Synthesis and enhanced ethanol sensing characteristics of alpha-Fe2O3/SnO2 core-shell nanorods.

Alpha-Fe(2)O(3)/SnO(2) 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 microm, 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 alpha-Fe(2)O(3) nanorods. The sensor response is up to 19.6 under 10 ppm ethanol exposure at 220 degrees 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 SnO(2) 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.