Nitrogen incorporation into boron carbide films deposited by dc-magnetron sputtering: film microstructure and tribological properties

The effects of nitrogen incorporation into amorphous boron carbide films deposited by dc-magnetron sputtering in argon–nitrogen atmospheres were studied. The partial pressures of nitrogen, pN2, ranged from 0 to 50% and the total pressure was 0.25 Pa. A negative bias voltage, Vb, was applied to the substrates (0 to −100 V). Rutherford backscattering spectrometry was used to determine the overall film composition and nuclear reactions were used for the measurement of the nitrogen and boron content. The nitrogen content of the films increases with pN2 at the expense of boron content. A reduction of the oxygen contamination was also observed upon nitrogen incorporation. The film density decreases with pN2 and, for the same nitrogen partial pressure, increases with Vb. The main feature of infrared absorption spectra obtained from B4C films is a broad band at approximately 1000 cm−1 that shifts to higher wavenumbers upon nitrogen incorporation. The IR spectra obtained from films with the higher nitrogen content have a broad band at approximately 1400 cm−1 and a smaller one at 800 cm−1, typical of hexagonal BN. The friction coefficient of the film and its roughness were investigated in nano-scale by atomic force microscopy. The roughness and friction coefficient for BCxNy films are nearly independent of the bias, while a direct correlation between friction and roughness was obtained for B4C films deposited at different substrate bias voltages: the friction and roughness decreasing with Vb.