Vibrational response of Au-Ag alloy and porous Au single nanowires probed by ultrafast pump-probe spectroscopy.

We report on the ultrafast vibrational response of single Au-Ag alloy and Au porous nanowires obtained by the template method. The oscillations of the sample reflectivity are correlated with eigenmodes (EM) confined in the nanowire. Taking advantage of a free standing geometry, we are able to detect few harmonics. Coupling electron microscopy and pump-probe investigations with a very high spectral resolution performed on the same wire, we demonstrate that both longitudinal and transverse sound velocities could be obtained for variable Au concentrations. An additional quadrupolar mode is also observed and reproduced by finite element simulation. Finally, porous nanowires are investigated. [ABSTRACT FROM AUTHOR]