Direct observation of potential phase at joining interface between p-MgO and n-MgFe₂O₄

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Effective material design for gas sensors relies on visualizing the depletion layer.
• Understanding potential barriers at interfaces is key to optimizing sensor performance.

Purpose of the Study:

• To measure the potential barrier at the interface of p-MgO/n-MgFe2O4/Fe2O3 core-shell microspheres.
• To visualize the depletion layer formation and its impact on gas sensor properties.

Main Methods:

• High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) for structural analysis.
• Kelvin probe force microscopy (KPFM) for potential barrier measurement.
• Elemental mapping for compositional analysis.

Main Results:

• Characterized hollow core-shell microspheres (approx. 70% hollow, 200 nm wall thickness) composed of MgO, MgFe2O4, and Fe2O3.
• Identified a 0.2 V potential difference at the p-MgO/n-MgFe2O4 interface, indicative of a p-n junction.
• Observed increased air resistance (Ra) in core-shell hollow microspheres compared to other configurations.

Conclusions:

• KPFM is a viable method for measuring potential barriers and visualizing depletion layer enlargement.
• The formation of a p-n junction in core-shell structures significantly influences sensor resistance.
• This approach offers a promising route for tuning the gas sensitivity of oxide semiconductor gas sensors.