Structure and optical properties of Cu-DLC composite films deposited by cathode arc with double-excitation source

Abstract

Copper-doped diamond-like carbon films (Cu-DLC) were fabricated on silicon and quartz substrates by cathode arc technique with direct-current and pulse double-excitation source. The microstructure, composition, morphology, hardness and optical properties of the films were studied by Raman, XPS, AFM and SEM, UV-Vis, laser ellipsometer and Vickers sclerometer. The results showed that Cu doping increases the size, ordering and amount of sp2-C clusters in the Cu-DLC composite films. The microstructure parameters enhance with increasing the Cu content to 22.4wt%. All the films show specific nano-structural surface, however, the lower Cu content induces finer particle formation in the Cu-DLC films. When the arc current is higher than 60A, the roughness and particle size of Cu-DLC composite films increase with increasing the Cu content. The average transmittance of the Cu-DLC films in Vis-NIR region is smaller than 40% when the Cu content exceeds 12.6wt%. With increasing the Cu content, the optical band gap (Eg) of the films decreases from 3.54eV to 0.25eV. The relationships among the Eg, refractive index and extinction coefficient for the Cu-DLC films were found and indirectly revealed the correlation of microstructure and optical properties of the films with the Cu content variation.