Effects of tensile strain and finite size on thermal conductivity in monolayer WSe 2 .

In this paper, first-principles calculations along with the phonon Boltzmann transport equation are used to study the strain- and size-dependent thermal conductivity of monolayer WSe2. The thermal conductivity of monolayer WSe2 is primarily contributed by the acoustic phonons and decreases with tensile strain due to the reduction in both the group velocity and phonon lifetime. Shrinking the system size also restricts the thermal conductivity significantly by ruling out the contributions of long mean free path phonons. The rate of decrease in thermal conductivity with tensile strain is found to be size dependent, which is attributed to the competition between the phonon-phonon scattering and the phonon-boundary scattering. The decreasing trend of the thermal conductivity of monolayer WSe2 through tensile strain paves the way for high-efficiency thermoelectric materials combining the strain-tuned electronic structure.