摘要
Pure ZnO thick films, prepared by screen-printing technique, were almost insensitive to NHb>3b>. Pure ZnO thick films were surface activated with Cr3+ by dipping them into an aqueous solution (0.01 M) of chromium trioxide CrOb>3b> for different intervals of time and fired at 500 b0;C for 24 h. The CrOb>3b> is known to be unstable above 197 b0;C and transforms into Crb>2b>Ob>3b> upon firing above 197 b0;C. The grains of Crb>2b>Ob>3b> would disperse around the grains of ZnO base material. The Cr3+-activated ZnO films dipped for 5 min were observed to be sensitive and highly selective to 300 ppm of NHb>3b> gas at room temperature. The effects of surface microstructure and Cr3+ concentrations on the sensitivity, selectivity, response and recovery of the sensor in the presence of NHb>3b> and other gases were studied and discussed. The better performance could be attributed to an optimum number of surface misfits in terms of Crb>2b>Ob>3b> on the ZnO films.