Avec l'augmentation accrue du nombre de fonctions embarquées directement au dessus du circuit intégrés, les capacités Métal Isolant Métal (MIM) sont devenues des composants essentiels en microélectronique. Pour permettre une augmentation de la densité d'intégration des composants, des matériaux à forte permittivité ou high κ sont utilisés comme diélectriques. Cet isolant doit satisfaire plusieurs critères: une forte valeur de capacité surfacique, de faibles courants de fuite ainsi qu'une très bonne stabilité de la capacité surfacique avec la tension appliquée (linéarité en tension). Cependant, aucun n'est parvenu à satisfaire tous les critères, ce qui nécessite d'autres approches comme l'utilisation d'oxyde en structures multicouches ou alliées. De plus, la linéarité en tension des capacités est mal maîtrisée et son origine mal comprise. Ainsi, nous avons tout d'abord étudié le rôle du matériau d'électrode (TiN, Pt, WSi2,3 et WSi2,7) et de son interface avec l'oxyde d'yttrium déposé par MOCVD avec ou sans assistance plasma sur les performances électriques. On observe une dépendance de la linéarité en tension selon le matériau d'électrode utilisée. Un modèle double couche a été proposé pour décrire la non linéarité des capacités MIM en tension. Puis, différentes structures bicouches, multicouches ou alliées ont été étudiées (LaAlO3/Y2O3, structures à base de HfO2 et Al2O3, SrTiO3/Y2O3). Les bicouches SrTiO3/Y2O3 ont permis l'obtention d'une valeur de capacité surfacique de 10 fF/µm² et de minimiser la non-linéarité (paramètre α de -750 ppm/V²).

Die vorliegende Dissertation behandelt Charakterisierung, Modellbildung sowie Anwendung einer magnetfeldgestützten Hohlkathoden-Bogenentladung. Hohlkathoden sind seit den 1960er Jahren Gegenstand grundlagen- sowie anwendungsorientierter Forschung und werden seit 20 Jahren am Fraunhofer-Institut für Elektronenstrahl- und Plasmatechnik für die Anwendung auf dem Gebiet der Vakuumbeschichtung weiterentwickelt. Ziel dieser Arbeit ist es, die technologischen Fortschritte physikalisch zu verstehen und gezielte Weiterentwicklungen für spezifische Einsatzgebiete zu ermöglichen. In der untersuchten Hohlkathodenbauform ist das aus Tantal bestehende, vom Arbeitsgas Argon durchströmte Kathodenröhrchen koaxial von einer Ringanode sowie von einer Magnetfeldspule umgeben. Die Entladung wird durch Hochspannungspulse gezündet, worauf sich ein diffuser Bogen im Röhrchen (internes Plasma) ausbildet. Das Röhrchen wird von Plasmaionen auf hohe Temperaturen geheizt, die eine thermionische Emission von Elektronen ermöglichen, welche das Plasma speisen. Das technologisch nutzbare externe Plasma wird im Vakuumrezipienten durch Wechselwirkung der Gasteilchen mit Strahlelektronen aus der Kathode erzeugt. Bei starker Reduktion des Arbeitsgasflusses wird die Entladung durch das Magnetfeld der Spule stabilisiert. Der experimentelle Befund, dass dadurch Plasmadichte und -reichweite sowie ggf. die Ladungsträgerenergien im Rezipienten aufgrund des intensiveren Elektronenstrahls wesentlich gesteigert werden können, wird durch ortsaufgelöste Langmuir-Sondenmessung, optische Emissionsspektroskopie und energieaufgelöste Massenspektrometrie ausführlich belegt und nach der Lösung von Strom- und Wärmebilanzgleichungen durch die Verhältnisse im Kathodenröhrchen begründet. Neben Argon werden auch typische Reaktivgase der Vakuumbeschichtung im Hohlkathodenplasma betrachtet: zum einen Stickstoff und Sauerstoff, die in reaktiven PVD-Prozessen (physikalische Dampfphasenabscheidung) zur Beschichtung mit Oxid- bzw. Nitridschichten zum Einsatz kommen und durch Ionisation, Dissoziation und Anregung im Hohlkathodenplasma verbesserte Schichteigenschaften ermöglichen; zum anderen Azetylen, das bei PECVD (plasmagestützte chemische Dampfphasenabscheidung) von amorphen wasserstoffhaltigen Kohlenstoffschichten z. B. für tribologische oder biokompatible Beschichtungen genutzt wird. Azetylen wird durch Streuprozesse mit Elektronen und Ionen im Plasma aufgespalten, wodurch schichtbildende Spezies erzeugt werden, die am Substrat kondensieren. Durch die Wahl der Plasmaparameter sowie durch abgestimmte Substratbiasspannung und Substratkühlung lassen sich die Beschichtungsrate einstellen sowie polymer-, graphit- oder diamantartige Eigenschaften erzielen. Neben der Plasmadiagnostik mittels energieaufgelöster