Characterization of amorphous carbon-hydrogen films by solid-state nuclear magnetic resonance

Abstract

The structure and properties of thin amorphous carbon films are critically dependent upon the preparation conditions. Hydrogenated amorphous carbon films, prepared by both ion beam sputtering and glow discharge techniques, have been investigated by solid-state 13C magic angle spinning nuclear magnetic resonance measurements of the sp2 and sp3 bonding sites. Film hardness and density correlate with the incorporated hydrogen, whereas the optical band gap is controlled by the fraction of tetrahedral (sp3) versus graphitic (sp2) bonding. It is shown that structural trade-offs prevent the formation of so-called amorphous diamond, i.e., a material with simultaneous extreme hardness and wide optical band gap.