Tesi sul tema "Metal doping"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Metal doping".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
Crawford, Kevin G. "Surface transfer doping of diamond using transition metal oxides". Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8561/.
Testo completoTaub, Samuel. "Transition metal oxide doping of ceria-based solid solutions". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18845.
Testo completoFei, Wenwen. "Au25(SR)18: Metal Doping, Ligand Exchange, and Fusion Reactions". Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3424837.
Testo completoTrapatseli, Maria. "Doping controlled resistive switching dynamics in transition metal oxide thin films". Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/423702/.
Testo completoPRADA, STEFANO. "Enhancing oxide surface reactivity by doping or nano-structuring". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/50011.
Testo completoDerk, Alan Richard. "Understanding and Controlling Light Alkane Reactivity on Metal Oxides| Optimization Through Doping". Thesis, University of California, Santa Barbara, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3724768.
Testo completoMetal oxide catalysts have numerous industrial applications and have garnered research attention. Although oxides catalyze many important reactions, their yields to products are too low to be of economic value due to low conversion and/or low selectivity. For example, some oxides can catalyze the conversion of methane to intermediates or products that are liquefiable at yields no higher than 30%. With improved yield, such a process could help reduce the trillions of cubic feet of natural gas flared every year, saving billions of dollars and millions of tonnes of greenhouse gases. To this end, one goal of this work is to understand and improve the catalytic activity of oxides by substituting a small fraction of the cations of a "host oxide" with a different cation, a "dopant." This substitution disrupts chemical bonding at the surface of the host oxide, which can improve reactant and lattice oxygen activation where the reaction takes place. Another goal of this work is to combine catalysts with metal oxides reactants to improve thermodynamic limitations. Outstanding challenges for the study of doped metal oxide catalysts include (1) selection of dopants to ix synthesize within a host oxide and (2) understanding the nature of the surface of the doped oxide during reaction.
Herein, strongly coupled theoretical calculations and experimental techniques are employed to design, synthesize, characterize, and catalytically analyze doped oxide catalysts for the optimization of light alkane conversion processes. Density Functional Theory calculations are used to predict different energies believed to be involved in the reaction mechanism. These parameters offer valuable suggestions on which dopants may perform with highest yield and activity and why. Synthesis is accomplished using a combination of wet chemical techniques, suited specifically for the preparation of doped (rather than supported or mixed) metal oxide catalysts of high surface area and high reactivity. Characterization is paramount in any doped-oxide investigation to determine if the catalyst under reaction conditions is truly doped or merely small clusters of supported catalyst. With that goal, diffraction, X-ray, electron microscopies, infrared spectroscopy, and chemical probes are used to determine the nanoscopic nature of the catalysts. Additional novel measurement techniques, such as transient oxidation reaction spectroscopy, determined the nature of the active site's oxidation state.
Crowley, Kyle McKinley. "Electrical Characterization, Transport, and Doping Effects in Two-Dimensional Transition Metal Oxides". Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1597327584506971.
Testo completoBanerjee, Tanushree. "Impact of Nickel Doping on Hydrogen Storage in Porous Metal-Organic Frameworks". VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2265.
Testo completoButa, Sarah H. (Sarah Hume) 1972. "A first principles investigation of transitional metal doping in lithium battery cathode materials". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9550.
Testo completoIncludes bibliographical references (p. 77-82).
The goal of this work is to understand the properties of mixed-metal intercalation oxides. Using first-principles methods, the effect of doping on the mixing, energetic, and voltage properties as well as the phase diagrams of lithium transition-metal oxides for lithium battery cathode materials was investigated. The effect of doping on the phase separation tendencies of layered transition-metal oxides was examined and it was found that for normal processing temperatures, Al is miscible in layered transition metal oxides (LiMO2) for five of the eight first-row transition metals studied. Temperature-composition phase diagrams for both Li(Al,Co)O2 and Li(Al,Cr)O2 were calculated. In these two systems, Al-doping is limited above 600°C by the formation of [gamma]-LiA1O2 and at very low temperatures owing to the existence of a miscibility gap. Reduced solubility is expected in the layered phase above 600°C for all oxides which have substantial solubility with LiA1O2 due to the formation of yLiAlO2. The effect of transition-metal doping on the average voltage properties in Mn-based spinets was calculated and the large increase in average voltage found experimentally was reproduced. A detailed analysis on the layered structure Li(Al,Co)O2 was performed, studying the energetics of different lithium sites and the effect of short-range clustering on the shape of the voltage curve. Though the average voltage is raised by Al substitution, the unexpected stability of sites with a few Al nearest neighbors leads to an initial decrease in voltage. For the Al-doped LiCoO2 system, a step in the voltage curve is found only for micro-segregated materials. When the Al and Co ions are randomly distributed in a solid solution, the voltage curve shows a continuous, gradual slope. The effect of oxygen defects in the Li(Al,Co)O2 system was investigated. A model for the effect of oxygen vacancies on the free energy of doped layered oxides was created by combining an ideal gas approximation and first-principles energy defect calculations. The results qualitatively confirm experimental studies on oxygen release in lithium battery materials.
by Sarah H. Buta.
