Investigation On The Controlled Synthesis And Physical Properties Of One-dimensional SnO₂ Nanomaterials

In this thesis, one-dimensional SnO₂ nanostructures (including nanowires, zigzag nanobelts and cobalt-doped nanowires) were successfully synthesized by vapor transport method. Meanwhile, the field emission properties of SnO₂ zigzag nanobelts and the magnetic properties of cobalt-doped SnO₂ nanowires were investigated in detail. This thesis contains the following works and innovations:1. High quality SnO₂ nanowires were successfully prepared by chemical vapor transport process on various substrates such as rigid silicon and flexible stainless-steel grid. The effect of the nature of the substrate and the distance between substrate and source on the size distribution and the morphology of the SnO₂ nanowires and their substrate-surface-coverage were investigated. The formation of SnO₂ nanowires has been attributed to the self-catalyzed vapor-liquid-solid growth mechanisms depending on the processing conditions. The successful synthesizing of SnO₂ nanowires on the stainless-steel grid substrate makes them more flexible for further applications in chemical sensors. Other SnO₂ nanostructures were also successfully prepared vie adjusting the location of the substrates.2. A novel process was developed for synthesizing SnO₂ zigzag nanobelts on a silicon substrate with the assistance of CuO powder. The crystalline structure and morphology of SnO₂ zigzag nanobelts were characterized using x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The growth habits and formation mechanism of the obtained SnO₂ zigzag nanobelts were discussed in detail based on a series of experimental results. The optical property was evaluated by room temperature Photoluminescence spectra. Field emission properties of SnO₂ zigzag nanobelts was measured for the first time leading to good performance with a turn-on field of 1.9 V/μm and a threshold field of 5.1 V/μm.3. We observed ferromagnetism in dilute cobalt-doped SnO₂ nanowires at room temperatures. The Co-doped SnO₂ nanowires with an average diameter of 50 nm were synthesized by the vapor transport process. High-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy analyses demonstrate that the nanowires are single-crystal structures and Co is homogeneously doped into the SnO₂ lattice. The ferromagnetic hysteresis curves and temperature dependent magnetization measurement provide evidence for ferromagnetic properties with a Curie temperature above room temperature. Oxygen annealing were performed to study the roles played by the oxygen vacancies in determining the ferromagnetic properties of the nanowires.