Laser-assisted synthesis of vertical WS2/MoS2 heterostructures via oxide-to-sulfide conversion

• A transfer-free strategy enables the growth of WS 2 /MoS 2 vertical heterostructures. • Oxygen-deficient MoO 3 −x and WO 3 −x PLD films provide effective solid-state precursors. • Direct conversion of oxide bilayers yields uniform WS 2 /MoS 2 stacking and clean interfaces. The reliable fabrication of vertically stacked transition metal dichalcogenide (TMD) heterostructures with clean, well-defined interfaces is essential for next-generation opto-electronic and quantum technologies. Here, we demonstrate a fully transfer-free synthesis route for WS 2 /MoS 2 heterostructures by combining pulsed laser deposition (PLD) of oxygen-deficient MoO 3 −x and WO 3 −x thin films with high-temperature sulfurization. Oxygen vacancies in the reduced oxides act as reactive sulfur incorporation sites, enabling efficient conversion into a crystalline monolayer of MoS 2 and few-layer WS 2 . We compare two routes direct sulfurization of an in situ WO 3 −x /MoO 3 −x bilayer and a sequential process in which WO 3 −x is deposited onto pre-formed MoS 2 . Both approaches yield vertically stacked WS 2 /MoS 2 heterostructures with clean interfaces and strong interlayer coupling; however, the direct bilayer conversion produces more uniform stacking and better structural quality. This vacancy-driven oxide conversion strategy provides scalable control over layer thickness, morphology, and interfacial sharpness while avoiding polymer residues and the mechanical damage inherent to transfer-based assembly. These results establish oxygen-deficient metal oxides as versatile solid-state precursors for the growth of high-quality TMD heterostructures suitable for advanced photonic, electronic, and quantum devices.