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, Cls 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 sp(3) hybridized, with H stabilizing the associated tetrahedral bond. A maximum of approximate to 35% sp(2) bonded carbons exists in the system. The sp(2) sites do not gather into extended pi 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/cm(3)) and hardness (approximate to 10 GPa) of the film which both classify it, in spite of the high sp(3) fraction, at the border between soft and hard a-C:H materials. (c) 2005 Elsevier B.V. All rights reserved.