Characterization of Hydrogen-Free and Hydrogenated DLC Films

Diamond-like carbon (DLC) films are an amorphous carbon film with sp2 and sp3 bonding structures of carbons. The DLC films have been used widely in industry owing to have superior properties such as high mechanical hardness and low friction coefficient. The DLC films are divided into the following of four categories: ta-C and a-C films are hydrogen-free DLC with high and low C–C sp3 bonds, respectively, and ta-C:H and a-C:H films are hydrogenated DLC with high and low C–C sp3 bonds, respectively. As the industrial application of DLC films is expanding, it is important to clarify the definition of these DLC film types and to able to easily evaluate the types. There are various DLC deposition methods. Filtered arc deposition (FAD) method which is one of the vacuum arc deposition methods is a few deposition methods can form hydrogen-free DLC films with high hardness. In addition, hydrogenated DLC films can be prepared under the deposition condition in which a hydrogen or a hydrocarbon gas is introduced into the chamber on the FAD system. Various DLC films prepared using T-shape FAD system were characterized by the sp3 fraction and hydrogen content measured using near edge X-ray absorption fine structure spectroscopy and Rutherford back scattering/elastic recoil detection analysis, respectively. It was found that the sp3 fraction, nanoindentation hardness, and film density of DLC films have a correlation. Based on these results, DLC films were classified from the film density and hydrogen content.