Fig. 9
Chemical sensor applications. a Schematic showing fabricated transparent sensors based on nanocolumnar oxide films [16]. b Sensing transients of the dense-planar and nanocolumnar WO3 thin film sensors to 1–5 ppm NO2 at an applied bias voltage of 5 V [16]. c 40°-tilted SEM image of nanocolumnar WO3 film between and on ITO IDEs. Parts highlighted in reddish color indicate localized current pathways which meander with narrow necks [16]. d Optical microscopy (OM) image of the fabricated e-nose chip after the deposition of six different layers and corresponding cross-sectional SEM images (scale bar = 300 nm) [15]. e Radar chart patterns of the prototype e-nose chip for H2 200 ppm, CO 200 ppm, and NO2 10 ppm. Each vertex of the radar corresponds to each sensor of the array, where the devices were measured at 150 °C with 0.2 V applied bias [15]