Influence of nitrogen pressure on bonding structure and mechanical properties of pulsed laser deposited BCN thin films

• We explored the possibility of improving the mechanical properties by controlling the bonding structure.
• The bonding structure and mechanical properties are changed with increasing nitrogen pressure.
• The change of hardness is in accordance with B–C and sp3 N–C bonds, but contrary to that of sp2 h-B–N bond.

Boron carbon nitride (BCN) thin films were deposited on Si (100) substrates by pulsed laser deposition (PLD) under various nitrogen pressures (pN2) changing from 2.5 to 5.0 Pa. The influences of pN2 on the deposition rate, bonding structure and hardness of the films were studied, so as to explore the possibility of improving their mechanical properties by controlling bonding structure. The deposition rate was found to be increased with increasing pN2, while the hardness of the films fluctuated in the scope of 14.8 to 25.2 GPa. The bonding structure identified by X-ray photoelectron spectroscopy indicated the coexistence of B–N, B–C, and N–C bonds in the films, suggesting the formation of a ternary B–C–N hybridization. The variation of hardness as a function of pN2 was in accordance with the evolution of C–B and sp3 N–C bonds whereas contrary to that of sp2 h-B–N bond. The hardness reached the maximum value of 25.2 GPa at pN2 = 3.5 Pa, where the BCN films possessed the highest intensity of C–B and sp3 N–C bonds and the lowest fraction of sp2 h-B–N bond.