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

Abstract

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, p N 2 , ranged from 0 to 50% and the total pressure was 0.25 Pa. A negative bias voltage, V b, 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 p N 2 at the expense of boron content. A reduction of the oxygen contamination was also observed upon nitrogen incorporation. The film density decreases with p N 2 and, for the same nitrogen partial pressure, increases with V b. The main feature of infrared absorption spectra obtained from B 4C 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 BC x N y films are nearly independent of the bias, while a direct correlation between friction and roughness was obtained for B 4C films deposited at different substrate bias voltages: the friction and roughness decreasing with V b.