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Title: Low temperature growth of high aspect ratio nanostructures
Author: Hofmann, S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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Carbon nanotubes and -fibres were selectively grown by chemical vapour deposition on pre-patterned catalysts. A systematic study was performed relating the growth and crystallinity of the carbon nanostructures to reactor characteristics, gaseous precursors and diluents as well as catalyst type and material. A DC plasma excitation at low discharge currents (<30 mA) not only resulted in vertical alignment of as-grown carbon nanofibres but, in combination with an acetylene feedback and nickel, cobalt or iron catalysts, enabled an onset of growth at temperatures below 300°C. Extended activation energies of 0.23 eV - 0.35 eV for the growth rate were much lower than for thermal growth (1.2 - 1.5 eV). This suggests a surface diffusion limited growth mechanism on a solid phase catalyst. The result allowed the direct synthesis of patterned, aligned carbon nanofibres onto polyimide foils to fabricate flexible field emitters. Carbon nanofibre-based scanning probes were achieved by novel catalyst patterning techniques, and complex shaped electrochemistry electrodes could be homogeneously covered with free-standing carbon nanofibres by using colloidal catalyst systems. The growth of silicon nanowires was studied based on silane as precursor gas and gold as thin film or colloidal catalyst. A low power RF (10 W) plasma significantly increased the growth rate at temperatures below 400°C. The as-grown silicon nanowires were highly crystalline with diameters (inner core <10 nm) small enough for the observation of quantum confinement effects. Element specific and general growth mechanisms of plasma enhanced chemical vapour deposition are highlighted.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available