Oxygen-Plasma Defect Engineering of Epitaxial Graphene on 4H-SiC for Enhanced NO ₂ Sensing

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 °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.