The role of methane in the formation of fullerene-like nanostructure in amorphous carbon film deposited by reactive magnetron sputtering

The formation of fullerene-like nanostructure in amorphous carbon film is an efficient way to improve the toughness without reducing the hardness of hydrogenated amorphous carbon film. In this paper, a convenient approach to regulating the growth of fullerene-like nanostructure by reactive magnetron sputtering process utilizing graphite target in mixed methane and argon plasma was reported and the role of methane in the formation of fullerene-like nanostructure in amorphous carbon film was discussed. By adjusting the degree of graphite target poisoning, fullerene-like nanostructure was successfully produced in the carbon film. In order to reveal the growth mechanism of this special structure, the structural evolution of the film and graphite target surface were studied. The results suggest that the structure of the target surface and the film are both amorphous carbon when target poisoning severely, and the fullerene-like nanostructure appears in carbon film when target poisoning slightly. However, when methane was not admitted into the chamber, the target was not poisoned, non‑hydrogenated carbon film was prepared. The structure of non‑hydrogenated carbon film is graphite-like. Therefore, that shows the important effect of target poisoning on the structure of film and methane plays an important role in the formation of fullerene-like nanostructure in amorphous carbon film. The formation of the fullerene-like nanostructure is attributed to the deposition of ionized methane on the target surface, which is introduced sp3-hybridized carbon atoms into the graphite structure, resulting in the curvature of the graphite 2D-plane. Nonetheless, when a large amount of methane plasma deposits on the target surface will cause target poisoning severely, the structure of the target surface and the film are both amorphous carbon.