Synthesis, composition, surface roughness and mechanical properties of thin nitrogenated carbon films

In this study, we explored the properties of amorphous nitrogenated carbon films grown in a standard magnetron sputter-deposition system without a magnetic trap. Silicon wafers and hard disk substrates were used. To simplify process control, we operated the graphite target at constant voltage and used 3% nitrogen in argon from a premixed feed. Under these conditions, most nitrogenated carbon films contain about 6-8 a/o of nitrogen. Films with the highest hardness values (28 GPa) and lowest root-mean-square surface roughness (0.2 nm on hard disk substrates) were obtained at low sputtering pressure (5 mTorr) and large substrate pulse bias (-300 V). These observations demonstrate the importance of ion bombardment in controlling film morphology and properties. The harder films appear to have better resistance against scratch damage, as is demonstrated by the nano-scratch tests using a two-dimensional nanoindentor.