Layered Van der Waals solids, due to their highly anisotropic structure as well as their availability in mono, few and multi-layer form constitute a perfect playground, where a variety of possibility in structural variation as well as functionalities are expected. This potentially gives rise to a library of unique and fascinating 2D materials systems. These systems appear to demonstrate some spectacular variety of fundamental physics as well as indicate that some of these systems can be beneficial for several niche applications directly or indirectly resulting from their electrical and optical properties.

Nas últimas décadas, a ocorrência de atividade estrogênica e interferentes endócrinos (IEs) no ambiente aquático têm se tornado uma crescente preocupação. Dentre as diversas substâncias classificadas como IEs, destacam-se os fármacos, produtos de higiene e cuidados pessoais, hormônios naturais e sintéticos, produtos químicos industriais, praguicidas e muitos outros compostos que atingem o ambiente aquático por meio de descargas de esgoto doméstico, industrial ou de escoamento agrícola. Os objetivos deste estudo foram determinar a atividade estrogênica em amostras de águas superficiais, e avaliar seus efeitos biológicos no desenvolvimento de embriões de Danio rerio, a fim de propor faixas baseadas em valores de desencadeamento de efeitos para categorizar a atividade estrogênica. As amostras ambientais também foram analisadas por cromatografia líquida acoplada com a espectrometria de massas para identificar as substâncias que são suspeitas de causar alteração endócrina. Os compostos analisados foram: praguicidas, hormônios, triclosan, bisfenol A, octilfenol, nonilfenol, e a cafeína como indicador de atividade antrópica. A atividade estrogênica foi medida pelo ensaio Bioluminescent Yeast Estrogen (BLYES), que fornece os resultados em equivalente de 17β-estradiol (EEQ). No entanto, este ensaio não é capaz de prover informações sobre os efeitos adversos em organismos aquáticos. Para observação de possíveis efeitos na biota, os embriões foram expostos a amostras de águas superficiais com resultados acima de 0,1 EEQ no BLYES. Os ensaios foram realizados de acordo com a OECD No. 236 (2013), verificando efeitos agudos como: ausência de batimento cardíaco, não formação de somitos, não desprendimento da cauda, e embrião coagulado. Malformações embrionárias tais como: redução do tamanho do organismo, edema cardíaco e vitelínico, curvatura da coluna vertebral, também foram avaliadas. As informações obtidas pelo ensaio com embriões de Danio rerio foram adequadas para mostrar os efeitos da mistura de contaminantes em organismos não-alvo. A atividade estrogênica medida pelo BLYES ficou abaixo do limite de quantificação (0,1 EEQ) em 44,8% do total de 116 amostras analisadas, e a faixa de atividade estrogênica variou de 0,11 a 14,6 EEQ. Além disso, a presença de contaminantes mesmo que em concentrações baixas ressalta a necessidade de mais estudos para entender os efeitos dessas substâncias nos organismos aquáticos. / Over the last few decades, the occurrence of estrogenic activity and endocrine disrupting chemicals (EDCs) in aquatic environment has become a worldwide issue of increasing environmental concern. The EDCs have the ability to alter the endocrine system of organisms, and includes pharmaceuticals, personal care products, steroid hormones, industrial chemicals, pesticides and many other compounds. Such compounds are present in several industrial and domestic activities and reach the aquatic environment via wastewater discharges or agricultural runoff. The aim of this study was to determine the overall estrogenic activity of surface water, evaluate biological effects on fish embryos development, in order to propose concentrations range based on trigger value to categorize estrogenic activity. Environmental samples were also analyzed by liquid chromatography tandem mass spectrometry to identify substances that are suspected to be an endocrine disruptor. The analyzed compounds were: pesticides, hormones, triclosan, bisphenol A, octylphenol, nonylphenol, and caffeine as an indicative of anthropic activity. The estrogenic activity was measured by Bioluminescent Yeast Estrogen assay (BLYES), with the results expressed in 17β-estradiol equivalent quotient (EEQ). However, this assay is not able to provide information about adverse effects to aquatic organisms. In order to observe effects on aquatic organisms, organic extracts of surface water with results ≥ 0.1 EEQ in BLYES were tested in a bioassay using Danio rerio embryos. The methodology was conducted according OECD No. 236 and verified effects such as: lack of heart beat, lack of somites formation, non-detachment tail and coagulated embryo. Embryonic malformations were also evaluated, such as: reduction of organism size, edema and spine curvature, which are chronic effects. These effects probably are associated with contaminants mixtures. The obtained information by embryonic assay with Danio rerio was suitable to show the effects of contaminants mixture and was used to a categorization proposal of estrogenic activity. Estrogenic activity was below the limit of quantification (0.1 EEQ) in 44.8% of 116 analyzed samples, and range of estrogenic activity was from 0.11 to 14.6 EEQ. The tested samples in FET test were analyzed for acute or chronic toxicity in Danio rerio embryos. Based on the obtained results, even when estrogenic activity is present in surface water, the contaminants mixture can cause toxic effects in non-target organisms. Besides this, the widespread presence of these chemicals highlight the need for further studies in order to understand the harmfulness of these contaminants to aquatic organisms.

