This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. In situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

The extraordinary properties of the single wall carbon nanotubes (SWCNTs) have stimulated an enormous amount of research towards the realization of SWCNT-based products for different applications ranging form nanocomposites to nanoelectronics. Their high charge mobility, exceedingly good current-carrying capacities and ability to be either semiconducting or metallic render them ideal building blocks for nanoelectronics. For nanoelectronic applications, either individual or parallel aligned SWCNTs are advantageous. Moreover, closely packed arrays of parallel SWCNTs are required in order to sustain the relatively large currents found in high frequency devices. Two key areas still require further development before the realization of large-scale nanoelectronics. They are the reproducible control of the nanotubes spatial position/orientation and chiral management. In terms of nanotube orientation, different techniques have been demonstrated for the fabrication of horizontally aligned SWCNTs with either post synthesis routes (e.g. dielectrophoresis and Langmuir-Blodgett approach) or direct growth (e.g. chemical vapor deposition (CVD)). The low temperature of the production process, allowing the formation of aligned nanotubes on pretty much any substrate, is the main advantage of the post synthesis routes, while the poor levels of reproducibility and spatial control, and the limited quality of the aligned tubes due to the inherently required process steps are limitations. The simplicity, up-scalability, along with the reproducible growth of clean high quality SWCNTs with well-controlled spatial, orientation and length, make CVD the most promising for producing dense horizontally well-aligned SWCNTs. These CVD techniques suffer some drawbacks, namely, that because they are synthesized using catalyst particles (metals or non-metals) the catalyst material can contaminate the tubes and affect their intrinsic properties. Thus, the catalyst-free synthesis of aligned SWNT is very desirable. This thesis comprises detailed and systematic experimental investigations in to the fabrication of horizontally aligned SWCNTs using both post growth (Dielectrophoresis) and direct growth (CVD) methods. Both catalyst-assisted and catalyst-free SWCNTs are synthesized by CVD. While metallic nanoparticles nucleate and grow SWCNTs, opened and activated fullerene structures are used for all carbon catalyst-free growth of single wall and double wall carbon nanotubes. The systematic studies allow for a detailed understanding of the growth mechanisms of catalyst and catalyst-free grown SWCNTs to be elucidated. The data significantly advances our understanding of horizontally aligned carbon nanotubes by both post synthesis alignment as well as directly as-synthesized routes. Indeed, the knowledge enables such tubes to be grown in high yield and with a high degree of special control. It is shown, for the first time, how one can grow horizontally aligned carbon nanotubes in crossbar configurations in a single step and with bespoke crossing angles. In addition, the transport properties of the aligned tubes at room temperature are also investigated through the fabrication of devices based on these tubes. / Die außergewöhnlichen Eigenschaften von einwandigen Kohlenstoffnanoröhren (engl. single wall carbon nanotubes, SWCNTs) haben bemerkenswerte Forschungsaktivitäten zur Verwirklichung von auf SWCNTs basierenden Anwendungen für verschiedene Bereiche, die von Nanokompositen bis hin zur Nanoelektronik reichen, stimuliert. Ihre hohe Ladungsträgermobilität und die außerordentlichen hohen Ladungsdichten, die in SWCNTs erreicht werden können sowie ihre Eigenschaft, entweder halbleitend oder metallisch zu sein, machen sie zu idealen Konstituenten von nanoelektronischen Schaltkreisen. Für Anwendungen in der Nanoelektronik sind entweder einzelne oder parallel angeordnete SWCNTs vorteilhaft. Darüber hinaus sind dicht gepackte Anordnungen von SWCNTs erforderlich, um die relativ hohen Ströme in Hochfrequenzbauelementen zu transportieren. Für eine erfolgreiche Realisierung von großskaligen nanoelektronischen Bauteilen, die auf SWCNTs basieren, sind noch zwei enorm wichtige Kernprobleme zu lösen, die weitere Forschungsanstrengungen erfordern: die reproduzierbare und verlässliche Kontrolle der räumlichen Positionierung und Orientierung der Nanoröhren sowie die Kontrolle der Chiralität der einzelnen SWCNTs. Hinsichtlich der Orientierung der Nanoröhren kann die horizontal parallele Ausrichtung von SWCNTs mit verschiedenen Techniken erreicht werden. Diese setzen entweder nach dem eigentlichen Wachstum der Röhren ein (Post-Synthese-Methoden wie z.B. Dielektrophorese oder Langmuir-Blodgett-Techniken) oder erreichen direkt während des Wachstums (z.B. durch Chemical-Vapor-Deposition-Methoden (CVD)) die parallele Anordnung. Durch die niedrigen Prozesstemperaturen, die während des Herstellungsprozesses erforderlich sind, erlauben die nach der eigentlichen Synthese stattfindenden Ausrichtungsmethoden die parallele Anordnung von Nanoröhren auf nahezu jedem Substrat, jedoch stellen die geringe Reproduzierbarkeit dieser Prozesse, die schwierige Kontrollierbarkeit der räumlichen Anordnung und die limitierte Qualität der ausgerichteten Röhren aufgrund der erforderlichen Prozessschritte natürliche Beschränkungen dieser Techniken dar. Die einfache Durchführung und ihre Skalierbarkeit, zusammen mit dem reproduzierbaren Wachstum qualitativ sehr hochwertiger SWCNTs mit hoher Kontrolle von räumlicher Anordnung, Orientierung und Länge machen die CVD-Methode zur erfolgversprechendsten Technik für die Herstellung von dichtgepackten hochparallelen horizontalen Anordnungen von SWCNTs. Diese CVD-Ansätze weisen jedoch auch einige Nachteile auf, die in den bei der Synthese verwendeten Katalysatorpartikeln (metallisch oder nicht-metallisch) begründet liegen, da das Katalysatormaterial die Röhren kontaminieren und dadurch ihre intrinsischen Eigenschaften beeinflussen kann. Daher ist eine katalysatorfreie Synthesemethode für ausgerichtete SWCNTs ein höchst erstrebenswertes Ziel. Die vorliegende Arbeit beschreibt detaillierte und systematische experimentelle Untersuchungen zur Herstellung von horizontalen, parallel ausgerichteten Anordnungen von SWCNTs unter Verwendung von Methoden, die sowohl nach dem eigentlichen Wachstum der Nanoröhren (Dielektrophorese) als auch während des Wachstums ansetzen (CVD). Bei den CVD-Methoden werden sowohl solche, die auf der Verwendung von Katalysatoren basieren, als auch katalysatorfreie Techniken verwendet. Während metallische Nanopartikel den Ausgangspunkt für das Wachstum von SWCNTs darstellen, werden geöffnete und aktivierte Fullerenstrukturen verwendet, um das katalysatorfreie Wachstum von reinen ein- oder mehrwandigen Nanoröhren zu erreichen. Die systematischen Untersuchungen ermöglichen ein tiefgehendes Verständnis der Wachstumsmechanismen von SWCNTs, die unter Verwendung von Katalysatoren oder katalysatorfrei erzeugt synthetisiert wurden. Die erzielten Ergebnisse erhöhen in einem hohen Maß das Verständnis der Herstellung von horizontal parallel angeordneten Nanoröhren, die durch Post-Synthese-Methoden oder direkt während des Wachstumsprozesses ausgerichtet wurden. Die erzielten Einsichten erlauben die Herstellung solcher Strukturen mit hoher Ausbeute und mit einem hohen Maß an räumlicher Kontrolle der Anordnung. Zum ersten Male kann ein Verfahren präsentiert werden, mit dem horizontal parallel angeordnete Nanoröhren in gekreuzten Strukturen mit wohldefinierten Kreuzungswinkeln hergestellt werden können. Zusätzlich werden die Transporteigenschaften von parallel ausgerichteten Nanoröhren bei Raumtemperatur, durch die Herstellung von auf den dargestellten Strukturen basierenden Bauelementen, untersucht.

