Femtosecond Laser-Driven Phase Engineering of WS₂ for Nano-Periodic Phase Patterning and Sub-ppm Ammonia Gas Sensing

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Laser-driven phase transitions in 2D transition metal dichalcogenides offer flexibility but face challenges like surface ablation and limited patterning.
• Existing methods struggle with nanoscale control and exploiting new material phases.

Purpose of the Study:

• To achieve well-controlled femtosecond laser-driven phase transition of 2D tungsten disulfide (WS2) from metallic 2M to semiconducting 2H phase.
• To demonstrate nanoscale phase patterning with high resolution and explore the properties of the resulting material.

Main Methods:

• Utilizing femtosecond (fs) laser irradiation for controlled phase transformation of 2D WS2.
• Investigating single-crystal to single-crystal transition without significant ablation or layer thinning.
• Achieving nanoscale phase patterning through selective plasmon energy deposition.

Main Results:

• Successful single-crystal to single-crystal phase transition from 2M-WS2 to 2H-WS2 without ablation.
• Creation of highly ordered 2H/2M nano-periodic phase transition with a resolution of approximately 435 nm.
• Demonstration that laser-induced 2H-WS2 exhibits rich sulfur vacancies, leading to excellent ammonia gas sensing (detection limit < 0.1 ppm, response/recovery 43/67 s).

Conclusions:

• Femtosecond laser irradiation provides a precise method for phase engineering in 2D materials.
• This technique enables nanoscale phase patterning and the creation of materials with enhanced properties.
• The developed approach offers a new strategy for phase-selective transition homojunctions and advanced electronic applications, particularly in gas sensing.