Unusual Isotope Effect on Thermal Transport of Single Layer Molybdenum Disulphide (MoS2)

TL;DR

This study uses molecular dynamics simulations to reveal that isotopes significantly scatter phonons in single-layer MoS2, reducing thermal conductivity by up to 30%, with effects varying by isotope type and sample size.

Contribution

It demonstrates a novel isotope effect on thermal transport in MoS2, highlighting the limitations of conventional scattering models and emphasizing the importance of isotope type and sample size.

Findings

Natural isotopes reduce thermal conductivity by 30% in large samples.

Isotope scattering is stronger for Mo than S due to phonon eigenvector contributions.

Boundary scattering suppresses isotope effects in small samples.

Abstract

Thermal transport in single layer molybdenum disulfide (MoS2) is critical to advancing its applications. In this paper, we use molecular dynamics (MD) simulations with first-principles force constants to study the isotope effect on the thermal transport of single layer MoS2. Through phonon modal analysis, we found that isotopes can strongly scatter phonons with intermediate frequencies, and the scattering behavior can be radically different from that predicted by conventional scattering model based on perturbation theory (Tamura's formula). Such a discrepancy becomes smaller for low isotope concentrations. Natural isotopes can lead to a 30% reduction in thermal conductivity for large size samples. However, for small samples where boundary scattering becomes significant, the isotope effect can be greatly suppressed. It was also found that the Mo isotopes, which contribute more to the phonon eigenvectors in the intermediate frequency range, have stronger impact on thermal conductivity than S isotopes.