Towards the scalable synthesis of two-dimensional heterostructures and superlattices beyond exfoliation and restacking.

Two-dimensional transition metal dichalcogenides, which feature atomically thin geometry and dangling-bond-free surfaces, have attracted intense interest for diverse technology applications, including ultra-miniaturized transistors towards the subnanometre scale. A straightforward exfoliation-and-restacking approach has been widely used for nearly arbitrary assembly of diverse two-dimensional (2D) heterostructures, superlattices and moiré superlattices, providing a versatile materials platform for fundamental investigations of exotic physical phenomena and proof-of-concept device demonstrations. While this approach has contributed importantly to the recent flourishing of 2D materials research, it is clearly unsuitable for practical technologies. Capturing the full potential of 2D transition metal dichalcogenides requires robust and scalable synthesis of these atomically thin materials and their heterostructures with designable spatial modulation of chemical compositions and electronic structures. The extreme aspect ratio, lack of intrinsic substrate and highly delicate nature of the atomically thin crystals present fundamental difficulties in material synthesis. Here we summarize the key challenges, highlight current advances and outline opportunities in the scalable synthesis of transition metal dichalcogenide-based heterostructures, superlattices and moiré superlattices.