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No description available.

Carbon nanostructures have been extensively used in different applications; ranging from electronic and optoelectronic devices to energy conversion. The interest stems from the fact that covalently bonded carbon atoms can form a wide variety of structures with zero-, one- and two-dimensional configuration with different physical properties. For instance, while fullerene molecules (zero-dimensional carbon structures) realize semiconductor behavior, two-dimensional graphene shows metallic behavior with exceptional electron mobility. Moreover the possibility to even further tune these fascinating properties by means of doping, chemical modification and combining carbon based sub-classes into new hybrid structures make the carbon nanostructure even more interesting for practical application.  This thesis focuses on synthesizing SWCNT and different C60 one-dimensional structures as well as tuning their properties by means of different chemical and structural modification. The purpose of the study is to have better understanding of the synthesis and modification techniques, which opens for better control over the properties of the product for desired applications. In this thesis carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD) on iron/cobalt catalyst particles. The effect of catalyst particle size on the diameter of the grown CNTs is systematically studied and in the case of SWCNTs it is shown that the chirality distribution of the grown SWCNTs can be tuned by altering the catalyst particle composition. In further experiments, incorporation of the nitrogen atoms in SWCNTs structures is examined. A correlation between experimental characterization techniques and theoretical calculation enable for precise analysis of different types of nitrogen configuration in SWCNTs structure and in particular their effect on growth termination and electronic properties of SWCNTs are studied. C60 one-dimensional structures are grown through a solution based method known as Liquid-liquid interfacial precipitation (LLIP). By controlling the crystal seed formation at the early stage of the growth the morphology and size of the grown C60 one-dimensional structures where tuned from nanorods to large diameter rods and tubes. We further introduce a facile solution-based method to photo-polymerize the as-grown C60 nanorods, and show that such a method crates a polymeric C60 shell around the nanorods. The polymeric C60 shell exhibits high stability against common hydrophobic C60 solvents, which makes the photo-polymerized nanorods ideal for further solution-based processing. This is practically shown by decoration of both as grown and photo-polymerized nanorods by palladium nanoparticles and comparison between their electrochemical activities. The electrical properties of the C60 nanorods are also examined by utilizing a field effect transistor geometry comprising different C60 nanorods. In the last part of the study a variant of CNT is synthesized in which large diameter, few-walled CNTs spontaneously transform to a collapsed ribbon shape structure, the so called collapsed carbon nanotube (CCNT). By inserting C60 molecules into the duct edges of CCNT a new hybrid structure comprising C60 molecules and CCNT is synthesized and characterized. A further C60 insertion lead to reinflation of CCNTs, which eventually form few-walled CNT completely filled with C60 molecules.

