This thesis discusses the research, experimental methods, and data gathered for the investigation of a novel method for the diagnosis of melanoma skin cancer. First, a background about human skin tissue is presented. Then, a detailed description of melanoma along with current diagnosis techniques and treatment options are presented. In the experimental methods, the electrical properties of several types of tissue were analyzed, the purpose of which was to discover if a tissue type can be distinguished by its electrical properties alone. This would allow for the diagnosis of melanoma to be done by examining the electrical properties of the suspected tumor and comparing the results to known values of healthy and cancerous skin. After analyzing the data, it was concluded that tissue types can be identified by their electrical properties and it may be possible to diagnose melanoma through this method. Finally, the possibility of using a similar technology and radiofrequency tissue ablation to treat melanoma is presented.

To investigate the relationship between the structural characteristics of rough single fracturesand the electrical properties of the rock. In this study, a series of physical models of roughand smooth single fractures were established using the finite element method and Ohm's lawto test the electrical conductivity. By varying the distance between the fracture surfaces, arange of individual fractures with different surface roughness characterized by the relativestandard deviation (RSD) was generated using COMSOL Multiphysics software.Subsequently, the intensity of current passing through the fractures and the influence of roughsurfaces on rock electrical properties were monitored. Numerical simulations demonstrated anon-linear relationship between the current intensity through the models and the RSDroughness, with the equivalent resistivity of the fractured rock increasing with higher RSDvalues. As the RSD roughness increased, the difference in equivalent resistivity betweenrough and smooth fractures also increased, indicating a greater impact of rough surfaces onelectrical properties. The equivalent resistivity of the rock model was 1.05-1.45 times that ofthe parallel plate model with same average aperture. The novelty of this study lies in directlyinvestigating the relationship between roughness of single fractures and rock electricalproperties in three-dimensional, providing insights for understanding the electrical behaviorof rock fractures. / För att undersöka sambandet mellan strukturella egenskaper hos ojämna enkelstrålar och deelektriska egenskaperna hos bergarten. I denna studie etablerades en serie fysiska modeller avojämna och jämna enkelstrålar genom att använda finita elementmetoden och Ohms lag föratt testa elektrisk ledningsförmåga. Genom att variera avståndet mellan strålytornagenererades en rad individuella strålar med olika ytjämnhet som karakteriseras av relativstandardavvikelse (RSD) med hjälp av COMSOL Multiphysics-programvara. Därefterövervakades intensiteten av ström som passerade genom strålarna och inflytandet av ojämnaytor på bergens elektriska egenskaper. Numeriska simuleringar visade på ett icke-linjärtsamband mellan strömintensiteten genom modellerna och RSD-ytjämnheten, där denekvivalenta resistiviteten hos den spruckna bergarten ökade med högre RSD-värden. NärRSD-ytjämnheten ökade, ökade även skillnaden i ekvivalent resistivitet mellan ojämna ochjämna strålar, vilket indikerar en större påverkan av ojämna ytor på de elektriskaegenskaperna. Den ekvivalenta resistiviteten hos bergmodellen var 1,05–1,45 gånger högreän den hos parallellplattanmodellen med samma genomsnittliga apertur. Nyheten i dennastudie ligger i att direkt undersöka sambandet mellan ytjämnheten hos enkelstrålar ochbergens elektriska egenskaper på en tredimensionell skala, vilket ger värdefulla insikter föratt förstå det elektriska beteendet hos bergstrålar och ytterligare förbättra modeller.

