Ar-dilution effects on the elastic properties of hydrogenated amorphous hard-carbon films grown by plasma-enhanced chemical vapor deposition

Hydrogenated amorphous carbon (a-C:H) films were deposited, at room temperature, from a CH4/Ar plasma produced by a radio frequency (rf) glow discharge system at 13.56 MHz, and different power values. X-ray reflectivity and Brillouin light scattering have been used to investigate the relationship between deposition conditions and elastic properties of hydrogenated amorphous carbon films. The composition of the initial gaseous mixture and the rf power input are shown to affect significantly both the mechanical and the microstructural properties of deposited films. As the fraction of methane in the feed gas is increased, both the film density and the phase velocity of the surface Rayleigh wave exhibit an enhancement, thus indicating the production of a harder material. On the other hand, x-ray reflectivity measurements suggest the occurrence of a higher degree of structural order in the sp(2) lattice. Experimental findings are discussed in terms of the different chemical composition of the plasma.