Ces dernières décennies, les couches minces de semiconducteurs nitrures III-V dopés avec des terres rares ont fait l'objet d'un intérêt grandissant et ont donné lieu à de nombreuses études. En raison de leur bande interdite directe, les nitrures III-V constituent des matrices hôtes adéquates permettant la luminescence des terres rares (TR). Ainsi, en combinant les propriétés des III-V et des TR, il est possible d'envisager des applications prometteuses dans le domaine optoélectronique. Dans cette étude, l'erbium (Er) a été choisi en raison de son émission de photons à la fois dans le visible et dans l'infrarouge. Dans ce travail, les films minces d'AlN dopé à l'Er ont été élaborés avec un réacteur expérimental de pulvérisation cathodique réactive magnétron radiofréquence. Pendant le dépôt, une polarisation négative appliquée sur le substrat a permis d'obtenir des films présentant différents types de morphologies cristallines, qui ont été étudiés par diverses techniques de caractérisation telles que l'AFM, les DRX, l'ellipsométrie, le MEB, le MET. Les propriétés de luminescence des films ont été examinées expérimentalement et à l'aide d'un modèle de simulation optique par spectroscopie de photoluminescence (excitation lumineuse). Des mesures expérimentales par spectroscopie de cathodoluminescence (excitation électronique) ont également été réalisées. Le but de cette thèse était d'optimiser le procédé d'élaboration et le matériau et de mieux comprendre l'influence de la morphologie cristalline de la matrice AlN sur l'efficacité de luminescence de l'erbium. L'AlN-Er représente un système modèle et les résultats obtenus pourront être étendus aux autres TR / During the last decades, rare-earth-doped III-V thin films have been the subject of growing interest and the topic of many studies. Because III-V nitrides possess a direct gap, they are suitable host matrices to allow rare-earth (RE) luminescence. Thereby, by combining the III-V and the RE characteristics, it becomes possible to consider promising applications in the optoelectronic field. In this study, erbium (Er) was chosen because of its emission both in the visible and in the infrared range. In this work, Er-doped AlN thin films were prepared in an experimental PVD sputtering magnetron radiofrequency reactor. During the deposition, an applied negative bias on the substrate allowed to obtain different kinds of crystalline morphology of the deposited layers, which were studied by several characterization techniques such as AFM, DRX, ellipsometry, MEB, MET. Luminescence properties of the films were investigated both experimentally and with an optical model by photoluminescence (light excitation) spectroscopy. Experimental measurements by cathodoluminescence (electronic excitation) spectroscopy were also performed. This thesis aimed to optimize the elaboration process and the material and to get a better understanding of the influence of AlN host matrix crystalline morphology on the erbium luminescence efficiency. The AlN:Er system stood as a model system and the obtained results could be extended to the other RE

Ce projet est consacré à l'étude des propriétés optiques des films minces en nitrure d'aluminium dopé par des terres rares. Plus particulièrement, le travail est orienté pour étudier les mécanismes de luminescence des éléments RE sélectionnés incorporés dans des films minces AlN pour être utilisés comme candidats aux dispositifs d'éclairage. Au cours de cette thèse, la technique de pulvérisation de magnétron réactif est utilisée pour synthétiser les films minces AlN non dopés et dopés. La technique et le traitement des films sont discutés en détail. L'effet des conditions de pulvérisation sur la structure et les propriétés optiques des films préparés est étudié. La corrélation entre les conditions de pulvérisation cathodique, l'orientation cristallographique, la morphologie, la microstructure et les propriétés optiques sont établies. Les analyses de structure et de composition des échantillons préparés ont été étudiées par plusieurs moyens, tels que la microscopie électronique à transmission, la spectroscopie à rayons X à énergie dispersive et la spectrométrie de rétrodiffusion Rutherford. Les propriétés optiques des films sont caractérisées par une transmission UV-Visible, une spectroscopie d'Ellipsometry et une spectroscopie de photoluminescence / This project is dedicated to study the optical properties of rare earth-doped aluminum nitride thin films. More particularly, the work is oriented to investigate the luminescence mechanisms of selected RE elements incorporated in AlN thin films to be used as a candidate for lighting devices. During this thesis, reactive magnetron sputtering (RMS) technique is used to synthesize the undoped and doped AlN thin films. The technique and films processing are discussed in details. The effect of sputtering conditions on the structure and optical properties of the prepared films are investigated. The correlation between the sputtering conditions, the crystallographic orientation, the morphology, the microstructure and the optical properties are established. The structure and composition analyses of the prepared samples have been investigated by several means, such as transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The optical properties of the films are characterized by UV-Visible transmission, Ellipsometry spectroscopy, and Photoluminescence spectroscopy