[ES] Uno de los retos más importantes de la sociedad actual es la obtención de energía de forma sostenible, limpia y eficiente. Por ello, gran parte de la investigación actual en el campo de la química y la ciencia de los materiales centra sus esfuerzos en la búsqueda y estudio de nuevas generaciones de materiales que permitan una transición energética desde el modelo energético tradicional hacia un modelo más sostenible. En este contexto, las propiedades eléctricas de los materiales, relacionadas con la generación y transformación de energía, juegan un papel esencial. En esta tesis se estudian dos tipos de materiales híbridos con distinta estructura y composición, pero que combinan excelentes propiedades eléctricas y ópticas. Por una parte, los clústeres octaédricos de molibdeno, ya conocidos desde hace décadas, han demostrado ser excelentes materiales en catálisis. En los últimos tiempos, la investigación alrededor de este material se ha centrado en el estudio de sus propiedades ópticas y electrónicas y sus aplicaciones en sensores y dispositivos emisores de luz. Por otra parte, las perovskitas híbridas halogenadas son ampliamente conocidas en el campo de la generación energética por sus elevadas eficiencias, movilidad de cargas y alta eficiencia de emisión de luz. Se han estudiado dos estructuras de perovskita híbrida halogenada: una 3D, cuyas propiedades son ampliamente conocidas, y otra con estructura multidimensional 2D-3D, donde el carácter laminar le confiere una mejora en la estabilidad. Con el propósito de comprender mejor su interacción luz-materia, en los trabajos desarrollados en la presente tesis, se han realizado mediciones optoelectrónicas a nivel monocristalino. Esto incluye un análisis combinando de medidas de emisión, fotocolección y transporte de carga. Además, se ha investigado su comportamiento como cavidad resonante, así como sus propiedades como generador de energía. Por lo tanto, se ha corroborado que los materiales objeto de estudio, presentan unas propiedades que les confieren diferentes posibilidades de aplicación en diversos ámbitos dentro del campo de la generación energética. / [CA] Un dels reptes més importants de la societat actual és obtenir energia de forma sostenible, neta i eficient. Per això, gran part de la investigació actual en el camp de la química i la ciència dels materials centra els seus esforços en la cerca i l'estudi de noves generacions de materials que permeten una transició energètica des del model energètic tradicional cap a un model més sostenible. En aquest context, les propietats elèctriques dels materials, relacionades amb la generació i la transformació d'energia juguen un paper essencial. En aquesta tesi s'estudien dos tipus de materials híbrids amb diferent estructura i composició, però que combinen propietats elèctriques i òptiques excel·lents. D'una banda, els clústers octaèdrics de molibdè, ja coneguts des de fa dècades, han demostrat ser materials idonis en catàlisi. De fet, en els darrers temps, la recerca al voltant d'aquest material s'ha centrat en l'estudi de les propietats òptiques i electròniques i les aplicacions en sensors i dispositius emissors de llum. D'altra banda, les perovskites híbrides halogenades són àmpliament conegudes al camp de la generació energètica per les seues elevades eficiències, mobilitat de càrregues i alta eficiència d'emissió de llum. S'han estudiat dues estructures de perovskita híbrida halogenada: una de 3D, les propietats de la qual són àmpliament conegudes, i una altra amb estructura multidimensional 2D-3D, el caràcter laminar de la qual li confereix una millora en l'estabilitat. Amb el propòsit de comprendre millor la seua interacció llum-matèria, en els treballs desenvolupats en aquesta tesi, s'han realitzat mesuraments optoelectrònics a nivell monocristal·lí. Això inclou una anàlisi que combina mesures d'emissió, fotocol·lecció i transport de càrrega. A més, s'ha investigat el seu comportament com a cavitat ressonant, així com les seues propietats com a generador d'energia. Per tant, s'ha corroborat que els materials objecte d'estudi presenten unes propietats que els confereixen diferents possibilitats d'aplicació en diversos àmbits dins del camp de la generació energètica. / [EN] One of the most important challenges of today's society is obtaining energy in a sustainable, clean, and efficient way. For this reason, much of the current research in the field of chemistry and materials science focuses its efforts on the search and study of new generations of materials that allow an energy transition from the traditional energy model to a more sustainable model. In this context, the electrical properties of materials, related to the generation and transformation of energy, play an essential role. In this thesis, two types of hybrid materials with different structure and composition, but which combine excellent electrical and optical properties, are studied. On the one hand, octahedral molybdenum clusters have been known for decades and have proven to be excellent materials in catalysis. In fact, in recent times, research around this material has focused on the study of its optical and electronic properties and its applications in sensors and light-emitting devices. On the other hand, halogenated hybrid perovskites are widely known in the field of energy generation for their high efficiencies, charge mobility and high light emission efficiency. Two halogenated hybrid perovskite structures were studied: one 3D, whose properties are widely known, and another with a 2D-3D multidimensional structure, where the laminar character confers an improvement in stability. To better understand its light-matter interaction, in the work developed in this thesis, optoelectronic measurements have been carried out at the monocrystalline level. This includes a combined analysis of emission, photocollection and charge transport measurements. In addition, its behavior as a resonant cavity has been investigated, as well as its properties as an energy generator. Therefore, it has been confirmed that the materials under study have properties that give them different application possibilities in various areas within the field of energy generation. / Segura Sanchis, E. (2024). Propiedades ópticas y eléctricas de monocristales de materiales híbridos [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202755

No description available.

