Sound attenuation in amorphous silica at frequencies near the boson peak

Abstract

We use molecular dynamics phonon wave packet (WP) simulations to study acoustic propagation and attenuation in amorphous silica $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$ at frequencies near the boson peak (BP) position and compare them with the results of equilibrium molecular dynamics (EMD) simulations. The sound attenuation coefficients obtained from WP simulations are generally consistent with those from EMD predictions and have reasonable agreement with the existing experimental data. Near the BP position, we found the frequency-dependent sound attenuation coefficients for longitudinal and transverse modes both follow the Rayleigh-scattering fourth power law. Above the BP frequency, however, the propagating phonon is essentially attenuated in $a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ within a few nanometers, and the accurate determination of the sound attenuation coefficients by the WP simulation becomes challenging. The modeling results provide a reference for future experimental investigations of sound attenuation in $a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ thin film using narrow-band coherent phonons.