Measurement of Lateral and Interfacial Thermal Conductivity of Single- and Bilayer 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 39,40 to measure the thermal transport properties of two TMDC materials, MoS 2 and MoSe 2 , 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 MoS 2 and MoSe 2 , the roomtemperature thermal conductivities are (84±17) W/mK and (59±18) W/mK, respectively. For 2L MoS 2 and MoSe 2 , 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/m 2 K, substantially smaller than previously assumed, a finding that has important implications for design and modeling of electronic devices.

Thermal Conductance of the 2D MoS2/h-BN and graphene/h-BN Interfaces

“…Raman spectroscopy has been demonstrated to be an effective method to probe the temperatures of 2D materials31333437404158, based on the fact that the Raman spectra red-shifts as temperature rises due to lattice softening and anharmonic scattering of phonons. To measure temperatures with Raman spectroscopy, the experiment is divided into two parts.…”

“…Although such measurements further our understanding of phonon interactions within the 2D system, they are of limited relevance to realistic device applications for which the supported configuration is more practical. The thermal properties of this supported configuration are still not well studied, and there are only few works reported on graphene36373839 and MoS 2 4041 on various bulk substrates. TMDC flakes situated on another 2D material such as h -BN being the substrate, i.e., two 2D-material interface/heterostructure, is far less investigated, which is in great demand in the emerging heterostructures and optoelectronic devices involving stacked 2D materials.…”

“…measured the total G across MoS 2 /Si including a thin SiO 2 layer to be 1.94 MW/m 2 K41, and Zhang et al . measured G to be 0.44 MW/m 2 K for MoS 2 /Au40. These results were obtained by solving the heat diffusion equation based on the temperatures obtained from Raman spectroscopy, and the thermal conductivity was obtained simultaneously.…”

Single- and few-layer WTe2and their suspended nanostructures: Raman signatures and nanomechanical resonances

“…Among various device structures, suspended, movable 2D flakes make a special platform with controllable mechanical degrees of freedom, which not only frees the crystal from the bonding of substrates, but can also enhance device performance and versatility. For examples, suspended graphene transistors exhibit ultrahigh mobility up to 200,000 cm 2 V −1 s −1 [8], and suspended monolayer MoS 2 crystal can have orders of magnitude enhancement in photoluminescence (PL) intensity over its on-substrate counterpart [ 9 ]. Moreover, suspended structures based on atomic layers are essential for enabling 2D nanoelectromechanical systems (NEMS) such as ultrasensitive transducers and radio-frequency (RF) resonators.…”

Phonon transport in single-layerMo1−xWxS2alloy embedded withGu1, Yang2 2016Phys. Rev. B202120View full textAdd to dashboardCite

“…Many efforts have been devoted to investigate the thermal conductivity of 2-D TMDs, both theoretically [13][14][15] and experimentally [16][17][18][19] . While the 2-D TMDs with high thermal conductivity might be beneficial to thermal management and electronic cooling, those with low thermal conductivity could be used as the thermal barrier materials 20 and thermoelectric materials.…”