Rozprawy doktorskie na temat „FIELD EMISSION OF CNT”

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.
Includes bibliographical references (p. 108-114).
There is a need for massively parallel, individually addressed and focused electron sources for applications such as flat panel displays, mass storage and multi-beam electron beam lithography. This project fabricates and characterizes double-gated field emission devices with high aspect ratio. One of the gates extracts the electrons while the second gate focuses the electrons into small spots. High aspect ratio silicon field emitters were defined by reactive ion etching of silicon followed by multiple depositions of polycrystalline oxide insulators and silicon gates. The layers were defined by a combination of lithography, chemical mechanical polishing and micromachining. We obtained devices with gate and focus apertures of 0.4[mu]m and 1.2[mu]m diameter. The anode current has very little dependence on the focus voltage and the ratio of the focus field factor to the gate field factor βF / βG is 0.015. Scanning electron micrographs of the devices, numerical simulation and spot size measurements on a phosphor screen confirmed these results. An e-beam resist, PMMA, was successfully exposed using the FEA device as an electron source.
by Liang-Yu Chen.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.
Includes bibliographical references (p. 207-218).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Field emission displays (FEDs) show great promise as high performance flat panel displays. The light emission process is efficient, long lifetimes are possible with high brightness, and bright passive matrix displays can be built. Because passive matrix displays don't need a transistor backplane, it was once thought that these displays would be cheaper to fabricate than their competitors. It is now clear that this is not the case. Fabricating a transistor backplane has turned out to be less expensive than micromachining an array of uniform field emitter tips with aligned gates. Competing technologies which use an active backplane (such as active matrix liquid crystal panels) have become ubiquitous, and FED technologies developed to date have been too expensive for the consumer market. This thesis presents a new strategy for creating a low-cost field emission display. This strategy begins by creating a field emitter out of organic conductors-a class of materials mostly neglected to date for this application. The organic emitter is made by copying a non-lithographic template. The process takes 5 minutes, occurs at room temperature and at atmospheric pressure, and does not damage the template. We show that organic conductors are easy to pattern into regular patterns and can form structures which exhibit field emission, with field enhancement factors of about 100-600 times. The field emission follows a Fowler-Nordheim characteristic. Also explored are some of the properties of organic conductors in vacuum such as conductivity over time, the interaction of the organic field emitter with background gases, and the conduction mechanism. In particular, we show that oxygen degrades the emission properties of organic field emission tips, and that organic materials retain sufficient conductivity in vacuum to serve as field emitters.
(cont.) The second prong of the strategy is to combine the field emitter with an inexpensive transistor. A thin-film transistor made using an organic semiconductor is used to control the emission from the field emitter. We demonstrate a circuit architecture which allows the transistor to control the field emitter without creating a micromachined gate. This architecture uses only one high voltage supply for the panel to extract and accelerate electrons toward the phosphor screen. We show that the field emitter current can be controlled over a range of about 1000:1 using only 30V. This is verified through measurements of spot brightness on a phosphor screen. We then show that using the transistor has additional advantages. The current noise is reduced by a factor of 20, and DC current degradation is eliminated for oxygen partial pressures up to 1 x 10-6 torr. A new linearized analysis is presented which explains the DC current control and noise reduction, and also estimates the work function fluctuation on the emitter tip. The experimental results are examined in the context of this analytical framework. The work in this thesis shows (1) that a field emitter can be made from an organic conductor using a simple process (2) a field emission display can be controlled without making an array of micromachined gates and (3) using a transistor has a number of advantages in addition to controlling the field emitter ...
by Ioannis Kymissis.
Ph.D.

One of the important properties of carbon nanostructures is their cold electron emission ability. Carbon nanotubes and other nanostructures are capable of emitting high currents at relatively low electrical fields. They are already used in functional devices such as field emitters. The conventional method of carbon nanostructured cathodes manufacturing is thin film nanocarbon deposition using CVD process on electrically conducting substrate like metal or doped silicon plates. The alternative way of manufacturing of carbon field emission cathodes is based on a special processing of carbon microfibers or composite materials in metal holders. We used the similar approach to produce composite metal-nanocarbon material which may be easily processed and shaped to produce an effective field emission cathode which can be easily fixed an any environment. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20585

In the quest for reliable, repeatable and stable field electron emission that has commercial potential, whilst many attempts have been made, none yet has been truly distinguishable as being successful. Whilst I do not claim within this thesis to have uncovered the secret to success, fundamental issues have been addressed that concern the future directions towards achieving its full potential. An exhaustive comparison is made across the diverse range of materials that have, over the past 40-50 years, been postulated and indeed tested as field emitters. This has not previously been attempted. The materials are assessed according to the important metrics of turn on voltage, Eon, and maximum current density, Jmax, where low Eon and high Jmax are seen as desirable. The nano-carbons, carbon nanotubes (CNTs), in particular, perform well in both these metrics. No dependency was seen between the material work function and its performance as an emitter, which might have been suggested by the Fowler Nordheim equations. To address the issues underlying the definition of the local enhancement factor, β, a number of variations of surface geometry using CNTs were fabricated. The field emission of these emitters was measured using two different approaches. The first is a Scanning Electrode Field Emission Microscope, SAFEM, which maps the emission at individual locations across the surface of the emitter, and the parallel plate that is more commonly encountered in field emission measurements. Finally, an observed hysteretic behaviour in CNT field emission was explored. The field emitters were subjected to a number of tests. These included; in-situ residual gas analysis of the gas species in the emitter environment, a stability study in which the emitters were exposed to a continuing voltage loop for 50 cycles, differing applied voltage times to analyse the effects on the emitted current, and varying maximums of applied field in a search for hysteresis onset information. These studies revealed the candidate in causing the hysteresis is likely to be water vapour that adsorbs on the CNT surface. A six step model if the emission process was made that details how and when the hysteresis is caused.

