Kinetic Pathways to Control Nanocrystal Shapes

forthcoming

The shape of nanocrystals is crucial in determining surface area, reactivity, optical properties, mechanical strength, and self-assembly behavior. The current theory on shape formation is based on thermodynamic equilibrium and predicts that each crystal structure should enforce a unique shape, with few morphological variations depending on solution chemistry. Whereas this theory succeeded in explaining crystal habits in mineralogy, it mispredicts many nanocrystals, pointing out the necessity of a non-equilibrium description of shapes. Critical to this project are robust and scalable simulation techniques that capture kinetic effects of ligands and ions in solution at the atomic/molecular scale, while enabling the formation of facets and shapes at mesoscopic scales. Research questions include understanding (i) kinetically trapped shapes in metastable equilibria, (ii) symmetry-breaking from the underlying crystal structure, (iii) the bifurcation of growth pathways leading to synthesis yield, (iv) the emergence of chiral and asymmetric features, and (v) the role of the concentration field in the solution. Central will be the finding of shape diagrams that pinpoint thermodynamic conditions and kinetic factors to tune crystallographic direction and surface area of facets with maximum synthesis yield. Shapes of interest include classic polyhedra, 1D and 2D geometries, multiply twinned particles, concave and high Miller index facets, and branched shapes. This project will allow theory- and computer-aided design and optimization of synthesis protocols of nanocrystals with kinetic shapes.