ABSTRACT
Hydrogen-free (or non-hydrogenated) amorphous carbon (a-C) has found many engineering applications for more than two decades [1, 2]. Various techniques have been used to deposit a-C coatings on Si wafers, steels or tungsten carbide tools. These techniques include magnetron sputtering [3], pulsed laser deposition [4], cathodic vacuum arc deposition [5], etc. The applications of an a-C coating strongly depend on its adhesion to the substrate. Adhesion strength dictates the ability of a coating to remain attached to the substrate under operating conditions. A coating adheres to the substrate due to interfacial forces comprising valence and interlocking forces. The residual stress in the coating and at the interface between the coating and the substrate, and the coating toughness all exert strong in-
fluence on the adhesion strength [6, 7]. Under physical vapor deposition conditions, a-C coatings grow under energetic ion bombardment, thus a compressive residual stress is developed in the coating [8]. High values of compressive stress, up to 10 GPa, have been reported [8-10]. Such a high compressive stress limits the coating thickness and contributes to poor adhesion between an a-C coating and substrate.