Os efeitos do campo elétrico, que surgem pela aplicação de uma voltagem no contato Schottky, na estrutura eletrônica de heteroestruturas semicondutoras utilizadas nos recentes transistores de efeito de campo (FET) e numa super-rede finita são simulados numericamente. Estas heteroestruturas apresentam poços quânticos bidimensionais e camadas que podem estar tensionadas pela diferença entre os parâmetros de rede cristalinos. Através de um procedimento numérico auto-consistente várias grandezas físicas são estudadas, os auto-estados e as densidades eletrônicas nas sub-bandas são calculadas. A variação destas grandezas é associada à capacitância e à transcondutância intrínseca, em função da voltagem no gate. Os resultados da simulação são comparados aos dados experimentais. Este procedimento possibilita a compreensão dos fenômenos quânticos envolvidos com a previsão de certas características de dispositivos sem a necessidade prévia de sua produção e testes / Eletric field effects on the electronic characteristics of semiconductor heterostructures used in recent field effect transistors (FETs) and in a finite superlattice are numerically simulated. This field is due to a voltage bias applied on a Schottky contact. These heterostructures have two-dimensional quantum wells and layers wich can be stressed due to different lattice parameters of the materials involved. Through a numerical self-consistent procedure, many physical quantities are studied, such as the eigen-states and the electronic densities at the sub-bands. The changes in such quantities are associated to the capacitance and to the intrinsic transconductance as a function of the gate voltage. The results are compared to experimental data. This procedure allows the comprehension of the quantum phenomena involved and the prediction of device characteristics, without the need to fabricate and test it

Nas últimas décadas, a ocorrência de atividade estrogênica e interferentes endócrinos (IEs) no ambiente aquático têm se tornado uma crescente preocupação. Dentre as diversas substâncias classificadas como IEs, destacam-se os fármacos, produtos de higiene e cuidados pessoais, hormônios naturais e sintéticos, produtos químicos industriais, praguicidas e muitos outros compostos que atingem o ambiente aquático por meio de descargas de esgoto doméstico, industrial ou de escoamento agrícola. Os objetivos deste estudo foram determinar a atividade estrogênica em amostras de águas superficiais, e avaliar seus efeitos biológicos no desenvolvimento de embriões de Danio rerio, a fim de propor faixas baseadas em valores de desencadeamento de efeitos para categorizar a atividade estrogênica. As amostras ambientais também foram analisadas por cromatografia líquida acoplada com a espectrometria de massas para identificar as substâncias que são suspeitas de causar alteração endócrina. Os compostos analisados foram: praguicidas, hormônios, triclosan, bisfenol A, octilfenol, nonilfenol, e a cafeína como indicador de atividade antrópica. A atividade estrogênica foi medida pelo ensaio Bioluminescent Yeast Estrogen (BLYES), que fornece os resultados em equivalente de 17β-estradiol (EEQ). No entanto, este ensaio não é capaz de prover informações sobre os efeitos adversos em organismos aquáticos. Para observação de possíveis efeitos na biota, os embriões foram expostos a amostras de águas superficiais com resultados acima de 0,1 EEQ no BLYES. Os ensaios foram realizados de acordo com a OECD No. 236 (2013), verificando efeitos