The main aim of this work was to develop a method of screening HgCdTe materials for carrier concentration and mobility using Faraday rotation θ and absorption α. Faraday rotation provides N/m*2, where N is the carrier concentration and m* is the effective mass. Since m* was not known in HgCdTe, a Faraday rotation spectrometer was developed to systematically measure it as a function of temperature and Cd mole fraction. Effective masses in n-InSb, and n-GaAs were measured and compared with known values in the literature to validate the method. Mobility is proportional to θ/α. The proportionalities were determined in HgCdTe, n-InSb, and n-GaAs at infrared wavelengths. The dissertation consists of the preface, introduction, three chapters, summary and main conclusions, references, list of publications and abstract (in Lithuanian).

The main aim of this work was to develop a method of screening HgCdTe materials for carrier concentration and mobility using Faraday rotation θ and absorption α. Faraday rotation provides N/m*2, where N is the carrier concentration and m* is the effective mass. Since m* was not known in HgCdTe, a Faraday rotation spectrometer was developed to systematically measure it as a function of temperature and Cd mole fraction. Effective masses in n-InSb, and n-GaAs were measured and compared with known values in the literature to validate the method. Mobility is proportional to θ/α. The proportionalities were determined in HgCdTe, n-InSb, and n-GaAs at infrared wavelengths.

Automated narrow-gap girth-butt welds are replacing conventional welding methods to join sections of austenitic stainless steel pipe in the primary circuit of Pressurised Water Reactors, to reduce manufacturing costs and improve quality. To ensure the safe operation of these systems, reliable structural integrity assessments have to be undertaken, requiring the mechanical properties of welded joints to be characterised alongside the weld residual stress magnitude and distribution.This research project characterised, for the first time, the weld residual stress field and the tensile and ductile fracture toughness properties of a 33 mm thick narrow-gap 304L stainless steel pipe weld. The residual stress was characterised using two complementary approaches: deep hole drilling and neutron diffraction. A novel neutron diffraction scanning technique was developed to characterise the residual stress field, without cutting an access window into the component, leaving the original weld residual stress field undisturbed. A modified deep hole drilling technique was developed to characterise the residual stress retained in fracture mechanics specimens extracted from the pipe weld in two orientations. The modified technique was shown to measure the original weld residual stress field more accurately than through conventional deep hole drilling. Residual stresses, exceeding 50% of the weld material proof strength, were retained in axially-orientated fracture mechanics specimens.Tensile tests showed that the weld was approximately 60% overmatched. It was demonstrated that neither retained residual stress, nor specimen orientation, had a discernible effect on the measured fracture toughness of the weld material. In less ductile materials, however, the level of retained residual stress may unduly influence the measurement of fracture toughness. At initiation, the fracture toughness properties of both the parent and weld materials were far in excess of the measuring capacity of the largest fracture mechanics specimens that could be machined from the weld.The influence of residual stress and fracture toughness on the performance of narrow-gap welded pipework was investigated. Full elastic-plastic finite element analyses were used to model the pipe weld, containing a postulated defect under combined primary and secondary loading. The results, applied within the framework of an R6 structural integrity assessment, compared different plasticity interaction parameters on the prediction of failure load; the conventional ρ-parameter approach was compared with the recently developed, more advanced, g-parameter. It was shown that the g-parameter significantly reduced the conservatism of the ρ-parameter approach. However, for this pipe weld, plastic collapse was predicted to precede failure by ductile initiation, suggesting that a plastic collapse solution may be an appropriate failure criterion to use in structural integrity assessments of similar component and defect combinations.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19522号 / 理博第4182号 / 新制||理||1600(附属図書館) / 32558 / 京都大学大学院理学研究科化学専攻 / (主査)教授 吉村 一良, 教授 有賀 哲也, 教授 北川 宏 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The goal of this project was to study some unexplored optical and magneto-optical properties of the newest member of III-V ferromagnetic structures, InMnSb, as well as InSb films and InSb/AlInSb quantum wells. The emphasis was on dynamical aspects such as charge and spin dynamics in order to address several important issues of the spin-related phenomena. The objectives in this project were to: 1) understand charge/spin dynamics in NGS with different confinement potentials, 2) study phenomena such as interband photo-galvanic effects, in order to generate spin polarized current, 3) probe the effect of magnetic impurities on the spin/charge dynamics. This thesis describes three experiments: detection and measurement of spin polarized photocurrents in InSb films and quantum wells arising from the circular photogalvanic effect, and measurements of the carrier and spin relaxation in InSb and InMnSb structures by magneto-optical Kerr effect and differential transmission. The samples for our studies have been provided by Prof. Heremans at Virginia Tech, Prof. Santos at the University of Oklahoma, and Prof. Furdyna at the University of Notre Dame. / Ph. D.

