Дисертації з теми "Electron gas states"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Electron gas states.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Electron gas states".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Yu, Wing Wa. "Low temperature spintronics : probing charge and spin states with two-dimensional electron gas." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/12580.
Повний текст джерелаАнотація:
This thesis is based on two low temperature experiments in spintronics - physics and engineering of electronic spins. The measurements were performed on a GaAs/AlGaAs two-dimensional electron gas with geometries defined by tunable surface gates. The first experiment is about detection of electrons in a quantum dot. A quantum point contact (QPC) and a quantum wire (QW) is coupled to a single-lead few-electron quantum dot. By measuring the conductance of the QPC and the QW, one can gain information on the average number of electrons in the dot as well as energy-level structure of the dot. The second experiment investigates anisotropy of spin-orbit interaction in GaAs/AlGaAs heterostructure by measuring spin polarization in a narrow channel. Polarized electrons are injected into the channel through a spin-selective injector QPC and diffuse towards the end of the channel. This diffusion generates a pure spin current and the spin polarization 25 microns away is measured by a detector QPC. A periodic spin-orbit field induced by motion of the electrons in the channel causes the spins to resonate with external magnetic field. Spin-orbit anisotropy is demonstrated by the different resonance strength observed in channels aligned along two different crystal axes.
2
Yokota, Takeru. "Functional-renormalization-group aided density-functional theory - ab-inito description of ground and excited states of quantum many-body systems -." Kyoto University, 2019. http://hdl.handle.net/2433/242609.
Повний текст джерела
3
Wright, Timothy Grahame. "Studies of some gas-phase oxidation reactions using electron spectroscopy and the electronic structure of some small molecules." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358873.
Повний текст джерела
4
Ouali, Fatma Fouzia. "Phonon emission from a two dimensional electron gas." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293620.
Повний текст джерела
5
McFadden, C. "Electron transport in GaAs semiconductor devices." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332168.
Повний текст джерела
6
Gilbert, Timothy George. "Electronic states of ultrathin GaAs/AlAs superlattices." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/35893.
Повний текст джерелаАнотація:
The continuing refinement of crystal growth techniques has made possible the fabrication of semiconductor superlattices where the period can be as small as one lattice constant. Prediction of many of the properties of such systems requires a detailed description of their electronic structure. In this thesis, a self-consistent pseudopotential method which includes a parametrization scheme has been used to calculate the electronic properties of (GaAs)n(AlAs)n superlattices with n ranging from 1 to 4. The parametrization scheme is used to reproduce energy gaps at the principal symmetry points for the bulk constituents and the resulting parameter set is employed in all subsequent calculations. The n=l superlattice is found to be indirect with the conduction band minimum at R (equivalent to the zincblende L point) and all the thicker systems are pseudodirect in good agreement with experimental results. The lowest conduction band state at the zone centre for all systems is found to be mainly X-derived reflecting the importance of zone translating effects here. By analysing the states near to the band edges, the observed pattern of confinement in states of the n=l superlattice shows the band offsets to have at most a small role, in contrast to the thicker systems where a definite relationship was established. Moreover, the results suggest that Dingle's "15% rule" is consistently violated and that a valence band offset of about 30-40% is obtained which changes little with layer thickness. Attempts to study the effects of hydrostatic pressure on the n=3 superlattice were in part successful and predicted quite complex behaviour for the electronic states. Much of the discrepancy between the results obtained and the experimental data was attributed to the inadequacies of the empty-core pseudopotential to model the ions.
7
Hedberg, James. "Low temperature force microscopy on a deeply embedded two dimensional electron gas." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97016.
Повний текст джерелаАнотація:
Experimental physics in the low temperature limit has consistently produced major advances for condensed matter research. Likewise, scanning probe microscopy offers a unique view of the nanometer scale features that populate the quantum landscape. This work discusses the merger of the two disciplines via the development of the Ultra Low Temperature Scanning Probe Microscope, the ULT-SPM. We focus on the novel characterization of an exotic condensed matter system: a deeply buried two dimensional electron gas with a cleaved edge overgrowth geometry. By coupling the dynamics of the force sensing probe microscope to the electrostatics of the electron gas, we can remotely and non-invasively measure charge transport features which are normally only observable using physically contacted electrodes. Focusing on the quantum Hall regime, we can exploit the high sensitivity of the local force sensor to study spatially dependent phenomena associated with electronic potential distributions. The instrument shows promise for many exciting experiments in which low temperatures, high magnetic fields, and local measurements are critical.Designed for operation at 50 mK, in magnetic fields reaching 16 T, many components of the instrument are not commercially available and were therefore designed and constructed in- house. As such, the intricate details of its design, construction and operation are documented thoroughly. This includes: the microscope assembly, the modular components such as the scan head and coarse motors, the electronics developed for controlling the instrument, and the general integration into the low temperature infrastructure. A quartz tuning fork is used as the force sensor in this instrument, enabling a wide selection between different modes of operation, the most relevant being electrostatic force microscopy. Noise limits are investigated and matched sources of experimental noise are identified. Detailed schematics of the instrument are also included.La physique expérimentale aux limites des basses températures contribue constamment à des percées majeures dans le domaine de la matière condensée. Pour sa part, la microscopie à balayage de sonde offre la possibilité unique d'observer les éléments nanométriques qui car- actérisent le paysage quantique. Ce projet allie les avantages de ces deux disciplines par le développement d'un microscope à balayage de sonde opérant à très basse température (Ultra Low Temperature Scanning Probe Microscope), le « ULT-SPM. » Nous étudions en particulier un système exotique de la matière condensée : un gaz d'électrons bidimensionnel profondément enfoui, comportant une croissance latérale sur le bord clivé. Le couplage des forces dynamiques de la sonde du microscope et électrostatiques du gaz à électrons, nous permet de mesurer à distance et de façon non invasive, les caractéristiques de transport des charges, qui ne sont normalement observables qu'à l'aide d'électrodes et donc, par un contact physique. Dans le régime de l'effet Hall quantique, nous pouvons exploiter la grande sensibilité du capteur de force local pour étudier des phénomènes spatiodépendants associés aux distribu- tions de potentiel électronique. L'instrument se révèle prometteur pour la poursuite de nom- breuses expériences passionnantes où les conditions de basse température, champ magnétique élevé et mesures locales sont essentielles. Comme il est conçu pour fonctionner à 50 mK et sous un champ magnétique pouvant at- teindre 16 T, plusieurs composantes du microscope ne sont pas disponibles commercialement et ont donc été entièrement conçues et fabriquées sur place. Les détails intrinsèques de la con- ception, de la construction et du fonctionnement sont ainsi documentés à fond. Ceci inclut : l'assemblage du microscope, les composantes modulaires comme la tête de balayage et les mo- teurs, l'électronique des contrôles de l'instrument et l'intégration à l'infrastructure opérant à basse température. Dans cet instrument, un diapason de quartz fait office de capteur, ce qui permet une grande flexibilité quant aux différents modes d'opération, le plus utile étant la mi- croscopie de force électrostatique. Les limites de bruit sont étudiées et comparées aux sources de bruit expérimentales. Les schémas détaillés de l'instrument sont également inclus.