Massenspektrometrie werden die erzeugten Kohlenstoffschichten vorgestellt und hinsichtlich Härte, Zusammensetzung und Morphologie analysiert. / In the present thesis, characterization, modeling and application of a magnetically enhanced hollow cathode arc discharge are presented. Since the 1960s, hollow cathodes are being studied in basic and applied research. At Fraunhofer Institute for Electron Beam and Plasma Technology, further development concerning the application in vacuum coating technology has been carried out for about twenty years. The present work targets on physically understanding the technological progress in order to enable specific further development and application. In the investigated hollow cathode device, a ring-shaped anode and a magnetic field coil are arranged coaxially around the tantalum cathode tube, which is flown through by argon as the working gas. The discharge is ignited by high voltage pulses establishing a diffuse arc within the cathode tube (internal plasma). The cathode is being heated by the plasma ions to high temperatures, which leads to thermionic emission of electrons sustaining the plasma. The external plasma in the vacuum chamber, which can be used for technological applications, is generated by collisions of gas atoms with beam electrons originating from the cathode. In the case of strongly reduced working gas flow, the discharge is stabilized by the magnetic field of the coil; the related experimental findings such as significantly increased plasma density and range as well as higher charge carrier energies in the external plasma are extensively proved by spatially resolved Langmuir probe measurements, optical emission spectroscopy, and energy-resolved ion mass spectrometry. Furthermore, the results are correlated to the conditions within the cathode tube by solving the current and heat balance equations. Besides argon, typical reactive gases used in vacuum coating are examined in the hollow cathode plasma, too. First, nitrogen and oxygen, which are applied in PVD (physical vapor deposition) processes for the deposition of oxide and nitride layers, are ionized, dissociated, and excited by plasma processes. In the case of practical application, this plasma activation leads to improved film properties. Second, acetylene is used as a precursor for PECVD (plasma-enhanced chemical vapor deposition) of amorphous hydrogenated carbon films, e.g. for tribological or biocompatible applications. Acetylene is cracked by electron and ion scattering in the plasma providing film-forming species to be deposited on the substrate. The deposition rate as well as the polymeric, graphitic, or diamond-like properties can be controlled by plasma parameters, a defined substrate bias, and substrate cooling. The hollow cathode-generated acetylene plasma has been characterized by energy-resolved ion mass spectrometry, and the carbon films obtained are analyzed regarding hardness, film composition, and morphology.

Les mémoires résistives PCRAM sont basées sur le passage rapide et réversible entre un état amorphe hautement résistif et un état cristallin faiblement résistif d’un matériau à changement de phase (PCM). Ces mémoires constituent un des candidats les plus prometteurs pour la nouvelle génération de mémoires non-volatiles grâce à un large éventail de propriétés uniques comme une vitesse de fonctionnement élevée, une capacité de stockage multi-niveaux sur plusieurs bits, une bonne endurance et une possibilité de miniaturisation poussée. Cependant, la nécessité d’utiliser des courants d’effacement (IRESET) importants pour l’étape d’amorphisation du PCM représente l’un des principaux freins à l’explosion de la technologie PCRAM sur le marché des mémoires non volatiles. Dans ce contexte, il a été démontré que le confinement du PCM dans des structures possédant des facteurs de forme élevés permet d’améliorer l’efficacité du chauffage nécessaire au changement de phase du PCM et donc de réduire les courants d’amorphisation. Afin d’incorporer des matériaux PCM dans de telles structures, il est alors nécessaire de développer un procédé de dépôt très conforme. C’est pourquoi un procédé de dépôt PE-MOCVD (Plasma Enhanced- Metal Organic Chemical Vapor deposition) à injection liquide pulsée a été développé dans ce travail. Dans un premier temps des films amorphes et