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Nanostructure characterization by transmission electron microscopy

Authors Chan, Yu Fai
Issue Date 2002
Summary One-dimensional nanostructures, namely zinc oxide (ZnO) nanowires, 4Å single-walled carbon nanotubes (SWNTs) in the channels of zeolite single crystals and 4Å carbon nanotubes (CNTs) in multi-walled carbon nanotubes (MWNTs), were investigated by high-resolution transmission electron microscopy (HRTEM) and theoretical image simulations. Hexagonal rod-like and bi-crystal structured ZnO nanowires were achieved by the thermal evaporation of ZnO powder mixed with graphite. The nanowires in single crystalline structures with flat surfaces and nearly no structural defects were observed. The lengths were up to 20μm and diameters were on the order of 50nm. From electron diffraction and HRTEM imaging, the growth direction of hexagonal rod-like ZnO nanowires was [001]. While, bi-crystal ZnO nanowires showed a growth direction near [5 10 6]. In bi-crystal nanowires, an asymmetrical tilt grain boundary was identified. The 4Å SWNTs formed in the channels of zeolite and pure zeolite crystals were systematically studied by HRTEM and theoretical simulations. Pure zeolite and the 4Å SWNTs-containing zeolite crystals showed distinct fringe features in the HRTEM images, which mainly determined by the difference in the atomic density of the zeolite channels. The existing of the ultra thin SWNTs in the channels of zeolite increased the atomic density of the channels and hence the contrast of the channels in the HRTEM images. The HRTEM image contrast of the SWNTs-containing zeolite crystals depended sensitively on the defocus condition of HRTEM. This can be used to distinguish SWNTs-containing zeolite and pure zeolite crystals. The HRTEM image of a 4Å CNT in an 18-shell MWNT was theoretically simulated and compared with the experimental results. It was found that due to the Fresnel diffraction effect, the simulation image of a 17-shell MWNT (without 4Å CNT) showed a similar image contrast with that of an 18-shell MWNT and the experimental image under certain transmission electron microscopy (TEM) imaging conditions.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2002
Language English
Format Thesis
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