Plasma-Activated Oxygen Vacancies in ZnFe ₂ O ₄ Nanoparticles: A Defect-Centric Strategy for Alcohol Detection

Semiconducting metal oxide (SMO)-based gas sensors often suffer from limited sensitivity due to an insufficient density of surface-active sites. Among the key factors governing surface reactivity and sensing performance, oxygen vacancies play a pivotal role; however, effective and controllable strategies for engineering these defects remain inadequately explored. In this work, we report a controlled plasma surface activation approach to significantly enhance the alcohol vapor sensing performance of zinc ferrite (ZnFe 2 O 4 ). The plasma treatment conditions were systematically optimized by varying the RF power and exposure duration. Plasma treatment under optimized conditions induces nanoscale surface restructuring without altering the bulk crystal structure, leading to increased surface roughness, elevated defect density, and a markedly higher concentration of oxygen vacancies. These plasma-generated active sites facilitate enhanced adsorption and surface reactions of alcohol molecules, resulting in a substantial improvement in the sensing response. Notably, the optimized plasma-activated sensor exhibits an approximately 5-fold higher response toward butanol vapor compared to pristine ZnFe 2 O 4 . The cross-sensitivity, repeatability, and reproducibility of the sensor and the effect of humidity on it are systematically verified. Additionally, distinct sensing signal features are observed for different vapors, and principal component analysis (PCA) enables effective discrimination among them. This study establishes plasma-induced oxygen vacancy engineering as a robust and versatile strategy for tailoring the surface chemistry and enhancing the performance of SMO-based gas sensors.