Self-aligned and self-limiting van der Waals epitaxy of monolayer MoS2 for scalable 2D electronics.

Unidirectional nucleation followed by seamless stitching has emerged as a promising strategy for the scalable epitaxial growth of single-crystalline monolayer transition metal dichalcogenides on sapphire substrates, which holds potential for post-silicon electronics. In contrast, here we present a different growth mechanism for single-crystalline MoS2 on c-plane sapphire via metal-organic chemical vapor deposition (MOCVD). We show that the initial nucleation generates not only 0° and antiparallel 60° domains but also low-angle twisted domains, consistent with the coincidence site lattice framework. However, these rotationally misoriented domains are observed to deterministically self-align and merge into energetically preferred 0° domain during coalescence, yielding a continuous, unidirectional single-crystal. Additionally, by employing MoO2Cl2 as a molybdenum precursor, we demonstrate that the growth of MoS2 occurs in a self-limiting manner. This epitaxial strategy is substantiated by a carrier mobility of 66 cm2/Vs at room temperature and 749 cm2/Vs at low temperatures. Our approach offers a practical and reproducible scheme for MOCVD-based van der Waals epitaxy for 2D electronics.