ABSTRACT PRODUCTION OF CARBON NANOTUBES BY CHEMICAL VAPOR DEPOSITION Ayhan, Umut BariS M.S., Department of Chemical Engineering Supervisor: Prof. Dr. G&uuml / ng&ouml / r G&uuml / nd&uuml / z Co-Supervisor: Assoc. Prof. Dr. Burhanettin &Ccedil / i&ccedil / ek July 2004, 75 pages Carbon nanotubes, which is one of the most attractive research subject for scientists, was synthesized by two different methods: Chemical vapor deposition (CVD), a known method for nanotube growth, and electron beam (e-beam), a new method which was used for the first time for the catalytic growth of carbon nanotubes. In both of the methods, iron catalyst coated silica substrates were used for the carbon nanotube growth, that were prepared by the Sol-Gel technique using aqueous solution of Iron (III) nitrate and tetraethoxysilane. The catalytic substrates were then calcined at 450 &deg / C under vacuum and iron was reduced at 500&deg / C under a flow of nitrogen and hydrogen. In CVD method the decomposition of acetylene gas was achieved at 600 &deg / C and 750 &deg / C and the carbon was deposited on the iron catalysts for nanotube growth. However, in e-beam method the decomposition of acetylene was achieved by applying pulsed high voltage on the gas and the carbon deposition on the silica substrate were done. The samples from both of the methods were characterized using transmission electron microscopy (TEM) and Raman spectroscopy techniques. TEM images and Raman spectra of the samples show that carbon nanotube growth has been achieved in both of the method. In TEM characterization, all nanotubes were found to be multi-walled carbon nanotubes (MWNT) and no single-walled carbon nanotubes (SWNT) were pictured. However, the Raman spectra show that there are also SWNTs in some of the samples.

Metal oxide thin films are dynamic materials that have revolutionised the nature of semiconductor and electronic thin film devices. Recently, progress has stagnated in some aspects due to the increasingly complex deposition apparatus required, and the dearth of suitable precursor complexes of certain ???difficult??? metals. This thesis seeks to address both of these issues. The application of a precursor complex, Mg6(O2CNEt2)12 to the SSCVD of MgO thin films delivered the highest quality films ever reported with this technique. The resultant films were found to be of purely (111) orientation. Due to the nature of the precursor, the chemical reactions occurring at the surface during SSCVD growth result in a high growth rate, low flux environment and films of (111) orientation have been achieved without the amorphous underlayer. This finding has important implications for buffer layers in perovskite thin film devices. The unprecedented precursor chemistry has been used as a basis for the extremely high quality material produced, along with the unusual, yet beneficial structural morphology it possesses. A new range of barium complexes with single encapsulating ligands have been prepared for use in chemical vapour deposition (CVD) of BaTiO3 thin films. A novel pathway to an unprecedented class of barium carbamates is reported, and also new dianionic bis ??-ketoesterates and their barium, strontium, and calcium analogues were synthesised. High resolution mass spectrometry showed the barium bis ??-ketoesterate derivatives to be monomeric, and preliminary testing indicated some volatility in these species. Insights were gained into the likely successful pathways to building a volatile heterobimetallic precursor complex containing an alkaline earth metal. The knowledge of intimate mixing in heterobimetallic precursor complexes was extended by some novel chemistry to develop the first mixed Zn/Mg carbamato cluster complexes. These complexes were found to be excellent SSCVD precursors for ZnxMg1-xO thin films. Thin films were deposited with these precursors and exhibited a single preferred orientation, with a constant amount of magnesium throughout the bulk of the films. Investigation of the light emission properties of the films revealed significant improvements in the structural order commensurate with the incorporation of magnesium, and the formation of the ZnxMg1-xO alloy.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--Ohio University, June, 2000. / Title from PDF t.p.

Thesis (M.S.)--Ohio University, November, 2003. / Title from PDF t.p. Includes bibliographical references (leaves 58-62).