S.M.
Wang, Junwei. "Chemical doping of metal oxide nanomaterials and characterization of their physical-chemical properties". Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1333829935.
Testo completoOla, Oluwafunmilola. "Effect of metal doping and supports on TiO₂-based catalysts for CO₂ photoreduction". Thesis, Heriot-Watt University, 2014. http://hdl.handle.net/10399/2820.
Testo completoJayasinghe, Ashini Shamindra. "Exploring the unique water properties of metal-organic nanotubes". Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5521.
Testo completoRandell, Heather Eve. "Applications of stress from boron doping and other challenges in silicon technology". [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010292.
Testo completoLuo, Ming. "Transition-metal ions in II-VI semiconductors ZnSe and ZnTe /". Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4630.
Testo completoTitle from document title page. Document formatted into pages; contains xiv, 141 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 135-141).
Fu, Jie. "Advanced doping techniques and dehydrogenation properties of transition metal-doped LiAlH 4 for fuel cell systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-159024.
Testo completoWasserstoff ist ein effizienter, kohlenstofffreier und sicherer Energieträger. Jedoch die kompakte und gewichtseffiziente Speicherung ist ein permanentes Forschungs- und Entwicklungsthema. Unter den intensiv untersuchten Materialien für die Wasserstoffspeicherung ist aufgrund der hohen theoretischen Speicherdichte (volumetrisch: 96,7 g H2/L, gravimetrisch: 10.6 Gew.%-H2) in Kombination mit sehr niedrigen Zersetzungstemperaturen (Anfangstemperatur < 100°C nach Dotierung) Lithium Aluminiumhydrid (LiAlH4) ein vielversprechender Kandidat. Obwohl die reversible Dehydrierung von LiAlH4 mit Hilfe von organischen Lösungsmitteln durchgeführt werden muss, kann LiAlH4-Pulver als Einweg-Speichermaterial für verschiedene Anwendungen dienen, beispielsweise für Wasserstoff/Brennstoffzellensysteme. Diese Doktorarbeit beschäftigt sich mit LiAlH4 dotiert mit Übergangsmetall, mit dem Ziel maßgeschneiderte Dehydrierungseigenschaften zu erreichen. Die Kristallstruktur und die Morphologie der mit Übergangsmetallen dotierten LiAlH4-Pulver wurden mit Röntgenbeugung (XRD) und Rasterelektronenmikroskopie (REM) charakterisiert. Weiterhin wurde der positive Effekt der Dotanden auf die reaktionsfördernde Dehydrierung von LiAlH4 systematisch mit Hilfe thermoanalytischer Methoden untersucht. Für jedes Übergangsmetall, welches in Form von Übergangsmetallchloriden vorlag, wurden drei Dotierungsmethoden mit niedrigem Energieeintrag (Kugelmahlen mit geringer Rotations-geschwindigkeit, manuelles Schleifen/Magnetrühren, Magnetrühren mit Ethylether) verglichen, um LiAlH4-Pulver mit einer maximalen Wasserstofffreisetzungsmenge in Kombination mit einer schnellen Dehydrierungskinetik zu erzielen. Die Dehydrierung des dotierten LiAlH4-Pulvers wurde unter isothermen Bedingungen bei 80°C und einem H2-Druck von 1 bar gemessen, was im Bereich der Betriebstemperatur von PEM-Brennstoffzellen (Proton Exchange Membran) liegt. Dadurch sollen Anwendungen anvisiert werden, bei denen die entstehende Abwärme der Brennstoffzelle genutzt wird, um die Dehydrierung des Wasserstoffspeichermaterials auszulösen. Zudem wurde das Dehydrierungsverhalten des dotierten LiAlH4 bis zu einigen Monaten kontrolliert, um die mittelfristige Haltbarkeit zu testen. Weiterhin wurde die Pelletierung des mit Übergangsmetallen dotierten LiAlH4 mit dem Ziel untersucht, eine hohe volumetrische Speicherkapazität zu erreichen. Der Einfluss des Pressdrucks, der Dehydrierungstemperatur und des H2-Gegendrucks auf die Dehydrierungseigenschaften der mit Übergangsmetallen dotierten LiAlH4-Presslinge wurde systematisch analysiert. Außerdem wird die Volumenveränderung durch die Dehydrierung und die Kurzzeitspeicherung der mit Übergangsmetallen dotierten LiAlH4-Presslinge im Hinblick auf praktische Anwendungen unter Nutzung der Brennstoffzelle diskutiert
Khanyile, Sfiso Zwelisha. "Silicon nanowires by metal-assisted chemical etching and its incorporation into hybrid solar cells". University of Western Cape, 2021. http://hdl.handle.net/11394/8340.
