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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:604141 |
| Date | January 2004 |
| Creators | Hofmann, S. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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