Colloidal 2D Mo_1-WS₂ nanosheets: an atomic- to ensemble-level spectroscopic study

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Two-dimensional (2D) transition metal dichalcogenide (TMDC) alloys offer tunable electronic and optical properties for optoelectronics.
• Controlling the composition of TMDC alloys is crucial for tailoring their performance.

Purpose of the Study:

• To report a solution-based synthesis for producing predominantly monolayered 2D semiconducting Mo_1-xW_xS₂ nanosheets (NSs) with controlled composition.
• To demonstrate the viability of colloidal methods for upscaling low-cost synthetic approaches toward application-tailored colloidal TMDCs.

Main Methods:

• Solution-based synthesis of Mo_1-xW_xS₂ nanosheets.
• High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with energy dispersive X-ray spectroscopy (EDXS) for atomic-level structural analysis.
• Steady-state optical spectroscopy for characterizing electronic and optical properties.

Main Results:

• Successfully synthesized substrate-free colloidal inks of predominantly monolayered Mo_1-xW_xS₂ NSs with controlled composition.
• Atomic-level analysis revealed the distribution of Mo and W atoms and the tendency for domain formation.
• Band gap tuning in the range of 1.89–2.02 eV (614–655 nm) and tunable spin-orbit coupling-related exciton splitting (0.16–0.38 eV) were achieved.

Conclusions:

• The developed colloidal method is suitable for large-scale, low-cost synthesis of compositionally controlled 2D TMDC alloys.
• The tunable optoelectronic properties of Mo_1-xW_xS₂ make them promising for various optoelectronic applications.