Résumé : INTRODUCTION : Il a été démontré que la ventilation assistée nasale (AIn) provoque la fermeture laryngée active chez les agneaux nouveau-nés sans sédation. Ceci pourrait limiter la ventilation alvéolaire, entrainer l’air insufflé dans l’appareil digestif et provoquer des conséquences délétères graves. Le neuro-asservissement de la ventilation assistée nasale (NAVAn) et la ventilation nasale par oscillations à haute fréquence (VOHFn) sont des modes de ventilation attractifs. La NAVA semble être plus physiologique que l’AIn, car elle est synchronisée avec le contrôle neural. Cependant, la VOHF ne nécessite pas de synchronisation et diminue les lésions pulmonaires provoquées par la ventilation mécanique conventionnelle. Le but de mon projet est d’étudier l’effet de la NAVAn et de la VOHFn sur la dynamique laryngée chez les agneaux nouveau-nés sans sédation, en testant l’hypothèse que, contrairement à l’AIn, la fermeture laryngée active n’apparait pas durant la NAVAn et la VOHFn. MÉTHODES : deux groupes d’agneaux nés à terme (NAVAn : 8 agneaux ; et VOHFn : 7 agneaux) ont été instrumentés chirurgicalement à 2 jours de vie, afin de recueillir l’électromyogramme des muscles constricteur et dilatateur laryngés, du diaphragme, les pressions au masque, trachéale, pression de CO[indice inférieur 2] en fin d’expiration (P[indice inférieur ET]CO[indice inférieur 2]) et des gaz sanguins artériels. 48h suivant l’instrumentation, un enregistrement polysomnographique a été réalisé pour chaque groupe (AIn / VOHFn et AIn / NAVAn) dans un ordre randomisé. La pression inspiratoire (AIn & NAVAn) et la puissance des oscillations (VOHFn) ont été progressivement augmentées. RÉSULTATS : Les résultats démontrent que l’augmentation des niveaux de NAVAn et de la puissance de VOHFn n’entraine pas de fermeture laryngée active, contrairement à l’AIn. De plus, la diminution du PaCO[indice inférieur 2] provoquée par l’hyperventilation en AIn pourrait contribuer à la fermeture laryngée active. En VOHFn, la diminution progressive de la fréquence des oscillations jusqu’à 4 Hz induit des apnées centrales. En revanche, aucune fermeture laryngée active n’a été observée à 4 Hz. CONCLUSION : La NAVAn et la VOHFn ne provoquent pas la fermeture laryngée active chez l’agneau nouveau-né, et pourraient constituer des nouvelles alternatives dans le traitement des pathologies respiratoires en période néonatale. //Abstract : INTRODUCTION : We have previously shown that nasal pressure support ventilation (nPSV) can lead to an active laryngeal closure in non-sedated newborn lambs. This, in turn, can limit lung ventilation and divert air into the digestive system, with potentially deleterious consequences. Nasal neurally adjusted ventilator assist (nNAVA) and nasal high frequency oscillatory ventilation (nHFOV) are new attractive non-invasive ventilation modalities in newborns. Neurally adjusted ventilator assist (NAVA) seems to be a more physiological ventilator mode than PSV: it is more synchronized with neural control. However, HFOV is associated with less lung injury and does not require synchronization. Thus, the aim of the present study was to assess the effects of nNAVA and nHFOV on laryngeal dynamics in non-sedated newborn lambs, testing the hypothesis that active laryngeal closure does not develop during both nHFOV and nNAVA. METHODS : Polysomnographic recordings were performed in two groups of non-sedated chronically instrumented lambs (nHFOV, 7 lambs) and (nNAVA, 8 lambs), which were ventilated with progressively increased levels of nPSV and nHFOV or nNAVA, in random order. States of alertness, diaphragm and glottal muscle electrical activity, mask and tracheal pressure, tracheal end tidal CO[subscript 2] (P[subscript ET]CO[subscript 2]) and blood gases were continuously recorded in each group. RESULTS: While active laryngeal closure appeared with increasing levels of nPSV, it was never observed at any nHFOV power or nNAVA levels in any lamb. In addition, a decrease in PaCO[subscript 2] was neither necessary nor sufficient for the development of active laryngeal closure. nHFOV at 4Hz dramatically inhibited central respiratory drive. However, no active laryngeal closure was observed at 4 Hz. CONCLUSION: nHFOV and nNAVA does not induce active laryngeal closure in inspiration in non-sedated newborn lambs, in contrast to nPSV. nNAVA and nHFOV could be an alternatives in the treatment of neonatal respiratory disorders.