Coordinated electrical activation of the heart is essential for the maintenance of a regular cardiac rhythm and effective contractions. Action potentials spread from one cell to the next via gap junction channels. Because of the elongated shape of cardiomyocytes, longitudinal resistivity is lower than transverse resistivity causing electrical anisotropy. Moreover, non-uniformity is created by clustering of gap junction channels at cell poles and by non-excitable structures such as collagenous strands, vessels or fibroblasts. Structural changes in cardiac disease often affect passive electrical properties by increasing non-uniformity and altering anisotropy. This disturbs normal electrical impulse propagation and is, consequently, a substrate for arrhythmia. However, to investigate how these structural changes lead to arrhythmias remains a challenge. One important mechanism, which may both cause and prevent arrhythmia, is the mismatch between current sources and sinks. Propagation of the electrical impulse requires a sufficient source of depolarizing current. In the case of a mismatch, the activated tissue (source) is not able to deliver enough depolarizing current to trigger an action potential in the non-activated tissue (sink). This eventually leads to conduction block. It has been suggested that in this situation a balanced geometrical distribution of gap junctions and reduced gap junction conductance may allow successful propagation. In contrast, source-sink mismatch can prevent spontaneous arrhythmogenic activity in a small number of cells from spreading over the ventricle, especially if gap junction conductance is enhanced. Beside gap junctions, cell geometry and non-cellular structures strongly modulate arrhythmogenic mechanisms. The present review elucidates these and other implications of passive electrical properties for cardiac rhythm and arrhythmogenesis.

The term "topological insulator" (TI) represents a novel class of compounds which are insulating in the bulk, but simultaneously and unavoidably have a metallic surface. The reason for this is the non-trivial band topology, arising from particular band inversions and the spin-orbit interaction, of the bulk. These topologically protected metallic surface states are characterized by massless Dirac dispersion and locked helical spin polarization, leading to forbidden back-scattering with robustness against disorder. Based on the extraordinary features of the topological insulators an abundance of new phenomena and many exciting experiments have been proposed by theoreticians, but still await their experimental verification, not to mention their implementation into applications, e.g. the creation of Majorana fermions, advanced spintronics, or the realization of quantum computers. In this perspective, the 3D TIs Bi2Te3 and Bi2Se3 gained a lot of interest due to their relatively simple electronic band structure, having only a single Dirac cone at the surface. Furthermore, they exhibit an appreciable bulk band gap of up to ~ 0.3 eV, making room temperature applications feasible. Yet, the execution of these proposals remains an enormous experimental challenge. The main obstacle, which thus far hampered the electrical characterization of topological surface states via transport experiments, is the residual extrinsic conductivity arising from the presence of defects and impurities in their bulk, as well as the contamination of the surface due to exposure to air. This thesis is part of the actual effort in improving sample quality to achieve bulk-insulating Bi2Te3 films and study of their electrical properties under controlled conditions. Furthermore, appropriate capping materials preserving the electronic features under ambient atmosphere shall be identified to facilitate more sophisticated ex-situ experiments. Bi2Te3 thin films were fabricated by molecular beam epitaxy (MBE). It could be shown that, by optimizing the growth conditions, it is indeed possible to obtain consistently bulk-insulating and single-domain TI films. Hereby, the key factor is to supply the elements with a Te/Bi ratio of ~8, while achieving a full distillation of the Te, and the usage of substrates with negligible lattice mismatch. The optimal MBE conditions for Bi2Te3 were found in a two-step growth procedure at substrate temperatures of 220°C and 250°C, respectively, and a Bi flux rate of 1 Å/min. Subsequently, the structural characterization by high- and low-energy electron diffraction, photoelectron spectroscopy, and, in particular, the temperature-dependent conductivity measurements were entirely done inside the same ultra-high vacuum (UHV) system, ensuring a reliable record of the intrinsic properties of the topological surface states. Bi2Te3 films with thicknesses ranging from 10 to 50 quintuple layers (QL; 1QL~1 nm) were fabricated to examine, whether the conductivity is solely arising from the surface