agudos como: ausência de batimento cardíaco, não formação de somitos, não desprendimento da cauda, e embrião coagulado. Malformações embrionárias tais como: redução do tamanho do organismo, edema cardíaco e vitelínico, curvatura da coluna vertebral, também foram avaliadas. As informações obtidas pelo ensaio com embriões de Danio rerio foram adequadas para mostrar os efeitos da mistura de contaminantes em organismos não-alvo. A atividade estrogênica medida pelo BLYES ficou abaixo do limite de quantificação (0,1 EEQ) em 44,8% do total de 116 amostras analisadas, e a faixa de atividade estrogênica variou de 0,11 a 14,6 EEQ. Além disso, a presença de contaminantes mesmo que em concentrações baixas ressalta a necessidade de mais estudos para entender os efeitos dessas substâncias nos organismos aquáticos. / Over the last few decades, the occurrence of estrogenic activity and endocrine disrupting chemicals (EDCs) in aquatic environment has become a worldwide issue of increasing environmental concern. The EDCs have the ability to alter the endocrine system of organisms, and includes pharmaceuticals, personal care products, steroid hormones, industrial chemicals, pesticides and many other compounds. Such compounds are present in several industrial and domestic activities and reach the aquatic environment via wastewater discharges or agricultural runoff. The aim of this study was to determine the overall estrogenic activity of surface water, evaluate biological effects on fish embryos development, in order to propose concentrations range based on trigger value to categorize estrogenic activity. Environmental samples were also analyzed by liquid chromatography tandem mass spectrometry to identify substances that are suspected to be an endocrine disruptor. The analyzed compounds were: pesticides, hormones, triclosan, bisphenol A, octylphenol, nonylphenol, and caffeine as an indicative of anthropic activity. The estrogenic activity was measured by Bioluminescent Yeast Estrogen assay (BLYES), with the results expressed in 17β-estradiol equivalent quotient (EEQ). However, this assay is not able to provide information about adverse effects to aquatic organisms. In order to observe effects on aquatic organisms, organic extracts of surface water with results ≥ 0.1 EEQ in BLYES were tested in a bioassay using Danio rerio embryos. The methodology was conducted according OECD No. 236 and verified effects such as: lack of heart beat, lack of somites formation, non-detachment tail and coagulated embryo. Embryonic malformations were also evaluated, such as: reduction of organism size, edema and spine curvature, which are chronic effects. These effects probably are associated with contaminants mixtures. The obtained information by embryonic assay with Danio rerio was suitable to show the effects of contaminants mixture and was used to a categorization proposal of estrogenic activity. Estrogenic activity was below the limit of quantification (0.1 EEQ) in 44.8% of 116 analyzed samples, and range of estrogenic activity was from 0.11 to 14.6 EEQ. The tested samples in FET test were analyzed for acute or chronic toxicity in Danio rerio embryos. Based on the obtained results, even when estrogenic activity is present in surface water, the contaminants mixture can cause toxic effects in non-target organisms. Besides this, the widespread presence of these chemicals highlight the need for further studies in order to understand the harmfulness of these contaminants to aquatic organisms.

