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Characterization of planar defects in silicon carbide nanowires
Wieligor, Monika Katarzyna
Wieligor, Monika Katarzyna
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[Fort Worth, Tex.] : Texas Christian University,
Date
2010
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Abstract
Stacking faults and twins were identifying in SiC nanowires produced according three different synthesis methods. By direct observation of high resolution TEM images, analysis of Raman spectra, and from X-ray diffraction results we concluded that planar defects were present in all specimens, regardless the synthesis method. The study of TEM images revealed that concentration of defects was not uniform. The amount of stacking faults and twins varied between the samples, and seems to be dependent on the size of nanowires. Concentration of twins appeared to be highest in nanowires obtained from raw carbon blacks of small diameters. The quantitative analysis of concentration of defects was not conducted because Raman and conventional X-ray cannot discern stacking faults and twins.^Therefore, the estimation of concentration of planar defects was based on the examination of TEM images.^The application of two TEM modes, bright field and dark field, let to deduce that twins played a dominant role in observed defects. A minimum surface energy and strain energy argument was proposed to explain the formation of twins in the SiC nanowires. The high pressure measurements in DAC were performed and the results validated the core-shell model. The application of new carbon precursor revealed with new, highly efficient method of synthesis of SiC nanowires. We proved that it is possible to produce low-cost, catalyst-free, and high-yield SiC nanowires of 10 nm diameter and narrow size distribution. Morphology of the nanowires depended on carbon precursor used. That technique was described in details in Chapter IV.^The model of typical nanowire, composed of crystalline SiC core, coated by thin, 2 nm amorphous SiC layer, was presented.^After analysis of produced SiC nanowires we were able to construct the possible model of growth mechanism, and explain the differences in dimensions and morphology for nanowires, obtained from graphitized and not graphitized carbon blacks precursors. We deduced that vapor-solid growth mechanism is more plausible in nanowires synthesis from carbon black, than the vapor-liquid-solid mechanism--Abstract.
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Subject(s)
Silicon carbide Analysis.
Nanowires.
Nanostructured materials.
Raman spectroscopy.
Nanowires.
Nanostructured materials.
Raman spectroscopy.
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Dissertation
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Physics and Astronomy