Dynamic Charge Redistribution as the Key Mechanism for NO₂ Detection in MoS₂ Revealed by In Operando Scanning...

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Sensing

Background:

• Molybdenum disulfide (MoS2) is a promising material for low-power chemoresistive sensing of nitrogen dioxide (NO2).
• The exact sensing mechanism and the influence of MoS2 morphology, defects, and thickness on charge redistribution are not well understood.
• Understanding these factors is crucial for developing efficient MoS2-based NO2 sensors.

Purpose of the Study:

• To investigate the microscopic origin of resistance changes in MoS2 upon exposure to NO2.
• To elucidate the MoS2-NO2 interaction mechanism and the role of material properties.
• To establish design principles for scalable MoS2-based NO2 sensing applications.

Main Methods:

• Investigated MoS2 thin films grown by ionized jet deposition (IJD) and exfoliated monolayer MoS2.
• Utilized controlled gas sensing experiments combined with *in operando* micro-focused X-ray photoelectron spectroscopy and scanning photoemission microscopy.
• Performed density functional theory calculations to support experimental findings.

Main Results:

• Observed Mo 3d and S 2p core-level shifts to higher binding energies in both MoS2 monolayers and IJD-MoS2 films upon NO2 exposure.
• Attributed these shifts to local charge redistribution and modified core-level screening, not net charge-transfer doping or band bending.
• Identified a transient Mo 3d component in IJD-MoS2 due to weak Mo-O bonding at defect sites, which was reversible.

Conclusions:

• The study provides the first *in operando* insight into the sensing mechanism of technologically scalable MoS2 chemoresistors.
• NO2 interaction with MoS2 involves dynamic electronic structure modulation rather than permanent doping.
• Findings offer crucial design principles for optimizing MoS2-based NO2 sensors.