Single-walled carbon nanotube conductive thin films
Lipscomb, Leonard David
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This research focuses on the following two criteria concerning single-walled carbon nanotube (SWNT) thin films: morphological control and electrical characterization. Various types of morphological control has been achieved by utilizing the following three unique deposition techniques: bubble paint coat and dry (BPCAD), limited puddle spin (LPS), and bubble paint spin (BPS). The BPCAD method results in dense uniform coatings of bundled SWNTs. It has been observed that subsequent BPCAD deposition cycles result in thicker tube bundles as well as a rougher thin film. The LPS method has three distinctive deposition zones within the droplet or puddle used in this technique. The three deposition zones include the center, the outer band and the edge. These zones generate randomly oriented curved morphologies, tightly packed monolayer morphologies, and particulate morphologies, respectively. The BPS method provides for well dispersed random networks of SWNTs with the network density being directly related to the number of BPS deposition cycles as well as to the SWNT concentration of the suspension. Various tunable electrical characteristics are obtainable using these three deposition methods. The BPCAD technique allows for low sheet resistance (10 kΩ) SWNT thin films with single deposition cycles. Electrically the LPS deposition method is observed to be most useful in the outer band zone as this area results in monolayer sheets of tubes with sheet resistances in the MΩ range for single deposition cycles. Tunable sheet resistances ranging from MΩ to kΩ are observed when LPS depositions are repeated atop the same puddle footprint on a substrate. A capacitance effect is observed when the concentric puddle LPS method is used. The BPS method has been effectively demonstrated to fabricate thin films with tunable sheet resistance as well as tunable semiconductive properties. This method has been used to generate tunable sheet resistances ranging from the MΩ range to the kΩ range. When used in the Schottky barrier field effect transistor (SBFET) design these networks are shown to have tunable semiconductive response with a maximum observed drain current on to off ratio of 2.5 X 105. All these methods are ambient condition methods which utilize fundamental wetting and spreading dynamics of surfactant based SWNT suspensions and represent a foundational effort for future use with flexible transparent polymer substrates.