X-ray photoelectron spectroscopy study of carbon nitride films

The demand for hard and superhard coatings has inspired many investigators in their attempts to synthesise beta-C3N4. CNx thin films were deposited on c-silicon substrates with simultaneous nitrogen ion bombardment. An electron beam was used for graphite target evaporation, and d.c, gas discharge for creation:of nitrogen ion flow. In this process, plasma that occurs in the space between electrodes and the electron beam ionises nitrogen and carbon atoms. For characterisation of the carbon nitride films, X-ray photoelectron spectroscopy was used. A rapid change of composition occurs in the first 10-15 nm of the material, and then saturation is reached. The N/C ratio passes through the value of 1.33 (which is characteristic of C3N4) and reaches an even higher value at 15 nm. The N1s peak consists of four components. The number of carbon-nitrogen bonds with sp(3) hybridisation goes through a minimum at 5 min sputtering time, reaches a maximum at 10 min and again decreases at 15 min. The behaviour of the area of the peak at about 400.9 eV resembles a mirror reflection through the same interval. This peak position is ascribed to C-N bonding with sp(2) hybridisation. The Cls peak includes five components. The area of the peak at about 287.2 eV, which is due to C-N bonds with sp(3) hybridisation, passes this interval of sputtering time in parallel with the area of the N1s peak at about 399.2 eV, which is also due to this type of bonding. It is ascribed to beta-C3N4. The area of the peak at about 286.3 eV is in parallel with the flow curve for the N1s peak at 400.9 eV, and this behaviour supports the supposition that both peaks are due to C-N bonds with sp(2) hybridisation. Based on the behaviour of curves concerned with sp(2) and sp(3) bonding which resemble a mirror reflection, the conclusion can be drawn that redistribution of C-N bonds between sp(2) and sp(3) bonding occurs during the growth of the film, and a structure is proposed consisting of nanoclusters of beta-C3N4 embedded in an amorphous matrix of C-N bonds with sp(2) hybridisation. (C) 2000 Elsevier Science S.A. All rights reserved.