Ultrafast acoustic resonance spectroscopy of gold nanostructures: Towards a generation of tunable transverse waves

Femtosecond pump-probe experiments have been carried out on circular single gold nanostructures lithographed on a silicon substrate with diameters ranging from 1.1 down to 0.3 mu m and thicknesses of 175 down to 55 nm. Using three-dimensional finite-element simulations coupled to the specific detection rule of interferometric measurements, we illustrate the effect of intrinsic parameters such as the size and the boundary conditions on the vibrational spectrum. The possibility of using these artificial nanostructures for acoustic transduction in the underlying substrate is investigated. Gold nanostructures are good candidates to generate monochromatic transverse bulk waves in the gigahertz frequency range, with frequency tuned by the dot size.