Lattice thermal conductivity of Janus MoSSe and WSSe monolayers

In this work, the heat transport properties of Janus MoSSe and WSSe monolayers are systematically investigated using non-equilibrium molecular dynamics simulations. Strong size dependence of the thermal conductivity is found in the Janus MoSSe and WSSe monolayers. In the two-dimensional limit, the Mo-based Janus MoSSe monolayer shows a higher thermal conductivity but similar phonon mean free path as MoS₂, while the W-based Janus WSSe monolayer shows a similar thermal conductivity but longer phonon mean free path than WSe₂. These two Janus monolayers also present quite different temperature dependencies. With temperature increasing from 100 K to 350 K, the reduction in thermal conductivity of MoSSe is up to 28.4%, but only 12.75% in WSSe, because of the weak temperature dependence in the phonon density of states. With 2% vacancy density, the thermal conductivity of defective MoSSe is only 16.03% that of pristine MoSSe, while for defective WSSe, the thermal conductivity is 14.04% that of pristine WSSe. The strong dependence on vacancy is explained by atomic heat flux vector analysis. The present study demonstrates rich physical phenomena in the thermal transport properties of Janus transition metal dichalcogenide monolayers, which may offer a new degree of freedom for manipulating their thermal conductivity for applications including thermal management and thermoelectric devices.