states. Angle resolved photoemission spectroscopy (ARPES) demonstrates that the chemical potential for all these samples is located well within the bulk band gap, and is only intersected by the topological surface states, displaying the characteristic linear dispersion. A metallic-like temperature dependency of the sheet resistance is observed from the in-situ transport experiments. Upon going from 10 to 50QL the sheet resistance displays a variation by a factor 1.3 at 14K and of 1.5 at room temperature, evidencing that the conductivity is indeed dominated by the surface. Low charge carrier concentrations in the range of 2–4*10^12 cm^−2 with high mobility values up to 4600 cm2/Vs could be achieved. Furthermore, the degradation effect of air exposure on the conductance of the Bi2Te3 films was quantified, emphasizing the necessity to protect the surface from ambient conditions. Since the films behave inert to pure oxygen, water/moisture is the most probable source of degeneration. Moreover, epitaxially grown elemental tellurium was identified as a suitable capping material preserving the properties of the intrinsically insulating Bi2Te3 films and protecting from alterations during air exposure, facilitating well-defined and reliable ex-situ experiments. These findings serve as an ideal platform for further investigations and open the way to prepare devices that can exploit the intrinsic features of the topological surface states. / Der Begriff "Topologischer Isolator" (TI) beschreibt eine neuartige Klasse von Verbindungen deren Inneres (engl. Bulk) isolierend ist, dieses Innere aber gleichzeitig und zwangsläufig eine metallisch leitende Oberfläche aufweist. Dies ist begründet in der nicht-trivialen Topologie dieser Materialien, welche durch eine spezielle Invertierung einzelner Bänder in der Bandstruktur und der Spin-Bahn-Kopplung im Materialinneren hervorgerufen ist. Diese topologisch geschützten, metallischen Oberflächenzustände sind gekennzeichnet durch eine masselose Dirac Dispersionsrelation und gekoppelte Helizität der Spinpolarisation, welche die Rückstreuung der Ladungsträger verbietet und somit zur Stabilisierung der Zustände gegenüber Störungen beiträgt. Auf Grundlage dieser außergewöhnlichen Merkmale haben Theoretiker eine Fülle neuer Phänomene und spannender Experimente vorhergesagt. Deren experimentelle Überprüfung steht jedoch noch aus, geschweige denn deren Umsetzung in Anwendungen, wie zum Beispiel die Erzeugung von Majorana Teilchen, fortgeschrittene Spintronik, oder die Realisierung von Quantencomputern. Aufgrund ihrer relativ einfachen Bandstruktur, welche nur einen Dirac-Kegel an der Oberfläche aufweist, haben die 3D TI Bi2Te3 und Bi2Se3 in den letzten Jahren großes Interesse erlangt. Weiterhin besitzen diese Materialien eine merkliche Bandlücke von bis zu ~0,3 eV, welche sogar Anwendungen bei Raumtemperatur ermöglichen könnten. Dennoch ist deren experimentelle Umsetzung nachwievor eine enorme Herausforderung. Das Haupthindernis, welches bis jetzt insbesondere die elektrische Charakterisierung the topologischen Oberflächenzustände behindert hat, ist die zusätzliche Leitfähigkeit des Materialinneren, welche durch Kristalldefekte und Beimischungen, sowie die Verunreinigung der Probenoberfläche durch Luftexposition bedingt wird. Die vorliegende Arbeit liefert einen Beitrag zu aktuellen den Anstrengungen in der Verbesserung der Probenqualität der TI um die Leitfähigkeit des Materialinneren zu unterdrücken, sowie die anschließende Untersuchung der elektrischen Eigenschaften unter kontrollierten Bedingungen durchzuführen. Weiterhin sollen geeignete Deckschichten identifiziert werden, welche die besonderen elektronischen Merkmale der TI nicht beeinflussen sowie diese gegen äußere Einflüsse schützen, und somit die Durchführung anspruchsvoller ex situ Experimente ermöglichen können. Die untersuchten Bi2Te3 Schichten wurden mittels Molekularstrahlepitaxie (MBE) hergestellt. Es konnte gezeigt werden, dass es allein durch Optimierung der Wachstumsbedingungen möglich ist Proben herzustellen, die gleichbleibend isolierende Eigenschaften des TI Inneren aufweisen und Eindomänen-Ausrichtung besitzen. Die zentralen Faktoren sind hierbei die Aufrechterhaltung eines Flussratenverhältnisses von Te/Bi ~8 der einzelnen Elemente, sowie die Wahl einer ausreichend hohen Substrattemperatur, um ein vollständiges Abdampfen (Destillation) des überschüssigen Tellur zu erreichen. Weiterhin müssen Substrate mit gut angepassten Gitterparametern verwendet werden, welches bei BaF2 (111) gegeben ist. Optimales MBE Wachstum konnte durch ein Zwei-Stufen Prozess bei Substrattemperaturen von 220°C und 250°C und einer Bi-Verdampfungsrate von 1 Å/min erreicht werden. Die nachfolgende Charakterisierung der strukturellen Eigenschaften, Photoelektronenspektroskopie, sowie temperaturabhängige Leitfähigkeitsmessungen wurden alle in einem zusammenhängenden Ultrahochvakuum-System