Testo completoThe rapid increase in global energy demand in recent decades coupled with the adverse environmental impact of conventional fuels has led to a high demand for alternative energy sources that are sustainable and efficient. Renewable solar energy technologies have received huge attention in recent decades with the aim of producing highly efficient, safe, flexible and robust solar cells to withstand harsh weather conditions. c-Si has been the material of choice in the development of conventional inorganic solar cells owing to it superior properties, abundance and higher efficiencies. However, the associated high costs of Si processing for solar cells have led to a gravitation towards alternative organic solar cells which are cheaper and easy to process even though they suffer from stability and durability challenges. In this work, combination of both inorganic and organic materials to form hybrid solar cells is one of the approaches adopted in order to address the challenges faced by solar cell development.
Grüne, Philipp. "Structure and reactivity of metal and semiconductor clusters in the gas phase". Berlin mbv, Mensch-und-Buch-Verl, 2009. http://d-nb.info/995894353/04.
Testo completoLee, Edwin Wendell II. "Growth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480686917234143.
Testo completoSAVINO, UMBERTO. "Physical properties of metal-oxide surfaces for CO2 valorisation". Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2823956.
Testo completoMeroueh, Laureen. "Effects of doping and microstructural variables on hydrogen generated via aluminum-water reactions enabled by a liquid metal". Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129067.
Testo completoCataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages [110]-127).
Hydrogen has the potential to replace fossil fuels in numerous industrial sectors, considering its high energy density, ability to be used within our existing power or heating infrastructure, and lack of CO₂ emissions upon conversion of hydrogen's chemical energy into electricity. However, 96% of hydrogen is currently produced through steam methane reformation, which emits ~12 tons of CO₂ for every 1 ton of hydrogen produced. Consequently, hydrogen production accounts for roughly 830 million tons of annual global CO₂ emissions. Additionally, hydrogen storage can be impractical and expensive. The aluminum-water reaction presents itself as a hydrogen storage and generation solution. Without a passive oxide layer, aluminum will react with water to produce emission-free hydrogen, on-demand.
We enable the reaction by harnessing eutectic gallium-indium (eGaIn), an ambient temperature liquid metal that permeates through aluminum grain boundaries, disrupting its passive oxide layer and inhibiting passivation of its grain surfaces. The focus of this work is on the investigation of the underlying aluminum-water reaction mechanism in the presence of eGaIn and on understanding the effects of using scrap aluminum (i.e. doped aluminum) as feedstock. Surprisingly, experiments show that silicon doping has a tremendous accelerating effect on the aluminum-water reaction in the presence of eGaIn. In combination with grain size manipulation, Si-doping can increase hydrogen evolution rates by two orders of magnitude compared to pure aluminum. Doping with magnesium significantly retards the aluminum-water reaction, resulting in relatively steady hydrogen evolution rates. It is also shown that eGaIn permeates through aluminum as a line dislocation front.
These discoveries demonstrate that doping, grain refining and grain coarsening offer latitudes in the engineering of aluminum microstructures to tune hydrogen generation rates across three orders of magnitude and to tune the reaction efficiency. Using the results of this work, I provide a guide to the design/selection of aluminum for controllable hydrogen generation according to application. Lastly, while the corrosion of aluminum and its commercial alloys has been historically studied, results of this work show that the redox behavior of aluminum in the presence of eGaIn strays from what can be understood within the classical corrosion (galvanic theory) framework.
by Laureen Meroueh.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering
Nakayama, Ryo. "Exploration into an Innovative Science of Hydrogen Functional Materials Using Low-temperature Ion Beam Irradiation". Kyoto University, 2019. http://hdl.handle.net/2433/236604.
Testo completoPeleckis, Germanas. "Studies on diluted oxide magnetic semiconductors for spin electronic applications". Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20070821.145447/index.html.
Testo completoVinogradov, Nikolay. "Controlling Electronic and Geometrical Structure of Honeycomb-Lattice Materials Supported on Metal Substrates : Graphene and Hexagonal Boron Nitride". Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-194089.
Testo completoXing, Shihui. "Rational design of bi-transition metal oxide electrocatalysts for hydrogen and oxygen evolutions". Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/209307/1/Shihui_Xing_Thesis.pdf.
Testo completoAlmeida, Cristiane Gomes. "Síntese, caracterização e avaliação da atividade fotocatalítica de BiTa(Nb)O4 dopados com cromo e molibdênio na geração de hidrogênio". Instituto de Química, 2013. http://repositorio.ufba.br/ri/handle/ri/16253.
