Thermal conductance across harmonic-matched epitaxial Al-sapphire heterointerfaces

Zhe Cheng,Christopher M Matthews,Yee Rui Koh,Tengfei Luo,Yekan Wang,Evan A Clinton,Luke Yates,Eungkyu Lee,Tingyu Bai,Zachary Engel,Jingjing Shi,Michael Liao ,Mark S Goorsky,Habib Ahmad,Patrick E Hopkins,W Alan Doolittle,Ruiyang Li,Zhiting Tian,Renjiu Hu,Samuel Graham

doi:10.1038/s42005-020-0383-6

Abstract

A unified fundamental understanding of interfacial thermal transport is missing due to the complicated nature of interfaces. Because of the difficulty to grow high-quality interfaces and lack of materials characterization, the experimentally measured thermal boundary conductance (TBC) in the literature are usually not the same as the ideally modelled interfaces. This work provides a systematic study of TBC across the highest-quality (atomically sharp, harmonic-matched, and ultraclean) epitaxial (111) Al||(0001) sapphire interfaces to date. The comparison of measured high TBC with theoretical models shows that elastic phonon transport dominates the interfacial thermal transport and other mechanisms play negligible roles. This is confirmed by a nearly constant transmission coefficient by scaling the TBC with the Al heat capacity and sapphire heat capacity with phonon frequency lower than 10 THz. Finally, the findings in this work will impact applications such as electronics thermal management, thermoelectric energy conversion, and battery safety.

Highlights

A unified fundamental understanding of interfacial thermal transport is missing due to the complicated nature of interfaces
A key step is that the sapphire was cleaned through a high temperature annealing step in ultrahigh vacuum (UHV) prior to the epitaxial deposition of the Al in-situ by molecular beam epitaxy (MBE)
The measured high thermal boundary conductance (TBC) is compared than the other Al–sapphire TBC reported in the literature

Summary

Introduction

A unified fundamental understanding of interfacial thermal transport is missing due to the complicated nature of interfaces. Due to the complicated nature of interfaces, most of the theoretical calculations cannot capture the detailed features of the interface It still remains an open question whether the modeled interfaces are the same as the measured ones in most previous works due to the lack of detailed simultaneous material and thermal characterization of the interfaces[34]. This is especially true for metal–non-metal interfaces because of the complicated interfacial structures and multiple carrier transport mechanisms near the interfaces. Costescu et al.[9] reported the TBC of epi-grown TiN on MgO and

Methods

Results

Conclusion