Synthesis And Gas/Humidity Sensing Properties Of Al/Fe-doped SnO₂ Flower-like Nanospheres

Low-dimensional Al/Fe-doped SnO₂ flower-like nanospheres with hierarchical nanorods have been synthesized by a simple template-and surfactant-free hydrothermal method.The SnO₂-based powder were characterized by X-ray diffraction（XRD）,field emission scanning electron microscopy（FESEM）,transmission electron microscopy（TEM）and Raman spectrum analysis.It was observed that the crystallinity and crystallite sizes of SnO₂-based samples can be improved at the higher alkaline concentration（10:1）.Nanostructure evolution of SnO₂-based powders was found to be influenced by alkaline concentration and hydrothermal reaction time.A possible growth mechanism of SnO₂ flower-like microspheres with hierarchical nanorods was proposed.H₂ sensing properties of n-type SnO₂-based sensors were also studied at working temperature（WT）from room temperature（RT）to 470 °C using N2 as a reference.The results showed that most sensitivities of 1–2 wt% Al-doped SnO₂ sensors were higher than 50% at optimal working temperature（OWT,270°C）.The highest H₂ gas sensitivity was approach to be 74.2% at 270 °C,which was six times of undoped SnO₂ sensor.Our study shed important light on a feasible approach to design and fabricate H₂ gas sensors with high performances.The hierarchical 2% Fe-doped SnO₂ humidity sensors exhibit an outstanding thermal stability（weight loss less than 2.5%）,an exceptionally fast response/recovery speed（< 1/4 s）,a high humidity sensitivity（S = |ZRH11|/|ZRH95| = 6479.5（|ZRH11|,|ZRH95|: impedance values in 11% RH and 95% RH,respectively）,impedance variation: 100 – 104 k?）and an excellent breath sensing,which are superior to most of the SnO₂-based humidity sensors under the similar conditions.It is probably ascribing to the strong affinity of Fe3+ ions on SnO₂ interfaces during the alkaline circumstance and the complex band configuration of γ-Fe2O3/SnO₂ nanorods.These results open the door to traditional metal oxide based humidity sensors for ultrafast breathing sensing and potential application of touchless user interfaces.