homogènes du composé binaire GeTe ont été déposés à partir des précurseurs organométalliques TDMAGe et DIPTe. Les analyses XPS révèlent que les couches de GeTe déposées sont stoechiométriques mais présentent une forte contamination en carbone. Ainsi, un des objectifs de cette thèse a été de réduire le taux de carbone dans les couches afin d’optimiser leurs propriétés de changement de phase. Une étude de l’impact des paramètres de dépôt tel que la puissance, la pression, la nature et le débit des gaz utilisés est alors présentée. En étudiant et en optimisant les paramètres de dépôt, des couches de GeTe contenant seulement 2 % at. de carbone ont pu être obtenues. Dans un second temps, des films du composé ternaire GeSbTe ont été déposés en injectant simultanément les trois précurseurs TDMAGe, TDMASb et DIPTe dans le plasma de dépôt. Une large gamme de composition peut alors être obtenue en variant les paramètres d’injection et de dépôt. L’un des principaux avantages de ce procédé est la capacité de couvrir une large gamme de compositions permettant d’obtenir des films possédant des propriétés de changement de phase très variées. L’impact des paramètres plasma sur la conformité du dépôt a aussi été étudié. Il est montré que l’ajout d’une composante BF à la puissance RF du plasma permet d’améliorer le remplissage des structures possédant des facteurs de forme élevés. Enfin, l’intégration dans des dispositifs mémoires PCRAM tests de matériaux PCM obtenus par ce procédé PE-MOCVD a mis en évidence des propriétés électriques proches de celles obtenues avec des matériaux déposés par les procédés de dépôt conventionnels de type PVD. / Phase change random access memories PCRAM are based on the fast and reversible switch between the high resistive amorphous state and the low resistive crystalline state of a phase change material (PCM). These memories are considered to be one of the most promising candidates for the next generation of non volatile memories thanks to their unique set of features such as fast programming speed, multi-level storage capability, good endurance and high scalability. However, high power consumption during the RESET operation (IRESET) is the main challenge that PCRAM has to face in order to explode the non volatile memory market. In this context, it has been demonstrated that by integrating the phase change material (PCM) in high aspect ratio lithographic structures, the heating efficiency is improved leading to a reduced reset current. In order to fill such confined structures with the phase change material, a highly conformal deposition process is required. Therefore, a pulsed liquid injection Plasma Enhanced-Metal Organic Chemical Vapor Deposition process (PE-MOCVD) was developed in this work. First, amorphous and homogeneous GeTe films were deposited using the organometallic precursors TDMAGe and DIPTe as Ge and Te precursors. XPS measurements revealed a stoichiometric composition of GeTe but with high carbon contamination. Thus, one of the objectives of this work was to reduce the carbon contamination and to optimize the phase change properties of the deposited PCMs. The effect of deposition parameters such as plasma power, pressure and gas rate on the carbon contamination is then presented. By tuning and optimizing deposition parameters, GeTe films with carbon level as low at 2 at. % were obtained. Thereafter, homogeneous films of GeSbTe were deposited by injecting simultaneously the organometallic precursors TDMAGe, TDMASb and DiPTe in the plasma. A wide range of compositions was obtained by varying the injection and deposition operating parameters. Indeed, one of the main advantages of this process is the ability of varying films composition, which results in varying phase change characteristics of the deposited PCM. The impact of plasma parameters on the conformity of the process was also studied. It was shown that by adding a low frequency power component to the radio frequency power of the plasma, structures with high aspect ratio were successfully filled with the phase change material. Finally, electrical characterization of PCRAM test devices integrating phase change materials deposited by PE-MOCVD as active material have presented electrical properties similar to the ones obtained for materials deposited by conventional physical vapor deposition (PVD) process.

