Dispositivos fotovoltaicos híbridos baseados em polímeros conjugados e semicondutores inorgânicos estão sendo utilizados nos últimos anos para a produção de células de energia solar com baixo custo. Para que haja uma alta eficiência é necessária dissociação eficiente de éxcitons, por isso é importante conhecer os níveis de energias dos componentes do dispositivo fotovoltaico. O presente estudos mostra que o sistema híbrido formado por nanofios cilíndricos preparados com heteroestrutura radial de camadas alternadas de GaAs/AlGaAs/GaAs recobertas com polímero conjugado poli-fenileno vinileno (PPV) forma uma opção alternativa para a fabricação de dispositivos fotovoltaicos. Os nanofios foram fabricados por Epitaxia por Feixe Molecular (MBE). Tanto potencial interno radial e modulação energética axial produzem a separação eficiente de elétrons e buracos fotoexcitados, que gera emissões de natureza e origem distintas e singulares nos nanofios: emissões envolvendo a impurezas aceitadoras no centro do núcleo de GaAs, bem como éxcitons indiretos presos a interface WZ e BZ e a interface da barreira estreita de AlGaAs na casca do nanofio. Medidas do decaimento temporal da emissão mostram uma forte dependência tempo de vida com o comprimento de onda, o que está associado com o afunilamento e distribuição energética destes estados emissivos. Medidas da emissão com a temperatura dão forte evidencia experimental de que a energia de ligação das impurezas tem uma forte dependência na direção radial. Este sistema híbrido funciona como coletor eficaz de luz tanto no visível quanto no infravermelho próximo. O trabalho demonstra também por espectroscopia resolvida no tempo que éxcitons são dissociados nas interfaces formadas por filmes ultrafinos de polímeros conjugados e nanofios e que esse material à base de arseneto de gálio (GaAs) atua como um forte receptor e separador de elétrons (alta afinidade eletrônica). / Hybrid photovoltaic devices based on conjugated polymers and inorganic semiconductors are being used in recent years to the production of solar cells at low cost. So there is a high efficiency is required efficient exciton dissociation, so it´s important to know the levels of energy of the components of the photovoltaic device. The present studies show that the hybrid system formed by cylindrical radial heterostructure nanowires prepared from alternating layers of GaAs / AlGaAs / GaAs covered with the conjugated polymer poly-phenylene vinylene (PPV) forms an alternative option for the manufacture of photovoltaic devices. Nanowires were manufactured by Molecular Beam Epitaxy (MBE). Both radial and axial inner potential energy modulation produce the efficient separation of electrons and photoexcited holes, which generates distinct and unique nature and source emissions in nanowires: emissions involving the acceptor impurities in the center core of GaAs and indirect excitons attached to the interface WZ and BZ and narrow barrier interface of AlGaAs on the shell of the nanowire. Measures the time decay of the issue show a strong dependence lifetime with the wavelength, which is associated with the bottleneck and energy distribution of emissive states. Emission measurements with temperature provide strong experimental evidence that the impurity binding energy has a strong dependence on the radial direction. This hybrid system works as an efficient collector of light both in the visible and near infrared. The work also shows for time resolved spectroscopy that excitons are dissociated at the interfaces formed by ultrathin conjugated polymers and films and nanowires that this material based on gallium arsenide (GaAs) acts as a strong receiver and electrons separator (high electron affinity ).

