Surface-Induced Phase Transition During Coalescence of Au Nanoparticles: A Molecular Dynamics Simulation Study

TL;DR

This study uses molecular dynamics simulations to explore how surface melting influences the coalescence of gold nanoparticles, revealing that coalescence occurs at lower temperatures than melting and is driven by surface diffusion.

Contribution

It provides new insights into the surface-induced phase transition mechanisms during nanoparticle coalescence, highlighting the role of surface melting and reduction.

Findings

Coalescence occurs at temperatures below melting point.

Surface melting begins several hundred degrees below melting.

Surface reduction accelerates coalescence kinetics.

Abstract

In this study, the melting and coalescence of Au nanoparticles were investigated using molecular dynamics simulation. The melting points of nanoparticles were calculated by studying the potential energy and Lindemann indices as a function of temperature. The simulations show that coalescence of two Au nanoparticles of the same size occurs at far lower temperatures than their corresponding melting temperature. For smaller nanoparticles, the difference between melting and coalescence temperature increases. Detailed analyses of the Lindemann indices and potential energy distribution across the nanoparticles show that the surface melting in nanoparticles begins at several hundred degrees below the melting point. This suggests that the coalescence is governed by the liquid-phase surface diffusion. Furthermore, the surface reduction during the coalescence accelerates its kinetics. It is found that for small enough particles and/or at elevated temperatures, the heat released due to the surface reduction result in a melting transition of the two attached nanoparticles.