Visible light activated gas sensors based on semiconductors: an operando investigation by DRIFT and confocal micro-Raman spectroscopy (LEVANTO)

Gas sensors play a crucial role in modern technology and are employed in a wide range of fields, spanning from environment to healthcare and industry. Commonly used chemiresistive gas sensors, due to the high operating temperature necessary to activate chemical reactions at the surface for the majority of semiconductors, do not completely match the requirements imposed by the current innovation paradigm, addressed to a safe, green and reduced power-consumption technology. Therefore, the search for diverse sensing materials which embrace novel activation mechanisms is of groundbreaking importance. The use of visible light to activate gas sensitivity in semiconductors is a further, fundamental step towards the design of gas sensors with low power consumption and improved selectivity.

In this respect, the LEVANTO project aims at the study and exploitation of the gas sensing mechanisms, which lead to response formation of visible light activated semiconductors.

Among the wide palette of functional materials probed for gas sensing applications, the project will be focused on high quality nanocrystalline zinc selenide (ZnSe) and zinc telluride (ZnTe), still slightly explored as gas sensing materials, which feature an energy band gap suitable for visible light activation and high surface area to enhance the solid-gas interaction at the surface. Fundamental phenomena behind the absorption spectrum, optical properties of defects/vacancies and transport parameters of the photoexcited carriers in semiconducting films, as well as innovative strategies to complement investigation methodologies currently used will be pursued. Photoluminescence and photoconductivity measurements together with transient absorption spectroscopy will lead to a complete understanding of the optical and conductive properties of materials, together with an effective definition of illumination parameters tuning the compromise between sensitivity and maintenance of real measuring conditions. The LEVANTO project will combine two unexplored operando spectroscopic systems for the study of photoactivated chemoresistive gas sensors: diffuse reflectance infrared (DRIFT) and micro-Raman spectroscopy. Such innovative synergic experimentation will provide for a confident route to actually identify gas sensing mechanisms, simultaneously performing a spectroscopic investigation on chemical reactions occuring at the surface during sensor operation under light activation while acquiring the resistance variation of the sensing films. The vision of the project is to demonstrate the reliable operability at room temperature of photoactivated gas sensors with a deep understanding of the physical and chemical mechanisms acting at the surface. This can enable a viral overspreading of miniaturized devices in which sensing layers and light-emitting elements are embedded, e.g. for portable/wearable sensors.