A comparison study of microstructure and bonds composition of carbon nitride (CNx) films fabricated at atomic and ionic nitrogen source by pulse cathode arc method was presented. The relative fractions of CN/CC bonds, N-sp(3)C/N-sp(2)C and graphite-like/pyridine-like N bonding configurations in the CN films were evaluated by combining C1s and N1s X-ray photoelectron spectroscopy with the hardness and optical band gap measurement. The dependence of microstructure (quantity, size and disordering degree of Csp(2) clusters) of CNx films on the nitrogen source and pulse frequency was determined by Raman spectroscopy. Films with high atomic ratio of nitrogen/carbon (0.17) and high hardness were produced at ionic nitrogen source and low pulse frequency. The results showed that ionic nitrogen source facilitated the formation of CN bonds and N-sp(2)C bonding configurations (mainly in graphite-like N form). Moreover presenting an optimum pulse frequency (similar to 10 Hz) leaded to the most nitrogen coordinated with sp(3)-C and the highest ratio of CN/CC bonds in the CNx films. An equilibrium action mechanism might exist between the quantity and energy of carbon and nitrogen ions/atoms, giving more nitrogen-incorporated carbon materials. These allow us to obtain the high content of N-Csp(3) bonding and expected bonding structure by optimizing pulse frequency and nitrogen source. (C) 2013 Elsevier B. V. All rights reserved.