There are many semiconductors with nominally superior electronic properties compared to silicon. However, silicon became the material of choice for MOSFETs due to its robust native oxide. With Moore's observation as a guiding principle, the semiconductor industry has come a long way in scaling the silicon MOSFETs to smaller dimensions every generation with engineering ingenuity and technological innovation. As per the 2012 International Technology Roadmap for Semiconductors (ITRS), the MOSFET is expected to be scaled to near 6 nm gate length by 2025. However, materials, design and fabrication capabilities aside, basic physical considerations such as source to drain quantum mechanical tunneling, channel to gate tunneling, and thermionic emission over the channel barrier suggest an end to the roadmap for CMOS is on the horizon. The semiconductor industry is already aggressively looking for the next switch which can replace the silicon FET in the long term. My Ph.D. research is part of the quest for the next switch. The promises of process compatibility with existing CMOS technologies, fast carriers with high mobilities, and symmetric conduction and valence bands have led to graphene being considered as a possible alternative to silicon. This work looks at three devices based on graphene using first principles atomistic transport simulations and compact models capturing essential physics: the large-area graphene RF FET, the Bilayer pseudoSpin FET, and the double electron layer resonant tunneling transistor. The characteristics and performance of each device is explored with a combination of SPICE simulations and atomistic quasi static transport simulations. The BiSFET device was found to be a promising alternative to CMOS due to extremely low power dissipation. Finally, I have presented formalism for efficient simulation of time dependent transport in graphene for beyond quasi static performance analysis of the graphene based devices explored in this work. / text

Die vorliegende Arbeit befasst sich mit der Anwendbarkeit von transparenter Elektronik basierend auf oxidischen Halbleitern in Multielektrodenarrays zur Messung von neuronalen Signalen. Im ersten experimentellen Kapitel werden auf Zinkoxid basierende Bauelemente untersucht. Verschiedene Varianten von Feldeffekttransistoren (FETs) werden charakterisiert und ihre Eignung zur Detektion von Zellsignalen überprüft. Die Anwendbarkeit physikalischer Modelle zur Beschreibung von ZnO-basierten Metal-Halbleiter-FETs (MESFETs) wird behandelt. Weiterhin wird die Eignung von einfachen Inverterschaltungen zur Spannungsverstärkung diskutiert. Das zweite Kapitel thematisiert Rauschmessungen an unterschiedlichen ZnO-basierten Proben, darunter Dünnfilme, Mikronadeln, MESFETs und Inverter. Darauf aufbauend wird die Auswirkung des gemessenen Stromrauschens auf die Sensitivität der Bauelemente nachvollzogen und theoretisch modelliert. Im dritten Kapitel wird das Verhalten der Bauelemente im Kontakt mit Elektolyt beschrieben. Die Signalübertragung von Spannungsänderungen im Elektrolyt auf die Chipelektronik wird mit verschiedenen Messmethoden charakterisiert. Dabei kommt teilweise ein selbstgebauter Vorverstärker zum Einsatz, dessen Aufbau ebenfalls beschrieben wird. Die Stabilität der verwendeten Materialien in physiologischen Salzlösungen und ihre Biokompatibilität wird überprüft. Darüber hinaus werden FETs mit Elektrolytgate und Zinkzinnoxid-Kanal vorgestellt.

Techn. Hochsch., Diss., 2003--Aachen.

Parmi les plus important dispositifs pour l'industrie des semi-conducteurs, le transistor “Metal Oxide Semiconductor Field-Effect Transistor” (MOSFET) est largement utilisé pour le développement d'un grand nombre d'applications électroniques. La miniaturisation de ces dispositifs MOSFET a été un processus très efficace pour améliorer la performance de la technologie “Complementary Metal-Oxide Semiconductor” (CMOS). La mise à l'échelle des transistors selon “scaling rules” a permis l'amélioration des performances jusqu'à nœud technologique 90 nm, mais la diminution continue des dimensions MOSFET fait face à des limitations physiques et économiques. Afin de surmonter ces limitations et de parvenir à l'exigence de performance, plusieurs “boosters” ont été explorées par l’industrie des semi-conducteurs, notamment l'utilisation de dispositifs efficaces tel que "Fully Depleted Silicon On Insulator" (FDSOI), dont l'architecture a été choisie pour être explorée dans ce travail.Pour la technologie CMOS ultime, la modélisation fiable du transport électronique est une préoccupation majeure. Ce travail de thèse vise à améliorer la modélisation de dispositifs ultimes FDSOI, concentré sur le transport des porteurs. Dans ce scénario, “Technological Computer-Aided Design” (TCAD) basé sur des modèles Densité-Gradient et de Dérive-Diffusion se présente comme un outil rapide et puissant pour soutenir le développement technologique dans le secteur technologique. Cependant, nous avons montré que leur précision pour prédire les nœuds avancés est souvent douteuse. Afin de surmonter ce problème, nous avons présenté un outil de simulation à deux dimensions (UTOXPP) basé sur des modèles physiques et qui est implementé sur une