Temperature effect on the ordering and morphology of CoPt nanoparticles

In the present work, we report a growth and structural study of Co50Pt50 nanoparticles prepared on amorphous carbon substrate by ultra high-vacuum evaporation and investigated by transmission electron microscopy. The size evolution with the amount of CoPt shows a Volmer Weber behavior. At room temperature the nanoparticle diameter follows a t0.41 power law. Temperature effect on the growth and chemical ordering is presented. A bimodal size distribution is observed and an evolution of particle composition is demonstrated for the nanoparticles prepared on heated substrate. The nanoparticles prepared at room temperature and annealed present an homogeneous size and composition evolution. Annealing at temperature higher than 650 °C induces a transformation from the chemically disordered fcc A1 phase to the L10 chemically ordered phase. The nanoparticle shape evolution and the mechanism of the disorder-order transformation are discussed.