NAP-XPS as a new tool for in-situ studies of SMOX gas sensors

The development of near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) allows scientists to perform spectroscopic investigations of solid-gas interfaces at elevated pressures in a defined gas atmosphere. Due to the high surface sensitivity and element specificity, this technique promises to be a valuable and powerful tool in gas sensor research. A Pt doped SnO2 sample was studied to explore a variety of phenomena in sensor research that can be addressed using NAP-XPS at a synchrotron. The change of several parameters, including chemical shifts, band bending, and valence band structure, could be observed in-situ and highlights the enormous potential of the method in this field. Furthermore, a series of DC resistance measurements has been performed to study the impact of pressure. The decrease of resistance at low pressure strongly indicates that both the electronic characteristics as well as the surface composition under the conditions of NAP-XPS are dissimilar to operando conditions at atmospheric pressure.