In situ investigation of 1T'/1H phase transition in colloidal WS₂ monolayers

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Controlling crystal phase in 2D transition metal dichalcogenides (TMDs) is crucial for tailoring electronic and optical properties.
• The metastable 1T' phase of WS₂ offers distinct quantum functionalities compared to the semiconducting 1H phase.
• Colloidal synthesis allows for functionalization of WS₂ nanosheets with organic ligands.

Purpose of the Study:

• To investigate the temperature-induced phase transition from 1T' to 1H in WS₂.
• To understand the role of organic ligands and doping in stabilizing the 1T' phase.
• To analyze the kinetics and influencing factors of the 1T'/1H phase transition.

Main Methods:

• Colloidal synthesis of monolayer WS₂ nanosheets.
• Functionalization with organic ligands.
• In situ monitoring of structural and electronic properties during annealing.
• Temperature-dependent characterization techniques.

Main Results:

• The 1T' phase of WS₂ is stabilized by electron doping from reducing ligands and remains stable up to 300 °C.
• A mixed 1T'/1H phase regime is observed between 300 °C and 350 °C, tunable by annealing time.
• Complete transformation to the 1H phase occurs above 350 °C, triggered by ligand decomposition.
• Smaller WS₂ nanosheets exhibit slower phase transition kinetics.

Conclusions:

• Ligand decomposition is the primary trigger for the 1T' to 1H phase transition in WS₂.
• A strong interplay exists between doping, surface chemistry, and lattice structure.
• Finite size effects can influence the phase transition kinetics in WS₂ nanosheets.