Testo completoApproved for entry into archive by Fatima Cleômenis Botelho Maria (botelho@ufba.br) on 2014-10-03T15:55:32Z (GMT) No. of bitstreams: 1 Dissertação Cristiane.pdf: 9154051 bytes, checksum: aa1fa030f760c514e3fc02dbacb83066 (MD5)
Made available in DSpace on 2014-10-03T15:55:32Z (GMT). No. of bitstreams: 1 Dissertação Cristiane.pdf: 9154051 bytes, checksum: aa1fa030f760c514e3fc02dbacb83066 (MD5)
Hidrogênio obtido a partir de água é uma atrativa fonte de energia, visto que pode ser produzido por fontes renováveis e inesgotáveis, e é não poluente. Atualmente, a principal forma de produção de hidrogênio é através da reforma catalítica de gás natural; porém, um novo processo baseado na fotólise da água com auxílio de semicondutores fotocatalíticos é considerado uma alternativa promissora. Diversos materiais já foram testados e outros desenvolvidos com o intuito de aumentar a atividade fotocatalítica na decomposição da água, dentre estes estão o niobato e o tantalato de bismuto (BiNbO4 e BiTaO4), fotocatalíticamente ativos quando irradiados com luz ultravioleta. No entanto, é possível que modificações químicas e nas dimensões de partículas resultem em melhor atividade. O método citrato de precursores poliméricos foi empregado para preparar BiTaO4 e BiNbO4 com a determinação da temperatura ideal de polimerização empregando técnicas termoanalitícas, e um estudo exploratório da temperatura mínima de calcinação foi realizado para obtenção da fase pura desejada, confirmada por difratometria de raios X. A fim de ativar os semicondutores com radiação visível foi realizada a dopagem desses semicondutores com íons de metais de transição, Cr(III) e Mo(V), com concentrações que variaram de 1 – 4% (mol/mol), e um estudo de como as energias de band gap sofreram modificações. Foi observado que a atividade fotocatalítica dos óxidos dopados com molibdênio ou cromo, nas condições avaliadas, é fortemente influenciada pelos teores dos metais e a amostra que apresentou melhor atividade fotocatalítica na geração de hidrogênio foi BiTaO4 dopado com Cr(III) a 2%. Os resultados desse trabalho podem contribuir para o desenvolvimento de sistemas fotoquímicos eficientes empregados na produção fotocatalítica de hidrogênio, utilizando matérias- primas abundantes, renováveis e ambientalmente amigáveis, como água e luz solar.
Hydrogen obtained from water is an attractive energy source, since it can be produced by renewable and inexhaustible primary source, besides it is not pollutant. Nowadays, the principal form of hydrogen production is through catalytic reform of natural gas; although, a new process based on water splitting, with the support of photocatalytic semiconductors, is considered a promising alternative. Many materials have already been tested and developed with the intention of increasing the photocatalytic activity for water splitting, in which are present bismuth niobates and tantalates (BiNbO4 e BiTaO4), photocatalyticly active under UV light irradiation. However, it is possible that chemical modifications and modifications in particle dimensions result in better activity. The citrate method of polymeric precursors was used to prepare BiTaO4 e BiNbO4 with the determination of the ideal temperature of polymerization using thermoanalytical techniques, and an exploratory study of the minimal temperature of calcination was used to obtain a pure desired phase, confirmed by X rays diffractometry. In order to activate the semiconductors with visible radiation, a doping of these semiconductors with ions of transition metals, Cr(III) and Mo(V), with concentrations that ranged from 1 – 4% (mol/mol), and a study of how the band gap energies suffered modifications. The results suggest that the type and the concentration of metal doping exercise great influence on the crystalline structure and morphology of the oxides. While Cr(III) favors a beta phase (triclinic), Mo(V) favors an alpha phase (orthorhombic). Also, the presence of Cr(III) induces the formation of materials with more homogeneous morphologies and size of particles smaller than the obtained in presence of Mo(V). It was observed that a photocatalytic activity of the doped oxides with Molybdenum or Chromium, in the evaluated conditions, is strongly influenced by the metal concentrations and the sample that presented the best photocatalytic activity in hydrogen generation was BiTaO4 doped with Cr(III) at 2%. The experimental ratio H2/CO2, in this case, is much higher than the theoretical, suggesting that the isopropyl alcohol is not completely mineralized. The results of this work can contribute for the development of efficient photochemical systems applied in the photocatalytic production of hydrogen, using raw material in abundance, renewable and environmentally friendly like water and solar light.
Paniagua, Barrantes Sergio. "Interfacial engineering of transparent electrodes and nanoparticles with phosphonic acids and metal-organic dopants for organic electronic applications". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52920.
Testo completoBrazda, Petr. "Preparation of Fe2O3/SiO2 nanocomposites from molecular precursor by the sol-gel method and the doping of iron (III) by trivalent metal cations". Strasbourg, 2009. http://www.theses.fr/2009STRA6289.
