Comparison between picosecond ultrasonics and nanoindentation characterization in thin film

Picosecond ultrasonics is an ultrafast time-resolved technique which offers an unique way of measuring elastic properties in thin films and multi-layers. In the conventional setup only longitudinal waves can be excited by the laser. But in order to have a complete characterization, we need in-plane informations. Here, we show that using a nanostructured aluminum film as a transducer, we can excite longitudinal and high-frequency surface waves using a standard setup. By measuring longitudinal and surface velocities, we can deduce the Young Modulus and the Poisson Ratio which complete the characterization of any isotropic materials. Here we applied this technique and nano-indentation to three SiO₂ films with different thicknesses. The idea is to compare the size reduction effect between this two techniques.