Heat guiding and focusing using ballistic phonon transport in phononic nanostructures

TL;DR

This paper demonstrates control over ballistic phonon transport in silicon nanostructures, enabling heat guiding, focusing, and localization at the nanoscale through engineered nanostructures.

Contribution

It introduces a method to manipulate the directionality of ballistic phonons using nanostructured silicon films with hole arrays, enabling heat focusing and guiding.

Findings

Directional heat fluxes form between holes in nanostructures.

Nanostructures act as directional sources of ballistic phonons.

Phonons can be focused into a nanoscale spot.

Abstract

Unlike classical heat diffusion at the macroscale, nanoscale heat transport can occur without energy dissipation because phonons can travel in straight lines for hundreds of nanometres. Despite recent experimental evidence of such ballistic phonon transport, control over its directionality, and thus its practical use, remains a challenge, as the directions of individual phonons are chaotic. Here, we show a way to control the directionality of ballistic phonon transport using silicon thin-films with arrays of holes. First, we demonstrate the formation of directional heat fluxes in the passages between the holes. Next, we use these nanostructures as a directional source of ballistic phonons and couple the emitted phonons into nanowires. Finally, we introduce a nanoscale thermal lens in which the phonons converge at a focal point, thus focusing heat into a spot of a few hundred nanometres. These results provide a basis for ray-like heat manipulations that enable nanoscale heat guiding, dissipation, localization, confinement and rectification.