Atomic fast dynamic motion on the Cu nanoparticle’s surface before melting: A molecular dynamics study

The Cu nanoparticle solder owns a broad potential application prospect for the ultra-fine pitch interconnection. It is reported that the Cu nanoparticles can be sintered at about 500–600 K, which is only about 40% of the bulk melting point. The extremely low temperature sintering is generally thought to be caused by the surface melting of the nanoparticle. We perform a simulation on the Cu nanoparticle via molecular dynamic simulation, and find that the surface melting is insufficient to cause the low temperature sintering. An unusual atomic fast dynamic motion is observed on the surface of nanoparticles at about 500–600 K. The atoms on the nanoparticle's surface jump between lattice positions contributing to an extremely high diffusivity. It plays a crucial role when nanoparticles sinters at a low temperature. Further investigations show that the fast dynamic motion strongly depends on the high atomic potential energy and local atomic arrangement on the surface, which is even more vigorous at the sintering neck. The effect of the heating rate and the nanoparticle’s curvature on the fast dynamic motions are discussed further. Our study reveals the atomic mechanism on the nanoparticle's surface in low temperature conditions and provides a deep understanding of the low temperature sintering.