Extreme Near-Field Heat Transfer Between Gold Surfaces

TL;DR

This paper develops a comprehensive model for extreme near-field heat transfer between gold surfaces, incorporating radiation, phonon, and electron transport, revealing how bias voltage influences dominant energy carriers at nanometer gaps.

Contribution

It introduces a combined theoretical framework that accounts for multiple heat transfer mechanisms and their dependence on bias voltage and gap size, clarifying previous experimental-theoretical discrepancies.

Findings

Acoustic phonon transport dominates below ~2 nm gap without bias.

Bias voltage enhances phonon and electron contributions, shifting dominant carriers.

Electron tunneling is dominant at sub-1 nm gaps with bias.

Abstract

Extreme near-field heat transfer between metallic surfaces is a subject of debate as the state-of-the-art theory and experiments are in disagreement on the energy carriers driving heat transport. In an effort to elucidate the physics of extreme near-field heat transfer between metallic surfaces, this Letter presents a comprehensive model combining radiation, acoustic phonon and electron transport across sub-10-nm vacuum gaps. The results obtained for gold surfaces show that in the absence of bias voltage, acoustic phonon transport is dominant for vacuum gaps smaller than ~2 nm. The application of a bias voltage significantly affects the dominant energy carriers as it increases the phonon contribution mediated by the long-range Coulomb force and the electron contribution due to a lower potential barrier. For a bias voltage of 0.6 V, acoustic phonon transport becomes dominant at a vacuum gap of 5 nm, whereas electron tunneling dominates at sub-1-nm vacuum gaps. The comparison of the theory against experimental data from the literature suggests that well-controlled measurements between metallic surfaces are needed to quantify the contributions of acoustic phonon and electron as a function of the bias voltage.