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 in-volves a vapour-liquid-solid phase reaction between MoOx (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 envi-ronment. 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 which 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.

Automated summary

Alkali-assisted chemical vapor deposition has been proven effective in growing large single crystals of transition metal dichalcogenides. In this study, a vapor-liquid-solid phase reaction between MoOx precursors and metal alkali halide (i.e., NaF) was utilized to synthesize highly crystalline MoS2 nanoribbons. The growth process involves the formation of Na-Mo-O liquid phase in a sulfur-rich environment. The as-grown MoS2 nanoribbons are surrounded by mono- and multilayer triangles of MoS2 and exhibit a preferential alignment dictated by both crystal symmetry and substrate. The method offers flexibility in designing nanoelectronic devices based on tunable TMD dimensions.