Direct Observation of Propagating Gigahertz Coherent Guided Acoustic Phonons in Free Standing Single Copper Nanowires

TL;DR

This study demonstrates the direct observation of gigahertz coherent guided acoustic phonons in free-standing copper nanowires using femtosecond spectroscopy, enabling detailed characterization of nanowire properties.

Contribution

It provides the first direct measurement of propagating coherent acoustic phonons in single nanowires, combining experimental data with analytical modeling.

Findings

Observation of gigahertz phonon waveguiding in copper nanowires

Analytical modeling matches experimental oscillations

Potential for nanolateral acoustic transducers and thermal studies

Abstract

We report on gigahertz acoustic phonon waveguiding in free-standing single copper nanowires studied by femtosecond transient reflectivity measurements. The results are discussed on the basis of the semianalytical resolution of the Pochhammer and Chree equation. The spreading of the generated Gaussian wave packet of two different modes is derived analytically and compared with the observed oscillations of the sample reflectivity. These experiments provide a unique way to independently obtain geometrical and material characterization. This direct observation of coherent guided acoustic phonons in a single nano-object is also the first step toward nanolateral size acoustic transducer and comprehensive studies of the thermal properties of nanowires.