Recently, carbon nanosheets (CNS), a novel nanostructure, were developed in our laboratory as a field emission source for high emission current. to characterize, understand and improve the field emission properties of CNS, a ultra-high vacuum surface analysis system was customized to conduct relevant experimental research in four distinct areas. The system includes Auger electron spectroscopy (AES), field emission energy spectroscopy (FEES), field emission I-V testing, and thermal desorption spectroscopy (TDS). Firstly, commercial Mo single tips were studied to calibrate the customized system. AES and FEES experiments indicate that a pyramidal nanotip of Ca and O elements formed on the Mo tip surface by field induced surface diffusion. Secondly, field emission I-V testing on CNS indicates that the field emission properties of pristine nanosheets are impacted by adsorbates. For instance, in pristine samples, field emission sources can be built up instantaneously and be characterized by prominent noise levels and significant current variations. However, when CNS are processed via conditioning (run at high current), their emission properties are greatly improved and stabilized. Furthermore, only H2 desorbed from the conditioned CNS, which indicates that only H adsorbates affect emission. Thirdly, the TDS study on nanosheets revealed that the predominant locations of H residing in CNS are sp2 hybridized C on surface and bulk. Fourthly, a fabricating process was developed to coat low work function ZrC on nanosheets for field emission enhancement. The carbide triple-peak in the AES spectra indicated that Zr carbide formed, but oxygen was not completely removed. The Zr(CxOy) coating was dispersed as nanobeads on the CNS surface. Although the work function was reduced, the coated CNS emission properties were not improved due to an increased beta factor. Further analysis suggest that for low emission current (10 uA), thermal, ionic or electronic transition effects may occur, which differently affect the field emission process.

