Beyond Perturbation: Role of Vacancy-Induced Localized Phonon States in Thermal Transport of Monolayer MoS₂

Abstract

Sulfur vacancies in monolayer MoS2 can provide unexpected opportunities for tailoring the properties and device applications via defect engineering. However, determining the effect of vacancies in thermal transport remains a big challenge. Using a first-principles supercell approach, we reveal the dominant role of defect-induced quasi-localized phonon states in reducing thermal conductivity of MoS2. These states are related to flattened dispersions in phonon spectrum, which comes from perturbations in atomic mass and interatomic bonding. Although the scattering strength of each modes remains similar, the phonon group velocities are much lower near the quasi-localized modes, while the Umklapp scattering are significantly enhanced. Thus, the thermal conductivity of defective MoS2 is severely reduced. Our results contribute to fundamental understanding of the effect of vacancies on thermal transport, and can be used to assess the defect concentrations in semiconductors quantitatively.

Chemical intuition for high thermoelectric performance in monolayer black phosphorus, α-arsenene and aW-antimonene

“…Generally, the a transport direction with higher κ L is preferred in nanoelectronics, while the b direction is preferred in thermoelectric devices. For monolayer black phosphorus, the κ L along the a direction is comparable to that for the perfect monolayer MoS 2 using the same approach 121,122 , indicating efficient heat dissipation; along the b direction, the κ L is even For α-arsenene, the κ L along the a direction is similar to that for low-buckled silicene (28.3 W/mK) 123 . As noted in our previous study, by adding Si adatoms, the κ L of silicene can be reduced to 2.86 W/mK after the dumbbell structure is formed 36 .…”

First principle investigation of the influence of sulfur vacancies on thermoelectric properties of single layered MoS2

“…33 Such defects induce the localization of phonon modes and a reduction of thermal conductivity due to an enhancement in Umklapp scattering. 34,35 Furthermore, first principle studies have pointed out that the zT may be as high as 6.24 for MoS 2 with S defects at room temperature. 36 The understanding of the interplay between Umklapp processes and defect scattering is still an open and complex issue that implies a realistic treatment of the disordering and thus of the Anderson localization phenomenon.…”

Effects of Defects on the Temperature‐Dependent Thermal Conductivity of Suspended Monolayer Molybdenum Disulfide Grown by Chemical Vapor Deposition

“…Such correlation is paramount for understanding transport physics in such 2D systems as it is evident by the many papers reporting on their electrical and optical properties where intrinsic structural defects and their effects on transport mechanism cannot be ignored . On the other hand, in the recent years an increasing number of atomistic calculations have been done to theoretically predict the thermal conductivity of the MoS 2 monolayer and a wide range of thermal conductivity at room temperature, that is, κ = 23.2–155 W m −1 K −1 has been reported . Moreover, it was demonstrated theoretically that defects such as vacancies and isotopes suppress the thermal conductivity of monolayer MoS 2 .…”

“…For example, molecular dynamic (MD) simulations showed that introducing vacancies to the lattice structure of MoS 2 keeps phonon specific heat and group velocity almost unchanged but decreases phonon relaxation time compared to its pristine form. Calculation based on first‐principles revealed that phonon group velocities are significantly lower near the vacancy‐induced quasi‐localized phonon modes. Also, isotopes were found to strongly scatter phonons with intermediate frequencies in the large‐size MoS 2 samples where boundary scattering has a minor effect .…”