[Influence of nitrogen doping on electron structure and optical properties of amorphous carbon thin films]

Nitrogen doped amorphous carbon (a-C : N) thin films were prepared by DC magnetron sputtering. The films were investigated by AES, UV-Vis and ellipsometer. A parameter 'D' defined as the distance between the maximum of positive going excursion and the minimum of negative going excursion was calculated in the derivative AES spectra. The values of 'D' were used to calculate the percentage of sp2 hybrid bonds. The optical transmission and the optical band gap of the films were characterized by an UV-Vis spectrophotometer. The results showed that the optical band gap decreased and then increased with the increase of N2 gas source. The transmission and refractive index changed in reverse order. It was demonstrated that the thin film with low percentage of nitrogen was beneficial to the formation of sp3 hybrid bonds and caused the optical band gap of the thin film to increase. As a result, the thin film should be prepared under low percentage of nitrogen pressure to ensure that it possesses fine optical properties.