8
Woolfe, Adam. "Electronic transport through localised states in GaAs transistors." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390216.
Повний текст джерела
9
Brummell, M. A. "High magnetic field studies of the two-dimensional electron gas formed in semiconductor heterostructures." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355716.
Повний текст джерела
10
Ibraheim, K. S. "Angular and polarisation correlation measurements on the 2'1P and 3'1P states of helium." Thesis, University of Stirling, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375414.
Повний текст джерела
11
Latt, Kyaw Zin. "Interactions of Two Dimensional Surface State Electron Gas with Zero, One and Two Dimensional Structures." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1383242271.
Повний текст джерела
12
Brown, Robert James. "Electronic transport in GaAs/AlGaAs microstructures." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335681.
Повний текст джерела
13
Wong, K. B. "Electronic properties of GaAs-GaAlAs superlattices." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356158.
Повний текст джерела
14
Tanaka, Yasunori, Yasunobu Yokomizu, Motohiro Ishikawa, and Toshiro Matsumura. "Particle Composition of High-Pressure SF_6 Plasma with Electron Temperature Greater than Gas Temperature." IEEE, 1997. http://hdl.handle.net/2237/7280.
Повний текст джерела
15
Lovering, David James. "Time resolved optical spectroscopy of electronic states in GaAs quantum wells." Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305754.
Повний текст джерела
16
Zhang, Ningjiao. "Low Frequency Noise Characterization of AlGaN/GaN High Electron Mobility Transistors." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366369049.
Повний текст джерела
17
Huang, Ying. "Electronic states and optical properties of GaAs/AIGaAs and GaInP/AlGaInP quantum wells." Thesis, Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B31479820.
Повний текст джерела
18
Honda, S., H. Itoh, J. Inoue, H. Kurebayashi, T. Trypiniotis, C. H. W. Barnes, A. Hirohata, and J. A. C. Bland. "Spin polarization control through resonant states in an Fe/GaAs Schottky barrier." American Physical Society, 2008. http://hdl.handle.net/2237/11246.
Повний текст джерела
19
Veal, Timothy David. "High resolution electron energy loss spectroscopy of narrow gap III V semiconductor surfaces and interfaces." Thesis, University of Warwick, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252483.
Повний текст джерела
20
Humphreys, Richard David. "In-beam electron spectroscopy of ²âµâ´No and ²²â¶U in conjunction with a gas-filled recoil separator." Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288233.
Повний текст джерела
21
Ciro, Guido. "TD-DFT and TD-DFT/PCM approaches to molecular electronic excited states in gas phase and in solution." Doctoral thesis, Scuola Normale Superiore, 2011. http://hdl.handle.net/11384/85797.
Повний текст джерела
22
Brannick, A. "Modelling of steady-state and transient effects in advanced AIGaN/GaN high electron mobility transistors." Thesis, University of Essex, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.528850.
Повний текст джерела
23
Blankenship, Thomas Keith. "Rapidity gap in the final state hadron distribution in deep inelastic electron scattering at HERA." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06062008-170753/.
Повний текст джерела
24
Wen, Yuan. "Theoretical and experimental studies of electronic states in InAs/GaAs self-assembled quantum dots." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43224003.
Повний текст джерела
25
Choi, Hyun-jin. "Investigation of resonant Raman scattering in type II GaAs/A1As superlattices." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365725.
Повний текст джерела
26
Mand, R. S. "Characterisation and applications of heterostructures : Characterisation of GaAs/GaAlAs heterostructures and GaAs/GaAlAs double heterostructure electronic and photonic switches." Thesis, University of Bradford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371479.
Повний текст джерела
27
North, Stephen Michael. "Electronic structure of GaSb/GaAs and Si/Ge quantum dots." Thesis, University of Newcastle Upon Tyne, 2001. http://hdl.handle.net/10443/551.
Повний текст джерелаАнотація:
There are significant differences between experiment and theoretical calculations of the electronic structure of GaSb/GaAs self-assembled quantum dots. Using a multi-band effective mass approximation it is shown that the influence of size and geometry of quantum dots has little or no effect in determining the hydrostatic strain. Furthermore, the valenceband ground state energies of the quantum dots studied are surprisingly consistent. This apparent paradox attributed to the influence of biaxial strain in shaping the heavy-hole and light-hole potentials. Consequently, it is shown that a simple, hydrostatically derived potential is insufficient to accurately describe the electronic structure of such quantum dots. In addition, using the latest experimental results measuring the conductionband offset, it has been shown that much better experimental contact may be achieved for the magnitude of the transition energies derived compared to theoretically derived transition energies. The transition energies of Si/Ge self-assembled quantum dots has also been calculated. In particular, a range of quantum dot structures have been proposed that are predicted to have an optical response in the 3-5 micron range.
