Backward Propagating Acoustic Waves in Single Gold Nanobeams

Cyril Jean (1) , Laurent Belliard (1) , Loic Becerra (1) , Bernard Perrin (1)

1 INSP - Institut des Nanosciences de Paris

Femtosecond pump-probe spectroscopy has been carried out on suspended gold nanostructures with a rectangular cross section lithographed on a silicon substrate. With a thickness fixed to 110 nm and a width ranging from 200 nm to 800 nm, size dependent measurements are used to distinguish which confined acoustic modes are detected. Furthermore, in order to avoid any ambiguity due to the measurement uncertainties on both the frequency and size, pump and probe beams are also spatially shifted to detect guided acoustic phonons. This leads us to the observation of backward propagating acoustic phonons in the gigahertz range (∼3 GHz) in such nanostructures. While backward wave propagation in elastic waveguides has been predicted and already observed at the macroscale, very few studies have been done at the nanoscale. Here, we show that these backward waves can be used as the unique signature of the width dilatational acoustic mode.

Mots clés: backward wave; time-resolved pump-probe spectroscopy; picosecond ultrasonics; gold nanostructures

Domaines: Systèmes mésoscopiques et effet Hall quantique [cond-mat.mes-hall]

Cyril Jean, Laurent Belliard, Loic Becerra, Bernard Perrin. Backward Propagating Acoustic Waves in Single Gold Nanobeams. Applied Physics Letters, 2015, 107 (19), pp.193103. ⟨10.1063/1.4935351⟩. ⟨hal-01226570⟩