Fabricationand Gas Sensing Properties Of Zno Nanoarrays

As one of important wide band gap semiconductor materials, zinc oxide hasexcellent optical, electrical and piezoelectric properties, and has beenextensively used in many hi-tech areas, such as laser machinery,field-emission cells, and gas sensors. Highly ordered ZnO nanostructurearrays are potential candidates for chemical sensors due to the highsurface-to-volume ratio and the rapid electron transmission. Currently,fabrication of nanoarrays still remains a challenge. The approach based onchemical solution growth exhibits obvious advantages in terms of preparationcost, facilities, complexity, energy consumption and production yielding. Inthis study, the controllable fabrication of ZnO nanorod and nanotube arrayswere realized by the method of chemical solution and their gas-sensingperformance and mechanism were investigated. The details of the work wereas follows:（1） The controllable fabrication of zinc oxide nanoarrays on glass andceramic tube were carried out by a facile chemical solution method thatexhibits obvious advantages in terms of low preparation cost, handy facilities,simplicity, low energy consumption and high production yielding. The results of characterization indicated that ZnO nanorod and nanotube arrays weresingle-crystalline and grew along c axis. The lengths and diameters of the ZnOnanorods and nanotubes and the depths of the nanotubes were increased withthe growing time. The density of nanorods and nanotubes were enlarged withthe increase of the Zn2+concentrations of coating and growth solution.（2） The gas-sensing properties of zinc oxide nanorod and nanotube arrays tonitrogen dioxide and ethanol were studied, and their differences wereexplained. The optimum testing temperatures of ethanol and nitrogen dioxidewere355℃and230℃, respectively. Sensing test results showed that the ZnOnanoarray sensors had short response and recovery times and high stability. Inaddition, the sensitivity of the ZnO nanorod array was higher than that of theZnO nanotube array. Raman, XPS and PL were used to investigate thedifference of the surface structure of ZnO nanoarrays. The spectral analysisindicated that the ZnO nanorod array had more donors （VOand Zni）, feweracceptors （VZn, Oiand OZn） and more active oxygen (O₂^2-and O₂^-) than thoseof ZnO nanotube array, which resulted in the higher sensitivity of ZnO nanorodarray than that of ZnO nanotube array. Moreover, the gas-sensing mechanismwas proposed.（3） Au-doped ZnO nanoarrays were prepared and their sensing properties tomethane were investigated. The optimum working temperature was355℃.In addition, the methane gas-sensing mechanism of Au-doped ZnO nanoarrayswas proposed. Au increased the adsorption sites, which was in favor of the sensitivity of CH4. In addition, Zn-doped In2O3nanoparticles weresynthesized and their gas-sensing performance were better than In2O3. Theoptimum molar ratio was0.0376. At230℃, the sensitivity of Zn-dopedIn2O3to100ppm ethanol was103, which was0.8times higher than that ofundoped In2O3. At230℃, the sensitivity of the Zn-doped In2O3to10ppmnitrogen dioxide was249, which was2.8times higher than that of undopedIn2O3. Zn-doped In2O3had excellent gas-sensing properties to ethanol andnitrogen dioxide, such as low working temperature, rapid response andrecovery, and good selectivity, suggesting a promising application in sensor.