Modification of vibrational damping times in thin gold films by self-assembled molecular layers

The mechanical contact between a thin gold film and a silicon substrate is investigated by ultrafast pump-probe spectroscopy providing quantitative values on the damping time of coherent longitudinal vibrations of the gold film. A distinct increase in damping times is observed when a self-assembled molecular layer is introduced between the gold film and the substrate. We deduce the frequency dependence of the damping times by varying the thickness of the gold films. Experimental results are compared to numerical simulations based on a visco-elastic model and the acoustic mismatch model.