Les capsules, formées d’une goutte protégée par une membrane élastique, sont très présentes naturellement et dans diverses applications industrielles, mais peu d’études ont exploré les phénomènes transitoires de leur relaxation. L’objectif est d’étudier l’influence de l’inertie et du confinement sur la relaxation d’une capsule sphérique (1) pré-déformée en ellipsoïde et relâchée dans un canal carré où le fluide est au repos, (2) sous écoulement dans un canal carré à expansion soudaine (‘marche’). La capsule est modélisée comme un fluide Newtonien dans une membrane hyper-élastique sans épaisseur ni viscosité, et simulée en couplant les méthodes Volumes Finis - Eléments Finis - frontières immergées. Sa relaxation dans un fluide au repos comporte 3 phases : amorçage du mouvement du fluide, phases rapide puis lente de rétraction de la membrane. Trois régimes existent selon le rapport de confinement et le rapport des nombres de Reynolds et capillaire : amortissements pur, critique ou oscillant. Un modèle de Kelvin-Voigt inertiel est proposé pour prédire les temps de réponse et aussi appliqué à une capsule en écoulement dans le canal microfluidique avec marche. La comparaison aux simulations 3D montre sa pertinence aux temps courts de la relaxation. Ces travaux ouvrent la voie à l’étude d’écoulements transitoires de capsules confinées dans des systèmes microfluidiques complexes. / Capsules, made of a drop protected by an elastic membrane, are widly present in nature and in diverse industrial applications, but few studies have explored the transient phenomena governing their relaxation. The objective of the PhD is to study the influence of inertia and confinement on the relaxation of a spherical capsule (1) pre-deformed into an ellipsoid and released in a square channel where the fluid is quiescent, (2) flowing in a square channel with a sudden expansion (‘step’). The capsule is modeled as a Newtonian fluid in a hyperelastic membrane without thickness or viscosity and is simulated coupling the Finite Volume - Finite Element - Immersed Boundary Methods. Its relaxation in a quiescent fluid exhibits three phases: the initiation of the fluid motion, the rapid and then slow retraction phases of the membrane. Three regimes exist depending on the confinement ratio and the Reynolds to capillary number ratio: pure, critical or oscillating damping. A Kelvin-Voigt inertial model is proposed to predict the response time constants and also applied to a capsule flowing in the microfluidic channel with a step. The comparison to 3D simulations shows its relevance at short relaxation times. This work paves the way to the study of transient flows of capsules confined in microfluidic devices.

Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.

A new theory for predicting the windprofile over a canopy has been evaluated. The theory was first presented by Harman and Finnigan (2007). The theory relies on the forming of a mixing-layer above the canopy, due to different mean wind in and above the canopy. Characteristics from both mixing-layer and Monin Obukhov similarity theory have been used to develop the governingequations that give the wind profile. The theory has been used to calculate wind profiles for sixdifferent atmospheric stabilities. In order to evaluate the theory, profiles from the theory have beencompared to measurements from Jädraås forest, Sweden. Profiles from Monin Obukhov similarity theory were also used for comparison.In general the mixing-layer theory gives better results than Monin Obukhov similarity theory. Agreement with measurements is good in neutral conditions, but fails when the atmospheric stability is altered, especially in convective conditions. This is believed to be due to the canopy lacking in thickness. The mean wind speed is systematically underestimated and this is also believed to be caused by insufficient thickness of the canopy. A correction for this behaviour is proposed. The theory gives higher values of the mean wind speed in convective conditions with the correction and the calculated values of mean wind speed are closer to the measurements.