As the switching rates in electronic and optoelectronic devices are pushed to even higher frequencies, it is crucial to probe carrier dynamics in semiconductors on femtosecond timescales. Time resolved spectroscopy is an excellent tool to probe the relaxation dynamics of photoexcited carriers; where after the initial photoexcitation, the nonequilibrium population of electrons and holes relax by a series of scattering processes including carrier-carrier and carrier-phonon scattering. Probing carrier and spin relaxation dynamics in InAs and InSb based narrow-gap semiconductors is crucial to understand the different scattering mechanisms related to the systems. Similar studies in InSb quantum wells are also intriguing, especially for their scientifically unique features (such as small effective mass, large g-factor etc). Our time resolved techniques demonstrated tunability of carrier and spin dynamics which might be important for charge and spin based devices. The samples studied in this work were provided by the groups of Prof. Wessels (Northwestern University) and Prof. Santos (University of Oklahoma). Theoretical calculations were performed by the group of Prof. Stanton (University of Florida). The THz measurements were performed at Wright State University in collaboration with Prof. Jason Deibel. This work has been supported by the National Science Foundation through grants Career Award DMR-0846834, AFOSR Young Investigator Program 06NE231. A portion of this work was performed at the National High Magnetic Field Laboratory (in collaboration with Dr. Stephen McGill), which is supported by National Science Foundation Cooperative Agreement No. DMR-0654118, the State of Florida, and the U.S. Department of Energy. / Ph. D.

Accessing Topological Phases of Mercury Cadmium Telluride Heterostructure Devices presents a broad study on quantum transport effects in the major topological transport phases of devices fabricated from mercury cadmium telluride quantum wells. The initial Chapter 1 introduces the material system and its band structure, focusing of the versatile phases accessible by changing confinement (layer thickness), strain, material composition and magnetic field. In Chapter 2, the experimental requirements for conducting low-temperature magnetotransport studies are addressed. Following the introduction of standard low-frequency AC lock-in techniques, the standard electric circuit is modified by employing DC test equipment for rapid single-parameter (e.g. gate voltage) sweeps, which are completed in less than a millisecond. This technique requires a precise understanding of parasitic effects in the circuit, mainly stemming from the interplay of wire and device capacitance with the typically high impedance of mercury telluride devices (order 10 kW), which are identified and eliminated through precise circuit modeling. Fast pulsing of the gate voltage is employed to perform common time-consuming measurement protocols like Landau level fancharts or temperature-dependent gating at least an order of magnitude faster than the established AC technique while revealing results of similar high quality. Subsequently, the technique is successfully applied to measure the quantum Hall effect in pulsed magnetic fields as high as 65 T, which is inaccessible with the AC configuration due to the limited pulse lifetime of less than 100 ms per pulse. Chapter 3 delves into the fabrication of transport devices from mercury cadmium telluride heterostructures, featuring two reports on lithographic advancements. Firstly, the Ohmic contact to mercury telluride quantum wells is comprehensively measured using the transfer-length model, and optimized regarding the depth of ion-milling into the top barrier. Compared to previously reported results, the contact resistance of (2.2 ± 1.6) · 10^(−4) Ωcm^2 is reduced by a factor of ten. Secondly, a novel gate geometry, called overlapping top gates, is introduced. The technique employs multiple lithographically defined top gates to minimize the ungated area between neighboring gate electrodes by overlapping them. The approach overcomes the necessity of a back gate-top gate combination to fabricate gate-defined reconfigurable junctions (nn′, np, pn, pp′), while featuring sharp density gradients at the junction that are unattainable with standard split gates. The advantages are demonstrated by calculating the electrostatic gate potentials. Transport measurements on gatedefined reconfigurable ambipolar junctions reveal a small rectification at zero magnetic field. In the quantum Hall regime, contacting through a gate-defined junction demonstrates that contacting from a high-density to a low-density region forms robust quasi-Ohmic contacts. This is applied in a so-called ring gate device to ensure the clear differentiation between the breakdown of contacts and actual physics when studying metal-insulator transitions at high magnetic fields. Quantum transport in thin, strongly confined quantum wells is studied in various topological transport phases in Chapter 4. Firstly, the trivial phase is investigated, focusing on the quantum Hall effect in it. The insulating ν = 0 state, a quantum Hall phase not observed in gallium arsenide, is discussed and unambiguously related to the occupation of edge states when broadened Landau levels are probed. The insulating state, observed for any filling factor |ν| < 1/2, aligns with the pattern of all other integer quantum Hall plateau and is inherently observed in any materials exhibiting negligible electron-electron interactions (single-particle limit). The same arguments explain why the fractional quantum Hall effect is not observed in mercury telluride quantum wells despite their very high mobility. The transmission and equilibration of quantum Hall edge channels at a lateral junction reveals an unprecedented match with Landauer-Büttiker theory, reemphasizing the role of mercury telluride as a prototype material to explore single particle quantum Hall physics. Secondly, the two-dimensional topological insulator phase and particularly the quantum spin Hall effect are probed. The breakdown of helical edge transport in a perpendicular magnetic field is resolved, aligning precisely with a magnetic field-induced lifting of the band inversion. Additionally, a study of decoherence in helical quantum spin Hall edge channels unravels that scattering off charge puddles via an isotropic Kondo interaction is one of the leading sources of backscattering at very low temperatures (Kondo temperature < 100 mK). Thirdly, the topologically inverted semimetallic state is covered. It is demonstrated that applying a back gate potential has a significant impact to the band structure of mercury telluride quantum wells via (actively tunable) structural inversion asymmetry. This suggests a plausible path towards a future quantum spin Hall transistor device. Subsequently, the emergence of topological phases when a mercury telluride quantum well is alloyed with cadmium or manganese is explored. For example, alloying an inverted mercury telluride quantum well with cadmium drives it back to the trivial phase, as unambiguously demonstrated for a series of 10 nm thick quantum wells. Remarkably, the match between band structure calculations, transport measurements and infrared-optical methods is striking. Quantum wells alloyed with manganese experience a similar evolution of their topological phases, but in the narrow window of a direct band gap inverted quantum well a special transport effect is observed, as a p-type quantum Hall plateau appears as early as 100 mT. This early onset quantum Hall effect is shown to emerge within a variation of the quantum well thickness of 1 nm. Additionally, the early onset plateau is demonstrated to transition into the insulator regime like any undoped quantum well at the filling factor |ν| = 1/2 (referring to the geometrically induced carrier density). In Chapter 5, the influence of reducing confinement in strained mercury telluride layers is studied, which accesses the phase of the three-dimensional topological insulator. An analysis scheme based on multi-carrier transport features in low magnetic fields is presented, revealing that pure surface state transport only occurs in a narrow thickness-dependent charge carrier density window. For all other carrier densities, bulk sub-bands (conduction sub-band and valence sub-band) contribute to the transport signatures significantly. A