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Sanborn, Graham Patrick. "A thin film triode type carbon nanotube field electron emission cathode." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50302.
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The current technological age is embodied by a constant push for increased performance and efficiency of electronic devices. This push is particularly observable for technologies that comprise free electron sources, which are used in various technologies including electronic displays, x-ray sources, telecommunication equipment, and spacecraft propulsion. Performance of these systems can be increased by reducing weight and power consumption, but is often limited by a bulky electron source with a high energy demand.
Carbon nanotubes (CNTs) show favorable properties for field electron emission (FE) and performance as electron sources. This dissertation details the developments of a uniquely designed Spindt type CNT field emission array (CFEA), from initial concept to working prototype, to specifically prevent electrical shorting of the gate. The CFEA is patent pending in the United States. Process development enabled fabrication of a CFEA with a yield of up to 82%. Furthermore, a novel oxygen plasma etch process was developed to reverse shorting after CNT synthesis. CFEA testing demonstrates FE with a current density of up to 293 μA/cm² at the anode and 1.68 mA/cm² at the gate, with lifetimes in excess of 100 hours. A detailed analysis of eighty tested CFEAs revealed three distinct types of damage. Surprisingly, about half of the damaged chips are not electrically shorted, indicating that the CFEAs are very robust.
Potential applications of this technology as cathodes for spacecraft electric propulsion were explored. Exposure to an operating electric propulsion thruster showed no significant effect or damage to the CFEAs, marking the first experimental study of CNT field emitters in an electric propulsion environment. A second effort in spacecraft propulsion is a collaboration with the Air Force Institute of Technology (AFIT). CFEAs are the payload on an AFIT developed Cube Satellite, called ALICE, to test electron emission in the space environment. ALICE has passed flight tests and is awaiting launch scheduled for 5 December 2013.
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Ludwick, Jonathan. "Physics of High-Power Vacuum Electronic Systems Based on Carbon Nanotube Fiber Field Emitters." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613745398331048.
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Kong, Xiangliang, Fan Guo, Joe Giacalone, Hui Li, and Yao Chen. "The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626416.
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Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study that including the process in which a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared to the case with a simple radial magnetic field, mainly due to perpendicular shock geometry and the natural trapping effect of closed magnetic fields. Our results suggest that the coronal magnetic field configuration is an important factor for producing large SEP events. We further show that the coronal magnetic field configuration strongly influences the distribution of energetic particles, leading to different locations of source regions along the shock front where most high-energy particles are concentrated. This work may have strong implications for SEP observations. The upcoming Parker Solar Probe will provide in situ observations for the distribution of energetic particles in the coronal shock region, and test the results of the study.
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West, Ryan Matthew. "Work function fluctuation analysis of polyaniline films." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47586.
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In this thesis, the development of a novel experimental technique for measuring the spontaneous, stochastic work function (WF) fluctuations of conducting polymer films, at equilibrium, is discussed. Polyaniline (PANI) is studied as a representative conducting polymer. This technique utilizes an insulated-gate field-effect transistor (IGFET) with PANI gate electrode (PANI-IGFET). The fluctuations of PANI WF are transduced into measurable drain current fluctuations of the device. By analyzing these fluctuations while systematically controlling the temperature, electric field and doping level, a model of WF fluctuations in PANI films is developed. These experiments suggest that the source of WF fluctuations is the hopping of charge carriers, or trapping/detrapping of charge carriers, around the Fermi level of the PANI film at the PANI-insulator interface. This process is thermally activated with a field and doping dependent activation energy in the range of 0.1 to 0.5 eV. Thus, this new technique provides detailed information about charge-carrier dynamics in the space-charge region of the PANI film, at equilibrium. These results have important implications for organic electronics and furthering fundamental understanding of the relationship between doping, disorder and work function in organic semiconductors.
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Seidemann, Johanna. "Iontronic - Étude de dispositifs à effet de champ à base des techniques de grilles liquides ioniques." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY075/document.
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Les liquides ioniques sont des fluides non volatiles, constitués de cations et d’anions, qui sont conducteurs ioniques, isolants électriques, et peuvent avoir des valeurs de capacité très élevées. Ces liquides sont susceptibles non seulement de remplacer les électrolytes solides, mais également de susciter des champs électriques intenses (>SI{10}{megavoltpercentimetre}) au sein d’une couche dite double couche électronique (electric double layer, EDL) à l’interface entre le liquide et le matériau sur lequel il est déposé. Ceci conduit à une injection de porteurs de charge bidimensionelle avec des densités allant jusqu’à SI{e15}{cm^{-2}}. Cet effet de grille remarquablement fort des liquides ioniques est réduit en présence d’états piégés ou de rugosité de surface. À cet égard, les dicalchogénures de métaux de transitions, de très haute qualité cristalline et atomiquement plats, font partis des semi-conducteurs les plus adaptés aux grilles EDL.Nous avons réalisé des transistors à effet de champ avec des EDL dans des nanotubes multi-couches de ce{WS2}, avec des performances comparables à celles de transistors EDL sur des ilots de ce{WS2}, et meilleurs que celles de nanotubes de ce{WS2} avec une grille solide. Nous avons obtenu des mobilités allant jusqu’à SI{80}{squarecentimetrepervoltpersecond} pour les porteurs n et p, et des ratios de courants on/off dépassant SI{e5}{} pour les deux polarités. Pour de forts dopages de type électron, les nanotubes ont un comportement métallique jusqu’à basse température. De plus, utiliser un liquide ionique permet de créer une jonction pn de manière purement électrostatique. En prenant avantage de cet effet, nous avons pu réaliser un transistor photoluminescent dans un nanotube.La possibilité de susciter de très forte densités de charges donne la possibilité d’induire des phases métalliques ou supraconductrices dans des semi-conducteurs a large bande interdite. Nous avons ainsi réussi à induire par effet de champ une phase métallique à basse température dans du diamant intrinsèque avec une surface hydrogénée, et nous avons obtenu un effet de champ dans du silicone dopé métallique.Les liquides ioniques offrent beaucoup d’avantages, mais leur champ d’application est encore réduit par l’instabilité du liquide, ainsi que par les courants de fuites et l’absorption graduelle d’impuretés. Un moyen efficace de s’affranchir de ces inconvénients, tout en conservant la possibilité d’induire de très fortes densités de porteurs, est de gélifier le liquide ionique. Nous sommes allés plus loin en fabriquant des gels ioniques modifiés, avec les cations fixés sur une seule surface et les anions libres de se mouvoir au sein du gel. Cet outil nous a permis de réaliser une nouvelle diode à effet de champ de faible puissanceIonic liquids are non-volatile fluids, consisting of cations and anions, which are ionically conducting and electrically insulating and hold very high capacitances. These liquids have the ability to not only to replace solid electrolytes, but to create strongly increased electric fields (>SI{10}{megavoltpercentimetre}) in the so-called electric double layer (EDL) on the electrolyte/channel interface, which leads to the injection of 2D charge carrier densities up to SI{e15}{cm^{-2}}. The remarkably strong gate effect of ionic liquids is diminished in the presence of trapped states and roughness-induced surface disorder, which points out that atomically flat transition metal dichalcogenides of high crystal quality are some of the semiconductors best suited for EDL-gating.We realised EDL-gated field-effect transistors based on multi-walled ce{WS2} nanotubes with operation performance comparable to that of EDL-gated thin flakes of the same material and superior to the performance of backgated ce{WS2} nanotubes. For instance, we observed mobilities of up to SI{80}{squarecentimetrepervoltpersecond} for both p- and n-type charge carriers and our current on-off ratios exceed SI{e5}{} for both polarities. At high electron doping levels, the nanotubes show metallic behaviour down to low temperatures. The use of an electrolyte as topgate dielectric allows the purely electrostatic formation of a pn-junction. We successfully fabricated a light-emitting transistor taking advantage of this utility.The ability of high charge carrier doping suggests an electrostatically induced metal phase or superconductivity in large gap semiconductors. We successfully induced low temperature metallic conduction into intrinsic diamond with hydrogen-terminated surface via field-effect and we observed a gate effect in doped, metallic silicon.Ionic liquids have many advantageous properties, but their applicability suffers from the instability of their liquid body, gate leakage currents and absorption of impurities. An effective way to bypass most of these problems, while keeping the ability of ultra-high charge carrier injection, is the gelation of ionic liquids. We even went one step further and fabricated modified ion gel films with the cations fixed on one surface and the anions able to move freely through the film. With this tool, we realised a novel low-power field-effect diode
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Quentin-Schindler, Marie. "Étude et développement d’une source d’ions équipée d’une cathode à nanotubes de carbone, émettrice d’électrons par effet de champ avec une application aux tubes neutroniques scellés." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS251.
