Formation of hard amorphous hydrogenated carbon films with low hydrogen concentration and their erosion in air

Hard amorphous hydrogenated carbon (a-C:H) films are prepared by radio-freq uency plasma deposition from a mixture of CH4 and Ar. When these films are heated up to 1220 K under vacuum, they release Ar, a large amount of H-2 an d a small amount of hydrocarbon, but the thickness of the films does not de crease. In addition, their micro-Vickers hardness decreases, but they remai n hard. If these hydrogen-free semihard a-C:H films are heated at 670 K in air for 1 hi they become soft and uptake oxygen and hydrogen. On the other hand, if the original hard a-C:H films are heated under similar conditions, they remain hard without releasing argon or uptaking oxygen. It is conclud ed that the reduction of hydrogen does not lead to the formation of new cro ss linking C-C bonds, and the pore size of tile films increases after heati ng allowing the penetration of oxygen and water vapor into the films.