?rea de concentra??o: Produtos e coprodutos. / Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2017-10-03T14:42:21Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) wayler_silva_santos.pdf: 9149649 bytes, checksum: 7d300a18f29fb2d1bfa9a3ab5c806ad3 (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2017-10-09T14:02:32Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) wayler_silva_santos.pdf: 9149649 bytes, checksum: 7d300a18f29fb2d1bfa9a3ab5c806ad3 (MD5) / Made available in DSpace on 2017-10-09T14:02:32Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) wayler_silva_santos.pdf: 9149649 bytes, checksum: 7d300a18f29fb2d1bfa9a3ab5c806ad3 (MD5) Previous issue date: 2017 / Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM) / Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG) / A convers?o da energia da radia??o solar em H2(g), combust?vel verde, usando-se c?lulas fotoeletroqu?micas (PEC) ? uma estrat?gia atraente para armazenar energia e minimizar o uso extensivo de combust?veis f?sseis. Neste trabalho, foram fabricados fotoeletrodos por deposi??o spray pyrolysis de um comp?sito de BiVO4/Bi4V2O11 puro ou dopado com W, depositado diretamente sobre um substrato condutor FTO (sigla para fluorine-doped tin oxide) ou sobre uma camada de SnO2 previamente depositada sobre o substrato FTO. Inicialmente, os materiais foram testados na clivagem molecular da ?gua. Verificou?se a forma??o de uma camada de invers?o de buracos induzida pela perovskita ferroel?trica Bi4V2O11 na interface com BiVO4 de tipo?n criando uma jun??o p?n virtual. A fotovoltagem de sa?da elevada da jun??o, em rela??o a uma heterojun??o p?n convencional, que pode ser ainda aumentada alterando-se a polariza??o e dopando-se o material ferroel?trico com tungst?nio, acarreta diminui??o da recombina??o dos pares el?tron?buracos fotogerados na superf?cie e aumenta a fotocorrente em at? 180%. O comportamento de semicondutores de tipo?p e n quando iluminados sugere o uso potencial da heterojun??o como fotoanodo e fotocatodo em uma c?lula PEC (ou photoelectrochemical cell) com dois fotoeletrodos. Este conceito foi comprovado pela conex?o do fotoanodo BiVO4/Bi4V2O11 dopado com 1% em massa de tungst?nio com o fotocatodo BiVO4/Bi4V2O11 n?o dopado. O sistema formado pelo acoplamento fotoanodo-fotocatodo produziu uma fotovoltagem de 1,54 V, e 0,36% de efici?ncia STH (solar-to-hydrogen efficiency). Um fotoeletrodo BiVO4/Bi4V2O11 dopado com 2% em massa de W foi otimizado. Evidenciou-se a forma??o da camada de invers?o de buracos na interface semicondutora no filme mais denso. Este ?ltimo foi testado em diferentes solu??es, obtendo-se elevadas densidades de corrente em NaAc 0,5 mol L-1, ? medida que se adicionou glicerina e vinha?a. Obteve?se a menor resist?ncia na transfer?ncia de cargas na interface eletrodo/eletr?lito 1,16 k? sob ilumina??o, utilizando a solu??o NaAc 0,5 mol L-1 contendo 20 %v/v de vinha?a. Nessas condi??es, a efici?ncia da convers?o de energia foi aumentada em aproximadamente 100%, e dependendo do potencial aplicado a efici?ncia aumentou cerca de 30% em solu??o contendo 10 %v/v de glicerina, com rela??o ? solu??o NaAc 0,5 mol L-1 pura, demonstrando que glicerina e vinha?a atuam como agentes de sacrif?cio eficazes no sequestro de buracos eletr?nicos, para evitar a recombina??o dos pares de el?tron?buraco, no processo de foto?oxida??o acionado por buracos. / Tese (Doutorado) ? Programa de P?s-gradua??o em Biocombust?veis, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / The conversion of solar energy into green fuel H2(g) using photoelectrochemical cells (PEC) is an attractive strategy for storing energy and minimizing the extensive use of fossil fuels. In this work, photoelectrodes were prepared by pyrolysis spray deposition from a pure or W?doped BiVO4/Bi4V2O11 composite deposited directly onto an FTO (fluorine-doped tin