28
Moro, Alberto, and Laura Lonza. "Electricity carbon intensity in European Member States: Impacts on GHG emissions of electric vehicles." Elsevier, 2017. https://publish.fid-move.qucosa.de/id/qucosa%3A73241.
Повний текст джерелаАнотація:
The Well-To-Wheels (WTW) methodology is widely used for policy making in the transportation sector. In this paper updated WTW calculations are provided, relying on 2013 statistic data, for the carbon intensity (CI) of the European electricity mix; detail is provided for electricity consumed in each EU Member State (MS). An interesting aspect presented is the calculation of the GHG content of electricity traded between Countries, affecting the carbon intensity of the electricity consumed at national level. The amount and CI of imported electricity is a key aspect: a Country importing electricity from another Country with a lower CI of electricity will lower, after the trade, its electricity CI, while importing electricity from a Country with a higher CI will raise the CI of the importing Country. In average, the CI of electricity used in EU at low voltage in 2013 was 447 gCO2eq/kWh, which is the 17% less compared to 2009. Then, some examples of calculation of GHG emissions from the use of electric vehicles (EVs) compared to internal combustion engine vehicles are provided. The use of EVs instead of gasoline vehicles can save (about 60% of) GHG in all or in most of the EU MSs, depending on the estimated consumption of EVs. Compared with diesel, EVs show average GHG savings of around 50% and not savings at all in some EU MS.
29
Ding, Yi. "Quantum well state of cubic inclusions in hexagonal silicon carbide studied with ballistic electron emission microscopy." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1086207334.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xv, 150 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Jonathan P. Pelz, Dept. of Physics. Includes bibliographical references (p. 144-150).
30
Erslev, Peter Tweedie 1979. "The electronic structure within the mobility gap of transparent amorphous oxide semiconductors." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/10566.
Повний текст джерелаАнотація:
xix, 142 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.Transparent amorphous oxide semiconductors are a relatively new class of materials which show significant promise for electronic device applications. The electron mobility in these materials is at least ten times greater than that of the current dominant material for thin-film transistors: amorphous silicon. The density of states within the gap of a semiconductor largely determines the characteristics of a device fabricated from it. Thus, a fundamental understanding of the electronic structure within the mobility gap of amorphous oxides is crucial to fully developing technologies based around them. Amorphous zinc tin oxide (ZTO) and indium gallium zinc oxide (IGZO) were investigated in order to determine this sub-gap structure. Junction-capacitance based methods including admittance spectroscopy and drive level capacitance profiling (DLCP) were used to find the free carrier and deep defect densities. Defects located near insulator-semiconductor interfaces were commonly observed and strongly depended on fabrication conditions. Transient photocapacitance spectroscopy (TPC) indicated broad valence band-tails for both the ZTO and IGZO samples, characterized by Urbach energies of 110±20 meV. These large band-tail widths imply that significant structural disorder exists in the atomic lattice of these materials. While such broad band-tails generally correlate with poor electronic transport properties, the density of states near the conduction band is more important for devices such as transistors. The TPC spectra also revealed an optically active defect located at the insulator-semiconductor junction. Space-charge-limited current (SCLC) measurements were attempted in order to deduce the density of states near the conduction band. While the SCLC results were promising, their interpretation was too ambiguous to obtain a detailed picture of the electronic state distribution. Another technique, modulated photocurrent spectroscopy (MPC), was then employed for this purpose. Using this method narrow conduction band-tails were determined for the ZTO samples with Urbach energies near 10 meV. Thus, by combining the results of the DLCP, TPC and MPC measurements, a quite complete picture of the density of states within the mobility gap of these amorphous oxides has emerged. The relationship of this state distribution to transistor performance is discussed as well as to the future development of device applications of these materials.
Committee in charge: Stephen Kevan, Chairperson, Physics; J David Cohen, Member, Physics; David Strom, Member, Physics; Jens Noeckel, Member, Physics; David Johnson, Outside Member, Chemistry
31
Zhang, Xin. "Electrochemical and structural investigations of a layered AU,PT-YSZ mixed potential gas sensing electrode." Doctoral thesis, Technische Universität Dresden, 2019. https://tud.qucosa.de/id/qucosa%3A36877.
Повний текст джерелаАнотація:
In recent developments of mixed potential gas sensors based on Yttrium Stabilized Zirconia (YSZ), the combination of Au/AuPt-admixtures and oxides was found to be promising electrode materials. With this material combination, satisfactory sensing characteristics were achieved, but the role of Au addition, especially its effect on the processes contributing to the mixed potential formation, has not yet been well understood. Deeper insights of the influence of Au on the electrochemical behaviors of this kind of electrodes are necessary for better understanding of the sensing behaviors and for achieving further technological improvements, as for instance, enhancement of the long-term stability.
This situation motivated studies of a layered Au,Pt-YSZ mixed potential gas sensing electrode and its dependence on the thickness of the Au-layer and the sintering conditions. In this work, for the first time three variations of this kind of electrode, which generally comprises a thick-film Pt-YSZ electrode and a thin-film Au layer deposited on top, were studied by different kinds of material analytical approaches and electrochemical methods. These studies elucidated the correlation among the electrochemical behaviors of the electrodes, the amount of gold deposition and its non-uniform distribution over the electrode. Based on these structural and electrochemical data, a qualitative model for the first time is proposed to interpret the sensing mechanism of the layered Au,Pt-YSZ electrodes. In the past such a theory was only available for the electrodes at which the Au was homogeneously admixed with the Pt-YSZ composite.
