Hydrogenated amorphous carbon films were deposited by magnetron sputtering of a carbon target in a methane/argon atmosphere. A postdeposition annealing at 300• C was performed and the microstructure, bonding structure and mechanical properties of the as-deposited and annealed films were analyzed and compared directly by high-resolution transmission electron microscopy, micro-Raman spectroscopy, XPS, and nanoindentation. The results showed that the carbon films are quite stable upon annealing, since there are only minor changes in microstructure and chemical bonding in the amorphous matrix. The hardness of the films remained unaffected, but the elastic properties were somewhat deteriorated. In comparison to the outcomes of our previous work on the growth of fullerene-like hydrogenated carbon films, we can state that the formation of fullerene-like carbon structures requires different sputtering process conditions, such as a higher ion energy and/or different sputtering target. Copyright c 2011 John Wiley & Sons, Ltd.Keywords: mechanical; carbon films; magnetron sputtering
IntroductionDiamond-like amorphous (hydrogenated) carbon films, which are composed of one or more of three bonding configurations -sp 3 (diamond), sp 2 (graphite), or sp -have been extensively investigated due to their excellent properties, [1 -3] like high hardness, low coefficient of friction, chemical inertness and infrared transparency. It is generally agreed that the hardness of amorphous (hydrogenated) carbon films (a-C(:H)) depends on the content of sp 3 -hybridized C-C bonding. [4,5] However, there are some studies giving evidence that the hardness of the a-C(:H) films seems not dominated by the content of sp 3 bonds. [6 -8] Fullerene-like carbon nitride (FL-CNx) films with hardness up to 45 GPa were obtained in the effort to prepare crystalline carbon nitride (beta-C 3 N 4 ). [9] Recently, Zhang et al. fabricated a new kind of hard, highly elastic hydrogenated carbon films with extremely low friction by d.c.-pulse plasma chemical vapor deposition (PDC-PECVD) [10 -12] and middle frequency magnetron sputtering (MF-MS) of Ti target, [13] respectively. The exceptional properties can be assigned to the presence of a fullerene-like structure embedded in the amorphous diamond-like carbon matrix. Buijnsters et al. also synthesized fullerene-like structured films by electron cyclotron resonance CVD. [14] Very interestingly, the amorphous carbon films with fullerene-like structure are in conflict with the general understanding that the hardness of a-C(:H) films depends on the sp 3 bonds. Therefore, the sp 3 bonds content is not the only factor that determines the hardness of amorphous carbon films, as a fullerene-or onion-like microstructure might also contribute to the hardness.A deep understanding of the growth mechanism of this unique fullerene-like structure might help us to probe the hardness dependence of amorphous carbon films on the microstructure. A system that was employed for the deposition of fullerene-like structured films by react...