The Synthesis And Characterization Of Low-dimensional Zinc Oxide Nanostructure By Template

Zinc oxide has been widely used in different industries due to its excellent semiconductor, piezoelectric,pyroelectric and fluorescent properties.In recent years,ZnO was found to be a unique direct band semiconductor with band gap of 3.37eV and exciton binding energy of 60meV at room temperature,which makes it a very attractive for the potential application as a nano-device in the fields of short wavelength semiconductor laser,UV light emission and detector,transparent semiconductor and electromechanical coupling sensor etc.,thus ZnO has been a hot topic in the last decades in "Nano" science.A comprehensive and detailed review about the synthesis methods of preparing ZnO nanostructure was done in this thesis.Due to the shortcomings encountered in the vapor condensation methods,including expensive and complicated equipment,high reaction temperatures and difficult product collection procedures,the simple and easy-to-realize liquid route,including low-cost and easy-to-scale-up hydrothermal/solvothermal,sol-gel and reaction precipitation,were focused in this thesis as the tools to make ZnO nanostructures with preferred morphologies and properties.The mechnisms of controlling ZnO morphologies through different synthesis parameters were discussed.For the final purpose of making ordered and controllable growth of ZnO,further investigation with the growth of ZnO by applying templates were also done,the microstructure and properties of these nanostructures are analysed.Accordingly,the main work done and main results are summarized as followings:1.In hydrothermal synthesis,PEG was selected to work as a soft template to modulate the morphology and water as the solvent.ZnO nanostructures including nano-bowl,nano-rod and nano-"flower" were successfully synthesized by changing Zn²⁺/OH^- concentrations and ratios.The phase separation and aggregation phenomean are the key factors for the formation of nano-bowl and nano-"flower".2.In solvothermal synthesis,PEG was selected to work as a soft template to modulate the morphology while ethanol and water as the solvent.ZnO nanostructures including nanowire, nano-rod,hexagonal nut and prism were successfully synthesized by changing OH^-concentrations and ratios.The morphology is controlled by the PEG in solution due to its chemical bonding interactions with solvent molecule and Zn²⁺.When[OH^-]/[Zn²⁺]=2:1,the final products are one-dimensional nanostructure;when[OH^-]/[Zn²⁺]=1:1,the final products are hexagonal nuts and prism;and the final products are nanorod or polyhedral at higher reagent concentration3.Two-step anodic method is chosen to fabricate ordered porous alumina oxide template by using oxalic acid as electrolyte.With the proper anodization parameter,ordered honeycomb structure with uniform channel diameters and spacing of the pores can be fabricated with this method.This affords a promising route to synthesize large-area,ordered nanostructure with high aspect ratio.4.Combining template and sol-gel method,zinc oxide sol prepared from zinc acerate as precursor can be introduced into the nanosized channel of anodic alumina oxide template by the capillary force,gravity or gas pressure as the driving force,thus ZnO nanowire can be grown under the confinement of the channel size afterwards.Different methods of dipping, dripping and vacuum pumping were applied for the best performance.Through vaccum pumping method,as the best in three,nanowire array with diameter of 60nm and length of several micrometers can be prepared.5.In the direct reaction precipitation method,amonia was selected as the simple precipitation reagent.ZnO nanostructures with morphologies of star,rod or needle can be harvested by changing Zn²⁺concentration,pH values and temperatures.Based on the results of getting 1-dimentional ZnO nanostructures,anodic alumina oxide template was introduced to grow ZnO on the surface by heterogenous crystallization process.Ordered and highly compacted ZnO nanostructured film composed of erected hexagonal nano-flakes is successfully prepared on the top of AAO template.6.Well-crystallized zinc oxide nanostructures synthesized by hydrothermal method and precipitation method show not only intrinsic violet emission but also green and orange emission coming from the oxygen vacancy.Take advantage of the ordered structure of anodic alumina oxide,the growth position and morphology of the zinc oxide nanostructures are controllable,highly ordered zinc oxide nanowire array is further synthesized using vacuum pumping mehod,which shows very good violet emission.