Carbon nitride thin films synthesized from the gas-phase by laser-induced reactions: A parametric study

The possibility of a new ultrahard phase of carbon nitride, with hardness comparable to or greater than that of diamond was first suggested by Liu and Cohen. The presence of α- and β-C₃N₄ phases has been suggested on the basis of electron and X-ray diffraction studies but the overall composition of the films was not stoichiometric. In this study we focused on the chemical composition and morphology of CN_x thin films deposited from the gas phase (ternary gas mixtures of C₂H₄/N₂O/NH₃) by laser-induced chemical vapour deposition (LCVD), in connection with some important experimental parameters: i) laser wavelength; ii) gas phase composition and iii) nature of the substrate. Alternatively, the radiation at 10.6 μm (cw CO₂ laser) and the radiation at 248 nm (KrF excimer laser) were used, perpendicularly irradiating the substrates (alumina, quartz, sapphire). During irradiation the gaseous composition was monitored by IR spectrophotometry. X-ray photoelectron spectroscopy (XPS), transmission electron diffraction (TED) and scanning electron microscopy (SEM) were used to analyze the chemical composition and the morphology of the deposited films. SEM and TED analysis showed the polycrystalline nature of the deposited films.