Visualization and analysis of structural ordering during crystallization of a gold nanoparticle

Abstract

In this molecular dynamics study, we provide an insight into the crystallization of a liquid droplet by following the structural ordering of the surface and core atoms in a 10 179 atom gold nanoparticle quenched from the melt down to $298\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We use the $Q6$ order parameter and ring statistics to measure the degree of crystallization during quenching and a topological structure measure based on planar graphs to visualize the time evolution of structural ordering of the nanoparticle core at the temperature where significant crystallization first occurs $(949\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. Our results indicate that crystallization of the surface precedes that of the core and, in fact, provides a template for the ordering of the core region. There is also evidence presented that hcp twin planes form directly below the region where the edges of two (111) surface planes meet. At $298\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the nanoparticle forms a defected icosahedral structure, and we observe the formation of fcc fragments and hcp planes characteristic of an icosahedral structure in the core as a function of temperature.