From the structural studies including the ESEM, the XRD and the Glow Discharge-Optical Emission Spectroscopy analysis (GD-OES), it was shown that the thin film Au layer at the layered Au,Pt-YSZ electrodes is not uniformly admixed with the Pt-YSZ bulk after firing, but results in a non-uniform lateral distribution on the electrode surface and a concentration gradient of Au from top over the thickness of the electrode. This Au distribution is strongly affected by the sintering temperature. The higher sintering temperature (1050 °C) results in not only a more uniform morphology of the electrode surface without a separate crystalline phase of gold , but also a better alloying of Au and Pt in the inner parts of the electrode during the sintering process, compared to the electrodes sintered at a lower temperature (850 °C). These clear structural differences of the electrodes fired at different temperatures are related to different catalytic activities over the electrode layer, and accordingly affect their open circuit potential (OCP) sensing behaviors and other electrochemical properties.
With respect to selectivity and stability of the sensors, the highest sensing response was observed in the H2 containing gases compared to the other gas species like CO, CH4, and C3H6 for both the type II (low temperature sintered) and the type III (high temperature sintered) sensors. However, clear response and potential stability losses were observed at exposure to C3H6. Formation of coking layers on the electrode seems to be correlated with this response decrease.
Surprisingly, the response degradation was even observed by aging the sensors at 600 °C in ambient air. Combined OCP, CV and EIS studies revealed that, the aging process results in some minor irreversible but mainly reversible changes at the electrode/electrolyte interface. Both induce the response degradation which is well correlated with an impedance increase and a CV current decrease. The reversible changes are assumed to be attributed to the formation of an oxidation phase of the metallic parts at the TPB, which is well described in literature. Now, for the first time in this work it could be demonstrated that this reversible response degradation can be nearly fully recovered by the application of cathodic polarization sequences.
Consequently, due to the strong correlation between the OCP response to CO and the dynamic electrochemical behaviors ((EIS and CV)) at ambient air, both the EIS and the CV method can be used as efficient tools to check the sensitivity of the sensor at ambient air conditions. In case of OCP response degradation, the sensitivity can be almost fully regenerated by application of cathodic polarization at enhanced temperatures (T700°C). This combination of OCP measurements with dynamic electrochemical methods and the application of cathodic polarization procedures is of enormous practical relevance and was filed for a patent. It excited high interest of the sensor chip producer (Lamtec Meß- und Regeltechnik für Feuerungen GmbH, Walldorf) because it allows sensitivity estimation and regeneration of layered Au,Pt-YSZ gas sensing electrodes whenever ambient air conditions are given. For instance, in case of long-term CO/HC-monitoring for improvement of automated combustion process control of firing appliances, this procedure could be carried out in breaks between firing batches without the need of de-installation of the sensor and, indeed, without any exposure to model gases.
32
Lowman, Jennifer Lee. "School principal's views of No Child Left Behind, the achievement gap, and the student groups assessed by NCLB." abstract and full text PDF (free order & download UNR users only), 2005. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433376.
Повний текст джерела
33
Liu, Shuhao. "Electronic Transport in Functional Materials and Two-Dimensional Hole System." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1522893320666086.
Повний текст джерела
34
Gozcu, Ferhat Can. "Estimation Of Steady-state Temperature Distribution In Power Transformer By Using Finite Difference Method." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611592/index.pdf.
Повний текст джерелаАнотація:
Estimating the temperature distribution in transformer components in
the design stage and during the operation is crucial since temperatures
above the thermal limits of these components might seriously damage
them. Thermal models are used to predict this vital information prior to
actual operations. In this study, a two-dimensional, steady-state model
based on the Finite Difference Method (FDM) is proposed to estimate
the temperature distribution in the three-phase, SF6 gas insulatedcooled
power transformer. The model can predict the temperature
distribution at the specific discredited locations in the transformer
successfully. This study also compares predicted temperatures of the
model proposed in this study with the results of the previous study
which is based on Finite Element Method (FEM) and the results of the
research performed by the designers of the transformer. The results
show that FDM model proposed in this study can be used to estimate
the temperature distribution in the transformer with an acceptable
accuracy and can be an alternative of the previous study which is based
on FEM.
35
Hadiya, Maheshkumar. "Case study of offshore wind farm integration to offshore oil and gas platforms as an isolated system - System Topologies, Steady State and Dynamic Aspects." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14148.
Повний текст джерелаАнотація:
The objective of this thesis work has been to investigate the electric system stability, reliability and power security of an “off-grid” isolated network system integration of an offshore wind farm to offshore oil and gas platforms via HVAC transmission, considering different network topologies for wind power penetration, network losses, application of FACTS devices and different system voltage levels. The system stability studies were performed by steady state and dynamic simulations, analysing different perturbation events in the system. The power system model under study was established as a continuation of a previous work concerning a single platform system. The model can be seen to represent the Oseberg oilfield in the Norwegian Sea consisting of five offshore platforms. The complete model represents a grid integration of the five offshore platforms with a total load demand of 147MW to an offshore wind farm of 100MW production via HVAC as an isolated system. Wind farm capacity is less but of comparable size to the total load. Each platform has its own offshore power generation units (Gas Turbines - GTs) to cover the load demand at each platform. Load demands were selected based on recently collected real operational power consumption data from Statoil, ASA. In this study, 8 GTs were installed at different specific platforms to cope with the load of 150MW. Three different network topology configurations were considered, denoted Star, Star-F and Meshed. Four types of perturbation/disturbance events were analysed: Starting of 9MW asynchronous motor at Platform4, loss of a GT at Platform4, sudden loss of wind power production and loss of interconnection cable between Platform1 and Plaform4. The dynamic system stability was assessed by measuring frequency and voltage deviations at specific load buses to ensure whether transient deviations were following offshore NORSOK or IEC standards correctly or not. For each type of disturbances, different topology aspects were considered and analysed for different outages and different cases of percentage of wind power penetration. It could be seen that generators at platforms in all cases were able to regain synchronism by maintaining terminal voltage and power factor within allowed ranges after disturbances caused by Starting of 9MW motor, loss of wind power, loss of a GT and loss of cable. This can be explained because the isolated network system has a strong spinning reserve capacity. But not all studied scenarios were dynamically stable, following NORSOK standards for transient of voltage and frequency variations. The results showed the importance of an integrated grid system: Starting of big induction motor was found not to give large frequency or voltage deviations compared to the previous study of a single platform system since the integrated system has a larger inertia. Voltage deviations were found most critical in case of starting big motors. In addition, a meshed topology have better performace with less voltage and frequency deviation compared to the other two topologies for all perterbation events and cases. The results also showed that loss of wind power was more critical at high wind power penetration levels. A 100% sudden loss of wind power gave unacceptable frequency deviations. The study of two different voltage levels, 36kV and 52kV showed that a 52 kV network gave better dynamic stability behaviour compared to the other one. The study of FACTS devices applications showed that a STATCOM was more efficient in dynamic control of voltage than an SVC due to its better reactive power compensation capability at lower voltage, thus improving power transmission capability for the same power ratings.
