UBC Theses and Dissertations
Fabrication of carbon nanotube structures using dielectrophoresis Kashefian Naieni, Ali
Carbon nanotubes (CNTs) are promising materials for many applications due to their attractive electronic, optical, mechanical and thermal properties. Currently, the main challenge facing their widespread usage is the inability to fabricate nanotube devices reproducibly. Dielectrophoresis (DEP) is a versatile method for the fabrication of nanostructures from a solution. However, while this method offers advantages such as overall control over the positioning of the nanotubes and the possibility of pre-selecting the types of CNTs, there are many unknowns about how the process works, leading to unreliability and irreproducibility. Although there have been reports on different parameters affecting DEP results, some important factors such as the movement of the solution and the interactions among nanotubes during the process have often been neglected. This thesis presents a combination of experimental and modeling efforts to investigate the mechanisms at work during DEP. Experiments were performed to evaluate the influence of the conductivity of the solution. A framework based on finite-element method simulations was developed to unveil the mechanisms involved. The results showed that variations in the conductivity of the solution, leading to changes in electrothermal movements, could lead to substantial differences in the outcome. Higher levels of repeatability were achieved by using low-conductivity solutions. The mutual interactions of nanotubes during DEP were also investigated using both experiments and simulations; it was shown that these could lead to the formation of periodic patterns in the deposited nanotubes. Finally, a particle tracing simulation formalism was developed, allowing one to follow the CNTs in their journey from the solution to the substrate, taking into account several influential factors: the DEP force, the movement of the solution itself, and the Brownian movement of the CNTs. Metallic and semiconducting nanotubes were traced in various scenarios and the effective forces were explored every step of the way. The work reported in this thesis thus leads to a better understanding of the DEP process and the mechanisms involved in the deposition of nanotubes, and potentially that of other nano-objects, taking us a step closer to engineering reproducible processes for nano-device fabrication.
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