Mechanical properties of nanostructured copper-hydrogenated amorphous carbon composite films studied by nanoindentation

Nanostructured copper/amorphous hydrogenated carbon (a-C:H) composite films approximately 500 nm in thickness have been deposited on silicon substrates by an hybrid technique combining a microwave plasma-enhanced chemical vapor deposition (PECVD) process with a sputter-deposition process from argon–acetylene mixtures and copper target. In these films, the a-C:H phase would act as a tough matrix while reinforcing nanocrystallites of copper are imbedded in the amorphous matrix. The mechanical behavior of nanocomposite films under point loading conditions was studied by nanoindentation using a Berkovich indenter. The transition from deposition of soft polymer-like to ion-hardened polymer-like a-C:H films was observed with increasing concentration of acetylene in the gas phase. The hardness of the Cu/a-C:H composite films is higher by a factor of two than that of pure a-C:H films deposited under similar conditions. The increase in hardness is probably related to the strengthening effect of copper nanocrystallites dispersed in the amorphous carbon matrix.