Single-walled carbon nanotubes (SWNTs) exhibit extraordinary properties: mechanical, thermal, optical and, possibly the most interesting, electrical. These all-carbon cylindrical structures can be metallic or semi-conducting depending on their precise structure. They have the potential to allow faster transistor switching speeds and smaller, more closely-packed interconnects in microelectronics. However, such applications are hindered by the difficulties of positioning the correct type of SWNT in a spatially precise location and orientation. In addition, greater understanding of the fundamental limits of SWNTs, such as the limit of current density, is needed for optimum operation in applications. The primary aim of this project was to increase the understanding of current density limitation by using in situ plasmonically enhanced Raman spectroscopy during electrical transport. The use of plasmonic metal nanostructures to enhance the Raman scattering should allow the acquisition of informative spectra from SWNTs away from their intrinsic resonance conditions. To achieve this aim, SWNTs must be integrated with plasmonic metal structures as well as electrical connections. This thesis presents two approaches for the integration of SWNTs with other nanometre-scaled features, in particular plasmonic nanoparticles. Fountain pen nanolithography uses a hollow nanopipette in place of the probe tip in an atomic force microscope (AFM), through which material can be delivered to a spatially precise position on a surface. Aqueous SWNT dispersion was delivered to chemically-functionalised silicon in this way, through pulled quartz pipettes with aperture diameters of 50 nm, 100 nm and 150 nm. The heights, widths and continuity of lines drawn on the surface by the nanopipette depended on the size, setpoint and lateral speed of the tip. A small bias voltage applied between the SWNT dispersion inside the pipette and the substrate allowed the deposition to be switched on or off depending on the polarity of the voltage, through the action of electroosmotic effects within the quartz capillary. The quality and density of the SWNT dispersion was found to be important for successful deposition to occur, since too low a concentration results in the lines deposited from the pipette being only surfactant but too high a concentration of bundles would quickly block the small tip of the pipette. Polarised Raman spectroscopy on SWNT deposited by fountain pen nanolithography showed that they had a high level of alignment parallel to the direction in which the pipette moved. Spherical gold nanoparticles with plasmonic properties suitable for enhancing Raman scattering were dropped onto samples containing individual SWNTs supported on a Si/SiO2 surface. Nanomanipulation with an atomic force microscope was used to push the gold nanoparticles onto the SWNTs. Raman spectra measured with and without the gold particles showed that the gold nanoparticles gave local enhancement factors of 24 for a single 150 nm nanoshell and 130 for a small cluster of 150 nm nanoshells. Polarised Raman studies on the cluster showed that the angle dependence deviated significantly from that expected of a bare SWNT. Electrical transport experiments with in situ plasmonically enhanced Raman spectroscopy may be performed on samples prepared from the methods described here. Such experiments would increase understanding of the electrical properties of SWNTs and how they relate to the vibrational and optical properties.

Lead-tin solder has been widely used as interconnection material in electronics packaging for a long time. In response to environmental legislation, the lead-tin alloys are being replaced with lead-free alloys and electrically conductive adhesives in consumer electronics. Lead-free solder usually require higher reflow temperatures than the traditional lead-tin alloys, which can cause die crack and board warpage in assembly process, thereby impacting the assembly yields. The high tin content in lead-free solder forms tin whiskers, which has the potential to cause short circuits failure. Conductive adhesives are an alternative to solder reflow processing, however, conductive adhesives require up to 80 wt% metal filler to ensure electrical and thermal conductivity. The high loading content degrades the mechanical properties of the polymer matrix and reduces the reliability and assembly yields when compared to soldered assemblies. Carbon nanotubes (CNTs) have ultra high aspect ratio as well as many novel properties. The high aspect ratio of CNTs makes them easy to form percolation at low loading and together with other novel properties make it possible to provide electrical and thermal conductivity for the polymer matrix while maintaining or even reinforcing the mechanical properties. Replacing the metal particles with CNTs in conductive adhesive compositions has the potential benefits of being lead free, low process temperature, corrosion resistant, electrically/thermally conductive, high mechanical strength and lightweight. In this paper, multiwall nanotubes (MWNTs) with different dimensions are mixed with epoxy. The relationships among MWNTs dimension, volume resistivity and thermal conductivity of the composite are characterized. Different loadings of CNTs, additives and mixing methods were used to achieve satisfying electrical and mechanical properties and pot life. Different assembly technologies such as pressure dispensing, screen and stencil printing are used to simplify the processing method and raise the assembly yields. Contact resistance, volume resistivity, high frequency performance, thermal conductivity and mechanical properties were measured and compared with metal filled conductive adhesive and traditional solder paste.

