Experimental Observation of Localized Interfacial Phonon Modes

TL;DR

This study provides the first experimental evidence of localized interfacial phonon modes at a Si-Ge interface, revealing their significant role in thermal boundary conductance and advancing understanding of heat transfer at the atomic scale.

Contribution

It combines advanced spectroscopy, electron microscopy, and molecular dynamics simulations to directly observe and confirm localized phonon modes at interfaces, a key factor previously only predicted theoretically.

Findings

Localized phonon modes observed at ~12 THz at the interface.

Interfacial phonon modes significantly contribute to thermal boundary conductance.

Experimental measurements of TBC align with simulation predictions.

Abstract

Interfaces impede heat flow in micro/nanostructured systems. Conventional theories for interfacial thermal transport were derived based on bulk phonon properties of the materials making up the interface without explicitly considering the atomistic interfacial details, which are found critical to correctly describing thermal boundary conductance (TBC). Recent theoretical studies predicted the existence of localized phonon modes at the interface which can play an important role in understanding interfacial thermal transport. However, experimental validation is still lacking. Through a combination of Raman spectroscopy and high-energy resolution electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope, we report the first experimental observation of localized interfacial phonon modes at ~12 THz at a high-quality epitaxial Si-Ge interface. These modes are further confirmed using molecular dynamics simulations with a high-fidelity neural network interatomic potential, which also yield TBC agreeing well with that measured from time-domain thermoreflectance (TDTR) experiments. Simulations find that the interfacial phonon modes have obvious contribution to the total TBC. Our findings may significantly contribute to the understanding of interfacial thermal transport physics and have impact on engineering TBC at interfaces in applications such as electronics thermal management and thermoelectric energy conversion.