Vibrational and optical properties of carbon nitride films prepared by reactive magnetron sputtering

Carbon nitride films were prepared by reactive magnetron sputtering of a gr aphite target in a nitrogen atmosphere at different pressures and temperatu res. The films were characterized by infrared, Raman and ultraviolet-visibl e spectroscopies, as well as by ellipsometry. We obtained hydrogen-free dar k films when a negative bias was applied to the substrates; the samples pre pared at room temperature without bias were soft and hydrogen could be dete cted in their infrared spectra. The most prominent features, between 1000 a nd 1700 cm(-1), in both the Raman and infrared spectra were modelled using two Gaussian curves. As the nitrogen content was varied, the ratio between their areas followed opposite trends in the Raman and the infrared spectra. The presence of hydrogen caused the main feature to absorb more strongly a t lower frequencies but did not alter the trend. The presence of six and fi ve membered heteroaromatic rings is suggested to explain the increase of th e infrared vibrations associated with double conjugated double bonds. The i ndex of refraction can be correlated with features in the infrared spectra suggesting that its value increases as the number of carbon and nitrogen do uble bonds increases. Ion bombardment reduces nitrogen incorporation; it is responsible for the densification of the films and the introduction of sev eral defects that make films prepared under bias more absorbing in the low energy region.