oxide) electron-conductive substrate or onto a SnO2 layer previously deposited on an FTO substrate. Initially, these materials were tested for molecular water cleavage. It was observed a hole inversion layer induced by the ferroelectric perovskite Bi4V2O11 at the interface of the n?type BiVO4; a virtual p?n junction with high output photovoltage in relation to a conventional p?n heterojunction was also created. Altering the polarization and doping the ferroelectric material with tungsten may increase the p-n heterojunction. This polarization also reduces the recombination of the photogenerated electron?hole pairs on the surface, to increase the photocurrent to as much as 180%. This characteristic behavior of the p?type and n?type semiconductors when illuminated suggests the use of such a heterojunction as photoanode and photocatode in a PEC cell with two coupled photoelectrodes. This concept was proved to effectively work, by connecting the photovoltaic BiVO4/Bi4V2O11 doped with 1 mass% of W to the non?doped BiVO4/Bi4V2O11 photocathode, which produced a high photovoltage of 1.54 V, and 0.36% STH (solar-to-hydrogen) efficiency. A BiVO4/Bi4V2O11 photoelectrode doped with 2 mass% tungsten was optimized, evidencing the inversion of the hole layer at the semiconductor interface in the resulting denser film. This film tested in different liquid solutions revealed to produce high current densities in 0.5 mol L-1 sodium acetate (NaAc), if glycerol and vinasse were added. The electric resistance in the charge transfer at the electrode/electrolyte interface was relatively low, or 1.16 k? under illumination using 0.5 mol L-1 NaAc solution containing 20 %v/v vinasse. Adding vinasse meant an increase of the energy conversion efficiency corresponding to approximately 100%, and depending on the applied potential efficiency increased by about 30% in solution containing 10% v/v glycerin, relatively to the pure 0.5 mol L-1 NaAc solution. These results evidence that glycerin and vinasse act as effective sacrificing agents, to sequester holes and avoid the recombination of electron?hole pairs in the photo?oxidation driven by holes.

L'objectif de cette thèse porte sur la fabrication et la caractérisation de cellules solaires à jonction radiale à base d'assemblée de nanofils de silicium cristallin. Une étude sur la croissance des nanofils à partir de deux catalyseurs métalliques (cuivre et aluminium) dans une machine de dépôt chimique en phase vapeur (CVD) à pression réduite est présentée. L'influence des conditions de croissance sur la morphologie, le dopage et la contamination des nanofils par le catalyseur est analysée par des mesures électriques, chimiques (SIMS, Auger) et structurales (SEM, TEM, Raman). Le cuivre est utilisé pour la fabrication d'une cellule solaire avec des nanofils de type p et une jonction radiale créée avec du silicium amorphe de type n. Les performances photovoltaïques de la cellule solaire sont ensuite mesurées et interprétées. Un rendement de conversion de 5% est mesuré sur une cellule avec des nanofils de hauteur 1,5µm. / The objective of this PhD is the study of the fabrication and characterization of radial junction solar cells based on crystalline silicon nanowires. A study of the nanowire growth with two metallic catalysts (copper and aluminum) in a reduced pressure chemical vapor deposition system is presented. The influence of the growth conditions on the morphology, doping density and catalyst contamination inside the nanowires is analyzed by electrical, chemical (SIMS) and structural (SEM, TEM, Raman) characterizations. Copper catalyst is used to fabricate a solar cell with p-type nanowire with a radial junction created by n-type amorphous silicon (a-Si:H) deposition. Photovoltaic performances are measured and interpreted. A conversion efficiency of 5% is measured on a solar cell with 1.5µm high silicon nanowires.

