Suc Chiu Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 57-60). / Abstracts in English and Chinese. / TITLE PAGE --- p.i / THESIS COMMUTE --- p.ii / ABSTRACT (English) --- p.iii / ABSTRACT (Chinese) --- p.iv / ACKNOWLEDGMENTS --- p.v / TABLE OF CONTENTS --- p.vi / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.ix / Chapter CHAPTER ONE --- General introduction and methodology / Chapter 1.1 --- General introduction --- p.1 / Chapter 1.2 --- Approximation in ab initio calculation --- p.4 / Chapter 1.2.1 --- Born-Oppenheimer approximation --- p.5 / Chapter 1.2.2 --- Density function theory (DFT) --- p.6 / Chapter 1.2.3 --- Periodic supercell approach for solid reaction --- p.8 / Chapter 1.2.4 --- Pseudopotential approximation --- p.11 / Chapter CHAPTER TWO --- "Adsorption of N02 molecules on zigzag (6,0) and (8,0) single-walled carbon nanotubes (SWNTs)" / Chapter 2.1 --- Introduction --- p.15 / Chapter 2.2 --- Computational details --- p.17 / Chapter 2.3 --- Resultsand discussion --- p.19 / Chapter 2.3.1 --- "Adsorption of a single N02 on (6,0) SWNT" --- p.19 / Chapter 2.3.2 --- "Adsorption of a second N02 on (6,0) SWNT" --- p.22 / Chapter 2.3.3 --- "Comparison of NO2 adsorptions on (8,0) SWNT with different cutoff energies" --- p.25 / Chapter 2.3.4 --- "Adsorption of more N02 on a (8,0) SWNT" --- p.28 / Chapter 2.4 --- Summary --- p.34 / Chapter CHAPTER THREE --- Diameter dependence for the adsorption of N02 molecules on zigzag single-walled carbon nanotubes (SWNTs) (n=6~12) / Chapter 3.1 --- Introduction --- p.35 / Chapter 3.2 --- Computational method --- p.37 / Chapter 3.3 --- Results and discussion --- p.38 / Chapter 3.3.1 --- Adsorption of a single N02 on SWNT --- p.38 / Chapter 3.3.2 --- Adsorption of a second on N02 SWNT --- p.40 / Chapter 3.3.3 --- Electronic structures of SWNTs after NO2 adsorption --- p.42 / Chapter 3.4 --- Summary --- p.55 / References --- p.57

Carbon nanotubes (CNTs) have been extensively studied for their electrical and mechanical properties since its discovery. Owing to their minute dimensions, good mechanical, electrical and chemical properties, different groups started to utilize CNTs as nano sensors or actuators for different applications in nanoelectronic or nano-electro-mechanical systems (NEMS). In order to build practical CNTs based devices, fast and batch techniques to build them have to be developed. To manipulate these nano-sized tubes, atomic force microscopy (AFM) is typically used to manipulate each of them one-by-one. However, this is time-consuming and unrealistic for batch fabrication. In this dissertation, dielectrophoretic manipulation of carbon nanotubes was employed to rapidly and batch fabricate practical nano sensors. The proposed technology will potentially enable fully automated assembly of CNTs based devices. We have also shown that this electrokinetic based manipulation technique is compatible with room-temperature MEMS fabrication processes, and hence, MEMS structures embedded with carbon nanotubes sensing elements can be built. This encapsulation process ensures that the multi-walled carbon nanotubes (MWNTs) elements can be protected from moisture and contaminates in an operational environment, and thus, allows the sensors to be useful for potential applications such as temperature measurement in water, sensing human touch and body temperature, or as ultra-sensitive sensors in manufacturing plants. Different structures of the polymer thin films embedded CNTs sensors were designed and fabricated on silicon and polymer substrates and also integrated to polymer diaphragm and microfluidic channel for micro and nano scale sensing. In this work, CNTs were found as a novel sensing elements for ultra-low-power micro thermal, fluid-flow and piezoresistive pressure sensors---which may serve as alternative sensors for silicon based sensors when bio-compatibility and low-cost applications are required. / Fung Kar Man. / "August 2005." / Adviser: Wen Tung Li. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4058. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 91-98). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Balaji Panchapakesan, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

