Reduced thermal conductivity of supported and encased monolayer and bilayer MoS2

Electrical and thermal properties of atomically thin two-dimensional (2D) materials are affected by their environment, e.g. through remote phonon scattering or dielectric screening. However, while it is known that mobility and thermal conductivity (TC) of graphene are reduced on a substrate, these effects are much less explored in 2D semiconductors such as MoS2. Here, we use molecular dynamics to understand TC changes in monolayer (1L) and bilayer (2L) MoS(2)by comparing suspended, supported, and encased structures. The TC of monolayer MoS(2)is reduced from similar to 117 W m(-1)K(-1)when suspended, to similar to 31 W m(-1)K(-1)when supported by SiO2, at 300 K. Encasing 1L MoS(2)in SiO(2)further reduces its TC down to similar to 22 W m(-1)K(-1). In contrast, the TC of 2L MoS(2)is not as drastically reduced, being >50% higher than 1L both when supported and encased. These effects are due to phonon scattering with remote vibrational modes of the substrate, which are partly screened in 2L MoS2. We also examine the TC of 1L MoS(2)across a wide range of temperatures (300 K to 700 K) and defect densities (up to 5 x 10(13)cm(-2)), finding that the substrate reduces the dependence of TC on these factors. Taken together, these are important findings for all applications which will use 2D semiconductors supported or encased by insulators, instead of freely suspended.

Automated summary

The thermal conductivity of monolayer MoS(2) significantly decreases when supported by SiO2 or encased in SiO(2), while that of bilayer MoS(2) is less affected. These effects are attributed to phonon scattering with remote vibrational modes of the substrate, which are partly screened in bilayer MoS2. This study also reveals that the substrate reduces the dependence of thermal conductivity on temperature and defect densities in monolayer MoS(2).