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 gamma-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.
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