Efeitos ópticos não-lineares foram estudados em filmes finos de silício amorfo hidrogenado através da técnica de varredura-Z, que utiliza um único feixe de luz laser de onda contínua, modulado na escala de tempo de milissegundos. Em tal técnica, amostras do material foram deslocadas ao longo da região focal de um feixe com perfil de intensidade gaussiano e comprimento de onda de 532 nm, enquanto a transmitância da luz foi medida no campo distante. Os filmes foram depositados sobre vidro pela técnica PECVD a baixas temperaturas (entre 50 °C e 200 °C) e foi utilizado fósforo como impureza dopante: variando-se a concentração do gás fosfina durante a deposição do material, obtêm-se diferentes quantidades de fósforo incorporado no Si-a:H. Durante a realização da varredura-Z, foi observado o efeito de lente térmica no sinal da transmitância e a resolução temporal do sinal medido possibilitou o ajuste dos dados experimentais ao Modelo de Lente Térmica. A partir dos parâmetros desse ajuste, foi possível determinar a difusividade térmica das amostras (D ~ 3x10-³ cm²/s) e estimar sua condutividade térmica (K ~ 5x10-³ W/Kcm) e seu coeficiente de temperatura do caminho óptico (ds/dT). Além disso, os valores dos deslocamentos de fase do feixe (´teta\') e dos tempos característicos de formação da lente térmica (tc0) foram obtidos. Efeitos ópticos de origem térmica geralmente são indesejados em dispositivos fotônicos e, para evitá-los, o estudo e o conhecimento das propriedades ópticas não-lineares dos materiais que compõem tais dispositivos são de grande importância. Ademais, aplicações em microssensores podem ser baseadas nas propriedades do Si-a:H estudadas neste trabalho, como, por exemplo, sua condutividade térmica. / Nonlinear optical effects have been studied in hydrogenated amorphous silicon films through the single beam Z-scan technique, using a modulated CW laser in the millisecond time-scale regime. In this technique, the samples were moved along the focal region of a focused gaussian laser beam with wavelength of 532 nm, while the light transmittance in the far field was measured. The films were deposited on glass by low temperature PECVD technique (from 50 °C to 200 °C) and phosphorus were used as a dopant impurity: during the material deposition, different concentrations of phosphine gas cause different amounts of incorporated phosphorus into a-Si:H. The thermal lens effect was observed in the transmittance signal, so the experimental data from the time-resolved Z-scan mode could be fitted in the Thermal Lens Model. It was possible to determine the samples thermal diffusivity (D ~ 3x10-³ cm²/s) and to estimate their thermal conductivity (K ~ 5x10-³ W/Kcm) and temperature coefficient of the optical path length change (ds/dT) through those fittings. Besides, the phase shift (\'teta\') and the thermal lens characteristic time (tc0) were achieved. Thermal optical effects are unwanted to photonics devices, therefore studying and knowing these effects is very important to avoid them. Moreover, applications to microsensor devices may use the a-Si:H properties studied in this work as, for example, its thermal conductivity.

Afin de rendre les piles à combustible de type PEMFC réellement compétitives, un certain nombre d'inconvénients liés à l'utilisation du Nafion® restent à contourner, en particulier sa mauvaise conductivité protonique à des températures supérieures à 80°C. Dans l'optique de pouvoir opérer à plus hautes températures (jusqu'à 120°C), le développement de membranes moins sensibles à l'eau s'avère donc déterminant. Les polymères à base de fonctions acide phosphonique sont considérés comme des candidats potentiels pour une intégration en tant que matériau électrolyte dans les PEMFC « hautes températures » (> 80°C) grâce à leur fort caractère amphotère qui leur confère une bonne conductivité protonique dans des conditions d'humidité réduites. Dans ce contexte, la majeure partie de ce travail de thèse concerne l'élaboration par polymérisation plasma (PECVD) de polymères à base de groupements acide phosphonique à partir du monoprécurseur diméthyl allyl phosphonate. Dans un premier temps, nous avons démontré la faisabilité d'élaborer par polymérisation plasma des polymères à base de fonctions acide phosphonique à partir d'un monoprécurseur. Nous avons confirmé par IRTF, EDX et XPS la présence des groupements acide phosphonique favorables au transport protonique et l'homogénéité de la composition chimique de la surface jusqu'au cœur du matériau plasma. Les matériaux plasma montrent une bonne stabilité thermique dans la gamme de température 80°C - 120°C. Ensuite, une