Microstructure and mechanical properties of pulsed laser deposited boron nitride films

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 without or at weak ion bombardment (such films will be called 1-BN in this paper) are hexagonal with amorphous to turbostratic microstructure (1-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. 1-BN films and 1-BN/h-BN/c-BN layer systems have been investigated by in-situ ellipsometry, infrared spectroscopy and cross-section and plan-view high-resolution transmission electron microscopy, including diffraction. The mechanical properties, i.e. stress and hardness, of these films and layer systems are presented. 1-BN films deposited at higher laser energy densities have compressive stresses as high as 11.5 GPa. Films deposited at lower laser energy densities have stresses in the range of 4.7 to 1.3 GPa and a Vickers hardness in the range of 18.6 to 7.5 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. (C) 1999 Elsevier Science S.A. All rights reserved.