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Scalable Fabrication of High-Performance NO2 Gas Sensors Based on Tungsten Oxide Nanowires by On-Chip Growth and RuO2-Functionalization

Thi Hong Van, Phung, Hoang Thanh, Nguyen, Van Quang, Vu, Van Duy, Nguyen, Duc Hoa, Nguyen, Van Hieu, Nguyen
ACS applied materials 2014 v.6 no.15 pp. 12022-12030
adsorption, ammonia, annealing, gases, hydrogen sulfide, nanowires, nitrogen dioxide, sensors (equipment), tungsten oxide
The on-chip growth and surface-functionalization have been recently regarded as promising techniques for large-scale fabrication of high performance nanowires gas sensors. Here we demonstrate a good NO₂ gas-sensing performance of the tungsten oxide nanowires (TONWs) sensors realized by scalable on-chip fabrication and RuO₂-functionalization. The gas response (Rg/Rₐ) of the RuO₂-functionalized TONWs to 5 ppm of NO₂ was 186.1 at 250 °C, which increased up to ∼18.6-fold compared with that of the bare TONWs. On the contrary, the responses of the bare and functionalized sensors to 10 ppm of NH₃, 10 ppm of H₂S and 10 ppm of CO gases were very low of about 1.5, indicating the good selectivity. In addition, the TONW sensors fabricated by the on-chip growth technique exhibited a good reversibility up to 7 cycles switching from air-to-gas with a response of 19.8 ± 0.033 (to 1 ppm of NO₂), and this value was almost the same (about 19.5 ± 0.027) for 11 cycles after three months storage in laboratory condition. The response and selectivity enhancement of RuO₂-functionalzied TONWs sensors was attributed to the variation of electron depletion layer due to the formation of RuO₂/TONWs Schottky junctions and/or the promotion of more adsorption sites for NO₂ gas molecule on the surface of TONWs, whereas the good reversibility was attributed to the formation of the stable monoclinic WO₃ from the single crystal of monoclinic W₁₈O₄₉ after annealing at 600 °C.