Elastic and thermal properties of free-standing molybdenum disulfide membranes measured using ultrafast transient grating spectroscopy

Taeyong Kim,Jong-Hyuk Yim,Austin J Minnich,Young-Dahl Jho,Ding Ding

doi:10.1063/1.4999225

Abstract

Molybdenum disulfide (MoS2), a member of transition-metal dichalcogenide family, is of intense interest due to its unique electronic and thermoelectric properties. However, reports of its in-plane thermal conductivity vary due to the difficulty of in-plane thermal conductivity measurements on thin films, and an experimental measurement of the in-plane sound velocity has not been reported. Here, we use time-resolved transient grating spectroscopy to simultaneously measure the in-plane elastic and thermal properties of free-standing MoS2 membranes at room temperature. We obtain a longitudinal acoustic phonon velocity of 7000 ± 40 m s−1 and an in-plane thermal conductivity of 74 ± 21 W m−1K−1. Our measurements provide useful insights into the elastic and thermal properties of MoS2 and demonstrate the capability of transient grating spectroscopy to investigate the in-plane vibrational properties of van der Waals materials that are challenging to characterize with conventional methods.

Highlights

Transition-metal dichalcogenides (TMDCs) are of considerable interest due to their unique layer-thickness-dependent electronic properties and robust thermal stability.[1,2,3,4,5] In particular, molybdenum disulfide (MoS2), a member of the TMDC family, has been extensively investigated due to its potential applications in electronics, photovoltaics, and thermoelectrics.[6,7,8,9] In addition to its intriguing electronic properties such as high electron mobility (up to 200 cm[2] V1 s1) and indirectto-direct transition of bandgap with reduced dimensionality,[6,9] MoS2 has further revealed promising thermoelectric features such as high Seebeck coefficient.[10]
Theoretical and experimental studies report a broad range of in-plane thermal conductivity values of MoS2
The cross-plane longitudinal sound velocity of MoS2 has recently been characterized by a transient reflection method.[30]

Summary

Introduction

Transition-metal dichalcogenides (TMDCs) are of considerable interest due to their unique layer-thickness-dependent electronic properties and robust thermal stability.[1,2,3,4,5] In particular, molybdenum disulfide (MoS2), a member of the TMDC family, has been extensively investigated due to its potential applications in electronics, photovoltaics, and thermoelectrics.[6,7,8,9] In addition to its intriguing electronic properties such as high electron mobility (up to 200 cm[2] V1 s1) and indirectto-direct transition of bandgap with reduced dimensionality,[6,9] MoS2 has further revealed promising thermoelectric features such as high Seebeck coefficient.[10]. Elastic and thermal properties of free-standing molybdenum disulfide membranes measured using ultrafast transient grating spectroscopy

Results

Conclusion