36
Cardwell, Drew. "Investigation of electrically-active defects in AlGaN/GaN high electron mobility transistors by spatially-resolved spectroscopic scanned probe techniques." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373894407.
Повний текст джерела
37
Balaguer, Ramírez María. "New solid state oxygen and hydrogen conducting materials. Towards their applications as high temperature electrochemical devices and gas separation membranes." Doctoral thesis, Universitat Politècnica de València, 2013. http://hdl.handle.net/10251/31654.
Повний текст джерелаАнотація:
Los materiales conductores mixtos de electrones e iones (oxígeno o
protones) son capaces de separar oxígeno o hidrógeno de los gases de combustión
o de corrientes de reformado a alta temperatura. La selectividad de este proceso
es del 100%. Estos materiales, óxidos sólidos densos, pueden usarse en la
producción de electricidad a partir de combustibles fósiles, así como formar parte
de los procesos que forman parte del sistema de captura y almacenamiento de
CO2. Las membranas de transporte de oxígeno (MTO) se pueden utilizar en las
plantas energéticas con procesos de oxicombustión, así como en reactores
catalíticos de membrana (RCM), mientras que las membranas de transporte de
hidrógeno (MTH) se aplican en procesos de precombustión. Además, estos
materiales encuentran aplicación en componentes de sistemas energéticos, como
electrodos o electrolitos de pilas de combustible de óxido sólido, de ambas clases
iónicas y protónicas (SOFC y PC-SOFC).
Los procesos mencionados implican condiciones de operación muy
severas, como altas temperaturas y grandes gradientes de presión parcial de
oxígeno (pO2), probablemente combinadas con la presencia de CO2 and SO2. Los
materiales más que mayor rendimiento de separación presentan y más
ampliamente investigados en este campo son inestables en estas condiciones. Por
tanto, existe la necesidad de encontrar nuevos materiales inorgánicos estables que
proporcionen alta conductividad electrónica e iónica.
La presente tesis propone una búsqueda sistemática de nuevos
conductores iónicos-electrónicos mixtos (MIEC, del inglés) con diferente
estructura cristalina y/o diferente composición, variando la naturaleza de los
elementos y la estequiometría del cristal. La investigación ha dado lugar a materiales capaces de transportar iones oxígeno, protones o cargas electrónicas y
que son estables en las condiciones de operación.
La caracterización de una amplia serie de cerias (CeO2) dopadas con
lantánidos proporciona una comprensión general de las propiedades estructurales
y de transporte, así como la relación entre ellas. Además, se estudia el efecto de la
adición de cobalto a dicho sistema. Se ha completado el análisis con la
optimización de las propiedades de trasporte a partir de la microestructura. Todo
esto permite hacer una clasificación inicial de los materiales basada en el
comportamiento de transporte principal y permite adecuar la estructura y las
condiciones de operación para obtener las propiedades deseadas para cada
aplicación.
Algunos de los materiales extraídos de este estudio alcanzaron las
expectativas. Las familias de materiales basadas en Ce1-x
Tbx
O2-¿
y Ce1-x
Tbx
O2-¿
+2 mol% Co proporcionan flujos de oxígeno bajos pero competitivos, ya que son
estables en atmósferas con CO2. Además, la inclusión de estos materiales en
membranas de dos fases aumenta el flujo de oxígeno. La combinación con una
espinela libre de cobalto y de metales alcalinotérreos como es el Fe2
NiO4, ha
dado lugar a un material prometedor en cuanto a flujo de oxígeno y estabilidad en
CO2 y en SO2, que podría ser integrado en el proceso de oxicombustión.
Por otra parte, se ha añadido metales como codopantes en el sistema
Ce0.9-x
Mx
Gd0.1O1.95. Estos materiales, en combinación con la perovskita La1-
x
Srx
MnO3 usada comúnmente como cátodo de SOFC, han sido capaces de
disminuir la resistencia de polarización del cátodo. La mejora es consecuencia de
la introducción de conductividad iónica por parte de la ceria.
Las perovskitas dopadas basadas en CaTiO3 forman el segundo grupo de
materiales investigados. La dificultad de obtener perovskitas estables y que presenten conducción mixta iónica y electrónica se ha hecho evidente. De entre
los dopantes utilizados, el hierro y la combinación hierro-magnesio han sido los
mejores candidatos. Ambos materiales presentan conductividad principalmente
iónica a alta temperatura, mientras que a baja predomina la conductividad
electrónica tipo p. CaTi0.73Fe0.18Mg0.09O3-¿ se ha mostrado como un material
competente en la fabricación de membranas de oxígeno, que proporciona flujos
adecuados a la par que estabilidad en CO2.
