Synthesis of few-layer graphene flakes by magnetically rotating arc plasma: effects of input power and feedstock injection position

A magnetically rotating arc plasma system is used for the synthesis of graphene flakes by methane decomposition. Effects of input power and feedstock injection position on product microstructures are investigated. The morphology and composition of the products are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, etc. Results show amorphous spherical particles with a diameter in the range of 10–40 nm and graphene flakes with 1–20 layers are generated in the plasma process. The graphene flakes are produced under a high gas temperature and long thermal history, while the spherical particles are favored by the opposite conditions. As the gas temperature increases, the products change from spherical particles to graphene flakes; moreover, the graphene flakes have larger size, fewer layers, straighter graphitic layers and better crystalline structure under a higher gas temperature. Emission spectral analysis indicates there exist lots of H atoms when the feedstock gas has a long thermal history in the plasma, revealing the importance of H atoms in the graphene flake formation. It is suggested that a high temperature and rich H environment can suppress the formation of curved or closed structures, leading to the production of graphene flakes with high crystallinity.