Mechanistic Discovery for Materials Synthesis Across Scales using Atomically Precise Cluster Building Blocks

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With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Dr. Brandi M. Cossairt of the University of Washington is developing new nanoscale materials using cluster precursors. The structure and surface chemistry of new and known clusters are first deduced. Next, the mechanisms of cluster transformation are controlled by modulating chemical environments, moving between clusters serving as sources of solute, as seeds, and as discrete building blocks. Finally, site differentiation is used to direct cluster and nanocrystal assembly to access new mesoscale structures including wires, sheets, and crystals. This fundamental chemistry research opens a new frontier in materials discovery and provides graduate and undergraduate student training opportunities in materials chemistry. This training is strengthened by coordination of the “Nanocrystals Northwest” biennial workshop, which brings together nanocrystal researchers in the Pacific Northwest from R1 and PUI institutions as well as industry. In addition, graduate student experiences in scholarship, mentorship, and broadening participation are documented through a University of Washington graduate student oral histories project. This project also sustains progress on the Chemistry Women Mentorship Network, which has a demonstrated track record in supporting the academic pipeline for women in chemistry.This research involves the synthesis and assembly of novel nanoscale materials using atomically precise semiconductor clusters as precursors. The inorganic core and surface chemical structure of atomically precise clusters are used to encode structure across length scales. In addition, new strategies to tune the mechanisms of cluster conversion and nanocrystal assembly are being developed. This includes elucidation of structure, symmetry, and surface chemistry of new and known semiconductor clusters using a combination of single crystal X-ray diffraction, pair distribution function analysis, and transmission electron microscopy. Examination and control of cluster transformation mechanisms enable the subsequent selection of clusters as solute, seeds, and discrete building blocks. This is accomplished by controlling surface stoichiometry and ligand density under prescribed reaction conditions. Finally, development of new mechanisms of site differentiation are being pursued for the formation of desired mesoscale structures including wires, sheets, and 3D crystals from isotropic cluster and nanocrystal building blocks. This is accomplished by adjusting nanocrystal valency using steric control. Success is expected to lead to change how nanomaterial synthesis is approached and to open a vast and untapped parameter space for materials discovery.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.