Structural characterisation of CNx thin films deposited by pulsed laser ablation

Carbon nitride (CNx) film growth by 193 nm pulsed laser ablation of graphite in a low pressure of N-2 has been investigated both by studying optical emission from the plume and by analyses of the composition, structure and bonding of material deposited at a range of substrate temperatures. Spectral analysis of the emission reveals the presence of C+ ions, C atoms, C-2 and CN radicals and N-2(+) molecular ions within the ablation plume travelling towards the substrate. Films deposited at low substrate temperature (T-sub) are amorphous, with an N/C ratio of similar to20 at.%. Raman analysis shows CNx films grown at higher T-sub to be increasingly nanocrystalline, but thinner, and suggests that N inclusion encourages nanocrystallite formation. X-ray photoelectron spectroscopy reveals that CNx films grown at higher T-sub also have a reduced overall N content. The observations have been rationalised by assuming an increased propensity for sputtering or desorption of more labile CN species from the growing film surface at higher T-sub, resulting in a higher fraction of C-C bonding-most probably in the form of graphitic nanocrystallites embedded in an amorphous matrix. (C) 2003 Elsevier Science B.V. All rights reserved.