durchgeführt. Auf diese Weise wird eine zuverlässige Erfassung der intrinsischen Eigenschaften der TI sichergestellt. Zur Überprüfung, ob die Leitfähigkeit der Proben tatsächlich nur durch die Oberflächenzustände hervorgerufen wird, wurden Filme mit Schichtdicken im Bereich von 10 bis 50 Quintupel-Lagen (QL; 1QL~ 1 nm) hergestellt und charakterisiert. Winkelaufgelöste Photoelektronenspektroskopie (ARPES) belegt, dass das chemische Potential (Fermi-Niveau) in allen Proben innerhalb der Bandlücke der Bandstruktur des Materialinneren liegt und nur von den topologisch geschützten Oberflächenzuständen gekreuzt wird, welche die charakteristische lineare Dirac Dispersionsrelation aufweisen. Die temperaturabhängigen Widerstandsmessungen zeigen ein metallisches Verhalten aller Proben. Bei der Variation der Schichtdicke von 10 zu 50QL wird eine Streuung des Flächenwiderstandes vom Faktor 1,3 bei 14K und 1,5 bei Raumtemperatur beobachtet. Dies beweist, dass die gemessene Leitfähigkeit vorrangig durch die topologisch geschützten Oberflächenzustände hervorgerufen wird. Eine geringe Oberflächenladungsträgerkonzentration im Bereich von 2–4*10^12 cm^−2 und hohe Mobilitätswerte von bis zu 4600 cm2/Vs wurden erreicht. Weiterhin wurden die negativen Auswirkungen auf die Eigenschaften der TI durch Luftexposition quantifiziert, welches die Notwendigkeit belegt, die Oberfläche der TI vor Umgebungseinflüssen zu schützen. Die Proben verhalten sich inert gegenüber reinem Sauerstoff, daher ist Wasser aus der Luftfeuchte höchstwahrscheinlich der Hauptgrund für die beobachtbare Verschlechterung. Darüber hinaus konnte epitaktisch gewachsenes Tellur als geeignete Deckschicht ausfindig gemacht werden, welches die Eigenschaften der Bi2Te3 Filme nicht beeinflusst, sowie gegen Veränderungen durch Luftexposition schützt. Die gewonnenen Erkenntnisse stellen eine ideale Grundlage für weiterführende Untersuchungen dar und ebnen den Weg zur Entwicklung von Bauelementen welche die spezifischen Besonderheiten der topologischen Oberflächenzustände.

Magnetisch-induktive Techniken finden seit langer Zeit viele Anwendungsfelder in der Medizin, Sicherheitstechnik und der Industrie. Obwohl die technischen Grundlagen seit vielen Jahrzehnten bekannt sind, werden auf Basis detaillierter Analysen spezielle Lösungsansätze verfolgt, die neuartiges Anwendungspotential erschließen sollen. Dazu dienen verbesserte Werkzeuge wie Computersimulationen und analytische Berechnungen sowie neu kombinierte Methoden und Aufbauten aus Leistungselektronik und Signaldetektion. Die Vorteile magnetisch-induktiver Techniken sind dabei u.a., dass sie das Prüfobjekt nicht schädigen, berührungslos arbeiten, robust gegenüber Verschmutzungen und einfach im Aufbau sind. Ein Nachteil dieser Technik ist die unzureichende Auflösung von feinen Strukturen. In der aktuellen Forschung und Entwicklung werden unterschiedliche Spulenanordnungen zur Anwendung in industriellen und medizinischen Fragestellungen untersucht und optimiert. Thema dieser Arbeit ist es, durch Verbesserung der Spuleneigenschaften, neue Anwendungsbereiche für die zerstörungsfreie Materialprüfung zu erschließen. Es wird eine Methode vorgestellt, die Eigenschaften magnetisch-induktiver Tastspulen zu verbessern und so den Aufwand bei der Signalverarbeitung zur Rekonstruktion im Rechner zu reduzieren sowie die Auflösung zu erhöhen. Dazu werden zwei Spulenanordnungen, Transmissions - Tastspulen und Gradiometer - Tastspulen, vergleichend gegenübergestellt und ihre technischen Grenzen aufgezeigt. / Magneto-inductive techniques are found in many fields of application areas so in medicine, security technology and industry. Although the technical basis has been known for many decades, special solutions are pursued on the basis of detailed analysis that should open new application potential. These are enhanced tools such as computer simulations, analytical calculations, new combined methods and structures of power electronics and signal detection. The advantages of magneto-inductive techniques are that they do not damage the test object, are contactless, robust against dirt and simple in construction. A disadvantage of this technique is the insufficient resolution of fine structures. In current research and development different coil assemblies are investigated in industrial and medical applications. The aim of this work is to improve the coil properties by changing geometric constructions and current patterns of the coils, in order to allow a sharper localization of objects in space and to tap new application areas for non-destructive testing. A method to improve the properties of magneto-inductive coils and thus to reduce the effort in signal processing and image reconstruction as well as to increase the resolution is presented. Two different coil assemblies, gradiometer – coils and transmission – coils, are compared and their technical limits shown.

