Molecular dynamics simulation of the formation of bimetallic core-shell nanostructures with binary Ni–Al nanoparticle quenching

Employing isothermal molecular dynamics, we simulated the self-assembly of core-shell nanostructures in the course of quenching binary Ni–Al nanoparticles (NPs) with initially homogeneous distributions of both components. The process of quenching was reproduced via the uniform rapid cooling of initial configurations from temperatures of 1000 K down to 0.001 K. To increase the reliability of the simulation results, we used two independently developed computer programs (our own and the well-known open program LAMMPS) in conjunction with the tight-binding potential (TBP) model and the embedded atom method (EAM). Simulations employing both force fields predict the self-assembly of the core-shell nanostructures whose shells consist of Al atoms. However, involving TBP predicts the formation of more perfect Ni@Al structures, in which the central area (core) consists almost completely of Ni atoms, whereas EAM simulations predict formation of a more complex integral structure Ni–Al@Ni@Al. In the last case, the first (outer) monolayer also entirely consists of Al atoms, the second—of Ni atoms, while the core is comprised of both types of atoms. At the same time, the core is enriched by Ni atoms. It is concluded that the spontaneous surface segregations of Al atoms should be considered as the main driving force for the formation of the core-shell structures during quenching of Ni–Al NPs with initially homogeneous distributions of components.