Deposition of amorphous carbon films from C60 fullerene sublimated in electron beam excited plasma

C60 fullerene clusters are used as a carbon source for amorphous carbon films deposition in an electron beam excited plasma. C60 clusters are sublimated by heating a ceramic crucible containing the C60 powders up to 850 °C, which is located in a highly vacuumed process chamber. The sublimated fullerene powders are injected to the electron beam excited argon plasma and dissociated to be active species that are propelled toward the substrates. Consequently, the carbon species condense as a thin film onto the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 μm/h and the average surface roughness of 0.2 nm over an area of 400 μm2 are achieved. Decomposition of the C60 fullerene after injecting into the plasma is confirmed by optical emission spectroscopy that shows existence of small carbon species such as C2 in the plasma. X-ray diffraction pattern reveals that the microstructure of the film is amorphous, while fullerene films deposited without the plasma show crystalline structure. Raman spectroscopic analysis shows that the films deposited in the plasma are one of the types of diamond-like carbon films. Different negative bias voltages have been applied to the substrate holder to examine the effect of the bias voltage to the properties of the films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 28 GPa. In addition, the films are droplet-free and show superior lubricity.

Research highlights
► We introduced C60 fullerene sublimation as a new method for the deposition of amorphous carbon films in the plasma.
► Fullerene cages would be broken down into many active species that form amorphous carbon films on the substrates.
► The applied bias voltage to the substrate remarkably affects the hardness and thickness of the carbon films.
► We found that the average surface roughness of the films is 0.2 nm and no droplet found on their surfaces.