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Ce projet de thèse, réalisé au sein de Sodern, filiale d'ArianeGroup, est dédié à l'optimisation des tubes neutroniques scellés. Ces dispositifs sont utilisés pour l'analyse de matière, principalement dans les secteurs pétrolier et minier. Ils fonctionnent sur le principe des accélérateurs de particules miniaturisés, générant des neutrons par la réaction de fusion deutérium-tritium.La problématique centrale de cette recherche concerne la source d'ions des tubes, actuellement reposant sur une cathode froide de type Penning. Cette configuration présente des limitations significatives, telles qu'un contrôle inefficace de la décharge de plasma génératrice d'ions. Ce problème est exacerbé par une gigue (jitter), qui caractérise une variabilité dans les largeurs de pulsations, et un retard à l'amorçage, qui est le décalage entre la mise sous tension de la source et l'extraction des ions. Pour surmonter ces obstacles, tout en limitant la puissance d'entrée, l'introduction d'une cathode émettrice d'électrons à base de nanotubes de carbone (CNT), fonctionnant par effet de champs, est envisagée du fait de la possibilité d'émettre sous relativement faible potentiel et sans ajout de température.La méthodologie adoptée inclut initialement des tests d'émission électronique des CNT pour évaluer leur intégration pratique dans la source d'ions. Les paramètres opérationnels examinés comprennent l'environnement gazeux dans la gamme de pression des tubes, la durée de vie, la répétabilité, la température, et la pulsation neutronique. Ces investigations ont conduit au développement d'une source d'ions modifiée, intégrant une source de CNT. Cette intégration a d'abord été réalisée par simulation sur le logiciel CST Studio, puis par la conception d'une maquette. Cette dernière a été réalisée et testée en laboratoire pour caractériser ses propriétés temporelles. Les résultats montrent une réduction significative du retard à l'amorçage et du jitter, bien que cela ait entraîné une dégradation irréversible des CNT après quelques heures de fonctionnement. Ces essais montrent qu'un courant d'émission minimum permettrait ces améliorations.En conclusion, cette thèse démontre le potentiel de l'ajout d'une source d'électrons pour améliorer les performances temporelles d'une source d'ions de type PenningThis doctoral project, carried out at Sodern, a subsidiary of ArianeGroup, is dedicated to the optimization of sealed neutron tubes. These devices are used for material analysis, primarily in the oil and mining sectors. They operate on the principle of miniaturized particle accelerators, generating neutrons through the deuterium-tritium fusion reaction.The central issue of this research concerns the ion source of the tubes, currently based on a cold Penning-type cathode. This configuration presents significant limitations, such as inefficient control of the ion-generating plasma discharge. This problem is exacerbated by jitter, which characterizes variability in pulse widths, and a delay in ignition, which is the lag between powering the source and ion extraction. To overcome these obstacles while limiting power input, the introduction of a carbon nanotube (CNT) based electron-emitting cathode, operating by field effect, is considered due to its ability to emit under relatively low potential and without added temperature.The methodology adopted initially includes tests of CNT electron emission to evaluate their practical integration into the ion source. The operational parameters examined include the gaseous environment in the pressure range of the tubes, lifespan, repeatability, temperature, and neutron pulsation. These investigations led to the development of a modified ion source, integrating a CNT source. This integration was first carried out by simulation on CST Studio software, then by the design of a prototype. This prototype was realized and tested in the laboratory to characterize its temporal properties. The results show a significant reduction in ignition delay and jitter, although this has led to irreversible degradation of the CNTs after a few hours of operation. These tests show that a minimum emission current would allow these improvements.In conclusion, this thesis demonstrates the potential of adding an electron source to improve the temporal performance of a Penning-type ion source
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Cooper, Joseph Andrew. "Investigation of the effects of process variables on the properties of europium-doped yttrium oxide phosphor." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/20503.
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Andrew), Patterson Alex A. (Alex. "An analytical framework for field electron emission, incorporating quantum- confinement effects." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84863.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 141-151).
As field electron emitters shrink to nanoscale dimensions, the effects of quantum confinement of the electron supply and electric field enhancement at the emitter tip play a significant role in determining the emitted current density (ECD). Consequently, the Fowler-Nordheim (FN) equation, which primarily applies to field emission from the planar surface of a bulk metal may not be valid for nanoscale emitters. While much effort has focused on studying emitter tip electrostatics, not much attention has been paid to the consequences of a quantum-confined electron supply. This work builds an analytical framework from which ECD equations for quantum-confined emitters of various geometries and materials can be generated and the effects of quantum confinement of the electron supply on the ECD can be studied. ECD equations were derived for metal emitters from the elementary model and for silicon emitters via a more physically-complete version of the elementary model. In the absence of field enhancement at the emitter tip, decreasing an emitter's dimensions is found to decrease the total ECD. When the effects of field enhancement are incorporated, the ECD increases with decreasing transverse emitter dimensions until a critical dimension dpeak, below which the reduced electron supply becomes the limiting factor for emission and the ECD decreases. Based on the forms of the ECD equations, alternate analytical methods to Fowler-Nordheim plots are introduced for parameter extraction from experimental field emission data. Analysis shows that the FN equation and standard analysis procedures over-predict the ECD from quantum-confined emitters. As a result, the ECD equations and methods introduced in this thesis are intended to replace the Fowler-Nordheim equation and related analysis procedures when treating field emission from suitably small field electron emitters.
by Alex A. Patterson.
S.M.
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Mo, Yudong. "The Effects of Residual Gases on the Field Emission Properties of ZnO, GaN, ZnS Nanostructures, and the Effects of Light on the Resistivity of Graphene." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500202/.
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In this dissertation, I present that at a vacuum of 3×10-7 Torr, residual O2, CO2, H2 and Ar exposure do not significantly degrade the field emission (FE) properties of ZnO nanorods, but N2 exposure significantly does. I propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. I also present the effects of O2, CO2, H2O, N2, H2, and Ar residual gas exposure on the FE properties of GaN and ZnS nanostructure. A brief review of growth of ZnO, GaN and ZnS is provided. In addition, Cs deposition on GaN nanostructures at ultra-high vacuum results in 30% decrease in turn-on voltage and 60% in work function. The improvement in FE properties could be due to a Cs-induced space-charge layer at the surface that reduces the barrier for FE and lowers the work function. I describe a new phenomenon, in which the resistivity of CVD-grown graphene increases to a higher saturated value under light exposure, and depends on the wavelength of the light—the shorter the wavelength, the higher the resistivity. First-principle calculations and theoretical analysis based on density functional theory show that (1) a water molecule close to a graphene defect is easier to be split than that of the case of no defect existing and (2) there are a series of meta-stable partially disassociated states for an interfacial water molecule. Calculated disassociation energies are from 2.5 eV to 4.6 eV, that match the experimental observation range of light wavelength from visible to 254 nm UV light under which the resistivity of CVD-grown graphene is increased.
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Narayanan, Sruthi Annapoorny. "Effect of magnetic seed fields on Lyman Alpha emission from distant quasars." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105651.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-57).
There are indications that weak magnetic fields originating in the early Universe and magnified via magnetohydrodynamic (MHD) processes could cause perturbations in the thermodynamic state of the gas in the intergalactic medium which affect the Lyman-Alpha spectrum we observe. In this work we investigate to what extent the properties of the Lyman-Alpha forest are sensitive to the presence of large-scale cosmological magnetic fields as a function of the seed field intensity. To do so, we develop and use a series of numerical tools to analyze previously constructed cosmological MHD simulations that include state-of-the-art implementation of the relevant physical processes for galaxy formation. The inclusion of these physical mechanisms is crucial to get the level of magnetic field amplification currently observed in the structures that populate our Universe. With these tools we isolate characteristics, namely the Flux Probability Density Function and the Power Spectrum, of the Lyman-Alpha forest that are sensitive to the magnetic field strength. We then examine the implications of our results.
by Sruthi Annapoorny Narayanan.
S.B.
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Lewis, Richard Henry. "The reproducibility of field measurements and the effect of wind speed on the sampling of airborne dust." Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335409.
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Wadhawan, Atul. "The Effects of Cesium Deposition and Gas Exposure on the Field Emission Properties of Single Wall and Multiwall Carbon Nanotubes." Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3110/.
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The effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotube (SWNT) bundles were studied. In addition, a comparative study was made on the effects of O2, Ar and H2 gases on the field emission properties of SWNT bundles and multiwall carbon nanotubes (MWNTs). We observed that Cs deposition decreases the turn-on field for FE by a factor of 2.1 - 2.9 and increases the FE current by 6 orders of magnitude. After Cs deposition, the FE current versus voltage (I-V) curves showed non-Fowler-Nordheim behavior at large currents consistent with tunneling from adsorbate states. At lower currents, the ratio of the slope of the FE I-V curves before and after Cs deposition was approximately 2.1. Exposure to N2 does not decrease the FE current, while exposure to O2 decreases the FE current. Our results show that cesiated SWNT bundles have great potential as economical and reliable vacuum electron sources. We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurred after operation in UHV. The higher operating voltages in an O2 environment caused a permanent decrease of FE current and increase in turn-on field of MWNTs. The ratios of the slopes before and after O2 exposure were approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively. SWNTs compared to MWNTs would appear to make more economical and reliable vacuum electron sources.
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Burdette, Don Joesph. "A Study of the Effects of Strong Magnetic Fields on the Image Resolution of PET Scanners." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1245095497.
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Jermain, Robert F. "Effects of EMF Emissions from Undersea Electric Cables on Coral Reef Fishes." NSUWorks, 2016. http://nsuworks.nova.edu/occ_stuetd/418.
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The objective of this project was to determine if the electromagnetic field (EMF) emissions from undersea power cables impacted the local and transient marine life, with an emphasis on reef fishes. The work was done at South Florida Ocean Measurement Facility of Naval Surface Warfare Center, Carderock Division, Broward County, Florida. This facility functions as the hub for a range of active undersea detection and data transmission cables. It has multiple active submarine power cables that extend several miles offshore and which can deliver power and enable data transmission to and from a range of acoustic and EMF sensors. The cables lie directly on the seabed, are buried in the sand, or are suspended in the water column. EMF emissions from a selected cable were created during SCUBA fish surveys. During the surveys the transmission of either alternating current (AC) or Direct Current (DC) was randomly intiated by the facility with no transmitted current (OFF) provided a control. The surveys were conducted using standardized transect and stationary point count methods to acquire reef fish abundances prior to and immediately after a change in transmission frequency (the divers were aware of the time of frequency change but not the specific frequencies). The divers were also tasked to note the reaction of the reef fishes to the immediate change in the EMFs emitting from the cable during a power switch. The surveys were conducted on a quarterly basis at three sampling sites offshore on the same cable. These sites were in water depths of approximately 5, 10, and 15 m, respectively and were selected based on their robust reef fish community and are representative of each of the three primary hardbottom coral reef habitats in the local offshore environment: the Inner (Shallow), Middle, and Outer (Deep) reef tracts. A total of 263 surveys were conducted: 132 transect-counts and 131 point-counts over 15 months. There were 24,473 fishes counted during transect-count surveys and with point-counts, 36,115 fishes were counted. With count types and sites combine a total of 151 species representing 35 families were recorded. An analysis of the data primarily did not find statistical differences among power states and any variables. However, this may be a Type II error as there are strong indications of a potential difference of a higher abundance of reef fishes at the sites when the power was off. There are a number of caveats to consider with this finding: the data set needs to be larger in terms of numbers of: counts, sites and eletro-sensitive species to allow for rigorous statistical analysis; also a longer time between frequency changes to allow for slower, but nonetheless important, reactions to differing EMFs might lead to differing conclusions. Obviously, more research is required to confirm the results of this study.
