Spectral heat flux redistribution upon interfacial transmission

TL;DR

This paper reveals how phonon-mediated heat flux redistributes among frequencies at interfaces between dissimilar solids, leading to nearly identical spectra in superlattices, which has implications for thermal management in nanostructures.

Contribution

It uncovers the mechanism of spectral heat flux redistribution across interfaces and its development over space and time in layered nanostructures.

Findings

Heat flux redistributes among phonon frequencies at interfaces.

In superlattices, phonon spectra of dissimilar solids become nearly identical.

Redistribution occurs gradually over distance and time, not instantaneously.

Abstract

In nonmetallic crystals, heat is transported by phonons of different frequencies, each contributing differently to the overall heat flux spectrum. In this study, we demonstrate a significant redistribution of heat flux among phonon frequencies when phonons transmit across the interface between dissimilar solids. This redistribution arises from the natural tendency of phononic heat to re-establish the equilibrium distribution characteristic of the material through which it propagates. Remarkably, while the heat flux spectra of dissimilar solids are typically distinct in their bulk forms, they can become nearly identical in superlattices or sandwich structures where the layer thicknesses are smaller than the phonon mean free paths. This phenomenon reflects that the redistribution of heat among phonon frequencies to the equilibrium distribution does not occur instantaneously at the interface, rather it develops over some time and distance.