Molecular dynamics simulation of nanoparticle coalescence and sintering

Abstract

In spite of practical significance of nanoparticle coalescence and sintering for processing of nanomaterials, the nanoparticle sintering mechanism is poorly understood. In particular, the high sintering rates observed near room temperature can not been explained by known mechanisms. In this study, to provide additional insight and to better understand coalescence and sintering processes of nanoclusters under femtosecond laser irradiation, molecular dynamics (MD) simulations using the Quantum Sutton-Chen potential have been employed. Gold nanoclusters have been selected as an example of a typical material system. MD simulations of sintering have been performed at constant energy and under a femtosecond laser pulse irradiation. The femtosecond laser pulse affects are simulated by combining two-temperature model with the MD model. For a single nanoparticle, computations show that a remarkable reduction of melting temperature occurs for gold nanoparticles smaller than 5nm (at 2nm the melting temperature is about forty percent of that of the bulk). For particles larger than 10nm, melting temperature is close to that of the bulk. During sintering in the liquid phase, the initial neck growth can be well described by the viscous flow model. For two particles with initial temperature just below the single particle melting temperature, the initial neck growth is initially controlled by viscous flow and then later by grain boundary diffusion. At initial temperatures well below melting, the sintering process occurs very rapidly and ends with a non-spherical oval particle shape. Remarkably, the initial growth rate of the neck region at these temperatures is similar to that in the liquid state. It is shown that by in-creasing laser input energy, nanoparticles can be melted, forming a single larger nanoparticle. The effects of multi-particle melting, solidification and sintering are also investigated.In spite of practical significance of nanoparticle coalescence and sintering for processing of nanomaterials, the nanoparticle sintering mechanism is poorly understood. In particular, the high sintering rates observed near room temperature can not been explained by known mechanisms. In this study, to provide additional insight and to better understand coalescence and sintering processes of nanoclusters under femtosecond laser irradiation, molecular dynamics (MD) simulations using the Quantum Sutton-Chen potential have been employed. Gold nanoclusters have been selected as an example of a typical material system. MD simulations of sintering have been performed at constant energy and under a femtosecond laser pulse irradiation. The femtosecond laser pulse affects are simulated by combining two-temperature model with the MD model. For a single nanoparticle, computations show that a remarkable reduction of melting temperature occurs for gold nanoparticles smaller than 5nm (at 2nm the melting temperature is ab...