Local structure of composite Cr-containing diamond-like carbon thin films

Composite Cr-containing hydrogenated amorphous diamond-like carbon (Cr-DLC) films were synthesized by a hybrid PVD/CVD plasma-assisted deposition process. In a recent study, it was found that Cr-DLC films with <∼12 at.% Cr possess excellent tribological properties. However, the role of Cr in inducing these characteristics is not clear. In the present report, the local structure around the Cr atoms in the latter films was studied as a function of Cr content by X-ray absorption spectroscopy. The Cr K-edge X-ray absorption near edge structure spectra show that Cr in DLC has a chemical state similar to that of chromium carbide. Analysis of the extended X-ray absorption fine structure spectra shows that at low Cr content (<0.4 at.% Cr), Cr is dissolved in the amorphous DLC matrix forming an atomic-scale composite. Simulation studies suggest that in the latter films, Cr tends to be present as very small atomic clusters of 2–3 Cr atoms. At higher Cr contents (>1.5 at.%), Cr is present as nanoparticles (<10 nm) of a defected carbide structure forming a nanocomposite.