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4 June 2014 Use of nanostructured oxides for selective gas-sensing
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Titania nanotubular layers (TiO2-NTs) are better known with their use in dye-synthesized solar cells. In the field of gas sensors, the best known application of TiO2-NT layers is given with H2 sensing. TiO2–NT structures are commonly synthesized from pure titanium by anodic oxidation method. As literature indicates, gas sensing with titania can be modified by doping to obtain p- or n-type semiconductor behaviour. As undoped titania is widely used for CO and H2- sensing, Al- and Cr-doped titania is reported to be effective for NO2-sensing. Nanostructuring of TiO2 yields faster and more stable response toward CO and NO2 with almost no drift in sensor signal. Dopants are introduced by wet-chemistry method or by simultaneous anodization in an alloy. We introduced Cr3+ to TiO2 NT-layers by soaking in nitrate salt and Al3+ by anodization of Ti6Al4V alloy. All doped TiO2 NTs are tested for NO2 sensing at temperatures up to 500°C in the presence of CO. The characteristics of doping are investigated by XRD, EDX-TEM methods. Cr-doping of nanotubular TiO2 sensors displays p-type semiconductor behaviour and a considerably increased NO2-selectivity, while Aldoping emphasizes the CO-selectivity. Effect of Cr-doping on sensing is further investigated by means of impedance spectroscopic measurements and equivalent circuit modeling in order to optimize the sensors for real-time measurements.
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Y. Gönüllü and B. Saruhan "Use of nanostructured oxides for selective gas-sensing", Proc. SPIE 9083, Micro- and Nanotechnology Sensors, Systems, and Applications VI, 90830Z (4 June 2014);

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