Sulphur-affected microstructural evolution mechanism of WS₂

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Chemistry

Background:

• Two-dimensional tungsten disulfide (2D WS₂) exhibits exceptional properties, making it vital for optoelectronics and field-effect transistors.
• Precise control over WS₂ nanostructure growth is essential for optimizing device performance.
• Limited understanding exists regarding the structural evolution of out-of-plane layered WS₂.

Purpose of the Study:

• To elucidate the distinct growth mechanisms of in-plane and out-of-plane layered 2D WS₂.
• To investigate the influence of precursor materials and sulfur concentration on WS₂ nanophase evolution.
• To provide insights into the controlled synthesis of low-dimensional WS₂ materials.

Main Methods:

• Utilized a custom-built chemical vapor deposition (CVD) system.
• Systematically varied precursor materials (WO₂.₇ and WO₃) and sulfur concentrations.
• Analyzed the structural evolution of WS₂ nanophases under different conditions.

Main Results:

• Identified two distinct conversion growth mechanisms: an 'outside-in' mechanism for out-of-plane WS₂ from WO₂.₇ nanowires, and a 'self-seeding' mechanism for in-plane WS₂ from WO₃.
• Out-of-plane 1D and 2D WS₂ form via layer-by-layer sulfurization.
• In-plane WS₂ evolves from a WO₃ precursor through a WO₃₋ₓ-WS₂ core-shell intermediate.

Conclusions:

• Clarified the growth processes for both in-plane and out-of-plane 2D WS₂.
• Provided fundamental insights into the formation mechanisms of low-dimensional WS₂.
• Findings facilitate the synthesis of high-quality, large-scale 2D WS₂ and guide the growth of other transition-metal dichalcogenides.