Structural and optical properties of nitrogen-containing tetrahedral amorphous carbon films

Tetrahedral amorphous carbon films (ta-C) and nitrogen-containing ta-C films have been prepared using a magnetic-filtered plasma-deposition method in pure Ar, and Ar with N2 ambient, respectively. The structural and optical properties of these films have been studied using UV-visible optical absorption spectroscopy, Raman spectroscopy, and measurements of electrical conductivity in the temperature range from 300 to 500 K. The value of the optical band gap for the ta-C films deposited at suitable conditions were found to be larger than 3 eV. For nitrogen-containing ta-C films deposited at low partial pressure of nitrogen, the incorporation of a small amount of nitrogen will result in a slight drop in activation energy of conductivity and a decrease in band gap, which indicates that there are evidently both doping effect of nitrogen and graphitization of bonding. The study of surface morphology has been performed using atomic force microscopy (AFM), and results show that the surface roughness increases with the amount of nitrogen incorporated in ta-C films. The correlation between surface roughness and configuration of N atoms in ta-C network is also discussed.