Le développement des énergies renouvelables est aujourd’hui devenu un enjeu mondial majeur comme alternative aux énergies fossiles dans la production d'énergie. Parmi elles, l’énergie solaire est considérée comme la source la plus prometteuse, permettant de couvrir l’ensemble des besoins énergétiques liés à l’activité humaine. Les cellules photovoltaïques les plus performantes aujourd’hui, entre 16 et 18 % en modules, sont composées de silicium, un semi-conducteur inorganique. Cependant, leur coût de production élevé a nécessité le développement de matériaux alternatifs moins couteux. Parmi les voies explorées, les cellules solaires organiques ont émergé comme une alternative prometteuse pour produire l’électricité à faible coût. Le sujet de cette thèse s’intègre dans ce contexte de recherche. Deux types de cellules solaires ont été étudiés : les cellules à hétérojonction en volume (BHJ) et sensibilisées au colorant (DSSCs). Le courant photogénéré repose généralement (i) dans les cellules BHJ, sur le transfert entre de charge entre un polymère donneur et un accepteur d’électrons (fullerène), tels que le couple poly(3-hexyl)thiophène (P3HT) et [6,6]-phényl-C61-butanoate de méthyle (PCBM), et (ii) dans les DSSCs, la sensibilisation de la surface d’un semi-conducteur inorganique tel que l’oxyde de titane par un colorant et la présence d’un électrolyte, jouant le rôle de médiateur redox. Bien qu’ayant atteint des rendements de photoconversion respectifs de 5 et 13 %, ces cellules nécessitent des améliorations pour une commercialisation à grande échelle. Tout d’abord, les performances des cellules BHJ à base de P3HT sont considérablement limitées par sa faible absorption, ne couvrant pas la globalité du spectre solaire. Afin de palier ce problème, nous avons combiné le P3HT avec des chromophores, i.e. des porphyrines, ayant une absorption plus étendue. Ensuite, pour assurer une meilleure extraction des charges au sein du dispositif, une couche interfaciale cathodique à base de polyélectrolytes pi-conjugués a été ajoutée. Enfin, des colorants extraits de la biomasse ont été préparés afin de remplacer les colorants coûteux à base de ruthénium. En outre, les électrolytes liquides étant volatils et corrosifs, ce qui limite considérablement la stabilité des DSSCs, des électrolytes solides à base de polymères ont été étudiés comme alternative. / Among renewable energies, the sunlight has by far the highest theoretical potential to meet the worldwide need in energy. Photovoltaic devices are thus currently the subject of intense research for low-cost conversion of sunlight into electrical power. In particular, organic photovoltaics have emerged as an interesting alternative to produce electricity due to their low manufacturing cost compared to silicon solar cells, their mechanical flexibility and the versatility of the possible chemical structures. In this dissertation, we focused our research on the development of new organic pi-conjugated materials for organic solar cells applications. Two types of solar cells have been studied during this work: bulk heterojunction and dye-sensitized solar cells. The charge transfer leading to the photocurrent is usually based on (i) a polymer donor and a fullerene acceptor in BHJ solar cells, such as the widely studied poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) materials and (ii) a metal oxide (titanium oxide) sensitized with a dye and an electrolyte in DSSCs. Despite power conversion efficiencies have reached 5 and 13 % respectively for these two types of devices, they still display several drawbacks that limit their commercialization. P3HT displays a narrow absorption of the solar spectrum thus limiting the conversion efficiency. To overcome this limitation, we combined P3HT with chromophores, i.e. porphyrins, having an extending absorption. Then, to ensure better charge transfer and extraction within the device, a cathode interfacial layer based on cationic pi-conjugated polyelectrolytes was added. Finally, dyes extracted from the biomass (chlorophyll a derivatives) were synthesized to replace the expensive ruthenium dyes in DSSCs. Since liquid electrolytes are volatile and corrosive, which considerably limit the DSSCs stability, solid polymer electrolytes were also developed as an alternative.

