Surface acoustic waves interaction with confined acoustic phonons in a coupled nanoridges dimer set atop of a multilayer design

Abstract

We present a comprehensive study using finite element numerical analysis of the acoustic localized phonons supported by a gold nanoridges dimer-based multilayer design. The latter consists in a SiO2-substrate over which a gold film covered with a thin polymer is deposited. We investigate first the mechanical eigen-modes analysis of a single monomer ridge, where we find flexural and compressional type modes in the sub-GHz frequency range. This is realized by either setting the ridge in a periodic structure, which enables to get the dispersion curve of the modes, or by considering an isolated system bounded by perfect matched layers, where we use the equivalent of the local density of states to track the modes. A good agreement is obtained between the two methods. Similarly, we find in case of the coupled dimer ridges hybridized modes, namely the flexural and compressional modes of a monomer split-up into in- and -out-of-phase type modes. We demonstrate efficient coupling between the monomer/dimer localized phonons with surface acoustic waves (SAWs) as the simulated transmission spectra show dips at the frequencies of the monomer/dimer eigenmodes. For symmetry reasons, some of the dimer modes are expected to be optomechanically active. The proposed SAW-based device is meant to help design acousto-optic modulators or ultrasensitive sensors.