Testo completoPresented work is focused on preparation of nanocomposite of epsilon-Fe2O3 crystallites embedded in amorphous SiO2 matrix using new sol-gel technique. Another aim of our study was to prepare epsilon iron(III) oxide with part of iron atoms substituted by diamagnetic aluminium or gallium atoms. From this reason nanocomposites of compositions of Al0. 25Fe1. 75O3/SiO2, Al0. 50Fe1. 50O3/SiO2, Al0. 75Fe1. 25O3/SiO2, Ga0. 25Fe1. 75O3/SiO2, Ga0. 50Fe1. 50O3/SiO2 and Ga0. 75Fe1. 25O3/SiO2 were prepared. Thanks to the optimal conditions, the non-substituted samples prepared were very pure. The majority of substituted samples did not contain other than epsilon phase. The anisotropy of hyperfine fields at 4. 2 K observed by NMR spectroscopy led to an alternative assignment of the subspectra in Mössbauer spectrum of epsilon phase. Fine structure of Mössbauer spectra induced by the substitution permitted a deeper understanding of the relationship between structure and magnetic properties of epsilon-Fe2O3
Ramamurti, Rahul. "Synthesis of Diamond Thin Films for Applications in High Temperature Electronics". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1145630189.
Testo completoElhag, Sami. "Chemically Modified Metal Oxide Nanostructures Electrodes for Sensing and Energy Conversion". Doctoral thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-134275.
Testo completoLi, Xianlong. "Insight into complex systems in heterogeneous catalysis : ab initio study of solid supported metal clusters and the effects of oxygen doping on catalytic activity". Thesis, Queen's University Belfast, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.727421.
Testo completoJanzen, Oliver. "Untersuchungen zur Wechselwirkung von Buckminsterfullerenen mit Siliziumoberflächen und zur Dotierung von Metall/Silizium-Grenzflächen mit Buckminsterfullerenen Interaction between Buckminsterfullerenes and Silicon Surfaces and Interface Doping of Metal/Silicon Interfaces with Buckminsterfullerenes". Gerhard-Mercator-Universitaet Duisburg, 2001. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-05182001-091725/.
Testo completoEscobar, Diego. "Investigation of ZrNi, ZrMn2 and Zn(BH4)2 Metal/Complex Hydrides for Hydrogen Storage". Scholar Commons, 2007. https://scholarcommons.usf.edu/etd/701.
Testo completoKrishnan, Bharat. "DEVELOPMENT OF SIMULATION FRAMEWORK FOR THE ANALYSIS OF NON-IDEAL EFFECTS IN DOPING PROFILE MEASUREMENT USING CAPACITANCE ? VOLTAGE TECHNIQUE". MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04082005-092339/.
Testo completoKönig, Andreas. "Charge-Density Waves and Collective Dynamics in the Transition-Metal Dichalcogenides: An Electron Energy-Loss Study". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-126887.
Testo completoIn der vorliegenden Arbeit wird eine detaillierte Untersuchung der elektronischen Eigenschaften von ausgewählten Übergangsmetall-Dichalcogeniden präsentiert. Unter Anwendung von Elektronenenergieverlust-Spektroskopie wird die Verbindung der negativen Plasmomendispersion in Tantaldiselenid zum Auftreten eines Ladungsdichtewelle-Zustands (CDW) in diesem und in verwandten Materialien untersucht. Die Untersuchungen schließen Dotierungsexperimente mit dem Zusatz von Alkalimetallen ein, die die Ladungsdichte der Proben beeinflussen. Einerseits unterdrückt dies die CDW. Es wird außerdem gezeigt, dass sich der Anstieg der Plasmonendispersion von negativ zu positiv ändert. Ein Dichtefunktional-Theorie-Zugang zur Abschätzung der Dotierungsraten der untersuchten Tantaldiselenid-Proben wird genutzt, um verlässliche Ergebnisse für die quantitative Analyse unserer Messungen zu erhalten. Ein theoretisches Modell wird einbezogen, welches die Verbindung der Ladungsordung zur kollektiven Anregung der Ladungsdichte beschreibt, Untersuchungen der nicht-CDW Substanz Niobdisulfid geben weitere Einblicke in die Verbindung der beiden Phänomene. Die experimentellen Resultate werden weiterhin mit einer Kramers-Kronig-Analyse ausgewertet. Strukturelle Untersuchungen mit elastischer Elektronenstreuung zeigen, wie die CDW unterdrückt wird und einer auftauchenden Überstruktur, verursacht von den interkalierten K-Atomen, Raum gibt
Fu, Jie [Verfasser], Bernd [Akademischer Betreuer] Kieback e Rüdiger [Akademischer Betreuer] Lange. "Advanced doping techniques and dehydrogenation properties of transition metal-doped LiAlH 4 for fuel cell systems / Jie Fu. Gutachter: Bernd Kieback ; Rüdiger Lange. Betreuer: Bernd Kieback". Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://d-nb.info/1069092673/34.
