Tesi sul tema "Thermionics"
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1
Humphrey, Tammy Ellen Physics Faculty of Science UNSW. "Mesoscopic quantum ratchets and the thermodynamics of energy selective electron heat engines". Awarded by:University of New South Wales. Physics, 2003. http://handle.unsw.edu.au/1959.4/19186.
Testo completoAbstract (sommario):
A ratchet is an asymmetric, non-equilibrated system that can produce a directed current of particles without the need for macroscopic potential gradients. In rocked quantum electron ratchets, tunnelling and wave-reflection can induce reversals in the direction of the net current as a function of system parameters. An asymmetric quantum point contact in a GaAs/GaAlAs heterostructure has been studied experimentally as a realisation of a quantum electron ratchet. A Landauer model predicts reversals in the direction of the net current as a function of temperature, amplitude of the rocking voltage, and Fermi energy. Artifacts such as circuit-induced asymmetry, also known as self-gating, were carefully removed from the experimental data, which showed net current and net differential conductance reversals, as predicted by the model. The model also predicts the existence of a heat current where the net electron current changes sign, as equal numbers of high and low energy electrons are pumped in opposite directions. An idealised quantum electron ratchet is studied analytically as an energy selective electron heat engine and refrigerator. The hypothetical device considered consists of two electron reservoirs with different temperatures and Fermi energies. The reservoirs are linked via a resonant state in a quantum dot, which functions as an idealised energy filter for electrons. The efficiency of the device approaches the Carnot value when the energy transmitted by the filter is tuned to that where the Fermi distributions in the reservoirs are equal. The maximum power regime, where the filter transmits all electrons that contribute positively to the power, is also examined. Analytic expressions are obtained for the power and efficiency of the idealised device as both a heat engine and as a refrigerator in this regime of operation. The expressions depend on the ratio of the voltage to the difference in temperature of the reservoirs, and on the ratio of the reservoir temperatures. The energy selective electron heat engine is shown to be non-endoreversible, and to operate in an analogous manner to the three-level amplifier, a laser based quantum heat engine. Implications for improving the efficiency of thermionic refrigerators and power generators are discussed.
2
Tanner, Peter Godfrey. "Some developments of thermionic converters". Thesis, King's College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248055.
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3
Vashaee, Daryoosh. "High efficiency heterostructure integrated thermionic coolers /". Diss., Digital Dissertations Database. Restricted to UC campuses, 2004. http://uclibs.org/PID/11984.
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4
Hirt, Benjamin David. "Impact of Additives on Thermionic Cathodes". Ohio University Honors Tutorial College / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1524832507214002.
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5
Lough, Benjamin C. C. "Investigations into thermionic cooling for domestic refrigeration". School of Engineering Physics - Faculty of Engineering, 2004. http://ro.uow.edu.au/theses/230.
Testo completoAbstract (sommario):
Thermionic refrigeration using semiconductor heterostructures is examined theoretically and experimentally. A theory of single-barrier devices is first developed where two classes of single-barrier devices are defined and compared. So-called class 1 devices are found to always perform better. A theory of multiple-barrier devices based on class 1 barriers is then developed using a numerical solution. Experimentally, three generations of 10-barrier devices based on A1(subscript x)Ga(subscript 1-x)As-GaAs heterostructures were made and electrically characterised. This material is by no means ideal (as will be discussed) but was used to availability and because, at the commencement of this work, had never been used for this purpose before. Thermal measurements were made to determine if any cooling occurred at room temperature. No cooling was observed but the electrical characteristics allowed for examination of the models developed. It was found that the earlier models used did not accurately model the I-V characteristics of the devices. This was attributed to the fact that the initial models did not take space-charge into account. A more robust numerical model is developed in which the I-V characteristics of devices are predicted much more accurately. This model is then used to design new generations of devices. The work concludes by recommending a next generation design in which substantially more cooling is expected compared to the samples examined here. The probability of cooling being observed in the future is therefore increased. The types of devices described here will always be hindered because of heat conduction. Other methods incorporating thermionic emission, such as an opto-thermionic system in which removed heat is given off as light, may ultimately prove to be the best solution. This aside, it is hoped that the work presented here will contribute to the understanding of the field.
6
Koeck, Franz Alexander. "Thermionic Emission from Doped and Nanocrystalline Diamond". NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-04032003-161449/.
Testo completoAbstract (sommario):
Microwave Plasma assisted Chemical Vapor Deposition (MPCVD) has been utilized to synthesize nitrogen doped and intrinsic nanocrystalline diamond films to investigate thermionic field emission behavior. Sulfur-doped nanocrystalline diamond films prepared by hot filament chemical vapor deposition (HFCVD) have been included in the thermionic field emission measurements. The samples were imaged in UHV by photo electron emission microscopy (PEEM) using a UV Hg lamp for photoemission excitation. The same instrument was used to obtain the thermionic-field emission electron microscopy images (T-FEEM) at temperatures up to 900ºC. The Raman spectra of the films showed a strong diamond peak at 1332cm-1 and weaker signal from the graphitic regions in the sample. Field emission could not be measured at room temperature, but the PEEM images showed relatively uniform emission. The PEEM images showed little change as the temperature is increased. At temperatures as low as 640ºC the T-FEEM images exhibited strongly enhanced electron emission with increasing temperature. Doped and undoped nanocrystalline diamond films showed localized emission from small emission sites with a significant temperature dependence of the electron emission for the sulfur doped films at around 600ºC. This thesis focuses on developing a consistent model of thermionic emission from doped and nanocrystalline diamond films.
7
Stephen, Alexander. "Enhancement of thermionic cooling using Monte Carlo simulation". Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=210113.
Testo completoAbstract (sommario):
Advances in the field of semiconductor physics have allowed for rapid development of new, more powerful devices. The new fabrication techniques allow for reductions in device geometry, increasing the possible wafer packing density. The increased output power comes with the price of excessive heat generation, the removal of which proves problematic at such scales for conventional cooling systems. Consequently, there is a rising demand for new cooling systems, preferably those that do not add large amount of additional bulk to the system. One promising system is the thermoelectric (TE) cooler which is small enough to be integrated onto the device wafer. Unlike more traditional gas and liquid coolers, TE coolers do not require moving parts or external liquid reservoirs, relying only on the flow of electrons to transport heat energy away from the device. Although TE cooling provides a neat solution for the extraction of heat from micron scale devices, it can normally only produce small amounts of cooling of 1-2 Kelvin, limiting its application to low power devices. This research aimed to find ways to enhance the performance of the TE cooler using detailed simulation analysis. For this, a self consistent, semi-classical, ensemble Monte Carlo model was designed to investigate the operation of the TE cooler at a higher level than would be possible with experimental measurements alone. As part of its development, the model was validated on a variety of devices including a Gunn diode and two micro-cooler designs from the literature, one which had been previously simulated and another which had been experimentally analysed. When applied to the TE cooler of focus, novel operational data was obtained and signification improvements in cooling power were found with only minor alterations to the device structure and without need for an increase in volume.
