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

Xian Zhang, Dezheng Sun+7 more|arXiv (Cornell University)|Sep 23, 2015

2D Materials and Applications30 references22 citations

TL;DR

This study introduces a refined optothermal Raman technique to measure lateral and interfacial thermal conductivity in single- and bilayer MoS2 and MoSe2. By improving optical absorption measurements and independently quantifying substrate interfacial conductance and lateral thermal conductivity via supported vs. suspended sample comparisons, the authors report room-temperature lateral thermal conductivities of 84±17 W/mK (1L MoS2) and 59±18 W/mK (1L MoSe2), with interfacial thermal conductance on the order of 0.1–1 MW/m²K—significantly lower than previously assumed.

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.

Motivation & Objective

• To accurately measure lateral thermal conductivity in single- and bilayer MoS2 and MoSe2.
• To determine interfacial thermal conductance between 2D materials and substrates with improved precision.
• To address discrepancies in prior thermal conductivity measurements by refining optical absorption estimates.
• To validate the method using radial illumination response on suspended samples.
• To provide reliable thermal transport parameters for device design and modeling of 2D semiconductor heterostructures.

Proposed method

• A refined optothermal Raman technique is employed, using laser heating and Raman shift monitoring to infer temperature rise.
• Optical absorption of suspended samples is measured directly, yielding values ~40% lower than previously assumed.
• Comparison of temperature responses between fully supported and suspended samples enables independent extraction of interfacial thermal conductance and lateral thermal conductivity.
• Different laser spot sizes are used to decouple thermal transport contributions from substrate and 2D material.
• Radial illumination on suspended films validates the method's consistency and spatial resolution.
• The approach accounts for thermal boundary resistance and enables quantitative analysis of thermal transport in 2D van der Waals heterostructures.

Experimental results

Research questions

• RQ1 What is the true lateral thermal conductivity of single- and bilayer MoS2 and MoSe2 at room temperature?
• RQ2 How does the interfacial thermal conductance between 2D materials and substrates compare to previously reported values?
• RQ3 To what extent do errors in optical absorption assumptions affect thermal conductivity measurements in 2D materials?
• RQ4 Can the refined optothermal Raman method independently resolve interfacial thermal conductance and lateral thermal conductivity?
• RQ5 How does thermal transport vary between MoS2 and MoSe2 in single- and bilayer forms?

Key findings

• The room-temperature lateral thermal conductivity of single-layer MoS2 is measured as (84±17) W/mK.
• The lateral thermal conductivity of single-layer MoSe2 is (59±18) W/mK at room temperature.
• For bilayer MoS2, the lateral thermal conductivity is (77±25) W/mK, showing a slight reduction from the single-layer case.
• Bilayer MoSe2 exhibits a lateral thermal conductivity of (42±13) W/mK, indicating a stronger thickness dependence than MoS2.
• The interfacial thermal conductance between 2D materials and substrate is found to be on the order of 0.1–1 MW/m²K, substantially lower than earlier estimates.
• Direct measurement of optical absorption reveals values ~40% lower than previous assumptions, correcting a major source of error in prior thermal conductivity measurements.