Transient thermal characterization of suspended monolayer MoS$_2$

TL;DR

This study measures the thermal response of suspended monolayer MoS₂ drums to determine their thermal properties, revealing device-to-device variability and proposing a method to estimate specific heat of 2D materials.

Contribution

It provides the first direct measurement of thermal diffusivity and conductivity of suspended monolayer MoS₂ and introduces a new method to estimate specific heat from thermal data.

Findings

Thermal diffusivity of monolayer MoS₂ is approximately 1.14×10⁻⁵ m²/s.

Thermal conductivity ranges from 10 to 40 W/(m·K).

Device-to-device variations are linked to microscopic defects affecting phonon scattering.

Abstract

We measure the thermal time constants of suspended single layer molybdenum disulfide drums by their thermomechanical response to a high-frequency modulated laser. From this measurement the thermal diffusivity of single layer MoS$_2$ is found to be 1.14 $\times$ 10$^{-5}$ m$^2$/s on average. Using a model for the thermal time constants and a model assuming continuum heat transport, we extract thermal conductivities at room temperature between 10 to 40 W/(m$\cdot$K). Significant device-to-device variation in the thermal diffusivity is observed. Based on statistical analysis we conclude that these variations in thermal diffusivity are caused by microscopic defects that have a large impact on phonon scattering, but do not affect the resonance frequency and damping of the membrane's lowest eigenmode. By combining the experimental thermal diffusivity with literature values of the thermal conductivity, a method is presented to determine the specific heat of suspended 2D materials, which is estimated to be 255 $\pm$ 104 J/(kg$\cdot$K) for single layer MoS$_2$.