Ce travail de thèse est une contribution à la thématique de l’intégration de matériaux actifs en photonique silicium pour la réalisation de fonctions actives. L’accent a été mis sur des matériaux préparés en couches minces pouvant être dépose sur substrats silicium pour la réalisation de sources de lumière intégrées. L’approche classique en photonique silicium dans le fenêtre télécom (1.55μm) repose sur l’utilisation de guides strip fabriqués à partir de substrats silicium sur isolant, SOI). Le choix qui été fait dans ce travail repose en revanche sur l’utilisation de guides à cœur creux (‘slot waveguides’) en raison de l’excellent recouvrement qu’ils permettent entre leur mode optique fondamental quasi-TE et les matériaux de couverture utilisés. Les contributions de cette thèse ont porté à la fois sur les étapes de conception/simulation et sur celles liées à l’optimisation des étapes de fabrication en salle blanche. Des guides slot Si/SiO2 et SiN/SiO2 et des résonateurs en anneaux basés sur ces guides ont conduit à : - des pertes de propagation typiquement comprises entre 1dB/cm et 7dB/cm. - des résonateurs à facteur de qualité de quelques dizaines de milliers pour des structures couvertes par des liquides d’indice. Dans un deuxième temps, les travaux poursuivis ont visé à l’intégration de matériaux actifs dopés à l’Erbium dans les guides à fentes présentés en première partie en vue de la démonstration de gain optique sur puce dans la fenêtre télécom (1.55μm). Une première collaboration nous a amené à la démonstration de gain optique sur puce à partir d’une géométrie de guide en arête inversée fabriqué en polymère actif. Un gain interne de l’ordre de 25dB sur puce a été obtenu par cette approche pour une puissance de pompe optique de l’ordre de 70 à 80mW. Une seconde collaboration s’est focalisée, quant à elle, sur l’intégration d’oxyde Al2O3 dans des guides à fentes SiN fabriqués à Orsay. Les problématiques d’intégration des matériaux ont été étudiées dans un premier temps. Le résultat le plus marquant a été obtenu pour un guide de longueur 400μm, pour lequel un gain relatif de 1.5dB a été obtenu pour une puissance de pompe de l’ordre de 50mW à longueur d'onde 1480nm. De manière complémentaire, nous avons exploré une seconde voie destinée à la démonstration de structures émettrices/amplificatrices sur puce, exploitant l’utilisation de nanotubes de carbone semi-conducteurs. Notre équipe du C2N, en forte collaboration avec le CEA-Saclay, a développé une méthode de préparation de solutions riches en nanotubes de carbone semi-conducteurs (séparation par centrifugation). Au final, les couches minces qui en ont résulté ont constitué un milieu actif qui a pu être intégré de manière planaire sur des échantillons de silicium pour le développement de fonctions optiques intégrées par intégration hybride. Par cette approche, nous avons démontré : - qu’un pompage vertical des structures photoniques pouvait donner lieu à une extraction de photoluminescence (PL) en sortie guidée par la tranche, dans des guides à fentes, - qu’un renforcement significatif de la PL était obtenu par effet de recyclage des photons dans des résonateurs diélectriques à base de guides à fente. Pour conclure, l’ensemble des travaux présentés dans cette thèse apporte une contribution au développement d’une photonique hybride sur silicium exploitant les propriétés de la plateforme de guidage optique sur SOI et celles de matériaux actifs (polymères dopés à l’Erbium ou aux nanotubes de carbone)
This thesis is a contribution to the hybrid integration of active materials including Erbium-doped and carbon nanotubes rich layers on silicon for on-chip light emission.In a first step, we designed, fabricated, and characterized within the silicon-on-insulator and silicon nitride platforms a range of photonic structures including strip/slot waveguides, micro disks, strip/slot ring resonators, and micro cavities aiming at preparing a set of passive device building blocks needed for hybrid integration on Si. Silicon slot waveguides and slot ring add-drop resonators filled with index liquids with linear propagation losses 2-7 dB/cm and Q-factors up to 30,000, have been demonstrated around wavelength=1.55µm. Propagation loss of silicon nitride slot waveguides were minimized down to ~4dB/cm for compact spiral structures (2cm long, within ~500µm×500µm area). Air-band mode Nano beam cavities were also investigated, leading to Nano cavities with mode volumes V ~0.03(wavelength/n)^3 and Q-factors ~70,000 when filled with soft materials.In a second step, hybrid integration of Erbium doped materials and semiconducting single-wall carbon nanotubes (SWCNTs) was investigated for light emission under optical pumping.Integration of Erbium-doped materials was studied within the framework of two collaborations: Prof. Daming Zhang’s team, in State Key Laboratory on Integrated Optoelectronics, Jilin University, China, and Prof. Zhipei Sun, in Department of Micro- and Nanosciences, Aalto University, Finland. Erbium doped layers coming from Jilin were composed of Er3+ and Yb3+ co-doped core {shell} nanoparticles which were copolymerized with methyl methacrylate (MMA) to synthesize nanocomposite (PMMA-NPs: Er3+/Yb3+). We conducted the experimental characterization that led to the demonstration of an internal net gain up to 10-17dB/cm at wavelength=1.53µm in Erbium doped polymer rib waveguides fabricated in Jilin. The second Erbium doped material available during this thesis was based on Er2O3/Al2O3 atomic layers, grown in Aalto University. This collaboration was devoted to integrate high Erbium ion concentration (10E21/cm3) in oxide cladding layers on top of silicon nitride slot waveguides, which were fabricated in our group for the demonstration of on-chip optical net gain. The carried out experiments have conducted to the demonstration of 1.5-22.8dB/cm gain for sub millimeter length waveguides.In another direction, hybrid integration of SWCNTs emitting at wavelengths around 1.3 µm on ring resonators and Nano beam cavities has been investigated. First, we studied the coupling of SWCNTs photoluminescence (PL) in silicon micro-ring resonators and compared it with the PL intensity coupled into the bus waveguide . It has been shown that the pump beam polarization controls the light coupling into the straight bus waveguide. We demonstrated an enhancement of the PL intensity of 20dB at resonance. We also explored CNT hybrid integration with ultra-small mode volume Nano beam optical cavities, and hence with larger Purcell-like Q/V factors in comparison with the one obtained in micro-ring resonators. The results revealed that the PL resonance enhancement due to Nano beam cavity field confinement exhibited a nonlinear growth as a function of the pump power. It was also shown that the resonance of the PL peak intensity grows faster with the pump power than the PL background, which is accompanied by a line width narrowing of the resonance PL peak. This result is the first step to achieve an integrated laser based on carbon nanotubes

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.
Includes bibliographical references (p. 101-105).
Field emission devices have demonstrated several research and commercial applications in the areas of flat panel displays, microwave power devices, imaging sensors and electron sources. Recent work has shown the feasibility of using integrated MOSFETs to control and enhance field emission stability and operating characteristics. This research effort investigates the integration of vertical MOS transistors with field emitter arrays as a means to enhance field emission device capabilities and range of applications. Vertical MOSFET device modeling was performed using MEDICI, a commercially available electrostatic simulator. In addition, process modeling was conducted using SUPREM to optimize design and layout sequencing for device fabrication. Working devices were fabricated and tested in the Integrated Circuits Laboratory within the Microsystems and Technology Laboratory at MIT. Techniques to achieve high-density field emitter arrays necessary for integrated VMOS / FEA devices were also investigated. This study determined that it is feasible to integrate and control field emitter arrays with vertical MOSFET devices.
by Paul Richard Herz.
S.M.

This work is mainly divided into three parts. Firstly, with the aim of integrating electron field emitter with other circuit elements on a single chip, silver-silicon dioxide (Ag-SiO2) nanocomposites are fabricated and studied. The Ag-SiO2 nanocomposites are synthesised by Ag implantation into thermally oxidised SiO2 layers on Si substrates and their fabrication processes are fully compatible with existing integrated circuit technology and their threshold fields are less than 20 V/mum. The local field enhancement mechanisms were studied and the fabrication processes of these layers optimised. Secondly, the electron field emission (FE) properties of two-dimensional quantum confinement structure were studied. Band gap modulated amorphous carbon (alpha-C) nanolayers were synthesised by pulsed laser deposition. In these structures, electrons are confined in a few nm thick low band gap sp2 rich alpha-C layer, which is bound by the vacuum barrier and a 3 nm thick high band gap sp3 rich alpha-C base layer. Anomalous FE properties, including negative differential conductance and repeatable switching effects, are observed when compared to control samples. These properties will be discussed in terms of resonant tunnelling and are of great interest in the high-speed vacuum microelectronic devices. Finally, due to the interesting electrical transport properties and rare FE characteristics of metal quantum dots (QDs), cobalt QDs were synthesized in a SiO2 matrix by ion implantation. Staircase-like current-field characteristics were observed for the first time from these samples and give an experimental insight into existing Coulomb Blockade effects in the metal QDs during the FE process. Moreover, these samples also achieve excellent FE properties with threshold fields less than 5 V/mum and are comparable with other popular FE materials.