efficace architecture C++ avec une bonne interface graphique. Au moyen de la méthode Finite-Difference, nous décrivons une stratégie de modélisation complète pour les parties les plus importantes de ce outil, à savoir 1.5D Poisson-Schrödinger, Quantum Drift-Diffusion et les modèles de mobilité de la formulation Kubo-Greenwood et de la fonction de Green hors equilibrium (NEGF). Les résultats de simulation ont montré l'efficacité de UTOXPP pour résoudre les effets quantiques à la fois pour la distribution de charge et également pour le transport des dispositifs choisis. L'objectif de ce travail de thèse a été réalisée puisque UTOXPP se montré capable de fournir des résultats fiables et rapides pour les nœuds avancés, raison d'être un excellent choix pour l'usage quotidien dans la industrie. / One of the most important device for semiconductor industry nowadays is the Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) which is hugely applied in the development of a vast number of electronic applications. The downscaling of MOSFET geometry has been a very successful process to improve the performances of Complementary Metal-Oxide Semiconductor (CMOS) devices. The scaling of transistors dimensions according to scaling rules enabled the performance improvements up to the 90 nm technology node, but the continuous shrinking of MOSFET dimensions faces both physical and economical limitations. In order to overcome these limitations and achieve the performance requirement, several “boosters” have been explored by the semiconductor industries, notably the use of alternative device structures such as “Fully Depleted Silicon On Insulator” (FDSOI), whose architecture has been chosen to be explored in this work.For advanced CMOS technology, robust and predictive electronic transport modeling is a major concern. This PhD work intended to improve the device modeling for ultimate FDSOI devices, with a particular focus on carrier transport. In this scenario, Technological Computer-Aided Design (TCAD) based on Density-Gradient and Drift-Diffusion models arise as a fast and powerful tool to support the technological development within the industry, however we have shown that their accuracy for predicting advanced nodes is often doubtful. In order to overcome this issue, we presented a two-dimensional simulation tool (UTOXPP) based on physical models which makes use of state of the art C++ architecture and accounts for a complete and friendly GUI. By means of Finite-Difference method, we describe a complete modeling strategy for the most important parts of the solver, namely 1.5D Poisson-Schrödinger, Quantum Drift-Diffusion and the mobility models from Kubo-Greenwood formulation and Nonequilibrium Green’s function (NEGF). Simulation results showed the efficiency of UTOXPP for solving electrostatics and the quantum effects for both carrier distribution and transport for the given devices. The objective of this PhD work has been achieved as UTOXPP delivers reliable results for advanced nodes in a timely manner, being an excellent choice for the industrial daily use.

Os efeitos do campo elétrico, que surgem pela aplicação de uma voltagem no contato Schottky, na estrutura eletrônica de heteroestruturas semicondutoras utilizadas nos recentes transistores de efeito de campo (FET) e numa super-rede finita são simulados numericamente. Estas heteroestruturas apresentam poços quânticos bidimensionais e camadas que podem estar tensionadas pela diferença entre os parâmetros de rede cristalinos. Através de um procedimento numérico auto-consistente várias grandezas físicas são estudadas, os auto-estados e as densidades eletrônicas nas sub-bandas são calculadas. A variação destas grandezas é associada à capacitância e à transcondutância intrínseca, em função da voltagem no gate. Os resultados da simulação são comparados aos dados experimentais. Este procedimento possibilita a compreensão dos fenômenos quânticos envolvidos com a previsão de certas características de dispositivos sem a necessidade prévia de sua produção e testes / Eletric field effects on the electronic characteristics of semiconductor heterostructures used in recent field effect transistors (FETs) and in a finite superlattice are numerically simulated. This field is due to a voltage bias applied on a Schottky contact. These heterostructures have two-dimensional quantum wells and layers wich can be stressed due to different lattice parameters of the materials involved. Through a numerical self-consistent procedure, many physical quantities are studied, such as the eigen-states and the electronic densities at the sub-bands. The changes in such quantities are associated to the capacitance and to the intrinsic transconductance as a function of the gate voltage. The results are compared to experimental data. This procedure allows the comprehension of the quantum phenomena involved and the prediction of device characteristics, without the need to fabricate and test it