8
Larson, Gregg D. "Two-dimensional modeling of a proposed auxilliary ionization scheme for thermionic converters". Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/15964.
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Day, Christopher M. "Field enhanced thermionic emission from oxide coated carbon nanotubes". Virtual Press, 2006. http://liblink.bsu.edu/uhtbin/catkey/1348860.
Testo completoAbstract (sommario):
A cathode structure was demonstrated that utilizes aligned carbon nanotubes (CNTs) to improve the thermionic electron emission by increasing the field enhancement of the cathode surface. Aligned CNTs were grown on the surface of a tungsten substrate by plasma enhanced chemical vapor deposition. The tungsten-CNT structure was further coated with a thin film of low work function emissive materials by magnetron sputtering. Numerous cathodes with varying CNT morphology and oxide layer thickness were created. The field and thermionic emission of the cathodes were tested in order to study the effects of the surface properties on the emission characteristics. It was observed that the introduction of CNTs into an oxide cathode structure improves both the thermionic and field emission, even in cathodes with relatively low field enhancement factors. Because of the high field enhancement factors that are available for CNTs, there remains a potential for dramatically improved electron emission.Department of Physics and Astronomy
10
SCHOENEMAN, DONALD WARREN. "COMPUTER-AIDED DESIGN OF THERMIONIC INTEGRATED CIRCUIT ACTIVE DEVICES". Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188077.
Testo completoAbstract (sommario):
Two computer-aided design methods are described in this dissertation for the design of Thermionic Integrated Circuits (TIC). Such circuits combine vacuum tube techniques with modern integrated circuit techniques to produce microminiature vacuum tube circuits, with possibly hundreds of vacuum triodes on a single substrate. The first method described in the line charge approximation technique in which the TIC devices are modelled as collections of line charges. A TIC is produced by evaporating metal electrodes on one or two sapphire substrates. The entire structure is heated to about 850°C so that electrons are emitted from the cathode electrodes to travel to the plate electrodes as in a conventional vacuum triode. The line charge approximation method is easy to implement and provides a simple means of satisfying the sapphire dielectric boundary conditions of the TIC basic problems, which are electrostatics problems since space charge effects are neglected. The method requires only a single matrix inversion and is a finite element Green's function approach. The method uses no iteration as in previous TIC analysis methods. Later as the development of TIC devices proceeded further it was found that conducting shields had to be placed over the unused sapphire surface so that the basic problem became a metal box problem. For this case a second method was developed called the step and ramp function method in which each electrode is modelled by a step function, which is the electric field solution for a potential step on a zero potential boundary. A superposition of these step functions models the TIC electrodes. The method provides direct calculation of the electric fields from equations and requires no iteration or matrix inversion. The potential variation between electrodes is modelled by linear potential functions called ramps. A superposition of steps and ramps completely specifies a TIC structure. The method does not solve for the case of electrodes which are elevated above substrates. For this case a modified line charge method was developed but not implemented.
11
McKinstry, Kevin Dale. "Interaction of oxygen with a LaBb6s(310) surface". Oregon Health & Science University, 1985. http://content.ohsu.edu/u?/etd,89.
Testo completoAbstract (sommario):
M.S.Applied Physics
The interaction of oxygen with the (310) surface of LaB[subscript 6] has been investigated using Auger electron spectroscopy and mass spectrometric analysis. Measurements were made on both preadsorbed layers of oxygen and in fixed oxygen pressures. Desorption products observed were BO, B2O2, B2O3, and LaO. Oxygen saturation of the surface at room temperature was observed with adsorptions of 50L. Oxides on the surface appear as B2O3 and an unidentified lanthanum bearing oxide. Temperature and pressure dependencies of the desorption products were studied in detail. Faceting [sic Facetting] of the surface into (100) planes was observed.
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McKinstry, Kevin Dale. "Interaction of oxygen with a LaB₆(310) surface /". Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,89.
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13
Hickey, Thomas R. "Temperature dependence of dark current in quantum well infrared detectors". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Jun%5FHickey.pdf.
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Torgasin, Konstantin. "Study on Methods for Performance Improvement of Thermionic RF Gun". Kyoto University, 2019. http://hdl.handle.net/2433/236633.
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Halliwell, Sarah Clare. "Characterisation of co-doped CVD diamond for potential thermionic applications". Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715781.
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Chen, B. L. B. "High-brightness limited-area thermionic electron sources for microscopy and lithography". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597531.
Testo completoAbstract (sommario):
Electron Microscopy and Electron Beam Lithography Systems are widely used in industry and research. The ultimate performance of such systems is determined by the brightness of the source from which the electrons are derived, a higher brightness allowing greater resolution at a given probe current. In addition to brightness, lithographic systems frequently require high absolute current. This dissertation addresses theoretically and experimentally the formation and characteristics of electron beams with a brightness of 106A/cm2-sr or more using limited-area thermionic sources. The various emission mechanisms used in electron guns are described and the brightness of an electron source is discussed. Space charge limits the available current density in the gun region and the focused current in the drift space of an electron beam analyser. Two models for predicting the performance of limited-area-cathode guns are proposed and agree well with the experimental results. Taguchi's methodology is introduced to undertake a systematic optimal design of an electron gun using an electron optical program, the 'Source' program. The experimental and theoretical results indicate that the major limitation to the performance of limited-area-cathode guns lies in the gun structure, especially, the emitting radius of the cathode and the manner of cathode emission itself rather than the drift-space. A new gun structure will be required if a brightness of 108Amp/cm2-sr at 30 kV (or an equivalent figure at lower voltages) is to be achieved. On the other hand, the analysing section can be modified so that such a brightness value can be measured.