We have studied coatings deposited using our inductively-coupled RF plasma ion implantation and desposition system to suppress field emission from large, 3-D electrode structures used in high voltage applications, like those used by Thomas Jefferson National Accelerator Facility in their DC-field photoelectron gun. Currently time and labor-intensive hand-polishing procedures are used to minimize field emission from these structures. Previous work had shown that the field emission from polished stainless steel (27 muA of field-emitted current at 15 MV/m) could be drastically reduced with simultaneous deposition of sputtered silicon dioxide during nitrogen implantation (167 pA of field-emitted current at 30 MV/m). We have determined that this unique implantation and deposition procedure produces high-purity silicon oxynitride films that can suppress field emission from stainless steel regardless of their initial surface polish. However, when this implantation procedure was applied to large, 3-D substrates, arcs occurred, damaging the coating and causing unreliable and unrepeatable field emission suppression.;We have developed a novel reactive sputtering procedure to deposit high-purity silicon oxynitride coatings without nitrogen ion implantation. We can control the stoichometry and deposition rate of these coatings by adjusting the nitrogen pressure and incident RF-power. Using profilometry, Auger electron spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection analysis, and current-voltage measurements, we have determined that the elemental composition, chemical bonding, density, and electrical properties of the reactively-sputtered silicon oxynitride coatings are similar to those produced by nitrogen implantation during silicon dioxide deposition. Furthermore, high voltage tests determined that both coatings similarly suppress field emission from 6" diameter, polished stainless steel electrodes.;We determined a quantitative, predictive electron emission model to describe electron emission from our silicon oxynitride coatings. Although Fowler-Nordheim theory adequately describes field emission from metals, it does not apply to our dielectric coatings. Several models exist in the literature to describe electron emission from dielectrics. Based upon our high voltage field emission results, electron emission from our silicon oxynitride coatings is described by the Schottky and Poole-Frenkel emission models. These models predict that increasing the band gap, dielectric constant, and electron affinity of our silicon oxynitride coatings would further reduce field emission.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 76-78).
Recent advances in micro and nanofabrication techniques have enabled modern vacuum field emission devices (VacFEDs) and have been demonstrated in the laboratory for use as diodes and transistors. Modern VacFEDs operate through cold emission of electrons across a vacuum gap. It has been proposed that these devices are "radiation insensitive" since they do not have a solid state junction as in other modern electronic devices. Radiation testing has been conducted to characterize the radiation response for these devices however, minimal supporting modeling has been performed. This thesis attempts to model and quantify the radiation effects of modern VacFEDs.
It focuses primarily on two effects associated with ionizing radiation exposure to a VacFED diode materials and structure: 1) The production of a net electron Direct Drive (DD) current in conductive layers due to imbalance in ionization rates in device layers and 2) Radiation Induced Conductivity (RIC) due to creation and drift of electron-hole pairs across an electric field of a dielectric insulating layer. These currents are treated as a noise sources that compete with the output signal of the device. Two radiation transport codes are used quantify interaction, electron charge and energy deposition of consequence to direct drive and RIC effects: 1) CEPXS/ONEDANT: a 1-dimensional electron-photon discrete ordinates code package and 2) MCNP6: a general-purpose, continuous-energy, generalized-geometry, time dependent, Monte Carlo radiation-transport code. RIC response was found to have the greatest current for all device models considered over all energies.
This thesis found a dose rate of 6 x 106 rad(Si)/s at the surface of a VacFED diode is required to cause a 0.1 [mu] A noise current in a device designed to operate at 1.0 [mu]A. This finding suggests that VacFED technology has the capability to operate continuously in a modern pressurized water nuclear reactor core gamma ray environment, which has an approximate dose rate of 3 x 105 rad(Si)/s.
by Adam Fisher Reynolds.
S.M.
S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling. The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE. To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization. The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance. EFE sources from planar Nb have been studied after various surface preparation, including chemical etching and electropolishing, combined with ultrasonic or high-pressure water rinse. Emitters have been identified, analyzed and the preparation process has been examined and improved based on EFE results. As a result, field-emission-free or near field-emission-free surfaces at ~140 MV/m have been consistently achieved with the above techniques. Characterization on the remaining emitters leads to the conclusion that no evidence of intrinsic emitters, i.e., no fundamental electric field limit induced by EFE, has been observed up to ~140 MV/m. Chemically etched and electropolished Nb are compared and no significant difference is observed up to ~140 MV/m. To address concerns on the effect of natural air drying process on EFE, a comparative study was conducted on Nb and the results showed insignificant difference under the experimental conditions. Nb thin films deposited on Cu present a possible alternative to bulk Nb in superconducting cavities. The EFE performance of a preliminary energetically deposited Nb thin film sample are presented.
Ph. D.

