VIBRATIONAL PROPERTIES OF CARBON NITRIDE FILMS BY RAMAN-SPECTROSCOPY

The Raman spectrum of amorphous carbon nitride films deposited by Penn ing-type opposed target DC reactive sputtering has been studied to obs erve the effect of nitro en concentration on the film bonding structur e. Previous FTIR studies have shown that if nitrogen is present at lev els >25 at.%, the excess above this occurs in an IR invisible bonding structure. The results presented here identify a heretofore unseen Ram an peak which occurs between the commonly found G and D bands of carbo n nitride films. This peak becomes visible at a nitrogen content of si milar to 25 at.% and thereafter increases with nitrogen content. XPS r esults have also shown that the peak due to nitrogen-nitrogen bonding increases in a similar manner. We therefore identify this new Raman pe ak 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 hig her wave numbers occurs due to a change in sp(2) domain size and overl apping of sp(2)-type bonding of C=C and C=N stretching bands. After an nealing, the nitrogen-nitrogen peak decreases due to the breaking of t he bonds and outdiffusion of nitrogen. The valence band XPS spectrum s hows the interlinked carbon backbone nature of the carbon nitride soli d and thus can be used as a fingerprint of the structural nature of th is solid, which is significantly different from diamondlike and graphi tic features. (C) 1998 Elsevier Science S.A. All rights reserved.