Process for producing an amorphous carbon film

A process for producing a thin, high hardness amorphous carbon film, comprising:

• generating bubbles in a salt-free liquid containing an organic compound while radiating electromagnetic waves continuously from an electrode disposed in the salt-free liquid to the bubbles so as to generate plasma inside the bubbles, wherein the salt-free liquid is an aqueous solution comprising water as a solvent and the organic compound comprises one or more selected from the lower monohydric alcohols having a carbon number of from 1 to 3 as a solute;
• moving the plasma within the bubbles through the salt-free liquid from the electrode to a substrate disposed in the salt-free liquid;
• contacting a surface of the substrate with the bubbles, so as to form an amorphous carbon film on the surface of the substrate, the formed amorphous carbon film having a thickness from 0.5 μm to 8 μm and a hardness of 11 GPa or more;
• and
• regulating the weight ratio of solute:solvent within a range from 10:90 to 50:50 so as to adjust the rate of forming the amorphous carbon film to deposit a film of the desired thickness and hardness.