A new regime of nanoscale thermal transport: collective diffusion counteracts dissipation inefficiency

TL;DR

This paper reveals a new nanoscale thermal transport regime where collective diffusion between closely spaced heat sources enhances heat dissipation, challenging previous assumptions and enabling phonon mean free path measurements.

Contribution

It uncovers a collective diffusion regime at nanoscale heat sources, demonstrating enhanced heat dissipation and enabling experimental phonon mean free path distribution extraction.

Findings

Collective diffusion facilitates efficient heat dissipation at small separations.

Thermal management may be easier in nanoscale systems than previously thought.

First experimental validation of phonon mean free path distributions from first-principles.

Abstract

Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics, thermoelectric devices, nano-enhanced photovoltaics and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier's law for heat conduction dramatically over-predicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interplay between neighboring heat sources can facilitate efficient, diffusive-like heat dissipation, even from the smallest nanoscale heat sources. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as projected. Finally, we demonstrate a unique and new capability to extract mean free path distributions of phonons in materials, allowing the first experimental validation of differential conductivity predictions from first-principles calculations.