Modulating Gas Reaction Pathways in Polycrystalline SnO2 Nanofibers through Oxygen Plasma-Assisted Defect Engineering for Gas Sensor Applications

Abstract

This study aims to optimize the performance of metal oxide gas sensors through surface defect engineering. We fabricated polycrystalline SnO2 nanofibers with varying defect densities via electrospinning and subsequent calcination at temperatures ranging from 400 to 1000 °C. The correlation between microstructural evolution and photoelectric properties was systematically analyzed using SEM, TEM, Raman spectroscopy, FTIR, and electrical measurements. The results indicate that the annealing temperature determines the grain size and the ratio of surface to bulk states. Regarding defect modulation, oxygen plasma treatment exhibited a dual mechanism: low-power treatment primarily passivated surface oxygen vacancies and removed organic residues, whereas high-power treatment induced the formation of interstitial oxygen. For nitrogen oxide (NO) gas sensing, experiments confirmed that NO molecules primarily interact with surface-bridging oxygen (O2c) sites rather than oxygen vacancies. Specifically, utilizing 5 ppm of NO gas exposure to probe the surface activity, the S800 sample treated with a 50 W oxygen plasma exhibited an outstanding sensitivity of 99.1% alongside a rapid reaction time of 62 s. Furthermore, applying this plasma treatment to the defective S400 sample systematically improved its sensitivity from 78.4% to 85.0% and reduced the reaction time from 549.5 to 415.1 s, thereby explicitly demonstrating the efficacy of defect modulation driven by plasma. This study demonstrates that oxygen plasma treatment holds great potential for precisely controlling the surface states and reaction pathways of SnO2. This work provides a facile and robust strategy for optimizing the performance of metal oxide gas sensors through surface defect engineering. Specifically, we introduce an approach utilizing oxygen plasma to overcome the control limitations of conventional thermal treatments, enabling the stable modulation of the surface oxygen vacancies.