Reconstructing phonon mean free path contributions to thermal conductivity using nanoscale membranes

TL;DR

This paper presents a method to determine the distribution of phonon mean free paths contributing to thermal conductivity by measuring thin membrane thermal conductivities across a wide thickness range, enabling comparison with theoretical models.

Contribution

It introduces a non-contact thermal measurement technique on nanoscale membranes to reconstruct phonon mean free path contributions to bulk thermal conductivity.

Findings

Thermal conductivity decreases significantly with membrane thinning due to boundary scattering.

The method accurately reconstructs the phonon mean free path distribution.

Results align with theoretical models of phonon transport.

Abstract

Knowledge of the mean free path distribution of heat-carrying phonons is key to understanding phonon-mediated thermal transport. We demonstrate that thermal conductivity measurements of thin membranes spanning a wide thickness range can be used to characterize how bulk thermal conductivity is distributed over phonon mean free paths. A non-contact transient thermal grating technique was used to measure the thermal conductivity of suspended Si membranes ranging from 15 to 1500 nm in thickness. A decrease in the thermal conductivity from 74% to 13% of the bulk value is observed over this thickness range, which is attributed to diffuse phonon boundary scattering. Due to the well-defined relation between the membrane thickness and phonon mean free path suppression, combined with the range and accuracy of the measurements, we can reconstruct the bulk thermal conductivity accumulation vs. phonon mean free path, and compare with theoretical models.