Adjustment of oxygen vacancy states in ZnO and its application in ppb-level NO2 gas sensor

Gaoda Li; Heng Zhang; Leixin Meng; Zhe Sun; Zhao Chen; Xiaoyu Huang; Yong Qin

doi:10.1016/j.scib.2020.05.027

Adjustment of oxygen vacancy states in ZnO and its application in ppb-level NO₂ gas sensor

Sci Bull (Beijing). 2020 Oct 15;65(19):1650-1658. doi: 10.1016/j.scib.2020.05.027. Epub 2020 May 28.

Authors

Gaoda Li¹, Heng Zhang¹, Leixin Meng¹, Zhe Sun¹, Zhao Chen¹, Xiaoyu Huang¹, Yong Qin²

Affiliations

¹ Institute of Nanoscience and Nanotechnology, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China.
² Institute of Nanoscience and Nanotechnology, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China. Electronic address: qinyong@lzu.edu.cn.

PMID: 36659041
DOI: 10.1016/j.scib.2020.05.027

Abstract

Oxygen vacancy (V_O) is long believed as a key factor influencing the gas sensing properties. However, the concentration of V_O is generally focused while the V_O state is neglected, which masks the inherent mechanism of gas sensor. Using a post annealing process, the influence of V_O states on the response of ZnO nanofilm to NO₂ gas is investigated in this study. The systematical analysis of the results obtained by different methods indicates a transformation of V_O from the neutral to the doubly ionized state during post annealing treatment. The results also imply that the gas sensing properties is not directly correlated with the V_O concentration. And due to the competitive adsorption of ambient O₂, the neutral V_O is majorly occupied by the adsorbed O₂ while the V_O in doubly ionized state can promote the adsorption of NO₂. Consequently, the transition of V_O from the neutral to the doubly ionized state can lead to a dramatic increase of the response to NO₂, from 733 to 3.34 × 10⁴ for 100 ppm NO₂. Guided by this mechanism, NO₂ gas sensing in ppb-level is also achieved: the response reaches 165% to 25 ppb (0.025 ppm) NO₂ with a good repeatability.

Keywords: Adsorption; Gas sensor; Oxygen vacancy states; Sensing mechanism.