Phonon-Grain-Boundary-Interaction-Mediated Thermal Transport in Two-Dimensional Polycrystalline MoS₂

Although dislocations and grain boundaries (GBs) are ubiquitous in large-scale MoS₂ samples, their interaction with phonons, which plays an important role in determining the lattice thermal conductivity of polycrystalline MoS₂, remains elusive. Here, we perform a systematic study of the heat transport in two-dimensional polycrystalline MoS₂ by both molecular dynamics simulation and atomic Green's function method. Our results indicate that the thermal boundary conductance of GBs of MoS₂ is in the range from 6.4 × 10⁸ to 35.3 × 10⁸ W m^-2 K^-1, which is closely correlated with the overlap between the vibrational density of states of GBs and those of the pristine lattice, as well as the GB energy. It is found that the GBs strongly scatter the phonons with frequency larger than 2 THz, accompanied by a pronounced phonon localization effect and significantly reduced phonon group velocities. Furthermore, by comparing the results from realistic polycrystalline MoS₂ to those from different theoretical models, we observe that the Casimir model is broken down and detailed phonon dynamics at a specific GB should be taken into account to accurately describe the phonon transport in polycrystalline materials. Our findings will provide useful guidelines for designing efficient thermoelectric and thermal management materials based on phonon-GB interaction.