Synthesis of core-shell nanoparticles with liquid core using magnetron sputtering and capacitively coupled dusty plasmas

We succeeded in depositing amorphous carbon films around tin nanodroplets retained in a capacitively coupled plasma (CCP). High-pressure magnetron sputtering was used for synthesizing tin nanoparticles at the top of a vacuum chamber. Tin nanoparticles were transported to CCP at the bottom of the chamber, and they were trapped in the sheath above an rf electrode. Tin nanoparticles were heated above the melting point by ion bombardment in CCP. We introduced methane into CCP to deposit amorphous carbon films around melted tin nanoparticles. The transmission electron microscope (TEM) images of core-shell nanoparticles showed completely spherical cores. We observed the melting of cores at the melting point of metal tin when we heated core-shell nanoparticles in TEM, suggesting that the amorphous carbon films protected cores from the oxidation. In addition, the amorphous carbon films were robust against the volume expansion of the cores due to melting.