Elastic constants of ultrathin diamond-like carbon films

The determination of all the elastic constants of a supported film of thickness smaller than 1 mu m is an unsolved problem. Various experimental procedures can be found in the literature, such as nano-indentation and laser spectroscopy methods based on the propagation of surface acoustic waves (SAWs), namely Surface Brillouin Scattering (SBS) and laser-induced SAWs. For the first time, the elastic constants of isotropic diamond-like films (ta-C and ta-C:H) have been determined by SBS from a modified Rayleigh wave and longitudinal guided mode. In SBS, the nano-mechanical response of the film is spontaneously probed by surface acoustic phonons scattering the light beam. A new fitting procedure gives a precise evaluation of the elastic constants even in the extremely difficult case of hard on soft structures. Tn contrast to nano-indentation, the Young's modulus, E, is determined directly. This provides a useful validation of the diverse approaches adopted to analyse nano-indentation data. (C) 2000 Elsevier Science S.A. All rights reserved.