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Van, Zandvoort Alisha. "The Effect of Control Tile Drainage on Soil Greenhouse Gas Emissions from Agricultural Fields in the South Nation Watershed of Ontario." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34567.
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Controlled tile drainage (CTD) is an agricultural management practice with well-documented water quality and agronomic benefits, however, by virtue of its effect upon soil hydrology, CTD could potentially impact soil greenhouse gas (GHG: CO2, CH4, N2O) emissions. This study aimed to determine whether: (1) CTD affects soil GHG emissions throughout a dry (2012) and a wet (2013) growing season for corn, soybean, and forage fields in eastern Ontario, and (2) the location in a field with respect to a tile drain (over tile (OT) versus between tile (BT)) is important in GHG emissions. Non-steady state chambers were used for sampling soil GHG emissions in order to analyze GHG fluxes, the δ13C of soil-respired CO2 (RT), and for separating total soil respiration into its rhizosphere and soil components. There was no significant difference in average GHG emissions from CTD and UTD fields (except for 1/5 field pairs studied for N2O) and from OT and BT locations. The means of δ13C of RT were not statistically different (p>0.05) between 4/5 CTD and UTD field pairs, and between OT and BT locations in 4/5 CTD fields. The mean contributions from rhizosphere respiration and soil respiration did not differ (p>0.05) in 3/4 CTD and UTD field pairs. This lack of difference in GHG emissions is believed to have resulted from their being no difference in surface soil water contents among CTD and UTD fields and among OT and BT locations. It is believed that surface soil moisture did not vary because: (1) the water table was too low in 2012 for effective water table control, and (2) significant precipitation created equally wet surface soil in 2013. In 2013, the surface soil moisture was approximately 10% greater and this may be why there was an approximate 5 kg C/ha/day greater CO2 flux from soybean fields in 2013 than in 2012. δ13C was useful for distinguishing the source of CO2 emissions (rhizosphere versus soil respiration) in CTD fields when the crop and plant δ13C signatures varied. The results are useful for helping to capture the carbon footprint of tile drainage management practices imposed at field-scale.
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Bertram, Janet. "Effects of cow urine and its constituents on soil microbial populations and nitrous oxide emissions." Diss., Lincoln University, 2009. http://hdl.handle.net/10182/1334.
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New Zealand’s 5.3 million strong dairy herd returns approximately 106 million litres of urine to pasture soils daily. The urea in that urine is rapidly hydrolysed to ammonium (NH₄⁺), which is then nitrified, with denitrification of nitrate (NO₃⁻) ensuing. Nitrous oxide (N₂O), a potent greenhouse gas (GHG), is produced via nitrification and denitrification, which are enzyme-catalysed processes mediated by soil microbes. Thus microbes are linked intrinsically to urine patch chemistry. However, few previous studies have investigated microbial dynamics in urine patches. Therefore the objective of these four experiments was to investigate the effects on soil microbial communities of cow urine deposition. Methods used included phospholipid fatty acid (PLFA) analyses of microbial community structure and microbial stress, dehydrogenase activity (DHA) assays measuring microbial activity, and headspace gas sampling of N₂O, ammonia (NH₃) and carbon dioxide (CO₂) fluxes. Experiment 1, a laboratory study, examined the influence of soil moisture and urinary salt content on the microbial community. Both urine application and high soil moisture increased microbial stress, as evidenced by significant changes in PLFA trans/cis and iso/anteiso ratios. Total PLFAs and DHA showed a short-term (< 1 week) stimulatory effect on microbes after urine application. Mean cumulative N₂O-N fluxes were 2.75% and 0.05% of the nitrogen (N) applied, from the wet (70% WFPS) and dry (35% WFPS) soils, respectively. Experiment 2, a field trial, investigated nutrient dynamics and microbial stress with plants present. Concentrations of the micronutrients, copper, iron and molybdenum, increased up to 20-fold after urine application, while soil phosphorus (P) concentrations decreased from 0.87 mg kg ⁻¹ to 0.48 mg kg⁻¹. Plant P was also lower in urine patches, but total PLFAs were higher, suggesting that microbes had utilised the available nutrients. Microbial stress again resulted from urine application but, in contrast to experiment 1, the fungal biomass recovered after its initial inhibition. Studies published during the course of this thesis reported that hippuric acid (HA) and its hydrolysis product benzoic acid (BA) significantly reduced N₂O-N emissions from synthetic cow urine, thus experiment 3 investigated this effect using real cow urine. Cumulative N₂O-N fluxes were 16.8, 5.9 and 4.7% of N applied for urine (U) alone, U+HA and U+BA, respectively. Since NH₃-N volatilisation remained unchanged, net gaseous N emissions were reduced. Trends in total PLFAs and microbial stress were comparable to experiment 1 results. Experiment 4 studied HA effects at different temperatures and found no inhibition of N₂O-N fluxes from HA-amended urine. However, mean cumulative N₂O-N fluxes were reduced from 7.6% of N applied at 15–20°C to 0.2% at 5–10°C. Total cumulative N emissions (N₂O-N + NH₃-N) were highest at 20°C (17.5% of N applied) and lowest at 10°C (9.8% of N applied). Microbial activity, measured as potential DHA, increased with increasing temperature. This work has clearly shown that the stimulation and inhibition of the soil microbial community by urine application are closely linked to soil chemistry and have significant impacts not only on soil nutrient dynamics but also on N₂O-N emissions and their possible mitigation.
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Constancias, Christophe. "Emission d'électrons par effet de champ à partir de micropointes pour écrans plats : simulations, caractérisations et confrontations expérimentales." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10002.
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Les feds (field emission displays) utilisent des millions de microcanons a electrons : les micropointes. L'uniformite et la stabilite de ces micropointes sont des qualites indispensables pour la fabrication optimisee des emetteurs et la performance des feds. L'objectif de cette etude est d'evaluer precisement les proprietes emissives de cathodes a micropointes fabriquees pour les ecrans plats. Il s'agit de correler les modeles developpes a partir de la simulation de micropointes avec les caracteristiques experimentales observees sur ces memes micropointes. Le travail est scinde en trois parties que nous avons comparees entre elles, afin d'obtenir la correlation globale des resultats de cette etude. Pour commencer, nous avons etudie et simule l'emission du courant de monopointes (en fonction de differents parametres geometriques) par la modelisation du parametre de champ , decrivant la finesse d'une pointe. Nous avons montre qu'un modele proche de la realite geometrique des pointes, (ne comportant qu'un seul site emetteur), permet d'evaluer l'influence des parametres geometriques et valide les resultats experimentaux obtenus pour la plupart des monopointes : voir courbes courant tension i(v). Dans un deuxieme temps, nous avons caracterise les proprietes emissives de monopointes, par des observations en microscopie a force atomique (afm), l'analyse des courbes i(v), et la mesure des spots produits par les faisceaux d'electrons ainsi que leurs angles d'ouvertures. Dans le cas de pointes particulierement emissives, nos resultats experimentaux (confrontes aux simulations) montrent que la structure nanometrique, des sites emetteurs, confere aux pointes des proprietes remarquables et que l'emission se distingue d'une emission fowler-nordheim pure. Enfin, la troisieme partie de cette these est consacree a l'evaluation des proprietes statistiques de l'emission de cathodes (avec une densite de pointes de plusieurs 10#4 ptes/mm#2) dont la structure est identique a celle des feds. Ainsi, nous avons mis au point un montage experimental appele projecteur a lentilles electrostatiques, pour comptabiliser directement le nombre d'emetteurs actifs d'une cathode en fonction du potentiel applique entre la grille d'extraction et les pointes, de l'environnement (gaz), de differents traitements ou du temps. Les resultats obtenus avec cet instrument montrent que plus de 50% des micropointes sont actives et que la deviation de l'emissivite est largement imputable aux dispersions geometriques des emetteurs. Un modele d'analyse statistique semi-empirique a ete developpe pour correler ces resultats experimentaux avec les simulations et les observations afm de la dispersion des parametres geometriques des pointes. Mots cles : emission par effet de champ, cathodes a micropointes, simulations de micropointes, optique electrostatique, instrumentation, feds (field emission displays), mesures topographiques afm
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Borz, Mario. "Propriétés d'émission et de conduction de nano-pointes de diamant sous éclairement laser ultra-bref : Etude par microscopies à effet de champ et spectroscopie en énergie." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR117.
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Le but de cette thèse est de comprendre les changements dans les propriétés électriques et optiques des matériaux à large bande interdite à l'échelle nanométrique par rapport au matériau massif et en présence d'un champ électrique statique intense. Le diamant en forme de nano-aiguille a été choisi comme matériau d'étude en raison de sa large bande interdite, sa haute résistance aux contraintes externes et sa conduction thermique élevée. Le diamant présente également une résistance électrique élevée, ce qui en fait un bon candidat pour l'étude des modifications de conduction électrique sous des champs électriques et optiques forts. Afin d'étudier les propriétés de conduction électrique, deux différentes techniques expérimentales ont été utilisées : la microscopie ionique à effet de champ et la microscopie électronique à effet de champ avec et sans éclairement laser. Les observations expérimentales ont été couplées à des modèles de conduction électrique qui décrivent qualitativement et quantitativement les résultats obtenus. Pour l'étude des propriétés optiques, une microscopie électronique à émission de champ assistée par laser a été réalisée. Dans ce cas, l'étude a été menée dans deux configurations expérimentales : l'une en éclairant l'ensemble de l'échantillon par le faisceau laser et l'autre en focalisant le laser uniquement sur le sommet de la nano-pointe où le champ électrique est augmenté et les électrons sont émis dans le vide. Les résultats décrivent les propriétés de conduction électrique et d'émission d'électrons des nano-aiguilles de diamant dans l'obscurité et sous un éclairement laser. En tant qu'émetteurs d'électrons, les nano-aiguilles de diamant présentent des avantages par rapport aux pointes métalliques telles qu'une stabilité d'émission et un seuil de dommage plus élevés sous éclairement laser. Les résultats sont prometteurs pour le développement d'une nouvelle source de photo- électrons pour la microscopie électronique résolue en tempsThe aim of this thesis is to understand the changes in the electrical and optical properties of large band-gap materials at the nanoscale in the presence of a huge static electric _eld. Diamond nano-needle has been chosen as a study material, thanks to its wide band gap, high resistance to external stress and high thermal conduction. Diamond presents also high electrical resistance, making it a good candidate for the study of electrical conduction modi_cations under high electric and optical _elds. In order to study the electrical conduction properties, two di_erent experimental tech- niques were used: Field Ion microscopy and Field Emission Microscopy with and without laser illumination. The experimental observations were coupled with electrical conduction models which describe qualitatively and quantitatively the obtained results. For the study of the optical properties, laser-assisted Field Emission Microscopy was performed. In this case, the study was performed in two experimental con_gurations: one by illuminating the whole sample by the laser beam and the other by focusing the laser beam only on the apex of the nano-tip where the electric _eld is enhanced and the electrons are emitted into vacuum. The results describe the electrical conduction and electron emission properties of the diamond nano-needles in dark and under laser illumination. As _eld emitters, diamond nano-needles show advantages compared to metallic tips such as: higher emission stability and higher damage threshold under laser illumination. The results are promising for the development of novel photo-electron sources for time- resolved electron microscopy
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Py, Christophe. "Construction d'un interféromètre électronique pour l'étude des propriétés émissives de micropointes à effet de champ : diffraction et interférences d'électrons lents." Grenoble 1, 1993. http://www.theses.fr/1993GRE10176.
