Influence of discharge power and bias potential on microstructure and hardness of sputtered amorphous carbon coatings

This work reports on the influence of the power density and bias potential on the structure-property relations of sputter deposited amorphous carbon coatings. Coatings were deposited at power densities between 4.4 and 28 W/cm2 in both Ar and Ne atmospheres at pressures of 1 and 1.25 Pa, respectively. Measurements of the substrate temperature during deposition indicate that the coating is subjected to a substantial thermal load during deposition, which leads to growth of the graphitic clusters at higher power densities. This change of the microstructure results in a drop of the hardness of up to 40% when the power density increased to 28 W/cm2. A high hardness of up to 30 GPa, however, can be achieved when either a bias potential of −100 V is applied or when Ne instead of Ar is used as process gas. This can be attributed to the high compressive stresses present as a result of an enhanced ion bombardment.