Toward Environmentally Responsive Hypersound Materials

Abstract

Engineering gigahertz (GHz) acoustic phonons holds promise for data processing, sensing, and quantum technologies. However,conventional nanophononic resonators lack adaptability to environmentalchanges. We introduce an open-cavity nanoacoustic resonator built frommesoporous SiO2 thin films (MTFs), whose ordered nanopores makethem intrinsically sensitive to humidity. Transient reflectivity measure-ments reveal pronounced resonance frequency shifts with varying relativehumidity, providing a straightforward means to tune the hypersoundconfinement. Systematic comparisons across pore sizes and filmthicknesses show that resonances are governed primarily by thicknessand intrinsic material properties rather than pore geometry. The pore size,however, governs the tunability dynamics due to the capillary action. Bydirect exposure of the mesoporous layer to its environment, this design establishes a versatile platform for coupling nanoscalemechanics with liquids and vapors. Our results highlight a simple route toward environmentally responsive hypersound devices witha potential impact in sensing and adaptive nanophononics.