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Oxide Scale Sublimation Chemical Vapor Deposition for Controllable Growth of Monolayer MoS2 Crystals.

A newly developed oxide scale sublimation chemical vapor deposition (OSSCVD) technique for 2D MoS2 growth is reported. Gaseous MoO3 , which is supplied separately from H2 S, can be generated in situ by flowing O2 over Mo metal with oxidation and sublimation processes. In this method, particularly, controllably and abruptly modulating the supply of MoO3 is achievable by precisely tuning O2 flow. Having appropriate conditions, where the generation rate of MoO3 on the Mo metal surface is not larger than its sublimation rate, is critical to enable stable growth. Otherwise, MoS2 deposition can be caused by accumulated MoO3 on the metal surface, regardless of oxygen supply. Proof-of-concept experiments with varied process parameters are conducted, confirming OSSCVD enables MoS2 growth with significantly improved flexibility, controllability, and reproducibility relative to conventional powder-source CVD. By utilizing alkali-aluminosilicate glass, Dragontrail, as catalytic substrate, single-crystalline MoS2 triangular domains as large as 25 µm are obtained, followed by a fully covered monolayer on Dragontrail in 25 min. Substrate pretreatment by H2 S yields enlarged domain size and reduced domain density, owning to the extracted alkali metals from Dragontrail into the growth zone. The study opens new avenues for the controllable growth of high-quality MoS2 and other transition metal dichalcogenides.