phase diagram of surface state transport is established for thicknesses between 22 and 110 nm, indicating that a guaranteed surface state transport can be anticipated within a carrier density range of 2.1 − 2.5 · 10^11 cm^(−2). This regime is identified as the necessary host of any future studies on the transport properties of topological surface states in strained mercury telluride. Furthermore, measurements conducted at high magnetic fields indicate that the surface character (even in the surface state transport window) rapidly diminishes with increasing magnetic field. The overall findings motivate a reevaluation of the conventional interpretation of transport in a mercury telluride three-dimensional topological insulator – past experimental claims and predictions derived from ideal theoretical models will need to be readdressed for their validity in any future experiments. Overall, this work provides a comprehensive exploration of topological phases in mercury cadmium telluride heterostructures, offering valuable insights into a variety of characteristic quantum transport phenomena in diverse device configurations. / „Messungen an topologischen Phasen von Quecksilber-Cadmium-Tellurid-Heterostruktur-Bauelementen“ (engl. Accessing Topological Phases of Mercury Cadmium Telluride Heterostructure Devices) ist eine Arbeit über charakteristische Quantentransportphänomene von Quecksilber-Cadmium-Tellurid-Quantentrögen. Im ersten Kapitel werden das Materialsystem und seine Bandstruktur vorgestellt, wobei schwerpunktmäßig die topologischen Phasen diskutiert werden, die durch Änderung der Schichtdicke, der Kristallverspannung, der Materialzusammensetzung und des Magnetfelds zugänglich sind. In Kapitel 2 werden die technischen Grundlagen einer Tieftemperatur-Transportmessung erläutert (Kryotechnik und Beschaltung). Auf eine Einführung in Transportmessungen mittels niederfrequenter AC-Lock-In Verfahren folgt die Vorstellung eines schnellen DC-Messprotokolls, welches Messungen über einen eindimensionalen Parameterraum (z.B. Gate-Spannung) in weniger als einer Millisekunde erlaubt. Da das schnelle Verfahren eine hohe Anfälligkeit gegenüber parasitärer Kapazitäten hat, welche zusammen mit der Bauteilimpedanz im Rahmen einer zeitaufgelösten Transportmessung RC-Effekte hervorrufen, werden letztere mittels Schaltungssimulation präzise nachgebildet und anschließend korrigiert. Gewöhnlich zeitaufwendige Messaufgaben, wie beispielsweise sogenannte Landau-Niveau-Fächerkarten, können unter Verwendung des neuartigen Messprotokolls bei gleichbleibender Datenqualität mehr als zehnfach schneller durchgeführt werden. Darüber hinaus ermöglicht das Verfahren Messungen in gepulsten Hochmagnetfeldern von bis zu 65 T (< 100 ms). Die Grundlagen der lithographischen Herstellung von Bauelementen werden in Kapitel 3 eingeführt und durch zwei Neuentwicklungen zur Bauteilherstellung ergänzt. In ersterer der beiden werden die Ohm’schen Kontakte von Standardbauteilen hinlänglich charakterisiert (Transferlängenmodell) und anschließend auf einen niedrigen Kontaktwiderstand hin optimiert. Letzter kann durch ein vollständiges Abtragen der Top-Barriere der Quantentrog-Heterostrukturen mittels präzisen Trockenätzens um eine Größenordnung auf (2.2 ± 1.6)·10^(−4) Ωcm^2 reduziert werden. Die zweite Neuentwicklung präsentiert eine neue Bauteilgeometrie, welche auf einander überlappenden Top-Gate-Elektroden beruht. Dieses Elektrodendesign kann in Bauteilen für pn-Übergänge eingesetzt werden, deren Polarität ausschließlich durch das Anlegen verschiedener Gate-Spannungen gesteuert werden kann (nn′, np, pn, pp′). Das neue Design sticht dabei durch die reine lithographische Herstellung (einsetzbar auf jedem Material) bei gleichzeitig sehr scharfem Ladungsträgergradienten am pn-Übergang (nicht zu erreichen mit nicht-überlappenden Top-Gate-Elektroden) hervor. Letzteres wird durch Berechnungen der Gate-Elektrostatik belegt. Anschließend wird gezeigt, dass in Gate-basierten pn-Übergängen leichte pannungsgleichrichtung beobachtet werden kann. Darüber hinaus wird nachgewiesen, dass ein solcher pn-Übergang im Quanten-Hall-Regime eine robuste quasi-Ohm’sche Kontaktierung erlaubt. Letztere wird eingesetzt, um in der