Este trabalho visa o desenvolvimento de um sistema de controle, para permitir a dirigibilidade de um veículo automotor, por meio do acionamento de um joystick por um usuário, que substitui o volante e os pedais do acelerador e do freio. Foi construída uma placa de controle, que recebe os sinais de controle tais como esterçamento, aceleração e frenagem vindos do joystick operado pelo usuário, processa esses sinais e aciona eletronicamente os atuadores mecânicos no volante da direção, no servo freio e no acelerador, permitindo o controle dinâmico do veículo. Para testar esse sistema de controle foi desenvolvido um simulador de dinâmica veicular, que fornece em tempo real, as respostas dinâmicas de um veículo quando solicitado pelo usuário, por meio de comandos de direção, aceleração e frenagem. Associada ao referido simulador foi desenvolvida uma bancada de testes, que inclui os atuadores mecânicos, sensores, placa de controle e o joystick, que são testados em tempo real por um usuário, dirigindo um veículo com o auxílio do simulador em uma estrada virtual, realizando manobras como curvas, acelerações e frenagens variadas. Durante os testes mencionados foi encontrada uma série de falhas, que comprometiam a segurança e a dirigibilidade do veículo. Com base nessas falhas foi construída uma árvore de falhas, para o sistema proposto, cuja falha principal era a perda da dirigibilidade do veículo. Partindo da análise qualitativa da árvore de falhas foi proposta uma série de ações corretivas, visando manter o sistema no âmbito da dirigibilidade segura, para o usuário. Finalmente, uma proposta de um protocolo de segurança, para desenvolvimento de sistemas drive-by-wire é sugerida tendo como base o desenvolvimento deste trabalho. / This work aims the development of a control system, to allow the handling of a automotive vehicle, by moving a joystick, which replaces the steering wheel, accelerator and braking pedals and is operated by a user. An electronic control board was built to receive control signals, such as steering, acceleration and braking signals, using a joystick handled by a user. It converts those signals and activates the mechanical actuators in the steering wheel, brake booster and accelerator, to allow the dynamic control of the vehicle. To test that control system, it was developed a vehicle dynamics simulator, which provides, in real time, the dynamics responses of a vehicle when driven by a user, by steering, braking and accelerating commands. Together with the simulator it was developed a test bench, with mechanical actuators, sensors, a control board and a joystick, which were tested in real time, by a user driving a vehicle with the assistance of the simulator, on a virtual road, performing maneuvers like curves, accelerations and varied braking. During the test it was found a series of faults, which affected the safety and driveability of the vehicle. Based on these faults, it was built a fault tree, to the proposed system, whose main fault was the loss of driveability of the vehicle. Based on the qualitative analysis of the fault tree, it was proposed a series of corrective actions, in order to keep the system on scope of the safe driveability. Finally, a proposal for a safety protocol for drive-by-wire systems was made, based on the development of this work.

Existe um grande interesse nos nitretos de Ga e In, assim como as suas ligas, por seu potencial na fabricação de dispositivos optoeletrônicos que operam na região do espectro eletromagnético de amarelo-verde até perto da região UV. Destes materiais, a estrutura cúbica (zíncblende) apresenta a vantagem sobre a sua contraparte hexagonal principalmente por estar livre do efeito piezoelétrico que separa os elétrons e buracos diminuindo a eficiência de recombinação. Este trabalho descreve o crescimento e caracterização de GaN cúbico dopado com carbono e de ligas, também cúbicas, de InGaN crescidas sobre diferentes substratos. As amostras foram crescidas por Epitaxia de Feixe Molecular (Molecular Beam Epitaxy ou MBE) assistido por plasma. Várias técnicas experimentais foram utilizadas para caracterizar as amostras assim crescidas. A aplicação destas técnicas nos permitiu obter informação detalhada sobre diversos aspectos importantes destes materiais. Estas técnicas vão desde várias formas de difração de raios-X até diversas formas de espalhamento de luz. O uso combinado de todas estas técnicas foi crucial para determinar as propriedades fundamentais destes materiais, tais como a qualidade cristalina, o estado de tensão das camadas ativas e, para as ligas, o grau e tipo de separação de fase (resultando em regiões de diferente conteúdo de In, com conseqüente diferença nas energias dos gaps). Dentre os resultados principais destacamos o de determinar o mecanismo de incorporação de carbono nos filmes de GaN, atingindo altas concentrações de portadores e boa qualidade cristalina. Nas ligas de InGaN depositadas sobre SiC (filmes tensionados), o único que indica que haveria uma separação de fase é o Stokes-like shift gigante e constante e o fato de que em medidas de PL, com energia de excitação abaixo da borda de absorção da liga, ainda pode ser visto o pico de recombinação. Já, em amostras parcialmente relaxadas como os filmes de InGaN depositados sobre substratos de GaAs, teríamos também esta separação de fase com uma fase minoritária (rica em In) e outras duas fases correspondente à liga bulk com fração molar de In próximas entre si. Em particular, as técnicas de fotoluminescência e fotoluminescência de excitação são insubstituíveis na detecção de fases segregadas. / There has been a great interest in nitrides of Ga and In, as well as their alloys, due to their great potential for the fabrication of optoelectronic devices operating from the yellow-green region to the near UV regions of the electromagnetic spectrum. Of these, the cubic (zincblende structure) varieties present the advantage over their more common hexagonal counterparts, of being free from piezoelectric fields (induced by the biaxial strain inherent in most growth techniques) which separate electrons and holes leading to the detriment of recombination efficiency. In the present work we report the growth and characterization of thin films of cubic GaN doped with carbon and undoped InGaN films. The samples were grown by plasma-assisted MBE (Molecular Beam Epitaxy) on different crystalline substrates. Characterization techniques varied from different forms of X-ray diffraction, electrical (Hall Effect) measurements to distinct forms of light scattering. The combination of these techniques was decisive in accessing physical properties of the materials, such as crystalline quality, state of tension and, for the alloys, phase separation (resulting in regions of different composition and energy gap). No single technique could have given us the answer to all these materials properties. Rather, the combination of all these experimental tools allowed us to obtain details about the composition and quality of The grown material. In particular, techniques related to the photoluminescence and photoluminescence excitation techniques were irreplaceable in detecting the presence of segregated phases that appear in such small quantities as to remain undetected by other techniques.