The electron emission characteristics of aluminum, molybdenum and carbon nanotubes were studied. The experiments were setup to study the emission behavior as a function of temperature and exposure to oxygen. Changes in the surface work function as a result of thermal annealing were monitored with low energy ultra-violet photoelectron spectroscopy for flat samples while field emission energy distributions were used on tip samples. The change in the field emission from fabricated single tips exposed to oxygen while in operation was measured using simultaneous Fowler-Nordheim plots and electron energy distributions. From the results a mechanism for the degradation in the emission was concluded. Thermal experiments on molybdenum and aluminum showed that these two materials can be reduced at elevated temperatures, while carbon nanotubes on the other hand show effects of oxidation. To purely reduce molybdenum a temperature in excess of 750 ºC is required. This temperature exceeds that allowed by current display device technology. Aluminum on the other hand shows reduction at a much lower temperature of at least 125 ºC; however, its extreme reactivity towards oxygen containing species produces re-oxidation. It is believed that this reduction is due to the outward diffusion of aluminum atoms through the oxide. Carbon nanotubes on the other hand show signs of oxidation as they are heated above 700 ºC. In this case the elevated temperatures cause the opening of the end caps allowing the uptake of water. Oxygen exposure experiments indicate that degradation in field emission is two-fold and is ultimately dependent on the emission current at which the tip is operated. At low emission currents the degradation is exclusively due to oxidation. At high emission currents ion bombardment results in the degradation of the emitter. In between the two extremes, molybdenum tips are capable of stable emission.

Flat panel displays based on electron field emission can provide the benefits of the high resolution of a cathode ray tube display while possessing the portability of a liquid crystal display. To date, the problem with a field emission flat panel display based on silicon is that it usually involves complex photolithography processing, making it too complex and expensive to be commercially viable. In this thesis, the emphasis of the research is to fabricate a three terminal silicon device for flat panel display based on field emission technology without using photolithography processes. Laser crystallised amorphous silicon is chosen for our material which creates a rough silicon surface whose roughness gives rise to field enhancement. Furthermore, this process is widely used in the display industry to fabricate silicon based display driver thin film transistors, which can be readily incorporated. It is important to understand the electron field emission mechanism from the laser crystallised amorphous silicon and to find optimum conditions for emission. In the course of our research, we established a regime for super sequential lateral growth or a hybrid sequential lateral solidification and super lateral growth in Nd:YAG crystallisation of amorphous silicon. Excimer laser crystallised amorphous silicon under optimum conditions gives emission currents of the order of 10-5A (current densities ~ 0.04 A/cm2) at threshold fields less than 15 V/mum in a diode configuration, without the need for a forming process. Through experiments, we concluded that the field emission mechanism from these samples is not controlled purely by surface phenomena, contrary to what was suggested by the Fowler Nordheim theory. Instead, it is the diffusion of the underlay metals into the silicon that create clusters of silicide that allow the electrons to become "hot" while travelling between the clusters. Lastly, a novel process illustrating that a three-terminal device based on laser crystallised amorphous silicon can be fabricated without the need for photolithography. However, the field emission data showed that some fine-tuning of the process is still required.

Large area displays such as laptop computers and flat screen televisions have enormous market potential. There are numerous technologies in existence today, including LCD (liquid crystal displays) and plasma, however they each suffer from unique limitations, mainly the size of the display and operating conditions. There is still a need for a method of depositing electronic materials over large areas at suitable temperatures. This is important since the construction of panels using sub-modules such as crystalline silicon wafers is very difficult and expensive. The displays based on liquid crystals that use thin film transistor (TFT) driven active matrix addressing is the most common flat screen technology at present. However, there are great problems associated with yield in fabrication, especially for screen dimensions over 14 inches. Hence the screens are very expensive. Field emission displays utilising the phenomenon of field emission in which electrons escape their work function and "jump" from the surface of the semiconductor into a vacuum has been proposed as a competing technology. Each pixel is controlled by many tip based emitters, therefore improving the yield. This thesis explores the field emission properties and mechanisms of tip based emitters, and also explore the possibility of utilising carbon nanotubes as electron sources for field emission displays.

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.
Title from electronic title page (viewed Dec. 18, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics and Astronomy." Discipline: Physics and Astronomy; Department/School: Physics and Astronomy.

This dissertation concerns the development and use of a novel form of field emission electron source in a medium-voltage (100 kV) scanning transmission electron microscope (STEM). It is the properties of the electron source, and particularly its brightness, which determine the extent to which interference effects are observable at the detection plane. These features directly contribute to high resolution image contrast. Interest was stimulated into the possibilities of improving the brightness of electron sources by at least an order of magnitude, by Hans-Werner Fink in the late eighties. He developed a process whereby a tungsten emitter could be produced which terminated in a single atom (a so-called nano-tip). The electron beam from such a source has been shown to exhibit high coherence, good current stability, a small cone angle and confinement of the emission surface to the atomically-sized apex. Experiments, however, were confined to tips in simple field emission chambers and the low-voltage point-projection microscope. In this dissertation, nanometre-sized protrusions have been grown at the apeces of tungsten emitters using a method whereby the surface metallic layer of atoms is melted under the action of strong electrostatic fields and applied heat. Such tips have shown emission characteristics, within an un-modified 100 kV STEM, which correspond with those previously observed from nano-tips. An evaluation of the suitability of the STEM for future use of these tips is included. In addition to requiring low levels of electrical instabilities, a mechanically reinforced tip base assembly was necessary. This was designed, constructed and shown to be an improvement over that of the commercially available source. A method to measure absolute beam coherence values at the specimen plane, and hence characterise tips, was also evaluated.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 143-147).
Field emitters are an exciting technology for high-frequency, high-power applications because of their excellent free space electron transport, and their potential for high current density and high current, especially when they are used in an array format. However, a major challenge preventing the widespread use of this technology are the spatial and temporal variations that arise from non-uniformity in emitter tip radius and work function, respectively. To address the problems, various methods of controlling the supply of electrons to the emitter have been developed. One method of current limiting is the vertical ungated field effect transistor (FET), which uses the channel pinch-o and velocity saturation of carriers in silicon combined with a high aspect ratio to provide an effective method of controlling current. To reduce the operating voltage, and likewise the energy spread of the emitted electrons, we created vertical ungated FET current limiters that were 100 nm in diameter, 8 m tall, and had a pitch of 1 m that were patterned using optical lithography. These devices demonstrated excellent current saturation, with output conductances lower than 10??11 S. In addition, a fabrication process for building nano-sharp emitters on these high aspect ratio pillars was developed. Using this process tip radii of less than 6 nm were obtained on top of the pillars. Process and device simulations were performed that indicate it will be possible to integrate extraction gates with small apertures into this structure, allowing for stable, uniform emission at gate voltages under 20 V in future work.
by Stephen A. Guerrera.
S.M.