A 48-layer version of the COMMA-LIM (Cologne Model of the Middle Atmosphere – Leipzig Institute for Meteorology) three-dimensional global mechanistic model of the Earth\''s atmosphere from 0 km to 135 km with logarithmic pressure height coordinates was developed. The model is capable of reproducing the global structures and propagation of different planetary waves in the middle atmosphere. The contribution of gravity waves, tides, Rossby and Kelvin waves into the zonally averaged momentum budget of the mesosphere / lower thermosphere region has been investigated. / Eine neue Version des COMMA-LIM (Cologne Model of the Middle Atmosphere – Leipzig Institute for Meteorology) wurde im Zusammenhang mit der Erhöhung der vertikalen Schichtauflösung entwickelt. Das COMMA ist ein dreidimensionales globales mechanistisches Modell der Erdatmosphäre mit einer Ausdehnung von ca. 0 – 135 km in logarithmischen Druckkoordinaten. Damit können globale Eigenschaften der mittleren Atmosphäre sowie die Ausbreitung verschiedener planetarer Wellen nachvollzogen werden. Die Beiträge der Schwerewellen, thermischer Gezeiten, Rossby und Kelvin Wellen zur zonal gemitteltem Impulsbalance der Mesosphäre und unteren Thermosphäre wurden untersucht.

La supraconductivité est intensément étudiée en physique de la matière condensée pour ses éventuelles applications. En effet, ce phénomène est caractérisé macroscopiquement par des propriétés remarquables, mais pour le moment, son exploitation est limitée par la nécessité de refroidir ces matériaux à des températures cryogéniques. Après la découverte de H₃S, dont la température de transition est de 200 K, un renouveau d’intérêt est apparu pour les matériaux supraconducteurs conventionnels. Pour ce composé, le couplage entre électrons et phonons est à l’origine de l’appariement électronique, une condition nécessaire à la supraconductivité. L’énergie associée à ce couplage se trouve généralement dans la gamme des infrarouges lointains, voire des THz, faisant de la spectroscopie infrarouge un outil idéal pour étudier ce mécanisme. Cette thèse présente les études de deux matériaux supraconducteurs dans des conditions expérimentales extrêmes de pression ou de température, permise grâce à la forte brillance du rayonnement synchrotron. Pour la phase supraconductrice H₃S à des pressions supérieures à 150 GPa, l’environnement en cellule à enclumes de diamant exclut la plupart des techniques pour déterminer la nature du mécanisme mais les études optiques restent adaptées. Les résultats spectroscopiques présentés ici démontrent un fort couplage entre électrons et phonons, qui explique l’origine d’une si haute température de transition. Des mesures complémentaires visant à caractériser NaCl sous pression sont également décrites car ce matériau est couramment utilisé comme transmetteur de pression dans les cellules `a haute pression, notamment pour le supraconducteur H₃S. La deuxième étude rapporte des résultats spectroscopiques dans le THz sur des couches nanométriques de Nb, dont les températures de transition supraconductrice sont de 4,5 K et 6,8 K. Ces mesures confirment que la nature conventionnelle du mécanisme subsiste au sein de ces films minces quasi-bidimensionnels. Pour ce travail, un ensemble instrumental permettant la mesure spectroscopique de matériaux jusqu’à des températures de 200 mK a été entièrement développé autour d’un cryostat à démagnétisation adiabatique. / Superconductivity is highly studied in condensed matter physics for its potential applications. Indeed, this phenomenon is macroscopically characterized by remarkable properties, but generally occurs in materials at cryogenic temperature thus limitating their exploitation. Recently, renewed interest has appeared for conventional superconducting materials with the discovery of H₃S, whose transition temperature is at 200 K. For this compound, the coupling between electrons and phonons is at the origin of the electronic pairing, a necessary condition for superconductivity. The associated energy for this coupling belongs to the far infrared range, even THz, making infrared spectroscopy an ideal tool to study the mechanism. This thesis presents the studies of two superconducting materials in extreme experimental conditions of pressure and temperature, allowed by the high brilliance of synchrotron radiation. For the superconducting phase H₃S under pressures superior to 150 GPa, the environment of diamond anvil cell excludes most of the techniques to determine the nature of the mechanism but the optical studies remain adapted. The spectroscopic results presented here demonstrate a strong coupling between electrons and phonons, which explains the origin of such a high transition temperature. Complementary measurements aiming at characterizing NaCl under pressure is also described because this material is often used as a pressure transmitting medium in high pressure cells, in particular for the superconducting H₃S. The second study reports spectroscopic results in the THz on nanometric layers of Nb, whose superconducting transition temperatures are 4,5 K and 6,8 K. These measurements confirm that the conventional nature of the mechanism subsists within these quasi-bidimensional thin films. For this work, an instrumental ensemble allowing the spectroscopic measurements of materials down to 200 mK has been entirely developed based on an adiabatic demagnetization cryostat.