optimisation des conditions de synthèse a été réalisée. Les plus importantes valeurs de vitesses de croissance (28 nm.min-1 sur plaquette de silicium, 22 nm.min-1 sur PTFE et 26 nm.min-1 sur Nafion®211), de CEI (4,65 meq.g-1) et de conductivité (0,08 mS.cm-1 à 90°C et 30% RH) sont celles de la membrane synthétisée à 60 W. Des mesures de perméabilité au méthanol, à l'éthanol et au glycérol ont été réalisées et montrent que les films plasma sont intrinsèquement 40 à 235 fois moins perméables au combustible que le Nafion®211 du fait de leur fort taux de réticulation. Les polymères ont été déposés en tant que liants sur des électrodes E-TEK® pour intégration en pile. Nous avons constaté que le liant phosphonique plasma possède une conductivité protonique suffisante pour permettre le transport des protons à l'interface membrane-électrodes. En parallèle, nous avons réalisé le traitement de surface par plasma d'une membrane phosphonique conventionnelle pour en améliorer la stabilité thermique et la rétention au combustible. Les analyses thermogravimétriques montrent une légère amélioration de la stabilité thermique suite au traitement de surface. Des tests de perméabilité au méthanol et à l'éthanol montrent que la membrane traitée par plasma est 2 à 4 fois moins perméable que la membrane vierge. Le traitement à 60 W conduit aux coefficients de diffusion les plus faibles (DMeOH = 9.10-12 m2.s-1 et DEtOH = 6.10-12 m2.s-1). Des tests en pile ont été effectués montrant de meilleures performances de la membrane traitée en comparaison de son homologue non traité. / The proton exchange membrane is a key component in the PEMFC-type fuel cell; it plays a decisive role as electrolyte medium for proton transport and barrier to avoid the direct contact between fuel and oxygen. The Nafion® is one of the most extensively studied proton exchange membrane for PEMFC applications. However, it has a number of drawbacks that need to be overcome, especially the poor performance at temperature above 80°C. That's why the development of effective and low cost membranes for fuel cell turned to be a challenge for the membrane community in the last years. Phosphonic acid derivatives are considered suitable candidates as ionomers for application in PEMFC at high temperature (> 80°C) thanks to their efficient proton transport properties under low humidity condition due to their amphoteric character.In this work, plasma polymers containing phosphonic acid groups have been successfully prepared using dimethyl allylphosphonate as a single precursor demonstrating the feasibility of plasma process for the manufacture of proton exchange membranes. Moreover, plasma polymers properties have been investigated as a function of the plasma conditions. The evolution of the films growth rate on three different supports as a function of the plasma discharge power is bimodal, with a maximum (close to 30 nm min-1 on Si) at 60 W. The chemical composition of plasma materials (investigated by FTIR, EDX and XPS) is quite homogeneous from the surface to the bulk; it is characterized by a wide variety of bond arrangements, in particular the presence of phosphonate and phosphonic acid groups which are above all concentrated in the plasma film synthesized at 60 W, characterized by the highest ion exchange capacity (4.65 meq g-1) and the highest proton conductivity (0.08 mS cm-1 at 90°C and 30% RH). TGA analysis has shown that phosphonic acid-based plasma polymers retain water and don't decompose up to 150 °C, which reveals a satisfying thermal stability for the fuel cell application. In terms of fuel retention, plasma films are intrinsically highly performing (methanol, ethanol and glycerol permeabilities being 40 to 235 lower than that of Nafion®211). The plasma films were deposited on fuel cell electrodes (E-TEK®) as binding agents. We have noticed that the phosphonic binder has a sufficient proton conductivity to allow proton transport at the electrode-membrane interface.A second part of this work concerns the surface treatment by plasma process of a conventional phosphonated membrane for improvement of thermal stability and fuel retention. TGA analysis has shown a slight improvement of the thermal stability for the treated membrane. Methanol and ethanol permeabilities tests show that the plasma-modified membrane is 2 to 4 times less permeable than the non-modified membrane. The treatment at 60 W shows the lowest fuel diffusion coefficients (DMeOH = 9.10-12 m2.s-1 and DEtOH = 6.10-12 m2.s-1). Fuel cell tests were realized showing better performance for the modified membrane compared to the non-modified one.