New thermal field electron emission energy conversion method for vacuum electron-optical systems (EOS) with a nanostructured surface electron sources is offered and developed. Physical and numerical modeling of an electron emission and transport processes for different EOS is carried out. It is shown that at the specific configuration of electrostatic and magnetic fields in the EOS offered method permits to realize energy conversion processes with high efficiency. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35247

This dissertation focuses on developing carbon nanostructures for application as the electron emissive material in novel back-gated triode field emission devices. The synthesis, characterization, and field emission properties of carbon nanostructures, including 1-D carbon nanofibers (CNF), 2-D carbon nanosheets (CNS), and chromium oxide coated carbon nanosheets (CrOx-CNS), are presented in this work.;First, we have fabricated aligned carbon nanofiber based back-gated triode field emission devices and confirmed the operation of these devices. 1-D carbon nanofibers were directly synthesized on blank TiW substrates using direct current plasma enhanced chemical vapor deposition. It was found that the morphology of carbon nanofibers could be tuned from spaghetti-like to aligned by adjusting the applied plasma power. Field emission properties of spaghetti-like and aligned carbon nanofibers on blank TiW substrates were studied using the cartridge holder assembly. Results demonstrated that spaghetti-like carbon nanofibers had better field emission performance than aligned carbon nanofibers, however, the electrostatic simulation of the triode device demonstrated that aligned carbon nanofibers should yield the best device performance.;Second, we have demonstrated that carbon nanosheets, a 2-D carbon nanostructure developed by our group, were a competitive electron emissive material for application as the cold cathode in vacuum microelectronic devices. Carbon nanosheets were synthesized on a variety of substrates, without the need for catalysts, by radio frequency plasma enhanced chemical vapor deposition. Materials characterization results revealed that carbon nanosheets consisting of vertically oriented ultra-thin graphitic sheets terminating with 1-3 graphene layers were hundreds of nanometers in length and height but less than 4 nm in thickness. By using the diode holder assembly, field emission properties of carbon nanosheets were studied from a broad perspective, including turn-on and threshold field, maximum total current, emission lifetime and stability, and emission uniformity. The results revealed that the threshold field of nanosheets ranged from 3.5 to 5.2 V/mum, which was in the same range as 1-D carbon nanotubes and 3-D diamond. Moreover, the lifetime of nanosheets showed milliampere current emission (1.5 mA in a dc mode and 13 mA in a slow pulse mode) for hundreds of hours without significant current degradation after the conditioning process. However, the emission uniformity of nanosheets was quite poor due to the existence of "hot runners" during PEEM and FEEM observations. Further, the effectiveness of carbon nanosheet based back-gated triode field emission device was briefly studied.;Third, we have demonstrated that the emission uniformity of nanosheets could be improved by incorporating a thin chromium oxide coating. The chromium oxide coated carbon nanosheets were fabricated by vacuum evaporating thin chromium films on carbon nanosheets and sequentially exposing them to the atmosphere. The stoichiometry of the oxide was estimated to be 0.37, very close to Cr2O3. PEEM and FEEM observations showed excellent emission uniformity of chromium oxide coated carbon nanosheets. The field emission properties of chromium oxide coated carbon nanosheets were dependent on the coating thickness. The enhanced field emission performance of chromium oxide coated carbon nanosheets was observed with an appropriate thickness (from 1.5 nm to 15 nm). An explanation for this thickness dependence is suggested.

碩士
國立中興大學
電機工程學系
92
In this research, the carbon nano tubes (CNTs) are grown by controlling methane flow, plasma power and nitrogen flow. The Raman spectrum is measured to analyze the relative concentration of diamond structure (D-band) and graphite structure (G-band). The growth rate of CNTs increases as the methane flow rate increase, however, the properties of CNT is not as good as that grown by lower flow rate. The tubes are twisty, some carbon black spots are observed in CNTs. The growth rate of CNTs becomes slow when nitrogen is mixed to dilute the reactant, but on the other side the quality of CNTs becomes better and the tubes are more straightly. The field emission data shoes that the current emitted has certain correlation with the D-band over G-band intensity ratio. The smaller the ratio means the higher the graphite structure concentration in the CNTs, and the better of the emission property. This observation is consistent with morphologic observations mention above. Key words: Carbon nano tubes, field emission, graphite structure, diamond structure

