Science of Shape-Selective Nanocrystal Synthesis

A significant challenge in the development of functional nanomaterials is understanding the growth of colloidal metal nanocrystals. From a practical perspective, a knowledge of how to selectively synthesize desired metal nanocrystal sizes and shapes will be important in achieving a sustainable energy future. The science of shape-selective nanocrystal synthesis has been advancing at a rapid pace, with numerous recent reports of syntheses of various beneficial nanocrystal morphologies. Despite many successes, it is still difficult to achieve high, selective yields in most synthesis protocols. Many aspects of these complex syntheses remain poorly understood, which impairs development of improved synthetic methods. The proposed research targets two key gaps in the fundamental understanding of these syntheses (1) Understanding the growth of nanocrystal seeds and (2) Understanding the role of halogens in controlling nanocrystal morphology.One project targets understanding the growth of nanocrystal seeds. Seeds play a critical role in nanostructure formation, as the shape of the seed often determines the final nanocrystal shape. The interplay between structural transitions, deposition, and etching as seeds grow leads to a myriad of metastable nanocrystal morphologies. To understand this interplay and its ramifications for seed structure, replica-exchange molecular dynamics and machine learning, as well as kinetic methods based on state-of-the-art reactive force fields and quantum density-functional theory will be employed to understand how the structures of metal seeds evolve in a solution environment. Knowledge from these studies will enable the development of strategic synthesis protocols to achieve selective nanostructure yields.A second project aims to understand the role of halogens in the synthesis of Cu, Ag, and Au nanostructures. Halogens are necessary ingredients in most nanostructure syntheses, but their role in these syntheses is poorly understood. To resolve the role of halogens, theoretical studies based on quantum density-functional theory will provide insight to experiments of collaborators. The knowledge gained in this work will enable robust halogen-mediated syntheses of a variety of nanocrystals and set the foundation for future syntheses of more elaborate nanostructures with higher functionalities.