Photoelectron emission and Raman scattering studies of nitrogenated tetrahedral amorphous carbon films

Nitrogenated tetrahedral amorphous carbon (N:ta-C) films prepared by the filtered cathodic vacuum arc technique were studied by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet photoelectron spectroscopy and temperature dependent resistance measurement. As the nitrogen flow rate varies from 0 to 20 sccm, the nitrogen content in the deposited film increases from 0 to 4.6 at. %. Curve fitting of the C 1s and N 1s XPS spectra shows that the C–C sp3 fraction decreases with an increase in nitrogen content and that the nitrogen atoms are mainly bonded in sp2 C–N bonds. The pure ta-C film has a work function of 4.35 eV and the N:ta-C films have a value around 4.55 eV. With an increase in nitrogen flow rate, the intensity ratio of the D peak to the G peak, ID/IG increases monotonously from 0.44 to 1.25 and the G peak width decreases from 220 to 199 cm−1. The Tauc optical band gap decreases from 2.2 to 1.8 eV.