Direct spectroscopic evidence of the crucial role played by surface oxygen vacancies in the O-sensing mechanism of SnO.

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 SnO, a common gas-sensitive material, and O, a ubiquitous gas central to the detection mechanisms of CGS. Using synchrotron radiation, we investigated a working SnO sensor under operando conditions near-ambient pressure (NAP) XPS with simultaneous resistance measurements, and created a depth profile of the variable near-surface stoichiometry of SnO as a function of O pressure.