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La substitution des filaments chauffants par des micropointes a effet de champ comporte des avantages dans plusieurs applications d'electronique: le leti a deja prouve l'interet de ce principe pour les ecrans plats; de nombreuses personnes croient que les micropointes pourraient fournir des sources micro-ondes innovantes. De plus, les proprietes de l'emission permettent d'aller plus loin en envisageant des applications d'optique electronique que n'etaient pas possible avec les filaments chauffants. En vue d'evaluer les potentialites des micropointes fabriquees au leti pour de telles applications, une experience d'interferometrie avec des electrons lents a ete imaginee, concue, realisee et caracterisee. L'instrumentation developpee est composee d'un biprisme de mollenstedt, d'un systeme de lentilles electrostatiques et d'un systeme d'imagerie compose de plaques de deflexion, d'un diaphragme de petite taille (1 m) et d'un multiapplicateur d'electrons. Des effets ondulatoires ont ete observes confirmant les bonnes proprietes de coherence de la source. L'experience permet par ailleurs potentiellement d'avancer dans la comprehension de phenomene d'emission par les pointes fabriquees au leti, et d'envisager des ameliorations technologiques pour les applications visees. Elle doit egalement permettre d'etudier l'application a l'holographie electronique, et par la suite d'imaginer des dispositifs d'optique electronique compacts tenant compte des proprietes ondulatoires des electrons emis par les micropointes
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Mohamed, Sherif. "Carrier Dynamics in InGaN/GaN Semipolar and Nonpolar Quantum Wells." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177906.
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InGaN based light emitting devices operating in the blue and near UV spectral regions are commercialized and used in many applications. InGaN heterostructures experience compositional inhomogeneity and thus potential fluctuations, such that regions of higher indium composition are formed and correspond to lower potentials. The indium rich regions form localization centers that save carriers from non-radiative recombination at dislocations, thus despite the large defect density, their quantum efficiency are surprisingly large. However, the conventional c-plane InGaN QWs suffer from high internal piezoelectric and spontaneous fields. These fields are detrimental for the performance of such structures as they lead to the quantum confined stark effect causing red-shift of the emission as well as reducing the electrons and holes wavefunctions overlap, thereby reducing the radiative recombination rate. However, growth of InGaN QWs on semipolar and nonpolar planes greatly reduced the polarization fields. Semipolar and nonpolar QWs experience an outstanding property which is polarized luminescence, opening a new frontier for applications for InGaN emitting devices. While nonpolar QWs have larger degree of polarized emission than semipolar QWs, semipolar QWs can emit in longer wavelengths due to their higher indium uptake. In this thesis, semipolar 20¯21 and nonpolar m-plane InGaN/GaN QWs were investigated. Photoluminescence, spectral and polarization dynamics were all studied in order to form a whole picture of the carrier dynamics in the QWs. Time resolved photoluminescence measurements were conducted for following carriers distribution between extended and localized states. Both the semipolar and nonpolar samples showed efficient luminescence through short radiative recombination times, as well as carrier localization in lower potential sites after thermal activation of excitons. Carrier localization was found to be benign as it didn’t degrade the performance of the samples or decrease the polarization ratio of their emission. However, the structures showed modest potential variations with the absence of deep localization centers or quantum dots. High polarization ratios were measured for both samples, which is well-known for nonpolar QWs. The high polarization ratio for the semipolar sample is of great importance, thus semipolar 20¯21 QWs should be considered for longer wavelength emitters with highly polarized spontaneous emission.
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CAVALIERI, TASSIO A. "Emprego do NCNP no estudo dos TLDs 600 e 700 visando a implementação da caracterização do feixe de irradiação na instalação de BNCT do IEA-R1." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10565.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Hajlaoui, Riadh. "Effet de la structure sur les propriétés électriques et optiques d'oligomères conjugués semi-conducteurs. Application à la réalisation de transistors à effet de champ et de diode électroluminescentes." Rouen, 1995. http://www.theses.fr/1995ROUES005.
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L'étude structurale des polymères conjugués montre que leur désordre moléculaire et structural limite la qualité de leurs propriétés électroniques, et restreint donc leur éventuelle application à des composants électroniques. L'utilisation de systèmes moléculaires structuralement bien définis devrait par contre permettre de s'affranchir de ces défauts chimiques et physiques, et d'améliorer ainsi l'efficacité du transport de charges dans ces matériaux semi-conducteurs. Cette démarche est illustrée ici par l'étude du sexithiophène (6T) et de ses dérivés substitués. La première partie est consacrée à la description des techniques expérimentales de préparation des films minces, puis des composants électroniques réalisés à partir de ces semi-conducteurs organiques, tels que transistors à effet de champ en couche mince et diodes électroluminescentes. L'étude des propriétés structurales et optiques a mis en évidence que ces films sont polycristallins, et que l'orientation des chaînes moléculaires sur le substrat est contrôlée par la nature du substrat, par la température de dépôt et par la position de substitution de groupes alkyles sur cette molécule (6T). Les mesures de conductivité et de mobilité d'effet de champ du sexithiophène et de ses dérivés montrent que pour le , -dihexyl-sexithiophène, la conductivité présente une anisotropie importante, alors que b,b'-dihexyl-sexithiophène se comporte comme un isolant. La température du substrat utilisée lors du dépôt du film influe sur la conductivité et sur la mobilité du sexithiophène. La mobilité plus faible de 6T à température ambiante est attribuée à une plus grande concentration de défauts tels que joints de grains. Les caractéristiques statiques des diodes électroluminescentes, dont les couches actives sont constituées de sexithiophène ou de l'un de ses dérivés, montrent un effet redresseur (semi-conducteur de type-p). Les caractéristiques transitoires montrent un courant capacitif bref, suivi d'un courant permanent donnant lieu à émission lumineuse. Dans une structure bicouche, on remarque une augmentation de l'émission lumineuse et une augmentation du rendement d'électroluminescence par rapport à la structure monocouche. L'intensité du spectre d'électroluminescence enregistré pour la structure bicouche dans la gamme 500-700 nm montre qu'en baissant la température l'émission augmente, ceci est attribué à une diminution du rendement des transitions non radiatives
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Nunes, Neto Oswaldo [UNESP]. "Estudo dos processos de transporte dependentes de Spin em materiais orgânicos." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/143066.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Materiais e dispositivos baseados em compostos orgânicos desempenham um importante papel em diversas áreas da aplicação tecnológica devido às suas interessantes propriedades eletro-magneto- ópticas, adicionadas às suas características mecânicas únicas, facilidade de processamento, versatilidade de síntese e baixo custo relativo. Apesar do proeminente campo de aplicação destes materiais, muitos aspectos associados à sua ciência básica são ainda pouco compreendidos. Nesse cenário destaca-se o fenômeno de Magnetoresistência Orgânica (OMAR, da sigla em inglês). Tal fenômeno encontra-se associado a variações significativas da condutividade elétrica de dispositivos orgânicos induzidas por pequenos campos magnéticos externos em temperatura ambiente e tem sido observado em diversificados materiais poliméricos e moleculares. No presente trabalho avaliou-se o fenômeno de OMAR apresentado por um Diodo Emissor de Luz baseado na molécula de Alq3. Medidas de Espectroscopia de Impedância Elétrica na presença de um Campo Magnético estático externo (EIE-CM) foram realizadas sobre o referido dispositivo para diferentes temperaturas. Métodos diferenciados de aquisição e manipulação de dados foram empregados a fim de remover a dependência temporal dos sinais tipicamente observados. Os seguintes Efeitos de Campo Magnético (MFE, da sigla em inglês) foram observados sobre a resposta elétrica do dispositivo: (i) redução de cerca de 1% na resistência, efeito praticamente constante para todo o espectro de frequência e; (ii) variações significativas na capacitância, com intensificação do efeito de Capacitância Negativa em baixas frequências. Como suporte para a interpretação dos resultados experimentais foram realizadas simulações empregando-se duas abordagens: Circuitos Equivalentes e Análise de perturbações de pequenos sinais (em inglês, Small Signal Analysis ) via soluções numéricas das equações de transporte de Boltzmann numa aproximação por Drift-Diffusion empregando-se dispositivos simplificados. As análises sugerem que os MFE evidenciados podem estar associados a um aumento da mobilidade efetiva dos portadores de carga e a uma redução na taxa de recombinação bimolecular no dispositivo. Os resultados foram interpretados em termos dos modelos atualmente aceitos para o fenômeno de OMAR. Esta tese também apresenta um estudo de processos de geração e transferência de carga em corantes Cianinas, materiais promissores para aplicações em células solares com absorção no infravermelho. Técnicas de Ressonância de Spin Eletrônico induzida por Luz foram empregadas em blendas destes corantes com o polímero MEH-PPV e com o fulereno (C60) a fim de avaliar, respectivamente, o caráter aceitador e doador de elétrons das Cianinas.
