NO2 sensing mechanism of ZnO–Eu2O3 binary oxide under humid air conditions

Abstract

In order to understand the role of ambient humidity on NO2 detection, electrical resistance and work function changes were recorded simultaneously on ZnO–Eu2O3 material. Thus, surface band bending and electron affinity could be evaluated, according to the Schottky model. The lack of electron affinity changes during NO2 exposure in dry air conditions, reveals that only the free charge concentration is affected. Exposure to NO2 in humid background leads to an increase in sensor signals and a significant change in the electron affinity as well. This effect suggests an interaction between NO2 and surface hydroxyl species; thereby additional charge carriers are involved in the overall sensing process. High resolution XPS analysis proves the presence of Eu solely in the 3+ oxidation state before and after NO2 exposure. A gas-sensing interaction mechanism has been proposed.