Phonon dynamics in novel materials and hybrid structures

Nanometer-thick multilayer structures, characterized by contrasts in elastic properties, present promising avenues for engineering and manipulating acoustic phonons at the nanoscale. Semiconductor nano-acoustic cavities, particularly those based on Distributed Bragg Reflectors (DBRs), have demonstrated unique capabilities in simultaneously confining light and acoustic phonons. This dual confinement enhances the generation and detection phononic fields, making these structures attractive for ultra-high-frequency applications and as platforms for simulating solid-state systems. In this study, we further explore the possibilities of hybrid nanostructures that could be both tunable and responsive to ultrafast changes in elastic properties induced by external stimuli such as temperature, humidity, and electrical fields. Building upon our theoretical simulations, our experimental investigation focuses on the dynamics of acoustic phonons spanning the frequency range of 5-500 GHz, utilizing near-infrared pump and probe ultrafast transient reflectivity experiments. The materials under investigation include mesoporous SiO₂/TiO₂ multilayers with a Nickel transducer, GaAs/AlAs DBR incorporating mesoporous SiO₂ as an open cavity layer, YBCO/STO multilayers, and other potential responsive materials. Our long-term objective is to uncover the interplay between these nanostructures and external stimuli through systematic experimentation, shedding light on their tunability and responsiveness. Our experimental findings pave the way for developing nanoacoustic sensing technologies and reconfigurable optoacoustic nanodevices.