Sulphur-affected microstructural evolution mechanism of WS₂

Two-dimensional tungsten disulfide (2D WS₂) has attracted significant attention across diverse application fields, particularly optoelectronic devices and field-effect transistors, due to its exceptional properties. A thorough elucidation of the WS₂ growth mechanism is crucial for device implementation, as it allows for precise modulation of the nanoscale properties. Despite significant efforts toward the growth of 2D WS₂ for increasing its size, detailed investigations into its structural evolution, especially for the out-of-plane layered WS₂, remain scarce. In this work, we identify two distinct conversion growth mechanisms for in-plane and out-of-plane layered WS₂ using a homemade chemical vapor deposition (CVD) system. We systematically investigate the evolution of different WS₂ nanophases by altering the precursor and regulating the sulphur concentrations. The results reveal that out-of-plane 1D and 2D WS₂ are formed via an outside-in mechanism during the layer-by-layer sulphurization of WO_2.7 nanowires, while in-plane layered WS₂ evolves from WO₃ precursors via a 'self-seeding' mechanism involving an island-like WO_3-x-WS₂ core-shell structure. This study clarifies the 2D WS₂ growth process, offering key insights into the evolution mechanisms of low-dimensional WS₂. These findings may not only pave the way for synthesizing high-quality, large-scale 2D-domain WS₂ but also offer guidance for the controlled growth of other transition-metal dichalcogenides.