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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23696号 / 理博第4786号 / 新制||理||1685(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 松田 祐司, 教授 柳瀬 陽一, 教授 石田 憲二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This work presents a study on stoichiometry and structure in perovskite-type oxide thin films and investigates the role of growth–induced defects on the properties of materials. It also explores the possibility to grow thin films with properties close or similar to the ideal bulk parent compound. A novel approach to the growth of thin films, atomic layer-by-layer (ALL) laser molecular beam epitaxy (MBE) using separate oxide targets is introduced to better control the assembly of each atomic layer and to improve interface perfection and stoichiometry. It also is a way to layer materials to achieve a new structure that does not exist in nature. This thesis is divided into three sections. In the first part, we use pulsed laser deposition (PLD) to grow LaAlO3 (LAO) thin films on SrTiO3 (STO) and LAO substrates in a broad range of laser energy density and oxygen pressure. Using x-ray diffraction (θ-2θ scan and reciprocal space mapping), transmission electron microscopy (TEM) and x-ray fluorescence (XRF) we studied stoichiometry and structure of LAO films as a function of growth parameters. We show deviation from bulk–like structure and composition when films are grown at oxygen pressures lower than 10-2 Torr. We conclude that the discussion of LAO/STO interfacial properties should include the effects of growth–induced defects in the LAO films when the deposition is conducted at low oxygen pressures, as is typically reported in the literature. In the second part, we describe a new approach to atomically layer the growth of perovskite oxides: (ALL) laser MBE, using separate oxide targets to grow materials as perfectly as possible starting from the first atomic layer. We use All laser MBE to grow Ruddlesden–Popper (RP) phase Lan+1NinO3n+1 with n = 1, 2, 3 and 4 and we show that this technique enables us to construct new layered materials (n=4). In the last and main section of this thesis, we use All laser MBE from separate oxide targets to build the LaNiO3 (LNO) films as near perfectly as possible by depositing one atomic layer at a time. We study the thickness dependent metal-insulator transition (MIT) in ultrathin LNO films on an LAO substrate. In LNO, the MIT occurs in thin films and superlattices that are only a few unit cells in thickness, the understanding of which remains elusive despite tremendous effort devoted to the subject. Quantum confinement and structure distortion have been evoked as the mechanism of the MIT; however, first-principle calculations show that LaNiO3 remains metallic even at one unit cell thickness. Here, we show that thicknesses of a few unit cells, growth–induced disorders such as cation stoichiometry, oxygen vacancies, and substrate-film interface quality will impact the film properties significantly. We find that a film as thin as 2 unit cells, with LaO termination, is metallic above 150 K. An oxygen K-edge feature in the x-ray absorption spectra is clearly inked to the transition to the insulating phase as well as oxygen vacancies. We conclude that dimensionality and strain are not sufficient to induce the MIT without the contribution of oxygen vacancies in LNO ultrathin films. Dimensionality, strain, crystallinity, cation stoichiometry, and oxygen vacancies are all indispensable ingredients in a true control of the electronic properties of nanoscale strongly–correlated materials. / Physics

This research introduces tellurium oxide (TeO2) glass doped with optically active erbium ions (Er3+) as an active oxide cladding material for silicon-on-insulator (SOI) waveguides for realization of a silicon-based erbium-doped waveguide amplifier (EDWA) for integrated optics. Optical amplification of this nature is enabled by energy transitions, such as stimulated absorption and emission, within the shielded 4f shell of the rare-earth atomic structure caused by excitation from photons incident on the system. Er3+ ions are doped into the TeO2 film during deposition onto the SOI waveguides using a reactive magnetron co-sputtering system operated by McMaster’s Centre for Emerging Device Technologies (CEDT). Prior to fabrication, the waveguides are designed using photonic CAD software packages, for optimization of the modal behaviour in the device, and Matlab, for characterization of the optical gain performance through numerical analysis of the rate and propagation equations of the Er3+-based energy system. Post fabrication, the waveguide loss and gain of the coated devices are experimentally measured. The fabricated waveguide amplifier produces a peak signal enhancement of 3.84 dB at 1533 nm wavelength for a 1.7 cm-long waveguide device. High measured waveguide losses (> 10 dB/cm) produce a negative internal net gain per unit length. However, the demonstration and implementation of an active rare-earth doped cladding material on a silicon waveguide is successful, which is a major step in developing integrated optical amplifiers for conventional silicon photonics platforms. / Thesis / Master of Applied Science (MASc)