Materials and devices based on organic compounds play an important role in various technological applications, mainly due to their interesting electrical-magneto-optical properties combined with their unique mechanical properties, easy processing, versatility of synthesis and relatively low cost. Despite the prominent application field of these materials many aspects associated with their basic science are still not well understood. In this context the Organic Magnetoresistance phenomenon (OMAR) deserves to be highlighted. This phenomenon is associated with significant changes in the electrical conductivity of organic devices induced by the presence of small external magnetic fields at room temperature, being observed in various polymeric and molecular materials. In this study we have investigated the OMAR phenomenon in Alq3-based OLEDs. Electrical impedance spectroscopy technique in the presence of an external static magnetic field (EIS-MF) was employed in the experiments; distinct temperatures were considered. Differentiated methods of acquisition and data manipulation were employed to remove the typically observed signal time dependence. The following magnetic field effects (MFE) were observed on the electrical response of the device: (i) a constant reduction of around 1% in the resistance over the entire frequency spectrum and; (ii) significant changes in the capacitance followed by an intensification of the negative capacitance effect at low frequencies. Simulations employing two different approaches were carried out for the interpretation of the experimental results: (i) Equivalent Circuits and (ii) Small Signal Analysis via numerical solutions of the Boltzmann transport equations by Drift-Diffusion approach. The results suggest that the observed MFE can be associated with an increase in the effective mobility of the charge carriers and a reduction in the bimolecular recombination rate in the device. The results were interpreted in terms of the currently accepted models for the OMAR phenomenon. This thesis also presents a study about generation and charge transfer processes in cyanine dyes (near infrared absorbing compounds) which are promising materials for applications in solar cells. Light induced Electron Spin Resonance (L-ESR) technique was employed to study the presence/formation of paramagnetic centers in blends of these dyes with MEH-PPV polymer and fullerene (C60) to evaluate, respectively, the electron acceptor and donor character of cyanine dyes.
FAPESP: 2011/21830-6
CNPq: 204432/2013-8
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Ford, Colleen D. "The fate of nitrogen in lactose-depleted dairy factory effluent irrigated onto land." Lincoln University, 2008. http://hdl.handle.net/10182/837.
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A two-year lysimeter study was undertaken to compare the environmental effects (e.g. nitrate leaching and nitrous oxide emissions) of soil applied lactose-depleted dairy factory effluent (LD-DFE) with lactose-rich DFE. The aim of this experiment was to determine the fate of nitrogen from LD-DFE and dairy cow urine applied to a Templeton fine sandy loam soil (Udic Ustrochrept), supporting a herbage cover of ryegrass (Lolium perenne) and white clover (Trifolium repens). Measurements were carried out on the amount of nitrogen lost from the soil via leaching, lost by denitrification, removed by the pasture plants, and immobilized within the soil organic fraction. Further, a comparison between the fate of nitrogen in LD-DFE irrigated onto land under a "cut and carry" system, as opposed to a "grazed" pasture system was undertaken. Lactose-depleted dairy factory effluent was applied at three-weekly intervals during the summer months at rates of 25 and 50 mm, until nitrogen loading targets of 300 and 600 kg N ha⁻¹ yr⁻¹ had been achieved. Measured leaching losses of nitrogen averaged 2 and 7 kg N ha⁻¹ yr⁻¹ for Control 25 and Control 50 treatments; 21, 20 and 58 kg N ha⁻¹ yr⁻¹ for 25 and 50 mm "cut and carry" treatments respectively; and 96 kg N ha⁻¹ yr⁻¹ for the 25 mm "grazed" treatment. The range of nitrate-N leaching loss from LD-DFE plus urine is no different from the lactose-rich DFE nitrate leaching loss. Uptake of nitrogen by the growing pasture averaged 153, 184,340,352,483, and 415 kg N ha⁻¹ yr⁻¹ for Control 25, Control 50, LD-DFE 25 and LD-DFE 50 mm "cut and carry" treatments, and the LD-DFE 25 mm "grazed" treatment, respectively. Denitrification losses were 0.06, 4.4, 1.69, 19.70, and 7.4 kg N ha⁻¹ yr⁻¹ for Control 25, the LD-DFE 25 "cut and carry" treatments, the LD-DFE 25 mm "grazed" treatment, and calculated "paddock losses", respectively. Isotopic nitrogen studies found that 29.4 and 25.8% of applied LD-DFE nitrogen was immobilised in the LD-DFE 25 and LD-DFE 50 "cut and carry" treatments. The results of this experiment confirm the findings of the previous lactose-rich DFE study, in that the effects of grazing stock are of greater environmental concern than the removal of lactose from the effluent waste stream.
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Zheng-DongLin and 林正東. "Fabrication of CNTs-based Gas Sensor, Field Emission, and Field-effect Transistor." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/3z3383.
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博士國立成功大學
微電子工程研究所
104
In this study, the growth of high-density multi-wall nanotubes (MWNTs) on oxidized Si substrate was investigated. The obtained average length and diameter of the CNTs were approximately 4.52 and 45 nm, respectively. The adsorption of metal nanoparticle on nanotube surfaces and the fabrication of MWNT-based gas sensors were also examined. Ag adsorption to the MWNTs significantly increased device sensitivity and provided a 5.31% increase in RT sensitivity over that of MWNTs for an ambient isopropyl alcohol gas concentration of 800 ppm. The response speed and stability of the fabricated sensor were favorable. Moreover, the direct transfer of high-density MWNTs from a SiO2/Si substrate to a flexible substrate was demonstrated. The strong adhesion of the MWNTs with the flexible substrate was maintained although the substrate was bent into an extreme state with a radius of curvature of 993 μm. The surface modification of the MWNT-networked films with size-controlled Au nanoclusters enhanced gas sensitivity. The flexible MWNT sensor exhibited reproducibility, fast response, high stability, and high sensitivity. Results demonstrate the feasibility of manufacturing flexible MWNT gas sensors using the transfer process. This finding represents a major step toward low-cost and large-scale production of this class of device. The measurements of MWNT-based field emission show that a low turn-on electric field with the emission current density of 10 μA/cm2 could be achieved because of metal adsorption. The measured values of Eto for Au- and Ag-coated MWNTs were 5.33, 4.84, and 3.94 V/μm. The comparative investigation indicates that Ag nanoparticle decoration on MWNT decreased work function from 5 eV to 3.94 eV. The enhanced field emission properties of metal-coated MWNTs were caused mainly by low effective work function. The flexible field emission with MWNT thin films was fabricated using a transfer method. In the turn-on electric field with emission current density of 10 μA/cm2, the measured values of Eto with and without bending test were 3.60 and 3.72 V/μm. The MWNT film showed good mechanical stability at a significantly small bending radius of 5 mm. The good mechanical bendability is due to the cracking-resistant nanotube morphology. A simple method for selectively separating semiconducting SWNTs (s-SWNTs) was developed. The samples were examined by Raman spectroscopy with an excitation laser of 633 and 785 nm wavelengths. The spectrum reveals that metallic SWNTs and regioregular poly(3-dodecylthiophene) were completely removed and s-SWNTs were remained. SWNT-based field-effect transistors (FETs) were fabricated by dip-coating method. The device with selective extraction had a high on/off ratio and low subthreshold swing. The transistor with selective extraction had an on/off ratio of 107 and a subthreshold swing of 154 mV/dec. The proposed convenient and effective s-SWNT sorting process can be used in the commercial manufacturing of SWNT-based FETs for low-cost and large-scale electronic devices.
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Tsai, Meng-Hsien, and 蔡孟弦. "The effect of field emission on CNTs for N2 detection." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/60666085232661592877.
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碩士國立雲林科技大學
電子與資訊工程研究所
94
Since their discovery in 1991, carbon nanotubes (CNTs) have been the most promising material due to their unique structure and properties. These unique properties of CNTs make them as field emission devices, tips for scanning probe microscopes, hydrogen storage, quantum wires, and gas sensor. The growth of vertically aligned carbon nanotubes was carried out by using thermal chemical vapor deposition (thermal CVD) system. Prior to CNTs growth, a 20 nm Fe thin film acting as catalyst was deposited on (100) p-type silicon substrate by Radio Frequency (RF) Sputtering system. Subsequently, the substrate was transferred to the thermal CVD chamber. The Fe-coated Si substrates were loaded on the alumina boat and put inside the thermal CVD quartz tube. The condition of catalyst pre-treatment as follows: the N2 gas was then introduced into reaction tube at a flow rate of 100 sccm with 6.5 Torr for 20 min. The pretreated process was maintained at 600℃. This process was formed nanoparticle. The quartz tube was then heated up to the growth temperature of 700℃, and then only C2H2 gas flow rate of 30 sccm for the synthesis of CNTs. The reaction pressure and time were maintained at 3.5 Torr and 20 min. The surface and cross-section morphology of CNTs were studied by field emission scanning electron microscope (FE-SEM, JEOL JSM-6700F). The length is about 9 ~ 10 μm and the diameter is 15 ~ 30 nm. The quality of CNTs was identified by Raman Spectrum. The intensity ratio of D to G band peaks of as-grown samples as found to be 0.61. Gas-sensing and field emission experiments were carried out by an ultrahigh vacuum measurement system with a Keithley 237 I-V suit. The N2 sensing process was as follows: The concentration of N2 changed from 5×10-2 Torr to 500 Torr. There was a rise in the sensitivity as the increasing of the voltage. From the sketch of concentration to sensitivity, the sensitivity was improved 10% in 5V bias voltage compared to 1V bias voltage. CNTs observed by using FESEM were spoilt after the treatment of field emission. The Raman spectrum showed that the quality of graphitized crystal decreased. The value of ID / IG was about 0.7~0.8. Therefore, the sensitivity was improved from 10% to 30%. The effect of field emission is not only the raise of sensitivity but also the damage of structure of CNTs. Consequently, the ability of gas sensing was raised by using the treatment of field emission.
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Chang, Di-Jie, and 張迪傑. "Study of Temperature Effect on Field Emission Characteristics of Carbon Nanotubes." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/zfuw3n.
