Carbon nitride films were prepared using a dual ion beam assisted deposition technique with a bombardment energy of 100-500 eV. The films were characterized using Auger electron spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy for chemical analysis. A thermal activation model of nitrogen decomposition is presented, which explains the deviation of the observed N/C composition ratio from the N/C arrival ratio. An analysis of the bonding configuration indicates that the ratio of the sp(2) trigonal component to the sp(3) tetrahedral component is strongly dependent on the bombarding energy. A characteristic ion energy is deduced for the formation of tetrahedral amorphous carbon nitrides. The threshold energy enhances the rearrangement of deposited atoms and reduces decomposition of nitrogen atoms.