In this age of wireless technology, Body Area networks (BAN) is revolutionising the concept of patient care and health monitoring. BAN provides people good assessment of their health status at any time, wherever they are physically. The increased interest in developing effective body (in, on & off) communication systems made phantoms which can mimic the electrical properties of an actual human body necessary. Wearable antennas which are the indispensable part of BAN got to be low pro file and above all influences that human body can make. There should also be a way to reduce the effect of antennas on human body namely specific absorption rate (SAR). In this work effort has been made to develop phantoms suitable for both On body and In body communications. The base materials which are selected for the study are of biological origin (bio ceramics and biopolymers) whose behaviour is closer to that of human tissues. As these phantoms are biocompatible they are essentially non toxic where the conventionally available phantoms are toxic in nature. Different kinds of low profile conformal wearable antennas working at 2.4GHz ISM band were developed and studied in the BAN perspective. Antennas suffer much in terms of matching and efficiency when they are in contact or in the premises of human body. This is a major hurdle in the way to setting up a good body communication network. This work encompasses various techniques adopted to limit the body interferences to an acceptable level. The techniques adopted (Such as Backing Ground Plane, High Impedance Surface & Polymeric Ferrite Sheets) proved to be effective in reducing the sway in antenna characteristics when they are mounted on body. Specific absorption rate is also brought to acceptable levels and thus avoiding the formation of hot spots due to microwave absorption. A safer and cost effective BAN can be set up using this work which will lead to a safer, mobile and healthy future. / Les réseaux BAN (Body Area Network) révolutionnent le concept de la surveillance et de la prise en charge à distance de la santé du patient. Le BAN fournit des informations sur l’état de santé du patient en temps réel quelque soit l’endroit où il se trouve. Dans le « télé monitoring », des capteurs de mouvement, de respiration ou du rythme cardiaque placés à l’intérieur ou sur le corps humain transmettent des données via le réseau sans fil constituant le BAN, une antenne étant associée à chaque nœud du réseau. La communication peut être in/on, on/on ou on/off selon que les antennes sont placées à l’intérieur, sur ou à l’extérieur du corps. Le développement des BAN nécessite la réalisation de modèles (ou fantômes) simulant au mieux les propriétés électromagnétiques du corps humain. Des antennes portables, miniaturisées doivent être réalisées avec des contraintes d’intégration d’une part (aux vêtements, à des objets type montre ou badge), des contraintes de résistance ou de prise en compte de l’influence du corps d’autre part. La réduction de l’impact des antennes sur les tissus en terme de SAR (Specific Absorption Rate) doit également être considérée. Dans ce travail, l’objectif est de développer des fantômes valables pour les communications dans et sur le corps. Les matériaux de base sélectionnés sont d’origine biologique (biocéramiques et biopolymères) avec des propriétés proches de celles des tissus humains. Ces fantômes étant biocompatibles, ils sont essentiellement non toxiques alors que les fantômes usuels le sont en général. D’autre part, différents types d’antennes conformables, fonctionnant dans la bande ISM 2.4 GHz ont été développées et étudiées dans la perspective du BAN. Les antennes voient leur adaptation et leur efficacité chuter au contact ou à proximité du corps, ce qui constitue un écueil majeur pour établir une bonne communication. Différentes méthodes permettant de réduire l’influence du corps (plan de masse à l’arrière, surface haute impédance, feuille de ferrite polymère) sont testés et leurs avantages et inconvénients développés. Des mesures de SAR permettent aussi de démontrer l’efficacité de ces méthodes sur la réduction de la puissance absorbée par les tissus. Au final, ce travail apporte une contribution à l’étude théorique et expérimentale de l’interaction entre corps humain et antenne dans le cadre des réseaux BAN appliqués à la télésurveillance de la santé.

