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

Abstract

International audienceWe 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. (C) 2013 AIP Publishing LLC

Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire

“…Unlike the 8 GHz case, these insets permit a direct and convincing comparison of the damping time of the oscillations between the two cases as the oscillation lifetime is shorter than the time delay between the two longitudinal echoes. Thus, this damping time can be accurately determined and reaches τ = 0.2 ns in transmission to be compared to τ = 0.3 ns in the frontside configuration, which corresponds to a quality factor Q = πf 0 τ ∼ 30 in good adequation with previous studies on supported metallic nanowires [24,37]. A pseudocolor x − t spatiotemporal surface displacement mapping along the spatial direction x is presented in the Figure 4c.…”

“…Because of the electrons fast diffusion, this ultrafast heating is not confined to the surface of the nano-object, the whole width of the nanowire subsequently undergoes periodic radial contrac- tions and expansions. These isotropic volume oscillations correspond to the fundamental breathing mode of the nanowire [24,26]. These periodic lattice oscillations induce a modulation of the metal refractive index, which shows up by a periodic variation of the relative probe reflectivity ∆R/R (Figure 2b).…”

Acoustic vibrations of metal nano-objects: Time-domain investigations

“…The much simpler and highly sensitive pump-probe setup demonstrated for investigating the electronic response of a metal particle [14,233] is now mostly used, monitoring either the probe beam transmission ∆T pr (Fig. 20) [235] or, less frequently, reflection [247]. The measured signal is proportional to the transient extinction crosssection change of the single nanoparticle (Eq.…”

“…Different particle environments were explored using particles deposited (by spin-coating a colloidal solution) or fabricated on a substrate (by nanosphere or electron beam lithography), embedded in sub-micron thick polymer film, or optically trapped in a liquid, or suspended over a trench [55,[67][68][69][70]108,169,234,247,249,248].…”

“…For gold nanospheres on silica, this mode presented a low (<10) quality factor, possibly related to strong hysteresis at the nanoparticle-substrate adhesive contact [254]. The effect of variable particle-substrate interaction concomitant with deposition of single nanoparticles can be suppressed, and a homogeneous environment recovered, using either an optically trapped particle (gold spheres and rods [234]) or investigating a nano-object in suspension upon a trench (gold and copper wires [67,247]). For trapped spheres and rods in water, the measured mean damping time τ ′ q,sp (or quality factor Q ′ q = ω q τ ′ q,sp /2) of their fundamental radial mode ( Fig.…”