Synthesis and characterization of pure crystalline C-N film

We report successful experimental synthesis of pure crystalline C-N film on silicon and nickel substrates by bias-assisted hot filament chemical vapor deposition (bias-HFCVD). The obtained films have been firmly characterized by energy dispersive X-ray (EDX) and Auger electron microscopy for the chemical composition, X-ray diffraction (XRD) and selective-area electron diffraction (SAED) for the lattice structure, and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for the crystal morphology and symmetry. Our experimental lattice constants of alpha-C3N4 (a = 6.38 Angstrom, c = 4.648 Angstrom) and beta-C3N4 (a = 6.24 Angstrom, c = 2.36 Angstrom) with a relative N/C composition of 1.30-1.40 on nickel are in good agreement with the ab initio calculations by less than 1.3% and 2.5%, respectively. A new tetragonal C-N phase with a = 5.65 Angstrom and c = 2.75 Angstrom was identified for the first time in the laboratory. Furthermore, a specific C3N4 phase growth was studied by adding a fraction of hydrogen. A ''lattice match selection'' for the growth of C3N4 crystals on silicon is proposed.