For two decades, single-wall carbon nanotubes (SWCNTs) have captured the attention of the research community, and become one of the flagships of nanotechnology. Due to their remarkable electronic and optical properties, SWCNTs are prime candidates for the creation of novel and revolutionary electronic, medical, and energy technologies. However, a major stumbling block in the exploitation of nanotube-based technologies is the lack of control of nanotube structure (chirality) during synthesis, which is intimately related to the metallic or semiconductor character of the nanotube. Incomplete understanding of the nanotube growth mechanism hinders a rationale and cost-efficient search of experimental conditions that give way to structural (chiral) control. Thus, computational techniques such as density functional theory (DFT), and reactive molecular dynamics (RMD) are valuable tools that provide the necessary theoretical framework to guide the design of experiments. The nanotube chirality is determined by the helicity of the nanotube and its diameter. DFT calculations show that once a small nanotube 'seed' is nucleated, growth proceeds faster if the seed corresponds to a high chiral angle nanotube. Thus, a strategy to gain control of the nanotube structure during chemical vapor deposition synthesis must focus on controlling the structure of the nucleated nanotube seeds. DFT and RMD simulations demonstrate the viability of using the structures of catalyst particles over which nanotube growth proceeds as templates guiding nanotube growth toward desired chiralities. This effect occurs through epitaxial effects between the nanocatalyst and the nanotube growing on it. The effectiveness of such effects has a non-monotonic relationship with the size of the nanocatalyst, and its interaction with the support, and requires fine-tuning reaction conditions for its exploitation. RMD simulations also demonstrate that carbon bulk-diffusion and nanoparticle supersaturation are not needed to promote nanotube growth, hence reaction conditions that increase nanoparticle stability, but reduce carbon solubility, may be explored to achieve nanotube templated growth of desired chiralities. The effect of carbon dissolution was further demonstrated through analyses of calculated diffusion coefficients. The metallic nanocatalyst was determined to be in viscous solid state throughout growth, but with a less solid character during the induction/nucleation stage.

Strain detecting with carbon nanotube (CNT) networks is one of the encouraging findings in sensor technologies. Two types of CNT based films are available for strain detection, namely CNT composite films and CNT films. Configurations of the CNT networks in these films can be made into random and aligned distributions. Understanding of fundamental knowledge regarding piezoresistive response in CNT networks in particular of the CNT film is not quite available, and this is the motivation of the present thesis. In this thesis, piezoresistive response of CNT networks under in-plane straining was studies in details first. Based on the stick percolation model, the relation between the density and conductance in CNT networks (with randomly distributed) was established and then the models which describe the relation between the density and piezoresistive sensitivity and the relation between density and piezoresistive linearity, respectively, were developed. After that, fabrication of CNT networks with aligned distributions was studied. Likewise, the models as developed for CNT network with random distributions were developed for ones with aligned distributions. Finally, modeling of the stress transfer between the nanotubes and polymer matrix was studied. This study has led to the following conclusions: (1) piezoresistive response in CNT networks of the CNT film follows the stick percolation model with the critical exponent coefficient (α) in the model being 1.938; (2) it is feasible to fabricate aligned CNT networks of varying densities with the technique which combines the spray deposition and externally applied magnetic field; (3) the configuration of CNT networks, in addition to their density, was a primary factor governing their piezoresistive response; (4) slipping occurs at the interface between the nanotube and polymer matrix when the films are subject to in-plane straining. The contributions of this study are: (1) the knowledge along with a percolation model for piezoresistive response of CNT networks of the CNT film, (2) a fabrication technique to align CNT networks of the CNT film, and (3) the knowledge along with a model for interaction between the CNT and polymer substrate in the CNT film.

