Comparative study of anneal-induced modifications of amorphous carbon films deposited by dc magnetron sputtering at different argon plasma pressures

This work investigates the evolution of the structural, mechanical and tribological properties of amorphous carbon films (a-C) undergoing thermal annealing. Two different types of a-C film were studied: hard, stressed and dense films, henceforth called 'diamond-like', and soft, more relaxed and less dense films, called 'polymer-like'. The two sets of films were deposited by dc magnetron sputtering at 0.36 and 1.4 Pa argon plasma pressures, respectively, and both were annealed in vacuum for 1 h at temperatures between 300 and 700°C. Raman results provided indications of a remarkable increase of the sp² hybridized domains, that occurs mainly at temperatures higher than 400°C for the diamond-like films and in a continuous way for the polymer-like films. The friction coefficient of both types of film approaches the same value with increasing temperature, whereas the surface roughness is nearly constant. For diamond-like films, the hardness and compressive internal stress are nearly constant up to 500°C, and then undergo a fast decrease. In contrast, the hardness of the polymer-like film continuously decreases with temperature, whereas the compressive stress remains constant. (C) 2000 Elsevier Science S.A. All rights reserved.