Finalmente, la perovskita La0.87Sr0.13CrO3 (LSC) ha sido dopada con el
objetivo de aumentar la conductividad mixta protónica electrónica. Este estudio
ha llevado al desarrollo de una nueva generación de ánodos para PC-SOFC
basadas en electrolitos de LWO. Las perovskitas dopadas con Ce en el sitio del
La (LSCCe) y con Ni en el sitio del Cr (LSCN) son estables en condiciones de
operación reductoras, así como en contacto con el electrolito. El uso de ambos
materiales como ánodo disminuye la resistencia de polarización con respecto al
LSC. El LSCCe está limitado por los procesos que ocurren a baja frecuencia
(BF), relacionados con los procesos superficiales, y que son atenuados en el caso
del LSCN debido a la formación de nanopartículas de Ni metálico en la
superficie. La infiltración posterior con nanopartículas de Ni permite disminuir la
resistencia a BF lo que sugiere que la reacción superficial de oxidación del H2
está siendo catalizada. La infiltración más concentrada en Ni (5Ni) elimina
completamente la resistencia a BF en ambos ánodos, de forma que los procesos
que ocurren a altas frecuencias son ahora limitantes. El ánodo constituido por
LSCNi20+5Ni dio una resistencia de polarización de 0.26 ¿·cm
2
at 750 ºC en H2
húmedo.Mixed ionic (oxygen ions or protons) and electronic conducting materials (MIEC) separate oxygen or hydrogen from flue gas or reforming streams at high temperature in a process 100% selective to the ion. These solid oxide materials may be used in the production of electricity from fossil fuels (coal or natural gas), taking part of the CO2 separation and storage system. Dense oxygen transport membranes (OTM) can be used in oxyfuel combustion plants or in catalytic membrane reactors (CMR), while hydrogen transport membranes (HTM) would be applied in precombustion plants. Furthermore, these materials may also be used in components for energy systems, as advanced electrodes or electrolytes for solid oxide fuel cells (SOFC) and proton conducting solid oxide fuel cells (PCSOFC) working at high and moderate temperature. The harsh working conditions stablished by the targeted processes include high temperatures and low O2 partial pressures (pO2), probably combined with CO2 and SO2 containing gases. The instability disadvantages presented by the most widely studied materials for these purposes make them impractical for application to gas separation. Thus, the need to discover new stable inorganic materials providing high electronic and ionic conductivity is still present. This thesis presents a systematic search for new mixed ionic-electronic conductors. It includes different crystalline structures and/or composition of the crystal lattice, varying the nature of the elements and the stoichiometry of the crystal. The research has yielded new materials capable to transport oxygen ions or protons and electronic carriers that are stable in the working condition to which they are submitted.
Balaguer Ramírez, M. (2013). New solid state oxygen and hydrogen conducting materials. Towards their applications as high temperature electrochemical devices and gas separation membranes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31654
TESIS
Premiado
38
Binus, Joshua D. "Bonneville Power Administration and the Creation of the Pacific Intertie, 1958 -1964." PDXScholar, 2008. https://pdxscholar.library.pdx.edu/open_access_etds/1724.
Повний текст джерелаАнотація:
Construction of the Pacific Northwest-Pacific Southwest Intertie (also known as the Pacific Intertie) began in 1964, following the culmination of a series of interrelated negotiations which included: 1) the planning for the construction and operation of the Pacific Intertie; 2) the passage of federal legislation that put limits on the export of electricity from the regions where it was generated; and 3) the full ratification of the Columbia River Treaty between the United States and Canada. By 1970, with construction complete, the Pacific Intertie allowed for the movement of more than 4,000,000 kilowatts of power among the electrical systems of British Columbia and eleven Western states, including 243 rural electrical cooperatives, municipal systems, and other public agencies. It had essentially become the backbone of the largest electrical grid in the Western world. In addition to widening the marketing area available to power producers throughout the grid, the Pacific Intertie also integrated the operations of the nation's largest hydropower system (Bonneville Power Administration), the largest privately owned electrical system (Pacific Gas & Electric), and the largest municipal power system (L.A. Department of Water and Power) in the country.
39
King, Graham Missell. "Structural, Magnetic, and Electronic Studies of Complex Perovskites." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1262114272.
Повний текст джерела
40
Goble, Nicholas James. "ELECTRONIC TRANSPORT AT SEMICONDUCTOR AND PEROVSKITE OXIDE INTERFACES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1454002713.
Повний текст джерела
41
Haidara, Modibo. "Impulsions de Trichel dans le cyclohexane liquide et les gaz comprimés." Grenoble 1, 1988. http://www.theses.fr/1988GRE10160.
Повний текст джерелаАнотація:
Resultats d'etude de la conduction electrique de liquides non polaires tres purs (cyclohexane, n-propane) en geometrie pointe-plan, en fonction du rayon de courbure de la pointe et de la pression hydrostatique (p<->10**(7)pa)
42
Widdifield, Cory. "Multinuclear Solid-State Magnetic Resonance Studies on ‘Exotic’ Quadrupolar Nuclei: Acquisition Methods, High-Order Effects, Quantum Chemical Computations, and NMR Crystallography." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20722.
Повний текст джерелаАнотація:
This dissertation attempts to extend the classes of halogen-containing systems which may be studied using solid-state nuclear magnetic resonance (SSNMR). As line shape broadening due to the quadrupolar interaction (QI) scales inversely with the applied field, high-field magnet technology is indispensable for this research. Combining advanced radiofrequency pulse sequences with high-field wideline data acquisition allowed for the collection of very broad SSNMR signals of all quadrupolar halogen nuclei (i.e., 35/37Cl, 79/81Br and 127I) within a reasonable amount of experimental time. The initial systems for study were of the MX2 variety (M = Mg, Ca, Sr, Ba; X = Cl, Br, I). In total, 9 anhydrous compounds were tested. The effects of hydrate formation were tested on 7 additional compounds. Systematic trends in the observed δiso values (and to a lesser extent, Ω and CQ) were found to be diagnostic of the extent of hydration in these materials. Resolving power was successfully tested using SrBr2, which possesses 4 magnetically unique sites. The composition of CaBr2•xH2O was convincingly determined using SSNMR data and the hydration trends noted above. The sensitivity of the QI to the local bonding environment (e.g., bond distance changes of less than 0.05 Å) was used to refine (when coupled with gauge-including projector augmented-wave density functional theory (GIPAW DFT) quantum chemical computations) the structure of MgBr2, and was used to correct prior NMR data for CaCl2 (earlier accounts had been performed upon a CaCl2 hydrate). During NMR data analysis of certain iodine-containing materials, it was found that standard fitting software (which uses perturbation theory) could not reproduce the observations. Proper analysis required the use of exact simulation software and allowed for the observation of high-order quadrupole-induced effects (HOQIE). This motivated further studies using rhenium-185/187 nuclei, where it was expected that HOQIE would be more dramatic. The observed rhenium SSNMR spectra possessed additional fine structure that had never been observed before experimentally, nor would be expected from currently-available perturbation theory analysis software. Lastly, preliminary results are shown where 127I SSNMR is used to study important supramolecular systems, and the composition of the popular synthetic reagent ‘GaI’ is elucidated.
