Inhomogeneous carbon bonding in hydrogenated amorphous carbon films

Hard-carbon films prepared by the rf-plasma decomposition of acetylene have been investigated by high-resolution 13C nuclear magnetic resonance spectroscopy, x-ray photoelectron spectroscopy (XPS), and the H( 15Nα,γ)C nuclear resonant reaction. It was found that the ratio of sp2 bound carbon was 1.6, and that virtually all sp3 carbon atoms are, in fact, bound to one or more hydrogen atoms. Bulk layers contain about 40% hydrogen; however, results of the measurements of the hydrogen concentration, as well as those of XPS, confirm that the composition and properties of these carbon films are a strong function of their distance from the initial growth interface, and are spatially varying over the first 40 nm.