La constante amélioration des technologies silicium permet aux transistors bipolaires à hétérojonction (HBT) SiGeC (Silicium-Germanium : Carbone) de concurrencer les composants III-V pour les applications millimétriques et sous-THz (jusqu’à 300GHz). Le cycle de développement de la technologie (caractérisation-modélisation-conception-fabrication) nécessite plusieurs itérations, entraînant des coûts élevés. De plus, les méthodologies de mesure doivent être réévaluées et ajustées pour adresser des fréquences plus élevées. Afin de réduire le nombre d’itérations et de permettre la montée en fréquence de la mesure, un travail de fond sur la première étape, la caractérisation, s’avère indispensable.Pour répondre à cette exigence, une description et une étude des instruments de mesure (VNA) est réalisée dans un premier temps. Un état de l’art des méthodes de calibrage permet de choisir la solution la plus pertinente pour la calibration sur puce valable dans la gamme de fréquences sous-THz. Ensuite, après avoir relevé plusieurs défauts dans la méthode choisie (à savoir la méthode Thru-Reflect-Line : TRL), des solutions sont proposées concernant la modification des calculs des coefficients d’erreur et également en modifiant les standards utilisés durant le calibrage. Finalement, une étude sur les méthodes d’épluchage est réalisée. Une amélioration est proposée par la modification de deux standards évitant le principal problème de l’état de l’art, la surcompensation des composants parasites. / The continuous improvement in Silicon technologies allows SiGeC (Silicon-Germanium-Carbon) heterojunction bipolar transistors (HBT) to compete with III-V components for millimeter wave and sub-THz (below 300GHz) applications. The technology development cycle (characterization, modeling, design and fabrication) needs several iterations resulting in high costs. Furthermore, the measurement methodologies need to be re-assessed and modified to address higher measurement frequencies. In order to reduce the number of iterations and to allow reliable measurement in the sub-THz band, the characterization procedure has been revisited.First, a description and investigation of the measurement instrument (VNA) has been made. After exploring all possible calibration methods, the best candidate for an “on-wafer” calibration for the sub-THz frequency range has been selected. Then, after analyzing the limits of the chosen calibration method (Thru-Reflect-Line: TRL), workarounds are proposed, by modification of the errors coefficients calculation and by changing the standards used during the calibration process. At last, a study concerning the de-embedding methods is carried out. It is shown, that using two new standards helps to reduce the over-compensation of parasitic components.

The properties of bulk 3D materials of metals or semiconductors are manifested with various length scales(e.g., Bohr excitonic radius, magnetic correlation length, mean free path etc.) and are important in controlling their properties. When the size of the material is smaller than these characteristics length scales, the confinement effects operate reflecting changes in their physical behavior. Materials with such confinement effects can be designated as low dimensional materials. There are exceedingly large numbers of low dimensional materials and the last half a century has probably seen the maximum evolution of such materials in terms of synthesis, characterization, understanding and modification of their properties and applications. The field of” nanoscience and nanotechnology”, have become a mature field within the last three decades where, for certain application, synthesis of materials of sizes in the nanometer range can be designed and controlled. Interface plays a very important role in controlling properties of heterogeneous material of every dimensionality. For example, the interface forms in 2D thin films or interface of heterogeneous nanoparticles(0D). In recent times, a large number of remarkable phenomena have triggered understanding and controlling properties arises due to nature of certain interface. In the field of nanoparticles, it is well known that the photoluminescence property depends very strongly on the nature of interface in heterostructured nanoparticles. In the recent time a large variety of heterostructured nanoparticles starting from core-shell to quantum dot-quantum well kind has been synthesized to increase the photoluminescence efficiency up to 80%. Along with improvement of certain properties due to heterostructure formation inside the nanoparticles, the techniques to understand the nature of those interfaces have improved side by side. It has been recently shown that variable energy X-ray Photoemission Spectroscopy (XPS) can be employed to understand the nature of interfaces (internal structure) of such heterostructure nanoparticles in great detail with high accuracy. While most of the previous studies of variable energy XPS, uses photonenergies sensitive to smaller sized particle, we have extended the idea of such nondestructive approach of understanding the nature of buried interfaces to bigger sized nanoparticles by using photon energy as high as 8000eV, easily available in various 3rd generation synchrotron