Controlling structure and morphology of CoPt nanoparticles through dynamical or static coalescence effects.

The structure and morphology of 1 to 3 nm size CoPt nanoparticles have been investigated in situ and in real time under different conditions: growth at 500 degrees C or at room temperature (RT) followed by annealing at 500 degrees C. The small-angle x-ray scattering measurements show size and temperature dependent growth mode with particle motions on the surface, while wide-angle scattering results, supported by Monte Carlo simulations, allow structure identification. If icosahedra are systematically detected at the first growth stages at RT, annealing at 500 degrees C yields the decahedral structure from the quasistatic coalescence of icosahedral morphology. Meanwhile, growth at 500 degrees C proceeds by a dynamical coalescence mechanism at the early stage, yielding truncated octahedral cubic structures.