Dramatic increase in the thermal boundary conductance and radiation limit from a Nonequilibrium Landauer Approach

TL;DR

This paper introduces a nonequilibrium Landauer approach that explains the unexpectedly high thermal boundary conductance measurements, redefining the radiation limit and aligning theory with experimental data.

Contribution

The authors develop a nonequilibrium Landauer model that accounts for phonon non-equilibrium near interfaces, significantly improving theoretical TBC predictions.

Findings

Nearly doubles theoretical TBCs with a simple DMM

Aligns theoretical results with experimental measurements

Redefines the radiation limit to be over 100% higher

Abstract

Thermal boundary conductance (TBC) is critical in many thermal and energy applications. A decades-old puzzle has been that many of the measured TBCs, such as those well characterized across Al/Si and ZnO/GaN interfaces, significantly exceed theoretical results or even the absolute upper limit called the ``radiation limit", suggesting the failure of the theory. Here, we identify that for high-transmission interfaces, the commonly assumed phonon local thermal equilibrium adjacent to the interface fails, and the measurable phonon temperatures are not their emission temperature. We hence develop a ``nonequilibrium Landauer approach" and define the unique ``dressed" and ``intrinsic" TBCs. Combining our approach even with a simple diffuse mismatch model (DMM) nearly doubles the theoretical TBCs across the Al/Si and ZnO/GaN interfaces, and the theoretical results agree with experiments for the first time. The radiation limit is also redefined and found to increase over 100\% over the original radiation limit, and it can now well bound all the experimental data.