ABSTRACT The present work examines the field emission from Conducting Hemispherical Carbon Nanotune (CNT) tip including the Effect of Image Force. An expression for electrostatic potential for a Hemispherical CNT tip at a distance from the centre of CNT has been derived. Using the time-independent Schrodinger equation corresponding expressions for transmission coefficient and field emission current density have been derived for the Hemispherical Conducting Carbon Nanotubes. The numerical calculations of potential, transmission coefficient and the current density function have been calculated for a typical set of carbon nanotube parameters. From the expression of potential energy we found that the potential energy for the hemispherical CNT tip first increases and then decreases with the radial distance. The transmission coefficient increases with the normalized radial energy. And the current density function also increases with the normalized Fermi energy. An important outcome of the present work is that both transmission coefficient and field emission current density function decreases as the hemispherical CNT tip radius increases.

碩士
國立臺灣科技大學
電子工程系
100
Anatase titanium dioxide (A-TiO2) were grown on top of carbon nanotube (CNT) bundle arrays by metal organic chemical vapor deposition (MOCVD) using titanium-tetraisopropoxide (TTIP, Ti[OCH(CH3)2]4) as the source reagents. The N-doped A-TiO2/CNTs nanocomposite was then fabricated with nitrogen plasma treatment. The surface morphology, structural and spectroscopic properties of the A-TiO2/CNTs and N-doped A-TiO2/CNTs nanocomposites were characterized using Field-emission scanning electron microscopy (FESEM), Raman spectroscopy, Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The FESEM image showed a dense coalescence of A-TiO2 with uniform size distribution on the nanotube walls. Raman spectra revealed that nanostructural A-TiO2 had been deposited on the CNT nanocrystals and a new vibration mode of D^'-band at higher wavenumber side was also found. The XPS spectra in the region of N 1s, Ti 2p and O 1s provided a conclusive evidence of the formation of O-Ti-N bond during nitrogen treatment process. The TEM image of A-TiO2 deposited CNT showed uniform distribution, and random directions of A-TiO2 had been grown on the surface of the CNT. The current density versus electric field measurements yielded turn-on field of 1.8 V/?慆 and 1.0 V/?慆 at a current density of 10 ?嫀/cm2, threshold field of 3.6 V/?慆 and 1.9 V/?慆 at a current density of 1 mA/cm2, and field enhancement factor of 2700 and 3000 for the A-TiO2/CNTs and N-doped A-TiO2/CNTs nanocomposites, respectively. Long term stability studies were also carried out. The results indicated that nitrogen doping decreased the turn-on field and threshold field of A-TiO2/CNTs, providing stable field emission applications. The probable mechanisms of field emission enhancement for N-doped A-TiO2/CNTs composite were proposed and discussed.

碩士
崑山科技大學
電子工程研究所
95
The iron, cobalt and nickel are three kinds of element most used as catalyst to grow CNT. However the research report pointed out that, the alloy catalyst which contains two different kinds of element has special effect on controlling CNT growth and caliber. The present research mainly uses RF Magnetron sputtering system to prepare the metal catalysts. The metal catalyst used in this study is nickel metal doped with different percent of iron metal and annealed to become a Ni-Fe alloy catalyst. By changing the composition of alloy catalyst, the growth of CNT and the character of field emission were studied. The alloy catalysts were etched by the microwave plasma enhanced chemical vapor deposition system in hydrogen atmosphere to produce nano scale catalysts. Then the mixture of methane and hydrogen were fed into the system to grow CNT at 500℃. The as-grown CNT samples were characterized by FE-SEM、TEM and Raman Spectroscopy. Its field emission properties were characterized by the I-V Measurement. The result shows that using Ni-Fe alloy catalyst will produce branched shape CNT. These CNT observed by the TEM showing a hollow bamboo structure with multi-walled CNT. Increasing the Fe amount in catalyst, the behavior of field emission is better. When Fe content in alloy catalyst is 39.4wt%, the lowest initial voltage of emission is 6.8V/μm and the highest current density is 314μA/cm2.

碩士
國立嘉義大學
光電暨固態電子研究所
94
The present paper mainly was used the microwave plasma enhanced-chemical vapor deposition(MP-CVD) growing carbon nanotube (CNTs) by (Ni) the array (10μm x 10μm) and different spaces (20μm、15μm、10μm、5μm) with four different metals (TiN，Ti，Ta) to be the barrier layer。 The advantage used MP-CVD in the catalyzed metal (Ni) the array to grow the high density and vertically aligned CNTs。Then changed diverse parameters to grow CNTs and compared field emission characteristic by penetration vacuum electric properties measurement system measured field emission properties，the scanning electron microscope (SEM) to visit the appearance of carbon nanotube。And the Raman spectrum to obtain D-band and G-band, two area compare by a type, if the degree more greatly graphitization is better。 By the experiment we can suppose that higher temperature or higher microwave power cause better degree of graphitization。Degree of graphitization:TiN ＞Ta＞Ti，Diameter of CNTs:TiN＞Ta＞Ti。Field emission properties: Ti ＞Ta＞TiN。

