Elastic constants of tetrahedral amorphous carbon films by surface Brillouin scattering

Abstract

The elastic constants of tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H) thin films were determined nondestructively by surface Brillouin scattering. Besides the usual Rayleigh surface mode, we also observe a new pseudosurface acoustic mode of longitudinal polarization, which is a modified version of the longitudinal guided mode usually found in slow-on-fast supported films. The Young’s modulus E of a ta-C with 88% sp3 is 757 GPa, and the shear modulus G is 337 GPa. The moduli of ta-C:H with 70% sp3 and 30 at. % H are lower, E=300 GPa and G=115 GPa.