17
Fuhrman, Brian Thomas. "Fabrication of advanced thermionic emitters using laser chemical vapor deposition-rapid prototyping". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17048.
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Swartzentruber, Phillip D. "MICROSTRUCTURE AND WORK FUNCTION OF DISPENSER CATHODE COATINGS: EFFECTS ON THERMIONIC EMISSION". UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/41.
Testo completoAbstract (sommario):
Dispenser cathodes emit electrons through thermionic emission and are a critical component of space-based and telecommunication devices. The emission of electrons is enhanced when coated with a refractory metal such as osmium (Os), osmium-ruthenium (Os-Ru), or iridium (Ir). In this work the microstructure, thermionic emission, and work function of thin film Os-Ru coatings were studied in order to relate microstructural properties and thermionic emission.
Os-Ru thin film coatings were prepared through magnetron sputtering and substrate biasing to produce films with an array of preferred orientations, or texture. The effect of texture on thermionic emission was studied in detail through closely-spaced diode testing, SEM imaging, and x-ray diffraction. Results indicated that there was a strong correlation with emission behavior and specific preferred orientations.
An ultra-high vacuum compatible Kelvin Probe was used to measure the work function of W-Os-Ru ternary alloy films to determine the effect W interdiffusion has on work function. The results indicated that a high work function alloy coating corresponded to low work function cathodes, as expected. It was inferred that a high work function alloy coating results in a low work function cathode because it aligns more closely with ionization energy of Ba. The results also proved that this method of evaluating dispenser cathode coatings can distinguish small variations in microstructure and composition and may be a beneficial tool in the development of improved dispenser cathode coatings.
A novel experimental apparatus was constructed to measure the work function of dispenser cathode coatings in-vacuo using the ultra-high vacuum Kelvin Probe. The apparatus is capable of activating cathodes at high temperature and measuring the work function at elevated temperature. The design of this apparatus allows for more rapid evaluation of dispenser cathode coatings.
19
Vaughn, Joel M. "Thermionic Electron Emission Microscopy Studies of Barium and Scandium Oxides on Tungsten". Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1279814656.
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MUTHIAH-NAKARAJAN, VENKATARAMAN. "A GENERALIZED THERMIONIC-TUNNELING MODEL OF CARRIER INJECTION ACROSS A METAL/POLYMER INTERFACE". University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054324006.
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Barber, Daniel. "Analytical interfacial studies of double carbonate thermionic oxide cathodes over accelerated operational life". Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/843464/.
Testo completoAbstract (sommario):
Cathode-ray tubes (CRT) have been used for the last 70 years and are expected to be incorporated in television sets for a further 15 years. The oxide cathode, located within the CRT, generates electrons which are focused and scanned across a phosphorescent screen to produce an image. The oxide cathode consists of a porous BaO/SrO spray layer deposited on a Ni alloy base. During operation, the Ni cap is heated. Activators (alloying additions, such as A1 and Mg) reduce BaO to 'free' Ba, which migrates to the emissive oxide surface, reducing the work function. It has been postulated for sometime that an interfacial layer forms between the nickel and emissive layer, leading to a decrease in the performance during life. Early work suggested that the interfacial layer inhibits diffusion of activating elements to the reaction area and reduces the electron flux drawn from the cathode surface. This work examines lifetime tested commercial cathodes using modern surface and interfacial analysis techniques. The results obtained are used to provide information on interfacial reactions, the role of activators, interface layer formation and the reasons for degradation in cathode performance. The nickel-emissive oxide interface has been studied after stripping off the emissive oxide. Auger electron spectroscopy (AES) and scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) analysis show the presence of an interfacial layer (composed of Ba, Sr, A1 and O) on cathodes (activated and aged) with no operational lifetime and those operated for 1000 and 2000 hours. Cross-sections of cathodes after varying operation times have also been examined. Cracks can be observed in the nickel cap and these cracks grow with increasing operational lifetime. There is a significant enrichment of Mg in the cracks. Focused ion beam (FIB) sections of samples exposed for 0, 1000 and 2000 hours have been prepared. Results from transmission electron microscopy (TEM) studies on these samples will be presented and clarify that the reaction products that form in the oxide cathode are composed of MgO and (Ba,Sr)Al204. Time of flight-secondary ion mass spectroscopy (ToF-SIMS) has also been used to acquire depth profiles from the underlying Ni cap and crack regions. These results are used as the basis of a model of the interactions occurring at the nickel/emissive oxide interface as a function of operational lifetime.
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Mackie, William Ansel. "Preparation and surface characterization of zirconium carbide single crystals /". Full text open access at:, 1987. http://content.ohsu.edu/u?/etd,147.
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Liu, Xiaotao. "CHARACTERIZATION OF NANOSTRUCTURE, MATERIALS, AND ELECTRON EMISSION PERFORMANCE OF NEXT-GENERATION THERMIONIC SCANDATE CATHODES". UKnowledge, 2019. https://uknowledge.uky.edu/cme_etds/96.
Testo completoAbstract (sommario):
Scandate cathodes, where scandia is added to the tungsten cathode pellets, have recently received substantial and renewed research interest owing to significantly improved electron emission capabilities at lower temperatures, as compared with conventional dispenser cathodes. However, there are several persistent issues including non-uniform electron emission, lack of understanding regarding scandium’s role in the emission mechanism, and unreliable reproducibility in terms of scandate cathode fabrication. As a result, scandate cathodes have not yet been widely implemented in actual vacuum electron devices (VEDs).
The surface structure and chemical composition of multiple scandate cathodes – prepared with the powder using the liquid-solid (L-S) technique – and exhibiting excellent emission behavior were characterized to give insight into the fundamental mechanism(s) of operation. This was achieved with high-resolution electron microscopy techniques that include high-precision specimen lift-out. These studies showed that the micron-sized tungsten particles that compose the largest fraction of the cathode body are highly faceted and decorated with nanoscale Ba/BaO (~10 nm), as well as larger (~150 nm) Sc2O3 and BaAl2O4 particles. The experimentally identified facets were confirmed through Wulff analysis of the tungsten crystal shape and were determined to consist of {110}, {100}, and {112} facets, in increasing order of surface area prevalence. Furthermore, it is estimated that Ba atoms decorating the tungsten crystal surfaces are present in quantities such that monolayer coverage is possible at elevated temperatures.
