Tunable Hypersonic Resonators via Electron-Irradiation-Induced Giant Modulation of Microparticle Elasticity.

The ability to modulate the elastic properties of nanostructured objects is crucial for the development of innovative materials able to control the propagation of acoustic waves (phonons) in the hypersonic frequency regime, with applications ranging from acousto- to thermo-optical devices. Here, an advanced strategy is explored to finely tune the elastic properties of Stöber silica microparticles, commonly used building blocks for phononic materials. Using moderate electron beam energies in a scanning electron microscope, a controlled, huge and rapid particle elasticity tuning is demonstrated, which is investigated by Brillouin light scattering. The findings are interpreted in terms of an irradiation-induced stiffening of the contacts between the primary nanoparticles composing the Stöber particle, attributable to changes in the silica network through radiolytic processes. The versatile control of the mechanical properties of microparticles, combined with their electret-like behavior upon charging, offers broad-spectrum possibilities for coupling phononic properties with external electromagnetic fields, paving the way for innovative phononic materials.