O estudo de sistemas voltados para a detecção e discriminação de compostos e substâncias gasosas tem se destacado nas áreas da nanociência e da nanotecnologia devido ao grande interesse no controle de odores e aromas presentes em alimentos, cosméticos e no meio ambiente. Dentre os diversos tipos de sensores matriciais de gases, conhecidos como narizes eletrônicos, os feitos à base de polímeros vêm se destacando devido ao baixo custo, fácil processabilidade, operação em temperatura ambiente e boa resposta sensorial. O presente trabalho mostra a confecção e análise de sensores poliméricos e um nariz eletrônico de pequenas dimensões, portátil e de baixo custo baseado em polímeros condutivos. Como materiais ativos dos sensores foram estudados materiais pertencentes à classe das polianilinas, politiofenos, polipirrol e ftalocianina de níquel, depositados por duas técnicas diferentes: spin coating e automontagem. As análises da espessura, reprodutibilidade e estabilidade elétrica mostraram diferenças em relação aos materiais empregados e a técnicas escolhidas, em que a uniformidade superficial não está associada diretamente com a estabilidade elétrica. Sensores que empregam PAni e POMA sofrem variação da resistência elétrica em função do tempo, o que está relacionado com a perda de dopagem desses materiais. O projeto e desenvolvimento de uma câmara de medidas são relatados com simulações que mostraram o perfil adequado para o posicionamento dos sensores. Para nortear a concepção do nariz, foi realizado um comparativo entre resistência e capacitância elétricas como parâmetros de interrogação mostrando resultados similares na discriminação, mas com diferenças de 100 vezes em valor relativo, o que resultou na escolha da resistência elétrica. O nariz eletrônico concebido apresenta poder de discriminação não só comparável ao da técnica de cromatografia gasosa, como também permite discriminar diversos tipos de analitos: perfumes, álcool etílico puro e adulterado, sucos de maçã, vinhos, cachaças e cachaças adulteradas e mel, tanto através da técnica de PCA quanto por redes neurais artificiais. O emprego de uma elipsóide como selecionador da região das classes facilitou o processo de visualização e análise dos dados enquanto que o uso de redes neurais mostrou classificações corretas próximas a 100% para praticamente todos os analitos. / The study of sensors for detection and discrimination of gaseous substances and compounds have been gaining much attention in areas such as nanocience and nanotechnology due to the great motivation in control of odors and substances associated with food, cosmetics and environment. Within several types of gas sensor arrays, known as electronic noses, polymeric-made ones distinguishes due to good sensory response, can be utilized at ambient temperature, are able to be easily processed and are of potential low cost. This work shows the fabrication and analysis of polymeric sensors and a small size, low cost and portable electronic nose. Polymeric materials belonging to polyaniline, polythiophene and polypyrrole classes and nickel phtalocyanines, deposited by two different techniques (spin coating and self assembly) were studied as active materials for the sensors. Analysis of thickness, reproducibility and electrical stability were performed and they showed differences among the studied materials and deposition techniques, where superficial uniformity is not associated directly with electrical stability. Sensors with PAni and POMA showed an electrical resistance variation in function of time which is related to dopant loss. Project and development of an analysis chamber are reported with simulations that showed an adequate profile for sensor positioning. A comparison between resistance and capacitance was performed aiming the electronic nose conceptualization. Both parameters showed similar discrimination capability but a 100 times difference in relative variation, leading to the choice of the electrical resistance. The conceived electronic nose shows a discrimination capability similar to gas chromatography and also allows the discrimination of many different analyte types: perfumes, pure and adulterated ethanol, apple juices, wines, pure and adulterated cachaças and honey, either with PCA technique or as well with artificial neural networks. The use of an ellipsoid to envelop class regions ease the visualization process and data analysis from PCA results while neural networks showed correct classifications near to 100% for almost all analytes.

