Abstract
Polarity-controlled epitaxial ZnO films with two types of surface morphologies were prepared using pulsed laser deposition, and their gas sensing responses to several reductive gases were determined. Gas response measurements of high-temperature-grown (HT) c(+)- and c(−)-polar ZnO films having large, densely packed grains with flat surfaces indicated that the selectivity for ethanol of the c(−)-polar film was lower than that of the c(+)-polar film. This is due to the absence of Zn ions, which facilitate the adsorption and reaction of ethanol, in the topmost layer of the surface. In the case of low-temperature-grown (LT) c(−)- and c(+)-polar ZnO films consisting of densely packed grains with diameters of several tens of nm, the c(−)-polar ZnO film had a higher selectivity for ethanol. The gas response behavior of the LT c(−)-polar film differed from that of the HT c(−)-polar film because the surface of the former can feature the h0h¯l crystal plane, which is terminated with undercoordinated Zn ions. The presence of undercoordinated Zn ions on the surface can greatly enhance the ethanol gas response of the LT c(−)-polarity film.
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