Thermal chemical vapor deposition of layered carbon nitride films under a hydrogen gas atmosphere

We prepared layered carbon nitride (g-C₃N₄) films via thermal chemical vapor deposition under an atmosphere of nitrogen (N₂) and hydrogen (H₂). Crystalline films ordered along the layered stacking direction were deposited using melamine powder as a precursor. A deposition rate of >3 μm was achieved at a synthesis temperature of 575 °C. The bonding states analyzed via X-ray photoelectron spectroscopy indicated the inclusion of H atoms in the g-C₃N₄ films. The number of H-related bonds, such as C–NH_x and C–NH₂, was greater for the deposition under a H₂ gas atmosphere than that under a N₂ gas flow and increased with increasing substrate temperature. In addition to the typical feature of g-C₃N₄ at an absorption edge of 2.80 eV, the energy state originating from the H-incorporation at ∼ 1.70 eV was observed for the deposition under H₂ gas conditions. Furthermore, the energy of the absorption edge was reduced to 2.05 eV when the substrate temperature was increased to 600 °C. The photoluminescence (PL) characteristics at the peak position were not significantly different, regardless of the temperature and flow gas used. Notably, the PL spectral width for the deposition under a H₂ gas atmosphere was narrower than that for the deposition under a N₂ gas atmosphere.