Testo completoCabral, Erika Dias. "Estudos de propriedades elétricas e magnéticas em nanoestruturas de GaMnAs de uso em spintrônica". Universidade do Estado do Rio de Janeiro, 2009. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=1462.
Testo completoConselho Nacional de Desenvolvimento Científico e Tecnológico
Um estudo da interação entre desordem e polarização de spin no GaMnAs ajuda a compreender a natureza dos estados, estendidos ou localizados, bem como as consequências para as transições observadas sobre as propriedades de transporte e às mudanças na ordem magnética de momentos magnéticos localizados em sítios de Mn. Este estudo pressupõe a ocorrência de uma banda impureza com baixas concentrações de Mn, que merge na banda valência no caso de concentrações mais elevadas. A abordagem teórica, baseada em um formalismo de espalhamento múltiplo auto-consistente, através do cálculo da função de Green para buracos determina-se a função densidade espectral no nível de Fermi. A escolha de uma figura de mérito, com base na largura e sobre a posição do máximo da função densidade espectral no espaço recíproco, leva a um diagrama de fase que determina o caráter metálicos ou não metálicos da amostra. Também é possível identificar a mobility edge, e como consequência, a densidade efetiva de portadores livre. Uma amostra é definida pelo par de parâmetros independentes, a concentração de Mn e a densidade buraco. As melhores amostras, aquelas com os maiores valores de mérito, tem uma relação entre a densidade de buracos estendidos e a concentração de Mn aproximadamente de 0.3, muito próximo do raio de 10-25% observada entre as amostras reais produzidos com a mais alta temperatura de transição. Além disso, a relação entre essas concentrações de Mn correspondente as transições metal-não-metal e não-metal-metal que é de aproximadamente 2.4, muito próximo do valor 2.1 da amostras reais. Uma interpretação da ocorrência de ferromagnetismo com alta temperatura de transição em GaMnAs é dada como uma consequência da interação entre o mecanismo de interação assistido por estados localizados e interações indiretas assistida pelo estdos buraco estendidos. Portadores mediando magnetismo em semicondutores mostram diferenças importantes e potencialmente úteis a diferenças de magnetismo em metais tais como o luz- ou voltagem elétrica -controlando ferromagnetismo. Motivado por experiências reportadas em poços quânticos de GaAs com uma dopagem delta de Mn com altas temperaturas Currier (temperatura de transição) mais elevadas do que em bulk de (Ga, Mn)As, nós exploramos teoricamente a viabilidade do campo elétrico controlar ferromagnetismo em poços quânticos. Nós calculamos auto-consistentemente a interação de troca indireta em Mn-Mn íons e aplicamos a simulação Monte Carlo para encontrar transição temperatura Tc. A nossa abordagem permite-nos estudar sistematicamente os efeitos de confinamento quântico e da posição da camada magnética de Mn e Tc, que vai além da aproximação do campo médio. Nós comparamos nossos resultados com os resultados experimentais e sugerimos caminho para o melhor controle do ferromagnetismo.
A study of the interplay between disorder and spin polarization in the diluted magnetic semiconductor GaMnAs helps to understand the character of states, extended or localized. This study assumes the occurrence of an impurity band which merges into the valence band at higher concentrations. The theoretical approach, based on a self-consistent multiple scattering formalism, determines the spectral density function at the Fermi level from the calculation of the hole's Green's functions. A choice of a figure of merit, based on the width and on the position of the maximum of the spectral density function in the reciprocal space, leads to a phase diagram determining the metallic or non-metallic character of the sample. It is also possible to identify mobility edges and, in consequence, the density of effectively free carriers. A model sample is defined by the pair of independent parameters, Mn concentration and hole density. The best samples, those with the highest figures of merit, have a ratio between the extended hole density and the Mn concentration near 0.3, very close to ratio of 10-30% observed among the real samples produced with the highest transition temperatures. Also, the ratio between those Mn concentrations corresponding to the metal-to-non-metal and non-metal-to-metal transitions is approximately 2.4, very close to the value 2.1 inferred from the real samples. An interpretation of the occurrence of high transition temperature ferromagnetism in GaM-nAs is given as a consequence of the interplay between interaction mechanism assisted by localized states and indirect interactions assisted by extended hole states. Carrier mediated magnetism in semiconductors show important and potentially useful differences from magnetism in metals,such as light- or bias-controlled ferromagnetism. Motivated by experiments reporting higher Currier temperatures in GaAs quantum wells with Mn-delta doping than the ones observed in bulk (Ga,Mn)As, we explore theoretically the feasibility of bias-controlled ferromagnetism these systems. We calculate self-consistently indirect Mn-Mn exchange interaction, and apply Monte Carlo approach to find transition temperature Tc. Our approach allows us to systematically study the eects of quantum confinement and the position of Mn layer on magnetic ordering and Tc, beyond mean field approximation. We compare our findings with the experimental results and suggest paths toward improving the control of ferromagnetism.