neuartigen Ring-Gate-Geometrie klar zwischen einem Kontaktversagen und einem Bandstruktur-induzierten Isolatorübergang im Quantentrog unterscheiden zu können. Kapitel 4 beleuchtet charakteristische Quantentransportphänomene in den bedeutendsten topologischen Phasen dünner Quecksilber-Tellurid-Quantentrögen. Zuerst wird die triviale Phase mithilfe des Quanten-Hall-Effekts untersucht: Es wird gezeigt, dass in den Quantentrögen ein Metall-Isolatorübergang bei großen Magnetfeldern stattfindet. Dieser Quanten-Hall-Isolator-Zustand kann durch ein einfaches Besetzungsmodell von Landau-Niveaus erklärt werden und impliziert, dass Quecksilber-Tellurid, anders als Gallium-Arsenid, nur vernachlässigbare Elektron-Elektron-Wechselwirkungen in solch großen Magnetfeldern zeigt. Dies erklärt darüber hinaus, warum der fraktionale Quanten-Hall-Effekt nicht beobachtet werden kann. Andererseits kann gezeigt werden, dass die Transmission und Co-Propagation von Quanten-Hall-Randkanälen an pn-Übergängen präzise durch das Landauer-Büttiker-Modell gestützt werden, was den Einteilchencharakter im Quanten-Hall-Regime unterstreicht. Als nächstes liegt der Fokus auf der Phase des zweidimensionalen topologischen Isolators. Der für diese Phase charakteristische Quanten-Spin-Hall-Effekt liegt dabei im Zentrum der Untersuchungen. Es wird nachgewiesen, dass der helikale Randkanaltransport genau dann zusammenbricht, wenn die Bandstrukturinversion durch ein orthogonales Magnetfeld aufgehoben wird. Darüber hinaus werden Kondo-Wechselwirkungen zwischen Randkanälen und „Ladungsträgerseen“ (engl. charge puddles) als eine der Hauptursachen für Dekohärenz im Quanten-Spin-Hall-Regime identifiziert. Als nächstes wird die Phase des invertierten Halbmetalls untersucht. In dieser wird gezeigt, dass ein Potentialabfall durch den Quantentrog die Bandstruktur signifikant verändern kann. Der Effekt wird der gebrochenen strukturellen Umkehrinvarianz zugeschrieben, welche durch eine Back-Gate-Elektrode aktiv gesteuert werden kann. Abschließend wird untersucht, wie das Legieren des Quantentrogs mit Cadmium oder Mangan die topologischen Phasen beeinflusst. Im Fall der Cadmium-Legierung wird anhand einer Serie von 10 nm dicken Trögen mit zunehmendem Cadmium-Gehalt gezeigt, dass die Bandstruktur von einer invertierten auf eine triviale Bandordnung übergeht. Der Übergang wird dabei durch eine beeindruckende Übereinstimmung von Bandstrukturrechnung, Transportmessung und Infrarot-Absoptionspektroskopie nachgewiesen. Wird Cadmium durch Mangan ersetzt, ergibt sich eine vergleichbare Änderung der topologischen Phasen. Darüber hinaus wird ein extrem früh einsetzender (< 100 mT) lochartiger Quanten-Hall-Effekt beobachtet, wenn sowohl eine Bandinversion als auch eine direkte Bandlücke vorliegt. Es wird gezeigt, dass dieser Effekt am Phasenübergang von indirekter zu direkter Bandlücker innerhalb einer Dickenvariation von 1 nm auftritt, und dass das früh einsetzende Quanten-Hall-Plateau, genauso wie in einem unlegierten Quantentrog, beim Füllfaktor |ν| = 1/2 in den Isolatorzustand übergeht. Die Betrachtungen in Kapitel 5 beziehen sich auf dicke, verspannte Quantentröge, welche dreidimensionale topologische Isolatoren darstellen. Anhand der Co-Existenz von Elektronen- und Lochleitung kann gezeigt werden, dass reiner Oberflächentransport nur in einem schmalen Ladungsträgerdichtefenster auftritt. Außerhalb dieses Fensters tragen neben (topologischen) Oberflächenzuständen auch Volumenzustände zum Quantentransport bei. Aus den Erkenntnissen an zwischen 22 und 110 nm dicken Quantentrögen wird ein Phasendiagramm des Oberflächentransports konstruiert, aus welchem das Ladungsträgerdichtefenster 2.1 − 2.5 · 10^11 cm^(−2) für gesicherten reinen Oberflächentransport hervorgeht. In diesem Fenster sollten alle zukünftigen Studien von Oberflächenzuständen angesiedelt werden. Darüber hinaus wird gezeigt, dass der Oberflächencharakter der Wellenfunktion schnell mit steigendem Magnetfeld verschwindet. Die Standard-Interpretation von dicken Quecksilber-Tellurid-Schichten als dreidimensionaler topologische Isolator gilt es zu reevaluieren, genauso wie die Schlussfolgerungen vergangener Arbeiten bezüglich ihrer Übertragbarkeit auf zukünftige Messvorhaben.

