Surface roughness, mechanical and tribological properties of ultrathin tetrahedral amorphous carbon coatings from atomic force measurements

Atomic force microscope (AFM), lateral force microscope and AFM-based scratch and wear testing techniques were used to evaluate and compare the surface roughness, tribological and mechanical properties of thin (2.7-43 nm) tetrahedral amorphous carbon coatings prepared by pulsed cathodic arc discharge. It was found that surface roughness of ultrathin (2-8 nm) coatings was mainly determined by the roughness of the Si substrate and their average density strongly depended on their thickness. Poor friction, mechanical properties of thinner (2.7-15 nm) coatings can be associated with their low average density. The dense coatings (>15 nm) had lower friction coefficient, better scratch and wear resistance properties that were independent of their thickness. It appears that the over 15-nm coatings studied are feasible for some wear-resistant and tribological applications.