Contactless electroreflectance (CER), a modulation spectroscopy (MS) technique, has been used to study the A and C exciton transitions in A1xGa1-xN layers for a composition range of 0 ≤ x ≤ 0.48 at room temperature. Taking the entire composition range (0 ≤ x ≤ 1) into account by incorporating a previously reported band gap energy for AlN, the dependence of the A-exciton transition on composition showed a downward bowing from linearity. A bowing parameter of b = 1.7 eV was found. Analysis of the lower composition range 0 ≤ x ≤ 0.48 resulted in a linear fit, as did the trend for the detectable C exciton transitions. The slope of the linear trendlines for the A and C exciton were practically the same.

L'objectif de cette thèse est de réaliser des hétérostructures packageless par l'intermédiaire d'une couche protectrice contre les environnements atmosphériques néfastes tels que l'oxydation et l'humidité mais aussi dans les milieux agressifs à hautes températures. La première hétérostructure envisagée dans cette étude, utilise le principe des ondes isolées. Le silicium a été employé en combinaison avec le ZnO car il offre de bonnes propriétés électroacoustiques mais aussi la possibilité de travailler à de hautes fréquences. Ainsi, cette configuration AlN/IDT/ZnO/Si a été principalement choisie pour des applications en environnements néfastes et intégrable dans la technologie CMOS. Par ailleurs, une couche de protection d'AlN permettra à l'onde de se confiner dans la couche active de ZnO et de rester insensible à la surface mais sensible à la température. Le ZnO étant toutefois conducteur à haute température (> 400°C), cette hétérostructure reste peut applicable en milieux sévères à haute température. C'est pourquoi une seconde hétérostructure packageless utilisant comme base l'IDT/AlN/Saphir a été étudiée dans ce manuscrit. Il s'agit donc de protéger les IDTs par un film mince contre les phénomènes d'agglomération des électrodes à hautes températures (1000 °C) / The objective of this thesis is to realize heterostructures packageless through a protective layer against harmful atmospheric environments such as oxidation and moisture and also in aggressive environments (high temperatures). The first heterostructure considered in this study, uses the principle of wave isolated. Silicon was used in combination with ZnO as it offers good performances and the possibility to work at high frequencies. Thus, this configuration AlN/IDT/ZnO/Si was chosen for applications in environments with harmful and integrated in CMOS technology. In addition, a protective layer of AlN allows the wave is confined in the active layer of ZnO and remains insensitive to the surface but sensitive to temperature. However, ZnO is conductive at high temperature (> 400 ° C) wich is limited her utilization in harsh environments. This is why a second packageless heterostructure using the IDT/AlN/sapphire has been studied in this manuscript. It is therefore to protect the IDTs by a thin film against the phenomena of agglomeration of the electrodes at high temperatures (1000 ° C)

There is an every increasing need to develop more durable and higher performing coatings for use in a range of products including tools, devices and bio-implants. Nano-structured coatings either in the form of a nanocomposite or a multilayer is of considerable interest since they often exhibit outstanding properties. The objective of this thesis was to use advanced plasma synthesis methods to produce novel nano-structured coatings with enhanced properties. Coatings consisting of combinations of aluminum (Al), aluminum nitride (AlN) and amorphous carbon (a-C) were investigated. Cathodic vacuum arc deposition and unbalanced magnetron sputtering were used to prepare the coatings. By varying the deposition conditions such as substrate bias and temperature, coatings with a variety of microstructures were formed. A comprehensive range of analytical methods have been employed to investigate the stoichiometry and microstructure of the coatings. These include Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), Electron Energy Loss Spectroscopy, Auger Electron Spectroscopy, X-ray diffraction and Raman spectroscopy. In addition to the investigation of microstructure, the physical properties of the coatings were measured. Residual stress has been recognized as an important property in the study of thin film coatings since it can greatly affect the quality of the coatings. For this reason, residual stress has been extensively studied here. Hardness measurements were performed using a nano indentation system, which is sensitive to the mechanical properties of thin films. This thesis undertook the most comprehensive investigation of the Al/AlN multilayer system. A major finding was the identification of the conditions under which layers or nanocomposite form in this system. A model was developed based on energetics and diffusion limited aggregation that is consistent with the experimental data. Multilayers of a-C and Al were also found to form nanocomposites. No hardness enhancement as a function of layer thickness or feature size was observed in either the Al/AlN or a-C/a-C systems. It was found that the most important factor which determines hardness is the intrinsic stress, with films of high compressive stress exhibiting the highest hardness. Nano-structured multilayers of alternating high and low density a-C were investigated. For a-C multilayers prepared using two levels of DC bias, evidence of ion beam induced damage was observed at the interfaces of both the low and high density layers. In addition, the structure of the high density (ta-C, known as tetrahedral amorphous carbon) layers was found to be largely unchanged by annealing. These results extend our understanding of how a-C form from energetic ion beams and confirms the thermal stability of ta-C in a multilayer. This thesis also presented the first attempt to synthesis a-C multilayered films with a continuously varying DC bias in sinusoidal pattern. The resulting films were shown to have a structurally graded interface between layers and verified that ion energy and stress are the most important factors which determine the structure of a-C films.

