Visible-light photoelectric effect of carbon-doped ZNO nanostructures.
Date of Issue2013
School of Mechanical and Aerospace Engineering
In this dissertation, a systematic study has been carried out on the synthesis, characterization and device fabrication of carbon-doped ZnO nanostructures. Firstly, a well understanding of growth mechanism of ZnO nanostructures on carbon fibers or carbon cloth at different pressures has been investigated. Especially, carbon fiber/ZnO nanorod core-shell hierarchical structure can be obtained with the ZnO microtube structure formed on the carbon fiber surface. It is believed that carbon-doped ZnO nanostructures can be obtained as carbon in the core, since carbon is ready to diffuse and dope into ZnO. Secondly, the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) results showed clearly that carbon was doped into ZnO through substitution of carbon for oxygen in the growth and annealing processes. Room temperature photoluminescence spectrum of the carbon-doped ZnO presented a strong defect-induced emission in the visible range of 400-800 nm. The optoelectronic properties in the range of the visible light were also demonstrated, indicating that carbon doping in ZnO extended its photoelectric specifics in the visible light region. Thirdly, the undoped and carbon-doped ZnO films deposited by radio frequency (RF) sputtering on glass substrates were investigated to clarify the contribution of carbon doping for the improved visible-light absorption. Moreover, the first-principle calculations were also performed to determine the electronic structures of carbon doping in ZnO, which indicated carbon substituting some oxygen sites in ZnO, leading to bandgap narrowing and introducing some intermediate energy states in the bandgap.In summary, carbon-doped ZnO nanostructures have been successfully synthesized by using carbon fibers or carbon cloth as substrates. Owing to carbon substituting some oxygen sites in ZnO, bandgap narrowing and some intermediate energy states are introduced in the bandgap. So the carbon-doped ZnO nanostructures have demonstrated to be well sensitive to visible light apart from UV. Their photoelectric properties indicated that carbon doping in ZnO could extend its light absorption to the visible light region. The unique visible-light activeness of C-doped ZnO nanostructures makes them particularly promising for applications to other photoelectric devices, i.e. water-splitting, photosensors and photodetectors.