The high-resolution electron microscopy techniques used to investigate the cross section (near-surface) of the L-S scandate cathodes also revealed that the BaAl2O4 particles (100-500 nm) that attach to the larger tungsten particles are either adjacent to the smaller Sc2O3 nanoparticles or encompass them. Furthermore, high-resolution chemical analysis and 3D elemental tomography show that the two oxides always appear to be physically distinct from each other, despite their close proximity. 3D elemental tomography also showed that the Sc2O3 particles can sometimes appear inside the larger tungsten particles, but are inhomogeneously distributed. Nanobeam electron diffraction confirmed that the crystal structure of the tungsten particles are body-centered cubic, and imply that the structure remains unchanged despite the numerous complex chemical reactions that take place throughout the impregnation and activation procedures.
The role of Sc and the emission mechanism for scandate cathodes are discussed. Based on characterization results and materials computation, the role of Sc in scandate cathodes is possibly related to tuning the partial pressure of oxygen in order to establish an oxygen-poor atmosphere around the cathode surface, which is a necessary condition for the formation of the (near) equilibrium tungsten shape. A thin Ba-Sc-O surface layer (~8 nm) was detected near the surface of tungsten particles, using electron energy loss spectroscopy in the scanning transmission electron microscope. This stands in stark contrast to models invoking a ~100 nm Ba-Sc-O semiconducting surface layer, which are broadly discussed in the literature. These results provide new insights into understanding the emission mechanism of scandate cathodes.
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Khoshaman, Amir Hossein. "Self-consistent Vlasov-Poisson analysis of carrier transport in vacuum-based thermionic/thermoelectronic devices". Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58943.
Testo completoAbstract (sommario):
Thermionic conversion involves the direct conversion of heat, including light-induced heat, from a source such as solar energy, to electricity. The progress of thermionic converters has been limited by issues such as the space charge effect and lack of materials with desirable mechanical, electrical and thermal properties. Nanotechnology could help address some of the main challenges that thermionic converters encounter. However, existing models, which were developed for macroscopic converters, are not adequate for many aspects of nanostructured devices. The work presented in this thesis primarily advances a new model to partially address this void and study emergent thermionic devices. We demonstrate a self-consistent and iterative approach to the Vlasov-Poisson system that overcomes the inherent limitations of the traditional methods. This approach serves as the foundation for more advanced and yet crucial cases of the operation of thermionic converters in the presence of back-emission, grids in the inter-electrode region and low-pressure plasmas. We develop the physics of the device in the presence of grids and demonstrate that momentum gaps could arise in the phase space of the electrons; taking into account these gaps, which had not been noticed in the past, is key to designing efficient thermionic converters and we predict improvements of 3 orders of magnitude in current density using a properly designed grid. We also develop the physics of the device in the presence of low-pressure plasmas, which are prime candidates for reducing space charge. We show that the output power density of a thermionic converter can improve by a factor of ~ 10 using a modest plasma pressure of 500 Pa. On a different front, we have also improved the traditional analytical model and developed an approach to extract the internal device parameters such as emission area and workfunction based on a limited set of experimental output characteristics. These parameters are highly dependent on the operating conditions and ex-situ measurements are not applicable. Therefore, our approach allows for a more systematic study of the device and material properties, which is key to further the development of thermionic converters, in particular based on novel materials and nanostructures.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
25
Benke, Steven M. "Operational testing and thermal modeling of a TOPAZ-II single cell thermionic fuel element test stand". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA293595.
Testo completoAbstract (sommario):
Thesis (M.S. in Astronautical Engineering) Naval Postgraduate School, December 1994.Thesis advisor(s): Oscar Biblarz, Ashok Gopinath. "December 1994." Bibliography: p. 95-96. Also available online.
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Venable, J. Richard. "Electrical characteristics and thermal analysis of a TOPAZ-II single-cell thermionic fuel element test stand". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA298796.
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VUMMIDI, MURALI KRISHNA PRASAD. "Thermionic Emission Diffusion Model of InP-based Pnp Heterojunction Bipolar Transistor with Non-Uniform Base Doping". University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1060110500.
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Bakr, Arby Mahmoud Abdel Aziem. "Studies on the Reduction of Back Bombardment Effect in Thermionic RF Guns Using Different Cathode Materials". Kyoto University, 2011. http://hdl.handle.net/2433/151905.
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Othman, Muhammad Zamir. "Studies of n-type doping and surface modification of CVD diamond for use in thermionic applications". Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658070.
Testo completoAbstract (sommario):
This thesis presents the investigation of potential shallow n-type donors that are candidates to be used as therm ionic emitters for converting solar energy to electrical energy. Due to the various problems associated with current n-type dopants in diamond, the work has examined the use of Li-N codoping as a possible alternative doping strategy in chemical vapour deposition (CVD) of polycrystalline diamond films. Lithium nitride (Li3N) suspension in 1 % w Iv polyoxy in chloroform and N2 or NH3 gas were used as Li and N precursors, respectively, in preparing Li-N co-doped diamond films using a hot-filament CVD system. Using this system, high dopant concentrations of Li (-5x1019 cm-3 ) and N (-3x1020 cm- 3) atoms were successfully incorporated into the diamond films. The addition of Li atoms into N-doped diamond films improved the resistance of the diamond film from >200 MO to <50 MO. A resistance as low as 85 kO was recorded for Li-N co-doped diamond grown on a SCD type Ib substrate, however, these values and the overall electrical characteristics of the films were not sufficient for electronic devices. Ab initio calculations predicted that a LiN cluster with a Li: N ratio of 1:4 should produce shallow donor characteristics with an energy level -0.1 eV below the diamond conduction band minimum. The model only favours the formation of Li in substitutional sites rather than in interstitial sites due to its lower formation energy (4.88 eV and >10 eV, respectively). This model also suggests that N atoms might act as traps to pin down Liatoms and reduced their mobility in diamond lattice. The thermionic emission characteristics of Li-N co-doped diamond films were tested in Arizona State University, Arizona, USA. The films exhibited 121 ~A cm -2 current density at 900 K with a threshold temperature at 800 K. The effective work function of the emitters varied from 2.87 eV to 3.62 eV. The presence of a negative electron affinity (NEA) surface is found to be crucial for increasing the electron emission from diamond. H terminated diamond exhibits NEA and is usually prepared by exposing the diamond films in hydrogen plasma. However, desorption of H atoms between 925-1050K limits the application for these films for thermionic-based solar panels at higher temperature. Thus, various metaloxygen- terminated diamond surfaces were examined to determine their thermionic electron yield and stability at high temperatures. Cr-"O, Al-O and Ti-O terminated diamond surfaces exhibit NEA characteristics and were thermally stable at 650°C. However, only Cr-O terminated diamond showed true NEA characteristics while Al-O and Ti-O terminated diamond showed effective NEA.
