Wafer-scale single crystals of 2D transition metal dichalcogenides (TMDs) could enable next-generation electronic devices, but they are challenging to produce. Now, writing in Nature Materials, Zheng Zhang, Yue Zhang and collaborators report an adaptation of the Czochralski method that enables the growth of centimetre-scale single-crystal MoS2 flakes with ultra-low defect density.

In the first stage of the process, a MoO3 powder is melted and reacts with a molten glass substrate to form small droplets that prevent the sublimation of MoO3 and ensure an adequate Mo source. Polycrystalline MoS2 is then pre-deposited in a sulfur atmosphere, forming dense multilayer MoS2 domains. Subsequently, an etching process transforms the pre-deposited MoS2 into a liquid precursor, at a temperature lower than that needed to melt MoS2 directly. The molten glass substrate helps the formation of a 2D liquid film, which forms a stable and homogeneous precursor. The final stage involves rapid crystallization through the Czochralski process following the addition of sulfur vapour, leading to the growth of large MoS2 domains.