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Identifying origin of response in SnO2-based gas sensors via in operando NAP XPS with simultaneous resistance measurements

Kucharski, Stefan Jozef; (2022) Identifying origin of response in SnO2-based gas sensors via in operando NAP XPS with simultaneous resistance measurements. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Conductometric gas sensors (CGS) are small, portable, easily mass-produced and provide a reproducible gas response at a low cost. However, they suffer from relatively poor detection characteristics, which stem from an insufficient understanding of their operating mechanism. This study aimed to develop a robust method for investigating gas sensors to provide insight into the atomistic interactions between the sensitive layer and the gas phase by means of the recently emerging technique of near-ambient pressure X-ray photoelectron spectroscopy (NAP XPS) using laboratory-based and synchrotron-based X-ray sources. Spectroscopic analysis with simultaneous resistance measurements was carried out on working sensors under temperature and pressure conditions close to their typical operating environment to produce a joint micro- and macroscopic picture of their operation, a hallmark of operando spectroscopy. The initial study of the interactions between SnO2, a prototype sensitive material, and O2, a ubiquitous gas central to the detection mechanisms of CGS, was extended to include interactions with CO and NO2 as examples of reducing and oxidising gases. The results of this study point to the importance of near-surface oxygen vacancies in the detection mechanisms governing the response of SnO2-based gas sensors and suggest that models based on variable surface vacancy density should be developed in place of the currently dominating ‘oxygen ionosorption’ description, for which there is no direct, convincing evidence despite decades of extensive research.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Identifying origin of response in SnO2-based gas sensors via in operando NAP XPS with simultaneous resistance measurements
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10158823
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