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Jimenez, Justin C. "A systematic cathode study activation of a thermionic cathode, and measuring cesium evaporation from a dispenser photocathode". Thesis, Monterey, California : Naval Postgraduate School, 2010. http://edocs.nps.edu/npspubs/scholarly/theses/2010/Jun/10Jun%5FJimenez.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2010.Thesis Advisor(s): Lewellen, John W. ; Harris, John R. "June 2010." Description based on title screen as viewed on July 14, 2010. Author(s) subject terms: Free Electron Laser, Thermionic, Dispenser, Cathode, Outgassing, Cessium evaporation. Includes bibliographical references (p. 119-124). Also available in print.
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Han, Gina S. B. Massachusetts Institute of Technology. "Analysis of slurry composition for the direct ink writing of mayenite electride for use in thermionic cathodes". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/128417.
Testo completoAbstract (sommario):
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2019Cataloged from PDF of thesis. "The Table of Contents does not accurately represent the page numbering"--Disclaimer page.
Includes bibliographical references (page 25).
Thermionic cathodes, for use in electric propulsion thrusters, often utilize materials of low work function to decrease operating temperature and thus decrease power consumption. The ability to form these materials into complicated geometries allows for design of more efficient thermionic cathodes, such as multi-channel hollow cathodes. Mayenite electride, a calcium aluminate ceramic with a cage-like lattice structure that traps in electrons, has been identified as a low-work function ceramic that could be used for these thermionic cathodes. This thesis explores an additive manufacturing (AM) process for mayenite electride components, including the synthesis process for insulating mayenite and the development of an acetone-based slurry composition for direct ink writing (DIW). As the ink composition is critical to the success of any direct ink writing process, an in depth analysis was performed on mayenite slurries, which focused on different solvents, binders, and the dispersion of the ceramic particles. Water and acetone-based slurries were developed with mayenite, and printing tests showed that the printing mayenite with acetone as the solvent is viable, but greater dispersion of the mayenite powder within the slurry is necessary. In order to make quality components, the mayenite powder needs to be ground to a finer powder, the slurry needs to be mixed more thoroughly, or a dispersant must be added.
by Gina Han.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering
32
Zen, Heishun. "Generation of high quality electron beam using a thermionic RF gun for mid-infrared free electron lasers". Kyoto University, 2009. http://hdl.handle.net/2433/126405.
Testo completoAbstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(エネルギー科学)
甲第14846号
エネ博第200号
新制||エネ||45(附属図書館)
27252
UT51-2009-F488
京都大学大学院エネルギー科学研究科エネルギー変換科学専攻
(主査)准教授 増田 開, 教授 長﨑 百伸, 教授 大垣 英明
学位規則第4条第1項該当
33
Colakoglu, Tahir. "The Growth And Characterization Of Galium Selenide Thin Films". Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1085240/index.pdf.
Testo completoAbstract (sommario):
GaSe thin films were deposited by thermal evaporation technique with and
without Cd doping. X-ray analysis showed that the crystallinity increases in (1014) preferred orientation direction with annealing for doped and undoped films. The room temperature conductivity and mobility values of the samples were found to be for doped and undoped films in between 1.3×101 - 3.4×
102 (&
#8486
-cm)-1, 1.2×
10-6 - 1.5×
10-6 (&
#8486
-cm)-1 and 5.9 &
#8211
20.9 (cm2/V.s) (for doped samples only), respectively. Due to the high resistivity of the undoped samples mobility measurements could not be performed. The dominant conduction mechanisms were determined to be thermionic emission in the high temperature region (250-400 K), tunneling in the range 160-250 K and between 100-150 K variable range hopping mechanism for the doped films. For the undoped films above 250 K thermionic emission was the dominant conduction mechanism. Space charge limited currents in parallel and perpendicular directions of the film surface showed two different localized energy levels with different concentrations for each case, namely, 99.8 meV with concentration 3.5×
1012 cm-3 and 418.3 meV with the concentration 2.2×
105 cm-3 for parallel direction and for perpendicular direction 58.3 meV with concentration 6.2×
1025 cm-3 and 486.1 meV with concentration 3.3×
1022 cm-3. Photocurrentillumination intensity dependences indicated that power exponent of illumination intensity with values n>
1 implied two recombination centers exist in studied samples.
34
Little, Scott A. "Experimental and numerical studies of a new thermionic emitter structure based on oxide coated carbon nanotubes operating at large emission currents". Virtual Press, 2007. http://liblink.bsu.edu/uhtbin/catkey/1380104.
Testo completoAbstract (sommario):
We have developed a thermionic cathode capable of high emission currents. The structure of this cathode is oxide coated carbon nanotubes (CNTs) on a tungsten (W) substrate. This cathode was superior in emission due to the combination of the field enhancement effect from the CNTs and the lowered work function from the semiconducting oxide surface. Such oxide coated CNTs were excellent electron emitters. Conventional electron emission theories, such as Richardson's and Fowler-Nordheim's, did not accurately describe the field enhanced thermionic emission from such emitters. A unified electron emission theory was adopted and numerical simulations were performed to explain the deviation of electron emission from conventional field and thermionic emission theories. Also, the thermionic measurement system and measurement methods were improved in order to measure and characterize the strong electron emission from this new cathode. Large electron emission current from such structures also made a new thermionic cooling device a possibility. Cooling due to the electron emission was measured in terms of temperature drop, and a large temperature drop was observed from this cathode structure. Finally, applications of this cathode in plasma discharge devices were explored. This new cathode was tested in a plasma environment and initial results were obtained.Department of Physics and Astronomy
35
Jánský, Pavel. "Coulombovské interakce v elektronových svazcích". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-233908.
Testo completoAbstract (sommario):
The thesis deals with numerical simulations of a hairpin thermionic electron gun, an electron source of the electron-beam welding machine. Simulations showed that the space charge in the electron gun has a significant influence on the beam current and electron trajectories. Simulation outputs are in a sufficient agreement with the experimental measurements.
