Synthesis, characterization and properties of the DLC films with low Cr concentration doping by a hybrid linear ion beam system

A small amount of Cr-doped diamond-like carbon (Cr-DLC) films were deposited on silicon wafers by a hybrid deposition system composed of a DC magnetron sputtering with a Cr target (99.99% purity) and a linear ion source. Cr concentration in the films was controlled by varying the gas flow ratio of Ar/CH4 in the supply gas. XPS, Raman spectroscopy, and HRTEM were employed to analyze the composition and microstructures of the films. The film residual stress was calculated via the Stoney equation, where the curvature of the film/substrate was measured by the laser reflection method. The mechanical properties and tribological behavior of the films were studied by the nano-indentor and ball-on-disc tribometer, respectively. With a small amount of Cr (< 0.3 at.%) doping, the films exhibited a typical amorphous structure feature as the pure DLC film, and neither Cr-C boding nor particulate microstructure was observed in the carbon matrix. The residual stress of the films showed a significant reduction compared with that of the pure DLC film, while the hardness of the films still retained a high value. Furthermore, the films with a low Cr content also exhibited a low friction coefficient and better wear resistance.