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碩士國立臺灣科技大學
材料科技研究所
94
In our investigation, we used methane as carbon source and used Plasma enhanced chemical vapor deposition (PECVD) to grow carbon nanotubes on substrate which had been coated with iron as catalyst. We fabricated carbon nanotubes (CNTs) that owned different surface morphology, different length and different density. And we investigate the field emission characteristics of the CNTs at varied temperature of these samples. Most samples which had better emission properties (lower turn on field) showed temperature independence in whole applied field range. But samples which had bad emission properties showed the temperature dependence phenomenon similar to thermionics emission. In other words, the temperature effect on field emission was directly influenced by the essential field emission abilities of carbon nanotubes. Finally, we found CNTs which was excellent in field emission showed outstanding temperature stability in the temperature range from 20K to 575K.
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Tai, Su, and 蘇泰. "A numerical simulation for a gated field emission triode considering temperature effect." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/71255991839973512206.
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碩士國立交通大學
電子研究所
81
Presented here is a new numerical siumlation tool for gated field emission triode(GFET) considering space charge effect and temperature effect. The mesh structure used in our simulation tool is very flexible, about 1 A near the tip and 1 um near anode. This kind of mesh structure can be used to accurately estimat the field at tip peak without using field enhancement factor and the CPU time is greatly reduced. In addition, the imporant of the number of meshes in obtaining correct simulation result is discussed and verified. The strong geometrical dependence of tip emission for GFET is usually observed in most simulation programs. However, we have shown that gate thickness can be optimized to reduce the leakage current between gate and cathode. Simulation including space charge effect has resulted in the speculation of the underestimation of area of GFET array. This can be used to explain the controversy of the value of the on-set voltage. And the space charge effect lowering the tip emitting current is observed, too. Finally, the thermal stability of GFET is discussed. If Nottingham effect is considered, the knowledge of the Eiffel-Tower shape tip is the most stable structure is questioned. Our results show that Nottingham effect is the dominant factor to heat tip other than Joule heating effect as some papers suggested. In addition, the influence of tip half angle and work function on thermal characteristics of GFET is discussed.
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Weng, Ting-Wei, and 翁廷維. "Area Effect of Patterned Carbon Nanotube Bundle on Electron Field Emission Characteristics." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/47921547387005309996.
Full textAbstract:
碩士國立臺灣科技大學
電子工程系
95
Patterned carbon nanotube (CNT) bundles were fabricated using the thermal chemical vapor deposition (CVD) method. The catalyst metal layer and buffer layer were Fe and Al, respectively, for CNT bundle growth. The optimal growth conditions were found to be Fe (3 nm), Al (5 nm), annealing for 1 hr and C2H2 flowing at 750℃. Patterns of different diameters and distances were defined on Si (100) substrates using photolithography. Bundle height was controlled using different hydrocarbon flow times. The inter-bundle distance to bundle height ratio was maintained at 2, a number predicted to have a maximum field emission for CNT, and left the patterned CNT bundle area as a variable parameter. The relationship between this area and the electron field emission characteristics was studied. The lowest threshold electric field of 0.7 V/um was obtained when the total area of patterned CNT bundles was approximately 46%.
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SHARMA, ANAND. "FIELD EMISSION OF ELECTRONS FROM HEMISPHERICAL CONDUCTING CARBON NANOTUBE TIP INCLUDING THE EFFECT OF IMAGE FORCE." Thesis, 2016. http://dspace.dtu.ac.in:8080/jspui/handle/repository/14632.
Full textAbstract:
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.
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Hung, Wei-Ren, and 洪違仁. "The Effect of Plasma Treatments on the Field Emission Characteristics of SiOx Nanowires." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23003781978011278812.
Full textAbstract:
碩士大葉大學
電機工程學系
96
In this work, a layer of nickel was evaporated onto a (100) silicon substrate to induce the precipitation of silicon at 1000°C for 2 hours in order to grow SiOx nanowires. The thickness of nickel layer was varied to study its effects on the field emission characteristics of SiOx nanowires. As observed from SEM graphs, the average diameter of SiOx nanowires varies almost linearly with the thickness of catalyst Ni layer. It can be concluded that thicker Ni layer produces lager and fewer catalyst balls in the nucleation stage resulting in larger and fewer SiOx nanowires. These larger and fewer SiOx nanowires in turn emit less current due to lower curvature at the tip and lower quantity of emission sites. Therefore, the thickness of Ni layer must be kept to minimum in order to obtain decent field emission characteristics. Even so, the emitted currents from SiOx nanowires are still lower than those emitted from carbon nanotube. It is found in this study that the screening effect of SiOx nanowires can be effectively reduced and the tip can be modified by Ar plasma treatment so that electrons can emit easily from the tips. On the other hand, conglomeration phenomenon of SiOx nanowires is found after CF4 plasma treatment which increases the surface density of SiOx nanowires and the number of emission sites. Hence, the field emission characteristics of SiOx nanowires are enhanced and field emission characteristics comparable to those of carbon nanotubes are achieved after plasma post-treatment. These results clearly manifest the potential of using SiOx nanowire in field emitter applications, and this is quite different to what people might think. Keywords: SiOx nanowires, field emission, metal-induced precipitation, Si-Ni alloy
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陳怡伶. "The Effect on Field Emission Characteristic of Carbon Nanotubes Coated by Boron Nitride Film." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/41024526219809707215.
Full textAbstract:
碩士國立清華大學
工程與系統科學系
94
This thesis investigates the field emission characteristic of periodic arrays of vertically aligned isolated carbon nanotubes (CNTs) coated by boron nitride (BN) using magnetron sputtering method and plasma-assisted chemical vapor deposition method. It has been reported that BN film could be one of the promising materials for field emitter because of its negative electron affinity (NEA) at the surface. In addition to its high aspect ratio, the field emission characteristics of CNTs have been widely studied due to its chemically and mechanically robust properties. The synergism of the combination of these two materials on the field emission mechanisms was investigated in this work. Vertically aligned CNTs were synthesized using catalytic chemical vapor deposition (CCVD) method to avoid screen effects due to high density of CNTs. After that, the periodic arrays of vertically aligned isolated CNTs coated with BN film were fabricated. The comparison between those with and without BN coating revealed a significant effect of the thickness and the NEA characteristics of BN coating on the field emission properties. The electron pathway and the field emission mechanisms of BN coated CNTs will be further discussed.
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Lo, Shao-kang, and 羅紹剛. "Effect of Pretreatment Methods on the Electron Field Emission Characteristics of the Diamond Films." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/8m4vv7.
Full textAbstract:
碩士大同大學
電機工程學系(所)
107
In this study, firstly we use the spin-coating to spin the mixture of different diamond Ti and titanium powders on the Si substrates, and then the samples were annealed by furnace tube.The results show that the samples compsed of black boron diamond (BBD) and μm-sized Ti powders possess the highest conductivity with the turn-on field of 3.2 V/μm and current density of 808.46 μA/cm2 when the applied field was fixed at 8V/μm. In the second part of the thesis, the samples annealed after the furnace annealing were processed by plasma post-treatment, we use three types of plasma(Ar, N2 and Ar first then N2 plasma).The Ar first then N2 plasmas).The Ar first then N2 plasmas show the best electron fild emission (EFE) properties , The samples composed of black boron diamond (BBD) and μm-sized Ti poweders possess the best EFE properties with turn-on field of 2.56 V/μm and current density of 336.52 μA/cm2 when the applied field was fixed at 8V/μm. In the third part of the thesis,we compare different three pre-treatment methods for growing diamond films.Theresults show that the samples with ultrasonication pretreatment possess the best EFE properties. Besides, the EFE properties. Besides, the EFE properties of the samples with spin-coating pretreatment are very close to that of samples with ultrasonication pretreatment, The spin-coating pretreatment is surperior to the ultrasonication pretreatment if we want to grow the diamond films on the fragile and vertical aligned carbon nanotubes (CNTs) or carbon nanowalls (CNWs), because the structure will not be destroyed using spin-coating preatment.
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Jana, Amit Kumar. "Effects of viscocity variation and very high permittivity on the magnetic field effect in pyrene- dimethyl aniline exciplex emission." Thesis, 2014. http://hdl.handle.net/10821/8195.
Full textAbstract:
Magnetic field induced change in the pyrene-N,N-dimethylaniline exciplex fluorescence
has been studied in condensed phase with very high permittivity. In contrast to the commonly
observed enhancement of exciplex fluorescence in presence of magnetic field (solvent
dielectric constant ranging between 7 to 33), the effect shows a complete reversal at
low DMA concentration in dimethyl sulfoxide (DMSO) which is observed only at the blue
end of fluorescence. At high DMA concentration the negative MFE at blue end slowly
reverts back to the normal. At the red end of the emission the MFE retains its normal
character for all donor concentrations even at very high permittivity.THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY (SCIENCE) IN CHEMISTRY (PHYSICAL)- DEPARTMENT OF CHEMISTRY UNIVERSITY OF CALCUTTA 2014
Under DST project and research conducted in the division of Physical Chemistry under Prof. Deb Narayan Nath
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TsaiMing-che and 蔡銘哲. "Effect of alloy catalyst on the growing characters of CNT and its field emission properties." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/47472912365598774275.
Full textAbstract:
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.
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Teng, Kuang-Yau, and 鄧光佑. "The study on the effect of graphitization processon the electron field emission propertiesof diamond films." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/46788371424000629124.
