The basics of ta-C coating fabrication
Diamond-like carbon coatings (DLC) are generally carbon coatings with a significant fraction of diamond-like atomic carbon bonds. In addition to the diamond-like bonded carbon (sp3 hybridized bonds) the rest of the carbon atoms is mostly graphite-like bonded (sp2 hybridized). The ratio of sp3/sp2 bonds and the hydrogen content in the coating are important for the properties. Some DLC coatings are produced from hydrocarbon gases and thus contain always a certain amount of hydrogen. According to Jacob/Moeller/Robertson most DLC coating types can be distinguished using a certain type of phase diagram.
Due to the nature of their synthesis process from solid graphite, ta-C coatings do not contain a significant amount of hydrogen. The sp3 fraction in ta-C coatings ranges from 50 to 90% depending on the fabrication conditions. Thus ta-C coatings are the closest of the DLC coatings that approach the properties of crystalline diamond.