Spectral energy analysis of locally resonant nanophononic metamaterials by molecular simulations

TL;DR

This study uses molecular dynamics simulations to analyze how local resonances in nanophononic metamaterials, like silicon membranes with nanopillars, reduce thermal conductivity through resonance hybridizations.

Contribution

It provides direct molecular simulation evidence of resonance hybridizations as a mechanism for thermal transport reduction in nanophononic metamaterials.

Findings

Resonance hybridizations slow down phonon transport.

Thermal conductivity is significantly reduced by local resonators.

Spectral energy density approach confirms hybridization effects.

Abstract

A nanophononic metamaterial is a new type of nanostructured material that features an array, or a forest, of intrinsically distributed resonating substructures. Each substructure exhibits numerous local resonances, each of which may hybridize with the phonon dispersion of the underlying host material causing significant reductions in the group velocities and consequently a reduction in the lattice thermal conductivity. In this paper, molecular dynamics simulations are utilized to investigate both the dynamics and the thermal transport properties of a nanophononic metamaterial configuration consisting of a freely suspended silicon membrane with an array of silicon nanopillars standing on the surface. The simulations yield results consistent with earlier lattice-dynamics based predictions which showed a reduction in the thermal conductivity due to the presence of the local resonators. Using a spectral energy density approach, in which only simulation data is utilized and no a priori information on the nanostructure resonant phonon modes is provided, we show direct evidence of the existence of resonance hybridizations as an inherent mechanism contributing to the slowing down of thermal transport in this system.