Ultraviolet and visible Raman studies of nitrogenated tetrahedral amorphous carbon films

Nitrogenated, tetrahedral amorphous carbon (ta-C) films prepared by the filtered cathodic vacuum are (FCVA) technique have been studied using ultraviolet (UV, 244 nm) and visible (514 nm) micro-Raman scattering. The nitrogen ions were produced by a RF ion-beam source with a nitrogen flow-rate varying from 0 to 10.0 sccm, which results in a nitrogen content from 0 to 10.8 at.% in the deposited films. In the visible Raman spectra, only vibrational modes of sp²-bonded carbon (G and D peaks) are observed, while a new wide peak, called the T peak, located at 1090-1320 cm^-1, associated with the vibrational mode of sp³-bonded carbon, appears in the UV-Raman spectra. In the visible Raman spectra, the G-peak width (100-113 cm^-1) and the intensity ratio I_D/I_G (0.34-0.94) are both sensitive to the structural changes induced by N incorporation. In the UV-Raman spectra, the G-peak position almost linearly decreases from 1665 to 1610 cm^-1, and the T-peak position increases tremendously from 1095 to 1314 cm^-1 with increasing N content. The G-peak position and width, and the T-peak position, are all sensitive to the bonding structure of the films.