This thesis focuses on two of the major challenges of carbon nanotube (CNT) research: understanding the growth mechanism of nanotubes by chemical vapour deposition (CVD) and the positioning of nanotubes on surfaces. The mechanism of growth of single–walled nanotubes (SWNTs) has been studied in two ways. Firstly, a novel iron nanoparticle catalyst for the production of single–walled nanotubes was developed. CVD conditions were established that produced high quality tubes. These optimised CVD conditions were then used as the basis of several comparative CVD experiments showing that the quality of nanotubes and the yield of carbon depended on the availability of carbon to react. The availability could be controlled by the varying concentration of methane in the gas phase or the residence time of the methane over the catalyst. Evidence is presented that the diameters of the tubes produced were affected by the availability of methane. A second mechanistic investigation was carried out to study the validity of the previously proposed ring addition mechanism for the growth of carbon nanotubes from camphor. In this mechanism, the formation of tubes is thought to occur through the addition of preformed carbon rings: so it would be expected that there would be a relationship between the molecular structure of the precursor and the resulting SWNTs. To explore this relationship, comparative CVDs were carried out to produce SWNTs with several different cyclic and acyclic compounds similar in structure to camphor. The vapour pressure and the chemical stability of the precursor were found to be important to the formation of nanotubes, while the compound’s structure was not related to the quality of tubes produced. The lack of a relationship between the structure of the precursor and the production of SWNTs suggests that preformed rings are not vital to the production of SWNTs. Differences in the growth of SWNT from benzene and methane were related to the stability of each compound. In particular, differences in the distributions of the diameters of the tubes formed from methane and benzene have been observed. These differences have been explained in terms of the relative kinetic stabilities of these molecules, and in terms of a competition between end–cap and sidewall growth. Positioning of nanotubes on surfaces has been explored using two approaches. In the first approach, commercially obtained SWNTs were functionalized by a sulfur plasma so that the products would form bonds with gold surfaces. The nanotubes were found to selectively deposit themselves onto gold surfaces from ethanolic dispersions of the functionalized samples. This selective deposition of the nanotubes allowed the production of prototype carbon nanotube field–effect transistors with higher device yields than were obtained with unfunctionalized tubes. In a second approach to positioning of carbon nanotubes, the growth of tubes on surfaces by CVD was explored. Iron nitrate and different magnesium compounds were dip–coated onto SiO2 surfaces so that MgO supported–Fe catalysts would be formed by calcination. SWNTs were grown on the surfaces by CVD. Surface area measurements of the equivalent powdered catalysts showed that a high surface area was vital to produce dense growth of high quality SWNTs. The morphology of the surface was also found to play a key role in the growth of the tubes. Patterned growth of carbon nanotubes was accomplished using soft lithography techniques to control the localization of catalyst deposition onto a surface. A long calcination step (10 h, 950 °C) before CVD, was found to improve the quality of nanotubes grown. Catalysts that had been calcined for 10 hours were also found to produce smaller diameter nanotubes than uncalcined samples. The formation of smaller diameter tubes was explained in terms of the formation of MgFe2O4 alloys, consistent with results reported previously in the literature. In addition, Raman spectroscopy of the calcined catalysts with 3% w/w loadings of Fe was used to confirm directly the presence of MgFe2O4.

This dissertation describes research into the synthesis of carbon nanotubes using traditional organic synthetic methods, as well as work on the fragmentation of β-hydroxy-α-diazoesters with a γ-hetero group and applications of their reactivity towards natural product synthesis. Carbon nanotubes are unique structures that can exhibit different electronic properties based on their chiral vector, and are a potential future source of semiconductors. Current methods of synthesis are unable to be adapted to commercial synthesis, providing the opportunity for the application of organic synthetic methods to generate them more uniformly and on a larger scale. The generation of tethered aldehyde ynoates and their utilization in 1,3-dipolar cycloadditions has been well developed by the Brewer group. Traditionally they have been generated from γ-siloxy-β-hydroxy-α-diazoesters, herein we explore utilizing an amino group as the fragmentation initializer. Additionally, application of the tethered aldehyde ynoate towards the synthesis of the natural products Demissidine and Aspidospermine are discussed.