Topological insulators (TI) exhibiting the quantum spin Hall effect (QSHE) have promised revolutionary applications in quantum computing, electronics and spintronics due to their remarkable properties. The insulating bulk and unique combination of spin-polarized and dissipationless edge or surface states - the two main features of the QSHE - have the potential to minimize heat development. There are a plethora of material systems predicted to host the QSHE especially in the two-dimensional (2D) case but to date only three showed the transport characteristics for it. Two of the three material systems are HgTe quantum wells embedded in CdTe barriers and a monolayer of WTe2. Unfortunately, HgTe-based 2D TIs cannot support operations at elevated temperatures due to the transition into the trivial state with increasing temperatures. For WTe2, the helical edge channels even persisted up to 100K for thicker flakes, which, however, are challenging to manufacture in terms of scalability and reproducibility. The other prominent example is the InAs/GaSb material system, which has the advantage of being compatible to III-V semiconductor industry standards and is therefore suitable for potential device applications. Furthermore, as the electron level in the InAs layer and hole level in the GaSb layer are spatially separated, an electric-field controlled transition between a normal-insulating (NI) and a TI phase is possible. Also, the band ordering is rather temperature insensitive, which should support to observe the QSHE even at elevated temperatures. However, despite promising results like the observation of the helical edge channels in InAs/GaSb bilayer quantum wells (BQWs), the possible parasitic contributions of trivial edge channels and residual bulk conductivity dampened the importance of these findings. Therefore, the main goal of this thesis was to investigate TIs based on InAs/Ga(In)Sb and make important steps to solving these critical issues. This was achieved by exploring a new tuning possibility by illumination and investigating the newly InAs/Ga(In)Sb/InAs trilayer quantum wells (TQWs), where higher topological band gaps are achieved. In addition, by substituting the GaSb layer in the TQW with GaInSb, the residual bulk conductivity is significantly reduced. By fabricating microscopic Hall bars, the transport through helical edge channels becomes dominant. Therefore, the QSHE was unambiguously observed in topological insulators based on InAs/Ga(In)Sb even at elevated temperatures up to T = 60 K. / Topologische Isolatoren (TI), die den Quanten-Spin-Hall-Effekt (QSHE) zeigen, versprechen revolutionäre Anwendungen in der Quanteninformatik, Elektronik und Spintronik aufgrund ihrer unvergleichlichen Eigenschaften. Der isolierende Volumenbereich und die einzigartige Kombination aus spinpolarisierten und verlustfreien Rand- oder Oberflächenzuständen - die beiden Hauptmerkmale des QSHE - ermöglichen es, die Wärmeentwicklung zu minimieren. Es gibt eine Vielzahl von Materialsystemen, die den QSHE insbesondere im zweidimensionalen (2D) Fall unterstützen sollen, aber bisher haben nur drei die Transportcharakteristika dafür gezeigt. Zwei der drei Materialsysteme sind HgTe- Quantenfilme eingebettet in CdTe-Barrieren und eine Monolage aus WTe2. Leider können HgTe-basierte 2D-TIs aufgrund des Übergangs in den trivialen Zustand bei steigenden Temperaturen keine Operationen bei erhöhten Temperaturen unterstützen. Für WTe2 blieben die helikalen Randkanäle sogar bis zu 100 K für dickere Flocken erhalten, die jedoch in Bezug auf Skalierbarkeit und Reproduzierbarkeit schwierig herzustellen sind. Ein weiteres prominentes Beispiel ist das InAs/GaSb-Materialsystem, das den Vorteil hat, kompatibel mit den Industriestandards der III-V-Halbleiterindustrie zu sein und daher für potenzielle Geräteanwendungen geeignet ist. Darüber hinaus ist ein durch elektrisches Feld kontrollierter Übergang zwischen einer normal-isolierenden (NI) und einer TI-Phase möglich, da das Elektronenniveau in der InAs-Schicht und das Lochniveau in der GaSb-Schicht räumlich getrennt sind. Auch die Anordnung der Bänder ist relativ temperaturunempfindlich, was es ermöglichen sollte, den QSHE auch bei erhöhten Temperaturen zu beobachten. Trotz vielversprechender Ergebnisse wie der