Characterization of hydrogenated amorphous carbon films by nuclear magnetic resonance techniques

Different nuclear magnetic resonance (NMR) methods have been used to investigate the structure of hydrogenated amorphous carbon films. Besides measuring the sp²-to-sp³ ratio by means of ¹³C cross-polarization magic-angle spinning total suppression of spinning sidebands NMR we studied the distribution of covalently bound hydrogen over sp²- and sp³-type carbon atoms using dipolar dephasing techniques. The reliability of the dipolar dephasing measurements is discussed and the results are compared with the data derived from a simple statistical model. Moreover they are compared with previous IR spectroscopy measurements. ¹H combined rotation-and-multipulse NMR spectra are presented which do not show resolved proton resonances in the case of as-deposited films but correspond in their line shape to the proton distribution measured with dipolar dephasing. Finally a few considerations concerning a refined structural model are presented.