Thermal Conductance Across Harmonic-matched Epitaxial Al-sapphire Heterointerfaces

TL;DR

This study systematically investigates thermal conductance across well-controlled epitaxial Al-sapphire interfaces, demonstrating elastic phonon scattering dominance and providing a benchmark for understanding interfacial heat transport mechanisms.

Contribution

It offers a detailed experimental and theoretical analysis of interfacial thermal conductance, validating models and establishing a benchmark for metal-nonmetal interfaces.

Findings

Elastic phonon scattering dominates interfacial thermal transport.

Nearly constant transmission coefficient scaled by Al heat capacity.

Provides a benchmark for interfacial thermal conductance studies.

Abstract

A unified understanding of interfacial thermal transport is missing due to the complicated nature of interfaces which involves complex factors such as interfacial bonding, interfacial mixing, surface chemistry, crystal orientation, roughness, contamination, and interfacial disorder. This is especially true for metal nonmetal interfaces which incorporate multiple fundamental heat transport mechanisms such as elastic and inelastic phonon scattering as well as electron phonon coupling in the metal and across the interface. All these factors jointly affect thermal boundary conductance (TBC). As a result, the experimentally measured interfaces may not be the same as the ideally modelled interfaces, thus obfuscating any conclusions drawn from experimental and modeling comparisons. This work provides a systematic study of interfacial thermal conductance across well controlled and ultraclean epitaxial (111) Al parallel (0001) sapphire interfaces, known as harmonic matched interface. A comparison with thermal models such as atomistic Green s function (AGF) and a nonequilibrium Landauer approach shows that elastic phonon scattering dominates the interfacial thermal transport of Al sapphire interface. By scaling the TBC with the Al heat capacity, a nearly constant transmission coefficient is observed, indicating that the phonons on the Al side limits the Al sapphire TBC. This nearly constant transmission coefficient validates the assumptions in AGF and nonequilibrium Landauer calculations. Our work not only provides a benchmark for interfacial thermal conductance across metal nonmetal interfaces and enables a quantitative study of TBC to validate theoretical thermal carrier transport mechanisms, but also acts as a reference when studying how other factors impact TBC.