pads, leading to an immense number of nanowires involved in the
gas-sensing process, resulting in highly reproducible and reliable
gas sensors. Fig. 4(c) shows that the diameters of the nanowires
range from 100 to 130 nm, and their length are several tens of
micrometers. The shape and geometrical dimension of the networked
SnO2 nanowires for superior sensing performances were
discussed in detail in our previous report [20]. Fig. 4(d) shows a
representative cross-sectional FE-SEM image of networked SnO2
nanowire sensors. It shows more clearly the networking nature of
SnO2 nanowires that were grown on the neighboring electrode pad
layers.