Controlling Twisted Angles in Directly Grown MoS 2 Bilayers via Tilt Grain Boundary Engineering

The moiré superlattices have garnered significant attention due to their unique twist-angle-dependent electronic and optical properties. Creating high-quality twisted bilayer structures stands as one of the major frontiers in the study of correlated moiré physical properties, however, which remains a challenge. Here, a cyclical-carrier-gas chemical vapor deposition method is employed to grow high-quality twisted bilayers MoS₂. Stacking configurations and the growth mechanism of twisted bilayer MoS₂ are systematically investigated, revealing that the relative rotation angle between the two layers is guided by the tilt grain boundaries (GBs) of the bottom layer. This relationship is elucidated through real-time monitoring of the formation process of the top layer from nucleation to coalescence. Meanwhile, the interlayer exciton (X^I) strongly couples to the twist angle, and the enhanced intensity of X^I peaks in TB-MoS₂ at specific twist angles of ≈22° and 38° is evidenced by low-temperature (10K) photoluminescence and second harmonic generation spectra, which can be ascribed to the X^I localization in the periodical moiré superlattice. The findings provide a viable method for the in- situ preparation of layered twisted materials guided by tilt GBs, which facilitates the exploration of novel optical and excitonic physics in moiré systems.