Investigation On The Synthesis, Optical And Field Emission Properties Of Semiconductor Oxide Nanostructures

Fabrication, optical and field emission properties of nanostructures of three kinds of oxide including Zinc oxide (ZnO), Tin oxide (SnO₂) and Hematite (α-Fe₂O3) were investigated in our thesis. It mainly contains the following works and innovations:1. Four different hierarchical ZnO nanostructures with the characteristic of spininess, such as nanosleeve-fishes, radial nanowire arrays, nanocombs and nanoflowers have been fabricated through thermal chemical vapor deposition by adjusting the source temperature and the gas flow rate. Field emission measurements of these nanostructures showed high emission current density and low turn-on field of, which can be compared to that of the one-dimensional ZnO nanostructures and carbon nanotubes. The good performance for field emission of the hierarchical ZnO nanostructures makes them promising candidates for further applications in FE microelectronic devices. Other ZnO nanostructures were also successfully prepared vie adjusting the experimental parameters.2. ZnO microtowers were synthesized on silicon substrate by vapor-phase transport method at a low temperature of around 550 ℃ under atmospheric pressure. The two-dimensional growth mechanism of the microtowers was investigated. Room-temperature photoluminescence spectra of the microtowers showed UV emission band centering at about 388 nm and wide green emissions around 500 nm. Field emission measurements demonstrated that the microtowers with sharp tips of several nanometers in curvature radius possessed good performance with turn-on field of about 1.8 V/μm and threshold field of 4.8 V/μm. In addition, other interesting structures such as mushroomlike, tubelike and bottlelike structures were also fabricated by raising the source temperature.3. Novel self-organized hierarchical SnO₂ nanostructures have been successfully prepared by vapor phase transport with the assistance of a stainless-steel grid at 950 ℃. Scanning electron microscopy shows that the synthesized product displays interesting sallow-like morphology, in which numerous secondary branches (beak-like nanowires) are grown randomly around the main stems (microwires). A room temperature photoluminescence spectrum of the present SnO₂ nanostructures shows a strong emission at 572 and 604 nm^-1. additionally, we also synthesized other SnO₂ nanostructures, such as nanowires, nanobelts, nanoflowers, throuth changing the experimental conditions. 4. Hematite (α-Fe-2O₃) nanowires were synthesized by the thermal oxidation of Fe-Ni alloy grids at 900 ℃. The effects of hydrogen (H₂) plasmas on the morphology and field emission properties of α-Fe₂O₃ nanowires were investigated. Many nanocrystallites with sharp tips were found to be produced on the surface of the originally smooth nanowires after H₂ plasmas treatment. Field emission measurements demonstrated that the treated α-Fe₂O₃ nanowires possessed much better performance with turn-on field of 3.7 V/μm at 0.1 μA/cm² of current density, compared with the as-grown samples.