Monitoring the structural and chemical properties of CNx thin films during in situ annealing in a TEM

Carbon nitride films synthesised by magnetron sputtering at different substrate temperatures have been studied using electron energy loss spectroscopy (EELS) during annealing performed in situ in a transmission electron microscope (TEM). The proportion of sp(2) hybridised carbon slightly decreases initially during heating, presumably because of the removal of defects in the structure, whilst it increases at higher temperatures when graphitisation tends to take place, as confirmed by high resolution electron microscopy (HREM). Substantial amounts of nitrogen (up to similar to 80%) are removed following annealing at 1000 degreesC. A corresponding decrease in the pre-peak of the nitrogen spectra suggests that pyridine-like N is released by annealing. As this peak component decreases, a second peak, of weaker intensity, is becoming apparent in the EELS spectra when the films are heated at temperatures above approximately 700 degreesC. The possibility has been suggested that this corresponds to N substituted for C in a graphitic structure, with possibly also some N-2 contributing to the peak.