Optically Controlled Nano-Transducers Based on Cleaved Superlattices for Monitoring Gigahertz Surface Acoustic Vibrations

Changxiu Li; Nikolay Chigarev; Théo Thréard; Kedong Zhang; Nicolas Delorme; Vincent Tournat; Samuel Raetz; Hong Lu; Vitalyi E Gusev

doi:10.1021/acsnano.3c07576

Optically Controlled Nano-Transducers Based on Cleaved Superlattices for Monitoring Gigahertz Surface Acoustic Vibrations

ACS Nano. 2024 Apr 2;18(13):9331-9343. doi: 10.1021/acsnano.3c07576. Epub 2024 Mar 18.

Authors

Changxiu Li¹, Nikolay Chigarev¹, Théo Thréard¹, Kedong Zhang², Nicolas Delorme³, Vincent Tournat¹, Samuel Raetz¹, Hong Lu², Vitalyi E Gusev¹

Affiliations

¹ Laboratoire d'Acoustique de l'Université du Mans (LAUM), UMR 6613, Institut d'Acoustique - Graduate School (IA-GS), CNRS, Le Mans Université, 72085 Le Mans, France.
² College of Engineering and Applied Sciences, Nanjing University, 210093 Nanjing, China.
³ Institut des Molécules et Matériaux du Mans (IMMM), UMR 6283 CNRS, Le Mans Université, 72085 Le Mans, France.

PMID: 38498702
DOI: 10.1021/acsnano.3c07576

Abstract

Surface acoustic waves (SAWs) convey energy at subwavelength depths along surfaces. Using interdigital transducers (IDTs) and opto-acousto-optic transducers (OAOTs), researchers have harnessed coherent SAWs with nanosecond periods and micrometer localization depth for various applications. These applications include the sensing of small amount of materials deposited on surfaces, assessing surface roughness and defects, signal processing, light manipulation, charge carrier and exciton transportation, and the study of fundamental interactions with thermal phonons, photons, magnons, and more. However, the utilization of cutting-edge OAOTs produced through surface nanopatterning techniques has set the upper limit for coherent SAW frequencies below 100 GHz, constrained by factors such as the quality and pitch of the surface nanopattern, not to mention the electronic bandwidth limitations of the IDTs. In this context, unconventional optically controlled nanotransducers based on cleaved superlattices (SLs) are here presented as an alternative solution. To demonstrate their viability, we conducted proof-of-concept experiments using ultrafast lasers in a pump-probe configuration on SLs made of alternating Al_xGa_1-xAs and Al_yGa_1-yAs layers with approximately 70 nm periodicity and cleaved along their growth direction to produce a periodic nanostructured surface. The acoustic vibrations, generated and detected by laser beams incident on the cleaved surface, span a range from 40 to 70 GHz, corresponding to the generalized surface Rayleigh mode and bulk modes within the dispersion relation. This exploration shows that, in addition to SAWs, cleaved SLs offer the potential to observe surface-skimming longitudinal and transverse acoustic waves at GHz frequencies. This proof-of-concept demonstration below 100 GHz in nanoacoustics using such an unconventional platform might be useful for realizing sub-THz to THz coherent surface acoustic vibrations in the future, as SLs can be epitaxially grown with atomic-scale layer width and quality.

Keywords: coherent GHz phonons; nanoacoustics; opto-acousto-optic transducers; picosecond laser ultrasonics; superlattices; surface and surface skimming acoustic waves; ultrafast laser spectroscopy.