Micro/nanostructured gas sensors: the physics behind the nanostructure growth, sensing and selectivity mechanisms

Micro/nano sensors based on oxide semiconductors have received much interest worldwide due to their remarkable electrical conductivity, good stability, wide range of dimensional structures, large-scale production potential, and cost effectiveness. The present review extensively investigates the physics behind the nanostructure growth, gas sensing, and selectivity mechanisms of different micro/nano-based devices. Mainly, planar, vertical, heterojunction, and thin film devices are discussed along with their pros and cons in relation to gas sensing and transport mechanisms. The sensing behaviours of such devices have been explained considering nanostructure morphology (particles and pore sizes), surface states (type of defect states and defect concentrations), and interfaces (intra- and inter-grain boundaries). Further, nanostructures with different dimensions, such as nanoparticles, nanowires, nanorods, nanoplates/nanosheets, nanotubes, hollow spheres, and nanoflowers, have also been taken under consideration.