43
Gina, Ervin. "Implementation and Optimization of an Inverse Photoemission Spectroscopy Setup." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4050.
Повний текст джерелаАнотація:
Inverse photoemission spectroscopy (IPES) is utilized for determining the unoccupied electron states of materials. It is a complementary technique to the widely used photoemission spectroscopy (PES) as it analyzes what PES cannot, the states above the Fermi energy. This method is essential to investigating the structure of a solid and its states. IPES has a broad range of uses and is only recently being utilized.
This thesis describes the setup, calibration and operation of an IPES experiment. The IPES setup consists of an electron gun which emits electrons towards a sample, where photons are released, which are measured in isochromat mode via a photon detector of a set energy bandwidth. By varying the electron energy at the source, a spectrum of the unoccupied density of states can be obtained. Since IPES is not commonly commercially available the design consists of many custom made components. The photon detector operates as a bandpass filter with a mixture of acetone/argon and a CaF2 window setting the cutoff energies. The counter electronics consist of a pre-amplifier, amplifier and analyzer to detect the count rate at each energy level above the Fermi energy.
Along with designing the hardware components, a Labview program was written to capture and log the data for further analysis. The software features several operating modes including automated scanning which allows the user to enter the desired scan parameters and the program will scan the sample accordingly. Also implemented in the program is the control of various external components such as the electron gun and high voltage power supply.
The new setup was tested for different gas mixtures and an optimum ratio was determined. Subsequently, IPES scans of several sample materials were performed for testing and optimization. A scan of Au was utilized for the determination of the Fermi edge energy and for comparison to literature spectra. The Fermi edge energy was then used in a measurement of indium tin oxide (ITO) determining the conduction band onset. This allowed the determination of the "transfer gap" of ITO. Future experiments will allow further application of IPES on materials and interfaces where characterization of their electronic structure is desired.
44
Teatro, Timothy A. V. "Dynamical effects in crystalline solid state systems: theory of temperature dependent optical response of bulk gaAs and vibrational modification of C(111) 2 x 1 Surface in Comparison to Experiment." Thesis, UOIT, 2009. http://hdl.handle.net/10155/33.
Повний текст джерелаАнотація:
This thesis presents a new theoretical formalism which incorporates dynamical effects in
atomistic electronic structure and related calculations.
This research, fundamental by nature, brings about a deeper understanding of the dynamical
processes in a range of materials. This establishes technologically important correlation
with experimentally measured macroscopic properties and materials characterization. This
method—the first of its kind—is a natural and long overdue extension of customary adiabatically
separated time-independent electronic structure methods. It accounts explicitly for
atomic motion due to thermal and zero-point vibration. The approach developed requires
no direct treatment of time dependence in the quantum mechanical calculations, making
the method widely applicable utilizing currently available electronic structure and ab-initio
molecular dynamics software.
The formalism is extensively applied and demonstrated for the linear optical response
of bulk gallium arsenide and electronic structure of the C(111) 2 x 1 surface. Both cases
are complimented by comparison of key observables to experimental data which may be
used to judge the quality of the results. The results are found to be in good agreement with
experimental data, with most exceptions being readily explainable and well understood.
45
M'AHAMEDI, OMAR. "Contribution a l'etude de l'interaction de l'hydrogene atomique avec les faces (110) et (100) de gaas et inp." Paris 6, 1987. http://www.theses.fr/1987PA066526.
Повний текст джерелаАнотація:
Etude de l'effet de l'adsorption de l'hydrogene, de l'unicite de la liaison forte que cet atome peut etablir avec les atomes de surface du substrat. Les spectres montrent qu'a forte dose d'hydrogene, il y a diminution du rendement de photoemission
46
Sahli, Salah. "Etude du comportement electrique de films minces de gaas amorphes ou polycristallins elabores par depots en phase vapeur ou par plasma a partir d'organometalliques." Toulouse 3, 1986. http://www.theses.fr/1986TOU30049.
Повний текст джерелаАнотація:
Des films de gaas polycristallin ont ete realises par depot en phase vapeur, a partir de molecules organometalliques. L'auteur a montre que les proprietes electriques de ce materiau semiconducteur sont controlees par les joints de grains. Une densite d'etats de surface uniforme entre les grains a ete mise en evidence. L'introduction entre les grains d'une phase amorphe de type si::(y)c::(1-y) modifie le mode de conduction. La resistivite des films augmente ou diminue suivant la valeur de la concentration de si::(y)c::(1-y). Un depot par plasma froid a partir des memes molecules que celles utilisees precedemment, conduit a un materiau amorphe polymerique. Celui-ci est compose d'atomes de gallium et d'arsenic. Ses proprietes electriques sont plutot celles d'un isolant que celles d'un semiconducteur. Enfin, il a ete montre qu'un film contenant des atomes de ga et d'as peut etre utilise pour la passivation de la surface de substrats de gaas monocristallin
47
Mandray, Ariane. "Etude magnéto-optique de centres D- confinés dans des multi-puits quantiques GaAs/AlGaAs." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10075.
