Growth of Nanoscale Materials: Insights from Multiscale Theory and Simulations*

Metal nanocrystals have applications ranging from selective catalysts to electronic devices to localized surface-plasmon resonance-related applications. The versatility of functional nanocrystals relies on their tunable size and shape. To this end, solution-phase synthetic protocols have been highly successful at producing a variety of nanocrystal structures. However, great challenges remain in achieving high selectivity. A significant difficulty lies in understanding and controlling shape evolution.

I will discuss our efforts to understand the workings of PVP, a capping polymer that facilitates the formation of {100}-faceted Ag nanoparticles. We use first-principles, dispersion-corrected density-functional theory (DFT) to characterize the binding of PVP to Ag(100) and Ag(111) surfaces. These studies indicate a binding preference of PVP to Ag(100), consistent with experimental observations. To understand the solution-phase binding of PVP to these Ag surfaces, we developed a new metal-organic many-body force field with high fidelity to DFT and experiment. We implement this force field into molecular-dynamics (MD) free-energy calclations to characterize the potential of mean force and the mean first-passage times for solution-phase Ag atoms to reach PVP-covered Ag facets. Using these mean first-passage times, we predict kinetic Wulff shapes of Ag nanocrystals and show that these should be {100}-faceted cubes. We also use MD simulations to characterize the interfacial free energies of PVP-covered Ag facets in solution. The thermodynamic Wulff shapes that we predict are truncated octahedra. These findings indicate that experimental nanocubes are kinetic in origin. We extend our approach to understand the growth of fivefold-twinned Ag nanowires and how strain and kinetic phenomena can influence their aspect ratio in growth.