Este trabalho tem por objetivo investigar as propriedades ópticas de sistemas poliméricos luminescentes submetidos a diferentes doses de radiação gama. Foram preparadas soluções de poli[2-metóxi-5-(2\'etil-hexilóxi)-p-fenilenovinileno] - MEHPPV em clorofórmio e filmes finos depositados a partir de soluções deste polímero sobre substrato de vidro. As soluções e filmes finos tiveram suas propriedades investigadas por meio de medidas de absorção ultravioleta-visível (UV-VIS). Os filmes finos também foram analisados por medidas de espectroscopia de infravermelho (FTIR) além da cromatografia HPSEC. Os resultados experimentais foram analisados buscando elucidar tanto os efeitos da radiação nas propriedades ópticas dos polímeros, como também o estudo da viabilidade destes materiais como elementos ativos de dosímetros para baixas doses de radiação gama (< 1 kGy) especialmente para aplicações no tratamento de esterilização de bolsas de sangue (~ 25 Gy) e altas doses de radiação gama (até 25 kGy) para aplicações como esterilização de materiais médicos hospitalares. / This work aims the investigation of the optical properties of luminescent polymeric systems when submitted to different gamma radiation doses. Solutions of poly[2-methoxi-5-(2\'etil-hexiloxi)-p-phenilenevinilene] - MEH-PPV in chloroform were prepared. From those solutions, thin film layers of MEH-PPV were deposited on glass substrates. The polymer solutions and the thin-film samples of MEHPPV had their properties investigated by ultraviolet-visible (UV-Vis) absorption spectroscopy. The thin-film prepared samples were, additionally, investigated by InfraRed Fourier Transform (FTIR) spectroscopy and HPSEC chromatography. The experimental results were investigated to elucidate the radiation effects on the optical properties of these polymeric systems. From the experimental results, the feasibility of using this material as active element in gamma radiation dosimeters was investigated. The research was conducted aiming the low dose gamma radiation (< 1 kGy) specifically for application in the sterilization treatment of blood bags (~ 25 Gy) and high gamma radiation doses (up to 25 kGy) as used for the sterilization of medical and hospital supplies.

Orientador: Antonio Batocchio / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T03:10:46Z (GMT). No. of bitstreams: 1 Ramos_Jose_D.pdf: 5427777 bytes, checksum: 0fc00db4fd4147b24ce787a2973fbe20 (MD5) Previous issue date: 2013 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The complete abstract is available with the full electronic document / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Title of dissertation: GROWTH OF Zn POLAR BeMgZnO/ZnO HETEROSTRUCTURE WITH TWO DIMENSIONAL ELECTRON GAS (2DEG) AND FABRICATION OF SILVER SCHOTTKY DIODE ON BeMgZnO/ZnO HETEROSTRUCTURE By Md Barkat Ullah, Ph.D A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering at Virginia Commonwealth University. Virginia Commonwealth University,2017 Major Director: Dr. Hadis Morkoç, Professor, Electrical and Computer Engineering This thesis focuses on growth of Zn polar BeMgZnO/ZnO heterostructure on GaN/sapphire template with two dimensional electron gas (2DEG) for the application of UV photodetector/emitter and high speed electronics. The motivation of using BeMgZnO as a barrier layer originates from the need to reach plasmon-LO phonon resonance in order to obtain minimum longitudinal optical (LO) phonon lifetime. Presence of 2DEG was realized in BeMgZnO/ZnO heterostructure only when the Zn polarity was achieved during the nucleation growth of ZnO on GaN/sapphire template. It was found that, polarity of ZnO on (0001) GaN/sapphire template can be controlled by the oxygen to Zn ratio used during the nucleation growth. To obtain high structural and optical quality of BeMgZnO quaternary alloy, growth kinetics of BeMgZnO layer has been studied at the temperature range from 450°C-500°C. We have achieved the growth of single crystal Be.03Mg00.15ZnO alloy at 500 °C, more than 100°C higher compared to what reported in literature, on the (0001) GaN/sapphire template through the control of Zn/(Be+Mg) flux ratio. We have also observed a thermodynamic limitation of Mg incorporation into the wurtzite BeMgZnO alloy where the excess Mg adatom accumulated in the growing surface as a MgO rich cluster. Two dimensional electron gas with high (1.2×1013cm-2) sheet carrier density was achieved at the Be0.03Mg0.41ZnO/ZnO interface through strain engineering by incorporating Be into MgZnO ternary alloy. To obtain the similar sheet carrier density it would require above 60% of Mg in MgZnO/ZnO heterostructure with reduced structural quality. A systematic comparison of sheet carrier density has been made with the already reported results from Zn polar MgZnO/ZnO heterostructure as well as with the theoretical calculation. Silver Schottky diode on Be0.02Mg0.26ZnO/ZnO heterostructure with barrier height 1.07 eV and ideality factor 1.22 was obtained with 8 order of rectification ratio. The temperature-dependent electrical characteristics were studied by using temperature dependent current-voltage (I-V) measurements. Richardson constant value of 34.8 Acm-2K-2 was found experimentally which was close to the theoretical value of 36 Acm-2K-2 known for Be0.02Mg0.26ZnO alloy.