36
Wan, Congshang. "Study of Scandate Cathode Surface Materials". Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1428022033.
Testo completo
37
Magnus, Sandra Hall. "An Investigation of the relationship between the thermochemistry and emission behavior of thermionic cathodes based on the BaO-Sc₂O₃-WO₃ ternary system". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19625.
Testo completo
38
Phumisithikul, Karen L. "Surface photovoltage transients for p-type AlGaN". VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3787.
Testo completoAbstract (sommario):
There is an understanding of surface photovoltage (SPV) behavior for GaN, yet little is known about the SPV behavior for AlGaN. In this work, a Kelvin probe was used to measure the SPV for p-type AlGaN. Very slow SPV transients were found in AlGaN, which could not be explained with a simple thermionic model. A possible explanation of this behavior is the segregation of impurities to the surface, which causes significant reduction of the depletion region width (down to 2 nm), with carrier tunneling and hopping becoming the dominant mechanisms responsible for the SPV transients. To verify this assumption, the near-surface defective region (about 40 nm) has been removed through the ICP-RIE process. After the etching, the SPV transients became fast and increased in magnitude by about 0.6 eV. By using the thermionic model, band bending was estimated to be -1 eV.
39
Higashi, Cristiane. ""Investigação do processo de obtenção de aluminatos de bário e cálcio para construção e caracterização de catodos termiônicos impregnados para aplicação em dispositivos de microondas de potência"". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-31052007-150633/.
Testo completoAbstract (sommario):
O presente trabalho descreve os processos de preparação do aluminato de bário e cálcio, material emissor de elétrons, empregados nos catodos do tipo impregnado para utilização em uma válvula de microondas do tipo TWT. Os catodos investigados constituem-se de uma pastilha de tungstênio porosa impregnada com aluminato de bário e cálcio com proporção molar 5:3:2. Para a síntese do aluminato, utilizaram-se três diferentes métodos: reação em estado sólido, precipitação e cristalização. A termogravimetria auxiliou na consolidação dos procedimentos de preparação dos aluminatos de modo a definir os parâmetros de pirólise/calcinação. Verificou-se que a técnica que apresentou melhores características de síntese foi o método da cristalização, pois esta apresentou uma menor temperatura de formação do aluminato (800ºC) em atmosfera oxidante (O2), quando comparada às técnicas de reação em estado sólido e de precipitação (temperatura de 1000ºC em atmosfera redutora H2). Utilizou-se o conceito da distribuição da função trabalho prática (PWFD) de Miram para a caracterização termiônica dos catodos impregnados. Empregando-se este método, foi possível traçar o perfil termiônico do catodo com aluminato de bário e cálcio. As curvas PWFD apresentaram a função trabalho média do catodo aluminato de, aproximadamente, 2,00 eV.In the present work it is described the barium calcium aluminate manufacture processes employed to produce impregnated cathodes to be used in a traveling-wave tube (TWT). The cathodes were developed using a tungsten body impregnated with barium and calcium aluminate with a 5:3:2 proportion (molar). Three different processes were investigated to obtain this material: solid-state reaction, precipitation and crystallization. Thermal analysis, thermogravimetry specifically, supported to determine an adequate preparation procedure (taking into account temperature, time and pirolisys atmosphere). It was verified that the crystallization showed a better result when compared to those investigated (solid-state reaction and precipitation techniques formation temperature is about 1000ºC in hydrogen atmosphere), whereas it presented the lower formation temperature (800ºC) in oxidizing atmosphere (O2). It was used the practical work function distribution theory (PWFD) of Miram to characterize thermionic impregnated cathode. The PWFD curves were used to characterize the barium-calcium aluminate cathode. PWFD curves shown that the aluminate cathode work function is about 2,00 eV.
40
Kummari, Rani S. "Improved SiC Schottky Barrier Diodes Using Refractory Metal Borides". Connect to resource online, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1266422079.
Testo completo
41
Glajc, Petr. "Testování a optimalizace iontového zdroje". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231360.
Testo completoAbstract (sommario):
A thorough description of the testing of a saddle-field ion source is presented in the diploma thesis. The most important experimental results, such as Faraday cup measurements of the ion beam current profile and of the ion energy spectra, are included. Based on these results it is shown that the optimized ion source works correctly and according to the expectations. At the end of the thesis, the development of the ion-optical and construction design of the focusing optics is described. The manufactured optics assembly attached to the ion source is also shown.
42
Stefanelo, Josiani Cristina. "Estudo das propriedades elétro-óptica de dispositivos eletroluminescentes confeccionados com um compósito híbrido /". Rio Claro : [s.n.], 2009. http://hdl.handle.net/11449/91900.
Testo completoAbstract (sommario):
Orientador: Dante Luis ChinagliaBanca: Clarissa de Almeida Olivati
Banca: Luiz Francisco Malmonge
Resumo: Neste trabalho foi desenvolvido um dispositivo eletroluminescente (EL) constituído de um compósito híbrido (CH), formado por uma blenda polimérica e um material EL inorgânico. A blenda é composta por um polímero condutor, a poli(o-metoxianilina) (POMA) dopada com ácido tolueno sulfônico (TSA), e um polímero isolante, o poli(fluoreto de vinilideno-co-trifluoretileno) (P(VDF-TrFE)). A esta blenda é acrescentado um material EL inorgânico, o silicato de zinco dopado com Manganês (Zn2SiO4:Mn), formando assim, o compósito híbrido. O dispositivo foi construído depositando o compósito por drop casting sobre um substrato de óxido de estanho dopado com flúor (FTO) e após cristalização em uma estufa foi depositado um eletrodo de metal por evaporação à vácuo formando uma estrutura tipo "sanduíche". Neste trabalho foram construídos dispositivos com eletrodo superior de Alumínio (Al) e Ouro (Au), denominados: FTO/CH/Al e FTO/CH/Au. O comportamento elétrico dos dispositivos de FTO/CH/Al foram analisados aplicando-se as teorias de Emissão Termoiônica, Emissão Schottky e Emissão Poole-Frenkel, o que tornou possível encontrar alguns parâmetros como: altura da barreira para a junção metal/CH, condutividade do CH e fator de retificação. O dispositivo de FTO/CH/Au foi caracterizado pela técnica de espectroscopia de impedância, sendo obtido também a altura da barreira para a junção metal/CH, a condutividade do CH, além da constante dielétrica do compósito e como variam esses dois últimos parâmetros com a temperatura. A aplicação das teorias de Emissão Termoiônica, Emissão Schottky e Emissão Poole-Frenkel produziram resultados semelhantes aos obtidos pela técnica de espectroscopia de impedância. Os espectros de luminescência apresentaram um pico em l = 528 nm com estabilidade temporal de emissão comparável a dos dispositivos inorgânicos puros.
