The Effect Of Shell Thickness On Sintering Of Cu-Ag Core-shell Nanoparticles

As a substitute for pure silver nanoparticles,Cu-Ag core-shell nanoparticles(CS NPs)have received significant attention in the fields of electronic packaging and conductive inks.Shell thickness is one of the important factors affecting the sintering performance of CS NPs.In this work,we conduct a molecular dynamic simulation based on double nanoparticle sintering model and multiple nanoparticle model to investigate the shell thickness effects on the sintering process of Cu-Ag CS NPs at different temperatures.A melting simulation was conducted before sintering simulation to investigate the shell thickness on the thermal stagbility of Cu-Ag core-shell nanoparticles.We found that the melting points of core-shell nanoparticle decreased first and then increased as the shell thickness decrease.The melting points of Ag₅Cu₃ was lowest,which was960K.During the heating process,as the temperature lower than the melting temperature,the premelting occurred on the surface of the nanoparticle.The premelting phenomenon was more significient as the shell thickness decreased.The results of double nanoparticles sintering,and multiple nanoparticles sintering showed that the less the shell thickness,the lower the potential energy reduction was during sintering.In double nanoparticle model,the shrinkage decreased with the shell thickness increased.But in multiple nanoparticles model,the densification did not increase when reached 0.59.As the temrpature was higher than 700K or equal to 700K,the effect of shell thickness on the densification was limited.This study mainly involved two sintering mechanisms,plastic deformation mechanism and diffusion mechanism.During the sintering process,the contribution of the plastic deformation mechanism decrease with the layer thickness decreases.The decrease of shell thickness can produce more lattice mismatches at the core-shell interface,which hinders crystallization during the sintering process.And we found more amorphous Ag atoms at the sintering neck.As for the diffusion mechanism,the self-diffusion coefficient at 500K is much lower than that at higher temperatures.However,the slow diffusion can increase the densification by filling the pores generated in the initial stage of sintering.The self-diffusion coefficient of surface atoms increases as the shell thickness decreases.A higher sintering temperature can induce the diffusion of Cu atom near the core-shell interface,especially for the particle with thinner shell thickness.