Context: The Human Machine Interface (HMI) for Intelligent Electronic Devices (IEDs) is limited in its capability and is often the most common cause of failure when interacting with devices. A new approach to interact with these devices is needed with focus on improving interaction and effective visualization of information. Objectives: In this thesis, we investigate and propose a solution to visualize data of existing IED in interactive way. A mobile based prototype is proposed to list alarms, events and disturbances. Further single line diagram shown with capability to switch controls. Objective of proposed solution is to investigate specific use of mobile device from the perspective of usability and compare the new prototype with existing use of IED monochrome screen interface. Methods: Mixed approach based on qualitative and quantitative methods is conducted for analysis of the problem, method and approach to solve the problems in the domain of Substation automation. Analysis of the problem was carried out with the literature review of the technical documentation of IEDs. Experiments are performed in real environment to test and verify the usability of prototype. Results: Experiments results of proposed solution indicate that new approach is acceptable. The interfaces developed in mobile provide better results than traditional interfaces of IED. The difference between them is significant. Conclusions: We conclude that mobile usability gives better interaction, freedom, visualization of information and enhance the users’ experience by providing context specific information as compared to the existing Local Human Machine Interface of Intelligent Electronic Devices. The study provides strong results that recent developments of mobile technologies have revolutionized users’ possibilities to access information in an easy and better way.

Abstract The concept design of small handheld electronic and telecommunication devices is a creative and dynamic process. Interaction between the designers plays an important role in the creation of new products. This thesis addresses the communication between product concept designers. The aim of this thesis is to examine new ways of developing computer systems for remote collaboration. Multiple research methods have been used so as to enrich the view of the research subject. Product concept design has been studied in field studies and at co-located concept design workshops where the object of design was uncertain. Co-located workshops were organised to examine the moment to moment interaction between designers to discover how designers collaborate when designing a design object in common. By applying the concepts of activity theory, the concept of instrument is elaborated. Four types of instruments to mediate between a designer and the object of design and collaborating designers are identified. These are the instruments used to externalize an understanding of the design object, the concrete means of interaction, the future artefact and the hypothetical user activity. The latter two make up the design object which designers' strive for, and can also be instruments for scaffolding each other. A conceptual model was developed to describe the design action and the instruments for collaboration. This model was used to gain insight into the creation of computer support for remotely collaborating designers by posing questions for computer systems design. To develop computer systems to support designers in remote collaboration, an understanding of both the requirements set by the field and the technological feasibility is needed. Three application prototypes are presented as proof of the concept and as an experiment with virtual prototyping technology. The concept of design action has been defined on the basis of activity theory. Computer-supported geographically distributed workshops have been organised and analysed using the design action as an analytical tool for the research material. I conclude that, in order to support remote collaboration of concept designers, computer systems should support collaborative construction of the object of design. Instruments, such as the future artefact, its various representations and the conceptual construct of hypothetical user activity are potential instruments for computation.

The outstanding electrical and material properties of Graphene have made it a promising material for several fields of analog applications, though its zero bandgap precludes its application in digital and logic devices. With its remarkably high electron mobility at room temperature, Graphene also has strong potential for terahertz (THz) plasmonic devices. However there still are challenges to be solved to realize Graphene’s full potential for practical applications. In this dissertation, we investigate solutions for some of these challenges. First, to reduce the access resistances which significantly reduces the radio frequency (RF) performance of Graphene field effect transistors (GFETs), a novel device structure consisting of two additional contacts at the access region has been successfully modeled, designed, microfabicated/integrated, and characterized. The additional contacts of the proposed device are capacitively coupled to the device channel and independently biased, that induce more carriers and effectively reduce access resistance. In addition to that, in this dissertation, bandgap has been experimentally introduced to semi-metallic Graphene, by decorating with randomly distributed gold nano-particles and zinc oxide (ZnO) nano-seeds, where their interaction breaks its sublattice symmetry and opens up bandgap. The engineered bandgap was extracted from its temperature dependent conductivity characteristics and compared with reported theoretical estimation. The proposed method of device engineering combined with material bandgap engineering, on a single device, introduces a gateway towards high speed Graphene logic devices. Finally, THz plasmon generation and propagation in Graphene grating gate field effect transistors and Graphene plasmonic ring resonators have been investigated analytically and numerically to explore their potential use for compact, solid state tunable THz detectors.