Single-walled carbon nanotubes (SWNTs), with their superior combination of electrical and mechanical properties, have drawn attention from many researchers for potential applications in electronics. Many SWNT-based electronic device prototypes have been developed including transistors, interconnects and flexible electronics. In this thesis, a fabrication method for patterned SWNT networks and devices based on colloidal lithography is presented. Patterned SWNT networks are for the first time formed via solution deposition on a heterogeneous surface. This method demonstrates a simple and straight-forward way to fabricate SWNT networks in a controllable manner.
Colloidal sphere monolayers were obtained by drop-casting from solution onto clean substrates. The colloidal monolayer was utilized as a mask for the fabrication of patterned SWNT networks. SWNT networks were shown to be patterned either by depositing SWNT solutions on top of a colloidal monolayer or by depositing a mixed SWNT-colloidal sphere aqueous suspension on the substrates. Colloidal monolayers were examined by optical microscopy and it was found that the monolayer quality can be affected by the concentration of colloids in solution. Polystyrene colloidal solution with concentration of 0.02 wt% ~ 0.04 wt % was found optimal for maximum coverage of colloidal monolayers on SiO2 substrates. After removing the colloidal spheres, the topology of the patterned SWNT networks was characterized by atomic force microscopy and scanning electron
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microscopy. Two-dimensional ordered arrays of SWNT rings and SWNTs interconnecting the SWNT rings were observed in the resulting network structure. The height of the rings was about 4-10 nm and the diameter was about 400 nm. In some samples, mesh-like patterned SWNT networks are also observed. It is hypothesized that the capillary forces induced by Van der Waals interaction at liquid/air/solid interfaces play an important role during the formation of the patterned SWNT networks. Raman spectroscopy was also employed to identify the chirality and diameter of the SWNTs in the networks. Both metallic and semiconducting SWNTs were found in the networks and the diameter of the SWNTs was about 1 to 2 nm.
The electrical properties of SWNT networks, including random SWNT networks, partially patterned SWNT networks and fully patterned SWNT networks were characterized by a probe station and a Keithley 4200 semiconductor measurement system. The random SWNT networks had two-terminal resistance varying between several MΩ to several hundred MΩ. Field effect behavior was observed in some devices with relatively high resistance and nonlinear I-V curves. Those devices had on/off ratio of less than 100. There was significant leakage current in the ―off‖ state likely due to metallic tube pathways in the networks. The partially patterned SWNT networks had resistance that varied from 20 KΩ to 10 MΩ, but did not display field effect behavior in our studies.
The resistance of the patterned SWNT networks was about 10 MΩ - 100 MΩ. The electrical characteristics of the patterned SWNT networks as thin film transistors were investigated, and the on/off ratio of the devices varied from 3 to 105. The upper limit of mobility in the devices was about ~ 0.71 – 5 cm2/V·s. The subthreshold slope of patterned SWNT network FETs can be as low as 210 meV/dec. / Graduate / 0544
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/5659 |
| Date | 03 September 2014 |
| Creators | Chen, Yingduo |
| Contributors | Papadopoulos, Christo |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web, http://creativecommons.org/publicdomain/zero/1.0/ |
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