Abstract: In this work was developed an electroluminescent (EL) device made up with a hybrid composite (CH), that is formed by a polymeric blend and an inorganic EL material. The conductive polymer, poly(o-methoxyaniline) (POMA) doped with p-Toluene sulphonic acid (TSA), and an isolating polymer, the poly(vinylidenefluoride-co-trifluoroethylene) (P(VDFTrFE)), was used to make the polymer blend. An inorganic EL material, the zinc silicate manganese-doped (Zn2SiO4:Mn), was added to the blend, forming the hybrid composite. The composite was deposited by drop-casting over a Fluoride Tin Oxide substrate (FTO) and after the crystallization in an oven a metal electrode was deposited by vacuum evaporation, forming a type "sandwich" structure. In this work were constructed different devices. Aluminum (Al) and Gold (Au) were used as upper electrodes, therefore the device structures were: FTO/CH/Al and FTO/CH/Au. To analyze the electrical behavior of the FTO/CH/Al device was applied the theories of Thermionic Emission, Schottky Emission and Poole- Frenkel Emission. Using these theories was possible to obtain parameters such as; the barrier height from the metal/CH junction, CH conductivity and diode rectifier factor. The FTO/CH/Au device was characterized using the impedance spectroscopy technique. For this device was also possible to obtain the barrier height from the metal/CH junction, CH conductivity and CH dielectric constant. For the last two parameters the dependence with the temperature were also observed. The application of the theories of Thermionic Emission, Schottky Emission and Poole-Frenkel Emission produced similar results to that obtained by the impedance spectroscopy technique. The luminescence spectra, for the devices, showed a peak at l = 528 nm with emission stability in time that it is comparable of pure inorganic devices.
Mestre
43
Mroz, Michael V. "Characterization of Morphological and Chemical Properties of Scandium Containing Cathode Materials". Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou158470102410177.
Testo completo
44
Fang, Jieping. "New Methods to Create Multielectron Bubbles in Liquid Helium". Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10673.
Testo completoAbstract (sommario):
An equilibrium multielectron bubble (MEB) in liquid helium is a fascinating object with a spherical two-dimensional electron gas on its surface. After it was first observed a few decades ago, a plethora of physical properties of MEBs, for example, a tunable surface electron density, have been predicted. In this thesis, we will discuss two new methods to create MEBs in liquid helium. Before the discussion, the way to generate a large number of electrons in a low temperature system will be discussed, including thermionic emission and field emission in helium. In the first new method to make MEBs, we used a dome-shaped cell filled with superfluid helium in which an MEB was created and confined at the dome. The lifetime of the MEB was substantially longer than the previously reported observations of MEBs. In the second method, MEBs were extracted from the vapor sheath around an electrically heated tungsten filament submerged in liquid helium, either by a high electric field (up to 15 kV/cm) or by a sudden increase of a negative pressure in liquid helium. High-speed photography was used to capture the MEB's motion. A method to determine the number of electrons was developed by monitoring the oscillations of the MEBs. Finally, an electromagnetic trap was designed to localize the MEBs created using the second method, which was important for future studies of the properties of MEBs.Physics
45
HIGASHI, CRISTIANE. "Investigação do processo de obtenção de aluminatos de bário e cálcio para construção e caracterização de catodos termiônicos impregnados para a aplicação em dispositivos de microondas de potência". reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11463.
Testo completoAbstract (sommario):
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
46
Renouf, Benjamin. "Matériaux et procédés pour la modulation spatiale de l’émissivité électronique d’une cathode thermoïonique". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1224.
Testo completoAbstract (sommario):
L’objectif de cette thèse est l’étude et la démonstration de la faisabilité d’un procédé de fabrication fiable et reproductible permettant la création d’un dispositif de modulation spatiale de l’émissivité électronique à la surface d’une cathode thermoïonique. Ce procédé doit permettre le maintien de la géométrie de la carte d’émissivité tout au long de la durée de vie opérationnelle de la cathode. Le premier sujet d’étude a donc été de mettre au point un procédé de dépôt localisé de deux types de couches minces : un matériau à faible travail de sortie pour les zones émissives et un matériau à fort travail de sortie pour les zones anti-émissives. Les essais réalisés au cours de la thèse ont permis de conforter les résultats obtenus lors de tests précédents, et de mettre en place un procédé répétable. Une étude complémentaire a également démontré qu’il était possible d’étendre ce procédé à d’autres configurations de surface, en apportant quelques modifications mineures. Le second axe principal de la thèse a été de compléter les connaissances concernant les phénomènes de diffusion pouvant dégrader la géométrie des dépôts localisés, qu’ils soient émissifs ou anti-émissifs. Une méthodologie a donc été pensée et mise en place, dans le but de caractériser et modéliser l’interdiffusion pour des couples de métaux réfractaires intervenant dans le procédé de dépôts localisés en surface d’une cathode. Le dispositif d’étude a ainsi permis de mettre en évidence l’interdiffusion en volume pour un couple de matériaux intervenant en zone émissive. L’interprétation des données récoltées a conduit à l’obtention de valeurs d’énergie d’activation et de coefficients de diffusion qu’il a été possible de comparer à la littératureThe aim of this thesis is to study and prove the feasibility of a reliable and repeatable process for the creation of a system allowing the areal modulation of the electronic emissivity on the surface of a thermionic cathode. This process should allow the preservation of the emission geometry all along the operational lifetime of the cathode. The first subject was to improve a process to locally deposit two kinds of thin layers: a material with a low work function for emissive areas and a material with a high work function for anti-emissive areas. The experiments investigated during the thesis allowed us to confirm the previous results, and to establish a repeatable process. An additional study has shown the possibility to extend this process to other surface configurations, with minor modifications. The second main subject of the thesis was to complete the knowledge for diffusion phenomena that could appear in the multilayers and degrade the geometry. A methodology was therefore shaped in order to characterize and simulate the diffusion behavior of refractory metal couples that could be involved on the surface of cathodes after the thin layers deposition. Finally, the devices specially made for this study, provided data for bulk interdiffusion between two refractory metals. Activation energy values and diffusion coefficients have been calculated and compared to the literature
47
Ho, Kang Jin. "Studies on Amorphous Silicon Thin Films Doped with Aluminium". Thesis, Indian Institute of Science, 1995. http://hdl.handle.net/2005/157.
