Surface segregation in binary Cu–Ni and Au–Co nanoalloys and the core–shell structure stability/instability: thermodynamic and atomistic simulations

Abstract

An approach combining thermodynamic and atomistic (molecular dynamics) simulations has been applied to predict surface segregation in binary metal A–B nanoparticles (Cu–Ni and Au–Co ones). The thermodynamic simulation method based on the Butler equation was additionally justified and extended to stationary non-equilibrium states using the energetic variant of non-equilibrium thermodynamics. The results of thermodynamic and atomistic simulations agree with each other predicting segregation of Cu atoms to the surface of Cu–Ni nanoparticles and the surface segregation of Au in binary Au–Co nanoparticles. A hypothesis is put forward on correlation between stability/instability of A (core)/B (shell) nanostructures and the spontaneous surface segregation of one of the components of binary A–B nanoparticles. In accordance with this hypothesis, the core–shell structure A (core)/B (shell) will be stable if the component B spontaneously segregates to the surface of binary A–B nanoparticles. At the same time, a trend to the surface segregation of this component should result in the instability of the B (core)/A (shell) structures. The hypothesis in question agrees with our molecular dynamics results and with available experimental data on stability/instability of Co (core)/Au (shell) and Au (core)/Co (shell) nanostructures.