Novel route for fabrication of nanostructured α-Fe2O3 gas sensor
Introduction
Extensive research in the past decade has revealed that the solid-state gas sensors play a crucial role in monitoring the environmental and chemical process, occupational health and safety and medical devices [1]. In comparison with other solid-state sensors, semiconductor metal oxide based sensors have been widely investigated owing to their small dimensions, low cost, fast response and good recovery speed, and high compatibility with Si-based microelectronics [2], [3]. Up to now, various semiconductor oxides, such as ZnO, TiO2 and NiO including Fe2O3 have been employed to design the solid-state gas sensors [4], [5], [6], [7].
In the past, development of the chemiresistive NO2 sensor has been based on the thin/thick films of metal-oxides, such as, SnO2 [8], In2O3, [9] WO3 [10], and ZnO [11]. These metal oxides suffer from the inherent drawbacks of poor selectivity, long response time, limited detection range and requirement of a high operating temperature (>300 °C).
As far as the gas sensor performance is concerned the gas sensitivity, selectivity, and durability are the most important properties. High gas sensitivity is the key factor in detecting gases at very low concentration as recognized by international standards [12]. The efficiency of the semiconductor gas sensor is strongly influenced by nature of surface sites, the electron donor/acceptor properties of the gas, the adsorption, the surface reaction and subsequent desorption of the gas species [13], [14], [15]. Extensive studies have been done to improve the gas sensing performances of the Fe2O3 based sensor, such as adding promoters, doping additives, decreasing grain size, controlling pore and surface defects, etc. [16], [17], [18], [19], [20]. It is well-known that the shape and size of Fe2O3 have a significant influence on its gas sensing properties. Nanosized particles have high surface to volume ratio and hence are ideal as potential gas-sensing materials. However the existing Fe2O3 sensors are suffers through the high operating temperature and low detection limit. Hence various strategies have been adapted to reduce operating temperature and improve the detection limit [16], [17], [18], [19], [20].
The present study deals with the simple and cost effective synthesis of α-Fe2O3 nanoparticles using sol–gel spin coating method for detection of NO2 at low concentration and low operating temperature (<300 ◦C). The effect of operating temperature, gas concentration and surface morphology on the NO2 gas sensing properties of nanostructured α-Fe2O3 were studied.
Section snippets
Synthesis of Fe2O3 nanoparticles and characterization
A sol gel spin coating method was employed for synthesis of Fe2O3 nanoparticles wherein the AR grade, ferric chloride (FeCl36H2O) and methanol (CH3OH) was mixed and the reaction mixture stirred vigorously at 60 °C for 1 h, leading to the formation of gel. This gel is further heated for 10 minute to obtain brown color powder. The obtained powder was then placed in an alumina boat and annealed at 700 °C for 1 h, subsequently cooled to room temperature. Samples were collected, washed several times with
Structural analysis
The structural and morphological investigations have been carried out due to their significant role in the gas-sensing properties. The diffraction patterns show characteristic α-Fe2O3 peaks with hexagonal structure (JCPDS no. 89-596). The average crystallite size (d) calculated from Sherrer's formula is in the range of 41–50 nm.where D is the average crystallite size, assuming particles to be spherical K=0.94, λ is the wavelength of X-ray radiation, β is the full width at half
Conclusion
Nanostructured α-Fe2O3 thin film sensor was fabricated on glass substrate by low cost sol–gel spin coating technique. Structural analysis showed formation of hexagonal α-Fe2O3. Microstructural analysis confirms nanostructured morphology suitable for gas sensing application. The gas sensing measurement at 200 °C showed that α-Fe2O3 films are selective to NO2 gas. α-Fe2O3 thin film sensor exhibits maximum response of 17.12% with 59.44% stability towards NO2 gas. The gas sensing properties viz,
Acknowledgments
Authors are grateful to the Department of Atomic Energy-Board of Research in Nuclear Science, Govt. of India, New Delhi for Financial support through the scheme no. 2010/37P/45/BRNS/1442
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