Thermal transport across nanometre gaps: phonon transmission vs air conduction

TL;DR

This paper investigates heat transfer mechanisms across nanometre gaps, showing phonons dominate even with air present, and introduces a new methodology for analyzing phonon transmission in nanoscale gaps.

Contribution

It provides a quantitative analysis of phonon-assisted heat transfer across nanometre gaps, revealing phonons' dominance even with air molecules present, and offers a novel methodology for such analysis.

Findings

Phonons dominate heat transfer for subnanometre gaps.

Phonons provide the main energy channel even with air in the gap.

Enhanced phonon heat transfer predicted compared to previous studies.

Abstract

Heat transfer between two surfaces separated by a nanometre gap is important for a number of applications ranging from spaced head disk systems, scanning thermal microscopy and thermal transport in aerogels. At these separation distances, near field radiative heat transfer competes with heat transfer mediated by phonons. Here we quantify the contribution of phonon assisted heat transfer between apolar solids using lattice dynamics combined with ab-initio calculations. We clearly demonstrate that phonons dominate heat transfer for subnanometre gaps. Strikingly, we conclude that even in the situation where the gap is filled with air molecules, phonons provide the dominant energy channel between the two solids nearly in contact. Our results predict orders of magnitude enhanced phonon heat transfer compared to previous works and bring forward a methodology to analyse phonon transmission across nanoscale vacuum gaps between apolar materials.