Room Temperature Ammonia Gas Sensing Using MnO<sub>2</sub>-Modified ZnO Thick Film Resistors
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Abstract
Pure ZnO thick film, prepared by screen-printing technique, was almost insensitive to NH<sub>3</sub>. Pure ZnO thick films were surface modified with MnO<sub>2</sub> by dipping them into 0.01 M aqueous solution of manganese chloride (MnCl<sub>2</sub>) for different intervals of time and fired at 500℃ for 12 h. The grains of MnO<sub>2</sub> would disperse around the grains of ZnO base material. The MnO<sub>2</sub> modified ZnO films dipped for 30 min were observed to be sensitive and highly selective to NH<sub>3</sub> gas at room temperature. An exceptional sensitivity was found to low concentration (50 ppm) of NH<sub>3</sub> gas at room temperature and no cross sensitivity was observed even to high concentrations of other hazardous and polluting gases. The effects of surface microstructure and MnO<sub>2</sub> concentrations on the sensitivity, selectivity, response and recovery of the sensor in the presence of NH<sub>3</sub>and other gases were studied and discussed. The better performance could be attributed to an optimum number of surface misfits in terms of MnO<sub>2</sub> on the ZnO films.
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