Deposition of boron nitride films by PVD methods: transition from h-BN to c-BN

A cross-section TEM image of a cubic-boron nitride film reveals the well-known layered structure: amorphous-BN, textured turbostratic BN with c-axis parallel to substrate, textured nanocrystalline (111) c-BN planes and turbostratic BN upper layer. The thickness of the sp2 layer depends on deposition conditions and in the case of IBAD techniques lies between 10 and 30 nm. A lack of knowledge about this sp2 BN layer with c-axis parallel to the substrate is mainly due to its small thickness and to the fact that it is a buried layer. Nevertheless, we consider that it is possible to obtain films with the same features using deposition conditions as close as possible to those for h-BN to c-BN transition. Pure h-BN films with thickness up to 200 nm were deposited and analysed using stress, density and HRTEM measurements. These sp2 films have compressive stress up to 10 GPa, density up to 3.2 and a rhombohedral structure.