Spin-vortices in vertically spaced pairs of thin elliptical Permalloy nanoparticles are investigated. The two vortex cores with parallel out-of-plane magnetization exhibit a strong monopole-like attraction through the spacer much thinner than the core length, thus forming a bound core-core pair. The material of the spacer is designed to suppress both direct and indirect exchange interactions, so the remaining inter-vortex coupling is purely dipolar. In the investigated vortex pairs, the in-plane magnetization in the vortex periphery, outside the vortex cores, curl in opposite directions (have opposite chirality). As a result, the two cores move in opposite directions in response to an in-plane magnetic field, the Zeeman effect of which acts to decouple the core-core pair. This leads to unique dynamics of the spin-vortex parallel-core/antiparallel-chirality pair, which strongly depend on whether the pair is coupled or decoupled. In the coupled state, the cores are held close together by the core-core attraction, which results in short-radius oscillations and a resonance frequency of about 2 GHz for the main rotational eigen-mode. In the decoupled state, the cores are separated by a distance much greater than the core length and gyrate independently with a resonance frequency of the order of 100 MHz. The dynamics of the vortex pair are investigated at 77 K, where there is a bistability between the coupled and decoupled core states. Resonant excitations are used to decouple the cores with pulses of ∼10 Oe in amplitude and ∼100 ps in duration. The ability to decouple a vortex pair using such fast low-power pulses can be useful for multifrequency oscillators and vortex based memory. A search for quantum effects is undertaken at sub-Kelvin temperatures using a dilution refrigerator. Square pulses of 100 ns duration and amplitudes of the order of 1 Oe are applied in-plane to bring the system closer to decoupling, giving the cores a chance to tunnel through the barrier between the coupled and decoupled states. The amplitude required for decoupling is measured as a function of temperature and a leveling off in the decoupling probability is seen below 400 mK, giving some indication of core tunneling. Macroscopic quantum tunneling of magnetization is interesting from the fundamental physics point of view, e.g., as a model system for studying the measurement paradox in quantum mechanics, as well as for current and future computer technology in terms of understanding the ultimate limitations of miniaturizing magnetic memory elements. / I detta arbete studeras spinnvirvlar i elliptiska skivor av Permalloy ordnade i vertikala par. Kärnor av parallell vertikal magnetisering attraherar varandra likt monopoler genom en film mycket tunnare än kärnorna och bildar därmed ett sammankopplat par. Materialet i filmen mellan virvlarna är designat för att förhindra både direkt och indirekt utbytesväxelverkan och lämnar endast kärnornas dipolväxelverkan. I de virvelpar som studeras går den plana magnetiseringen i virvlarnas periferi runt kärnorna åt olika håll (de har motsatt kiralitet). På grund av detta rör sig kärnorna åt olika håll vid applikation av magnetfält i planet (Zeeman effekten) vilket kan leda till att de kopplas isär. Detta ger virvelpar med parallella kärnor och antiparallell kiralitet unika dynamiska egenskaper som ändras med deras tillstånd, sammankopplade eller isärkopplade. I det sammankopplade tillståndet hålls kärnorna ihop av monopolattraktionen vilket gör att de bara kan röra sig i små banor kring sitt magnetiska masscentrum, med en resonansfrekvens på circa 2 GHz. I det isärkopplade tillståndet är kärnorna separerade med ett avstånd som är mycket större än kärnornas diameter, och de rör sig oberoende av varandra med en resonansfrekvens i storleksordningen 100 MHz. Virvelparets dynamik undersöks vid 77 K, där det finns en bistabilitet mellan det sammankopplade och det isärkopplade tillståndet. Pulser med längd ∼100 ps och styrka ∼10 Oe i resonans med det sammankopplade tillståndet används för att koppla isär kärnorna. Att kunna koppla isär dem med så korta lågeffektspulser kan vara användbart för virvelbaserade minnen och multifrekvensoscillatorer. Ett sökande efter kvanteffekter påbörjas vid temperaturer under 1 K med hjälp av en utspädningskyl. Fyrkantsvågor med en längd på 100 ns och en styrka i storleksordningen 1 Oe, orienterade i planet, används för att ge kärnorna en chans att tunnla genom barriären mellan det sammankopplade och det isärkopplade tillståndet. Den vågamplitud som krävs för att koppla isär kärnorna plottas mot temperaturen och kan ses plana ut under 400 mK, vilket ger viss indikation av tunnling. Dessa undersökningar av makroskopisk kvanttunnling av magnetisering kan vara användbar i grundforskning för att studera mätparadoxen i kvantmekanik, men också i modern datorteknologi för att förstå de absoluta begränsningarna i hur små magnetiska minneselement kan göras.