Pathogens in drinking water are the cause of over 1.5 million deaths around the world every year, mostly in developing countries. Practical, cheap, and effective tools for detection of these pathogens are critical to advance public health in many areas around the globe. Micro electro-mechanical systems (MEMS) are miniaturized structures that can be used for a variety of purposes, including, but not limited to, small scale sensors. Therefore, MEMS can be used in place of expensive laboratory equipment and offer a cheap and practical tool for pathogen detection. The presented work's research objective is to introduce a new technique called embedded passivated-electrode insulator-based dielectrophoresis (EπDEP) for preconcentration, separation, or enrichment of bioparticles, including living cells. This new method combines traditional electrode-based DEP and insulator-based DEP with the objective of enhancing the electric field strength and capture efficiency within the microfluidic channel while alleviating direct contact between the electrode and the fluid. The EπDEP chip contains embedded electrodes within the microfluidic channel covered by a thin passivation layer of only 4 μm. The channel was designed with two nonaligned vertical columns of insulated microposts (200 μm diameter, 50 μm spacing) located between the electrodes (600 μm wide, 600 μm horizontal spacing) to generate the nonuniform electric field lines to concentrate cells while maintaining steady flow in the channel. The performance of the chip was demonstrated using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial pathogens in aqueous media. Trapping efficiencies of 100% were obtained for both pathogens at an applied AC voltage of 50 V peak-to-peak and flow rates as high as 10 uL/min. / Master of Science

In this dissertation we report on the application of the Liouville Operator Resolvent technique (LRM) to two hamiltonians used to model highly correlated systems: Falicov-Kimball and Anderson Lattice. We calculate specific heats, magnetic susceptibilities, thermal averages of physical operators, and energy bands. We demonstrate that the LRM is a viable method for investigating many body problems. For the Falicov-Kimball, an exact calculation of the atomic limit shows no sharp metal-insulator transition. A truncation approximation for the full hamiltonian has a smooth evolution from the atomic limit with the opening of a band for the conduction electrons. No phase transition was observed. A bose space calculation using the proper boson norm indicates that the conduction band induces a correlation between localized electrons on nearest-neighbor sites. It is not known if this effect is real or a by-product of the approximation. We applied the LRM to the Anderson Lattice and several of its limiting cases. In the limit of no hybridization, for both the symmetric and asymmetric (mixed-valence) parameter sets, we found that the thermodynamics could be described as competition between closely-lying energy levels. The effects that dominate are those that minimize the thermal average of the hamiltonian. A simple model is presented in which only hybridization between two localized orbitals is allowed. It shows that hybridization can give rise to mixed valence phenomena as the temperature approaches zero. For the full Anderson Lattice hybridization causes relatively small shifts in the occupation numbers of the localized and conduction electrons. However, these shifts can have dramatic effects on the physical properties as demonstrated by the magnetic susceptibilities. Band structures of the eigenenergies of the Liouville operator, for both parameter sets, reveal that low-lying excitations associated with some of the basis vector operators may split out from the fermi level and become significant at low temperatures. In addition, we report on progress toward extending the calculation to bose space using a commutator norm. / Ph. D. / incomplete_metadata

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第25294号 / 工博第5253号 / 新制||工||2000(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 白石 誠司, 准教授 掛谷 一弘, 教授 柳瀬 陽一 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

