Vibrational properties of carbon nitride films by Raman spectroscopy

The Raman spectrum of amorphous carbon nitride films deposited by Penning-type opposed target DC reactive sputtering has been studied to observe the effect of nitro en concentration on the film bonding structure. Previous FTIR studies have shown that if nitrogen is present at levels >25 at.%, the excess above this occurs in an IR invisible bonding structure. The results presented here identify a heretofore unseen Raman peak which occurs between the commonly found G and D bands of carbon nitride films. This peak becomes visible at a nitrogen content of similar to 25 at.% and thereafter increases with nitrogen content. XPS results have also shown that the peak due to nitrogen-nitrogen bonding increases in a similar manner. We therefore identify this new Raman peak as being due to nitrogen-nitrogen bonding. As the nitrogen content in the film increases, an overall shifting of the G and D bands to higher wave numbers occurs due to a change in sp(2) domain size and overlapping of sp(2)-type bonding of C=C and C=N stretching bands. After annealing, the nitrogen-nitrogen peak decreases due to the breaking of the bonds and outdiffusion of nitrogen. The valence band XPS spectrum shows the interlinked carbon backbone nature of the carbon nitride solid and thus can be used as a fingerprint of the structural nature of this solid, which is significantly different from diamondlike and graphitic features. (C) 1998 Elsevier Science S.A. All rights reserved.