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 properties of hydrogenated amorphous carbonŽa-C:H.films as a function of deposition conditions are reported. A multi-technique approach has been adopted, combining Brillouin light scatteringŽBLS., Raman spectroscopy and X-ray reflectivityŽXRR.. The mass density of the films has been determined by XRR, while BLS has been adopted to test the elastic properties of the films. As the fraction of methane in the feed gas is increased, the deposited film shows both a higher phase velocity of the surface Rayleigh wave, and an increasing density, thus suggesting the synthesis of a harder material. This hardening effect has been attributed to the occurrence of a higher degree of structural order in the sp2 lattice, as suggested by Raman scattering measurements. These experimental findings are related to the different chemical composition of plasmas with different CH4Ar ratios.