Vibrational response of free standing single copper nanowire through transient reflectivity microscopy

We report on the ultrafast vibrational response of single copper nanowires investigated by femtosecond transient reflectivity measurements. The oscillations of the sample reflectivity are correlated with individual modes of resonance for wires with a diameter ranging from 100 to 500 nm and are compared with 2D finite element simulation. Fluctuation of the sample-substrate coupling is illustrated through its effect on the damping rate. We demonstrate elastic confinement in free standing wires which allowed the detection of up to the third harmonic of the breathing mode. By removing the energy relaxation channel towards the substrate, we obtained nano-oscillators with quality factors up to 130. Finally, taking advantage of the very high spectral resolution achieved on free standing wires, we could observe the elastic coupling between two close wires via their polymer cladding.