No presente trabalho foi realizado o estudo das propriedades ópticas e elétricas de dispositivos eletroluminescentes poliméricos, conhecidos como diodos emissores de luz poliméricos (PLEDs), e o desenvolvimento de camadas transportadoras de carga (HTL), que visam promover um aumento da eficiência elétrica dos dispositivos. Para o estudo das propriedades ópticas e elétricas dos PLEDs, foram fabricados dispositivos com estruturas do tipo Ânodo/HTL/Polímero Eletroluminescente/Cátodo. Foram apresentadas todas as etapas de fabricação dos dispositivos, assim como seus processos de caracterização. Para o ânodo, foi utilizado um óxido transparente condutor, óxido de índio-estanho - ITO, com tratamento superficial em plasma de oxigênio. Foram estudados três materiais diferentes para as HTLs. Filmes de PAni:PVS ou PAni:Ni-TS-Pc foram depositados pela técnica de automontagem (Layer-by-Layer) e os filmes de PEDOT:PSS foram depositados pelo método de spin-coating. O polímero eletroluminescente utilizado neste trabalho foi o MEH-PPV, também depositado pelo método de spin-coating. Para o cátodo foi utilizado o alumínio, evaporado termicamente. O encapsulamento dos dispositivos foi realizado em atmosfera inerte de argônio para diminuir os efeitos de degradação através do oxigênio e da luz. O emprego de camadas transportadoras de buracos (HTLs) resultou numa sensível diminuição no valor da tensão de operação dos dispositivos, quando empregados filmes de PAni:PVS e PAni:Ni-TS-Pc. Os valores das tensões de operação baixaram de 12 V para cerca de 3 V em relação aos dispositivos fabricados sem a utilização de HTLs. Através da microscopia de força atômica, foi possível determinar a espessura das bicamadas e a rugosidade superficial dos filmes de PAni:PVS para correlacionar estes resultados com a resposta elétrica dos dispositivos. Espessuras de 4nm (para 1 bicamada) resultaram em tensões de operação de 3 V. Foi possível verificar também, por espectroscopia no UV-VIS, que este tipo de filme absorve luz em freqüência diferente daquela emitida pelo MEH-PPV. Medidas elétricas em regime de corrente contínua, curvas de Corrente vs. Tensão e, em regime de corrente alternada, espectroscopia de impedância, foram realizadas em dispositivos para determinar o valor da tensão de operação e estudar os efeitos de interface nas diferentes camadas que compõe um dispositivo. Através das curvas obtidas pela espectroscopia de impedância, foi possível determinar os valores dos componentes dos circuitos equivalentes (capacitores e resistores). Com isso, é possível simular o comportamento destes dispositivos através de circuitos elétricos antes mesmo de serem fabricados. Pelos resultados obtidos, todas as HTLs estudadas contribuíram para uma sensível diminuição no valor da tensão de operação dos dispositivos, apontando-os como excelentes materiais a serem utilizados com o objetivo de alcançar uma maior eficiência e um melhor desempenho destes dispositivos. / In the present work, the study of the optical and electrical properties of polymeric electroluminescent devices known as Polymer Light-Emitting Diodes (PLEDs) and the development of Hole Transport Layers (HTLs) to promote an increase of the electrical efficiency of the devices was performed. PLEDs were constructed with structures like Anode/HTL/Electroluminescent Polymer/Cathode in order to study the optical and electrical properties of these devices. All the stages of the devices production were presented, as well as its characterization processes. For the anode a conductive transparent oxide (Indium Tin Oxide - ITO) with a superficial oxygen plasma treatment was used. Three different materials for the HTLs were used. Films of PAni:PVS or PAni:Ni-TS-Pc were deposited by the self-assembly technique (Layer-by-Layer) and the films of PEDOT:PSS were deposited by the spin-coating method. The electroluminescent polymer used in this work was MEH-PPV, also deposited by the spin-coating method. Aluminum was deposited by thermal evaporation for the cathode. The devices encapsulation was performed in Argon inert atmosphere to reduce the degradation effects through oxygen and light. The use of Hole Transport Layers (HTLs) resulted in a sensitive decrease in the devices operating voltage value when films of PAni:PVS and PAni:Ni-TS-Pc were used. The operating voltage values have decreased from 12 V to 3 V in relation to the devices assembled without the usage of HTLs. By the use of Atomic Force Microscopy measurements the thickness of the bilayers and the surface roughness of the PAni:PVS films was obtained to correlate these results with the devices electric characteristics. Thicknesses of 3 to 4 nm (for one bilayer) resulted in operating voltage of 3 V. It was possible to verify also, by UVVIS Spectroscopy, that this type of PAni:PVS films absorbs light in a different frequency than that emitted by MEH-PPV. Electric measurements in the direct current, Current vs. Voltage curves and, in alternating current, Impedance Spectroscopy, were performed in devices to determine the operating voltage value and to study the interface effects in the different layers used in the devices. Analyzing the curves obtained by the impedance spectroscopy, it was possible to determine the values of the equivalent circuit components (capacitors and resistors) and, with that, to simulate the behavior of these devices through electric circuits even before they were manufactured. By the experimental results, all the HTLs studied have contributed to a sensitive decrease in the devices operating voltage, indicating them as excellent materials to be used to reach a higher efficiency and a better performance of these devices.

