Characterization of the mechanical properties of diamond-like carbon films

A recently suggested method to measure the elastic modulus of diamond-like carbon (DLC) films was reviewed. This method used a DLC bridge or free overhang which is free from the mechanical constraint of the substrate. Because of the high residual compressive stress of the DLC film, the bridge or the overhang exhibited a sinusoidal displacement on removing the mechanical constraint. Measuring the amplitude and wavelength of the sinusoidal displacement made it possible to measure the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allowed the calculation of the biaxial elastic modulus of the DLC film. This method was successfully applied to obtain the elastic properties of various DLC films from polymeric hydrogenated amorphous carbon (a-C:H) to hard tetrahedral amorphous carbon (ta-C) films. Since the substrate is completely removed from the measurement system, this method is insensitive to the mechanical properties of substrate. The mechanical properties of very thin DLC films could be thus measured and then can reveal the structural evolution of a-C:H films during the initial stages of deposition.