Djongkah, Cissillia Young Chemical Sciences & Engineering Faculty of Engineering UNSW. "Effect of Pt and Ag metals to the degradation of trichloroethylene, ethylene, ethane, and toluene by gas phase photocatalysis". Awarded by:University of New South Wales. School of Chemical Sciences and Engineering, 2006. http://handle.unsw.edu.au/1959.4/26227.
Testo completoSimonov, Konstantin. "Effect of Substrate on Bottom-Up Fabrication and Electronic Properties of Graphene Nanoribbons". Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295884.
Testo completoD'angelo, Anthony Joseph. "Investigation and Synthesis of Novel Graphene-Based Nanocomposites for Hydrogen Storage". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4024.
Testo completoVargas, Hernandez Jesus. "Structural and Morphological modification of TiO2 doped metal ions and investigation of photo-induced charge transfer processes". Thesis, Le Mans, 2017. http://www.theses.fr/2017LEMA1018/document.
Testo completoThe thesis work is focused on the synthesis methods of titanium dioxide nanostructures and their physico-chemical studies in order to point out the correlations between the morphology, metal doping, structural features with the photocatalytic efficiency. The great interest on TiO2 nanomaterials deals with new sources of energy or in the environment preservation through the photocatalytic properties. However, the main limitations is due to the wide band gap (~3.2 eV) of the anatase polymorph. Thus, a major objective for improvement of the performance of TiO2 nanomaterials is to increase theirphotoactivity by shifting the onset of the electron-hole pairs creation from UV to the visible range. Moreover, it was found that using onedimensional (1-D) TiO2 (nanotubes) improved the charge collection by 1D nanostructures which consequently minimizes the recombination and prolongate the electron lifetimes. The first part of this work is focused on the synthesis of TiO2 nanopowders doped with metallic ions (Ag, Cu, Eu) prepared by Solgel. Even with different doping elements which apparently can adopt the same valence state (2+) such as (Cu2+, Ag2+,Eu2+), different behaviors were demonstrated for the effective incorporation of these ions in the host structure of TiO2. The discrepancy between ionic radii of the different used elements modulates the ratio of the substitutional doping. This is indeed achieved for Cu2+ but in less extent for Ag2+ while Europium ions form segregated phase as Eu2Ti2O7. The experiments on the degradation of methylene blue (MB)dyes have shown slight improvement with Ag-doped samples. The reason was tentatively attributed to the Ag clusters which were indeed demonstrated through their plasmon optical band. The second part of the work concerns thin films of TiO2 doped (Cu, Ag, and Eu) which were elaborated by spin coating and dip coating. The optimal parameters were obtained to achieve crystalline films but presenting mesoporous organisation which also depends on the doping process. Photocatalysis investigations were also realized and the efficiency of the films compared as function of the doping elements.The third part of the thesis is related to the morphological modification from nanoparticles to nanotubes by using the hydrothermal method with controlled pressure. An experimental design based on Taguchi Method was employed for the determination of the optimal parameters. TiO2 nanotubes increase the surface area in comparison with TiO2nanoparticles. TiO2 nanotubes were tested for the methylene blue degradation and show a higher photocatalytic efficiency than TiO2 nanopowders and TIO2 doped with Ag
Xu, Ying. "Fabrication and Characterization of Photodiodes for Silicon Nanowire Applications and Backside Illumination". University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1446313926.
Testo completoEllis, Wade C. "Fundamental Studies and Applications of Ambient Plasma Ionization Sources for Mass Spectrometry". BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6484.
Testo completoSilva, Lucas Barboza Sarno da. "Otimização das propriedades de transporte em supercondutores de MgB2 com a adição de compostos de estrutura cristalina tipo AlB2 e fontes distintas de carbono". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/97/97135/tde-08102013-085005/.
Testo completoIn January 2001, a new superconductor was presented by Nagamatsu, the magnesium diboride (MgB2), with a critical temperature, Tc, extremely high of 39 K. MgB2 is considered the high field conductor of the future. The exceptional high values of upper critical magnetic field, Hc2, (Hc2 + (0) ? 40 T for Tc ? 35 - 40 K) show that the MgB2 is able to replace the Nb3Sn (Hc2 (0) ? 30 T for Tc ? 18 K) as the choice for applications in high magnetic fields. In this work, superconducting pellets of MgB2 were prepared with addition of other metal diborides of ZrB2, TaB2, VB2, and AlB2, and simultaneous additions of metal diborides and different carbon sources, such as silicon carbide, graphite and carbon nanotubes. The objective of these additions of new elements was to create mechanisms to improve the transport capacity of the material, by substitutional doping and by generation of defects in the superconducting matrix, acting as effective pinning centers of magnetic flux lines. Two different methods for sample preparation were used, the in-situ and the ex-situ method. The in-situ preparation method followed conventional standards, such as powder mixing in a ball mill and heat treatment in argon flow. The ex-situ preparation method used more sophisticated techniques, such as high energy ball milling and heat treatment under high pressures (Hot Isostatic Press, HIP). In general, the additions of metal diborides improved the transport capacity of the material at low fields, the carbon sources increased the critical current density at high magnetic fields, whereas the combination of these two additions improved the transport capacity, for some samples, in all range of applied magnetic field.
