Effects of energetic species during the growth of nitrogenated amorphous carbon thin films on their nanomechanical properties

Amorphous carbon nitride (CNx) films are promising materials either as wear-resistant or as solid-lubricant coatings, depending on their mechanical and tribological behavior. In this work, we produced amorphous CNx films by reactive magnetron sputtering, and we varied independently the film density, sp3/sp2 content and [N] concentration. The morphology, density and hybridization state of the CNx films were studied ex situ by X-ray reflectivity (XRR). Also, the effects of energetic species (mainly N+ or Ar+) on their microstructure and composition were investigated. Using the assumptions of the subplantation model and the results of SRIM simulations, we correlated the density of the films and [N] with the N+ ion energy. The nanomechanical and tribological properties of CNx films were studied by nanoindentation and nanoscratch tests. While both adhesion and ploughing mechanisms contribute to the friction behavior in the intermediate and high load ranges, the dominant friction mechanism in the low-load range was attributed to adhesion of the film to the substrate. CNx films grown without ion bombardment (IBD), depending on the normal load, will deform either elastically or elastically-plastically, and may even delaminate. For loads below 5 mN, nanoscratching showed mainly elastic behavior of the film, while above 5 mN, a mixed elastic-plastic behavior was identified. However, the scratch and friction response of the films grown under high-energy ion bombardment (IBD) during ion beam assisted deposition showed a load-dependent transition. The results will be discussed in detail.