Oxygen-Assisted Direct Synthesis of Twisted Bilayer MoS₂ with Tunable Exciton Lifetime.

Abstract

Twisted bilayer transition metal dichalcogenides (TB-TMDs) have emerged as a versatile platform for fabricating moiré superlattices and exploring correlated electronic behavior, particularly in revealing the interplay between exciton dynamics and twisted angles. However, the direct synthesis of high-quality TB-TMDs nanosheets has been hindered by thermodynamic instability. Here, we develop an oxygen-assisted physical vapor deposition strategy to directly synthesize TB-MoS₂ nanosheets with twist-angle-dependent exciton dynamics. First-principles calculations reveal that oxygen incorporation significantly reduces the formation energy of TB-MoS₂. Guided by this analysis, an oxygen-modulated precursor system is successfully designed to synthesize high-quality TB-MoS₂ nanosheets with well-defined moiré patterns and a broad angular distribution. Besides, for A exciton, it is demonstrated that the time constant <i>t</i>₂ corresponding to the radiative recombination process is shorter at the twist angles of 0° and 60° compared to 12°, 24°, 40°, and 47°. This result is attributed to reduced interlayer distance and enhanced interlayer coupling, as supported by differential charge density and density of states calculations. Furthermore, <i>t</i>₂ is shorter at 24° and 40° than at 12° and 47°, owing to a smaller energy difference between indirect and direct bandgaps. Our work not only establishes an effective route for fabricating TB-TMDs but also deepens the understanding of twist-angle-engineered moiré photonics.