Les ondes acoustiques, démontrées théoriquement en 1885 par le scientifique anglais Lord Rayleigh, constituent de nos jours un sujet de recherches très intéressant. Elles sont devenues indispensables à la fabrication des systèmes de télécommunication miniatures et performants, tels que par exemple les filtres, les oscillateurs ou encore les capteurs. Les dispositifs fonctionnant grâce aux ondes acoustiques sont connus sous le nom de « dispositifs piézoélectriques » puisqu’ils transforment les signaux RF en ondes acoustiques, et vice versa, grâce au phénomène piézoélectrique direct. Le développement de ces dispositifs piézoélectriques a été indispensable pour répondre aux exigences particulières et extrêmes des systèmes de télécommunication actuels (sélectivité, miniaturisation, faible coût, facilité de fabrication et d’intégration). Cette thèse s’inscrit dans une démarche générale de développement des dispositifs piézoélectriques, notamment des micro-résonateurs piézoélectriques qui en constituent la dernière génération. Deux axes principaux ont été développés au cours de ces travaux de recherches : l’étude théorique des micro-résonateurs piézoélectriques à travers une modélisation électrique d’une part, et, d’autre part, la description des procédés de fabrication réalisés en salle blanche du laboratoire d’XLIM. / The acoustic waves, theoretically demonstrated in 1885 by the English scientist Lord Rayleigh, are nowadays an interesting research subject. It became essential to the fabrication of miniature and efficient systems of telecommunication, such as filters, oscillators or sensors. Devices using the acoustic waves are known as piezoelectric devices, because they transform RF signal into acoustic waves, and vice versa, thanks to the direct piezoelectric phenomenon. The development of these piezoelectric devices was essential to meet the particular and extreme requirements of the current systems of telecommunication (selectivity, miniaturization, low cost, ease of manufacturing and integration). This thesis is part of a global approach to develop the piezoelectric devices, notably the piezoelectric micro-resonators which constitute the latest generation. Two main axes have been developed during the research work: the theoretical study of piezoelectric micro-resonators through an electric modelling, on one hand, and, on the other hand, the description of the manufacturing processes accomplished in clean room of XLIM’s laboratory.

The work and results presented in this dissertation concern two complimentary studies that are rooted in surface acoustic waves and transducer study. Surface acoustic wave devices are utilized in a variety of fields that span biomedical applications to radio wave transmitters and receivers. Of interest in this dissertation is the study of surface acoustic wave interaction with polydimethylsiloxane. This material, commonly known as PDMS, is widely used in the microfluidic field applications in order to create channels for fluid flow on the surface of a piezoelectric substrate. The size, and type of PDMS that is created and ultimately etched on the surface of the substrate, plays a significant role in its operation, chiefly in the insertion loss levels experienced. Here, through finite element analysis, via ANSYS® 15 Finite Element Modeling software, the insertion loss levels of varying PDMS sidewall channel dimensions, from two to eight millimeters is investigated. The simulation is modeled after previously published experimental data, and the results demonstrate a clear increase in insertion loss levels with an increase in channel sidewall dimensions. Analysis of the results further show that due to the viscoelastic nature of PDMS, there is a non -linear increase of insertion loss as the sidewall dimensions thicken. There is a calculated variation of 8.31 decibels between the insertion loss created in a microfluidic device with a PDMS channel sidewall thickness of eight millimeters verse a thickness of two millimeters. Finally, examination of the results show that insertion loss levels in a device are optimized when the PDMS sidewall channels are between two and four millimeters. The second portion of this dissertation concerns the calibration of an ultrasonic transducer. This work is inspired by the need to properly quantify the signal generated by an ultrasonic transducer, placed under a static loading condition, that will be used in measuring ultrasonic bone conducted frequency perception of human subjects. Ultrasonic perception, classified as perception beyond the typical hearing limit of approximately 20 kHz, is a subject of great interest in audiology. Among other reasons, ultrasonic signal perception in humans is of interest because the mechanism by which either the brain or the ear interprets these signals is not entirely understood. Previous studies have utilized ultrasonic transducers in order to study this ultrasonic perception; however, the calibration methods taken, were either incomplete or did not properly account for the operation conditions of the transducers. A novel transducer calibration method is detailed in this dissertation that resolves this issue and provides a reliable means by which the signal that is being created can be compared to the perception of human subjects.

Cette thèse porte sur l'élaboration d'un biocapteur, à bas coût, pour la détection de pathogènes dans les secteurs de l'agroalimentaire et de l'environnement. Le modèle visé est la bactérie Escherichia coli, dont les souches pathogènes sont responsables, chaque année, de plusieurs crises sanitaires. L'utilisation de biocapteurs pour une détection rapide, sensible et sélective de pathogènes répond ainsi aux inquiétudes quant aux risques d'infection pour la population. Le capteur est constitué d'une fine membrane en arsénieure de gallium (GaAs) vibrant sur des modes de cisaillement d'épaisseur générés par champ électrique latéral via ses propriétés piézoélectriques. Nous montrons dans ce travail que la GaAs offre des possibilités de microfabrication, de biofonctionnalisation et de régénération intéressantes pour la conception d'un dispositif à bas coût. Nous avons mis en parallèle deux méthodes d'usinage de membranes minces : par voie chimique et par plasma, avec pour objectif, l'obtention de structures planes et lisse. Nous nous sommes intéressés à la réalisation d'une interface de bioreconnaissance. La caractérisation de celle-ci, par les techniques de spectroscope infrarouge à transformée de Fourier, nous a fait progresser sur a compréhension du phénomène d'auto-assemblage de molécules sur GaAs et nous a permis de développer des interfaces à haute densité. Nous avons étudié sa régénération et la photo-oxydation par UV a démontré un fort potentiel pour des applications de capteurs réutilisables. Enfin à travers des caractérisations électriques du transducteur, nous avons mis en avant l'impact de différents paramètres de l'environnement sur la réponse du dispositif. / This thesis addresses the development of a potentially low cost sensor dedicated for detection of pathogens in food industry processing and environment sectors. Such a sensor could serve detection of Escherichia coli bacteria whose pathogenic strains are the source of foodborne illnesses encountered worldwide every year. Hence, biosensor devices are needed for a rapid, sensitive and selective detection of pathogens to prevent outbreak risks. The design of the sensor consists of a resonant membrane fabricated in gallium arsenide (GaAs) crystal that operates at shear modes of bulk acoustic waves generated by lateral field excitation. In addition to its piezoelectric properties, as shown in this work, fabrication of a GaAs-based biosensor benefits from a well-developed technology of microfabrication and biofunctionalization and the possibility of regeneration that should result in cost savings of used devices. The transducer was fabricated by using typical clean room fabrication techniques. Plasma and wet etching were investigated and compared for achieving thin membranes with high quality surface morphology. Extensive research was carried out by Fourier transform infrared spectroscopy to determine optimum conditions for biofunctionalization of the GaAs surface. This activity allowed to advance the fundamental knowledge of self-assembly formation and, consequently, fabrication of high density biointerfaces. Among different biochip regeneration methods, it has been demonstrated that liquid UV photooxidation has a great potential for re-usable devices. Finally, operation of the transducer device was evaluated in various medium, simulating real conditions for detection.

Ces travaux de thèe portent sur le développement d’un outil d’analyse numérique dédié à l’ étude de nouveaux résonateursà quartz à ondes de volume et utilisant les éléments finis. Cette méthode de caractérisation permet la détermination deséléments du schéma électrique équivalent (résistance, inductance et capacité) d’une fréquence de résonance donnée ainsique son facteur de qualité, tout en prenant en compte dans le modèle la sensibilité du cristal de quartz à la températureet aux contraintes induites par le montage. Une étape de validation est d’abord réalisée afin de vérifier nos choix, enterme de modélisation et de calcul, en confrontant les données issues de la simulation aux mesures de résonateurs déjàexistants. Les trois dispositifs analysés (40 MHz, 10 MHz et 100 MHz) montrent une bonne concordance entre théorieet expérience. Pour obtenir de tels résultats, la structure de maintien est prise en compte et modélisée sous forme dezones d’amortissement de Rayleigh lorsque le piégeage de l’énergie n’est pas optimal (présence d’un mode de plaque).Un aspect important des résonateurs est ensuite étudié : le comportement en température. En effet, les contraintes dedilatation thermique ainsi que l’évolution des coefficients élastiques en fonction de la température induisent une dérivefréquentielle. La comparaison entre théorie et expérience nous permet de vérifier l’allure des courbes et de quantifier ledegré de précision du modèle. L’effet d’une contrainte mécanique appliquée sur le pourtour de la lame de quartz est parla suite introduit dans le modèle en utilisant la méthode de perturbation de Sinha-Tiersten. Il est alors possible de définirl’impact des défauts de fabrication sur la fréquence du résonateur. Enfin, la méthode numérique est appliquée à l’étudede structures innovantes dans le cadre du projet FREQUENCE2009. Il s’agit de revisiter le concept du résonateur BVA etd’envisager des procédés de fabrication collective. L’idée consiste ainsi à remplacer le rayon de courbure d’un résonateur,dont la fréquence utile se trouve aux alentours de 9 MHz, par une série de marches, plus compatible avec les procédés dela micro électronique (DRIE : Deep Reactive Ion Etching). Bien que les résultats expérimentaux soient, dans ce cas, loin denos attentes, nous constatons que l’outil d’analyse est parfaitement capable de prédire les caractéristiques de nouvellesstructures. / This work is devoted to the development of a digital analysis tool dedicated to study new bulk acoustic waves quartz resonatorsby using finite elements. This method of characterization allows the calculation of the elements of the equivalentelectrical circuit (resistor, inductance and capacitor) of a given resonant frequency as well as the quality factor, while takinginto account its sensitivity to the temperature and to the stresses induced by the mounting support. Firstly, a validationphase is carried out in order to check our choices, in terms of modeling and computation, by comparing simulation data tothe measures of existing resonators. The three analyzed devices (40MHz, 10 MHz and 100 MHz) show good agreementbetween theory and experiment. To obtain such results, the mounting support is taken into account and modeled thanks toRayleigh damping areas when the trapping of energy is not optimal (presence of a spurious shell vibration mode). Then, animportant aspect of resonators is studied : the temperature behavior of its vibrating modes. Indeed, the thermal expansionstresses as well as the change of stiffness coefficients according to the temperature induce frequency shift. The comparisonbetween theory and experiment allows us to check the shape of curves and to quantify the accuracy of the model.Thereafter, the effect of mechanical stress applied on the edge of the blank of quartz is introduced in the model by usingthe perturbation method developed by Tiersten and Sinha. So, it is possible to define the influence of some manufacturingdefects on the resonant frequency. Finally, the digital method is applied to study innovative structures in the framework ofthe project FREQUENCE2009. The aim is to review the concept of BVA resonator and consider collective manufacturingprocesses. The idea involves replacing the radius of curvature of a resonator, for which the expected frequency is around9 MHz, by several steps, more compatible with microelectronics processes (DRIE : Deep Reactive Ion Etching). Althoughthe results are far from our expectations, we note that the analysis tool is perfectly able to anticipate the characteristics ofnew structures.

<div>Global warming is considered to result from excessive emission of CO₂ caused by human activity. The security of long term CO₂ capture and sequestration on the subsurface depends on the integrity of caprocks. Natural and engineered subsurface activities can generate fractures in caprocks that can lead to CO₂ leakage. Reactive fluids that flow through a fracture may seal a fracture through mineral precipitation or open a fracture through dissolution. It is extremely useful to CO₂ storage to understand the behavior of reactive fluids that generates mineral precipitation that can seal a fracture. Experiments on non-reactive and reactive fluid mixing were performed to explore gravity-driven chemical dynamics that control the mixing and spatial distribution of mineral precipitates. Fracture inclination, fracture apertures, fluid pumping rates, and density contrasts between fluids were studied for their effects on fluid mixing. From non-reactive fluid mixing experiments, a less dense fluid was found to be confined to a narrow path (runlet) by the denser fluid under the influence of gravity. Fracture inclination angle affected the shape of the less dense fluid runlet. As the angle of inclination decreased, the area of the less dense runlet increased. Improved mixing and a potentially larger area of precipitation formation will occur during reactive fluid mixing when the fracture plane is perpendicular to gravity. Fracture aperture affected the time evolution of the mixing of the fluids, while pumping rate affected fluid mixing by controlling the relative velocities between the two fluids. The fact that the spatial distribution of the two fluids, instead of the fracture roughness, dominated the fluid mixing sheds light on the potential behaviors of reactive fluids mixing in fractures. The location for the majority of precipitation formation and the transport of precipitates can be accordingly predicted from knowledge of the properties of the two reactive fluids and the orientation of the fracture.</div><div>From a small study on wave propagation across fractures with precipitates, simulation results showed that the impedance difference between the matrix material and the precipitate affects the transmitted signal amplitude. Both the aperture and fraction of aperture filled with precipitates affect signal amplitude.</div><div><br></div>

Au cours des 25 dernières années, il n'y a eu que quelques rapports sur des expériences de type optique quantique avec des électrons.Les progrès réalisés dans ce récent domaine de recherche ont permis de mettre au point des techniques originales pour piéger, déplacer et manipuler les électrons dans des dispositifs à l'état solide.Ces progrès ouvrent de nouvelles perspectives pour l'étude de phénomènes quantiques fascinants tels que l'effect tunnel ou l'intrication avec les électrons.En raison de la contrôlabilité exigée dans les implémentations possibles de circuits logiques quantiques, il est maintenant particulièrement intéressant de réaliser des expériences d'optique quantique électronique avec des électrons volants uniques.Dans cette thèse, nous abordons deux expériences liées, mais conceptuellement différentes, d'optique quantique électronique au niveau de la particule unique.Toutes les expériences menées dans le cadre de cette thèse ont été réalisées à des températures cryogéniques avec des dispositifs définis par Schottky-gates dans des hétérostructures AlGaAs/GaAs.Tout d'abord, nous effectuons une expérience d'interférence d'électrons de type Mach-Zehnder dans le régime de transport balistique.En formant un grand point quantique dans l'une des branches de l'interféromètre, nous étudions le déphasage de la fonction d'onde d'un électron transmis de façon résonnante.Au cours de nos mesures, nous trouvons des signatures d'un comportement de transmission qui reflète les symétries internes des états propres des boîtes quantiques.Nos résultats mettent en lumière la question de longue date d'un comportement de phase de transmission universelle dans des boîtes quantiques en grand taille.Nous avons ainsi posé un jalon important vers une compréhension globale de la transmission par résonance d'électrons volants simples par des boîtes quantiques.Dans une deuxième expérience, nous allons au-delà du régime de transport balistique.Nous utilisons des ondes acoustiques de surface pour transporter un seul électron entre les boîtes quantiques définies par la grille de surface dans un circuit couplé par l'effect tunnel.Nous développons deux blocs de base essentiels pour partitionner et coupler les électrons volants simples dans un tel circuit piloté par le son.En dépassant une efficacité de transfert simple de 99 %, nous montrons qu'un circuit électronique quantique piloté par le son est réalisable à grande échelle.Nos résultats ouvrent la voie à des opérations de logique quantique avec des qubits d'électrons volants qui surfent sur une onde acoustique. / In the last 25 years there were several reports on quantum-optics-like experiments that were performed with electrons.The progress is this young field of research brought up original techniques to trap, displace and manipulate electrons in solid-state devices.These advances opened up new prospects to study fascinating quantum mechanical phenomena such as tunneling or entanglement with electrons.Due to the controllability that is demanded in possible implementations of quantum logic circuits, it is now a particularly appealing idea to perform electron quantum optics experiments with single flying electrons.In this thesis we address two related, but conceptually different, electron-quantum-optics experiments at the single-particle level.All of the experiments that were conducted in the course of this thesis were performed at cryogenic temperatures with Schottky-gate defined devices in AlGaAs/GaAs heterostructures.In a first experiment, we perform a Mach--Zehnder type electron interference experiment in the ballistic transport regime.Forming a large quantum dot in one of the interferometer branches, we study the phase shift in the wave function of a resonantly transmitted electron.In the course of our experimental investigations, we find signatures of a transmission behaviour which reflect the internal symmetries of the quantum dot eigenstates.Our measurements shed light on the long-standing question about a universal transmission phase behaviour in large quantum dots.We thus set an important milestone towards a comprehensive understanding of resonant transmission of single flying electrons through quantum dots.In a second experiment, we go beyond the ballistic transport regime.We employ surface acoustic waves to transport a single electron between surface-gate defined quantum dots of a tunnel-coupled circuit of transport channels.In this course, we develop two essential building blocks to partition and couple single flying electrons in such a sound-driven circuit.By exceeding a single-shot transfer efficiency of 99 %, we show that a sound-driven quantum electronic circuit is feasible on a large scale.Our results pave the way for the implementation of quantum logic operations with flying electron qubits that are surfing on a sound wave.

Technological advances require novel solutions for contactless energy transfer. Many engineering applications require unique approaches to power electrical components without using physical wires. In the past decade, awareness of the need to wirelessly power electrical components spawned many forays into the field of wireless power transfer (WPT). WPT techniques include capacitive energy transfer, electromagnetic inductive power transfer, electromagnetic radiative power transfer, electrostatic induction, and acoustic energy transfer. Acoustic energy transfer (AET) has many advantages over other methods. These advantages include lower operating frequency, shorter wavelengths enabling the use of smaller sized receiver and transmitter, extended transmitter-to-receiver distance therefore more manageable design constraints, achieving lower attenuation, higher penetration depth, and no electromagnetic losses. Most AET systems operate in the ultrasonic frequency range and are more commonly referred to as ultrasonic acoustic energy transfer (UAET) systems. Through-wall UAET systems are constructed of a transmitter bonded to a transmission elastic layer, which in turn is bonded to a receiver. The transmitter and receiver layers are constructed of a piezoelectric material. Piezoelectric materials behave according to the piezoelectric effect, which is when a material generates an electric charge in response to mechanical strain. The transmitter utilizes the reverse of the piezoelectric effect. A sinusoidal input voltage is applied to the transmitter, inducing vibrations in the transmitter. The vibration-induced acoustic waves emanating from the transmitter travel through the initial bonding layer, the transmission layer, and the final bonding layer to the receiver. In turn, the acoustic waves cause the receiver to deform and undergo strain. This induces a flow of charge in the receiver, which is an electric current. The receiver feeds current to a resistive load. In this manner, energy is acoustically transferred between two transducers without wires. The performance of UAET systems can be evaluated based on power transfer efficiency, voltage magnification, and input admittance. UAET systems require extensive modeling before experimental assembly can be attempted. The analytical