Testo completoAbstract (sommario):
Amorphous Silicon(a-Si) films have attracted the attention of several investigators as it is an economical material for devices. One of the problems that is addressed is the doping of these films after they are prepared.
In this thesis, we investigated the effects of doping amorphous Silicon films(prepared by r.f. sputtering) with Aluminium(Al) by thermal diffusion. Amorphous Silicon films have been prepared on glass substrates at optimal process parameters. Then, the a-Si films are coated with Al by vacuum evaporation and subjected to heating in N2 atmosphere in the temperature range 300°C to 600°C for different durations.
After etching Al layer, it has been found that some of the films which are heated around 550°C contain filament like polycrystalline regions surrounding islands of a-Si.
This structure has been confirmed through Scanning Electron Mi-croscope(SEM) photographs and electrical conductivity measurements. SEM photographs indicate that, bright regions of amorphous material are surrounded by dark regions of relatively higher conducting
boundaries.
The electrical conductivity study shows that there is sharp increase in conductivity of Al doped films, which is attributed to the conducting polycrystalUne filament.
A simple model has been proposed to explain the variation of conductivity of these transformed films, with process parameters and with temperature.
Schottky barrier diodes have been fabricated using these transformed materials and their characteristics explained.
48
Stefanelo, Josiani Cristina [UNESP]. "Estudo das propriedades elétro-óptica de dispositivos eletroluminescentes confeccionados com um compósito híbrido". Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/91900.
Testo completoAbstract (sommario):
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stefanelo_jc_me_rcla.pdf: 1971755 bytes, checksum: f2545c6a190dc7a872bf14f2c2b4fce6 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Neste trabalho foi desenvolvido um dispositivo eletroluminescente (EL) constituído de um compósito híbrido (CH), formado por uma blenda polimérica e um material EL inorgânico. A blenda é composta por um polímero condutor, a poli(o-metoxianilina) (POMA) dopada com ácido tolueno sulfônico (TSA), e um polímero isolante, o poli(fluoreto de vinilideno-co-trifluoretileno) (P(VDF-TrFE)). A esta blenda é acrescentado um material EL inorgânico, o silicato de zinco dopado com Manganês (Zn2SiO4:Mn), formando assim, o compósito híbrido. O dispositivo foi construído depositando o compósito por drop casting sobre um substrato de óxido de estanho dopado com flúor (FTO) e após cristalização em uma estufa foi depositado um eletrodo de metal por evaporação à vácuo formando uma estrutura tipo “sanduíche”. Neste trabalho foram construídos dispositivos com eletrodo superior de Alumínio (Al) e Ouro (Au), denominados: FTO/CH/Al e FTO/CH/Au. O comportamento elétrico dos dispositivos de FTO/CH/Al foram analisados aplicando-se as teorias de Emissão Termoiônica, Emissão Schottky e Emissão Poole-Frenkel, o que tornou possível encontrar alguns parâmetros como: altura da barreira para a junção metal/CH, condutividade do CH e fator de retificação. O dispositivo de FTO/CH/Au foi caracterizado pela técnica de espectroscopia de impedância, sendo obtido também a altura da barreira para a junção metal/CH, a condutividade do CH, além da constante dielétrica do compósito e como variam esses dois últimos parâmetros com a temperatura. A aplicação das teorias de Emissão Termoiônica, Emissão Schottky e Emissão Poole-Frenkel produziram resultados semelhantes aos obtidos pela técnica de espectroscopia de impedância. Os espectros de luminescência apresentaram um pico em l = 528 nm com estabilidade temporal de emissão comparável a dos dispositivos inorgânicos puros.
In this work was developed an electroluminescent (EL) device made up with a hybrid composite (CH), that is formed by a polymeric blend and an inorganic EL material. The conductive polymer, poly(o-methoxyaniline) (POMA) doped with p-Toluene sulphonic acid (TSA), and an isolating polymer, the poly(vinylidenefluoride-co-trifluoroethylene) (P(VDFTrFE)), was used to make the polymer blend. An inorganic EL material, the zinc silicate manganese-doped (Zn2SiO4:Mn), was added to the blend, forming the hybrid composite. The composite was deposited by drop-casting over a Fluoride Tin Oxide substrate (FTO) and after the crystallization in an oven a metal electrode was deposited by vacuum evaporation, forming a type “sandwich” structure. In this work were constructed different devices. Aluminum (Al) and Gold (Au) were used as upper electrodes, therefore the device structures were: FTO/CH/Al and FTO/CH/Au. To analyze the electrical behavior of the FTO/CH/Al device was applied the theories of Thermionic Emission, Schottky Emission and Poole- Frenkel Emission. Using these theories was possible to obtain parameters such as; the barrier height from the metal/CH junction, CH conductivity and diode rectifier factor. The FTO/CH/Au device was characterized using the impedance spectroscopy technique. For this device was also possible to obtain the barrier height from the metal/CH junction, CH conductivity and CH dielectric constant. For the last two parameters the dependence with the temperature were also observed. The application of the theories of Thermionic Emission, Schottky Emission and Poole-Frenkel Emission produced similar results to that obtained by the impedance spectroscopy technique. The luminescence spectra, for the devices, showed a peak at l = 528 nm with emission stability in time that it is comparable of pure inorganic devices.
49
Vašíček, Martin. "Charakterizace autoemisních zdrojů pro elektronovou mikroskopii". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-220188.
Testo completoAbstract (sommario):
This work deals with the theoretical foundations of electron emission into vacuum, various types of emissions, focused on the cold-emission and Schottky emission and the principle of quantum tunneling. The next part deals with the technical implementation of electron sources with a detailed study of the methodology of laboratory production of cathodes by electrochemical etching and construction of electron microscopes, using field-emission sources. This work also contains methods for measuring, processing and evaluation of electrical characteristics of emission sources.
50
Yi-Chun, Wang. "A Thermionic RF-gun for Short Bunch Generation". 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0016-1303200709333545.
Testo completo