Structural and tribological characterization of multilayer ta-C films prepared by filtered cathodic vacuum arc with substrate pulse biasing

The filtered cathodic vacuum arc (FCVA) technique is reported to be an effective method for producing high quality hard coatings, but has limitations for preparing thick hard tetrahedral amorphous carbon (ta-C) films by the conventional method of floating conditions. Currently, the multilayer approach is the only way to overcome this limitation, and is of great interest because it enables the fabrication of films with varied thickness and properties to suit the application. A multilayer ta-C film of approximately 1 μm thickness is prepared on a silicon substrate by alternate soft (20 nm thick) and hard (100 nm thick) layers of tetrahedral amorphous carbon. The compressive stress of the film measured using the radius of curvature technique, profiled by stylus, is found to be approximately 5.4 GPa. The bond structure of the film is studied using Raman spectroscopy and is typical of films containing reasonably high sp3 fractions, with an ID/IG ratio of approximately 0.265. The hardness and elastic modulus of the film are approximately 57 and 550 GPa, respectively, which are fairly high for thick ta-C films. The coefficient of friction and wear rate of the ta-C film against a sapphire counter-face are observed to be relatively low. This investigation finds that the ta-C films of relatively high thickness, with favourable hardness and tribological properties, can be prepared by FCVA with alternate substrate pulse biasing.