Ethanol Gas Sensing by a Zn-Terminated ZnO(0001) Bulk Single-Crystalline Substrate

Taku T Suzuki; Takeshi Ohgaki; Yutaka Adachi; Isao Sakaguchi; Minoru Nakamura; Hideyuki Ohashi; Akihisa Aimi; Kenjiro Fujimoto

doi:10.1021/acsomega.0c02750

Ethanol Gas Sensing by a Zn-Terminated ZnO(0001) Bulk Single-Crystalline Substrate

ACS Omega. 2020 Aug 11;5(33):21104-21112. doi: 10.1021/acsomega.0c02750. eCollection 2020 Aug 25.

Authors

Taku T Suzuki¹, Takeshi Ohgaki¹, Yutaka Adachi¹, Isao Sakaguchi¹, Minoru Nakamura², Hideyuki Ohashi², Akihisa Aimi², Kenjiro Fujimoto²

Affiliations

¹ National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
² Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.

Abstract

Metal oxide semiconductor gas sensors have been widely studied for the selective detection of various gases with trace concentrations. The identification of the reaction scheme governing the gas sensing response is crucial for further development; however, the mechanism of ethanol (EtOH) gas sensing by ZnO is still controversial despite being one of the most intensively studied target gas and sensing material combinations. In this work, for the first time, the detailed mechanism of EtOH sensing by ZnO is studied by using a bulk single-crystalline substrate, which has a well-defined stoichiometry and atomic arrangement, as the sensing material. The sensing response is substantial on the ZnO substrate even with a millimeter-size thickness, and it becomes larger with resistance of the substrate. The large sensing response is described in terms of the adsorption/desorption of the oxygen species on the substrate surface, namely, oxygen ionosorption. The valence state of the ionosorbed oxygen involved in EtOH sensing is identified to be O^2- regardless of the temperature. The increase in the sensing response with the temperature is attributed to the enhanced oxidation rate of the EtOH molecule on the surface as analyzed by pulsed-jet temperature-programmed desorption mass spectrometry, which has been newly developed for analyzing surface reactions in simulated working conditions.