On the effects of the thermal treatment on the structural, mechanical and tribological properties of amorphous carbon-nitrogen films deposited by magnetron sputtering
Amorphous carbon-nitrogen films, a-CN_x, deposited by rf-magnetron sputtering in N_2 atmosphere were annealed in vacuum at temperatures between 300 and 700 deg C. The annealing time was 30 minutes. The modifications on the film microstructure were monitored by infrared spectroscopy (IR), while the composition and the atomic density were determined by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). The internal stress was determined by measuring the film-induced bending of the substrate and the hardness was measured by nanoindentation. Atomic force microscopy (AFM) providd the friction coefficient and the surface roughness. The ratio between nitrogen and carbon atomic concentrationd ecreases for temperatures higher than 500 deg C, whereas the film density increases with the annealing temperature: 40 percent in the temperature range here studied. The behavior of the D and G Raman bands, IR active due to the nitrogen incorporation in the carbon network, suggests a progressive increase of the size of the graphite-like domains. The hardness of the as-deposited a-CN_x film is around 2 GPa. However, both hardness and internal stress increase by a factor of three in samples annealed at 700 deg C, while the surface roughness and the friction coefficient decrease by a factor of about two.
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