Microjunction-Modulated Selective Ammonia Sensor with P-Type Oxides-Decorated WS₂ Microflakes

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Chemiresistive gas sensors are crucial for environmental monitoring and industrial safety.
• Tungsten disulfide (WS₂) and p-type metal oxides (NiO, Co₃O₄, CuO) are promising materials for gas sensing applications.
• Heterostructuring materials can enhance gas sensing performance by modulating electronic properties at interfaces.

Purpose of the Study:

• To fabricate and investigate NiO/WS₂ heterostructures for enhanced chemiresistive ammonia (NH₃) gas sensing at room temperature.
• To compare the sensing performance of NiO/WS₂ with Co₃O₄/WS₂ and CuO/WS₂ heterostructures.
• To elucidate the underlying mechanisms responsible for the improved sensing properties of NiO/WS₂.

Main Methods:

• Fabrication of p-type metal oxide (NiO, Co₃O₄, CuO) decorated WS₂ microflakes.
• Chemiresistive gas sensing measurements at room temperature for ammonia and various volatile organic compounds (VOCs).
• In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) computations to analyze sensing mechanisms.

Main Results:

• The NiO/WS₂ heterostructure exhibited superior sensing performance, including higher sensitivity and faster response/recovery times to NH₃ compared to Co₃O₄/WS₂ and CuO/WS₂.
• The NiO/WS₂ sensor demonstrated good selectivity towards NH₃ over other tested VOCs like formaldehyde, toluene, methanol, ethanol, acetone, and trimethylamine.
• DFT and DRIFTS studies revealed that the absence of "deep energy puddles" at the NiO/WS₂ interface and intensified NH₃ oxidation on NiO/WS₂ contribute to enhanced sensing.

Conclusions:

• NiO/WS₂ heterostructures are highly effective for room-temperature chemiresistive ammonia sensing.
• The enhanced performance is attributed to favorable interfacial properties and intensified surface reactions.
• This work provides insights into designing advanced WS₂-based heterostructures for selective and sensitive gas detection.