Nitrogen incorporated diamondlike carbon (a-C/N) films were deposited on silicon (111) wafers using a 90degrees-bend magnetic-filtered cathodic arc plasma system. The structure and properties have been studied by transmission electron microscope (TEM), glancing incident Xray diffraction (GXRD), scanning electron microscope (SEM), electron spectroscopy for chemical analysis (ESCA), Raman scattering (Raman), and Fourier transform infrared spectrometer (FTIR). For the a-C/N film depositions, a highly ionized energetic plasma was used to produce carbon ions with varying ion energies to form various carbon bonding in the film. Applying a bias voltage to the substrate can enhance the ion energy. In this study, nanocrystalline diamond clusters were observed in the a-C/N film because of the existence of a higher fraction of spa bonding contents. Our previous work indicated that the DLC films can have a higher hardness with a negative substrate pulsed bias between -100 and -350 V, and a maximum spa bonding content at about -350 V according to the result of ESCA. The sp(2) bonding content seems to be related to the Raman I-D/I-G ratio. The nitrogen content was also found to increase with substrate bias voltage. The maximum incorporation of nitrogen to the a-C/N film is up to N/C=0.38 (ESCA) using the 90degrees-bend magnetic-filtered cathodic arc plasma system. The hardness rises up to a maximum value of 12.18 GPa at appropriate substrate bias. (C) 2004 Elsevier B.V. All rights reserved.