Die untersuchten Ferekristalle sind neuartige Verwachsungs-Schichtverbindungen aus m Monolagen von Niobdiselenid (NbSe2), die wiederholt mit n atomaren Bilagen von Bleiselenid (PbSe) oder Zinnselenid (SnSe) geschichtet sind. Niobdiselenid als Volumenmaterial besitzt eine Schichtstruktur und ist ein Supraleiter. Aufgrund ihrer gezielt einstellbaren atomar geschichteten Struktur können Ferekristalle als Modellsysteme für geschichtete Supraleiter dienen. In dieser Arbeit werden ihre strukturellen und elektrischen Eigenschaften untersucht. Mittels Transmissionselektronenmikroskopie wird ihre turbostratisch ungeordnete, nanokristalline Struktur nachgewiesen. Die atomare Struktur innerhalb der einzelnen Schichten ist ähnlich wie in den Volumenmaterialien NbSe2, PbSe und SnSe, wobei die kristallographischen c-Achsen parallel zur Stapelrichtung der Ferekristalle zeigen. Eine quantitative Analyse unter Verwendung eines Zwei-Schicht-Modells für den spezifischen Widerstand, Hall-Koeffizienten und Magnetwiderstand liefert ähnliche Ladungsträgersorten, -dichten und –beweglichkeiten in den NbSe2-Schichten, wie sie für isolierte Einzellagen von NbSe2 berichtet wurden. Diese unterscheiden sich von denen des Volumenmaterials NbSe2. Erstmals wurde ein Übergang der Ferekristalle in den supraleitenden Zustand nachgewiesen. Die Sprungtemperaturen sind dabei in etwa auf die Hälfte der Sprungtemperaturen der jeweiligen nicht turbostratisch ungeordneten Misfit-Schichtverbindungen reduziert. Diese Reduzierung kann der turbostratischen Unordnung der Ferekristalle zugeordnet werden. Das Verhältnis zwischen der schichtsenkrechten Ginzburg-Landau-Kohärenzlänge und dem Abstand zwischen den supraleitenden Schichten ist bei den Ferekristallen kleiner als bei den nicht ungeordneten Misfit-Schichtverbindungen, was Ferekristalle zu vielversprechenden Kandidaten für (quasi-)zweidimensionale Supraleiter macht. / The investigated ferecrystals are novel layered intergrowth compounds consisting of m monolayers of niobium diselenide (NbSe2) stacked repeatedly with n atomic bilayers of lead selenide (PbSe) or tin selenide (SnSe). Bulk NbSe2 is a layered compound showing superconductivity. Due to their artificially atomic-scale layered structure, which is tunable on the atomic scale, ferecrystals can serve as model systems for layered superconductors. In this study, their structural and electrical properties are investigated. Using transmission electron microscopy their turbostratically disordered, nanocrystalline structure is revealed. The atomic structure within the individual layers is similar as for bulk NbSe2, PbSe and SnSe, with the crystallographic c-axes parallel to the stacking direction in the ferecrystals. A quantitative analysis using a two-layer model fit for the electrical resistivity, Hall coefficient and magnetoresistance yields a similar carrier type, density and mobility in the NbSe2 layers as reported for isolated NbSe2 monolayers. These values differ from those of bulk NbSe2. For the first time, a normal-to-superconducting transition has been detected in ferecrystals. The transition temperatures of the ferecrystals are reduced to about a half of those of analogous non-disordered misfit layer compounds. This reduction in transition temperature can be correlated to the turbostratic disorder in ferecrystals. The ratio between the cross-plane Ginzburg-Landau coherence length and the cross-plane distance between the NbSe2 layers for the ferecrystals is lower than for non-disordered misfit layer compounds, making ferecrystals promising candidates for (quasi-)two-dimensional superconductors.