Measurement of lateral and interfacial thermal conductivity of single- and bi-layer MoS2 and MoSe2 using refined optothermal Raman technique

TL;DR

This study refines the optothermal Raman technique to accurately measure the thermal conductivity and interfacial conductance of single- and bi-layer MoS2 and MoSe2, revealing lower absorption and interfacial conductance than previously thought.

Contribution

The paper introduces a refined measurement method that independently assesses lateral thermal conductivity and interfacial conductance in TMDC monolayers and bilayers, with improved accuracy.

Findings

Measured room-temperature thermal conductivities: 84 W/mK (MoS2), 59 W/mK (MoSe2) for monolayers.

Found interfacial thermal conductance to be 0.1-1 MW/m2K, much lower than previous estimates.

Validated the method by analyzing the response of suspended films at different radial positions.

Abstract

Atomically thin materials such as graphene and semiconducting transition metal dichalcogenides (TMDCs) have attracted extensive interest in recent years, motivating investigation into multiple properties. In this work, we demonstrate a refined version of the optothermal Raman technique to measure the thermal transport properties of two TMDC materials, MoS2 and MoSe2, in single-layer (1L) and bi-layer (2L) forms. This new version incorporates two crucial improvements over previous implementations. First, we utilize more direct measurements of the optical absorption of the suspended samples under study and find values ~40% lower than previously assumed. Second, by comparing the response of fully supported and suspended samples using different laser spot sizes, we are able to independently measure the interfacial thermal conductance to the substrate and the lateral thermal conductivity of the supported and suspended materials. The approach is validated by examining the response of a suspended film illuminated in different radial positions. For 1L MoS2 and MoSe2, the room-temperature thermal conductivities are (84+/-17) W/mK and (59+/-18) W/mK, respectively. For 2L MoS2 and MoSe2, we obtain values of (77+/-25) W/mK and (42+/-13) W/mK. Crucially, the interfacial thermal conductance is found to be of order 0.1-1 MW/m2K, substantially smaller than previously assumed, a finding that has important implications for design and modeling of electronic devices.