Length Dependent Thermal Conductivity Measurements Yield Phonon Mean Free Path Spectra in Nanostructures

TL;DR

This paper introduces a reconstruction method to derive phonon mean free path spectra from length-dependent thermal conductivity measurements in nanostructures, revealing detailed phonon transport characteristics.

Contribution

The authors develop a novel approach to extract MFP spectra from variable-length thermal conductivity data, moving beyond average MFP interpretations.

Findings

70% of heat in graphene is carried by phonons with MFPs longer than 1 micron

Reconstructed MFP spectra provide detailed insights into phonon transport in nanostructures

Method applied to SiGe nanowires and graphene ribbons

Abstract

Thermal conductivity measurements over variable lengths on nanostructures such as nanowires provide important information about the mean free paths (MFPs) of the phonons responsible for heat conduction. However, nearly all of these measurements have been interpreted using an average MFP even though phonons in many crystals possess a broad MFP spectrum. Here, we present a reconstruction method to obtain MFP spectra of nanostructures from variable-length thermal conductivity measurements. Using this method, we investigate recently reported length-dependent thermal conductivity measurements on SiGe alloy nanowires and suspended graphene ribbons. We find that the recent measurements on graphene imply that 70 % of the heat in graphene is carried by phonons with MFPs longer than 1 micron.