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, PN2 to 75 mtorr. The effects of PN2 on the chemical bond structure and nanomechanical properties of CNx films were investigated by Raman, Fourier transform infra-red, X-ray photoelectron spectroscopies and nanoindentation. Quantitative analysis of the Raman spectra indicated that the introduction of nitrogen induced a progressive long-range order in the amorphous carbon and an increase in the size of sp2 graphitic clusters. On the whole, the spectroscopic results suggest an increase of N-sp2 hybridised C sites with increasing PN2. Additionally, Raman spectroscopy established the presence of CN bonds at high PN2. 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 concentration of 19 at.%. The deterioration of the nanomechanichal properties with N incorporation is attributed to a transition from an amorphous structure consisting of predominately sp3 C bonds to a polymeric like structure involving predominately double bonded C and N atoms.Copyright © 2001 Elsevier Science B.V. All rights reserved.
- sp2 bonding
- Raman spectroscopy