First-principles insights into vacancy-induced thermal conductivity suppression in 2D MoS2 and MoSe2

Abstract

Point defects are prevalent in transition metal dichalcogenides formed during high-temperature synthesis. In this work, we quantify their impact on lattice thermal transport in monolayer MoS2 and MoSe2 using first-principles density functional theory coupled with solution of the phonon Boltzmann transport equations. The defects we investigated include mono- and di-chalcogen (S/Se) vacancies and mono-Mo vacancy. It is revealed that S/Se vacancies substantially suppress thermal conductivity, by ∼67% for a mono-S vacancy in MoS2 and by >77% for a mono-Se vacancy in MoSe2. A single Mo vacancy produces the most severe degradation, reducing thermal conductivity by ∼98%, far exceeding the effect of chalcogen vacancies despite expectations based on simple mass contrast. This extreme reduction arises from the removal of the Mo bonding hub, which induces pronounced local distortion and large perturbations of force constants, thereby enhancing phonon scattering and shortening mean free paths. Mode-resolved analysis further shows that in MoS2, a Mo vacancy increases the relative contribution of out-of-plane acoustic (ZA) phonons, whereas the ZA contribution in MoSe2 is largely unchanged. These results elucidate vacancy-induced degradation mechanisms and establish defect engineering as an effective route to tailor thermal transport in 2D materials. Unlike other computational approaches, our method accounts for scattering from both missing mass and altered force constants, enabling more accurate predictions of phonon-scattering rates and mean free paths, and achieving better agreement with experimental results.