Tuning bandstructure of folded MoS₂ through fluid dynamics

The variation of interlayer coupling can greatly affect the bandstructure of few layered transition metal dichalcogenides (TMDs), for instance, transition of indirect-to-direct bandgap and vice versa, which is correlated with the charge carrier and optical density. However, methods that can modulate the coupling strength in a controllable way are still lacking. Here, we report a fluidic dynamic strategy to tune the interlayer coupling of folded bi-layer MoS₂. By controlling the flow direction and particle size of the fluid, mono-layer MoS₂ can be folded into bi-layer with a controlled folding direction for designated twist angles as well as tunable interlayer coupling. Compared with normally folded bi-layer MoS₂, the photoluminescence (PL) peak of the direct-bandgap transition for folded bi-layer MoS₂ by fluid flow is weakened accompanied with the re-appearance of indirect-bandgap transition peak. Besides, the fluid flow creates a clear trajectory on the folded MoS₂, exhibiting various degrees of interlayer coupling along it. Field-effect transistors (FETs) were further fabricated on tunably coupled folded-bi-layers, proving that the bandstructure and electrical property is strongly correlated with the degree of interlayer coupling. This fluidic dynamic strategy can be extended to other TMDs on any substrate, and together with its excellent capability in controlled interlayer coupling, it will provide a new way for the development of TMDs optoelectronics.