Oxygen-Plasma Defect Engineering of Epitaxial Graphene on 4H-SiC for Enhanced NO2 Sensing

XT Trinh and AT Nguyen and TTH Nguyen and TQ Dang and HD Tran and PT Nguyen and TM Dao and LH Truong and CQ Le and TT Pham and V Nguyen-Si and HT Ngo, ACS OMEGA, 10, 63213-63225 (2025).

DOI: 10.1021/acsomega.5c09420

Developing sensitive, low-power, and manufacturable NO2 gas sensors is crucial for environmental and health monitoring. Epitaxial graphene on 4H-silicon carbide (Graphene@4H-SiC) is an ideal, device-ready platform, but its intrinsically inert surface limits its sensing performance. Here, we present a complete workflow that combines a scalable oxygen plasma treatment for defect engineering with the fabrication of a fully operational chemiresistive sensor device. The optimized sensor, treated at 150 W, demonstrates a nearly 8-fold response enhancement to NO2 compared to its pristine counterpart. It exhibits excellent recovery and sensitive detection down to 10 ppm at a low operating temperature of 70 degrees C. Crucially, a synergistic approach combining extensive experimental characterization with first-principles simulations reveals the underlying mechanism. Density functional theory calculations identify carbon vacancies as overwhelmingly potent adsorption sites, with a binding energy (-7.97 eV) and charge transfer far exceeding that of pristine graphene or common oxygen functional groups. The excellent correlation between the experimental performance peak and the theoretical superiority of vacancy defects provides a validated understanding of the enhancement. This work bridges the critical gap between atomic-scale theory and practical device performance, establishing a rational design pathway for high-performance graphene sensors.

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