Synthesis of cubic boron nitride films by activated reactive evaporation of H₃BO₃

Abstract

Hard cubic boron nitride films for wear-and-tear applications have been prepared by activated reactive evaporation of H₃BO₃ in the presence of an NH₃ plasma. The plasma was created by electrons emitted from a resistively heated filament and an anode. It was enhanced by an external magnetic field (about 60 G). H₃BO₃ was evaporated from a molybdenum boat in NH₃ at a pressure of 4.5× 10^-2 Pa. The substrates were maintained at 450°C during evaporation and a typical rate of deposition of the boron nitride films was found to be 150 nm min^-1. The films were characterized by electron diffraction, electron microscopy. Auger electron spectroscopy, IR spectra, optical reflectance and transmittance, microhardness and adhesion measurements. The f.c.c. phase of boron nitride was identified. The microstructure consisted of randomly oriented crystallites with an average grain size of 25 nm. Measurements of the reflectance R and the transmittance T suggest an optical gap of 3.64 eV. The films were found to be highly adherent and to have a microhardness of about 2128 kgf mm^-2.