Le travail présenté dans ce manuscrit traite de la compréhension des processus de croissance de structures colonnaires de matériaux semiconducteurs nitrures. La technique de croissance utilisée est l'épitaxie par jets moléculaires assistée par plasma (PA-MBE). Plusieurs types d'expériences viennent étayer ce travail: des expériences de microscopie électronique à balayage et à transmission, des expériences de diffraction multi-longueurs d'onde et de spectroscopie en condition de diffraction (menées à l'ESRF sur les lignes BM2 et BM32), et des expériences de photoluminescence. Tout d'abord les mécanismes de nucléation des nanofils nitrure de gallium (GaN) réalisés sur un fin (3nm) buffer de nitrure d'aluminium (AlN) épitaxié sur un substrat de silicium (111) sont étudiés. Il est démontré que la relaxation complète des précurseurs des nanofils GaN est un élément clé du mécanisme de nucléation. Dans le cas des fils de GaN, il apparaît en outre que la morphologie granulaire du buffer AlN joue un rôle essentiel. Ensuite le développement des nanofils GaN, une fois la nucléation achevée, est analysé. Nous identifions la diffusion du gallium dans le plan de croissance ainsi que sur les facettes des nanofils comme étant le mécanisme responsable de la croissance. Nous montrons en particulier que l'In, qui joue le rôle de surfactant, active la diffusion du Ga dans le plan et permet la croissance de nanofils GaN à des températures relativement basses. Sur la base de la compréhension de la nucléation et du développement des nanofils GaN, la croissance de nanofils AlN sur 4nm de SiO2 amorphe déposé sur Si(001) est développée. C'est la première fois que ce type de nanofils est réalisé par MBE. La relaxation des contraintes au cours de la réalisation d'un super réseau AlN/GaN sur des nanofils GaN a ensuite été étudiée. Nous comparons les résultats expérimentaux à des simulations théoriques pour conclure à la relaxation élastique des contraintes. La croissance de nanofils AlGaN est finalement abordée de façon préliminaire.

Abstract The search for nanoscale active electronic devices has been an important objective in nanoscience and nanotechnology. In this study, the electronic and transport properties of the benzene-1,4-dithiol-molecule (BDT) and Au-atom-S-benzene-ring-O-(SBO)-Au-atom junctions and the Au-AlN(0001)-Au polar semiconductor junction have been calculated using the first-principles calculation method and a new integrated piecewise thermal equilibrium approach for the current. The current-voltage (I-V) and conductance-voltage (C-V) characteristic curves obtained for the Au-BDT-Au molecular junction agreed reasonably well with experimental ones. The study of Au-BDT-Au identifies that treating Au 5d electrons as core electrons and letting the S end of BDT be bonded to the Au surface directly overestimated the current. Calculated I-V characteristic curve revealed that the asymmetric Au-SBO-Au molecular junction has a pulse-like I-V characteristic curve with dual differential conductance, which resembled well the one observed experimentally. The analysis of the electronic structures showed that this dual differential conductance transport property was due to a subtle charge transfer at the electrode-molecule contacts. The calculated J-V characteristic curve of the Au-Al(0001)-Au junction shows coexistence of ohmic, switching effect and negative differential conductance. The electronic structure calculations show the existence of an intrinsic band tilt due to the polar nature of the AlN(0001) film, which gives rise to an asymmetric transport property of the junction and the presence of hole states at the N-surface side and interface states at the Al-surface side of the AlN film. The bias induced changes of the hole states, interface states and the states of the Al and N ions in central layers in the vicinity of the local chemical potential give rise to the interesting transport property of the Au-AlN(0001)-Au junction.

