Record Low Thermal Conductivity of Polycrystalline MoS2 films: Tuning the Thermal Conductivity by Grain Orientation

TL;DR

This study demonstrates that by controlling grain size and orientation in polycrystalline MoS2 films, a record low thermal conductivity comparable to Teflon can be achieved, with potential applications in electronics and thermoelectric devices.

Contribution

It introduces a method to tune thermal conductivity in MoS2 films through grain orientation and size control, achieving record low values.

Findings

Thermal conductivity as low as 0.27 W/m·K in polycrystalline MoS2.

Grain orientation significantly influences grain boundary conductance.

Simulations confirm grain arrangement reduces thermal transport.

Abstract

We report a record low thermal conductivity in polycrystalline MoS2 obtained by varying grain sizes and orientations in ultrathin films. By optimizing the sulphurisation parameters of nanometre-thick Mo layer, we could grow MoS2 films with tuneable morphologies. The thermal conductivity is extracted from a Raman laser power-dependent study on suspended samples. The lowest value of thermal conductivity of 0.27 Wm-1K-1, which reaches a similar value as teflon, is obtained in a polycrystalline sample formed by a combination of horizontally and vertically oriented grains, with respect to the bulk (001) monocrystal. Analysis by means of molecular dynamics and finite element method simulations confirm that such grain arrangement leads to lower grain boundary conductance. We discuss the possible use of these thermal insulating films in the context of electronics and thermoelectricity.