Ozouf, Guillaume. "Electrodes à base d’aérogels de SnO2, résistantes à la corrosion pour la réduction de l’oxygène dans les piles à combustible à membrane échangeuse de protons (PEMFC)". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM060/document.
Testo completoIn order to tackle the problem of low durability, tin dioxide aerogels were studied to replace carbon black as a catalyst support in proton exchange membrane fuel cells (PEMFCs). SnO2 is a well-known n-type semi-conductor whose electronic conductivity can be improved by doping with hypervalent cations such as Nb5+, Ta5+ or Sb5+. In addition, as a catalyst support, this material has to develop a high specific surface area with adequate mesoporous morphology to allow both good dispersion and activity of the catalyst (Pt). To this end, our objective was to develop doped SnO2 aerogels. In this study, SnO2 based-aerogels were successfully synthesized following an acid-catalyzed sol–gel route starting with metal alkoxides as precursors. Our materials have shown a very interesting airy morphology with among other a reasonable specific surface area (80–90 m2/g). Moreover, all Sb-doped aerogels exhibited significant improvement in electronic conductivity and reach a value of around 0.12 S/cm. Platinum nanoparticles were then deposed on the Sb doped SnO2 aerogel surface using three different methods. The method based on chemical reduction using a polyol route provided the best result in term of mass catalytic activity measured by RDE (Is = 32 mA/mgPt). This value is even higher than that of the reference electrocatalyst TEC10E40E (Is = 27 mA/mgPt). Sb doped SnO2 aerogel based MEAs have exhibited a very good durability at high potentials
Davis, Taylor Matthew. "Feasibility and Impact of Liquid/Liquid-encased Dopants as Method of Composition Control in Laser Powder Bed Fusion". BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9256.
Testo completoPOLO, ANNALISA. "TERNARY OXIDE SEMICONDUCTOR PHOTOANODES FOR SOLAR ENERGY CONVERSION". Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/827287.
Testo completoChicot, Gauthier. "Effet de champs dans le diamant dopé au bore". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-01062250.
Testo completoBurnham, Shawn David. "Improved understanding and control of Mg-doped GaN by plasma assisted molecular beam epitaxy". Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-06122007-133821/.
Testo completoDoolittle, W. Alan, Committee Chair ; Ferguson, Ian T., Committee Member ; Cressler, John D., Committee Member ; Dorsey, John F., Committee Member ; Carter, W. Brent, Committee Member.
BONDARENKO, VLADIMIR. "The Synthesis and Study of TiO2/Aluminosilicate Composites as Components of Building Finishing Materials for Improvement of the Indoor Air Quality". Doctoral thesis, Università Politecnica delle Marche, 2017. http://hdl.handle.net/11566/251220.
Testo completoThis study offers the method for the synthesis of composite material by chemical deposition of TiO2 on aluminosilicate matrix from titanium sulfate solution (precursor). Relatively cheap and available raw materials were used during the preparation: the waste of mechanical processing of titanium (titanium shavings) for obtaining the precursor, montmorillonite, kaolinite, and fly ash as supports. The analysis of the literature sources allows assuming that such method produces the composite with a large specific surface area because of thermoacid activation and high photoactivity suitable for indoor conditions. These properties are confirmed by the experimental data for the obtained samples: Chemical contents; Morphology of surface and average particles size by SEM/optical microscopy; Adsorptive properties and parameters of porous structure, water vapor and benzene vapor adsorption capacity; X-rays analysis of phases; Photoactivity of the materials was estimated by the method of MEK removal in reactors of two different types (16 L & 0,45 L) with two types of UV-irradiation source (ULTRAVITALUX E27 lamp and DFL-5013UVC-380). The stability of the properties of the obtained composites after 3 years of storage was examine. Based on the results obtained, the recommendations for obtaining stable composites were discussed. The relative simplicity of technology allows organizing industrial production of the materials and possible upgrades of the method. Non-metal co-doping of the composites was examined as a method for providing visible light activity of the materials. The use of fly ash as matrix for composites was studied as possible way of valorization of industrial by-product. The building materials prepared with the obtained TiO2–containing component were tested by the method of methyl ethyl ketone removal.
Tewg, Jun-Yen. "Zirconium-doped tantalum oxide high-k gate dielectric films". Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/1346.
Testo completo