Full textAbstract:
博士淡江大學
物理學系博士班
100
In this thesis, we used 3 examples to demonstrate the effect of graphitization process on enhancing the electron field emission (EFE) properties of diamond films, viz. (i) high energy ion irradiation, (ii) ultrasonication-bias enhanced growth (U-BEG) process and (iii) N2-plasma MPECVD process. (i) In the high energy ion irradiation effect process, we observed that irradiation of 2.245 GeV Au-ions imposed significant modification on the granular structure of MCD diamond films but induced less marked influence on the microstructure of UNCD films. The extent of modification increased with the fluence of the irradiated ions. The critical fluence is around 8.4 x 1013 ions/cm2. For MCD films, the average grain size was reduced due to Au ion irradiation. Some of the grains remained intake and only structural defects were induced. Some of the grains were completely disintegrated to ultra-small grains in accompanied with the presence of amorphous carbons. These processes degraded the EFE properties of the films. Post-annealing the ion irradiated films healed the defects, recrystallized the amorphous carbons and induced the re-growth of the disintegrated diamond grains. The post-annealing process induced the formation of nano-graphite phase and resulted in the enhancement on the EFE properties for the films. In contrast, for the UNCD films, the high fluence energetic (2.245 GeV) Au ion irradiation induced the local heating that crystallized the grain boundary a-C phase into nano-graphite clusters and enhanced the EFE properties for the films.Post-annealing process further enhanced the re-crystalization process and improved the EFE properties. (ii) In the U-BEG (Ultrasonication-Bias Enhanced Growth) process, the granular structure was changed from faceted large grains microstructure to roundish nano-grain granular structure. The extent of size reduction for the diamond grains increased with the magnitude of negative voltage applied. However, TEM examination revealed that the prime factor enhancing the EFE properties for the diamond films grown by U-BEG process in the induction of graphitic phase along the grain boundaries of the films. (iii) In the diamond films grown by N2-plasma (CH4/N2), the granular structure was altered markedly from equi-axed geometry to acicular one. The aspect ratio of the needle-like diamond grains increase with substrate temperature first, reaching the largest on for the films grown at 700℃, and then decreased for higher substrate temperature. The conductivity of the films also increased with the substrate temperature and is largest for the films grown at 700℃. So does the EFE properties for the UNCD films. However, TEM investigation revealed the authentic factor, resulting in superior EFE properties for the 700℃-grown UNCD films is the formation of graphitic phase encasing the needle-like diamond grains. All the three cases show that the formation of graphitic phase among the diamond grains is the genuine factor that enhanced the EFE properties for the diamond films. Such an understanding sheds a light on how to enhance the EFE properties of diamond films via the modification on their granular structure.
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Lu, Shan-Jen, and 盧宣任. "The effect of field emission traits of carbon-nanotubes on the generation of negative air ions." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/38403545768069636163.
Full textAbstract:
碩士國立臺灣大學
環境工程學研究所
97
This study investigated the traits of field emission effect of carbon-nanotubes (CNTs) on generation of negative air ions (NAIs) by negative electric discharging, and the feasibility of developing a microscale air cleaner. The research evaluated the effect of the aspect ratio of CNTs, density of the CNTs, single-wall and multi-wall CNTs and double-wall CNTs, metal material, metal aspect ratio, and metal needle-point curvature on the discharging voltage of CNTs. It also evaluated the stability and the effective space of the generation of NAIs by using CNTs with negative electric discharging, and studied the possible generation of ozone. The results show that enhanced field emission gets bigger when the aspect ratio of CNTs increased, so that discharging voltage gets lower. The limited voltage value of multi-wall CNTs(aspect ratio ranged from 1666.66 to 5000) required only 0.5 kV when they used as discharging electrode. That was the first time the value lower than 1.0 kV. CNTs array can reduce screening effect because of regular alignment and also reduce discharging voltage effectively. The field emission from CNTs array could be optimized with the inter-tube distance of 10th of the height(CNTs array with density of 1~2×109 CNTs/cm2). No matter the number of layers of CNTs, the CNTs with greater aspect ratio have lower discharging voltage. At same discharging voltage, the stability of NAIs by negative electric discharging gets higher when the aspect ratio of CNTs increases. And we find out that the stability of generate NAIs by imitate pulsed corona is much better than continued discharging. If we close the electric field for 30sec and restart it for 1 minutes. We could keep the concentration of NAIs over than 4.0×105ions/cm3 for 30minutes. The NAIs concentration did not change with increasing space. CNTs on copper electrode can reach detecting limit range of NAIs at discharging voltage of 0.5kV without generation of ozone. At discharging voltage of 2.5 kV, CNTs on copper electrode begin to generate ozone at 0.2 ppb, this value is much lower than the Indoor Air Quality value (0.03 ppm), so we don’t have to worry about the problem of ozone pollution.
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Yang, Ming-Xun, and 楊銘勳. "Simulation Study of Junction Effect on Field Emission from One-dimensional Nanostructure Grown on Silicon Substrate." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/64466520859316879726.
Full textAbstract:
碩士國立成功大學
光電科學與工程研究所
94
Field emission display takes an important role in recent display technology. In this present study, junction effect on field emission from one-dimensional nanostructure grown on silicon substrate has been investigated by computer simulation. The classical transport equation is used to describe the carrier transportation in the material. The field emission at the emitter-vacuum interface is modeled by the Fowler-Nordheim equation. First, we discuss the field emission properties of the one-dimensional nanostructure grown on doped silicon substrate. The result of simulation reveals that for narrow-band-gap material, the p-type Si substrate will limit the field emission current in the high applied voltage region but for wide-band-gap material, the field emission current will be enhanced due to the p-type Si substrate. Continuously, we discuss the effect between nanostructures on field emission from three nanostructures with different height. From the result of simulation, we can realize that the field emission properties will reverse when the nanostructure with lower height is influenced by that with higher height. Furthermore, we analyze the effect of fixed charge among substrate-nanostructure interface on field emission. From the result of simulation, we can understand that for narrow-band-gap material, the positive fixed charge has no influence on the field emission current but the negative fixed charge will weaken the field emission current. On the contrary, for wide-band-gap material, the positive fixed charge will enhance the field emission current, but the negative fixed charge will still weaken the field emission current.
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Hsu, Jen-Hao, and 許仁豪. "Effect of underlying metals and emitter patterns on the field emission properties of CNT diode devices." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/92739368315904563539.
Full textAbstract:
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。
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Hsieh, Yun-Shuo, and 謝昀朔. "Study of thermal and optical effect on electron field emission properties of carbon nanotubes for emitter applications." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/65738971924391704277.
Full textAbstract:
碩士國立臺灣師範大學
物理研究所
91
In this thesis, the microwave plasma enhanced chemical vapor deposition method was used to synthesize carbon nanotubes on the tip of iron needle. The morphology of the carbon nanotubes changed with the gas species and the diameters of the carbon nanotubes increased with the gas pressure in the chamber. The organic iron catalysts precoated on the tip pronouncedly improved the carbon nanotubes grow uniformity. Moreover, carbon nanotubes were synthesized by using graphite powder and diamond powder as the carbon sources. Optical emission spectra of the microwave enhanced plasma in the synthesizing process were analyzed to optimize the growing process and to investigate the growth mechanism. From the gas species and the corresponding plasma temperature calculated from the spectra, solid-liquid-solid model was proposed to explain the growing mechanism for the carbon nanotubes on the tip of iron needle. The topography image of carbon nanotubes is characterized by scanning tunneling microscopy. The field emission properties are markedly influenced by heating and laser irradiation. Finally, a prototype electron field emitter was demonstrated, which shows that carbon nanotubes possess good potential for the application on the field emission devices.
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Huang, Yu-Hsuan, and 黃裕軒. "Effect of Field Emission Characteristics of Al and Mn-doped ZnO Nanorod Arrays Grown by Chemical Bath Deposition." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/00774803886589834295.
Full textAbstract:
碩士國立聯合大學
電子工程學系碩士班
103
ZnO, Al-doped ZnO and Mn-doped ZnO nanorod arrays were prepared on the ITO substrate by low-temperature chemical bath deposition (CBD) method. The effects of dopants (Al or Mn) and doping concentrations (1~3 mol%) on the structural and field emission properties were investigated in this work. SEM results show that the 3 mol% Al or Mn doping ZnO nanorods have length increased from 1.05 nm to 1.58 nm and 1.01 nm, respectively. Meanwhile, the diameter of the ZnO nanorods is significantly increased. XRD analysis shows that the Al-doped and Mn-doped ZnO nanorods possess a hexagonal phase of ZnO, indicating an excellent wurtzite structure with high crystallinity. Among the prepared samples, 3 mol% Al-doped ZnO nanorods exhibit higher intensity ratio of (002) to (101) diffraction peaks, indicating the well-aligned growth on the ITO substrate. Photoluminescence (PL) spectra show that Al-doped ZnO exhibits highest 380 nm feature peak, and the enhanced UV to visible emission ratio also reflects the high nanorod crystallinity. From the field emission measurement, Al-dopant effectively reduces the turn-on field to ~0.42 V/μm and improves the field enhancement factor (β) to about 17015 due to the improved crystallinity and oxygen defect properties.
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Chien-Kang, Kao, and 高建綱. "Effect of Plasma-to-film Interaction on Electron Field Emission Properties of Pulsed Laser Doposited Diamond-like Carbon Films." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/96846220484045811041.
Full textAbstract:
碩士中原大學
應用物理研究所
86
We synthesize the diamond-like carbon(DLC) films using pulsed laser deposition(PLD) process. And then post-treat the films using plasma, which is induced by radio frequency(RF). We are going to examine the effect of the plasma-to-film interaction on the physical and electrical properties of the DLC films. The characteristics of plasma; which includes Ar, N_2 or O_2 species, will be systematically varied in order to further understand their influence on electronfield emission. It is known that pulsed laser deposited DLC films contain high sp^3/sp^2 ratio, which significantly influences the electron field emission properties of the DLC films. We expect that plasma-to-film interaction will markedly modify the sp^3/sp^2 ratio and thus pronouncedly alter the field emission properties of thefilms. We systematically examine modifications on the post-treated films using Raman spectroscopy and atomic force microscopy. We found that the argon plasma modifies the characteristics of the DLC films mainly through the ionic bombardment, resulting in significant damage on the DLC films. By contrast, thenitrogen and oxygen-plasma interact with the DLC films chemically such that thesp^3-to-sp^2 bond ratio is altered. The modification on the electron field emission of the DLC films is proportional to the density of the plasma. The DLC/Cr/Si films (0.4 um) deposited at 200℃ possess good emission current density (J_e)=45 uA/cm^2, with turn-on field (E_0)=7.2 V/um, and the emission properties increase to (J_e)_Ar=942 uA/cm^2, with turn-on field (E_0)_Ar=6.8 V/um, after plasma treatment.
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Wang, Jiun-Yu, and 王俊喻. "Size effect on Field Emission properties of Si nanowires arrays and electronic properties of Ni-Silicide/Si heterostructure nanowires." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/44674757409904380085.
