Unusual isotope effect on thermal transport of single layer molybdenum disulphide

Thermal transport in single layer molybdenum disulfide (MoS₂) is critical to advancing its applications. In this paper, we use molecular dynamics 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, where Tamura's formula is combined with Matthiessen's rule to include isotope effects. 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