| The evolution of nanoscience and nanotechnology mainly involves three important steps, that is, the controlling growth of nanostructures, and then followed by characterizing, modeling and extracting optimizing properties, while the final aim is to achieve nanodevices with high performance which will deeply influence both the industrial and social development. In this dissertation, electrospinning was employed to prepare multifunctional ZnO nanofibers modified by doping and composition. Emphases were focused on the patterning and assembly of the nanofibers as well as their unique properties in the field of electrics, optics, photoelectronics and photocatalysis. The results demonstrate the potential applications of these 1D nanostructures in new types of nano-devices such as integrated circuits, photodetectors, and memories.Centimeter long aluminum-doped zinc oxide (AZO) nanofibers were prepared by electrospinning, and possible mechanisms were proposed to discuss the dependence of diameter and morphology on process parameters. Al acted as a cationic dopant that greatly enhanced the conductivity of AZO nanofibers. When exposed to the below-gap light, the conductivity of individual AZO nanofibers was increased by 20 times which was mainly attributed to the transition from defect levels, introduced by Al doping, to the conduction band. Also, a memory device constructed from an AZO nanofiber was observed to switch between two states differing in conductivity by about one order of magnitude, because of field-induced charge trapping and de-trapping. Besides, the Al doping lead to an obvious blue-shift within the ultraviolet region and the extension of ZnO band gap.Heterostructured ZnO-Ag nanofibers showed high UV photosensitivity up to over 4 orders of magnitude with relatively fast and stable response speed. The electric conductivity of the hybrids were found follow the percolation theory, and can reach as high as 115 S·cm-1 due to the electron transfer highway provided by Ag phase. Typical low-voltage varistor behavior was also observed for samples with proper Ag concentration. Moreover, as the heterojunction structure promoted the photoexcited charge separation, the photodegradation of RhB dye solution was remarkably enhanced.Core-shell structured ZnO-ZnS nanofibers and pure ZnS nanofibers were successfully prepared by sulfurizing the electrospun ZnO template. The ZnO-ZnS structure facilitated the exciton dissociation and thus exhibited higher photocatalytic activity. The photoluminescence spectrum of ZnS nanofibers consisted of a purple and a blue emission, associated with the defects and the trapped luminescence arising from the surface states.Nanofibers of Eu, Li co-doped ZnO with diameters of 50-80 nm was obtained. The fibers exhibited red luminescence from electric-dipole allowed 5D0→7F4 transition of Eu3+ inons under the excitation at 325 nm.Devices for I-V measurement and field-effect transistors (FETs) were assembled using electrospun ITO nanofibers by top contact configurations. The effect of Sn doping on the electrical conductivity was significant that enhanced over 107 times in conductance up to ~1 S·cm-1 for ITO nanofibers with Sn content of 17.5 at.%. The nanofiber FETs were operated in the depletion mode with electron mobility up to 0.45 cm2/V s and on/off ratio of 1000.
|
PDF Full Text Request