Novel Syntheses of Thermoelectric and Nanostructured Materials and a System for Purifying and Sorting Metallic and Semiconducting Single Walled Carbon Nanotubes in a Mixed Tube Suspension
Chi, Su chih
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The integration of materials science and engineering at the nanoscale has significant impact in many areas of science and technology. In this dissertation, I will present novel syntheses of lanthanum telluride thermoelectric materials, vertically-aligned nanowires, and nanoporous nickel membranes. I will also present a method that can collect industrially relevant quantity of purified and sorted metallic and semiconducting single-walled carbon nanotubes (SWCNTs) in a mixed-carbon nanotubes suspension by AC dielectrophoresis. In the Chapter 1: A Novel Approach to Synthesize Lanthanum Telluride Thermoelectric Materials, I will report on the electrochemical synthesis of lanthanum telluride thin films. The electrodeposition of lanthanum telluride thin films is performed in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bromide (EMIB), in ambient conditions. This novel procedure can serve as an alternative means of simple, inexpensive, and laboratory-environment friendly methods to synthesize rare-earth telluride thermoelectric materials that were difficult to make in aqueous solution. Characterization of the morphologies and chemical compositions of the deposited films using scanning electron microscopy (SEM), x-ray diffractometry (XRD), and energy-dispersive x-ray analysis (EDAX) will be presented. The Seebeck coefficient and electrical resistivity of deposited lanthanum telluride thin films will also be presented and compared with those of current state-of-the-art thermoelectric materials. In the Chapter 2: Synthesis and Characterization of Vertically-aligned Gold Nanowires Arrays Ferromagnetic Composite Films, I will report on the electrochemical synthesis of films composed of vertically-aligned gold nanowire arrays in ferromagnetic matrices (nickel and iron). This process involves first electrodepositing the Au nanowire arrays within commercially available anodic aluminum oxide (AAO) nanoporous membranes. After dissolving the templates, the ferromagnetic matrices are grown around the nanowires to produce the two-phase nanocomposites. In the Chapter 3: A Novel Approach to the Synthesis of Nanochanneled Nickel Films, I will report on an innovative technique to fabricate nickel nanochanneled membranes. This procedure involves transferring and imprinting the nanoporous arrays of the AAO membranes to a nickel film using a template-guided electrochemical etching technique. A detailed discussion of these processing techniques will be shown along with the characterization of the morphology of nickel nanochanneled membranes. Lastly, in the Chapter 4: Purification and Refinement of Single-Walled Carbon Nanotubes (SWCNTs) by AC Dielectrophoresis (DEP), a continuous flow device for purifying and sorting metallic and semiconducting SWCNTs from an initially random mixture of SWCNTs in suspension using AC dielectrophoresis is reported. The separation of two electronic types of SWCNTs takes advantage of the large difference of the relative dielectric constants between metallic and semiconducting SWCNTs with respect to the suspension, resulting in both a difference in magnitude and direction of a dielectrophoretic force imposed on the SWCNTs. This work presents a significant advancement in nanotubes purification in a facile and scalable manner, and can therefore significantly increase the feasibility of manufacturing reliable SWCNT-based nanoelectronic devices. A detailed discussion of the sorting techniques will be presented along with the fabrication of a dielectrophoretic force utilized microfluidic lab-on-a-chip device that can continuously refine and collect metallic and nonmetallic nanoparticles at industrially relevant processing rates. The effectiveness of the device is characterized using resonant Raman and ultraviolet–visible-near infrared (UV-Vis-NIR) spectroscopy analysis on sorted samples.