centers. The nature of the interface also plays an important role in multilayer thin films. Major components of various electronic devices, like read head memory devices, field effect transistors etc., rely on interface properties of certain multilayer thin film materials. In recent time wide range of unusual phenomenon such as high mobility metallic behavior between two insulating oxide, superconductivity, interface ferroelectricity, unusual magnetism, multiferroicity etc. has been observed at oxide interface making it an interesting field of study. We have shown that variable energy photoemission spectroscopy with high photon energies, can be a useful tool to realize such interfaces and controlling the properties of multilayered devices, as well as to understand the origin of unusual phenomenon exists at several multilayer interfaces. Chapter1 provides a brief description of low dimensional materials, overall perspective of interesting properties in materials with reduced dimensionality. We have emphasized on the importance of determining the internal structure of buried interface of different dimensionalities. We have given a brief overview and importance of different interfaces that we have studied in the subsequent chapters dealing with specific interfaces. Chapter 2 describes experimental and theoretical methods used for the study of interface and self-assembly reported in this thesis. These methods are divided into two categories. The first section deals with different experimental techniques, like, UV-Visible absorption and photoluminescence spectroscopy, X-Photoelectron Spectroscopy(XPS), X-Ray diffraction, Transmission Electron Microscopy(TEM) etc. This section also includes brief overview on synchrotron radiation and methods used for detail analysis of interface structure using variable energy XPS. In the second part of this chapter, we have discussed theoretical methods used in the present study. \ In Chapter 3A we have combined low energy XPS, useful to extract information of the surface of the nanoparticles, with high energy XPS, important to extract bulk information and have characterized the internal structure of nanoparticle system of different heterogeneity. We have chosen two important heterostructure systems namely, inverted core-shell(CdScore-CdSeshell) type nanoparticles and homogeneous alloy(CdSeS)type nanoparticles. Such internal structure study revealed that the actual internal structure of certain nanomaterial can be widely different from the aim of the synthesis and knowledge of internal structure is a prerequisite in understanding their property. We were able to extend the idea of variable energy XPS to higher energy limit. Many speculations have been made about the probable role of interface in controlling properties, like blinking behavior of bigger sized core-shell nanoparticles, but no conclusive support has yet been given about the nature of such interface. After successfully extending the technique to determine the internal structure of heterostructured nanoparticles to very high photon energy region, we took the opportunity to determine the internal structure of nanoparticles of sizes as large as 12nm with high energy photoemission spectroscopy for the first time. In Chapter 3B we emphasize on the importance of interface structure in controlling the behavior of bigger sized nanoparticles systems, the unsettled issues regarding their internal structure, and described the usefulness of high energy XPS in elucidating the internal structure of such big particles with grate accuracy to solve such controversies. The existence of high density storage media relies on the existence of highly sensitive magnetic sensors with large magnetoresistance. Today almost all sensor technologies used in modern hard disk drives rely on tunnel magnetoresistance (TMR) CoFeB-MgO-CoFeB structures. Though device fabrication is refined to meet satisfactory quality assurance demands, fundamental understanding of the refinement in terms of its effect on the nature of the interfaces and the MgO tunnel barrier leading to improved TMR is still missing. Where, the annealing condition required to improve the TMR ratio is itself not confirmatory its effect on the interface structure is highly debatable. In particular, it has been anticipated that under the proposed exotic conditions highly mobile B will move into the MgO barrier and will form boron oxide. In Chapter 4 we are able to shed definite insights to heart of this problem. We have used high energy photoemission to investigate a series of TMR structures and able to provide a systematic understanding of the driving mechanisms of B diffusion in CoFeBTMR structures. We have solved the mix-up of annealing temperature required and have shown that boron diffusion is limited merely to a sub-nanometer thick layer at the interface and does not progress beyond this point under typical conditions required for device fabrication. We have given a brief overview on the evolution of magnetic storage device and have described various concepts relevant for the study of such systems. The interface between two nonmagnetic insulators LaAlO3 and SrTiO3 has shown a variety of interface phenomena in the recent times. In spite of a large number of high