On the problem of stability/instability of bimetallic core-shell nanostructures: Molecular dynamics and thermodynamic simulations

Abstract

Earlier we put forward a hypothesis about relationship between the spontaneous surface segregation of one of the components of binary A-B nanoparticles and stability/instability of one of the two alternative core-shell nanostructures A@B or B@A. Here, the first symbol (before the @ sign) corresponds to the particle core, and the second (after @) to its shell. In accordance with our hypothesis, stable or at least more stable should be that of the two alternative nanostructures, the shell of which corresponds to the component spontaneously segregating to the surface. Verification of this hypothesis and revealing possible deviations from it have been carried out by using molecular dynamics simulation of Co@Au, Au@Co, Ni@Cu, Cu@Ni, Al@Ni and Ni@Al nanostructures. In addition, the atomistic and thermodynamic simulations were involved to predict the surface segregation in corresponding binary nanoalloys (Co-Au, Ni-Cu and Ni-Al). The thermodynamic simulation of segregation in binary metal nanoparticles was based on numerical solution of the Butler equation for a two-cell particle model. It has been established that the above hypothesis is indeed fulfilled but in some certain temperature ranges. During discussion of the results obtained, the concept was put forward of thermodynamic and kinetic factors of the core-shell nanostructure stability.