Synthesis And Characterization Of Quasi-One-Dimensional ZnO Nanomaterials

The carbothermal reduction method and the spray pyrolysis assisted thermal evaporation method were developed in this work to synthesize quasi-one-dimensional (Q1D) ZnO nanomaterials. The modification of ZnO morphologies as well as the mechanisms with the varying parameters of the carbotheraml reduction method has been clarified. Additional elements were successfully doped into the Q1D ZnO nanomaterials via the spray pyrolysis assisted thermal evaporation method. The morphologies, crystal structures and the surface chemical constructions of the Q1D ZnO nanomaterials were carefully characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The growth mechnanisms of the Q1D ZnO nanomaterials such as nanowheels have been revealed. The physical properties, including photoluminescence, electrical transportation and gas sensing property, were measured with respect to the effects and the mechanism of Pb and Sn addition.Various ZnO nanomaterials were synthesized by controlling the parameters of the carbothermal reduction method, such as temperature, flow rate, pressure, atomic ratio of initial materials and total mass. Several unique nanostructures, including nano-wires, rods, belts, combs, cones, hollow bulbs, towers, flags, flowers, wreathes and fish-bone-like combs were obtained in this work. Meanwhile, ZnO nanowires arrays were successfully fabricated without any catalyst.ZnO nanowheels have been obtained by the spray pyrolysis assisted thermal evaporation method and it can be formed as a result of the compititive cooperation of the vapor-solid (VS) and polar-surface-dominated (PSD) mechanisms. It is suggested that two sides of a nanobelt are dominated by Zn²⁺ and O^2- ions, respectively. The teeth preferential growth is along [0001] direction of the Zn-terminated (0001) polar surfaces. With the growth of the ridge, it began to bend with a small cross section where the electrostatic force generated due to the polarity surface, as a result of that nanowheel can be formed. The Sn-, In- and Pb doped ZnO nanostructures were obtained by means of adding a certain solute into the spray solution, respectively. Additionally, some unique nanostructures can be induced with additional elements. For example, ultra-long teeth nanocombs were achieved in Sn-ZnO, nanorings in In-ZnO and nanotubes in Pb-ZnO.The photoluminescence of pure ZnO nanostructures shows a strong ultra-violet emission but a relatively weak visible emission at room temperature. However, with Sn, In and Pb addition, the peak intensity of ultra-violet emission may be lessened with a slight blue-shift of 45, 22 and 16 meV, respectively.I-V characterization of the Al electrodes with Q1D ZnO nanomaterials deposition is supposed to be Schottky contact. In terms of the tunneling effect of semiconductor, the resistance decrease with the increasing temperature and slows down when the temperature is over 200℃due to the conversion from an oxygen physical into an oxygenchemical absorption.The oxygen absorption to ZnO nanomaterials surface are increased in the condition of Pb and Sn doping. Therefore, the sensitivities to oxygen and ethanol can be substantially improved. The largest sensitivity of the undoped ZnO nanomaterials with 50 ppm ethanol is of 11, approximately, as the measurement temperature is below 300℃, while that of Sn-ZnO and Pb-ZnO nanomaterials are increased to 62 and 102, repectively.