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Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

In this thesis, I present studies in the field of terahertz [THz] spectroscopy. It covers both the generation and detection of ultra-fast broadband THz pulses, as well as the transmission properties of vertically grown multi-walled carbon nanotube forests [MWCNTs]. We have found that these vertically grown MWCNTs respond strongly to THz radiation and exhibit an anisotropic optical response. The analysis done was a simplified model that is frequency-indepedent, which led to discrepancies between the theoretical and experimental data. This suggests that the response of the CNTs is frequency-dependent, and further, more complex analysis is required to fully describe their properties. / Graduation date: 2013

Carbon nanotubes (CNTs) discovered at 1991 have attracted great interest for applications in Nano-Electro-Mechanical-Systems (NEMS). However, the search for methods to join CNTs with metallic parts has been a worldwide challenge. Many efforts have been devoted to manipulating individual CNTs and joining them to each other. Joining processes so far attempted are premature and fall short of efficiency for joint quality evaluation. Thus, it has been found necessary to work on macro CNTs strands which are easy to handle via macro joining techniques. In this study, vacuum brazing technology has been developed for joining macro CNTs strands with Ni using a Ti-Ag-Cu alloy. The brazing mechanism has been confirmed as due to TiC formation at the CNTs/Ti-Ag-Cu interface. To evaluate this novel vacuum brazing technique for CNTs joining, the temperature effect on the brazing mechanism, microstructure and stoichiometry at joint interface needed to be understood. Firstly, the influence of temperature (from room temperature to 1000C) on mechanical behaviour of CNTs was well examined. The ultimate tensile strength (UTS) of CNTs was measured to be a maximum at 900C. Then, the mechanical performance of the joints was investigated from 850C to 1000C, and the fracture modes of the joints were identified. The UTS of joint also achieves maximum at 900C. Below 900C, due to little TiC formation, the bonding is weak thus leading to interfacial fracture. Above 900C, due to much TiC formation, the bonding is strong thus resulting in CNTs fracture. Furthermore, the vacuum brazing technique was applied to join CNTs to Ni contact wires used as a lamp filament. Compared to the filament joined by Ag paste or mechanical connection, the illumination of the brazed CNTs filament was stronger. The current density of the brazed filament was superior to the Ag paste connected filament. This may represent a promising way to produce energy saving lamps.

Carbon nanotubes (CNTs) discovered at 1991 have attracted great interest for applications in Nano-Electro-Mechanical-Systems (NEMS). However, the search for methods to join CNTs with metallic parts has been a worldwide challenge. Many efforts have been devoted to manipulating individual CNTs and joining them to each other. Joining processes so far attempted are premature and fall short of efficiency for joint quality evaluation. Thus, it has been found necessary to work on macro CNTs strands which are easy to handle via macro joining techniques. In this study, vacuum brazing technology has been developed for joining macro CNTs strands with Ni using a Ti-Ag-Cu alloy. The brazing mechanism has been confirmed as due to TiC formation at the CNTs/Ti-Ag-Cu interface. To evaluate this novel vacuum brazing technique for CNTs joining, the temperature effect on the brazing mechanism, microstructure and stoichiometry at joint interface needed to be understood. Firstly, the influence of temperature (from room temperature to 1000C) on mechanical behaviour of CNTs was well examined. The ultimate tensile strength (UTS) of CNTs was measured to be a maximum at 900C. Then, the mechanical performance of the joints was investigated from 850C to 1000C, and the fracture modes of the joints were identified. The UTS of joint also achieves maximum at 900C. Below 900C, due to little TiC formation, the bonding is weak thus leading to interfacial fracture. Above 900C, due to much TiC formation, the bonding is strong thus resulting in CNTs fracture. Furthermore, the vacuum brazing technique was applied to join CNTs to Ni contact wires used as a lamp filament. Compared to the filament joined by Ag paste or mechanical connection, the illumination of the brazed CNTs filament was stronger. The current density of the brazed filament was superior to the Ag paste connected filament. This may represent a promising way to produce energy saving lamps.

