Metal incorporation strategies in DLC (fullerene-like) thin films grown by ECR-CVD

Abstract

The main aim of this work is the comparison among different methods for metal incorporation in Diamond-Like Carbon (DLC, fullerene-like) Carbon for improving the tribological properties. The films have been grown by Electron Cyclotron Resonance Chemical Vapour Deposition (ECR-CVD) applying a negative bias voltage to the substrate. Structural characterization of the samples was performed by Raman spectroscopy and SEM microscopy. The tribological behaviour (friction coefficient and wear) was evaluated by pin-on-disc tests. We have dealt with several approaching methods for the introduction of metal (Cr, Mo) during the growth of carbon coatings. Metallic atoms supply has been provided in two approaches: a) by placing a target (bulk or biased-mesh) inside the deposition system ( in-situ methods), or b) from nanoparticles dispersions ( ex-situ). The metal-containing films present a low friction coefficient roughly similar to the reference DLC film. When in-situ methods are applied lower wear strength has been detected. Otherwise, we have seen that the incorporation of Cr nanoparticles, coming from 300 ppm ethanol dispersion, produces a significant improvement in the tribological behaviour of the sample, as shown by the severe increase in the sliding distance until coating rupture. Therefore, from the comparison among the three different methods we can infer the clear key role played by the incorporated metal nanoparticles into fullerene-like carbon films for the improvement in the tribological properties of the nanocomposites.