Thin Films Based On ZnO Nanostructure Prepared By Ultrasonic Spray Pyrolysis And Their Propetries

Among various namo-materials, wide direct band gap ZnO, as most common andpromising oxide semiconductors, have demonstrated great applications inphotoelectric device and chemical sensor due to its electronic, optical and magneticproperties. So far, various kinds of ZnO with different size and morphologies weresuccessfully synthesized by a variety of physical and chemical methods.One-dimensional (1D) ZnO, due to their high surface-to-volume ratio, high active sitedensity and special physical and chemical properties, have been proved to be thepromising candidates for achieving excellent device performances. Besides, theenhanced gas-sensing performances of the composite oxide with stratified, porous andhollow structure can be obtained by assembling the individual metal oxide together. Inorder to obtain the large area thin film with hierarchical nanostructure, we present asimple USP method for the synthesis of ZnO nanorod arrays, ZnO/SnO2andZnO/ZnFe2O4composites. Main contents included:1. We presented a simple USP method for the synthesis of well-aligned ZnOnanorod arrays. These rod-like nanostructures with the lengths of about9μm weregrown on the seed layer substrates. The spray time played an important role inextending the length of the ZnO nanorods. On the basis of the results of themorphology evolution, a possible formation mechanism was proposed.Room-temperature photoluminescence spectra of the nanorods were tested andshowed a near band-edge emission and a deep-level green light emission.2. Hollow cylinder comb-like ZnO/SnO2nanostructure was successfully synthesizedvia a two-step USP method. A hollow cylinder comb consists of secondary-grownnanowires and ZnO backbones. In the process of secondary growth, the innerportions of solid ZnO nanorods were dissolved gradually with prolonging the spray time. The TEM photos indicate that the nanobranch was not simplycomposed of SnO2but constructed by ZnO and SnO2randomly. Moreover,gas-sensing properties of our hierarchical ZnO/SnO2-based sensor were testedand exhibited high response and quick response to ethanol. For example, theresponse of ZnO/SnO2sensor was10to100ppm ethanol at275°C.3. In order to enhance the sensing performances of the ZnO namorods, hybridZnO/ZnFe2O4nanoforest was successfully synthesized via a simple two-stepmethod, which involved immersing ZnO nanorod arrays in0.2M aqueoussolution of ferrous sulfate and subsequent calcinations at500°C. The resultingZnO/ZnFe2O4nanoforest displayed enhanced gas-sensing properties compared tothe original ZnO nanorods.In conclusion，we successfully prepared the well-aligned ZnO nanorod arrays onquartz substrate with a USP method in this paper. In order to further enhance thesensing performance of ZnO nanorods, we used semiconductor compositiontechnology for modification of sensing material and hierarchical ZnO/SnO2andZnO/ZnFe2O4composites were prepared. It was found that such composites exhibitedan enhanced ethanol sensing properties compared with the single-component ZnOnanorods. The enhanced performance might be attributed to the novel structure aswell as the change of heterojuction barrier at the different gas atmosphere.