Structure of amorphous carbon-nitride thin films

CNx thin films were prepared in high vacuum by evaporation of C from a pair of graphite rods in a DC arc ignited in N2 at pressures of up to 1 mbar onto NaCl, Highly ordered pyrolytic graphite (HOPG) and Si substrates. The substrate temperature varied between room temperature and 800 °C. The effect of deposition temperature and N2 gas pressure on the morphology, structure, composition and electrical properties of CNx thin films was studied by high-resolution transmission electron microscopy (HRTEM), X-ray microanalysis (EDS), and scanning tunneling microscopy and spectroscopy (STM and STS). Morphology ranging from homogeneous layers through spherical or cylindrical particles embedded into the films to low-density globular deposits of CNx was observed as a function of the applied N2 gas pressure. The N composition found was between 1 and 20 at.% and the structure varied from amorphous through fullerene-like to nanocrystalline diamond composed of amorphous CNx, depending on the temperature and the plasma parameters. The behavior of the films during heat treatment was recorded by electrical conductivity measurements. The activation energy of electrical conductivity was found to be 0.18 eV for carbon and 0.38 eV for CNx films and was independent of the deposition temperature.