Thermodynamics versus kinetics in a morphology transition of nanoparticles

The morphology of cobalt, palladium, and platinum nanoclusters grown on a gold surface is analyzed from both thermodynamic and kinetic viewpoints. Although the thermodynamic equilibrium shape as a function of cluster size is similar for all three elements and shows a morphology transition from monolayer to bilayer, only Co clusters meet their stable state and undergo a transition. Atomistic simulations on a picosecond to nanosecond time scale evidence kinetic limitations for Pt and Pd, and allow us to understand the experimentally observed morphology for the different species. It is shown that stress relaxation, by strongly influencing the energy activation for atom hopping from first to second cluster layer and the magnitude of vibration of the atoms, is the determinant parameter for the existence or absence of the cluster morphology transition. DOI: 10.1103/PhysRevB.87.155404