Preparation And Properties Of Cu-doped ZnO Nanosheets

Because of its unique physical and chemical properties, nanostructural ZnO, hassignificantly potential applications in the field of spintronics, optoelectronics andbiosensors. Copper doped ZnO can change the electronic structure of ZnO, resulting indramatic changes of the optical, electrical and magnetic properties of ZnO, to meetspecific needs and applications. In this thesis, the design idea is how to obtain Cu-doped ZnO nanostructures on Zn/Cu double-layer material or Zn-Cu alloy.A new, fast and low-cost method to prepare copper-doped ZnO nanosheets hasbeen developed in this thesis. Zinc foils were dropped in different concentrations ofcopper sulphide solution for a short time, and dried in air. Copper sulphide etched zincfoils were then annealed at200℃to500℃in air. The specimens prepared duringdifferent stages were characterized by scanning electron microscopy (SEM), X-raydiffraction meter (XRD), high-resolution transmission electron microscopy (TEM).Results show the formation of a complex structure:’Cu-doped ZnO nanosheets/Cu-Zn layer/zinc substrate’ after zinc foils etched with copper sulphide solution. A Cu-doped ZnO nanosheet has a polycrystalline hexagonal crystal structure and grain sizeof5to10nm. Cu concentration in ZnO decreases with the increase in annealingtemperature, especially at annealing temperature higher than the melting point of zinc.When the annealing temperature is below the melting point of zinc (410℃), before andafter annealing the morphology of nanosheets remains almost same. When theannealing temperature is higher than the melting point of zinc, the morphology changeof ZnO nanosheets depends on the concentration of the original copper sulphide insolution during the process. According to the chemical reaction for copper sulphideand zinc, a physical model of the original cell reaction is established to explain theformation of copper-doped ZnO nanosheets. By oxidation thermodynamic analysis and equilibrium oxygen partial pressure calculation, Cu content changes in ZnOnanosheets during annealing process are explained and the morphology changes ofZnO nanosheets is also analyzed during annealing process.Photoluminescence properties of the annealed specimens were tested and it can beseen that the violet wave of ZnO nanosheets shifts to red direction from thephotoluminescence spectra. The wetting angle of water on the specimen surface wastested. The results show that ZnO morphology on the specimen or the duration of thespecimens in room temperature can affect the wetting angle of water on the specimensurface.Cu0.62Zn0.38brass foil was deformed by surface mechanical attrition treatment(SMAT). The brass foils with or without SMAT were oxidized at400℃~700℃inN25%-O2atmosphere. The oxidation products were characterized by SEM, XRD andTEM. The results show that ZnO nanosheets or nanowires could be formed on thesurface of the specimens oxidized at500℃~600℃. ZnO nanosheet or nanowire hassingle-crystalline hexagonal crystal structure. Compared to the brass without SMAT,the brass with SMAT processing can promote the formation of ZnO nanosheets duringthe oxidation. The thermal stress formed during oxidation process is used to explainthe formation of single-crystal ZnO nanostructures on the brass surface. And theSMAT treatment causing the formation of deformation twins is used to explain theSMAT treatment enhancing the formation of ZnO nanosheets during the oxidation.