L'amélioration de la compacité et du rendement des convertisseurs à découpage est une problématique centrale en électronique de puissance; elle l'est encore plus à bord des satellites où chaque gramme et chaque watt comptent. Chacun des nombreux émetteurs et récepteurs radiofréquence qui équipent les satellites de télécommunication a besoin d'être alimenté par diverses tensions, converties de façon isolée à partir du bus principal de distribution de puissance. En raison des lourdes contraintes thermiques, de fiabilité et de résistance aux radiations qui pèsent sur les composants électroniques dans les applications spatiales, les degrés de liberté pour améliorer les alimentations sont restreints, en tout cas avec les technologies actuelles de semiconducteurs qualifiés (couteuses et très en retrait des performances de l'état de l'art). La commercialisation assez récente de transistors de puissance en nitrure de gallium (GaN) à canal normalement bloqué, présentant des caractéristiques électriques supérieures à celles des meilleurs MOSFET de puissance en silicium, est prometteuse sur ce point. En effet leur robustesse intrinsèque aux radiations semble permettre leur emploi dans des convertisseurs spatiaux. Le but de ce travail est l'évaluation des apports possibles de cette technologie dans la réalisation d'alimentations DC/DC isolées pour des équipements typiques des charges utiles des satellites de télécommunication. Le fonctionnement à des fréquences de découpage plus élevées avec ces composants plus performants doit, au premier abord, réduire l'encombrement des convertisseurs à rendement égal (voire meilleur) tout en continuant à respecter le cahier des charges spécifique à chaque application. La pertinence de cette hypothèse et l'architecture de mise en œuvre la plus adéquate ont été explorées pour l'alimentation faible puissance d'un récepteur RF, avec réalisation et comparaison de plusieurs maquettes de démonstration. Afin d'aborder des convertisseurs de plus fortes puissances, une étude théorique et expérimentale des pertes par commutation dans les jambes de pont de transistors GaN a été menée. Un programme de calcul de performances a été développé en Python et mis en œuvre pour identifier l'optimum global du dimensionnement d'un convertisseur Dual Active Bridge destiné à l'alimentation d'un amplificateur RF de puissance (250 W DC). Une maquette prototype a été réalisée et a démontré l'intérêt de la topologie et des composants GaN dans cette application, tout en mettant en évidence la prédominance des pertes haute fréquence des composants magnétiques parmi les pertes totales du convertisseur. Ce dernier point s'avère finalement être la principale limitation de l'approche, précieuse pour l'ingénierie, de dimensionnement optimal par le calcul : les modèles actuellement existants d'estimation des pertes dans les éléments magnétiques se révèlent insatisfaisants pour prédire les performances de ce type de convertisseur. / Improving the compactness and efficiency of switching converters is a central issue in power electronics; even more so in satellites where every gram and every watt counts. Each of the many radio-frequency emitters and receivers onboard telecommunications satellites need to be powered by various voltages, converted in an isolated way from the main power distribution bus. Due to the strong thermal, reliability and radiation hardness constraints applying to electronic components in space applications, available degrees of freedom for improvement of power supplies are limited - at least with current qualified semiconductor technologies (which are both expensive and far behind state-of-the-art performance). The recent commercialization of gallium nitride (GaN) normally-off power transistors, having superior electrical characteristics compared to the best silicon power MOSFET, is promising on that regard. Indeed, their intrinsic radiation hardness seems to allow their use in space-grade converters. The aim of this work is the evaluation of how this technology can help improve the design of isolated DC/DC power supplies for typical hardware units of telecommunications satellite payloads. Operation at higher switching frequencies with these better performing components should, in principle, reduce converters' footprint while keeping the same (or better) efficiency level and still obeying each application's specific requirements. The accuracy of this hypothesis as well as the most adequate implementation architecture have been explored for the low power supply of a RF receiver, including realization and comparison of several demonstration boards. In order to approach higher power converters, a theoretical and experiment study of switching losses in GaN transistor bridge legs has been performed. A performance computation software has been developed in Python and used to identify the global optimum of the design of a Dual Active Bridge converter for a power RF amplifier (250 W DC). A prototype board has been built and demonstrated the interest of both the topology and GaN devices in this application, while clearly showing that high-frequency losses in magnetic components dominate total converter loss. This last issue happens to be the main limitation of the approach - precious to the engineer - of optimum design by computation: currently existing models for power loss estimation in magnetic elements are not satisfactory to predict performances of this type of converter.