Probing Gigahertz Coherent Acoustic Phonons in TiO$_{2}$ Mesoporous Thin Films

TL;DR

This paper demonstrates ultrahigh-frequency acoustic resonators using inexpensive mesoporous TiO2 thin films, achieving resonances up to 90 GHz, and explores their potential for reconfigurable optoacoustic sensors.

Contribution

It introduces mesoporous TiO2-based acoustic resonators with high-frequency operation and validates their performance through experiments and simulations, enabling cost-effective sensor development.

Findings

Resonances up to 90 GHz achieved

Good agreement between simulations and experiments

Potential for reconfigurable optoacoustic sensors

Abstract

Ultrahigh-frequency acoustic-phonon resonators usually require atomically flat interfaces to avoid phonon scattering and dephasing, leading to expensive fabrication processes, such as molecular beam epitaxy. In contrast, mesoporous thin films are based on inexpensive wet chemical fabrication techniques. Here, we report mesoporous titanium dioxide-based acoustic resonators with resonances up to 90 GHz, and quality factors from 3 to 7. Numerical simulations show a good agreement with the picosecond ultrasonics experiments. We also numerically study the effect of changes in the speed of sound on the performance of the resonator. This change could be induced by liquid infiltration into the mesopores. Our findings constitute the first step towards the engineering of building blocks based on mesoporous thin films for reconfigurable optoacoustic sensors.