Beobachtung der helikalen Randkanäle in InAs/GaSb-Doppelschicht-Quantenfilmen (BQWs) wurde die Bedeutung dieser Ergebnisse durch mögliche parasitäre Beiträge trivialer Randkanäle und der Restleitfähigkeit des Volumens gemindert. Daher war das Hauptziel dieser Dissertation, TIs basierend auf InAs/Ga(In)Sb zu untersuchen und wichtige Schritte zur Lösung dieser Hindernisse zu unternehmen. Dies wurde durch die Erforschung einer neuen Manipulationsmöglichkeit durch Beleuchtung und die Untersuchung der neuen InAs/Ga(In)Sb/InAs-Dreischicht-Quantenfilme (TQWs) erreicht, bei denen größere topologische Bandlücken erzielt werden. Außerdem wird durch den Austausch der GaSb-Schicht im TQW durch GaInSb die Restleitfähigkeit des Volumens erheblich reduziert. Zusätzlich wird durch die Herstellung von mikroskopischen Hallbars der Transport durch helikale Randkanäle dominant. Dadurch wurde der QSHE eindeutig in topologischen Isolatoren basierend auf InAs/Ga(In)Sb selbst bei erhöhten Temperaturen bis zu T = 60 K bewiesen.

La présente étude vise à comprendre les écoulements ainsi que les transferts de chaleur par convection dans une configuration représentative d’un moteur de traction automobile. La zone d’étude est constituée d’un stator extérieur lisse et fixe et d’un rotor intérieur tournant. Deux géométries de rotor ont été étudiées : un rotor cylindrique et un rotor encoché. Un écoulement axial est superposé à l’écoulement produit par la rotation. Pour le rotor lisse, des mesures ont été réalisées pour des valeurs du nombre de Reynolds axial de 2500 à 13900 et de rotation de 1250 à 4000. Pour le rotor encoché, le nombre de Reynolds axial varie également de 2500 à 13900 et le nombre de Reynolds de rotation de 5000 à 26000. Les mesures de vitesse réalisées par PIV au sein des encoches montrent un écoulement tourbillonnaire contrarotatif complexe. Dans la zone d’entrée, on peut noter une forte interaction entre l’écoulement des encoches et celui provenant des zones polaires. Les résultats thermiques obtenues par thermographie infrarouge sur le rotor encoché montrent que les transferts thermiques augmentent avec l’augmentation du nombre de Reynolds axial mais l’influence de la vitesse de rotation est plus complexe. Enfin, la comparaison des résultats thermiques entre rotors lisse et encoché, a permis de mieux comprendre l’effet des encoches sur le refroidissement global. / The present work aimed to experimentally study the flow and heat transfer in a configuration corresponding to the gap of an automotive electrical motor (a thin airlayer between the rotating (rotor) and stationary (stator) parts.) Two rotor geometries are studied: one cylindrical and the other one with four slots which reproduce a synchronous motor used in automotive traction. An axial flow is superimposed to the rotation flow thanks to a ventilation system. The two most important parameters are axial Reynolds number and rotational Reynolds number. Velocity measurements are performed by PIV and heat transfer by infrared thermography coupled with heated thin foils. A complex counter rotational vortex flow has been recorded in the slots. Moreover, this slot flow seems to interact with the pole flow in the inlet region. This interaction seems to disappear rapidly after entrance area. Heat transfer rate is 3D, with great differences between the two slots faces and the pole. Classically, heat transfer rate grows with increasing axial Reynolds number. The relation between heat transfer rate and rotation Reynolds number is more complex

LUKOSZ Ondřej: Welding of heat - resistent steels by method SMAW into the narrow gap. The project elaborated in frame of engineering studies branch 2307. The project is submitting design of technology production of the weld procedure creep metal. It uses in manufactory power equipment. The power equipment, the type of steam turbine, uses steel 30CrMoNiV 5-11. The welding into the narrow gap has its specifics. The most important parameter is the choice of flux and filler metal. We must decide appropriate flux for convenient disposing of slag. Based on the literature study these problems were proposed the specified welding procedure, appropriate flux and appropriate additional material. For the experiment was selected appropriate temperature of preheating.