Solid state C-13 and H-1 nuclear magnetic resonance investigations of hydrogenated amorphous carbon

Various hydrogenated amorphous carbon films have been analyzed by C-13 and H-1 nuclear magnetic resonance (NMR) spectroscopies. The films have been de posited from acetylene or cyclohexane by dc plasma enhanced chemical vapor deposition, at various dc biases and gas pressures. The total hydrogen cont ent has been measured by forward recoil elastic scattering (FRES). C-13 NMR investigations have been performed in various configurations: high power d ecoupled to determine the sp(2):sp(3) carbon ratio, cross polarized at magi c angle contact spinning with different contact times to provide informatio n on carbon atoms directly bound to hydrogen, and with dipolar dephasing to study the quaternary carbon atoms. By performing the C-13 and H-1 NMR meas urements on the same samples, it was possible to resolve for the first time the seven different forms of unprotonated and protonated CHx carbon, for b oth sp(2)(x = 0,1,2) and sp(3)(= 0,1,2,3) carbon hybridizations, as well as the ratio between bound and unbound hydrogen. The results are discussed an d compared with previously published FRES and Fourier transform infrared (F TIR) data. It is shown that NMR and FTIR combined with FRES do not agree sy stematically on the ratio of bound/unbound hydrogen. (C) 1999 American Inst itute of Physics.