Properties of ion-assisted pulsed laser deposited H-BN/C-BN layer systems

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 ion-to-arriving-target-atom (I/A) ratios at the substrate below 0.5 (1-BN) are hexagonal. Nucleation of the cubic phase (c-BN) takes place exclusively with ion bombardment at I/A ratios above 1.0, which may be reduced down to 0.6 after the completion of the nucleation process. The adhesion of c-BN films is improved significantly using 1-BN films as intermediate layers. Up to 400-nm thick c-BN films have been investigated by cross-section transmission electron microscopy (TEM). The 1-BN layers show a strong preferred orientation with the c-axis parallel to the substrate surface. The crystallites of the nearly phase purl c-BN layers show strong < 110 > preferred orientation. The Vickers microhardness of 1-BN films is in the range of 25-5 GPa and the compressive stresses in the range of 2-16 GPa, The compressive stresses of 400-nm thick c-BN films were in the range of 4-6 GPa. (C) 2000 Elsevier Science B.V. All rights reserved.