Elastic constants of tetrahedral amorphous carbon films by surface Brillouin scattering

The elastic constants of tetrahedral amorphous carbon (ta-C) and hydrogenat ed tetrahedral amorphous carbon (ta-C:H) thin films were determined nondest ructively by surface Brillouin scattering. Besides the usual Rayleigh surfa ce mode, we also observe a new pseudosurface acoustic mode of longitudinal polarization, which is a modified version of the longitudinal guided mode u sually found in slow-on-fast supported films. The Young's modulus E of a ta -C with 88% sp(3) is 757 GPa, and the shear modulus G is 337 GPa. The modul i of ta-C:H with 70% sp(3) and 30 at. % H are lower, E = 300 GPa and G = 11 5 GPa. (C) 1999 American Institute of Physics. [S0003-6951(99)02538-3].