L'introduction d'une contrainte mécanique dans le canal de MOSFETs sur SOI est indispensable pour les noeuds technologiques sub-22 nm. Son efficacité dépend de la géométrie et des règles de dessin du dispositif. L'impact des étapes du procédé de fabrication des transistors (gravure des zones actives, formation de la grille métallique, implantation des Source/Drain (S/D)) sur la contrainte du silicium contraint sur isolant (sSOI) a été mesuré par diffraction des rayons X en incidence rasante (GIXRD). Parallèlement, le gain en performances de MOSFETs sur sSOI a été quantifié par rapport au SOI (100% de gain en mobilité pour des nMOS longs et larges (L=W=10 μm), 35% de gain en courant de drain à saturation (IDsat) pour des nMOS courts et étroits (L=25 nm, W=77 nm)). Des structures contraintes innovantes ont aussi été étudiées. Un gain en IDsat de 37% (18%) pour des pMOS sur SOI (sSOI) avec des S/D en SiGe est démontré par rapport au sSOI avec des S/D en Si, pour une longueur de grille de 60 nm et des films de 15 nm d'épaisseur. Des mesures GIXRD, couplées à des simulations mécaniques, ont permis d'étudier et d'optimiser des structures originales avec transfert de contrainte d'une couche enterrée précontrainte (en SiGe ou en nitrure) vers le canal.

Die vorliegende Arbeit befasst sich mit dem Dünnfilmwachstum der ternären Oxide Na2IrO3, Li2IrO3, Y2Ir2O7 und YBiO3. All diesen oxidischen Materialien ist gemein, dass sie Verwirklichungen sogenannter Topologischer Isolatoren oder Spin-Flüssigkeiten sein könnten. Diese neuartigen Materiezustände versprechen eine zukünftige Anwendung in der Quantencomputation, in magnetischen Speichern und in elektrischen Geräten mit geringer Leistungsaufnahme. Die Herstellung der hier gezeigten Dünnfilme ist daher ein erster Schritt zur Umsetzung dieser Anwendungen in der Zukunft. Alle Dünnfilme werden mittels gepulster Laserplasmaabscheidung auf verschiedenen einkristallinen Substraten hergestellt. Die strukturellen, optischen und elektrischen Eigenschaften der Filme werden mittels etablierter experimenteller Verfahren wie Röntgenbeugung, spektroskopischer Ellipsometrie und elektrischenWiderstandsmessungen untersucht. Die strukturellen Eigenschaften von erstmalig in der Masterarbeit des Authors verwirklichten Na2IrO3-Dünnfilmen können durch Abscheidung einer ZnO-Zwischenschicht deutlich verbessert werden. Einkristalline Li2IrO3-Dünnfilme mit einer definierten Kristallausrichtung werden erstmalig hergestellt. Die Messung der dielektrischen Funktion gibt Einblick in elektronische Anregungen, die gut vergleichbar mit Li2IrO3-Einkristallen und verwandten Iridaten sind. Des Weiteren wird aus den Daten eine optische Energielücke von ungefähr 300 meV bestimmt. In Y2Ir2O7-Dünnfilmen wird eine mögliche (111)-Vorzugsorientierung in Wachstumsrichtung gefunden. Im Vergleich mit der chemischen Lösungsabscheidung zeigen die hier mittels gepulster Laserplasmaabscheidung hergestellten YBiO3-Dünnfilme eine definierte, biaxiale Kristallausrichtung in der Wachstumsebene bei einer deutlich höheren Schichtdicke. Über die gemessene dielektrische Funktion können eine direkte und indirekte Bandlücke bestimmt werden. Deren Größe gibt eine notwendige experimentelle Rückmeldung an theoretische Berechnungen der elektronischen Bandstruktur von YBiO3, welche zur Vorhersage der oben erwähnten, neuartigen Materiezuständen verwendet werden. Nach einer Einleitung und Motivation dieser Arbeit gibt das zweite Kapitel einen Überblick über den gegenwärtigen Forschungsstand der hier untersuchten Materialien. Die folgenden zwei Kapitel beschreiben die Probenherstellung und die verwendeten experimentellen Untersuchungsmethoden. Anschließend werden für jedes Material einzeln die experimentellen Ergebnisse dieser Arbeit diskutiert. Die Arbeit schließt mit einer Zusammenfassung und einem Ausblick. / The present thesis reports on the thin film growth of ternary oxides Na2IrO3, Li2IrO3, Y2Ir2O7 and YBiO3. All of these oxides are candidate materials for the so-called topological insulator and spin liquid, respectively. These states of matter promise future application in quantum computation, and in magnetic memory and low-power electronic devices. The realization of the thin films presented here, thus represents a first step towards these future device applications. All thin films are prepared by means of pulsed laser deposition on various single-crystalline substrates. Their structural, optical and electronic properties are investigated with established experimental methods such as X-ray diffraction, spectroscopic ellipsometry and resistivity measurements. The structural properties of Na2IrO3 thin films, that were previously realized in the author’s M. Sc. thesis for the first time, are improved significantly by deposition of an intermediate ZnO layer. Single-crystalline Li2IrO3 thin films are grown for the first time and exhibit a defined crystal orientation. Measurement of the dielectric function gives insight into electronic excitations that compare well with single crystal samples and related iridates. From the data, an optical energy gap of about 300 meV is obtained. For Y2Ir2O7 thin films, a possible (111) out-of-plane preferential crystal orientation is obtained. Compared to chemical solution deposition, the pulsed laser-deposited YBiO3 thin films presented here exhibit a biaxial in-plane crystal orientation up to a significantly larger film thickness. From the measured dielectric function, a direct and indirect band gap energy is determined. Their magnitude provides necessary experimental feedback for theoretical calculations of the electronic structure of YBiO3, which are used in the prediction of the novel states of matter mentioned above. After the introduction and motivation of this thesis, the second chapter reviews the current state of the science of the studied thin film materials. The following two chapters introduce the sample preparation and the employed experimental methods, respectively. Subsequently, the experimental results of this thesis are discussed for each material individually. The thesis concludes with a summary and an outlook.

