This paper reports the X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) studies of as grown and nitrogen incorporated tetrahedral amorphous carbon (ta-C) films deposited by pulsed unfiltered cathodic vacuum arc process. The effect of varying substrate bias and nitrogen content on the properties of the as grown and the nitrogen incorporated ta-C films has been studied. The XPS spectra indicate that in the as grown ta-C films the C Is peak occurs at 285.15 +/- 0.08 eV and the binding energy (BE) marginally decreases with the increase of substrate bias. The nitrogen incorporated ta-C films show N Is peak at 399.46 +/- 0.10 eV in addition to the C Is peak. The peak position of C 1 s remains unchanged with nitrogen incorporation, whereas the N Is peak seems to marginally decrease in BE, with increasing nitrogen content. From the values of the parameter D, the energy width between the highest maximum and the lowest minimum value of the derivative of C (KLL) spectra, sp(2), sp(3) and sp(3)/sp(2) ratio were evaluated. The values of D, sp(2), sp(3) and sp(3)/sp(2) ratio for the as grown ta-C films are found to be 17.16 eV, 35.7%, 64.3% and 1.80, respectively. The values of D and sp(2) fraction are found to decrease to 16.19 eV and 23.9% and those Of sp(3) and sp(3)/sp(2) ratio are found to increase to 76.1% and 3.18 in the case of ta-C films deposited at an applied substrate bias of 40 V. In the case of applied substrate bias beyond 40 V, the values of these parameters show a reversal in the trend. The nitrogen incorporated ta-C films with 3.6 at.% nitrogen content do not show any change in the values of D, sp(2), sp(3) and sp(3)/sp(2) ratio. With further increase in the nitrogen content up to 15.6 at.%, the values of D and sp(2) fraction decrease continuously to 15.87 eV and 20.1% and the values of sp(3) and sp(3)/sp(2) ratio increase to 79.9% and 3.98, respectively. The study suggests that, at certain conditions of nitrogen incorporation in the case of ta-C films, there is an increase in sp(3) fraction or the diamond like nature of the ta-C films. (C) 2003 Elsevier B.V. All rights reserved.