A comparative study was conducted to determine whether it would be advantageous to grow carbon nanotubes on the bottom surface of anisotropically-etched silicon microchannels to facilitate greater heat removal in electronic cooling applications. The effect of the samples was evaluated based on the fluid temperature rise through the channels, the silicon surface temperature increase above ambient, and the pressure drop. The height and deposition pattern of the nanotubes were the parameters investigated in this study. The working fluid, water, was passed through the microchannels at two different volumetric flow rates (16 mL/min and 28 mL/min). Additionally, two different heat fluxes were applied to the backside of the microchannel (10 W/cm2 and 30 W/cm2). Extensive validation of the baseline channels was carried out using a numerical model, a resistor network model, and repeatability tests. Finally, the maximum enhancement when using carbon nanotubes under single-phase, laminar, internal, forced convection was investigated using basic principles in regard to the additional surface area created by the carbon nanotubes, as well as their high thermal conductivity. For the devices tested, the samples with carbon nanotubes not only had a higher pressure drop, but also had a higher surface temperature. Therefore, the baseline samples had the best performance. Furthermore, based on a basic principles investigation, the increase to thermal performance gained by increasing the surface area with CNTs is overshadowed by the decrease in mass flow rate for a fixed pressure drop. The analysis suggests that the limiting factor for heat transfer in single-phase, laminar pressure driven flows is not convection heat transfer resistance, but the bulk resistance of the fluid.

Single walled carbon nanotube (SWNT)-based polymer nanocomposites have generated a lot of interest as potential multifunctional materials due to the exceptional physical properties of SWNTs. To date, investigations into the electromechanical response of these materials are limited. Previous studies have shown marginal improvements in the electromechanical response of already electroactive polymers (EAPs) with addition of SWNTs. However, in general, disadvantages of EAPs such as high actuation electric field, low blocked stress and low work capacity remain unaddressed. This dissertation targets a comprehensive investigation of the electromechanical response of SWNT-based polymer nanocomposites. Specifically, the study focuses on incorporating SWNTs in three polymeric matrices: a non-polar amorphous polyimide (CP2), a polar amorphous polyimide ((-CN) APB-ODPA), and a highly polar semicrystalline polymer (PVDF). In the first step, emergence of an electrostrictive response is discovered in the non-polar polyimide CP2 in the presence of SWNTs. Transverse and longitudinal electrostrictive coefficients are measured to be six orders of magnitude higher than those of known electrostrictive polymers like polyurethane and P(VDF-TrFE) at less than 1/100th of the actuation electric fields. Next, the effect of the polymer matrix on the electrostrictive response is studied by focusing on the polar (-CN) APB-ODPA. A transverse electrostriction coefficient of 1.5 m2/MV2 is measured for 1 vol percent SWNT- (-CN) APB-ODPA, about twice the value found for 1 vol percent SWNT-CP2. The high value is attributed to higher dipole moment of the (-CN) APB-ODPA molecule and strong non-covalent interaction between the SWNTs and (-CN) APB-ODPA matrix. Finally, polyvinylidene fluoride (PVDF) matrix is selected as a means to optimize the electrostrictive response, since PVDF demonstrates both a high dipole moment and a strong non-covalent interaction with the SWNTs. SWNT-PVDF nanocomposites fared better than SWNT-CP2 nanocomposites but had comparable response to SWNT-(-CN) APB-ODPA nanocomposites. This was attributed to comparable polarization in both the polar nanocomposite systems. To maximize the SWNT-PVDF response, SWNT-PVDF samples were stretched leading to increase in the total polarization of the nanocomposite samples and decrease in the conductive losses. However, the dielectric constant also decreased after stretching due to disruption of the SWNT network, resulting in a decrease of the electrostrictive response.