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RSC Advances
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DOI: 10.1039/C6RA23196A
RSC Advances
PAPER
The sensing mechanism of Co3O4-In2O3 heterojunction Kai Song and Xiaoqian Meng contributed equally to this work.
structure is somewhat different with n-type In2O3. It is known This investigation was supported by the Natural Science
that electron depletion layer would form at the contact Foundation of China (No. 51322212, 51472122), the
interface between n-type and p-type semiconductors.42, 51, 52 Fundamental Research Funds for the Central Universities (No.
Fig. 6b exhibits dynamic process of the formation of electron 30915011201), the PAPD and "333 project" of Jiangsu.
depletion layer in this work. Firstly, n-type In2O3 and p-type
Co3O4 nanoparticles are combined together tightly through
Notes and references
calcination process. As we know, in n-type semiconductors,
electrons are the majority carriers (labeled as nn in Fig. 6b).
And yet, in p-type semiconductors, holes are the majority
carriers (labeled as pp in Fig. 6b). So after these two kinds of
semiconductors come into contact with each other, it would
be easy for electrons transfer from n-type In2O3 to p-type
Co3O4. Finally, electrons and holes which belongs to p-type
Co3O4 will recombine at the contact interface, leading to the
rapidly reduced concentration of charge carrier and sharply
increased resistance compared with pure n-type In2O3. This
theory is also in agreement with previous consequence in this
work (Fig. 4c). Besides the electron depletion layer showed in
step 1 in Fig. 6a, another kind of electron depletion layer
would be formed in surfaces of sensing materials operated at
optimal temperature (step 2 in Fig. 6a), and the mechanism is
similar to pure n-type metal oxide semiconductors. Both the
two electron depletion layers contribute to the great
improvement of resistance. When ethanol molecules are
introduced, they would react with the ionized oxygen species.
At this time, the electrons would be released back to In2O3
semiconductor and p-n heterojunction through surface
interactions (step 3 in Fig. 6a). Therefore, these two kinds of
electron depletion layer would disappear gradually. This
phenomenon will cause the resistance of sensing devices
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decrease sharply, which also means higher response values.
53
The reactions in the sensing progress can be seen in Fig. 6c
.
The reactions can further describe the details of gas sensing
procedure. Generally, in the presence of heterojunction
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heterojunction structure have superior sensing performance
compared with pure In2O3 sensing devices.
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Conclusions
In summary, the Co3O4-In2O3 heterojunction structure was
successfully prepared through a simple grinding-calcination
process without any harmful agents. Gas sensing devices
based on Co3O4-In2O3 (1 %) heterojunction structure exhibit
higher response and selectivity to ethanol compared with pure
In2O3. Moreover, Co3O4-In2O3 (1 %) shows low operating
temperature, low detection limitation and high stability, which
are significantly important in practical application. This work
provides a new idea to fabricate high sensitivity gas sensing
devices in a simple, cheap and environmentally friendly
method.
Acknowledgements
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