Chemical bonding and nanomechanical studies of carbon nitride films synthesised by reactive pulsed laser deposition

Carbon nitride films were grown on Al2O3-TiC substrates by reactive pulsed KrF excimer laser ablation of graphite targets. Nitrogen contents up to 19 at.% were obtained by increasing the nitrogen partial pressure, P-N2 to 75 mtorr. The effects of P-N2 on the chemical bond structure and nanomechanica l properties of CNx films were investigated by Raman, Fourier transform inf ra-red, X-ray photoelectron spectroscopies and nanoindentation. Quantitativ e analysis of the Raman spectra indicated that the introduction of nitrogen induced a progressive long-range order in the amorphous carbon and an incr ease in the size of sp(2) graphitic clusters. On the whole, the spectroscop ic results suggest an increase of N-sp(2) hybridised C sites with increasin g P-N2. Additionally, Raman spectroscopy established the presence of C=N bo nds at high P-N2. Both the hardness and Young's modulus were significantly reduced from 45 and 463 GPa for pure carbon to 2 and 51 GPa at N concentrat ion of 19 at.%. The deterioration of the nanomechanichal properties with N incorporation is attributed to a transition from an amorphous structure con sisting of predominately sp(3) C bonds to a polymeric like structure involv ing predominately double bonded C and N atoms. (C) 2001 Elsevier Science B. V. All rights reserved.