An electron spectroscopy study of a-C:H films produced by PACVD in a CH4-CO2 gas mixture

The near surface region microstructure of a PACVD a-C:H film is investigated by probing the occupied electron states by electron energy loss spectroscopy (EELS) in the low loss region, C KVV Auger emission, C 1s photoemission, X-ray and UV excited valence band (VB) photoemission. The film, deposited under pulsed bias voltage, is described as a hydrogenated amorphous carbon material, possibly involving a small amount (a few at.%) of oxygen. The C electron states are dominantly sp3 hybridized, with H stabilizing the associated tetrahedral bond. A maximum of ≈35% sp2 bonded carbons exists in the system. The sp2 sites do not gather into extended π bonded graphite-like structures, thereby allowing the existence of a large (⩾1.8 eV) energy gap. The presence of H explains the mass density (≈1.7 g/cm3) and hardness (≈10 GPa) of the film which both classify it, in spite of the high sp3 fraction, at the border between soft and hard a-C:H materials.