Carbon nanotubes are promising candidates for enhancing electronic devices in
the future at the nanoscale level. Their integration into today’s electronics has however been challenging due to the difficulties in controlling their orientation, location, chirality
and diameter during formation. This thesis investigates and develops new techniques for
the controlled growth and assembly of carbon nanotubes as a way to address some of
these challenges.
Colloidal lithography using nanospheres of 450 nm in diameter, acting as a shadow mask during metal evaporation, has been used to pattern thin films of single-walled carbon nanotube multilayer catalysts on Si and Si/SiO2 substrates. Large areas of
periodic hexagonal catalyst islands were formed and chemical vapor deposition resulted
in aligned single-walled carbon nanotubes on Si substrates within the hexagonal array of
catalyst islands. On silicon dioxide, single-walled carbon nanotubes connecting the
hexagonal catalyst islands were observed. To help explain these observations, a growth
model based on experimental data has been used. Electrostatic interaction, van der Waals interaction and gas flow appear to be the main forces contributing to single-walled carbon nanotube alignment on Si/SiO2. Although the alignment of single-walled carbon nanotubes on Si substrates is still not fully understood, it may be due to a combination of the above factors, in addition to silicide-nanotube interaction. Atomic force microscopy and Raman spectroscopy of the post-growth samples show single-walled carbon nanotubes of 1-2 nm in diameter. Based on the atomic force microscopy data and Raman spectra, a mixture of individual and bundles of metallic and semiconducting nanotubes were inferred to be present.
A novel technique based on direct nanowriting of carbon nanotube catalysts in
liquid form has also been developed. The reliability of this method to produce nanoscale catalyst geometries in a highly controlled manner, as required for carbon nanotube growth and applications, was demonstrated. Chemical vapor deposition growth of the patterned regions shows individual and bundles of single-walled carbon nanotubes. This was confirmed by Raman spectroscopy of the samples, giving single-walled carbon nanotubes ~1-2 nm in diameter. The capabilities of the nanowriting process were also explored for direct-writing of carbon based nanomaterials such as single-walled carbon nanotubes and C60 molecules.
Finally, a brief survey on carbon nanotube field-effect transistor modeling tools
has been presented, followed by two-terminal current-voltage measurements on colloidal
lithography and nanowriting samples. Results show primarily ohmic behavior with
conductances of ~0.86-16.5 μS for the hexagonal catalyst array patterned samples for various geometries and ~0.27-1 μS for the nanowriting samples. In addition, compact
models have been used to gain insights into the device performance and the unique
advantages of the hexagonal array approach over devices fabricated using parallel or
randomly distributed SWCNTs. Device performance appears to be determined primarily by the contact resistance which includes both Schottky barrier resistances and an interface resistance.
In summary, colloidal lithography and direct-writing of single-walled carbon nanotube catalyst have been used to achieve the controlled growth and assembly of
carbon nanotubes. Electronic transport of carbon nanotube devices fabricated using these two methods showed near ohmic behavior with device performance modeled primarily
by the contact resistance. The approaches developed in this thesis allow nanoscale control over catalyst deposition and nanotube growth which makes them promising for the fabrication of future carbon nanotube electronic devices.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/2002 |
| Date | 17 December 2009 |
| Creators | Omrane, Badr |
| Contributors | Papadopoulos, Christo |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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