Synthesis, Characterization And Photoluminescence Studies Of SiO₂ Nano-wires And SnO₂ Nano-belts

One-dimensional(1D) nanostructures such as wires, belts, and tubes have recently becomethe focus of intensive research owing to their interesting geometries, novel properties, andunique applications in mesoscopic physics and fabrication of the nanoscale devices. In thispaper, SiOx and SnO2 nanowires and nanobelts have been synthesized by thermal evaporationmethod. XRD (X-ray diffraction), HRTEM (high-resolution transmission electron microscopy)and SAED (select area electron diffraction) were employed to characterize the structure featuresof the products. SEM (scanning electron microscope) was used to characterize the morphology.The optical properties have also been investigated by the photoluminescence (PL).SiO_x nano-wires have been synthesized on the silicon substrates by using the reduced tinas active catalyst. It is found that the higher the synthesis temperature, the denser and slipperierof the synthesized nano-wires. It is also found that when the temperature on the whole siliconsubstrate was uniform, the synthesized nano-wires would uniformly distribute on the siliconsubstrate with narrow diameter distribution, ranging from 50 nm to 70 nm.A simple method based on the thermal evaporation was developed for large-scale synthesisof very long silica nano-wires. It is found that large quantity of nano-wires with more uniformdiameters can be obtained by using platinum as the catalyst.The growth mechanism of the nano-lantern is discussed and a growth model is proposedfirst. The multi-nucleation sites round the Sn droplet's perimeter are responsible for theformation of many SiO₂ nano-wires. The growing direction of the nano-wires is not in the samedirection of the movement of the catalyst tin ball, resulting in the bending of the nano-wires andforming the lantern-like silicon oxide morphology.Yellow products were obtained first by thermal evaporation SnO powder at 1100℃for 4h and then annealed in air for 3 h at 900℃. After that the products were characterized by SEM,TEM, XRD, SAED and EDS. The results show that the products were SnO₂ nano-belts. Thegrowth of nano-belts were governed by VS growth mechanism. In the TEM picture, the brightspot on the nano-belt surface has the same crystal structure with the nano-belt, demonstratingthat these spots were probably the caves that formed during the nano-belt growth.The strong light emissions at 426 nm, 440 nm, 474 nm and 533 nm were found for theas-grown SnO₂ nano-belts. The intensity of these emission peaks decreased after the products were oxidized annealing in air at 900℃and these peaks strengthened again after theoxidized-products were deoxidized in H₂ at 750℃. The results of oxide/deoxide experiment ofthe SnO₂ nano-belts suggest that 426 nm, 440 nm, 474 nm, 533 nm light emission of SnO₂nano-belts possibly originate from oxygen vacancy. The strong blue luminescence bands of SiO₂nano-wires maybe ascribed to the defect centers that related to the oxygen.In summary, the thesis has explored the influence of experiment parameters on the synthesisof SiO₂ nano-wires, in which synthesis temperature, temperature uniformity and catalyst areincluded. The growth mechanism of the SiO₂ nano-wires is discussed and a growth model of thenano-lantern is proposed first. These results are helpful to control the synthesis of SiO₂nano-wires. SnO₂ nano-belts were obtained by thermal evaporation method andPhotoluminescence of SnO₂ nano-belts have been studied. The 426 nm, 440 nm, 474 nm and 533nm light emission of SnO₂ nano-belts possibly originate from oxygen vacancy. The PL of theSiO₂ nano-wires synthesized with/without catalyst was also studied, it is speculated that thestrong blue light emission maybe ascribed to oxygen-related defect centers.