In order to satisfy the mechanical requirements for space structures, achieving lightweight designs is of the greatest significance. The primary focus of this study is the utilization of Kelvin cell core in the design of sandwich structures for space applications. The research encompasses a variety of production techniques, analyzes, and tests related to the design of sandwich structures with Kelvin cells as the core material. While a variety of configurations are evaluated in a general sense, particular configurations are examined in greater extensive detail. In this context, the structure's bending stiffness, compression stiffness, and vibration characteristics are analyzed. The analytical procedure begins with a simplified structure analysis, followed by the modeling of the actual geometry. According to applicable standards, stiffness values are calculated based on the deflection results of the analyzes. However, it is important to note that the tests performed on the modeled structures are conducted in a laboratory environment using additively manufactured samples. This permits a comparison between the obtained test results and the findings of the analyzes, shedding light on the effect of the manufacturing method. This study demonstrates that the honeycomb sandwich structure is superior in terms of overall stiffness. In addition, a specially designed reinforced Kelvin Cell structure possesses exceptional bending rigidity properties. In light of these findings, it is clear that the combination of Kelvin Cell core and specific reinforcement strategies has the potential to improve the mechanical performance of sandwich structures. In addition, the deformation results revealed by the analyzes showed that the structure can be deformed in large amounts in directions other than the direction of the force it is exposed to. This situation is of great importance for damping in space applications. As a result of vibration analyzes and tests, the effect of stiffness and mass increase in a certain direction on natural frequencies has been revealed, and with 3-point bending tests, the facing elastic modulus and core shear modulus values of the structure have been determined separately and its effect on the sandwich structure has been shown. Accordingly, this study examined and evaluated many aspects of the possible role of the Kelvin Cell in space applications. / För att tillgodose de mekaniska kraven på rymdkonstruktioner är det av största vikt att uppnå lätta konstruktioner. Det primära fokuset för denna studie är utnyttjandet av Kelvin-Cellkärna vid design av sandwichstrukturer för rymdtillämpningar. Forskningen omfattar en mängd olika produktionstekniker, analyser och tester relaterade till design av sandwichstrukturer med Kelvin-Celler som kärnmaterial. En mängd olika konfigurationer utvärderas generellt, medan vissa specifika konfigurationer undersöks mer utförligt på detaljnivå. I detta sammanhang analyseras strukturens böjstyvhet, kompressionsstyvhet och vibrationsegenskaper. Den analytiska proceduren börjar med en förenklad strukturanalys, följt av modellering av den faktiska geometrin. Enligt gällande standarder beräknas styvhetsvärdena baserat på strukturanalysens resultat. Det är dock viktigt att notera att de tester som utförs på de modellerade strukturerna utförs i en laboratoriemiljö med hjälp av additivt tillverkade prover. Detta möjliggör en jämförelse mellan de erhållna testresultaten och resultaten av analysen, vilket belyser effekten av tillverkningsmetoden. Denna studie visar att sandwichstrukturen honeycomb är bäst när det gäller total styvhet. Dessutom har en specialdesignad förstärkt Kelvin-Cellstruktur exceptionella böjstyvhetsegenskaper. I ljuset av dessa fynd är det tydligt att kombinationen av Kelvin-Cellkärna och specifika förstärkningsstrategier har potential att förbättra den mekaniska prestandan hos sandwichstrukturer. Dessutom visade deformationsresultaten från analyserna att strukturen kan deformeras till hög grad i andra riktningar än den kraft som den utsätts för. Denna iaktagelse är av stor betydelse för dämpning i rymdapplikationer. Som ett resultat av vibrationsanalyser och tester har effekten av styvhet och massökning i en viss riktning på naturliga frekvenser upptäckts, och med 3-punkts böjtester har konstruktionens elasticitetsmodul och skjuvmodulsvärden bestämts separat och dess effekt på sandwichstrukturen har visats. Följaktligen undersökte och utvärderade denna studie många aspekter av Kelvin-Cellens möjliga roll i rymdtillämpningar.

