Investigation Of Thermal Conductivity Of Monolayer MoS₂

Thermoelectric materials can convert energy between heat and electricity, and have superior performance. We can rely on the thermoelectric materials to produce clean, pollution-free, noise-free thermoelectric generators and thermoelectric cooling devices. The thermoelectric efficiency is described by the thermoelectric figure of merit ZT, TSZT??2?, where S, ?, T and ? are the Seebeck coefficient,electrical conductivity, absolute temperature and thermal conductivity respectively. In research and application, we can improve the thermoelectric figure of merit by reducing thermal conductivity of thermoelectric materials. With the rise of nano-materials, nano-thermoelectric materials have been widely investigated.In the recent decade, two-dimensional nanomaterials have attracted intense interesting in scientific research since graphene has been successfully separated from the graphite. A series of two-dimensional nanomaterials are produced, such as monolayer hexagonal boron nitride and monolayer transition metal dichalcogenides.Among them, monolayer molybdenum disulfide(Mo S2) has low thermal conductivity and large Seebeck coefficient, these properties suggest potential thermoelectric applications of monolayer molybdenum disulfide. It is still necessary to reduce the thermal conductivity of Mo S2 for higher thermoelectric performance.We investigate the size and edge roughness dependence on thermal conductivity of monolayer Mo S2 by phonon Boltzmann transport equation combined with relaxation time approximation. It is found that the thermal conductivity of monolayer Mo S2 ribbons is size and roughness insensitive. In order to find out the ways to reduce the thermal conductivity of monolayer Mo S2, we investigate the effect of point defects,such as sulfur vacancies(SV) and oxygen substitutions to sulfur(OS) on thermal conductivity of Mo S2 nanoribbons by applying non-equilibrium molecular dynamics simulation. It is found that bothSV andOS can significantly reduce the thermal conductivity of monolayer Mo S2 nanoribbons, but the suppression of thermal conductivity by vacancies is stronger than that by substitutions. We perform the vibrational eigenmodes analysis and find that the strong localization of phonons of all modes by defects results in the severe reduction of thermal conductivity of Mo S2 nanoribbons. Further spectra analysis reveals that the localized modes are located in the sites of defects and the sites around defects, due to the change of force constant at these sites. Our findings are helpful for understanding and tuning the thermalconductivity of Mo S2 nanoribbons by defect engineering.