Spatio-Temporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire Copper Nanowires Fabrication

TL;DR

This study uses femtosecond pump-probe experiments and simulations to analyze the anisotropic acoustic fields emitted by copper nanowires, revealing their shape and orientation through spatio-temporal imaging.

Contribution

It introduces a combined experimental and simulation approach to characterize the acoustic emission and shape anisotropy of individual copper nanowires.

Findings

Detection of radial breathing and longitudinal modes

Finite Difference Time Domain simulations match experimental data

Nanowire shape anisotropy and orientation are deduced acoustically

Abstract

The monochromatic and geometrically anisotropic acoustic field generated by 400 nm and 120 nm diameter copper nanowires simply dropped on a 10 $\mu$m silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both side of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite Difference Time Domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced.