Second Harmonic Characteristics of Large‐Area ALD‐Grown MoS ₂ Monolayers and MoS ₂ /WS ₂ Heterostructures with Sub‐Millimeter Crystalline Orientation

Abstract The crystal orientation uniformity of MoS 2 monolayers grown by atomic layer deposition (ALD) on sapphire substrates is investigated, and their integration with spin‐coated WS 2 in a MoS 2 /WS 2 heterostructure. Polarization‐resolved second harmonic generation (SHG) microscopy reveals that the heterostructure exhibits an exceptionally consistent orientation across 180 × 180 µm 2 areas, with deviations of less than two degrees, despite the polycrystallinity of the WS 2 layer. The SHG response of the heterostructure seems to be dominated by the orientation of the underlying MoS 2 layer; only locally aligned WS 2 domains (if present) contribute marginally. These findings demonstrate the robustness of the MoS 2 crystal orientation and provide insights into interfacial alignment mechanisms and the orientation coherence achievable by ALD, providing a foundation for layer‐selective studies of interfacial ordering in wafer‐scale transition metal dichalcogenide heterostructures.