Preparation and characterization of carbon nitride thin films

Carbon nitride (CNx) thin films were deposited by carbon-are evaporation (with and without a bias applied to the substrate) in a low pressure of N-2 or NH3, and by d.c. and r.f. sputtering in N-2 or Ar/N-2 mixture. Substrates were cleaved KCl, mica and {100} silicon, held at temperatures between - 100 degrees C and 600 degrees C. Transmission electron diffraction patterns showed the films to be mainly amorphous, with no evidence for the existence of a proposed beta-C3N4 crystalline phase. N/C ratios of the as-deposited CNx film, measured from electron energy-loss spectroscopy (EELS), were between 0 and 0.75 depending on deposition conditions. The bonding type was investigated from the fine structure of the carbon K-ionization edge; the pi*/sigma* intensity ratio was found to be higher than that of graphite, particularly at high nitrogen content, suggesting the existence of sp bonding and/or charge transfer between carbon and nitrogen atoms. After annealing to 800 degrees C, up to 75% of the nitrogen was released, indicating that most of the carbon-nitrogen bonds are weak.