Ar-dilution effects on the elastic and structural properties of hydrogenated hard carbon films deposited by plasma-enhanced chemical vapor deposition

Results of systematic investigations of the elastic and structural properti es of hydrogenated amorphous carbon (a-C:H) films as a function of depositi on conditions are reported. A multi-technique approach has been adopted, co mbining Brillouin light scattering (BLS), Raman spectroscopy and X-ray refl ectivity (XRR). The mass density of the films has been determined by XRR, w hile BLS has been adopted to test the elastic properties of the films. As t he fraction of methane in the feed gas is increased, the deposited film sho ws both a higher phase velocity of the surface Rayleigh wave, and an increa sing density, thus suggesting the synthesis of a harder material. This hard ening effect has been attributed to the occurrence of a higher degree of st ructural order in the sp(2) lattice, as suggested by Raman scattering measu rements. These experimental findings are related to the different chemical composition of plasmas with different CH4/Ar ratios. (C) 2001 Elsevier Scie nce B.V. All rights reserved.