Nitrogen-induced modifications in microstructure and wear durability of ultrathin amorphous-carbon films

Abstract

A systematic experimental investigation was carried out to understand the effects of nitrogenation on the microstructure and wear durability of thin amorphous-carbon films. The films were fabricated with 0%, 10%, 15%, 20%, 30%, 40%, and 50% N2 in the sputter gas. Microstructure properties were characterized using Rutherford backscattering spectroscopy, electrical resistance, Raman spectroscopy, and x-ray photoelectron spectroscopy. Nanohardness and scratch wear resistance of the films were studied with an atomic force microscope equipped with a diamond tip. The head–disk interface tribological properties of the films were tested with industrial standard contact–start–stop wear instrumentation. The results indicate that the introduction of nitrogen into the carbon film increases the film lattice disorder and allows for the formation of carbon–nitrogen single, double, and triple bonds. The nitrogen atomic concentration in the film, electrical resistance, and the ratio of carbon–nitrogen bonds to carbon–carbon bonds increase with increasing N2 in the sputter gas. A significant addition in C≡N bond percentage is observed when the N2 exceeds 30% in the sputter gas. Both the nanohardness and scratch wear resistance of the carbon film can be significantly improved by incorporating an optimized nitrogen concentration in the film. In this study, the film processed with 30% N2 showed the highest nanohardness and wear resistance. The degraded nanowear resistance for the films processed with 40% and 50% N2 is attributed to the significant addition of C≡N bonds. Within a wide process range (15%–30% N2), the films exhibit excellent tribological performances at the head–disk interface. The wear mechanisms from the contact–start–stop wear tests are interpreted based on the understanding of film structures and film mechanical properties.