Thesis advisor: Lawrence T. Scott / The Scott lab is interested in the functionalization of corannulene as a building block for large polycyclic aromatic hydrocarbons and carbon nanotube end-cap precursors. Toward that end, a new approach to the direct five-fold borylation of corannulene with iridium (I) catalysts via C-H activation has been explored. It has been discovered that the addition of catalytic amounts of base to the reaction mixture promotes the formation of symmetrical penta-borylated corannulene in a good yield on a sizable scale. All byproducts can be easily removed with iterative methanol washes. The present work also provides proof of the reversibility of the direct borylation reaction under the conditions used. Furthermore, modified Suzuki-Miyaura conditions have been employed to synthesize pentakis(2,6-dichlorophenyl)corannulene, a precursor for a [5,5] carbon nanotube end-cap. The reported reactions provide good yields and are scalable. / Thesis (MS) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Episódios de contaminação envolvendo hidrocarbonetos de petróleo são relatados com bastante freqüência, principalmente em função dos acidentes envolvendo transporte e estocagem de combustíveis, dentre os quais se destacam o benzeno, tolueno, etilbenzeno e xileno (BTEX). Assim, não é surpreendente o grande número de trabalhos, atualmente disponíveis, relacionados à remediação de águas subterrâneas. Entretanto, é conhecido que a total mineralização de benzeno, na maioria das tecnologias utilizadas para remediação de solos e águas subterrâneas, não ocorre totalmente podendo formar compostos fenólicos altamente tóxicos. Por este motivo, este trabalho teve por finalidade a análise dos subprodutos formados a partir da degradação do benzeno, que são eles: hidroquinona, resorcinol, catecol, fenol, p-benzoquinona. Para este propósito, os compostos fenólicos formados foram medidos utilizando um eletrodo de carbono vítreo modificado com filme de nanotubos de carbono e ftalocianinas metalicas. Os compostos fenólicos também foram analisados por cromatografia liquida de alta eficiência com detector espectrofotométrico, espectrometria no UV/Visível. Os sensores eletroquímicos propostos mostraram-se altamente eletrocatalíticos e sensíveis na determinação dos derivados da oxidação do benzeno, obtendo-se um limite de detecção de 4,54 μmol L-1 para a hidroquinona, de 1,63 μmol L-1 para o resorcinol, 0,14 μmol L-1 para o catecol, 4,19 μmol L-1 para o fenol e 1,78 μmol L-1 para a p-benzoquinona. Observa-se que existem algumas diferenças nos limites de detecção para cada composto fenólico estudado e que o eletrodo GC/MWCNT/CoPc apresentou menores limites de detecção para o catecol, resorcinol e p-benzoquinona podendo analisar predominantemente esses compostos fenólicos a partir da eletro-oxidação do benzeno. A metodologia proposta comparada com os métodos oficiais de análise e foi observado que os sensores atingem os limites mínimos necessários de detecção, demonstrando que sensores eletroquímicos baseados em CNTs tornam-se uma alternativa no desenvolvimento de metodologias altamente sensíveis, rápidas e de baixo custo. / Contamination episodes involving petroleum hydrocarbons are reported quite frequently, mainly because of accidents involving transportation and storage of fuels, among which stand out as benzene, toluene, ethylbenzene and xylene (BTEX). Thus, it is not surprising the large number of papers currently available relating to remediation of groundwater. However, it is known that the complete mineralization of benzene, most of the technologies used for remediation of soil and groundwater, it doesn\'t occur and it can form highly toxic phenolic compounds. For this reason, this paper aims to analyze the products formed from the degradation of benzene, which are: hydroquinone, resorcinol, catechol, phenol, p-benzoquinone. For this purpose, the phenolic compounds formed were measured using a glassy carbon electrode modified with a film of carbon nanotubes and metallic phthalocyanines. Phenolic compounds were also analyzed by high performance liquid chromatography with UV detection, spectroscopy in UV / Visible. The proposed electrochemical sensors were highly sensitive and the electrocatalytic determination of the oxidation of benzene derivatives, obtaining a detection limit of 4.54 μmol L-1 for hydroquinone, 1.63 μmol L-1 for resorcinol , 0.14 μmol L-1 for catechol, 4.19 μmol L-1 for phenol and 1.78 μmol L-1 for p-benzoquinone. It is observed that there are some differences in detection limits for each phenolic compound studied and the electrode GC/MWCNT/CoPc had lower detection limits for catechol, resorcinol and p-benzoquinone can analyze these phenolic compounds predominantly from the electro- oxidation of benzene. The proposed methodology was compared with the official methods of analysis and it was observed that the sensors reach the required minimum limits of detection, demonstrating that electrochemical sensors based on CNTs become an alternative for the development of high sensitivity, rapid and low-cost. methodologies.

