Fabrication And Properties Of Mn-doped ZnO Nanostructure (Hollow) Microspheres

In this dissertation, ZnO/Mn-doped ZnO micro/nano-materials were synthesized byhydrothermal synthesis method. The as-synthesized micro/nano-materials were investigated byscanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction(XRD) and X-ray photoelectron spectra (XPS) etc. The following conclusion can be drawn from thestudies:1. A series of controlled morphologies of ZnO crystallites have been successfully synthesized based onthe decomposition of zinc acetate precursor in water-ethylene glycol solution through hydrothermalmethod. In particular, the volume ratio of water to EG was found to play important roles in themorphological controlling of the resulting ZnO crystallites. With carefully controlling their volume ratio,different morphologies of ZnO crystallites, including hierarchical microrods, microrods, hollowmicrospheres and solid microspheres, can be obtained effectively. Corrsponding growth mechanism ofthe ZnO crystallites was briefly discussed.2. A series of manganese (Mn)-doped zinc oxide (ZnO) hierarchical microspheres (HMSs) areprepared by hydrothermal method only using zinc acetate and manganese acetate as precursors andethylene glycol as solvent. XRD indicates that all of the as-obtained samples including the highestMn (7%, mol) in the crystal lattice of ZnO have a pure phase (hexagonal wurtzite structure). Abroad Raman spectrum from the as-synthesized doping samples ranges from500to600cm-1, revealing the successful doping of paramagnetic Mn2+ions in the host ZnO. Optical absorptionanalysis of the samples exhibits a blue shift in absorption band edge with increasing dopantconcentration and corresponding photoluminescence (PL) spectra show that Mn doping suppressesboth of near band edge ultraviolet (UV) emission and defect related blue emission. In particular,magnetic measurements confirm robust room-temperature ferromagnetic behavior with a high curietemperature exceeding400K, signifying the as-formed Mn-doped ZnO HMSs will have immensepotential in spintronic devices and spin-based electronic technologies.3. Unique three-dimensional Zn0.98Mn0.02O hierarchical hollow microspheres (HHMs) withdiameters of5–8μm have been synthesized by a simple hydrothermal approach. In particular,room-temperature magnetization measurements indicate that novel co-existence ferromagnetism(FM)/paramagnetism (PM) and only PM behaviors for the as-annealed Zn0.98Mn0.02O HHMs at673K and1073K, respectively, in Ar gas atmosphere appear whereas the as-synthesized ones showmerely pure FM. Based on the PL and Raman spectra, it is confirmed that the concentrations ofoxygen vacancies in Zn0.98Mn0.02O HHMs happen to larger with increasing annealing temperature.Corresponding magnetic evolution mechanism is proposed to relate to oxygen vacancies based onannealing processes. This novel magnetic property will enrich our understanding of dilutedmagnetic semiconductors.