CARBON NITRIDE FORMATION BY LOW-ENERGY NITROGEN IMPLANTATION INTO GRAPHITE

Recently, some attempts to produce the new beta-C3N4 phase with hardness higher than diamond have been reported. In this paper, a model study of carbon nitride formation by low-energy nitrogen implantation into graphite is presented. Room temperature (RT) and hot (500 degrees C) nitrogen implantations were performed at saturation and low doses. The formation of chemical bonds between implanted nitrogen and carbon atoms was assessed by in situ X-ray photoelectron spectroscopy. It was found that two dominant nitrogen bonding states are formed in the implanted layer. The relative distribution of these states depends on the implantation temperature, dose and post-annealing process. Hot nitrogen implantation results in a predominant population of the more covalent (higher binding energy) nitrogen bonding state which has been suggested to be characteristic of the beta-C3N4 phase. Post-annealing of a low-dose nitrogen-implanted graphite results in a distribution of the nitrogen bonding states similar to the hot implantation case. RT implantation at saturation doses followed by annealing leads to a different distribution of the nitrogen bonding states. The implantation-induced damage was investigated by means of electron-excited C(KVV) Auger line shape measurements. Hot implantation results in point defect formation, although the graphite structure is not completely amorphized. The experimental results suggest that hot nitrogen ion beam-assisted deposition can lead to the formation of the new beta-C3N4 phase.