Molecular Simulation of the Nucleation and Growth of Gold Nanoparticles

Abstract

Using hybrid Monte Carlo as well as molecular dynamics simulation, we study the nucleation and growth of nanoparticles from a supercooled liquid of Au at ambient pressure. We simulate the nucleation step using an umbrella sampling scheme in the course of hybrid Monte Carlo simulations. We then monitor the subsequent growth of the critical nuclei so obtained. In particular, we carefully determine the growth kinetics as well as the molecular mechanisms underlying the growth step. Our results establish the following crystallization pathway. In the early stages of the nucleation process, the structure of the nucleus is dominated by the stable face-centered cubic polymorph. Then, when the size of the Au nucleus is close to the critical size, the metastable hexagonal close-packed polymorph nucleates heterogeneously (or cross-nucleates) on the surface of the nucleus. The growth of the crystallite proceeds through successive cross-nucleations between the two polymorphs. A detailed analysis of the kinetics of growth further establishes that the two polymorphs play symmetric (and similar) roles in the growth process.