Nitrogen driven structural transformation in carbon nitride materials

The variation of local bonding as a function of nitrogen concentration in plasma-assisted pulsed-laser deposited carbon Ž . nitride films has been systematically studied. Time-of-flight TOF mass spectroscopy and electron energy loss spectroscopy Ž . 3 Ž . EELS were combined to identify ablation conditions that produce highly sp -hybridized diamond-like-carbon DLC for typical carbon nitride growth pressures. EELS studies of carbon nitride films grown using these optimal conditions demonstrate that there is a structural transformation from ;70 to 0% sp-bonded carbon as the nitrogen concentration increases from 12 to 17%. Density measurements show that this transformation is accompanied by a density decrease from 3.3 to 2.1 grcm. Hartree–Fock and density functional calculations on nitrogen substituted diamond clusters show that there is a strong preference to form sp-bonded carbon when the local nitrogen concentration is larger than 12 atomic percent. These experimental results and calculations suggest that amorphous carbon nitride structures with highly sp-hybridized carbon are unstable. q 1998 Elsevier Science B.V. PACS: 61.43.Dq; 71.15.Nc; 81.15.Fg; 82.80.Pv