Physical Properties Of Low Dimensional Nanocomposites And Zn-N Local Structure And Thermal Stabilities In ZnO:N

In this dissertation, a simple method was proposed for controllable electrospinning polymer nanotubes via a single capillary; moreover, low dimensional ZnO composite nanostructures were prepared by combining sol-gel method, vapor transport deposition, and nitrification method with electrospinning technology; the structure and optical properties of these materials and ZnO:N thin film were also studied as follows:PVP/TEOS nanofibers and nanotubes have been electrospun by a single capillary. The diameters of products, the thicknesses of nanotubes walls, and the ratio of the nanotube wall to the nanotube diameter could be varied by controlling the effects of ethanol on evaporation process, TEOS on phase separation process, and the applied voltages on bending and stretching process. SiO₂ nanotubes could be fabricated by calcinating the PVP/TEOS composite nanotubes in air at 600℃. Moreover, silicon nanotubes could be prepared by magnesiothermic reduction of SiO₂ nanotube templates. The methods are effective to prepare PVP/TEOS composite nanotubes and silicon nanotubes. Such nanotubes are of interest for a broad range of applications in areas such as sensors, filter technologies, lithium ion batteries, and solar cells, etc.Highly dispersed ZnO QDs in PVP nanotubes have been prepared by a single capillary electrospinning. The composites exhibit narrower band edge emissions and less laser thermal effects due to the well dispersion of ZnO QDs and the passivation of PVP molecules on the surface defects of ZnO QDs. Thus, quantum confinement effects on the PL properties of ZnO QDs have been observed including blue shifted band gap, enlarged exciton binding energy and less exciton-LO phonon interaction. SiO₂/ZnO nanocables are obtained by the combination of electrospinning technology and vapor transport deposition procedure. The nanoshells of ZnO show good photoluminescence properties suggesting their high qualities. The anomalous behavior in temperature-dependent PL spectra is attributed to the carrier injection from thermal ionized carriers from the interface of the nanocables.By electrospinning technology and nitrifing process, N-In co-doped ZnO nanofibers have been prepared. By annealing the nitrified samples in air, the defect densities are decreased and the crystal qualities and visible photo-responsibilities were improved. The co-doped nanofibers photocatalyst shows good visible photocatalytic activity toward decomposing organic dye rhodamine B. The formation and evolvements of (Ga_1-xZn_x)(N_1-yO_y) alloy nanostructures are also studied. The alloys formation temperature is decreased remarkably due to their nanostructures morphologies. Thus, nitrogen atoms could be introduced into the nanofibers while zinc atoms could hardly lost in the materials. The Raman spectra were also investigated in detail. By co-doping and alloying methods, the electronic structure of ZnO could be tuned. The results could be applied for visible light photocatalyst of decomposing organics and visible light driven overall water splitting.PL properties and thermal stabilities of ZnO:N local structures are investigated. Acceptor related UV emissions indicate that the doped nitrogen atoms could act as acceptors. The blue and green emissions might be related to the donor to valence band transitions, while the red emissions origin from deep DAP transitions. Thus, nitrogen not only acts as an acceptor, but also induces some complex defects acting as deep donors. Temperature-dependent XPS measurements suggest that XPS peaks at ³96 and ³98 eV originate from the NO in N- and O-rich local environments (β- andα-NO). Compared toβ-NO, theα-NO, as a shallow acceptor, is more thermally stable up to 723 K. The careful studies on the emissions and local states of N impurity are helpful for achieving the stable, high-quality p-ZnO:N.