Microtribological Properties of DLC Films Prepared by Different Methods

Abstract

Diamond-like-carbon (DLC) films are considered ideal solid lubricating films for friction reduction and anti-wear on material surfaces. However, the microtribological properties of DLC films are sensitive to many factors. In this study, DLC films were prepared through three techniques by using a self-made microwave-electron cyclotron resonance-plasma source ion implantation apparatus to determine their microtribological properties under the working conditions in a microelectromechanical system (MEMS). The three adopted techniques were unbalanced magnetron sputtering, plasma source ion implantation, and plasma-enhanced chemical vapor deposition. The diamond-like properties of the prepared films were characterized by X-ray photoelectron spectroscopy. The microtribological properties of the DLC films were analyzed by atomic force microscopy. The effects of preparation techniques, slide number, load, and relative sliding velocity on the microtribological features of the thin films were also investigated. Results reveal that in the load range of 2-20 µN, the friction coefficients of the DLC films prepared by the three techniques are 1.8, 1.4, and 0.9 mV/nN. The prepared DLC films have lower friction coefficients than that of the Si surface (2.6 mV/nN). Under the same loading conditions, the changes of the frictional force are related to the slope of the rough peak, and the increase in frictional force is proportional to the square of the slope. The wearing depth of the DLC films is nonlinearly related to the number of wear cycles, and the wear resistance on the surface of the DLC film is worse than that in the deeper layers. Sliding velocity slightly affects the friction coefficients when the normal load is several nanonewtons. This study provides references for the application of DLC films in the surface modification of MEMS devices.