profile studies on the interface LaAlO3 and SrTiO3 there is still a raging debate on the nature, origin and the distribution of the two dimensional electron gas that is supposed to be responsible for its exotic physical properties, ranging from unusual transport properties to its diverse ground states, such as metallic, magnetic and superconducting ones, depending on the specific synthesis. The polar discontinuity present across the SrTiO3-LaAlO3 interface is expected to result in half an electron transfer from the top of the LaAlO 3 layer to each TiofSrTiO3 at the interface, but, the extent of localization that can make it behave like delocalized with very high mobility as well as localized with magnetic moments is not yet clear. In Chapter 5 we have given a description of this highly interesting system as well as presented the outcome of our depth resolved XPS investigation on several such samples synthesized under different oxygen pressure. We were able to describe successfully the distribution of charge carriers. While synthesizing and understanding properties of nanoparticles is one issue, using them for device fabrication is another. For example, to make a certain device often requires specific arrangements of nanoparticles in a suitable substrate. Self-assembly formation can be a potential tool in these regards. Just like atom or ions, both nano and colloidal particles also assemble by themselves in ordered or disordered structure under certain conditions, e.g., the drying of a drop of suspension containing the colloid particles over a TEM grid. This phenomenon is known as self-assembly. Though, the process of assembly formation can be a very easy and cost-effective technique to manipulate the properties in the nano region, than the existing ones like lithography but, the lack of systematic study and poor understanding of these phenomena at microscopic level has led to a situation that, there is no precise information available in literature to say about the nature of such assembly. In Chapter 6 we have described experiments that eliminate the dependence of the self-assembly process on many complicating factors like substrate-particle interaction, substrate-solvent interaction etc., making the process of ordering governed by minimum numbers of experimental parameter that can be easily controlled. Under simplified conditions, our experiments unveil an interesting competition between ordering and jamming in drying colloid systems similar to glass transition phenomenon Resulting in the typical phase behavior of the particles. We establish a re-entrant behavior in the order-disorder phase diagram as a function of particle density such that there is an optimal range of particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory. In summary, we were able to extend the idea of variable energy XPS to higher energy limit advantageous for investigating internal structure of nonmaterial of various dimensionalities and sizes. We were able to comprehend nature of buried interface indicating properties of heterostructures quantum dots and thin films. Our study revealed that depth resolved XPS combined with accessibility of high and variable energies at synchrotron centers can be a very general and effective tool for understanding buried interface. Finally, we have given insight to the mechanism of spontaneous ordering of nanoparticles over a suitable substrate.

Le principal objectif de ce travail est d’étudier les cellules solaires organiques de type hétérojonction en volume à l’aide d’un modèle bidimensionnel spécifique incluant un état intermédiaire pour la dissociation des charges dans les matériaux organiques. Ce modèle est mis en place dans un logiciel de simulation par éléments finis. Après validation, il est comparé à deux approches existant dans la littérature. Le grand nombre de paramètres requis pour décrire le mécanisme complexe de génération de charges nécessite un algorithme robuste, basé sur l’exploitation de chaînes de Markov, pour extraire ces paramètres physiques à partir de données expérimentales. Le modèle ainsi que la procédure d’extraction de paramètres sont utilisés dans un premier temps pour étudier le mécanisme de dissociation associé à une cellule comportant une nouvelle molécule. Ensuite le comportement en température de cellules à base de P3HT : PCBM est simulé et comparé à des mesures expérimentales. / The main objective of this work is to study bulk heterojunction organic solar cells with a specific two dimensional model that takes into account an intermediate state specific to organic materials. The model is solved numerically by a finite element software. After its validation, it is compared to two existing approaches in the literature. The large number of parameters needed to describe the complex charge generation mechanism requires a robust parameter extraction algorithm, based on the operation of Markov chains, in order to extract these physical parameters from experimental characterizations. The model and the parameter extraction method are then used to study the charge dissociation mechanism of a cell with a newly synthesized molecule. Finally, the temperature evolution of P3HT : PCBM solar cells are simulated and compared to experimental measurements.

