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Synthesis Of Nanostructures ZnO And Their Functional Properties

Posted on:2014-01-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:J H ZhengFull Text:PDF
GTID:1228330395996321Subject:Materials science
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ZnO nanomaterials nanostructures are attracting tremendous interest due to theirfascinating fundamental properties and wide spread applications in the fields of electronics,optoelectronics and spintronics. Therefore, it is very important to do the research on thefabrication and properties of undoped and doped ZnO nanomaterials. Transition metalelements doped ZnO nanomaterials with Curie temperature above room temperature havepotential application in the spintronic devices. Rare-earth elements have excellent opticaland magnetic properties because of their unique atomic shell structures. Rear-earth elementsdoped ZnO nanomaterials have attracted tremendous interest. In this thesis, undoped anddoped ZnO nanomaterials were synthesized by thermal evaporation method, hydrothermalmethod and sol-gel method. The morphological, structural, superhydrophobic, photocatalytic,magnetic and optical properties of undoped and doped ZnO nanomaterials were investigated.1ZnO nanorods with uniform diameter and length have been synthesized on an indium-tinoxide (ITO) substrate by using a simple thermal evaporation method which is suitable tolarger scale production and without any catalyst or additives. The single-phase ZnOnanorods grow well-oriented along the c-axis of its wurtzite structure on ITO substrate.The ZnO nanorods on ITO substrate possess much higher photocatalytic activity for thedegradation of methyl orange than the ZnO rods on Si substrate do. The ZnO nanorodson ITO substrate also show good PL behaviors.2ZnO film with claviform structure was synthesized on quartz substrates through ahydrothermal method at90℃. The microstructure of the film composing of clusters ofsubmicrometer rods, which therefore endues the film with good superhydrophobicity.Meanwhile, the film with such tan-glesome structure also shows high crystalline qualitytestified by a strong UV emission and very low deep-level emission observed on the PLspectrum as well as high transparence of about89%transmittance in visible light range.3Electronic band structure as well as ferromagnetic and optical properties of Zn1xCuxOpowders was studied experimentally and theoretically. Zn1xCuxO show ferromagnetism.Cu doping effectively quenches the UV emission and enhances the absorption invisible-light region. The strong p-d hybridization between Cu and its four neighbouringO atoms is responsible for the ferromagnetism, and the electronic intra-band transition from the occupied bands to the unoccupied ones under irradiation for the visible-lightemission. The Zn1xCuxO system is a potential candidate in spintronics andphotocatalytic.4Zn1-xYxO nanoparticles with different Y concentrations were synthesized by sol-gelmethod. The saturation doping concentration of Y in ZnO lattice is estimated to be about6.12at%. Photoluminescence spectrum reveals that doping of Y in ZnO can effectivelyincreased the UV emission intensity and suppress the deep level emission (DLE) of ZnO,as a result, the intensity ratio of UV/DLE increases to32for the sample of Yconcentration7at%.5Zn1-xNdxO nanoparticles with different concentrations were synthesized by sol-gelmethod. The structures, magnetic and optical properties of as-synthesized nanorods wereinvestigated. The saturation concentration of Nd in Zn1-xNdxO lattice is less than5at%.Zn1-xNdxO samples exhibit dilute ferromagnetic properties at room temperature. The VOvacancies and the s-f coupling between the rare-earth ions f and the ZnO host s stateswere contributed to the dilute ferromagnetis. The UV emission of PL spectrum ofZn1-xNdxO shows red shift with increasing Nd concentration. This is due to theintroduction of new unoccupied states by Nd4f electrons that are located close to thelower edge of conduction band of the ZnO energy levels.This thesis not only provides the optimized growth conditions for undoped, transitionmetal elements and rare-earth elements doped ZnO nanomaterials, but also obtains somebeneficial results in aspects of their superhydrophobic behavior, photocatalytic activity,optical properties and magnetic properties, which builds theoretical and experimentalfoundation for much better and broader applications of ZnO nanomaterials.
Keywords/Search Tags:ZnO, Transition metal elements, Rare-earth elements, Superhydrophobic behavior, Photocatalytic activity, Optical properties, Magnetic properties
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