Humidity sensors were fabricated with mesoporous
gadolinium-doped-ceria (CGO) powder obtained as replica of
the KIT-6 silica template. A complete micro-structural characterization
of the CGO powder was recently presented [14] (see
also Supplementary Information). After deposition and a sintering
process at 900 ◦C, the layers are homogeneous and firmly stuck to
the alumina substrate. The SEM images of Fig. 3a and c show a continuous
crack-free layer of the sensing material forming a network
with a thickness of ∼12–13 m, highly desirable to facilitate the
conduction of the water molecules along the surface. A very fine
and ordered microstructure with pores in the nanometric range
can be observed in the high magnification SEM image (Fig. 3b).
As expected from the previous studies, the thermally stabilized
mesoporous CGO oxides maintain the microstructure after the attachment to the alumina substrate at high temperatures (see Fig.S2 for a detailed structural characterization) [14].