| Summary: | 碩士 === 國立臺灣海洋大學 === 光電科學研究所 === 102 === The experiments of synthetic SnO2 nanostructures were performed at room temperature with CO2 laser heating tin foil. Growth speed of the nanostructure is about 11.06μm/s. Identification and analysis of SnO2 nanostructures were used field emission electron microscopy, energy dispersive spectroscopy, high resolution transmission electron microscopy, X-ray diffraction. In addition we use UV-Vis spectrometer to measure SnO2 nanostructure of optical band gap and absorption spectrum.
Observed by field emission electron microscope, we can find the shape of nanostructures were big grain structure, needle cone structure, foliage-like structure, columnar structure, vine-like structure. We also measured the lattice image of nanostructure by HRTEM, the lattice spacing of nanostructure are 0.262nm and 0.339nm, corresponding to the (101) and (110) crystal planes, respectively. After the X-ray diffraction analysis, we know that the crystal structure is rutile-type structure.
We also measure the absorption spectrum of SnO2 nanostructure by UV-Vis spectrometer, We found that the absorption spectrum of the optical absorption peak wavelength of the nanostructure is in the near ultraviolet region. The absorption spectrum presented strong absorption and weak absorption. The optical energy bandgap are indirect bandgap transition. The bandgap is higher than bulk SnO2 (3.6eV).
In order to investigate the absorption spectra before and after annealing, we used high-temperature furnace heating and CO2 laser annealing method by setting different annealing parameters. We compared the change in the absorption spectrum and particle sizes of the nanostructures at different annealing parameters. Its nanoparticles after annealing becomes large, and the optical bandgap becomes smaller. After high temperature furnace annealing the particle radius is about between 6.95nm-7.58nm, and the optical energy bandgap is between 4.72eV-4.54eV. After CO2 laser annealing the particle radius is about between 6.83nm-7.47nm, and the optical energy bandgap is between 4.76eV-4.57eV. Regardless of before and after annealing, we found that the optical absorption spectra have two weak absorption peaks at 250nm-300nm and 300nm-350nm, respectively. This is due to the two weak absorption peaks is formed by carbonyl (C = O), and the peaks also belong to the electronic transitions of n→π^* orbitals.
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