Solid State 13C and 1H Nuclear Magnetic Resonance Investigations of Hydrogenated Diamond-like Carbon

Various diamondlike carbon (DLC) films have been analyzed by 13C and 1H nuclear magnetic resonance (NMR) spectroscopies. The films have been deposited from acetylene or cyclohexane by d.c.plasma enhanced chemical vapor deposition (PECVD), at various bias and gas pressure, without any enrichment in 13C of the gaseous precursor. The total hydrogen content has been measured by forward recoil elastic scattering (FRES). 13C NMR investigations have been performed in various configurations: high power decoupled (HPDEC) to determine the sp2 : sp3 carbon ratio, cross-polarized at magic angle contact spining (CP-MAS) with different contact times to provide information on carbon atoms directly bounded by hydrogen, and with a dipolar dephasing to study the quaternary carbon atoms. By performing the 13C and 1H NMR measurements on the same samples, it was possible to resolve for the first time the different forms of unprotonated and protonated CHx carbon for both sp2 (x=1, 2) and sp3 (x=1, 2, 3) carbon hybridizations, as well as the ratio between bounded and unbounded hydrogen. The results are discussed and compared with previously published FRES and FTIR data. Recommendations for optimal NMR analysis of DLC films are finally suggested.