Hard and elastic amorphous carbon nitride thin films studied by 13C nuclear magnetic resonance spectroscopy

The chemical bonding of hard and elastic amorphous carbon nitride (a-CNx) thin films was examined using solid-state 13C NMR spectroscopy. The films were deposited by DC magnetron sputtering in a pure nitrogen discharge on Si(001) substrates at 300 deg. C. Nanoindentation tests reveal a recovery of 80%, a hardness of 5 GPa, and an elastic modulus of 47 GPa. This combination of low modulus and high strength means the material can be regarded as hard and elastic; the material gives when pressed on and recovers its shape when the load is released. The 13C NMR results conclusively demonstrate that hard and elastic a-CNx has an sp2 carbon bonded structure and that sp3 hybridized carbons are absent. Our results stand in contrast with earlier work that proposed that the interesting mechanical properties of hard and elastic a-CNx were due, in part, to sp3 bonded carbon