Annealing effect on the structure, mechanical and tribological properties of hydrogenated diamond-like carbon films

Hydrogenated diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapor deposition technique using CH4 plus H2 as the feedstock. The effect of annealing temperature on the structure, mechanical and tribological properties of the resulting films were investigated by means of Raman spectroscopy, Fourier transformation infrared spectroscopy nanoindentation, stress analyzer and friction and wear testing on a ball-on-disk test rig. The results showed that the structure, hardness, Young's modulus and the tribological properties of the films had no significant changes at lower annealing temperature up to 200 °C. At higher temperature above 200 °C, the annealing caused the effusion of hydrogen and the sp3 to sp2 transformation, which in turn, led to the more graphite-like structure with poorer mechanical and tribological properties. It was also found that the tribological properties were dependent not only on the annealing temperature, but also on the testing environment. The roles of annealing and environment in the tribological properties of DLC films are discussed in terms of the annealing-induced changes in the structure and mechanical properties of the films and the friction-induced physical and chemical interactions among the DLC films, steel ball and water and/or oxygen molecules.