L’objectif de cette étude était d’obtenir un capteur à bas coût, fonctionnant à température ambiante, et permettant d’obtenir une information sur la concentration d’ammoniac d’une atmosphère, sans tenir compte de l’humidité. Cela implique une très faible sensibilité à l’humidité et une faible synergie entre l’eau et l’ammoniac.Au terme d’une étude sur la mise en forme de films hybrides hydrophiles, par un procédé « propre » dans l’eau, un capteur a été développé, par un assemblage en couche par couche de polyélectrolytes hydrophiles, la polyaniline et la phtalocyanine tétrasulfonée de cuivre : PANI/TsPcCu. Ce capteur présente une limite de détection d’ammoniac inférieure au ppm et une très faible sensibilité à l’eau, permettant de détecter l’ammoniac sans informations sur l’humidité de l’air.De nouveaux dispositifs, basés sur un mode de transduction breveté, ont été étudiés : les heterojonctions MSDIs (Molecular Semiconductor-Doped Insulator). Ces dispositifs sont formés de deux couches superposées, une sous-couche isolante de type n, F16PcCu ou le PTCDA, et une couche supérieure semi-conductrice de type p, Pc2Lu. L’importance de la jonction entre les deux matériaux, mais aussi de la jonction entre les électrodes et la sous-couche, a été démontrée à l’aide de mesures d’impédances. Les propriétés capteurs des dispositifs MSDI ont été étudiées par exposition à l’ammoniac sur une large gamme d’humidité. Ils présentent une très faible sensibilité à l’eau et permettent de détecter des concentrations d’ammoniac inférieures au ppm. Suite au développement d’un banc de mesures spécifique permettant l’affinage de fromages, celui-ci a pu être suivi par des mesures capteur avec un résistor de PcCo et par GC-MS. Ces mesures ont mis en évidence l’intérêt de tels capteurs pour suivre l’évolution de la maturation des fromages. / The aim of this study was to obtain a low cost sensor, working at room temperature, capable to obtain an information about the ammonia concentration without any information about the humidity. These characteristics imply a very low sensitivity to humidity and a low cross sensitivity between humidity and ammonia.After a study on material processing of hydrophilic films using water as solvent, a sensors has been developed by using layer by layer assembly of polyelectrolytes, such as polyaniline and the tetrasulfonated copper phthalocyanine: PANI/TsCuPc. This sensor is able to detect sub ppm ammonia concentration, with a very low cross sensitivity between ammonia and water which allow ammonia sensing without any information about the humidity.New devices based on a patented transduction method were studied: the MSDIs heterojunctions (Molecular Semiconductor-Doped Insulator). This kind of device is prepared with two different layers, a sub layer of an n-type insulator, F16CuPc or PTCDA, and an upper layer of a p-type semiconductor, LuPc2. The importance of the junction between both materials and between the sub layer and the electrodes were studied by using ammonia exposure on a large humidity range. They exhibit a very low sensitivity to humidity and allow sub ppm ammonia sensing whatever the humidity is.A specific workbench has been developed and tested in the laboratory, to follow cheese ripening by using CoPc gas sensors and gas chromatography. These measurements showed readiness to the use of the kind of gas sensors for the follow up of dairy products.

