Strong reduction of thermal conductivity of WSe₂with introduction of atomic defects

The thermal conductivities of pristine and defective single-layer tungsten diselenide (WSe₂) are investigated by using equilibrium molecular dynamics method. The thermal conductivity of WSe₂increases dramatically with size below a characteristic of ~5 nm and levels off for broader samples and reaches a constant value of ~2 W/mK. By introducing atomic vacancies, we discovered that the thermal conductivity of WSe₂is significantly reduced. In particular, the W vacancy has a greater impact on thermal conductivity reduction than Se vacancies: the thermal conductivity of pristine WSe₂is reduced by ~60% and ~70% with the adding of ~1% of Se and W vacancies, respectively. The reduction of thermal conductivity is found to be related to the decrease of mean free path (MFP) of phonons in the defective WSe₂. The MFP of WSe₂decreases from ~4.2 nm for perfect WSe₂to ~2.2 nm with the addition of 0.9% Se vacancies. More sophisticated types of point defects, such as vacancy clusters and anti-site defects, are explored in addition to single vacancies and are found to dramatically renormalize the phonons. The reconstruction of the bonds leads to localized phonons in the forbidden gap in the phonon density of states which leads to a drop in thermal conduction. This work demonstrates the influence of different defects on the thermal conductivity of single-layer WSe₂, providing insight into the process of defect-induced phonon transport as well as ways to improve heat dissipation in WSe₂-based electronic devices.