This work reports the recent results achieved at the SENSOR Lab, Brescia (Italy) to address the selectivity of metal oxide based gas sensors. In particular, two main strategies are being developed for this purpose: (i) investigating different sensing mechanisms featuring different response spectra that may be potentially integrated in a single device; (ii) exploiting the electronic nose (EN) approach. The former has been addressed only recently and activities are mainly focused on determining the most suitable configuration and measurements to exploit the novel mechanism. Devices suitable to exploit optical (photoluminescence), magnetic (magneto-optical Kerr effect) and surface ionization in addition to the traditional chemiresistor device are here discussed together with the sensing performance measured so far. The electronic nose is a much more consolidated technology, and results are shown concerning its suitability to respond to industrial and societal needs in the fields of food quality control and detection of microbial activity in human sweat.
We demonstrate that conductometric gas sensing at room temperature with SnO 2 nanowires (NWs) is enhanced by visible and supraband gap UV irradiation when and only when the metal oxide NWs are decorated with Ag nanoparticles (NPs) (diameter < 20 nm); no enhancement is observed for the bare SnO 2 case. We combine the spectroscopic techniques with conductometric gas sensing to study the wavelength dependency of the sensors' response, showing a strict correlation between the Ag-loaded SnO 2 optical absorption and its gas response as a function of irradiation wavelength. Our results lead to the hypothesis that the enhanced gas response under UV−vis light is the effect of plasmonic hot electrons populating the Ag NPs surface. Finally, we discuss the chemiresistive properties of Ag-loaded SnO 2 sensor in parallel with the theory of plasmon-driven catalysis, to propose an interpretative framework that is coherent with the established paradigma of these two separated fields of study.
Abstract-The ideal chemical gas sensors would provide a device capable of being sensible, selective and stable. To improve the state of the art metal oxide gas sensors two approaches are pursued: obtaining nanosized, single crystalline metal oxide nanorods, and introducing innovative transduction principle. The first approach ensures high surface area for gas interaction coupled with the higher stability. The second approach could overcome limitations on the performances achievable and set a new milestone in the field. In this work magnetic gas sensing tests were carried out, using a MOKE (magneto-optical Kerr effect) magnetometer, showing that it is possible to exploit a new mechanism for sensing devices. The sensing layer, based on Co layer covered by ZnO nanorods, was entirely deposited by RF sputtering. The device showed very good H2 detection at room temperature. The current work focuses on the characterization of the sensing heterostructure based on Co/ZnO nanorods by volumetric magnetization measurements and by MOKE measurements in air and in gas. A model for H2 sensing is also formulated.
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