La théorie, la conception, l'optimisation et la caractérisation d'amplificateurs distribués en technologie TBDH InP 0,7 µm, pour les systèmes de communications optiques à 100 Gbit/s, sont présentés. Nous montrons comment l'exploitation adaptée du concept d'amplificateur distribué avec une technologie de transistors bipolaires à produit vitesse-amplitude élevé a permis la réalisation d'un driver de modulateur électro-optique fournissant une amplitude différentielle d'attaque de 6,2 et 5,9 Vpp, à 100 et 112 Gbit/s, respectivement, avec une qualité de signal élevée. Ce circuit établit ainsi le record de produit vitesse-amplitude à 660 Gbit/s.V sur tranche et 575 Gbit/s.V en module hyperfréquence. Dans le cadre du projet Européen POLYSYS, il a été associé à un laser accordable et un modulateur pour la réalisation d'un module transmetteur optoélectronique compact, démontrant des performances avançant l'état de l'art des communications optiques courtes distances à 100 Gbit/s. / The theory, design, optimisation and characterisation of distributed amplifiers in 0.7-µm InP DHBT technology, for 100-Gbit/s optical communication systems, are presented. We show how the appropriate implementation of the distributed amplifier concept in a bipolar transistors technology with high swing-speed product has enabled the realisation of an electro-optic modulator driver with 6.2- and 5.9-Vpp differential driving amplitude at 100 and 112 Gb/s, respectively, with a high signal quality. This circuit thus establishes the swing-speed product record at 660 Gb/s.V on wafer and at 575 Gb/s.V in a microwave module. In the frame of the European project POLYSYS, it has been co-packaged with a tunable laser and a modulator to realise a compact optoelectronic transmitter module, which has demonstrated performances advancing the state of the art of short reach 100-Gb/s optical communications.

Organic solar cells have great potential for cost-effective and large area electricity production, but their applicability is limited by the relatively low efficiency. In this dissertation I report investigations of novel materials and the underlying principles of organic solar cells, carried out at the University of St Andrews between 2011 and 2015. Key results of this investigation: • The charge carrier mobility of organic semiconductors in the active layer of polymer solar cells has a rather small influence on the power conversion efficiency. Cooling solar cells of the polymer:fullerene blend PTB7:PC₇₁BM from room temperature to 77 K decreased the hole mobility by a factor of thousand but the device efficiency only halved. • Subphthalocyanine molecules, which are commonly used as electron donor materials in vacuum-deposited active layers of organic solar cells, can, by a slight structural modification, also be used as efficient electron acceptor materials in solution-deposited active layers. Additionally these acceptors offer, compared to standard fullerene acceptors,advantages of a stronger light absorption at the peak of the solar spectrum. • A low band-gap polymer donor material requires a careful selection of the acceptor material in order to achieve efficient charge separation and a maximum open circuit voltage. • Metal structures in nanometer-size can efficiently enhance the electric field and light absorption in organic semiconductors by plasmonic resonance. The fluorescence of a P3HT polymer film above silver nanowires, separated by PEDOT:PSS, increased by factor of two. This could be clearly assigned to an enhanced absorption as the radiative transition of P3HT was identical beside the nanowires. • The use of a processing additive in the casting solution for the active layer of organic solar cells of PTB7:PC₇₁BM strongly influences the morphology, which leads not only to an optimum of charge separation but also to optimal charge collection.

The research conducted in this dissertation studies the issues regarding the improvement of phase noise performance in a BiCMOS Silicon Germanium (SiGe) cross-coupled differential-pair voltage controlled oscillator (VCO) in a narrowband application as a result of a tail-current shaping technique. With this technique, low-frequency noise components are reduced by increasing the signal amplitude without consuming additional power, and its effect on overall phase noise performance is evaluated. The research investigates effects of the tail-current as a main contributor to phase noise, and also other effects that may influence the phase noise performance like inductor geometry and placement, transistor sizing, and the gain of the oscillator. The hypothesis is verified through design in a standard 0.35 μm BiCMOS process supplied by Austriamicrosystems (AMS). Several VCOs are fabricated on-chip to serve for a comparison and verify that the employment of tail-current shaping does improve phase noise performance. The results are then compared with mathematical models and simulated results, to confirm the hypothesis. Simulation results provided a 3.3 dBc/Hz improvement from -105.3 dBc/Hz to -108.6 dBc/Hz at a 1 MHz offset frequency from the 5 GHz carrier when employing tail-current shaping. The relatively small increase in VCO phase noise performance translates in higher modulation accuracy when used in a transceiver, therefore this increase can be regarded as significant. Parametric analysis provided an additional 1.8 dBc/Hz performance enhancement in phase noise that can be investigated in future works. The power consumption of the simulated VCO is around 6 mW and 4.1 mW for the measured prototype. The circuitry occupies 2.1 mm2 of die area. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted