Melting behavior of copper nanocrystals encapsulated in onion-like carbon cages

Nanoparticulate materials are promising objects for studying the processes that trigger melting of solids. On a pyrolytic route, we successfully encapsulated 20-60 nm diameter Cu nanocrystals within multilayer graphitic carbon spheres. In situ electron microscope observations of the melting and displacement of the encapsulated Cu nanocrystals at temperatures up to 1175 K have provided clear evidence of the process of surface melting and its dependence on the quality of the metal/carbon interface. Detection of crystal defects inside the Cu particles during melting and vaporization has proved that the metal phase maintains its solid crystalline state in the particle center. Indications Of the influence of surface anisotropy on the melting behavior were obtained. The carbon cages as a whole remained unchanged during the observations.