Dans l’optique d’aller toujours vers le plus petit, un réacteur plasma micro-ondes en cavité résonnante fonctionnant à la pression atmosphérique a été développé à l’Institut Jean-Lamour (IJL, UMR 7198) dans l’équipe ESPRITS (Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces).Ce réacteur plasma présente la particularité de pouvoir fournir une post-décharge de petite dimension (de l’ordre du millimètre). Un mélange Ar-O2 est utilisé comme gaz composant le plasma. L’aspect filamentaire de ce type de plasma est une des caractéristiques majeures du dispositif. De plus, la post-décharge se trouve notamment composée d’oxygène atomique, espèce active très utilisée par exemple en PECVD ou pour la fonctionnalisation de surface.Notre travail a consisté à mettre au point ce réacteur plasma et à caractériser la post-décharge résultante. Après avoir maîtrisé les principaux paramètres pouvant jouer notamment sur la forme de la post-décharge, nous nous sommes intéressés à son utilisation en tant que source plasma pour des applications de traitements de surfaces.Nous avons ainsi étudié des dépôts de films minces de SiOx à partir d’hexaméthyldisiloxane (HMDSO) en utilisant la post-décharge comme source d’oxygène atomique permettant la décomposition du précurseur organosilicié. L’HMDSO est utilisé ici car il est assez simple à manipuler et il a été souvent étudié, nous permettant d’obtenir sur lui de nombreuses informations. Différentes structures auto-organisées sont apparues au sein de ces dépôts et ont été étudiées afin de comprendre leur mécanisme de formation / In order to always go to the smallest, a plasma reactor microwave in resonant cavity operating at atmospheric pressure was developed at the Institut Jean Lamour (IJL, UMR 7198) in the team ESPRITS (Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces).This plasma reactor has the particularity to provide post-discharge of small size (about one millimeter). An Ar-O2 gas is used as the plasma component. The filamentous appearance of this type of plasma is a major feature of the device. Furthermore, the afterglow is notably composed of atomic oxygen, active species such as widely used PECVD or surface functionalization.Our job was to develop the plasma reactor and to characterize the resulting afterglow. After mastering the key parameters that can play on the particular shape of the afterglow, we were interested in its use as a plasma source for surface treatment applications.We studied deposition of SiOx thin films from hexamethyldisiloxane (HMDSO) using post-discharge source of atomic oxygen for the decomposition of the organosilicon precursor. The HMDSO is used here because it is fairly easy to handle and it has often been studied, allowing us to obtain much information on him. Various self-organized structures appeared in these deposits and have been investigated to understand their formation mechanism

L'objectif de cette thèse est de contribuer à la compréhension des propriétés optoélectroniques des couches minces de silicium hydrogénée, une étude détaillée a été effectuée. Les échantillons ont été déposés par 13,56 MHz PECVD (Plasma Enhanced Chemical Vapor Deposition) à partir du silane dilué avec l'argon (96 %). La température du substrat a été fixée à 200 °C. L'influence des paramètres de dépôts sur les propriétés optiques des échantillons a été étudiée par spectroscopie UV -Vis -NIR. L'évolution structurelle a été étudiée par spectroscopie Raman, TEM, AFM, FTIR et par diffraction des rayons X (XRD). La déposition des couches intrinsèques a été faite dans cette étude dans le but d'obtenir la transition de l'état amorphe à la phase cristalline des matériaux. La pression de dépôt varie de 400 mTorr à 1400 mTorr et la puissance de 50 à 250 W. La caractérisation structurelle montre qu'au-delà de 160 W, nous avons observé une transition amorphe nanocristalline, avec une augmentation de la fraction cristalline en augmentant la puissance et la pression. Les couches sont déposées avec des vitesses de dépôt relativement élevées (3.5 - 8 Å/s), ce qui est très souhaitable pour la fabrication des cellules photovoltaïques. La vitesse de dépôt augmente avec l'augmentation de la puissance et de la pression. Des différentes fractions cristallines et tailles des cristallites ont été obtenues en contrôlant la pression et la puissance. Ces modifications de structure ont été corrélées avec la variation des propriétés optiques et électriques des couches minces déposées. / The main objective of this thesis is to contribute to the understanding of the optoelectronics properties of hydrogenated nanocrystalline silicon thin films, a detailed study has been conducted. The samples were deposited by 13.56 MHz PECVD (Plasma Enhanced Chemical Vapor Deposition) of silane argon mixture. The argon dilution of silane for all samples studied was 96% by volume. The substrate temperature was fixed at 200 °C. The influence of depositions parameters on optical proprieties of samples was studied by UV-Vis-NIR spectroscopy. The structural evolution was studied by Raman spectroscopy, TEM, AFM, FTIR and X-ray diffraction (XRD). Intrinsic-layer samples depositions were made in this experiment in order to obtain the transition from the amorphous to crystalline phase materials. The deposition pressure varied from 400 mTorr to 1400 mTorr and the RF power from 50 to 250 W. The structural evolution studies show that beyond 160 W, we observed an amorphous-nanocrystalline transition, with an increase in crystalline fraction by increasing RF power and working pressure. Films near the amorphous to nanocrystalline transition region are grown at reasonably high deposition rates (3.5- 8 Å/s), which are highly desirable for the fabrication of cost effective devices. The deposition rate increases with increasing RF power and process pressure. Different crystalline fractions and crystallite size can be achieved by controlling the process pressure and RF power. These structural changes are well correlated to the variation of optical and electrical proprieties of the thin films.