No description available.

Current magnetic data storage technology is encountering certain fundamental limitations that present roadblocks to its scalability to areal densities of 1 Tbit/in^2 and beyond. Next generation magnetic storage technology is expected to use optical near field techniques to heat the magnetic film locally to write data bits. This requires experimental measurement of thermal conductivity of materials with sub--100 nm resolution. This is essential for the tailoring of the thin film stack to optimize the heat transfer of the process. This can be accomplished with a simple modification to a traditional atomic force microscopy (AFM) system. The modification requires the deposition of a thin metal film on the AFM cantilever thus creating a bimetallic cantilever. The curvature of a bimetallic cantilever is sensitive to temperature. Another modification is the use of a heating laser to raise the temperature of the cantilever so that when it scans across a sample with areas of varying thermal conductivity the bimetallic deformation of the heated cantilever is altered. The resulting system is sensitive to local variations in thermal conductivity with nanoscale resolution. Nanoscale thermal conductivity measurements can then be used to optimize the heat transfer properties of the materials used in a heat assisted magnetic recording system. AFM technology can also play a key role in the development of next generation solid-state chemical sensors. An AFM can be used to measure the workfunction of a material with near atomic resolution thus enabling the study of chemical reactions with high spatial resolution. Since chemical sensors typically use a chemical reaction at their front end to monitor the prescience of a gas, an AFM system can thus be used to understand and optimize the properties of the chemical reaction by monitoring the local workfunction. In this thesis, I explain the use of atomic force microscopy in measuring thermal and chemical properties of materials with applications towards the magnetic storage industry and chemical sensing.

This dissertation details the study of band bending in n- and p-type GaN samples with a Kelvin probe utilizing different illumination geometries, ambients (air, oxygen, vacuum 10-6 mbar), and sample temperatures (77 – 650 K). The Kelvin probe, which is mounted inside an optical cryostat, is used to measure the surface potential. Illumination of the GaN surface with band-to-band light generates electron-hole pairs, which quickly separate in the depletion region due to a strong electric field caused by the near-surface band bending. The charge that is swept to the surface reduces the band bending and generates a surface photovoltage (SPV). Information about the band bending can be obtained by fitting the SPV measurements with a thermionic model based on the emission of charge carriers from bulk to surface and vice versa. The band bending in freestanding n-type GaN templates has been evaluated. The Ga-polar and N-polar surfaces exhibit upward band bending of about 0.74 and 0.57 eV, respectively. The surface treatment also plays a major role in the SPV behavior, where the SPV for mechanical polished surfaces restores faster than predicted by a thermionic model in dark. When measuring the photoluminescence (PL) signal, the PL from mechanically polished surfaces was about 4 orders of magnitude smaller than the PL from chemically mechanically polished surfaces. The PL and SPV behaviors were explained by the presence of a large density of defects near the surface, which quench PL and aid in the restoration of the SPV via electron hopping between defects. Temperature-dependent SPV studies have also been performed on doped n- and p-type GaN samples. In Si-doped n-type GaN, the estimated upward band bending was about 1 eV at temperatures between 295 and 500 K. However, in p-type GaN, the downward band bending appeared to increase with increasing temperature, where the magnitude of band bending increased from 0.8 eV to 2.1 eV as the temperature increased from 295 to 650 K. It appears that heating the p-type GaN samples allows for band bending values larger than 1 eV to fully restore. Pre-heating of samples was of paramount importance to measure the correct value of band bending in p-type GaN. The slope of the dependence of the SPV on excitation intensity at low temperatures was larger than expected; however, once the temperature exceeded 500 K, the slope began to reach values that are in agreement with a thermionic model.