Abstract
The sensing mechanism of resistive metal oxide gas sensors is quite complicated. Many factors determine the sensitivity and the response of these devices. In the past, many research works pointed out that an improved sensitivity and faster responses can be obtained, given a certain material, by using nano-grained or nanostructured metal oxide materials. This is due to the obvious reason that the grain size reductions imply the surface to volume ratio enhancement, and, consequently, the sensor response enhancement, being the sensing determined by surface phenomena. Actually, this intuitive explanation is not exhaustive, so in this paper the authors present a novel model for nano-grained metal oxide gas sensors, that is used to highlight the main factors influencing their sensing properties. The developed model, describing spherical grains, is applied to WO3 for NO2 detection, and is compared with different models already in the literature. What emerges as an interesting result is that the usual model of large grained films can give a rough but meaningful idea of the sensor sensitivity magnitude, whereas more fine models have to be used in order to predict some peculiar behaviors related to nano-sized grains.
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