Ultrafast breathing humidity sensing properties of low-dimensional Fe-doped SnO2 flower-like spheres

Abstract

Low-dimensional Fe-doped SnO₂ flower-like nanospheres are synthesized by a simple template- and surfactant-free hydrothermal method. Interestingly, the hierarchical nanostructures not only show a low dimension (the diameter is ca. 200 nm), but also present a dramatic humidity sensitivity compared with the undoped ones. These obviously enhanced properties are probably ascribed to the strong affinity of Fe³⁺ ions on the SnO₂ (101) interface in the alkaline conditions and the complex band configuration of the γ-Fe₂O₃/SnO₂ Schottky contact. 2% Fe-doped SnO₂ humidity sensors exhibit outstanding thermal stability (weight loss less than 2.5%), exceptionally fast response/recovery speed (<1@4 s, 95% relative humidity), as well as ultrahigh humidity sensitivity (S = 6479.5). Besides, Fe-doped SnO₂ sensors possess excellent breathing sensing properties, superior to most of the reported SnO₂-based humidity sensors under the same conditions. These results open the door for ultrafast breathing sensing and the potential application of touchless user interfaces to traditional metal oxide based humidity sensors.