Two-Steps Versus One-Step Solidification Pathways of Binary Metallic Nanodroplets

The solidification of AgCo, AgNi, and AgCu nanodroplets is studied by molecular dynamics simulations in the size range of 2-8 nm. All these systems tend to phase separate in the bulk solid with surface segregation of Ag. Despite these similarities, the simulations reveal clear differences in the solidification pathways. AgCo and AgNi already separate in the liquid phase, and they solidify in configurations close to equilibrium. They can show a two-step solidification process in which Co-/Ni-rich parts solidify at higher temperatures than the Ag-rich part. AgCu does not separate in the liquid and solidifies in one step, thereby remaining in a kinetically trapped state down to room temperature. The solidification mechanisms and the size dependence of the solidification temperatures are analyzed, finding qualitatively different behaviors in AgCo/AgNi compared to AgCu. These differences are rationalized by an analytical model.

Automated summary

The solidification of AgCo, AgNi, and AgCu nanodroplets in the size range of 2-8 nm was studied using molecular dynamics simulations. Despite the surface segregation of Ag in the bulk solid, the simulations revealed clear differences in the solidification pathways. AgCo and AgNi separate in the liquid phase and solidify close to equilibrium, while AgCu remains in a kinetically trapped state and solidifies in one step. An analytical model was used to rationalize these differences and analyze the size dependence of solidification temperatures.