Dual Twisted Interfaces Enable Tunable Second Harmonic Generation in Chemical Vapor Deposition Grown Trilayer MoS2.

Twisted bilayer transition metal dichalcogenides, governed by a single twisted interface, offer a versatile platform for manipulating interlayer coupling and emergent optical behavior. However, despite extensive studies on single twisted interface systems, how multi-interface twisted stacking influences nonlinear optical behavior remains unclear. Here, we address this gap by systematically investigating the nonlinear optical performance of chemical vapor deposition (CVD) grown twisted trilayer MoS2 (TT-MoS2) with multi-interface twisted stacking. We fabricate all nine distinct trilayer MoS2 configurations by CVD. Raman and photoluminescence show that twisted interfaces modulate interlayer coupling, giving rise to stacking-dependent phonon and excitonic responses. Atomic-resolution scanning, transmission electron microscopy, and selected area electron diffraction confirm dual twisted interfaces and a supermoiré lattice. Guided by these structural insights, we examine the second harmonic generation (SHG) response across all nine trilayer configurations. Extending the coherent SH field superposition model to a trilayer system with two independent twisted interfaces, we develop a framework that describes how the dual interfaces govern the SHG intensity and polarization orientation across stacking configurations. Our findings establish TT-MoS2 as a versatile nonlinear platform and open new avenues for understanding and exploiting multi-interface twisted coupling to engineer nonlinear optical responses in van der Waals materials.