Influence of low level nitrogenation on the structural properties of pulsed laser ablation deposited a-CNx films

The effect of the addition of up to 18% of nitrogen on the structure of diamond like carbon films deposited by laser ablation, has been investigated by means of visible micro-Raman spectroscopy and X-ray photoelectron spectroscopy. The Raman spectra of the films with nitrogen content up to 8%, are characterized by a broad asymmetric band near 1550 cm(-1) (G band), with a shoulder in the 1300-1400 cm(-1) (D band) typical of diamond like carbon systems. Increasing the nitrogen content the D band intensity increased and the G band position shifted towards higher frequencies while its width decreased. The C1s photoelectron peak was found to broaden and shift as the nitrogen content of the films increased. Such a behaviour is interpreted in terms of a transformation of sp(3) bonded carbon atoms into sp(2) ones, induced by the incorporation of nitrogen atoms, besides a clustering process of the sp(2) domains.