The microstructure and properties of energetically deposited carbon nitride films

• Films of ta-C:N or sp2 rich CNx formed by controlling nitrogen pressure and substrate bias conditions.
• Higher nitrogen pressure, bias and/or temperature facilitate graphitic bonding in the CNxfilms.
• Films of ta-C:N were hard (~50 GPa) whilst CNx films containing tangled graphitic sheets, were softer and highly ductile.
• The electrical conductance of the CNx films increased with both nitrogen content and substrate bias.

The intrinsic stress, film density and nitrogen content of carbon nitride (CNx) films deposited from a filtered cathodic vacuum arc were determined as a function of substrate bias, substrate temperature and nitrogen process pressure. Contour plots of the measurements show the deposition conditions required to produce the main structural forms of CNx including N-doped tetrahedral amorphous carbon (ta-C:N) and a variety of nitrogen containing graphitic carbons. The film with maximum nitrogen content (~ 30%) was deposited at room temperature with 1.0 mTorr N2 pressure and using an intermediate bias of − 400 V. Higher nitrogen pressure, higher bias and/or higher temperature promoted layering with substitutional nitrogen bonded into graphite-like sheets. As the deposition temperature exceeded 500 °C, the nitrogen content diminished regardless of nitrogen pressure, showing the meta-stability of the carbon–nitrogen bonding in the films. Hardness and ductility measurements revealed a diverse range of mechanical properties in the films, varying from hard ta-C:N (~ 50 GPa) to softer and highly ductile CNx which contained tangled graphite-like sheets. Through-film current–voltage characteristics showed that the conductance of the carbon nitride films increased with nitrogen content and substrate bias, consistent with the transition to more graphite-like films.