Characterization of pulsed laser deposited h-BN films and h-BN/c-BN layer systems

Abstract

Boron nitride films were prepared by pulsed laser ablation from a boron nitride target using a KrF-excimer laser, where the growing films were deposited in nitrogen atmosphere or bombarded by a nitrogen/argon ion beam. Films deposited at high growth rates or weak ion bombardment are hexagonal with turbostratic microstructure (called here l-BN) and show high adhesive strength to silicon and stainless steel substrates. By using them as intermediate layers, the adhesion of pure cubic boron nitride films (c-BN) can significantly be improved. l-BN films and l-BN/h-BN/c-BN layer systems have been investigated by in situ ellipsometry and cross-section transmission electron microscopy. The mechanical properties, i.e. stress and hardness, of those films and layer systems are presented. l-BN films deposited at high laser energy densities may have compressive stresses as high as 16 GPa. Their Vickers microhardness is in the range of 25–5.4 GPa depending on substrate temperature and ion bombardment. The compressive stresses of 400 nm thick adherent c-BN films were estimated to be 4.5 GPa.