Novel Sequential Detection of NO2 and C2H5OH in SnO2 MEMS Arrays for Enhanced Selectivity in E-Nose Applications

This study explores the surface chemistry and electrical responses of ultra-high-sensitivity SnO2 MEMS arrays to enable a novel sequential detection methodology for detecting nitrogen dioxide (NO2) and ethanol (C2H5OH) as a route to achieve selective gas sensing in electronic nose (E-nose) applications. Utilizing tin oxide (SnO2) thin films deposited via atomic layer deposition (ALD), the array achieves the lowest reported detection limits of 8 parts per billion (ppb) for NO2. The research delves into the detection mechanisms of NO2 and C2H5OH, both individually and in subsequent exposures, assessing the sensor’s dynamic response across various operating temperatures. It demonstrates rapid response and recovery times, with averages of 48 s and 277 s for NO2 and 40 and 48 for C2H5OH. Understanding the role of individual gases on the SnO2 surface chemistry is paramount in discerning subsequent gas exposure behavior. The oxidizing behavior of C2H5OH following NO2 exposure is attributed to interactions between NO2 and oxygen vacancies on the SnO2 surface, which leads to the formation of nitrate or nitrite species. These species subsequently influence interactions with C2H5OH, inducing oxidizing properties, and need to be carefully considered. Principal component analysis (PCA) was used to further improve the sensor’s capability to precisely identify and quantify gas mixtures, improving its applicability for real-time monitoring in complex scenarios.