Laser-Assisted Synthesis of Vertical WS₂/MoS₂ Heterostructures via Oxide-to-Sulfide Conversion.

The reliable fabrication of vertically stacked transition metal dichalcogenide (TMD) heterostructures with clean, well-defined interfaces is essential for next-generation optoelectronic and quantum technologies. Here, we demonstrate a fully transfer-free synthesis route for WS₂/MoS₂ 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 MoS₂ and few-layer WS₂. 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 MoS₂. Both approaches yield vertically stacked WS₂/MoS₂ 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.