The synthesis of anisotropic metal nanoparticles is procedurally well developed but mechanistic understanding is lacking in all but the simplest of reactions. One reasons for this is that although most metal crystal structures fall into the Oh point group (Face-centered Cubic lattice), a diversity of particle shapes with lower symmetry are observed as the products of growth reactions, e.g., Rods (D4h), Tetrahedra (Td), and Triangular Plates, (C3). Because the precursors to nanoparticle growth often lack any clear source for these products, the necessary symmetry-breaking processes that must occur during these reactions are poorly understood. In this talk, I will discuss efforts in my group to understand the formation of low symmetry nanoparticle morphologies by directly observing single-particle growth reactions using liquid-phase transmission electron microscopy. Careful tailoring of the solution conditions allows for the electron beam, and subsequent radiolytically-generated solvated electrons, to act as a reducing agent for metal precursors. Deposition of material onto pre-synthesized seed particles with well-defined shape and crystal orientation is then tracked over time to determine the mechanistic steps during which symmetry is broken. These results point to a complex interplay of thermodynamic and kinetic factors that is mediated by precursor supersaturation and the dynamics of surface ligand binding. This work highlights the power of single-particle characterization tools and facilitates a deeper fundamental understanding of crystal growth that will enable the fabrication of rationally-designed nanomaterials.

Understanding symmetry-breaking in nanocrystal growth at the single-particle level

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.