Investigation of the nature of surface defects of synthesized tin oxides: effects of reducing/oxidizing gas atmosphere and UV irradiation on their semiconductor metal oxide gas sensor response

Date

2026-2-26

Author

Atman, Berkan

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Light illumination of metal oxide semiconductors can induce “memory” effects, such as persistent photoconductivity (PPC) and persistent photocatalysis, which are related to the transfer, storage, and trapping or release of photogenerated charge carriers. Single rutile and mixed orthorhombic/rutile phase SnO2 and SnO/SnO2 samples were synthesized, and their thick films were used to investigate metastable effects induced by sub-bandgap illumination. Transient electrical resistance measurements were employed to investigate the photoconductance response and decay characteristics, as well as the CO gas sensing response, under sub-bandgap excitation in N2, dry air, and humid air at low to moderate temperatures. The PPC mainly stems from the nonequilibrium metastability of surface defects (oxygen vacancies) that form deep levels within the bandgap. Its metastable state results from lattice relaxation following photoionization. The lifetime of photogenerated charge carriers is kinetically controlled by the surface reaction kinetics of oxygen species and their charged states, along with the thermal activation barrier of the metastable defect state. The results of this study suggest that optically active sites and chemically active sites are different in tin oxides exposed to sub-bandgap light. In situ and ex situ measurements using XAS, Raman, and XPS show that sub-bandgap light excitation leads to surface reconstruction. After sub-bandgap light excitation, the surface of single rutile phase SnO2 tends to become more stoichiometric, whereas in mixed orthorhombic/rutile phase SnO2, new chemically active sites can form due to the metastable configuration of the defect, which becomes accessible under light.

Subject Keywords

Tin Oxide, Sub-bandgap, CO, Oxygen Vacancy, PPC

URI

https://hdl.handle.net/11511/119030

Collections

Graduate School of Natural and Applied Sciences, Thesis