SO2 sensing mechanism of nanostructured SiC-SiOxC core shell: An operando DRIFT investigation

The possible use of nanostructured silicon carbide for the manufacturing of chemiresistive gas sensors with high selectivity towards sulfur dioxide has been recently explored. In this work, we take this topic a step further with an in-depth investigation on the role played by the oxidation process occurring on the surface of silicon carbide nanoparticles during the detection of SO2. This study starts by understanding the oxidation process at different temperatures and subsequently investigates the reaction mechanism of SO2, in both dry and wet atmosphere, at the optimal working temperature for the sensor operation. The device was characterized using a diffuse reflectance infrared Fourier transform spectroscopy setup capable of working in operando conditions with a dedicated electronics for the simultaneous monitoring of surface chemical reactions on the sensing film together with its electrical activity. This work demonstrates that the oxidation of silicon carbide nanoparticles is at the core of the modification of the overall electrical characteristics of the device. It was also proved that the exposure to SO2 increases the oxidation rate of the silicon carbide film in working conditions. Moreover, it was observed that this behavior is magnified by the presence of humidity. Finally, a proposed sensing mechanism is suggested highlighting a mainly ionic electrical conduction, in which working conditions play a fundamental role in affecting the concentration and mobility of charge carriers.