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Instruments / Technical Area	Publication Details	Published	Actions
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Direct in situ spectroscopic evidence of the crucial role played by surface oxygen vacancies in the O2-sensing mechanism of SnO2 Stefan Kucharski , Pilar Ferrer , Federica Venturini , Georg Held , Alex S. Walton , Conor Byrne , James A. Covington , Sai Kiran Ayyala , Andrew Beale , Chris Blackman Chemical Science 121 DOI: 10.1039/D2SC01738E Diamond Proposal Number(s): [25766] Open Access Show Abstract ▼ Abstract: Conductometric gas sensors (CGS) provide a reproducible gas response at a low cost but their operation mechanisms are still not fully understood. In this paper, we elucidate the nature of interactions between SnO2, a common gas-sensitive material, and O2, a ubiquitous gas central to the detection mechanisms of CGS. Using synchrotron radiation, we investigated a working SnO2 sensor under operando conditions via near-ambient pressure (NAP) XPS with simultaneous resistance measurements, and created a depth profile of the variable near-surface stoichiometry of SnO2−x as a function of O2 pressure. Our results reveal a correlation between the dynamically changing surface oxygen vacancies and the resistance response in SnO2-based CGS. While oxygen adsorbates were observed in this study we conclude that these are an intermediary in oxygen transport between the gas phase and the lattice, and that surface oxygen vacancies, not the observed oxygen adsorbates, are central to response generation in SnO2-based gas sensors.	May 2022
I09-Surface and Interface Structural Analysis	Resonant Ta doping for enhanced mobility in transparent conducting SnO2 Benjamin A. D. Williamson , Thomas J. Featherstone , Sanjayan S. Sathasivam , Jack E. N. Swallow , Huw Shiel , Leanne A. H. Jones , Matthew J Smiles , Anna Regoutz , Tien-Lin Lee , Xueming Xia , Christopher Blackman , Pardeep K. Thakur , Claire J. Carmalt , Ivan P. Parkin , Tim D. Veal , David O. Scanlon Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b04845 Diamond Proposal Number(s): [18195, 21431] Open Access Show Abstract ▼ Abstract: Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO2 is an earth abundant, cheaper alternative to In2O3 as a TCO however, its performance in terms of electrical properties lags behind that of In2O3. Based on the recent discovery of mobility and conductivity enhancements in In2O3 from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy and semiconductor statistics modelling to understand what the optimal dopant is to maximise performance of SnO2-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO2, as it is a resonant dopant which is readily incorporated into SnO2 with the Ta 5d states sitting ca. 1.4 eV above the conduction band minimum. Experimentally, the electron effective mass of Ta doped SnO2 was shown to be 0.23m0, compared to 0.29m0 seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities.	Feb 2020

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