A TEM in situ experiment as a guideline for the synthesis of as-grown ordered CoPt nanoparticles

Co-x Pt1- x nanoparticles on amorphous alumina are synthesized by a finely tuned pulsed laser deposition ( PDL) technique. By means of an alternate deposition experiment using pure Co and Pt targets, we have shown that the composition of the nanoparticles can be controlled with a precision of 2%. This composition varies linearly with the lattice parameter of the nanoparticles following the well- known Vegard law. During the synthesis, the substrate temperature is a key parameter to control the structure and the morphology of the nanoparticles. We have performed an in situ heating experiment in an electron microscope using disordered Co55Pt\\\(45) nanoparticles to study their thermodynamic behaviour. We have observed both ordering within the nanoparticles and coalescence between the nanoparticles. The temperature regimes evidenced by the in situ experiment are used to determine the temperature of the substrate to synthesize as- grown L1(0) ordered nanoparticles with better control on their size and composition.