Deposition and characterisation of nanocrystalline Mo2N/BN composite coatings by ECR plasma assisted CVD

In this study, nanocomposite coatings consisting of the nitrides of Molybdenum and boron are deposited on Si using a hybrid ECR-CVD and sputtering of molybdenum using a BF3–H2–N2 reactive gas mixture in He plasma. By controlling the gas ratio, the film composition and crystallinity can be modified. The film structure, chemical and phase composition and mechanical properties are characterised by glancing incidence X-ray diffraction (GI-XRD), Fourier-transform Infrared spectroscopy (FTIR), Time-of-Flight Secondary Ion Mass Spectrometry (tof-SIMS), Scanning and transmission electron microscopy (SEM and HRTEM), and nanoindentation. FTIR measurements indicate that the mass fraction of the BN phase can be varied by changing the gas ratio BF3/H2. XRD and SEM observations reveal a decrease in the crystallite size of the γ-Mo2N phase below 50 nm associated with increasing the BN fraction. XRD line profile analysis indicated an exponential decay in the mean size of coherently diffracting γ-Mo2N crystallite domains which in turn develop large compressive strains by increasing the film BN fraction. Film hardness ranges from 10 ± 1 to 18.5 ± 0.5 GPa while the reduced elastic modulus decreases monotonously from 220 ± 22 to 94 ± 1 GPa by increasing the BF3 flow rate from 0 to 1.8 sccm, respectively. However, the ratio of hardness to reduced elastic modulus (H3/E2) shows a maximum for films prepared with 0.23 and 0.45 sccm BF3 suggesting that these nanocomposite films are expected to show improved tribological performance and can therefore be interesting for wear resistance applications.