This thesis focuses on the study of graphene application in electronics and technology of preparation. In addition to the basic properties of graphene, the theoretical part of the work also describes the methods of its preparation, transmission, characterization and possibilities of application in electronics. The experimental part is divided into three chapters. The first chapter deals with the production of graphene by deposition from the gaseous phase, its transmission and application in the field of solar cells. The Poly(methyl methacrylate) polymer was first used for transfer of graphene, which was later replaced by Rosin due to less contamination of graphene at the end of the transmission process. The second chapter deals with the preparation of quantum dots by exfoliation in the liquid phase from graphite and its application in voltammetry. Voltammetry was utilized in this work to detect hydrogen peroxide using a gold electrode modified by quantum dots from graphene and other dichalcogens (MoS2, MoSe2, WS2, WSe2). In the last chapter, the influence of the substrate and the deposition conditions of graphene is studied by means of a plasma-reinforced phase-out of gas to growth, while the prepared graphene was characterized by imaging and spectroscopic methods. The entire experimental growth of graphene was managed and evaluated using a planned experiment.

Thin-film silicon tandem solar cells based on a hydrogenated amorphous silicon (a-Si:H) top-cell and a hydrogenated microcrystalline silicon (μc-Si:H) bottom-cell are a promising photovoltaic technology as they use a combination of absorber materials that is ideally suited for the solar spectrum. Additionally, the involved materials are abundant and non-toxic which is important for the manufacturing and application on a large scale. One of the most important factors for the application of photovoltaic technologies is the cost per watt. There are several ways to reduce this figure: increasing the efficiency of the solar cells, reducing the material consumption and increasing the throughput of the manufacturing equipment. The use of very-high frequencies has been proven to be beneficial for the material quality at high deposition rates thus enabling a high throughput and high solar cell efficiencies. In the present work a scalable very-high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique for state-of-the-art solar cells is developed. Linear plasma sources are applied which facilitate the use of very-high frequencies on large areas without compromising on the homogeneity of the deposition process. The linear plasma sources require a dynamic deposition process with the substrate passing by the electrodes in order to achieve a homogeneous deposition on large areas. State-of-the-art static radio-frequency (RF) PECVD processes are used as a reference in order to assess the potential of a dynamic VHF-PECVD technique for the growth of high-quality a-Si:H and μc-Si:H absorber layers at high rates. In chapter 4 the influence of the deposition process of the μc-Si:H i-layer on the solar cell performance is studied for static deposition processes. It is shown that the correlation between the i-layer growth rate, its crystallinity and the solar cell performance is similar for VHF- and RF-PECVD processes despite the different electrode configurations, excitation frequencies and process regimes. It is found that solar cells incorporating i-layers grown statically using VHF-PECVD processes obtain a state-of-the-art efficiency close to 8 % for growth rates up to 1.4 nm/s compared to 0.53 nm/s for RF-PECVD processes. The influence of dynamic deposition processes on the performance of μc-Si:H solar cells is studied. It is found that μc-Si:H solar cells incorporating dynamically grown i-layers obtain an efficiency of 7.3 % at a deposition rate of 0.95 nm/s. There is a small negative influence of the dynamic deposition process on the solar cell efficiency compared to static deposition processes which is related to the changing growth conditions the substrate encounters during a dynamic i-layer deposition process. The changes in gas composition during a dynamic i-layer deposition process using the linear plasma sources are studied systematically using a static RF-PECVD regime and applying a time-dependent gas composition. The results show that the changes in the gas composition affect the solar cell performance if they exceed a critical level. In chapter 5 dynamic VHF-PECVD processes for a-Si:H are developed in order to investigate the influence of the i-layer growth rate, process parameters and deposition technique on the solar performance and