Using Amorphous CoB Alloy as Transducer to Detect Acoustic Propagation and Heat Transport at Interface

Liu Jian,Gyung-Min Choi

doi:10.3390/app11115155

Abstract

Acoustic oscillation provides useful information regarding the interfacial coupling between metal transducer layers and substrate materials. The interfacial coupling can be significantly reduced by a mechanically soft layer between the transducer and substrate. However, preserving a thin, soft layer at the interface during fabrication is often challenging. In this study, we demonstrate that an amorphous CoB alloy on top of a sapphire substrate can substantially amplify acoustic oscillations. By analyzing the attenuation of acoustic oscillations, we show that a thin, soft layer with a thickness of >2 ± 1 Å exists at the interface. The intermediate layer at the interface is further verified by investigating heat transport. By analyzing the slow decrease of the temperature of the transducer layer, we determine a thermal conductance of 35 ± 5 MW m−2 K−1 at the transducer/substrate interface. This low value supports the existence of a thin, soft layer at the interface. Our results demonstrate that an amorphous metal with B alloying effectively preserves the soft nature at the interface and detects the acoustic propagation and heat transport across it.

Highlights

An acoustic wave is the propagation of strain in a condensed matter, and its propagation speed is determined by the group velocity of low-energy phonons; that is, the speed of sound
By analyzing the attenuation of acoustic oscillations, we show that a thin, soft layer with a thickness of >2 ± 1 Å exists at the interface
We show that a high reflection of acoustic waves was achieved due to the presence of a soft intermediate layer between Co50 B50 and sapphire

Summary

Introduction

An acoustic wave is the propagation of strain in a condensed matter, and its propagation speed is determined by the group velocity of low-energy phonons; that is, the speed of sound. Time-resolved measurements of acoustic waves based on short-pulsed lasers, a time-resolved measurement of acoustic waves, often called “picosecond acoustics” or “picosecond ultrasonics”, have been employed to investigate thickness information [1,2,3,4,5], elastic properties [6,7,8,9,10], phonon properties [11,12,13,14,15], and interfacial quality [16,17,18,19]. The interfacial quality between two layers has been investigated from the perspectives of the amplitude and attenuation of acoustic waves [16,17,18,19]. Many condensed solid phases have a similar acoustic impedance, and acoustic oscillations are often suppressed. Inserting a mechanically soft layer with a small acoustic impedance between two layers can enhance acoustic oscillations, but a soft layer with a thickness of a few nanometers is prone to fabrication damage

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Conclusion