Ce travail porte sur l’étude expérimentale et théorique du comportement des gouttelettes d’eau (instabilité, déformation, coalescence), déposées à la surface d’un isolateur composite haute tension, en présence d’un champ électrique. La déformation des gouttelettes d’eau est étudiée en fonction de plusieurs paramètres tels que le volume, le nombre et la conductivité des gouttelettes ainsi que leurs positions par rapport aux électrodes. Un intérêt particulier est porté à la charge accumulée sur la surface d’une gouttelette. L’influence des gouttelettes sur la répartition du champ électrique ainsi que le facteur d’amplification du champ électrique par une méthode numérique sont étudiés. Une formulation mathématique de la déformation d’une gouttelette d’eau posée sur une surface d’isolateur est développée. Les mécanismes ainsi que les paramètres impliqués dans la coalescence d’une paire de gouttelettes d’eau sous l’effet du champ électrique sont également traités. Un modèle mathématique permettant d’analyser la coalescence d’une paire de gouttelettes d’eau posées sur la surface d’un isolateur en présence du champ électrique est proposé. Ce modèle est basé sur une approche à interface diffuse qui consiste essentiellement en un couplage entre les équations de Navier-Stokes, le calcul de la force électrique et une équation de type Cahn-Hilliard décrivant l’évolution de l’interface en prenant en compte les phénomènes de tensions superficielles. La démarche suivie et les résultats présentés dans ce travail ouvrent de multiples perspectives tant d’un point de vue expérimental que d’un point de vue de la modélisation et de la simulation numérique des phénomènes physiques intervenant sur des isolateurs de lignes de transport et de distribution de l’énergie électrique dans des conditions d’humidité (pluie, rosée ...). / This work is devoted to experimental and theoretical study of the behavior of water droplets (instability, deformation, coalescence), located on the surface of a high voltage composite insulator, in presence of electric field. The deformation of droplets is investigated according to several parameters such as volume, number and conductivity of the droplets as well as their positions with respect to the electrodes. A particular interest is focused on the electric charge accumulated on the droplet surface. The droplet influences on the electric field distribution as well as the amplification factor of the electric field are studied by a numerical method. A mathematical formulation of the deformation of water droplet located on a surface of insulator is developed. The mechanisms as well as parameters involved in coalescence of a pair of water droplets under the electric field stress are also investigated. A mathematical model is developed for analyzing the coalescence of a pair of water droplets sitting on the surface of an insulator in presence of the electric field. It is based on a diffuse interface model that essentially consists of a coupling between Navier-Stokes equations, the computing of electric force and a Cahn-Hilliard type equation describing the interface evolution including capillary phenomena. The approach followed and the results presented in this work open several perspectives as well from an experimental point of view as from a point of view of modeling and numerical simulation of physical phenomena affecting insulators of high voltage transport and distribution lines in humidity conditions (rain, dew...).