来发展对量子点结构和化学的基本理解。ITC方法有望广泛应用于半导体纳米晶体科学。这项技术在这里被用于推进知识，可能导致改进量子点太阳能电池的性能。格雷塔克博士在南卡罗来纳大学的研究项目涉及高中、本科和研究生阶段的学生。他在化学教育方面表现出了全国公认的领导能力。他还担任南卡罗来纳州米德兰兹地区高中生科学博览会的首席化学评委。胶体纳米晶体（NCs）是由一个晶体核和一个界面层组成的复杂组合，在一定的时间内，它可以与溶液和其他纳米晶体交换物质。拥有一组允许不同NC样品进行分析的指标是非常有利的，这样它们就可以以足够的精度进行表征，以预测合成和物理行为。对系统进行足够丰富的实验描述以约束开始捕捉nc -配体和配体-配体相互作用复杂性的模型也是偶然的。在这个项目中，Greytak博士被支持测量与无水溶剂中NC量子点（QD）表面的代表性配体交换和离子交换反应相关的平衡常数、焓、当量和相互作用项。纯化技术，如凝胶渗透色谱被用来提供量子点在一个明确的初始状态。从这些类型的测量中获得的知识代表了量子点化学的根本进步，加速了更高性能和更复杂的量子点组件和溶液结构的发现。特别是，通过提高对配体交换和离子交换反应的理解，可以扩展基于量子点的光伏电池的性能和材料范围。该项目还为研究生和本科生提供了研究培训机会，他们正在建立纳米晶体制备化学，量热法和其他分析技术方面的专业知识，这些技术对于将纳米科学领域推进到实用技术是必要的。格雷塔克博士一直积极通过科学倡导网络和美国化学学会的项目SEED计划扩大研究参与。他还发起了一年一度的南加州大学可持续发展研究与实践展示会，为研究小组、研究生和本科生以及工作人员创造了一个焦点，让他们相互教育研究参与、创业、综合学习和推广的机会，以提高地区和国家的竞争力。

Equilibrium thermodynamics of semiconductor nanocrystal ligand and ion exchange via calorimetryThis grant supports Dr. Andrew Greytak of the University of South Carolina in the effort to develop an improved understanding of colloidal quantum dot chemistry through the use of isothermal titration calorimetry (ITC). Nanocrystal quantum dots (QDs) are soluble, nanometer-scale particles composed of semiconductor materials. QDs can have bright and size-tunable fluorescence, and have current applications in flat-panel displays and in bio-imaging. QDs are also of interest for solution-processable solar cells that can be scaled sustainably to meet worldwide energy needs. However, the performance of QD solar cells remains far below the theoretical limit. There is considerable variability in fluorescence performance among QD samples of similar size and composition, due to structural differences at the QD surface. It is important to connect emerging analytical methods and theoretical models to the design of stable QDs with desirable surface properties. This project takes a new approach to developing a fundamental understanding of QD structure and chemistry by measuring the heat that is emitted or absorbed when chemical transformations of QDs take place. The ITC approach is expected to be broadly applicable to semiconductor nanocrystal science. The technique is being used here to advance knowledge that could lead to improved QD solar cell performance. Dr. Greytak's research program at the University of South Carolina engages students at the high school, undergraduate, and graduate levels. He has demonstrated nationally-recognized leadership in chemistry education. He also serves as the head judge for chemistry at the South Carolina Midlands Regional Science Fair for high school students.Colloidal nanocrystals (NCs) are complex assemblies of a crystalline core and an interfacial layer that, given time, may exchange matter with the solution and other NCs. It is highly advantageous to have a set of metrics that allows different NC samples to be profiled, both so that they can be characterized with sufficient precision to predict synthetic and physical behaviors. It is also adventitious to have a sufficiently rich experimental description of the system to constrain models that begin to capture the complexity of NC-ligand and ligand-ligand interactions. In this program, Dr. Greytak is being supported to measure equilibrium constants, enthalpies, equivalencies, and interaction terms associated with representative ligand exchange and ion exchange reactions at NC quantum dot (QD) surfaces in anhydrous solvents. Purification techniques such as gel permeation chromatography are used to provide QDs in a well-defined initial state. The knowledge acquired from these types of measurements represents a fundamental advance in QD chemistry that hastens the discovery of higher-performing and more sophisticated QD assemblies and solution structures. In particular, the performance and material scope of QD-based photovoltaics can be expanded through improved understanding of ligand exchange and ion exchange reactions. This project also provides research training opportunities to graduate and undergraduate students, who are building expertise in nanocrystal preparative chemistry, calorimetry, and other analytical techniques that are necessary to advance the field of nanoscience into practical technologies. Dr. Greytak has been active in broadening research participation through the Scientific Advocate Network and the American Chemical Society's Project SEED program. He has also initiated an annual USC Sustainability Research and Practice Showcase that creates a focal point for research groups, graduate and undergraduate students, and staff to educate each other about opportunities for research participation, entrepreneurship, integrative learning, and outreach that advances regional and national competitiveness.