A novel two-step route to unidirectional growth of multilayer MoS₂ nanoribbons

Alkali-assisted chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) has been shown to promote the growth of large single crystals of TMD monolayers. The morphology control of TMDs is a key parameter for the scalable synthesis of versatile layered materials. This work demonstrates that the alkali-assisted synthesis provides a route toward fabricating highly crystalline MoS₂ nanoribbons. Our proposed method involves a vapour-liquid-solid phase reaction between MoO_x (2 < x < 3) precursors grown by Pulsed Laser Deposition (PLD) and metal alkali halide (i.e., NaF). The growth process evolves via the emergence of the Na–Mo–O liquid phase, which mediates the formation of MoS₂ multilayer nanoribbons in a sulfur-rich environment. Moreover, the as-grown MoS₂ nanoribbons are surrounded by mono- and multilayer triangles of MoS2 and exhibit a preferential alignment defined by both MoS₂ crystal symmetry and the underlying Al₂O₃ substrate. In addition, we observe a significant built-in strain in the as-grown MoS₂ nanostructures, which increase in magnitude from the multilayer nanoribbons to the triangular monolayers and can be effectively released upon transfer onto another substrate. The growth method developed here can enable flexibility in designing nanoelectronic devices based on TMDs with tunable dimensions.