From diffusive to ballistic Stefan–Boltzmann heat transport in thin non-crystalline films

Abstract

Today, different theoretical models exist to describe heat transport in ultra-thin films with a thickness approaching the phonon mean free path length. Due to the influence of parasitic effects, the experimental assessment of heat transport in these ultra-thin films with the required sensitivity is extremely challenging. In this work, the heat transport through thin non-crystalline metal-oxide films is studied using scanning near-field thermal microscopy, which allows to minimize parasitic thermal effects and therefore provides uttermost sensitivity even for the study of thermal transport in ultra-thin films. For the first time, we provide experimental evidence of enhanced out-of-plane heat dissipation in these ultra-thin metal-oxide films by ballistic thermal phonon transport according to the Stefan–Boltzmann-like heat transport model.