models of UAET are either based on the mechanics of the constitutive relations of piezoelectricity and solid mechanics or using equivalent circuit methods. The equivalent circuit method approximates the physics of the UAET system with electrical assumptions. The mechanics-based method is the most comprehensive description of the physics of all the intermediate layers in a UAET system. The mechanics-based method has been based on the assumption that the UAET system is operated in the thickness mode of vibration, i.e., piston-like vibration mode where the transmitter and receiver disks vibrate only in the thickness direction. This poses an issue for disks with aspect ratios between 0.1 and 20 because the piezoelectric transducers vibrate in both the radial and thickness modes. In addition to this assumption, most of the works on UAET models only have accounted for the piezoelectric and transmission layers. The effects of the bonding layers were not considered. Bonding the piezoelectric layers to the transmission layer introduces epoxy material with mechanical properties that are not accounted for. The epoxy layers are extra barriers to the transmission that introduce attenuation and alter the vibrational and acoustical behaviors of the UAET system. Investigations into UAET commonly focus on metal through-wall applications. Alternate transmission layer materials are not investigated and the impact of varying mechanical properties on the performance of a through-wall UAET system has not been comprehensively studied. Even with the metal transmission layers, the impact of the metal thickness has not been extensively investigated thoroughly. This work addresses the issues of the thickness-mode assumption in UAET modeling, the effects of epoxy layers, the impacts of the metal layer geometry, and the performance of UAET systems with alternate transmission layer materials. Particularly, (1) we showed that the thickness-mode assumption, that has been used in the UAET modeling leads to inaccurate results. (2) We modified the available acoustic electro- elastic theoretical modeling to include the effects of radial modes as well as the epoxy bonding layers. (3) We showed that the geometry of the elastic/metal layer requires optimization for peak system efficiency. (4) The results show that using alternate transmission layer materials impacts the performance of UAET systems. The results of this work were investigated using an improved 5-layer analytical model and finite element modeling in COMSOL Multiphysics. / Master of Science / Wireless power transfer (WPT) is an innovative solution to the problem of powering sophisticated technological applications. Such instances include the powering of implanted medical devices, recharging inaccessible sensor networks, and wireless powering of components in sealed containers. Acoustic energy transfer (AET) is a feasible WPT method that addresses these needs. AET is based on the propagation of acoustic waves to a piezoelectric receiver which converts the vibrations caused by incident acoustic waves into electrical energy. Most AET systems operate in the ultrasonic frequency range, and so AET can also be referred to as ultrasonic acoustic energy transfer (UAET). Through-wall UAET systems are constructed from a transmitter that is bonded to a transmission elastic layer. The transmission layer is bonded to a receiver. The transmitter and receiver are made of a piezoelectric material. This thesis addresses the modeling process of through-wall UAET systems. In previous works, the fundamental assumption has been that such systems vibrate purely in the thickness mode. Additionally, other investigations did not comprehensively analyze the effects of the bonding layers, ascertain the performance of non-metal transmission layers, or provide practical insight on the effect of the resistive loading on such systems. This work addresses all these issues with a mathematical framework and finite element modeling results.

Ces travaux de thèse visent à proposer un nouveau type de modulateur acousto-optique intégré exploitantdes ondes élastiques guidées à la surface du niobate de lithium. Ce matériau piézoélectrique permet en effet deréaliser des guides d’ondes optiques intégrés ainsi que des transducteurs à ondes élastiques efficaces. La modulationacousto-optique y reste cependant classiquement limitée par le recouvrement partiel des deux types d’ondes. J’aicherché à développer un nouveau type de guide d’ondes élastiques de surface exploitant les résonances d’épaisseurd’électrodes épaisses et permettant une meilleure exploitation de la conversion d’énergie électrique en énergieélastique dans les dispositifs intégrés.Dans un premier temps, j’ai développé un moyen de confiner