Characterization of a-CNx:H particles and coatings prepared in a CH4/N2 r.f. plasma

Polymer-like hydrogenated amorphous carbon nitride a-CNx:H particles and coatings were synthesized in a CH4/N2 r.f. plasma with different CH4/N2 mixing ratios. Effects of nitrogen incorporation on microstructure, bonding states and chemical composition have been investigated. Information about chemical bonding and elemental composition has been obtained from FTIR, XPS and EDAX measurements. Infrared results suggest the appearance of different bond types between carbon and nitrogen. Four absorption bands associated with C–H, CC, CN and/or N–H (1300–1800 cm− 1), – CN and – NC (2000–2300 cm− 1), C–H (2800–3100 cm− 1) and N–H and/or O–H (3200–3600 cm− 1) bonds are observed both in particles and coatings. The increase of the nitrogen content leads to an increase of the absorption band at 2200 cm− 1 indicating the continuous increase of – CN bonds. At the same time, the stretching band around 2800 cm− 1 associated to CH stretching modes decreases. Combination between carbon and nitrogen is confirmed from XPS and EDAX analyses. The asymmetry and the width of all the C1s peaks confirm the incorporation of nitrogen-related bonds such as C–N, CN and CN links. The N/C ratio in the particles, provided by XPS, increases versus nitrogen ratio into the gas mixture. A maximum value around 0.5 (≈ 35 at.% of N incorporation) for nitrogen rich plasmas. For the coatings, the N/C ratio increases to reach a constant value about 0.3 for 60% of N2.