Formation of cubic boron nitride films on nickel substrates

Cubic boron nitride (c-BN) films were synthesized by radiofrequency (r.f.) magnetron sputtering at a frequency of 13.56 MHz from an h-BN target. The substrate used was high-purity polycrystalline nickel foil (0.125 mm thick). The deposition process was carried out in an Ar-N₂ gas mixture (in a ratio of 5:1) at a total pressure of 10-15 mTorr. The ion flux impinging on the substrate was enhanced by an auxiliary electrode placed between the magnetron and the substrate. The main deposition parameters included substrate temperature and negative bias voltage. The films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). By the proper cleaning procedure of substrate and parameter optimization, stable and adherent films with a c-BN fraction above 90% have been achieved. The substrate surface state and energetic bombardment, including the ion flux and energy, were essential factors controlling the formation of sp³-bonded cubic phase during deposition. It was found that the application of a negative bias voltage higher than 150 V at substrate temperature of 400-500°C promotes the growth of c-BN phase. The present experiment showed that nickel may also be a promising substrate material for the preparation of high quality and well adherent c-BN films under physical vapor deposition (PVD) conditions.