This thesis has investigated several complex situations that may be encountered in electrochemical studies. Three main situations have been examined, they include the formation of polymer films on electrode surfaces during measurements, a novel nanocatalyst modified electrode surfaces, and organised carbon nanotube (CNT) structures on electrode surfaces. These have been utilised for different electrochemical applications owing to their dissimilar properties. Voltammetric techniques of cyclic voltammetry (CV), square wave voltammetry (SWV) and Fourier transformed large amplitude ac voltammetry (FTACV) have been utilised to examine these reactions. Chapter 3 reports the investigation of catechol oxidation and subsequent polymerisation through crosslinking with D-glucosamine or chitosan. Hydrogel can be formed on the electrode surface during the process, which changes the viscosity of the solution and thus affects the diffusion of chemical species. This process has been examined by several voltammetric techniques. A further examination of the chemical system has also been conducted using FTACV for the first time. Chapter 4 describes the preparation of carbon microsphere supported molybdenum disulfide. The material has been utilised as electrocatalysts for hydrogen evolution reaction (HER) in acidic media, and the performance tested by traditional linear sweep voltammetry (LSV) and advanced FTACV techniques. The FTACV technique has been used for the first time for HER processes. In addition, the synthesised particles have also been used for thermal catalytic decomposition of hydrogen sulfide, which shows a significant improvement in the conversion rate over conventional examples. Chapter 5 demonstrates the direct growth of vertically aligned CNT forests on a gold electrode. The electrochemical response of the fabricated electrode has also been examined with ferrocyanide as the redox species. Furthermore, the immobilisation of anthraquinone onto CNT forest has been attempted. The fabricated electrode was utilised as a pH sensor via CV and SWV, and both indicates a well correlated pH-potential relationship in the pH range of 2 to 12. The sensor has also been assessed by the FTACV technique.

Extrapolating the properties of individual carbon nanotubes (CNTs) into macro-scale CNT materials using a continuous and cost effective process offers enormous potential for a variety of applications. The floating catalyst chemical vapour deposition (FCCVD) method discussed in this dissertation bridges the gap between generating nano- and macro-scale CNT material and has already been adopted by industry for exploitation. A deep understanding of the phenomena that occur within the FCCVD reactor and how to control the formation of the catalyst nanoparticles is, therefore, essential to producing a desired CNT product and successfully scaling up the FCCVD process. This dissertation connects information on the decomposition of reactants, axial catalyst nanoparticle dynamics and the morphology of the resultant CNTs and demonstrates how these factors are strongly related to the temperature and chemical availability of reactants within the reactor. For the first time, in-situ measurements of catalyst particle size distributions paired with reactant decomposition profiles and detailed axial SEM studies of formed CNT materials revealed specific temperature domains that have important implications for scaling up the FCCVD process. A novel observation was that the evaporation and re-condensation of catalyst nanoparticles results in the formation, disappearance and reformation of the nanoparticles along the reactor axis. The combined influences of pyrolytic carbon species and catalytic nanoparticles are shown to influence CNT aerogel formation. This work also examines the source of carbon in the formed CNTs and the location of aerogel formation. Axial measurements using isotopically-labelled methane (C13H4) demonstrate that carbon within all CNTs is primarily derived from CH4 rather than some of the early-forming CNTs being predominantly supplied with carbon from decomposed catalytic precursor components. Quantification of CNT production along the axis of the reactor dispels the notion that injection parameters influence CNT formation and shows that bulk CNT formation occurs near the reactor exit regardless of the carbon source (CH4, toluene or ethanol). By supplying carbon to different reactor locations, it was discovered that CNT aerogel formation will occur even when carbon is delivered near the exit of the reactor provided the carbon source reaches a temperature sufficient to induce pyrolysis (>1000°C). Furthermore, experimental studies that identify a new role of sulphur (S) in the CNT formation process are discussed in this work. Analogous to effects observed in other aerosol systems containing S, in the FCCVD reactor, S lowers the nucleation barrier of the catalyst nanoparticles and enhances not only CNT growth but catalyst particle formation itself. The new concept of critical catalyst mass concentration for CNT aerogel formation was identified by implementing the novel approach of completely decoupling catalyst particle formation from CNT aerogel production. Rather than aerogel formation being dependent on a critical particle number concentration and ideal sized catalyst nanoparticles at the entrance of the reaction furnace, it was identified that the important metric is instead a minimum critical catalyst mass concentration. Application of the principle using other catalyst precursors such as cobaltocene, with continuous CNT aerogel formation from cobalt based catalyst nanoparticles being reported for the first time, and iron-based nanoparticles from a spark generator, provides proof of the new principle’s robustness and ubiquity. In addition to the experimental studies above, theoretical studies have been carried out to understand the agglomeration occurring in a CNT aerosol. The agglomeration eventually leads to a gas phase synthesized CNT aerogel at the end of the reactor, which can be collected and spun continuously. The results of this work are not only scientifically interesting, they also provide a strong foundation for further research aimed at optimizing and controlling large-scale CNT reactors by modifying downstream dynamics.