Shear-mode thin film bulk acoustic resonator (TFBAR) devices with c-axis tilted AlN films are fabricated for the application of liquid sensors. To fabricate shear-mode TFBAR devices, the off-axis RF magnetron sputtering method for the growth of piezoelectric AlN thin films is adopted and influences of the relative distance and the sputtering parameters are investigated. The shrar-mode phenomenon of a TFBAR results from the tilted crystalline orientation of AlN thin films. In this thesis, the AlN thin films are deposited with tilting angles of 15¢X and 23¢X, set by controlling the deposition parameters. The properties of the AlN thin films are investigated by X-ray diffraction and scanning electron microscopy. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station. The frequency response of the TFBAR device with 23¢X tilted AlN thin film is measured to reveal its ability to provide shear-mode resonance. The resonance frequencies of the longitudinal and shear modes are 2.07 GHz and 1.17 GHz, respectively. To investigate the sensing characteristics of TFBAR, two basic experiments of mass and liquid loading are carried out. The sensitivities of the longitudinal and shear modes to mass loading are calculated to be 2295 Hz cm2/ng and 1363 Hz cm2/ng with the mechanical quality factors of 588 and 337, respectively. However, the mechanical quality factors of the longitudinal mode of TFBAR without and with a liquid loading decreased from 588 to 0, whereas those remain almost the same for the shear mode under liquid loading. The sensitivities of the longitudinal and shear modes are calculated to be 0 and 17.88 Hz cm2/£gg for liquid loading.

The piezoelectric transducer for vibration-energy harvesting is constructed of a piezoelectric layer, bottom electrode and a top electrode. In order to obtain an appropriate transducer for the low-frequency operating; environmentally-friendly and long-term, the flexible substrate, the piezoelectric layer, and the additional mass-loading (tip mass) have been investigated thoroughly. This study investigates the feasibility of a high-performance ZnO and AlN based piezoelectric transducer for vibration-energy harvesting applications. Firstly, the piezoelectric transducer is constructed of a Cu/ZnO/ITO/PET structure. Both scanning electron microscopy and X-ray diffraction indicate that, among the favorable characteristic of the ZnO piezoelectric film include a rigid surface structure and a high c-axis preferred orientation. Hence, an open circuit voltage of 1.87 V for the ZnO piezoelectric transducer at a vibration frequency of 100 Hz is obtained by an oscilloscope. After rectifying and filtering, the output power of the generator exhibits an available benefit of 0.07 £gW/cm2 with the load resistance of 5 M£[. Secondly, this investigation introduces novel means of integrating high-performance piezoelectric transducers using single-sided ZnO and AlN films with a flexible stainless steel substrate (SUS304). Hence, the SUS304 substrate exhibits the long-term stability under vibration. The single-sided ZnO and AlN transducers are deposited on the SUS304 substrate at a temperature of 300 oC by an RF magnetron sputtering system. Scanning electron microscopy and X-ray diffraction of piezoelectric films reveal a rigid surface structure and a high c-axis-preferred orientation. A mass loading at the front-end of the cantilever is critical to increase the amplitude of vibration and the power generated by the piezoelectric transducer. The open circuit voltage of the single-sided ZnO power generator is 10.5 V. After rectification and filtering through a capacitor with a capacitance of 33 nF, the output power of the single-sided ZnO generators exhibited a specific power output of 1.0 £gW/cm2 with a load resistance of 5 M£[. Finally, this investigation fabricates double-sided piezoelectric transducers for harvesting vibration-power. The double-sided piezoelectric transducer is constructed by depositing piezoelectric thin films on both the front and the back sides of SUS304 substrate. The titanium (Ti) and platinum (Pt) layers were deposited using a dual-gun DC sputtering system between the piezoelectric thin film and the back side of the SUS304 substrate. Scanning electron microscopy and X-ray diffraction of piezoelectric films reveal a rigid surface structure and highly c-axis-preferring orientation. The maximum open circuit voltage of the double-sided ZnO power transducer is approximately 18 V. After rectification and filtering through a 33 nF capacitor, a specific power output of 1.3 £gW/cm2 is obtained from the double-sided ZnO transducer with a load resistance of 6 M£[. The variation of the power output of ¡Ó0.001% is obtained after 24-hour continuous test. The maximum open circuit voltage of the double-sided AlN power transducer is approximately 20 V. After rectification and filtering through a 33 nF capacitor, a specific power output of 1.462 £gW/cm2 is obtained from the double-sided AlN transducer with a load resistance of 7 M£[.