Nanochemical Control of Crystal Structure and Heterostructuring in Metal Chalcogenides

金属硫化物和相关化合物是用于广泛应用的有用材料，包括太阳能电池、热电制冷器、显示器、数据存储和催化。为了推进这些和其他应用，重要的是能够以允许精确控制定义其属性的特征的方式设计和制造材料。在该项目中，由材料研究部门的固态和材料化学计划支持，PI和他的团队化学操纵金属硫化物和相关化合物的纳米颗粒，以合理和可控的方式生产新材料。为此，硫化物材料中的金属阳离子在温和的反应条件下被其他金属阳离子取代，以改变组成，而不显著改变原子的排列。当颗粒中的所有金属阳离子被替换时，可以产生新的化合物，这提供了一种合理靶向不能通过现有方法制备的材料的方法。通过仅替换一部分金属阳离子，形成的颗粒包含通过界面连接在一起的原始材料和新材料。通过在同一颗粒上多次进行这种部分置换反应，产生具有许多不同材料和界面的复杂颗粒。PI和他的团队正在研究这些完全和部分阳离子交换反应，以更好地了解有助于形成目标产品的因素，以便研究人员可以更有效地设计和制造预计有用的新材料，但使用现有知识无法轻松制造。PI和他的团队在本科生实验室中使用这些反应，向学生介绍设计和制造材料的新思维方式，并通过区域本科生研究网络与当地大学的教师和学生合作。技术概述该项目由材料研究部的固态和材料化学项目支持，提供了使用阳离子交换反应设计和合成金属硫属化物纳米颗粒的新能力。在这些反应中，胶体金属硫属化物纳米颗粒中的阳离子被来自溶液的阳离子取代，同时保持阴离子骨架。因此可以保留晶体结构，并且阳离子交换反应可以用于合理地靶向亚稳相（通过完全阳离子交换）和复杂的异质结构纳米颗粒（通过顺序的部分阳离子交换）。PI和他的团队研究金属硫族化物纳米颗粒的阳离子交换反应，以了解它们如何进行和控制，以使可访问系统的范围和复杂性多样化，并获得具有所需结构和特性的新材料。这对于拓展金属硫属化合物纳米材料的广阔应用空间具有重要意义。在该项目中，模型系统的研究提供了对前体纳米颗粒的晶体结构如何在完全阳离子交换后保留在产品中的见解，揭示了合理靶向亚稳相的指导方针。顺序部分阳离子交换反应的补充研究揭示了有用的设计规则，合理地合成一个库的异质结构的纳米粒子包含许多接口和材料。使用这些阳离子交换反应合成的条纹纳米棒超晶格作为研究低温扩散和结晶的纳米调制平台。将一个交换项目整合到本科化学实验室，向学生介绍固态，纳米材料和无机反应化学的现代方面。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical SummaryMetal sulfides and related compounds are useful materials for a wide range of applications, including solar cells, thermoelectric refrigerators, displays, data storage, and catalysis. To advance these and other applications, it is important to be able to design and make materials in ways that allow precise control over the features that define their properties. In this project, which is supported by the Solid State and Materials Chemistry program in the Division of Materials Research, the PI and his group chemically manipulate nanoscale particles of metal sulfides and related compounds to produce new materials in a rational and controllable way. To do this, metal cations in the sulfide materials are replaced with other metal cations under mild reaction conditions to change the composition without significantly changing the arrangements of the atoms. New compounds can be produced when all of the metal cations in a particle are replaced, which provides an approach for rationally targeting a material that cannot be made by established methods. By replacing only a fraction of the metal cations, the particles that are formed contain both the original material and a new material, joined together through an interface. By performing this partial replacement reaction multiple times on the same particle, complex particles are produced that have many different materials and interfaces. The PI and his group are studying these complete and partial cation exchange reactions to better understand the factors that contribute to the formation of targeted products so that researchers can more efficiently design and make new materials that are predicted to be useful, but that cannot be made easily using current knowledge. The PI and his group use these reactions in undergraduate laboratories to introduce students to new ways of thinking about designing and making materials and also partner with faculty and students from local colleges through a regional undergraduate research network.Technical SummaryThis project, which is supported by the Solid State and Materials Chemistry program in the Division of Materials Research, provides new capabilities for the design and synthesis of metal chalcogenide nanoparticles using cation exchange reactions. In these reactions, cations in a colloidal metal chalcogenide nanoparticle are replaced by cations from solution while maintaining the anion framework. Crystal structure can therefore be preserved, and cation exchange reactions can be used to rationally target metastable phases (through complete cation exchange) and complex heterostructured nanoparticles (through sequential partial cation exchange). The PI and his group study cation exchange reactions of metal chalcogenide nanoparticles to understand how they proceed and can be controlled, to diversify the scope and complexity of accessible systems, and to access new materials with desired structures and properties. This is important for advancing the broad application space of metal chalcogenide nanomaterials. In this project, studies of model systems provide insights into how the crystal structure of a precursor nanoparticle can be retained in the product after complete cation exchange, revealing guidelines for rationally targeting metastable phases. Complementary studies of sequential partial cation exchange reactions uncover useful design rules for rationally synthesizing a library of heterostructured nanoparticles containing many interfaces and materials. Striped nanorod superlattices synthesized using these cation exchange reactions serve as a nanomodulated platform for studying low-temperature diffusion and crystallization. Integration of a nanocrystal cation exchange project into an undergraduate chemistry laboratory is introducing students to modern aspects of solid-state, nanomaterials, and inorganic reaction chemistry. Expansion of a regional undergraduate research network partners the PI and his group with faculty and students from local colleges who are also interested in metal chalcogenides and related nanomaterials.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.