Properties of nitrogen doped tetrahedral amorphous carbon films prepared by filtered cathodic vacuum arc technique

The properties of nitrogen doped tetrahedral amorphous carbon films prepared by the filtered cathodic vacuum arc technique have been studied. The doping species, nitrogen ions, were produced by an ion beam source. The nitrogen flow rate was varied from 0.5 to 10 sccm while keeping other deposition conditions constant. The nitrogen content in deposited films was determined by Rutherford backscattering technique and ranged from 5 to 34 at.% depending on the nitrogen flow rate. The surface morphology, mechanical, optical, and electronic properties of the films were measured. The compressive stress, the hardness and the optical band gap all increased at low nitrogen content to a maximum at 5 at.% nitrogen and then decreased with increasing nitrogen content. The activation energy first increased and then decreased with increasing nitrogen content. We attribute these changes to the Fermi level moving up in the band gap, from below the midgap to near conduction band. We achieved continuously adjustable band gap and complex refractive index with nitrogen incorporation. Possible mechanisms of N ion in the ta-C:N films are discussed.