Thermal Stability and Morphological Transformations of Au_core−Co_shell Nanocrucibles

Au_core−Co_shell nanoparticles were synthesized by a wet-chemical method in organic solvent and their thermal stability was studied by annealing experiments over a wide temperature range (200−450 °C). During heating, atoms within the core−shell nanoparticles migrate to transform their initial core−shell morphology to a stable “peanut” structure. We show that this morphological transformation occurs by a well-defined series of energy minimization steps that sequentially reduce the energy due to intraphase grain boundaries within the cobalt shell, the interface energy between the gold core and the cobalt shell, and the overall strain energy.