Enhanced gas-sensing properties of ZnO nanorods encapsulated in an Fe-doped ZnO shell

Encapsulated ZnO nanorod arrays are synthesized on glass substrate by a two-step route, hydrothermal followed by dip coating. It was found that the encapsulating process increases the rod diameters from ∼20 to ∼40nm without any significant effects on the microstructure, even with an Fe-doped ZnO encapsulated layer. Optical studies indicated a reduction in the band gap of the encapsulated nanorods. The electrical measurements illustrated a remarkable reduction in resistance due to the encapsulation process, especially in the encapsulated ZnO nanorod film with an Fe-doped-ZnO shell layer. The gas-sensing properties of the sensors were systematically investigated to different concentrations of ethanol vapour at temperatures up to 270 ◦ C. An optimum operating temperature was found for each sensor in which high sensitivity and fast recovery were obtained. The response was improved from 11.7 to 19 by Fe doping on the ZnO encapsulated nanorod at a constant 500ppm concentration of ethanol. The response threshold decreased also by encapsulating at 165 ◦ C.