Nano-Cross-Junction Effect on Phonon Transport in Silicon-Nanowire-Cages

TL;DR

This study introduces a novel silicon nanowire cage structure with nano-cross-junctions that significantly reduces thermal conductivity through phonon localization, offering new ways to control heat flow in nanomaterials.

Contribution

It demonstrates a new 3D nanostructure with ultralow thermal conductivity achieved via phonon localization, without requiring periodicity or complex fabrication.

Findings

Thermal conductivity of SiNWC is 0.173 W/m·K, much lower than SiNWs.

Phonon localization is caused by local resonance and hybridization at junctions.

Localization effect occurs in a wide range of phonon modes.

Abstract

Wave effects of phonons can give rise to controllability of heat conduction beyond that by particle scattering at surfaces and interfaces. In this work, we propose a new class of 3D nanostructure: a silicon-nanowire-cage (SiNWC) structure consisting of silicon nanowires (SiNWs) connected by nano-cross-junctions (NCJs). We perform equilibrium molecular dynamics (MD) simulations, and find an ultralow value of thermal conductivity of SiNWC, 0.173 Wm-1K-1, which is one order lower than that of SiNWs. By further modal analysis and atomistic Green's function calculations, we identify that the large reduction is due to significant phonon localization induced by the phonon local resonance and hybridization at the junction part in a wide range of phonon modes. This localization effect does not require the cage to be periodic, unlike the phononic crystals, and can be realized in structures that are easier to synthesize, for instance in a form of randomly oriented SiNWs network.