Synthesis and enhanced ethanol sensing characteristics of α-Fe ₂O₃/SnO₂ core-shell nanorods

α-Fe₂O₃/SnO₂ core-shell nanorods are synthesized via a three-step process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses reveal that their diameters and lengths are respectively in the ranges 35-120 nm and 0.35-1.2 μm, and the thickness of the shell composed of 3.5 nm SnO ₂ nanoparticles is about 10 nm. The core-shell nanostructures exhibit a dramatic improvement in ethanol sensing characteristics compared to pure α-Fe₂O₃ nanorods. The sensor response is up to 19.6 under 10 ppm ethanol exposure at 220°C. Both the response time and the recovery time of the core-shell structures are less than 30 s. Based on the space-charge layer model and semiconductor heterojunction theory, the small thickness of the SnO₂ shell and the formation of heterojunctions contribute to the enhanced ethanol sensing characteristics. Our results demonstrate that one-dimensional metal oxide core-shell nanostructures whose shell thickness is smaller than the Debye length are very promising materials for fabricating gas sensors with good performances.