light-induced degradation. The results in this work indicate that a-Si:H solar cells incorporating i-layers grown dynamically by VHF-PECVD using linear plasma sources perform as good and better as solar cells with i-layers grown statically by RF-PECVD at the same deposition rate. State-of-the-art stabilized a-Si:H solar cell efficiencies of 7.6 % are obtained at a growth rate of 0.35 nm/s using dynamic VHF-PECVD processes. It is found that the stabilized efficiency of the a-Si:H solar cells strongly decreases with the i-layer deposition rate. A simplified model is presented that is used to obtain an estimate for the deposition rate dependent efficiency of an a-Si:H/μc-Si:H tandem solar cell based on the photovoltaic parameters of the single-junction solar cells. The aim is to investigate the individual influences of the a-Si:H and μc-Si:H absorber layer deposition rates on the performance of the tandem solar cell. The results show that a high deposition rate of the μc-Si:H absorber layer has a much higher potential for reducing the total deposition time of the absorber layers compared to high deposition rates for the a-Si:H absorber layer. Additionally, it is found that high deposition rates for a-Si:H have a strong negative impact on the tandem solar cell performance while the tandem solar cell efficiency remains almost constant for higher μc-Si:H deposition rates. It is concluded that the deposition rate of the μc-Si:H absorber layer is key to reduce the total deposition time without compromising on the tandem solar cell performance. The developed VHF-PECVD technique using linear plasma sources is capable of meeting this criterion while promoting a path to scale the processes to large substrate areas.

[pt] Esta dissertação teve como objetivo estudar as propriedades estruturais, mecânicas dos filmes de silício carbono nitrogenado amorfo (a-SiC:N) e a viabilidade do seu uso como camada adesiva entre filmes finos de carbono amorfo hidrogenado e aço inoxidável 316L. Os filmes de a-SiC:N foram crescidos pela técnica de deposição química na fase vapor assistida por plasma (PECVD) utilizando como precursor hexametildissilazano (HMDSN) sobre chapas de aço inoxidável 316L e lâminas de silício cristalino 100. Para a deposição foram variados os parâmetros de tensão de autopolarização (de -150V até -450V) e a temperatura de deposição (25 Graus Celsius, 200 Graus Celsius e 300 Graus Celsius). Os filmes foram caracterizados por técnicas de perfilometria, onde pudemos obter a taxa de deposição, a tensão interna dos filmes, análises por espectroscopia de fotoelétrons induzidos por raios-x (XPS) e espectroscopia de infravermelho onde identificamos a presença de ligações entre os átomos de silício, carbono e nitrogênio. Com a espectroscopia Raman observamos a presença das bandas D e G com características de filmes de carbono amorfo. As análises de nanoindentação determinaram que a dureza variou entre 8 e 12 GPa. A microscopia de força atômica evidenciou a presença de nanoestruturas sobre a superfície dos filmes. E por fim, obtivemos sucesso na deposição de filmes de carbono amorfo hidrogenado e carbono amorfo fluorado sobre chapas de aço inoxidável empregando filmes finos de a-SiC:N como camada adesiva. / [en] The objective of this dissertation has been to study the structural and mechanical properties of amorphous SiC:N thin films and the viability of their use as adhesive layer between amorphous C:N thin films and 316L stainless steel. The a-SiC:N films were grown via Plasma-Enhanced Chemical Vapor Deposition (PECVD), using Hexamethyldisilazane (HMDSN) as precursor on 316L stainless steel and crystalline silicon substrates 100. For the deposition, the parameters changed were the self-bias (from -150V to -450V) and the deposition temperature (25 Degree Celsius, 200 Degree Celsius and 300 Degree Celius). The characterization of the films was accomplished by using profilometry techniques, used to obtain the deposition rate and the internal stress of the films, x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy used to identify the presence of bonding between the Silicon, Carbon and Nitrogen atoms. The Raman spectroscopy was employed to observe the presence of the D and G bands with characteristics of amorphous carbon films. The nanoindentation analysis determined that the hardness varied between 8 and 12GPa. Atomic force microscopy (AFM) evidenced the presence of nanostructures on the surface of the films. Finally, we were able to perform deposition of hydrogenated amorphous carbon and of fluorinated amorphous carbon thin films on stainless steel substrates using a-SiC:N thin films as adhesive layer.