Background: Oxygen behaviors play essential roles in the receptor function in the gassensing
mechanism of SnO2 semiconductors, the size effect of which is a fundamental phenomenon
for the development of gas sensors.
Objective: This article discusses the size effect on the oxygen behaviors in the gas-sensitive SnO2
Methods: The first principle calculation was used to investigate size effect on the formation of oxygen
vacancies and adsorption of oxygen species in the SnO2 semiconductor. The electrical characteristics
of conductivity, bandgap, and electron transfer in SnO2 crystallites were analyzed by the density
of states and the Mulliken population.
Results: The defect of surface bridge oxygen has the lowest formation energy, and it is most likely to form
in the SnO2 semiconductor. The adsorption energies for O- and O2
- are from 1.717 to 3.791 eV and
2.371 to 4.683 eV, respectively. The Mulliken population distribution illustrates that O 2p orbit captures
the electrons from the orbits of Sn 5s and 5p as well as O 2s.
Conclusion: The formation energies of oxygen defects in complete and defective SnO2 super cells
are of positive correlation with crystallite size. The carrier concentration and conductivity are improved
by the incremental crystallite size. The adsorption energies of O- and O2
- species on defective
SnO2 super cells increase with crystallite size. With the assistance of connecting Sn atoms, the adsorbates
of O- and O2
- are able to capture electrons from the inner region of crystallites, resulting in
an expansion of depletion layer.