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

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.

• The paper refines optothermal Raman methods to directly assess lateral and interfacial thermal conductivities in both single- and bi-layer MoS2 and MoSe2.
• It reports room-temperature thermal conductivities of 84±17 W/mK for 1L MoS2 and 59±18 W/mK for 1L MoSe2, with 2L samples showing 77±25 W/mK and 42±13 W/mK respectively.
• Improved measurement accuracy challenges previous assumptions and offers significant implications for enhancing thermal management in TMDC-based electronic and optoelectronic devices.

Thermal Conductivity Measurements Using Refined Optothermal Raman Technique in MoS and MoSe

This paper explores the thermal transport properties of molybdenum disulfide (MoS) and molybdenum diselenide (MoSe), focusing on single-layer (1L) and bi-layer (2L) forms. Employing an enhanced optothermal Raman technique, this study addresses several parameters critical to accurate thermal conductivity measurements in two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs). Recent interest in 2D materials stems largely from their unique optoelectronic properties and potential applications in electronics, optics, and thermal management systems.

Methodology

The study presents a refined version of the optothermal Raman method, which includes direct measurement of optical absorption and independent assessments of interfacial thermal conductance and lateral thermal conductivity for both supported and suspended samples. These measurements were conducted by comparing responses of samples with varying laser spot sizes and radial illumination positions, revealing notable differences from previously assumed values. Notably, the optical absorption is found to be approximately 40% lower than prior assumptions, and interfacial thermal conductance values are significantly lower.

Key Findings

The study reports room-temperature thermal conductivities of 84±17 W/mK for suspended 1L MoS and 59±18 W/mK for 1L MoSe. For 2L forms, they identified 77±25 W/mK for MoS and 42±13 W/mK for MoSe. These findings contradict some earlier reports suggesting lower thermal conductivities in monolayers compared to their multilayered counterparts, urging a reconsideration and validation of prior experimental approaches and assumptions.

Interestingly, the interfacial thermal conductance values between these TMDCs and substrates were found to range from 0.1-1 MW/m²K, which are significantly smaller than those previously used in modeling heat dissipation in electronic devices.

Implications

The improved accuracy in thermal conductivity measurements and interfacial thermal conductance has profound implications for the design and optimization of electronic and optoelectronic devices using TMDC materials. These results facilitate a better understanding of heat dissipation processes in these devices, enabling more accurate thermal management and potentially boosting device performance.

Looking forward, the discrepancies in previous assumptions about thermal characteristics necessitate future research focusing on the interfacial phenomena and phonon transport mechanisms in 2D materials. Such investigations could lead to enhanced models for predicting thermal behavior and designing advanced electronic systems.

Conclusion

This work contributes significantly to the understanding of thermal transport phenomena in TMDCs, presenting robust measurement methodologies that address and rectify prior inaccuracies in thermal property determinations. The refined measurements and analyses underline the need for precise experimental setups in studying 2D materials, which are increasingly integral to next-generation computing and communication technologies. Future research may explore broader applications of these methodologies to a wider range of similar materials, delving deeper into the interaction between thermal and mechanical properties at the atomic scale.