l’énergie acoustique en surface afin de l’utiliserplus efficacement. Je me suis tourné vers la réalisation de transducteurs à peignes interdigités pour les ondes acoustiquesde surface permettant de confiner l’énergie qu’ils génèrent dans des électrodes à haut facteur de forme. Lacaractérisation de ces dispositifs a permis de démontrer un fort confinement de l’énergie mécanique, concomitantd’une absence de diffraction à la surface du matériau. Ces dispositifs acoustiques permettent ainsi un guidage del’énergie acoustique dans les trois dimensions de l’espace avec une largeur transverse aussi petite que la longueurd’onde.Dans un second temps, j’ai réalisé des modulateurs acousto-optiques utilisant les transducteurs précédents. Cesmodulateurs sont fondés sur un interféromètre de Mach-Zehnder dont un bras est soumis à l’interaction acoustooptique.Les expériences réalisées ont permis de montrer une modulation de l’onde optique aux fréquences de résonancedes transducteurs à haut facteur de forme. La transmission spectrale de ces interféromètres est par ailleurscannelée en raison d’une légère asymétrie des bras de l’interféromètre. Nous avons observé, à fréquence nulle, unfort décalage en longueur d’onde du spectre cannelé d’environ 20 nm. Ce décalage reste encore inexpliqué. / This thesis intended to propose a new kind of integrated acousto-optical modulator exploiting guided elasticwaves on the surface of a lithium niobate substrate. This piezoelectric material makes it possible to integrate opticalwaveguides as well as efficient elastic waves transducers. Classically, the acousto-optical modulation remainslimited by the partial overlap of the two kind of waves. I have sought to develop a new kind of surface elasticwaveguide exploiting the thickness resonances of thick electrodes allowing a better exploitation of electric energyto elastic energy conversion in integrated devices.First, I have developed a way to confine the acoustic energy at the surface to use it more efficiently. I turnedtowards the realization of interdigitated transducers for surface acoustic waves allowing to confine the generatedenergy in the high aspect ratio electrodes. The characterization of such devices allowed to demonstrate a strongconfinement of the mechanical energy at the surface of the material. These acoustic devices allowed for diffractionlessguiding of the acoustic energy in the three dimensions of space over a transverse width as small as thewavelength.The second part of this thesis was dedicated to the realization of acousto-optical modulators using the previoustransducers. These modulators are based on a Mach-Zehnder interferometer including one arm subjectd to theacousto-optical intercation. Due to a slight asymmetry of the interferometer arms, the spectrale transmission with awhite light source gives a channeled spectrum. Experiments have shown an optical wave modulation at resonancesfrequencies of the high aspect ratio transducers. We have observed, at zero frequency, a strong wavelength shift ofchanneled spectrum of about 20 nm. This shift remains unexplained.

Im Mittelpunkt dieser Arbeit stehen der Transport und die Manipulation optisch angeregter Elektronen-Spins in (110) Quantenfilmen (quantum wells, QWs) mittels akustischer Oberflächenwellen (surface acoustic waves, SAWs). Der starke räumliche Einschluss der Ladungsträger im akustisch erzeugten Potenzial erlaubt spinerhaltenden Ladungsträgertransport mit der akustischen Geschwindigkeit. Auf diese Weise wird langreichweitiger Spintransport über Distanzen > 60 microns demonstriert, welche Spinlebenszeiten von mehr als 20 ns entsprechen. Erreicht werden diese extrem langen Spinlebenszeiten durch drei Effekte: (i) Der D''yakonov-Perel''-Mechanismus ist für Spins in Wachstumsrichtung von (110)-QWs in III-V-Halbleitern unterdrückt. (ii) Aufgrund des Typ-II piezoelektrischen Potenzials der akustischen Oberflächenwelle ist der Bir-Aronov-Pikus Spinrelaxations-Mechanismus sehr schwach. (iii) Der starke Einschluss der Ladungsträger in mesoskopische Bereiche stabilisiert den Spin zusätzlich. In der vorliegenden Arbeit wird erstmals eine Anisotropie des Spintransports in einem externen Magnetfeld (Bext) nachgewiesen. Hierzu wurde die elektronische Spindynamik während des akustischen Transports entlang der [001]- bzw. [1-10]-Richtung untersucht. Während des Transports entlang der [001]-Richtung führt die Präzession der Elektronenspins um das fluktuierende interne Magnetfeld (Bint), das vom Fehlen eines Inversionszentrums im GaAs-Kristallgitter herrührt, zu Spinkohärenzzeiten von etwa 2 ns. Im Gegensatz hierzu ist beim Transport entlang der [1-10]-Richtung die Spinrelaxation für Spins in Wachstumsrichtung um eine Größenordnung langsamer. Grund hierfür ist die