Structure and ultrafast ethanol sensing properties of In2O3-capped Zn-doped Fe2O3 nanorods
Introduction
Hematite (α-Fe2O3) is an n-type semiconductor with many applications such as gas sensors, catalysts, magnetic recording media, electrode materials, and pigments owing to its high corrosion resistance, low toxicity and low cost [1], [2]. The thermal oxidation of iron (Fe) in an oxidizing atmosphere has attracted considerable attention as a facile method for growing high-quality α-Fe2O3 one-dimensional nanostructures over a larger area. p-type α-Fe2O3 can be obtained by doping with Mg [3], Zn [4], Cu [5], and N [6]. Oxide semiconductors are used widely as sensor materials because they show good sensing properties such as high sensitivity, fast sensing and low detection limits [7]. On the other hand, oxide semiconductors also have several drawbacks, including high operation temperature, poor selectivity and unsatisfactory reliability. Several techniques, such as noble metal doping [8], [9], [10], heterostructure formation [8], [9], [11], [12], and light activation have been developed to overcome these drawbacks [11], [13], [14]. In particular, the formation of a p–n heterostructure is now accepted widely as a promising strategy like catalyst metal doping [8], [9], [12], [15]. In this study, Zn-doped α-Fe2O3 and In2O3 were adopted as p- and n-type oxide semiconductors for the fabrication of p–n heterostructured gas sensors. The Zn-doped α-Fe2O3 are hereafter called simply Fe2O3(Zn). This paper reports the facile synthesis of In2O3-capped Fe2O3(Zn) nanorods by thermal oxidation of Fe foils and zinc (Zn) powders followed by In2O3 sputtering and their enhanced ethanol gas sensing performance.
Section snippets
Experimental
In2O3-capped Fe2O3(Zn) nanorods were synthesized by the thermal oxidation of Fe foils and Zn powders in an oxidizing atmosphere, followed by the sputter-deposition of In2O3. First, Fe2O3(Zn) nanorods were synthesized using a single step process. Fe foil (2 cm × 2 cm) and Zn powders were placed individually in two alumina boats that were separated by 5 cm inside a quartz tube. The tube furnace was evacuated to 1mTorr and heated to 600 °C at a heating rate of ∼5 °C/min. The samples were
Results and discussion
Fig. 1(a) presents a SEM image of the In2O3-capped Fe2O3(Zn) nanorods with a rod-like morphology grown vertically on a Fe substrate by thermal oxidation of an Fe foil. The diameters and lengths of the nanorods ranged from 50 to 150 nm and from 4 to 7 μm, respectively. The inset in Fig. 1(a) shows a typical Fe2O3(Zn) nanorod capped with an In2O3 shell where the nanorod diameter and shell layer thickness were ∼70 and ∼12 nm, respectively. Fig. 1(b) presents XRD patterns of the pristine and In2O3
Conclusions
In2O3-capped Fe2O3(Zn) nanorods were synthesized by a two-stage process involving the thermal oxidation of Fe foils and Zn powders in an oxidizing atmosphere and the sputter-deposition of In2O3. The multiple-networked In2O3-capped Fe2O3(Zn) nanorod sensor showed a significantly stronger electrical response to ethanol gas than their Fe2O3(Zn) nanorod counterpart. The former sensor also showed more rapid response and recovery to ethanol gas than the latter one. The enhanced sensing performance of
Acknowledgments
This study was supported by the National Research Foundation of Korea (NRF) grant funded by Korea government (MSIP) (No. NRF-2014R1A2A2A05002046).
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