Pressure Dependence of Carbon Film Coating by a Toroidal Methane Discharge

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Abstract
A pure methane discharge under a toroidal magnetic field has been used to deposit thin carbon layers in situ onto the walls of a toroidal vessel, with a view to application to magnetic fusion devices. Hard carbon films with high electrical resistivity were formed on stainless steel, silicon, and NaCl substrates, in a wide range of methane pressure (10-4 ∼10-2 Torr). The film properties and structures were examined by infrared absorption, X-ray photoemission analysis, electron microscopy (TEM, TED, SUM), and so forth. The results show that the films predominantly consist of tetrahedrally bonded carbon (sp3 bonding). Both the hydrogen atom concentration in the films and the binding energy of the carbon atoms increase with increasing methane pressure. Also, the size of microcrystallites on a background consisting of an amorphous structure grows with increasing pressure.