Повний текст джерелаАнотація:
Le centre d#-, ou ion donneur negatif, est l'analogue en physique du solide de l'ion hydrogene negatif h#-. Il s'agit donc d'un systeme correle simple, avec seulement deux electrons. Les transitions magneto-optiques permettant l'etude des donneurs peu profonds (neutres ou charges negativement) dans les multi-puits gaas/algaas se situent dans la gamme de l'infra-rouge lointain. Notre appareillage experimental est essentiellement constitue d'un spectrometre a transformee de fourier, couple a un aimant supraconducteur ou resistif. Nous avons etudie le mecanisme de formation des centres d#- confines dans des multi-puits quantiques. Dans cette configuration, contrairement au materiau massif, les centres d#- sont formes par construction, ce qui permet leur etude a l'equilibre thermodynamique. L'importance de la geometrie de dopage est soulignee, et la possibilite de realiser un dopage d#- de puits quantiques est mise en evidence. Le spectre d'energie des centres d#- confines a ete etudie pour une large gamme de champs magnetiques (jusqu'a 20 t) et pour differentes largeurs de puits. Ces mesures permettent d'observer, outre la non-parabolicite de bande de gaas, les effets de correlation electronique augmentes par la baisse de dimensionalite. L'etude des centres d#- en presence de desordre d'alliage dans des puits de al-gaas met en evidence la possibilite de coexistence, dans ce type de systeme, de centres profonds et de centres peu profonds, tous deux charges negativement
48
Chomette, André. "Proprietes electroniques et optiques des superreseaux gaas/gaalas de petites periodes." Paris 6, 1988. http://www.theses.fr/1988PA066146.
Повний текст джерела
49
GIGNOUX, CLAIRE. "Etude des proprietes electroniques de l'alliage quasicristallin alpdre." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10233.
Повний текст джерелаАнотація:
Ce travail de these est consacre a l'elaboration et l'etude des proprietes electroniques de la phase quasicristalline alpdre. La recherche d'une procedure d'elaboration nous a permis d'obtenir des echantillons de phase icosaedrique pure de tres grande qualite structurale. L'alliage quasicristallin alpdre presente des proprietes de transport exceptionnelles pour un alliage constitue uniquement de metaux. En particulier, nous avons confirme que la valeur de resistivite de certains echantillons de i-alpdre peut atteindre #4#37 1 cm, ce qui est 10#6 fois superieure a celle des metaux standards, et 10#3 fois superieure a celles des amorphes metalliques. Les valeurs de resistivite de ces echantillons et leur dependance en temperature semblent s'approcher de celles des systemes ayant franchi la transition metal-isolant. Toutefois, il existe de fortes variations des proprietes de transport entre differents echantillons de la phase i-alpdre. D'autres echantillons ont montre des proprietes electroniques semblables a celles des phases icosaedriques bien connues i-alpdmn et i-alcufe qui se trouvent du cote metallique d'une transition metal-isolant. Nous avons etabli que ces disparites de proprietes de transport sont liees a des variations de composition et de qualite structurale. A l'inverse des metaux, meilleure est la qualite structurale plus la resistivite des echantillons est elevee ce qui exclu la possibilite d'une transition metal-isolant par le desordre (anderson) dans cette phase. D'autre part, nos mesures de densite d'etats electroniques permettent d'etablir la presence d'un pseudogap au niveau de fermi mais pas de gap reel comme dans les semi-conducteurs. On a donc affaire a un type de transport nouveau qui n'obeit pas aux lois connues dans les materiaux classiques (amorphes, semi-conducteurs, metaux). Un modele de transport par sauts entre etats critiques pourrait expliquer une transition metal-isolant dans ces structures ordonnees sans gap. Nous avons entrepris, par ailleurs, des mesures d'energie de surface de couches minces quasicristallines en collaboration avec l'industrie de revetements aps. Ces mesures, nous ont permis d'etablir que les couches minces quasicristallines ont une faible mouillabilite
50
Montpied, Sylvie. "Contribution a l'etude de la passivation de composants sur arseniure de gallium : caracterisation de films dielectriques realises par depot en phase vapeur assiste par plasma." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21020.
Повний текст джерелаАнотація:
Les transistors a effet champ a contact metal-semiconducteur, non passives, realises sur arseniure de gallium sont sujet a une degradation progressive de leurs performances statiques et dynamiques aux hyperfrequences. Ce defaut de fonctionnement est en parti attribue aux surfaces d'arseniure de gallium situees de part et d'autres de la grille. La stabilisation des composants requiert donc de la passivation de ces zones grace a des materiaux de haute qualite dielectrique realisant une interface stable avec gaas. Dans cette optique, les proprietes physico-chimiques et electriques de films de silice et de nitrure de silicium deposes en phase vapeur assiste par plasma sont etudiees en fonction du rapport des debits des gaz employe, de la temperature du substrat, de la puissance et de la frequence de l'excitation du plasma. . . Cette approche systematique permet de determiner des parametres de depot qui donnent des films ayant tres bonnes proprietes electriques: une resistivite de 10**(14) a 10**(16) ohm. Cm et un champ de claquage superieur a 10**(6) v/cm sont ainsi obtenus apres un recuit dont on soulignera l'importance. Apres mise au point d'une preparation de surface avant depot, la densite d'etats sur la bande interdite du semiconducteur a l'interface gaas/si::(3)n::(4) presente un minimum de 7. 10**(11) ev**(-2). Les depots ainsi optimalises sont utilises pour la passivation des transistors mesfet gaas. Le recouvrement d'un composant par une couche mince introduit une modification de ses caracteristiques statiques; celle-ci est expliquee conjointement par un effet piezo-electrique et par un effet de surface inherent au mode de depot. Suivant les resultats obtenus en tests de fiabilite, le nitrure de silicium s'avere etre le meilleur choix pour reussir la passivation du composant. De plus, des pretraitements par plasma et une meilleure adaptation du procede de fabrication au mode de passivation sont proposes pour ameliorer encore la stabilite a long terme des caracteristiques des transistors