Optical and tribological properties of heat-treated diamond-like carbon

Diamond-like carbon, or DLC, films, prepared by the rf plasma decomposition of acetylene, have been deposited at substrate temperatures of 100 to 250 °C, with the substrate at a negative bias of 80 V dc. The DLC films have been annealed in vaccum at temperatures up to 600 °C for 3–4 h. The optical properties of the as-deposited and annealed films have been characterized by ellipsometry and Fourier transform infrared spectroscopy. The wear resistance of the thin DLC films and their friction coefficients have been characterized by a specially designed tribotester. The stresses in the films have also been determined. No significant differences were found between the index of refraction and IR absorption spectra of the as-deposited films, or films annealed at up to 390 °C. The DLC films begin losing hydrogen after annealing above 390 °C and only sp² bond carbon is observed after annealing at 590 °C. The wear behavior of the as-deposited films was identical for all deposition temperatures. DLC films deposited at 250 °C were more stable and could withstand higher annealing temperature than films deposited at lower temperatures, and remained wear resistant after anneling at 390 °C.