  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.
