Using nano-scaled Ti and TiN as interlayer, ionic nitrogen doped carbon (CNx (N+)) bilayer films were prepared at various pulse frequencies by cathode arc technique. Elemental distribution at the interface, bonding compositions, microstructure, and mechanical properties of CNx (N+) bilayer films were investigated in dependence of interlayer and pulse frequency by Auger electron spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, nanoindentation, and surface profilometer. The results showed that the diffusion extent of C atoms at the interface of CNx (N+) bilayers is higher than for the alpha-C and CNx (N-2) bilayers with the same interlayer. Nitrogen atoms could diffuse throughout the pre-deposited Ti and TiN layers into the Si substrate for all CNx (N+) bilayers. Ti interlayer facilitates the introduction of N atoms into the CNx (N+) films and exhibits a certain catalytic effect on the coordination of N atoms with sp(2)- and sp(3)-C binding. More nitrogenated and intense CN bonding configurations (mainly graphite-like N) form in the TiN/CNx (N+) bilayer. Ti/CNx (N+) bilayer prepared at low frequency possesses small size and disordering of Csp(2) clusters but TiN interlayer weakens the formation of Csp2 bonding and increases the disordering of Csp(2) clusters in the films. The residual stress in the bilayer is lower than for CNx (N+) monolayer. The higher hardness and the lower residual stress are present in the TiN/CNx (N+, 10 Hz) bilayer. (C) 2015 Elsevier B.V. All rights reserved.