Nanochemical Control of Crystal Structure and Heterostructuring in Metal Chalcogenides

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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.