Collaborative Research: Thermochemistry and Chemical Kinetics of Halide-driven Crystal Structure Control of Manganese and Lanthanide Chalcogenide Nanocrystals

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Drs. Emil Hernández-Pagán of the University of Delaware, Kristina Lilova of Arizona State University, and Robert Wexler of Washington University in St. Louis will investigate how the presence of halides (chloride, bromide, and iodide) influences the final arrangements of atoms (crystal structure) in the synthesis of certain classes of nanoparticles. The team will employ experimental techniques, including ones that provide information as the reaction occurs, and computational methods to gain in depth insight into this process. The particular crystal polymorph often dictates key properties of nanocrystalline materials and, consequently, the applications for which these can be used, for example, in photovoltaics, catalysis, and energy storage. Therefore, having the knowledge and ability to control the crystal structure is important. The broader impacts of this work are centered around (a) providing experimental and computational training to the students working on this project and (b) summer research experiences for undergraduate students from Puerto Rico that aim to complement the training they receive at their home institutions to better prepare them for the workforce and/or pursuing a graduate degree. The ability to rationally synthesize a given polymorph or phase of a nanoparticles is desirable as these dictate their mechanical, optical, and electronic properties. The proposed work synergistically combines experimental and computational methods to provide a holistic framework for a model system where halides drive the control of crystal structure/phase in the synthesis of manganese chalcogenide nanocrystals. This framework will encompass identifying pre-nucleation molecular species, performing thermochemical measurement of reaction and surface-ligand interactions, and monitoring the kinetics of nucleation and growth. A suite of in situ techniques will be employed to enable such measurements under the reaction conditions. Quantum-mechanics-based calculations will be used to identify atomic-scale interactions and the mechanisms that lead to the observed crystal structures/phases. These calculations will provide input for kinetic and thermodynamic models of nanocrystal nucleation and growth and, therefore, will produce multi-scale-based computational guidance for the controlled synthesis of metal chalcogenide nanocrystals. The studies will be extended to lanthanide chalcogenide nanocrystals, which have remained largely unexplored despite unique optical and magnetic properties. This work is anticipated to further increase the level of chemical understanding of the synthesis of Mn and Ln chalcogenide nanocrystals, and such insights have the potential to provide guidance to the scientific community for the synthesis of other classes of materials. 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.