Structural and mechanical properties of (B_0.5-xSi_x)N_0.5films synthesized by dual-ion-beam deposition

The structural and mechanical properties of ion-beam deposited (B0.5-xSix)N0.5films (0≤x ≤0.5) were characterized by x-ray photoelectron spectroscopy, infrared absorption experiments, and nanoindentation tests. A single-layer BN film (x = 0) has 70 vol. % in cubic phase (c-BN), and a hardness of 38 GPa. However, it peeled off very soon after deposition due to the high internal stress. If a buffer layer was deposited first, followed by a (B0.5-xSix)N0.5 film with x ≈ 0.013, the whole configuration adhered very firmly to both quartz and silicon substrates. This improvement in adhesion was probably due to the formation of Si-N bonds, which served to release partly the stress inside the (B0.5-xSixN0.5films. Since the Si content was low, the film structure remained highly cubic, and there was no observable drop in hardness. For higher x, the cubic structure in (B0.5-xSix)N0.5films disappeared rapidly and was replaced by a hexagonal structure. This structural change led to a rapid drop in hardness from 38 to 12 GPa. As x was further increased, more Si-N bonds were formed in the (B0.5-xSix)N0.5layers. As a result, the hardness increased from the minimum value to a value ≈24 GPa.