endliche mittlere Größe des internen effektiven Magnetfeldes Bint für Transport entlang dieser Richtung. Die beobachtete Anisotropie in der Spindynamik für die beiden Transportrichtungen wird vollständig im Rahmen der Spin-Bahn-Kopplung und des D''yakonov-Perel''-Mechanismus beschrieben und quantitativ erklärt. / In this work, we employ surface acoustic waves (SAWs) to transport and manipulate optically generated spin ensembles in (110) GaAs quantum wells (QWs). The strong carrier confinement into the SAW piezoelectric potential allows for the transport of spin-polarized carrier packets along well-defined channels with the propagation velocity of the acoustic wave. In this way, spin transport over distances exceeding 60 microns is achieved, corresponding to spin lifetimes longer than 20 ns. The demonstration of such extremely long spin lifetimes is enabled by three main factors: (i) Suppression of the D''yakonov-Perel'' spin relaxation mechanism for z-oriented spins in (110) III-V QWs; (ii) Suppression of the Bir-Aronov-Pikus spin relaxation mechanism caused by the type-II SAW piezoelectric potential; (iii) Suppression of spin relaxation induced by the mesoscopic carrier confinement into narrow stripes along the SAW wave front direction. A spin transport anisotropy under external magnetic fields (Bext) is demonstrated for the first time. Employing the well-defined average carrier momentum impinged by the SAW, we analyze the spin dephasing dynamics during transport along the [001] and [1-10] in-plane directions. For transport along [001], fluctuations of the internal magnetic field (Bint), which arises from the spin-orbit interaction associated with the bulk inversion asymmetry of the crystal, lead to decoherence within 2 ns as the spins precess around Bext. In contrast, for transport along the [1-10] direction, the z-component of the spin polarization is maintained for times one order of magnitude longer due to the non-zero average value of Bint. The dephasing anisotropy between the two directions is fully understood in terms of the dependence of the spin-orbit coupling on carrier momentum direction, as predicted by the D''yakonov-Perel'' mechanism for the (110) system.

Cette thèse concerne le développement d’outils microfluidique pour l’ingénierie d’enzymes d’intérêt thérapeutique. La microfluidique à base de gouttelettes présente un énorme potentiel dans le domaine de la biologie quantitative. Nous développons des outils microfluidiques pour l’évolution dirigée de l’enzyme L-asparaginase, enzyme utilisée comme traitement de laleucémie lymphoblastique aiguë. Ce traitement est basée sur une enzyme d’origine bactérienne,ce qui conduit à déclencher des réactions immunitaires qui se traduit par l’interruption du traitement, souvent fatale pour le patient. Cependant, une version humaine de l’enzyme L-asparaginase, qui est moins immunogénique, n’est à l’heure actuelle pas suffisamment active pour être utilisée. L’objectif principal de cette thèse est d’alors d’analyser et de cribler des banques de mutants d’enzymes en utilisant des méthodes classiques de mutagenèse et d’analyser chaque mutant individuellement par le biais de la microfluidique. Pour cela, plusieurs systèmes microfluidiques ont été développés et optimisés afin de répondre à différents critères de sélection pour l’analyse et la sélection de l’enzyme L-asparaginase. La version bactérienne a servi de contrôle positif pour l’optimisation des systèmes microfluidiques afin de pouvoir analyser et de cribler des banques de mutants de la version humaine de l’enzyme L-asparaginase. / This thesis deals with the development of microfluidic tools for the engineering ofenzymes of therapeutic interest. Droplet microfluidics has enormous potential in the field ofquantitative biology. We are developing microfluidic tools based on the directed evolutionof the enzyme L-asparaginase, an enzyme used to treat acute lymphoblastic leukemia. Thistreatment is based on an enzyme of bacterial origin, which leads to immune reactions thatresult in the interruption of treatment, often fatal for the patient. However, a human version ofthe enzyme L-asparaginase, which is less immunogenic, is currently not sufficiently active to beused. The main objective of this thesis is to analyze and screen enzyme mutant libraries usingstandard mutagenesis methods and to analyze each mutant individually through microfluidics.For this, several microfluidic systems have been developed and optimized for different selectioncriteria for the analysis and selection of the enzyme L-asparaginase. The bacterial versionserving as a positive control for the optimization of microfluidic workflows to analyze andscreen mutant libraries of the human version of the enzyme L-asparaginase.