Tribological properties of diamond-like carbon films deposited by negative carbon ion beam

Abstract

Excellent antiwear diamond-like carbon (DLC) films were prepared on silicon wafers by a novel negative carbon ion beam deposition system. This system does not need any gas in the chamber; deposition occurs under high vacuum. The ion source has good control of the C− beam energy (from 50 to 150 eV) and produces a 0.5-in.-diam ion beam for DLC coating. All coatings showed ultrasmooth surfaces (Ra∼1 nm) and good adhesion. The results of infrared and Raman spectroscopy show that the degree of diamond-like character in the films, the sp3 fraction, increases as a function of deposition energy in this particular energy range. The nanoindentation hardness of the films also increases from 15 to 50 GPa as deposition energy increases. The wear rates and friction coefficients against a M-50 steel bearing ball were measured in a pin-on-disk tribometer with a normal load of 9.8 N, calculated nominal Hertzian stress of 0.8–1.8 GPa. The measured wear rates of the DLC films were of the order of 10−7 and 10−8 mm3/N m depending on the deposition energy of the carbon beam. The friction coefficients in the steady state were found to be around 0.1. These results indicate excellent applications for abrasion resistant DLC coatings. We are developing a rectilinear negative carbon ion beam deposition system (up to 8 in.) for large area application, and many of the process scale-up issues have been solved.