Carbon Nanotubes (CNTs) have great potentials for Field Electron Emission (FEE) and Flow Boiling Heat Transfer (FBHT) applications. However, their weak adhesion on metallic substrates limits the development of CNTs in both applications. Diamond has high thermal conductivity and develops strong bonding with CNTs. The development of a diamond interlayer between CNTs and substrates is a feasible approach to address the adhesion problems. The purpose of this research was to develop a new CNT-based materials with a diamond interlayer for FEE and FBHT applications by focusing on four objectives: (1) enhancement of diamond thin film adhesion on a Cu substrate, (2) improvement of the CNT FEE stability, (3) reduction of the CNT FEE turn-on field, and (4) investigation of the FBHT performance of CNT based structures. The CNTs and diamond thin films in this thesis were prepared by Microwave Plasma enhanced Chemical Vapor Deposition (MPCVD) and Hot Filament enhanced Chemical Vapor Deposition (HFCVD). The structure and chemical states of the diamond films and CNTs were characterized by Scanning Electron Microscopy (SEM), cross-sectional Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Raman spectroscopy, synchrotron based X-ray Absorption Spectroscopy (XAS). To deposit diamond thin films on a Cu substrate with sufficient adhesion strength, a sandblasting pretreatment and alloying with a tiny amount of Al were investigated. The adhesion of diamond thin films to substrates was evaluated by Vickers micro-hardness indentation. The FEE stability and turn-on field were measured by a Keithley 237 high voltage measuring unit. The FBHT property of the structures was tested repeatedly at different flow velocities to explore the dependence of heat transfer performance on certain parameters, including the flow patterns, Critical Heat Flux (CHF), and stability. The results show that sandblasting pretreatment increases the surface roughness and surface defect density, thereby increasing diamond nucleation density and adhesion to the Cu substrate. Al alloying appears to inhibit the formation of graphite at the interface between diamond and the Cu substrate, which improves the chemical bonding between diamond and the Cu substrate and increases the adhesion strength between them. The FEE testing results show that ultra-high FEE stability (more than 5000 minutes) was achieved for the CNTs with a diamond interlayer. This is attributed to the good contact at the diamond-CNT and diamond-substrate interfaces. The main factors that affect the CNT FEE turn-on field were also studied. By optimizing the structure, an FEE turn-on field of 5.1 V/μm was achieved and an emission barrier model for CNTs with a diamond interlayer on Cu substrate was used to explain the results. FBHT testing was done on CNTs with different structures and the results show that high heat transfer efficiency can be achieved on CNTs with a diamond interlayer at low mass fluxes.

We have advanced the state-of-the-art for nano-fabrication of carbon nanotube (CNT) based field emission devices, and have conducted experimental and theoretical investigations to better understand the reasons for the high reduced brightness achieved. We have demonstrated that once the CNT emitter failure modes are better understood and resolved, such CNT emitters can easily reach reduced brightness on the order of 10⁹ A m⁻² sr⁻¹ V⁻¹ and noise levels of about 1%. These results are about 10% better than the best brightness results from a nanotip emitter archived to date. Our CNT emitters have order of magnitude better reduced brightness than state-of-the-art commercial Schottky emitters. Our analytical models of field emission matched our experimental results well. The CNT emitter was utilized in a modified commercial scanning electron microscope (SEM) and briefly operated to image a sample. We also report a successful emission from a lateral CNT emitter element having a single suspended CNT, where the electron emission is from the CNT sidewall. The lateral CNT emitters have reduced brightness on the order of 10⁸ A m⁻² sr⁻¹ V⁻¹, about 10X less than the vertical CNT emitters we fabricated and analyzed. The characteristics of the lateral field emitter were analyzed for manually fabricated and directly grown CNT emitters. There was no significant difference in performance based on the way the CNT emitter was fabricated. We showed that the fabrication technique for making a single CNT emitter element can be scaled to an array of elements, with potential density of 10⁶-10⁷ CNT emitters per cm². We also report a new localized, site selective technique for editing carbon nanotubes using water vapor and a focused electron beam. We have demonstrated the use of this technique to cut CNTs to length with 10s of nanometers precision and to etch selected areas from CNTs with 10s of nanometers precision. The use of this technique was demonstrated by editing a lateral CNT emitter. We have conducted investigations to demonstrate the effects of higher local water pressure on the CNT etching efficiency. This was achieved by developing a new method of localized gas delivery with a nano-manipulator.
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碩士
逢甲大學
紡織工程所
95
This study discussed field emission characteristics， film surface resistance and film surface morphology of CNT film contained sodium metasilicate and TEOS inorganic binder. The experimental results showed that the CNT paste containing sodium metasilicate(50 wt%) and TEOS inorganic binder both had good dispersion with CNT. SEM images showed that the CNT film containing sodium metasilicate(50 wt%) and TEOS inorganic binder had very smooth film surface . The CNT film containing sodium metasilicate(50 wt%) had better field emission characteristic than that of containing TEOS， and the turn-on electric field was 6.4 V/μm. In order to decrease CNT film surface resistance， nano Ag powder， nano Ag solution and silver epoxy were filled in the CNT paste containing sodium metasilicate(50 wt%). The surface resistance of CNT fim were decreased when nano Ag powder， nano Ag solution and silver epoxy were added and as a result of descending the turn-on electric field. The CNT film containing nano Ag powder had best field emission characteristics， the turn-on electric field was 3.7 V/μm and the film surface resistance was 550 (Ω•cm). The better dispersion of the CNT film was achieved when the nano Ag powder and nano Ag solution were added comparing with that of silver epoxy. Consequently， the optimal condition for a low turn-on electric field and high surface film conductivity were nano Ag powder and nano Ag solution instead of silver epoxy.