Layer thickness-dependent phonon properties and thermal conductivity of MoS2

TL;DR

This study investigates how the phonon properties and thermal conductivity of MoS2 change with layer thickness, revealing that thermal conductivity decreases with fewer layers due to altered phonon dispersion and anharmonicity.

Contribution

It provides first-principles-based insights into the layer-dependent phonon and thermal transport properties of MoS2, highlighting mechanisms behind thermal conductivity reduction in few-layer structures.

Findings

Thermal conductivity decreases from 138 to 98 W/mK in natural MoS2 as layers decrease from bulk to monolayer.

In isotopically pure MoS2, thermal conductivity drops from 155 to 115 W/mK with fewer layers.

Increased anharmonicity in bi-layer MoS2 enhances phonon scattering, affecting thermal transport.

Abstract

For conventional materials, the thermal conductivity of thin film is usually suppressed when the thickness decreases due to phonon-boundary scattering. However, this is not necessarily true for the van der Waals solids if the thickness is reduced to only a few layers. In this letter, the layer thickness-dependent phonon properties and thermal conductivity in the few-layer MoS2 are studied using the first-principles-based Peierls-Boltzmann transport equation approach. The basal-plane thermal conductivity is found to monotonically reduce from 138 W/mK to 98 W/mK for naturally occurring MoS2, and from 155 W/mK to 115 W/mK for isotopically pure MoS2, when its thickness increases from one layer to three layers. The thermal conductivity of tri-layer MoS2 approaches to that of bulk MoS2. Both the change of phonon dispersion and the thickness-induced anharmonicity are important for explaining such a thermal conductivity reduction. The increased anharmonicity in bi-layer MoS2 results in stronger phonon scattering for ZAi modes, which is linked to the breakdown of the symmetry in single-layer MoS2.