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Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 154-161).

Carbon nanotubes have become one of the most important building blocks critical to nanotechnology. Carbon nanotubes have attracted the interests of many scientists since their discovery due to their remarkable properties and have been widely used for various applications. However, the bottle neck in nanotube research has been the lack of a cheap, continuous and fast nanotube production method. This study concerns a reactor where nanotubes are continuously deposited on a carbon substrate using arc discharge at atmospheric pressure. This process appears to be the first to employ an arc discharge as the method for continuous mass deposition of nanotubes on a substrate. This nanotube deposition method eliminates the generic multistep process of nanotube deposition on substrates for its use in many applications. The effect of various parameters influencing growth and morphology of nanotubes on the substrate in the arc reactor (inter-electrode gap, atmosphere composition, current density, flushing, substrate type and speed and catalyst) have been systematically explored to optimise nanotube growth. The field emission properties of the nanotube laden substrate are studied for use and applicability as electron emitters. The nanotube samples demonstrated superior emission properties, low turn-on field and excellent current stability when put into applications such as a luminescent tube and an ionisation sensor. Theoretical modelling of the behaviour of a single nanotube during field emission was performed using finite element analysis software (COMSOL 3.2) to understand the effect of nanotube length, diameter, and vacuum gap on an individual nanotube. The results reveal that resistive heating (temperature) limits the maximum current carried by an individual nanotube. Furthermore, a new growth model is introduced to explain the formation of nanotubes from graphene fragments and nanocrystallites, due to polarisation of carbon species near the electrode surface suggesting that carbon vapour is unlikely to be responsible for nanotube growth.

A cathode structure was demonstrated that utilizes aligned carbon nanotubes (CNTs) to improve the thermionic electron emission by increasing the field enhancement of the cathode surface. Aligned CNTs were grown on the surface of a tungsten substrate by plasma enhanced chemical vapor deposition. The tungsten-CNT structure was further coated with a thin film of low work function emissive materials by magnetron sputtering. Numerous cathodes with varying CNT morphology and oxide layer thickness were created. The field and thermionic emission of the cathodes were tested in order to study the effects of the surface properties on the emission characteristics. It was observed that the introduction of CNTs into an oxide cathode structure improves both the thermionic and field emission, even in cathodes with relatively low field enhancement factors. Because of the high field enhancement factors that are available for CNTs, there remains a potential for dramatically improved electron emission. / Department of Physics and Astronomy

Field emission cathodes have proven themselves to be excellent candidates for some special medical X-ray applications. Spindt cathode and CNT (carbon nanotube) based field emission cathode have been widely studied for many years. Spindt cathode has the near perfect structure, but the material property limits its applications. On the other hand, low density vertically aligned CNT array has been proved the best candidate of field emission material. Several attempts have been made to combine the advantages of the Spindt cathode and CNT array, but some most important advantages of Spindt cathode have not been successfully utilized in CNT emitter design, for example: ballast resistor, self-aligned fabrication process, sub-micron scale gate electrode, and low control voltage. In this thesis, the design, fabrication and test of CNT based field emission cathode with a novel ballast resistor and coaxial cylinder shape gate electrode is reported. A connection pad has been reported for the first time. This structure makes the ballast resistor can be utilized in a CNT field emitter array. Therefore, the uniformity and stability of field emission current is improved significantly. In addition, the stabilized emission current heated up the sample to a high temperature and changes the emission from field emission to Schottky emission regime. This is the first report of the self-heating Schottky emission from a CNT emitter array. Coaxial cylinder shape gate electrode is another important improvement in the CNT emitter design. The gate electrode adopts the self-alignment property of the Spindt cathode, and adjusted to fit the structure and synthesis process of CNT array. This new design and fabrication process has all the advantages of both the Spindt cathode and CNT emitter. In addition to the field emission cathode design, a novel PMMA (poly methyl methacrylate) based FEM (field emission microscope) is designed to evaluate the emission uniformity and capture high resolution images of the distribution of field emitted electrons. Compare to the conventional phosphor screen based FEM, the PMMA based FEM has a much higher resolution and sensitivity. Images of this new FEM have a resolution of as high as 0.34 nm and clearly show the boundary of crystal facets.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Ben Wang, Florida State University, College of Engineering, Dept. of Industrial Engineering. Title and description from dissertation home page (viewed Sept. 22, 2006). Document formatted into pages; contains xii, 93 pages. Includes bibliographical references.

Téma doktorské práce se zabývá přípravou a popisem katod na bázi autoemise, jenž představují kvalitní a levný elektronový zdroj pro zařízení pracující s fokusovaným elektronovým svazkem. Pro přípravu kompozitní autoemisní katody byla využita elektrochemická metoda výroby. Kompozitní struktura katody zlepšuje proudovou stabilitu ve srovnání s čistě autoemisními katodami na bázi wolframu. Na základě charakterizace katody, jenž byla nově provedena metodou šumové spektroskopie, byla implementována technologická zlepšení stávající výroby. Metoda šumové spektroskopie je založena na analýze emisního proudu v časové a kmitočtové rovině, ale především poskytuje informace o nosiči náboje, o jeho pohyblivosti a dále o životnosti katody. Výsledky experimentální části byly rozšířeny teoretickými simulacemi, vedoucími k návrhu metodiky charakterizace vylepšené autoemisní katody.

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The interaction of active molybdenum field emission microcathode arrays with oxygen, water, carbon dioxide, methane, hydrogen and helium gases was studied. Experiments were setup to measure the emission characteristics as a function of gas exposures. The resulting changes in the surface work function of the tips were determined from the Fowler-Nordheim plots. The kinetics of the FEA-gas interaction were studied by observing the ion species originating from the array during and after gas exposures with a high resolution quadrupole mass spectrometer. With the work function data and the mass spectrometry information, the mechanisms responsible for emission degradation and subsequent device recovery after exposures have been determined. The data obtained was used in estimating the device lifetimes under various vacuum environments. Also it was found that the gas exposure effects are similar in dc and pulsed modes of operation of the arrays, thus permitting the use of dc mode testing as an effective acceleration method in establishing the device lifetimes under various vacuum conditions. The vacuum conditions required for the long term emission current stability and reliability of vacuum microelectronic devices employing FEAs are established. Exposure of Mo field emitter arrays to oxygen bearing species like oxygen, water and carbon dioxide resulted in serious emission current degradation. Whereas, exposure to methane and hydrogen caused a significant increase in emission current. The control of residual gases like 02, C02 and H20 in the vacuum envelope is essential for the emission current stability and long term reliability of vacuum microelectronic devices employing field emission microcathode technology.