Effect of Nitrogen Ion Beam Irradiation on Diamond-like Carbon Films

Diamond-like carbon (DLC) films were deposited on silicon single crystal substrates from toluene vapor using rf plasma. After deposition, the DLC films were irradiated with a nitrogen ion beam and the effects of this irradiation on surface morphology and composition were studied. Nitrogen ion irradiation was performed using a nitrogen ion beam of 0.2 keV for 10 min under a constant ion current density of approximately 70 μA/cm2. Surface morphology was observed by atomic force microscopy (AFM). Changes in composition and carbon-nitrogen bonding states were analyzed by X-ray photoelectron spectroscopy (XPS). Carbon structures were examined by Raman spectroscopy. AFM observations revealed that the DLC film surface became smooth after nitrogen ion beam irradiation. XPS studies showed that nitrogen was absorbed near the surface of the DLC films after nitrogen ion irradiation, and carbon-nitrogen bonding was confirmed in C1s and N1s photoelectron spectra. Carbon structures did not change remarkably after nitrogen ion irradiation. These results show that irradiated nitrogen ions are absorbed into the DLC films to form carbon nitride layers near the surface.