Mechanical properties of copper/carbon nanocomposite films formed by microwave plasma assisted deposition techniques from argon?methane and argon?acetylene gas mixtures

Abstract Nanostructured copper/amorphous hydrogenated carbon (a-C:H) composite films have been deposited on silicon substrates by a hybrid technique combining microwave plasma-enhanced chemical vapor deposition and sputter-deposition processes from argon–methane and argon–acetylene mixtures of various compositions. The size of crystallites, ratio between sp 2 and sp 3 types of carbon bonds, hardness, friction coefficient, and wear resistance of composite films were investigated as functions of the carbon content in the films expressed by the atom number ratio C/(C + Cu). The size of crystallites decreased down to 2 nm in films having high carbon contents (60%, C/(C + Cu)). Composite films formed from Ar–C 2 H 2 mixtures with a carbon content of 78% (C/(C + Cu)) exhibited relatively high hardness (6.1 GPa) and very high elastic recovery upon unloading (90%). However, the wear resistance of hard Cu/a-C:H films was very low ((5.7 ± 0.6) × 10 −6 mm 3 /Nm). During the friction tests, a very low resistance to crack formation and cross-sectional propagation was observed. Cu/a-C:H films formed from Ar–CH 4 mixtures and containing 75% of carbon (C/(C + Cu)) possessed low friction coefficients (0.02–0.04) and volume wear coefficients ((0.11 ± 0.02) × 10 −6 mm 3 /Nm). The intensity Raman peak ratio I D / I G (0.71) proved to be much lower for the films having a low value of volume wear coefficient. This is the result of the presence of nanosized carbon clusters in the polymer-like matrix and copper crystallites that provides very low shear stresses during friction tests and forms nanosized wear debris.