Full textAbstract:
碩士國立中興大學
材料科學與工程學系所
100
Nanoscale Schottky contact used for diodes, Schottky barrier field effect transistors and solar cells have been extensively studied. The Schottky metal silicide/Si heterojunctions in nanostructures have been widely investigated due to their applicability to Si-based devices. The free-standing Si NW arrays have been fabricated by the combining nanosphere lithography with metal-assisted catalytic etching. Further, chemical etching using a KOH solution was performed for adjusting the diameter of nanowires. Then, nickel silicide/Si heterostructure nanowires were formed by reactive deposition epitaxy and a glancing angle deposition technique. The results show that with reducing the diameter of Si nanowires, the turn-on field decreased and field emission enhancement factor increased. This phenomenon indicated that increasing the aspect ratio of nanowires can improve their field emission properties. Ni-silicides were formed at the apex of Si nanowires after depositing Ni at 400°C by the glancing angle deposition technique. The phase of silicide at the silicide/Si interface was NiSi2. When the diameter of nanowires reduced to 70 nm the front end of silicide was Ni2Si. The NiSi2/silicon heterojunction was Schottky contact. The Schottky barrier height was in the range of 0.39 to 0.45 eV, and the ideal factor was in the range of 3.1 to 3.5.
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Huang, Pin-Sang, and 黃品森. "Resistance effect on Field Emission for One-dimensional Nanostructures Grown on Silicon Substrates：A Simulation Study Using Classical Transport Model." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/15018448653138676751.
Full textAbstract:
碩士國立成功大學
光電科學與工程研究所
95
The Fowler-Nordheim (F-N) plots of the carbon nanotubes (CNTs) often exhibit a saturation-like phenomenon in the high-voltage region. This phenomenon is attributable to the resistance effect of the CNTs and/ or the interface effect between the substrate and CNTs. Jo et al. established a modified F-N equation to take the resistance effect into account. And their model can fit the experiment data well by adjusting the bulk resistance of the CNTs [52]. In this study, the carrier transport model is applied to investigate the resistance effect of the 1-D nanostructure grown on silicon substrate. The classical transport equation is used to describe the carrier transport in the material and solved together with the Poisson,s equation. The field emission at the emitter-vacuum interface is modeled by the F-N equation. My thesis simulation results exhibit that the F-N plots obtained from the simulation can also be fitted well by Jo,s modified F-N equation. And more importantly, the fitted resistance of the 1-D nanostructure is very close to the calculated resistance from the material mobility used in the simulation. Furthermore, the interface effect can also be considered as a large resistor which is in series with the bulk resistance of the 1-D nanostructure. The effect of carrier,s temperature on carrier,s mobility and resistance in the 1-D nanostructure is also examined.
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Liao, Mei-Chih, and 廖美枝. "The Effects on Field Emission Properties of CNTs by PIII." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/32423124414061481551.
Full text
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Lu, Duan Shao, and 盧端劭. "The effects of CNT graphitization on the field emission characterictics." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/76027330436978370735.
Full textAbstract:
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
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Guettler, Barbara Elisabeth. "Effect of Thermal and Chemical Treatment of Soy Flour on Soy-Polypropylene Composite Properties." Thesis, 2012. http://hdl.handle.net/10012/6702.
Full textAbstract:
Soy flour (SF), a by-product of the soybean oil extraction processing, was investigated for its application in soy-polypropylene composites for interior automotive applications. The emphasis of this work was the understanding of this new type of filler material and the contribution of its major constituents to its thermal stability and impact properties. For this reason, reference materials were selected to represent the protein (soy protein isolate (SPI)) and carbohydrate (soy hulls (SH)) constituents of the soy flour. Additional materials were also investigated: the residue obtained after the protein removal from the soy flour which was called insoluble soy (IS), and the remaining liquid solution after acid precipitation of the proteins, containing mostly sugars and minerals, which was called soluble sugar extract (SSE).
Two treatments, potassium permanganate and autoclave, were analyzed for their potential to modify the properties of the soy composite materials. An acid treatment with sulfuric acid conducted on soy flour was also considered.
The soy materials were studied by thermogravimetric analysis (TGA) under isothermal (in air) and dynamic (in nitrogen) conditions. SPI had the highest thermal stability and SSE the lowest thermal stability for the early stage of the heating process. Those two materials had the highest amount of residual mass at the end of the dynamic TGA in nitrogen. The two treatments showed minimal effect on the isothermal thermal stability of the soy materials at 200 ??C. A minor improvement was observed for the autoclave treated soy materials.
Fourier transformed infrared (FTIR) spectroscopy indicated that the chemical surface composition differed according to type of the soy materials but no difference could be observed for the treatments within one type of soy material.
Contact angle analysis and surface energy estimation indicated differences of the surface hydrophobicity of the soy materials according to type of material and treatment. The initial water contact angle ranged from 57 ?? for SF to 85 ?? for SH. The rate of water absorption increased dramatically after the autoclave treatment for IS and SPI. Both materials showed the highest increase in the polar surface energy fraction. In general, the major change of the surface energy was associated with change of the polar fraction. After KMnO4 treatment, the polar surface energy of SF, IS and SPI decreased while SH showed a slight increase after KMnO4 treatment. A relationship between protein content and polar surface energy was observed and seen to be more pronounced when high protein containing soy materials were treated with KMnO4 and autoclave. Based on the polar surface energy results, the most suitable soy materials for polypropylene compounding are SPI (KMnO4), SH, and IS (KMnO4) because their polar surface energy are the lowest which should make them more compatible with non-polar polymers such as polypropylene.
The soy materials were compounded as 30 wt-% material loading with an injection moulding grade polypropylene blend for different combinations of soy material treatment and coupling agents. Notched Izod impact and flexural strength as well as flexural modulus estimates indicated that the mechanical properties of the autoclaved SF decreased when compared to untreated soy flour while the potassium permanganate treated SF improved in impact and flexural properties. Combinations of the two treatments and two selected (maleic anhydride grafted polypropylene) coupling agents showed improved impact and flexural properties for the autoclaved soy flour but decreased properties for the potassium permanganate treated soy flour. Scanning electron microscopy of the fractured section, obtained after impact testing of the composite material, revealed different crack propagation mechanisms for the treated SF. Autoclaved SF had a poor interface with large gaps between the material and the polypropylene matrix. After the addition of a maleic anhydride coupling agent to the autoclaved SF and polypropylene formulation, the SF was fully embedded in the polymer matrix. Potassium permanganate treated SF showed partial bonding between the material and the polymer matrix but some of the material showed poor bonding to the matrix. The acid treated SF showed cracks through the dispersed phase and completely broken components that did not bind to the polypropylene matrix.
In conclusion, the two most promising soy materials in terms of impact and flexural properties improvement of soy polypropylene composites were potassium permanganate treated SF and the autoclaved SF combined with maleic anhydride coupling agent formulation.
48
Nnadili, Miriam Nchekwubechukwn. "Effect of relative humidity on chemical off-gassing in residences." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-3384.
Full textAbstract:
Relative humidity (RH) is an important parameter associated with occupant comfort in buildings. However, the effects of RH on indoor source off-gassing and interactions between air pollutants and indoor materials are poorly understood. For this study, air samples were collected in residential buildings to characterize “background” concentrations of volatile organic compounds (VOCs) in air. The interior space was then humidified for several hours prior to collection of another air sample to characterize the effects of increased RH on VOC concentrations. Samples were analyzed by GC/FID with abundance “binning” by elution time. Some samples were also analyzed using GC/MS to identify specific VOCs. Results indicate that increasing RH is associated with increases in VOC concentrations in residential indoor air. Many of the chemicals that show enhanced off-gassing are associated with architectural coating, moth repellents, and cleaning agents. The results of this study are novel and may have implications with respect to health effects associated with damp buildings and increased respiratory effects of children during sleep in bedrooms with elevated RH.text
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Yeh, Chih-Cheng, and 葉致成. "Screening Effects Study on Field Emission Characteristics of Diamond Nano-tip Array." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/24717835658730075248.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
98
Screening effect of field emission on the diamond nano-tip array with different pitches is investigated. The diamond nano-tip arrays are formed by hot-filament chemical vapor deposition (HFCVD) on aluminum oxide (AAO) template. The AAO template is fabricated by hard anodization. Compared with moderate anodization, there are many advantages for using hard anodization, such as fast growing and high regularity. The nano diamond particles are adhered onto the AAO template by Polyethylenimine pretreatment to increase the nucleation density of diamond. The diamond film is then deposited on the barrier layer of AAO template by HFCVD method. The diamond tips array is developed after removal of AAO template by wet chemical etching. The field emission effect with different nano-tip arrays are measured by field emission meter. The morphology and quality of diamond nano-tip array are examined by scanning electron microscopy (SEM) and Raman spectroscopy, respectively. The innovative triangular pyramidal structures are obtained successfully with tip radius of about 15 nm-30 nm, and height of 100 nm-200 nm at different pitches from 50 nm to 300 nm. As a result, the lowest turn-on voltage of 5.4 V/μm and highest field emission current density of 8.4 μA/cm2 can be obtained at the smallest pitch- height ratio of 0.25-1 without screening effect in the current study.
50
Chang, Ling-Ko, and 張綾珂. "Effects of silver content in MWNT paste on the field emission properties." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/9g58c8.
Full textAbstract:
碩士國立臺北科技大學
材料科學與工程研究所
95
In this work, effects of silver content in multi-walled carbon nanotubes （MWNTs）paste on the field emission properties were investigated for the application of carbon nanotube field emission display （CNT-FED）cathode. The diode cathode structures were fabricated by thick-film screen-printing technology, and TGA analysis was used to study relationship between CNT and silver during sintering process. By using adhesive tape to activate emitter surface, most of the carbon nanotubes （CNTs）can be aligned vertically. By constant-current measuring method, emission properties such as brightness, uniformity, emission intensity, can be examined. The surface morphologies were observed by field emission scanning electron microscopy. These results demonstrated that conductance was enhanced with increasing silver content in MWNT paste, but excess silver content degraded emission performance due to electric shielding effect.