Thermoelectric\nGrain Boundary in Monolayer MoS<sub>2</sub>

Defects such as grain boundaries (GBs) fundamentally\ncontrol thermal\nand electrical transport in two-dimensional (2D) transition metal\ndichalcogenide (TMDC) materials, but the mechanism remains elusive.\nWe have studied thermal and electrical transport across and along\nthe GB within a monolayer of a prototypical TMDC, MoS<sub>2</sub>,\nusing molecular dynamics simulation and first-principles quantum-mechanical\ncalculation. We found the existence of an interfacial phase (or “interphase”)\nwithin a few nanometers from the GB, which has anisotropic transport\nproperties that are distinct from those of a perfect crystal. Namely,\nthe GB interphase has reduced thermal conductivity across the GB.\nIn stark contrast, the electrical conductivity of electron-doped MoS<sub>2</sub> is enhanced in both directions, with higher conductivity\nacross the GB. These results are understood in terms of the alignment\nof energy levels and spatial distribution of electronic wave functions\naround the GB. Such contrasting thermal and electrical transport properties\nof the GB interphase suggest a promising application of GB superlattices\nto thermoelectric power regeneration for sustainable future 2D electronics.