This thesis addresses one of the major limiting factors in the performance of photomultipliers, that is that the photocathodes employed often only absorb a small fraction, typically less than 25%, of the power in the incident light. Current photocathodes are almost exclusively planar and the starting point of the thesis is the mathematical modelling of both, semitransparent and reflective planar photocathodes. The analysis shows that the absorptance of semitransparent photocathodes increases for light incident beyond the critical angle needed for Attenuated Total Internal Reflection (ATIR). Reflective type planar photocathodes could certainly have their absorptance enhanced by use of silver rather than nickel substrates, as increases in absorptance of 2-3 times are possible for red light. The proposed method for remedying the inherent loss in sensitivity of photomultipliers caused by the non-total absorption of light in the photocathode was to employ a ridged substrate in the photocathode. The ridged substrate, glass or metal for semitransparent and reflective type photocathodes respectively, allows the light multiple interactions with the photoemissive layer. In the case of semitransparent photocathodes ATIR would mean no power is transmitted for those interactions that take place beyond the critical angle of incidence. The mathematical modelling and subsequent analysis of ridged photocathodes show enhanced absorptance (20-30 fold improvements are certainly achievable), especially for light in the red end of the operating spectral range. Further gains in quantum efficiency can follow by the reduction of the optimum photocathode thickness, resulting from the structure, while maintaining high absorptance. Some subwavelength structures are also modelled and analysed to ascertain whether this route could be used to improve the absorptance of photocathodes, the results are inconclusive but generally indicate anti-reflective, rather than absorbing properties. Finally the extremely sparse nature of published permitivity data has been rectified by our own measurements for the permitivities of certain photocathodes over a wide wavelength range.

No description available.

Depuis les premières mémoires à semi-conducteurs, les mémoires intégrées sur les circuits électroniques ont beaucoup évolué. Celles-ci deviennent de plus en plus petites sans pour autant conserver moins de données. Cependant, la technologie mémoire non-volatile la plus répandue, la Flash, fait face à des problèmes de miniaturisation et de consommation. Plusieurs solutions alternatives ont donc émergé pour remplacer la Flash, ou pour être intégrées dans les objets connectés. Dans quelques années, des milliards d’appareils échangeront des données parfois personnelles qui ont donc besoin d’être sécurisées. La technologie Flash a déjà été l’objet de nombreuses études, permettant de la rendre sécurisée. Néanmoins, rien n’a été fait en ce qui concerne les technologies mémoires émergentes. Cette thèse propose donc d’évaluer le caractère sécuritaire d’une de ces technologies, particulièrement prometteuse par ses performances : l’OxRRAM. Le premier chapitre de ce manuscrit fera l’état de l’art des différents types de mémoires existant ainsi que des moyens utilisés pour évaluer la sécurité d’une technologie mémoire.Cela a permis de réaliser une première approche d’attaque sur un circuit embarquant de l’OxRRAM, mais les résultats montrent que des études plus fines sont nécessaires pour parvenir à comprendre de quoi il en retourne. Les chapitres 3 et 4 montrent les différentes vulnérabilités obtenues dans des cellules mémoires OxRRAM grâce à différent types d’attaques LASER.La source de ces vulnérabilités a également été identifiée, ce qui a permis par la suite de proposer des premières pistes de contre-mesures afin de protéger les circuits devant embarquer ce type de mémoires. / The first semi-conductor memories appeared in the 1960s. Since then,memories that are embedded on integrated circuits have evolved significantly. An important downsizing of these memories has been performed and they are still able to store more and more data. However, Flash technology-which is the most spread NVM technology nowadays - is facing scaling and power consumption issues. Numerous alternative solutions have emerged (emerging technologies) to replace Flash or to be integrated in smart objects, whose one of the main features is low power consumption. In the years to come, billions of devices connected to each other will exchange personal data that need to be secured. Flash technology has already been the subject of many studies, allowing it to be considered secured. Nevertheless, nothing has been performed yet on emerging NVM.This thesis proposes an evaluation of the secure character of one of these technologies, whose performances are promising: OxRAM. The first chapter of this manuscript deals with the state of the art of the different kind of existing memory technologies. It lists the different means that can be used to assess the security of a memory technology. This allowed to experiment attacks on an integrated circuit which embeds OxRAM. However, the results showed that more accurate studies are necessary to understand the observed effects. Chapters 3 and 4 will then demonstrate the vulnerabilities noticed on OxRAM memory cells through different LASER attacks. The source of these vulnerabilities has also been investigated, which allowed to propose tracks for countermeasures in order to protect integrated circuits that are to embed such memories.

Submitted by (lucia.rodrigues@ufrpe.br) on 2016-11-23T12:26:25Z No. of bitstreams: 1 Nelio Oliveira Ferreira.pdf: 784310 bytes, checksum: c0fb98c5a6c058e292abaf3e2e990e8c (MD5) / Made available in DSpace on 2016-11-23T12:26:25Z (GMT). No. of bitstreams: 1 Nelio Oliveira Ferreira.pdf: 784310 bytes, checksum: c0fb98c5a6c058e292abaf3e2e990e8c (MD5) Previous issue date: 2005-08-30 / This article aims to investigate the dual behavior of the light as a result of implementation of a new approach based on the Personal Constructs Theory by George Kelly, specifically, in the Experience Cycle. The five stages of this cycle (anticipation, investment, encounter, validation and constructive revision) had been distributed in three classes during which the conceptions by the students had been followed from the beginning detected through a posttest and through a production of a new poster. There had been investigated the conceptions of wave, particle, frequency and wavelength, as well as the photoelectrons, cutoff potential and cutoff frequency, aiming to register the Photoelectric Effect phenomenon. During the poster production, the acceptable answers had aroused from 64% to 100% concerning the wave definition. Concerning the particle, the results had been even more relevant; no answer was considered true at first, but after the usage of the cycle, they had been all accepted. These results had indicated how clearly the students could then distinguish wave from particle, which had been complemented by the comprehension of essential conceptions to the Photoelectric Effect phenomenon. Therefore, the students had started to understand the corpuscular behavior of the light, in the cited phenomenon, and wavy, in other phenomenon (reflection, refraction, diffraction and interference), as it can be comproved by comparison of the pre-test and the post-test. Concerning the wavelength conceptions, cutoff frequency and photoelectrons, all the answers had became acceptable. Besides, the answers concerning quantum and photon conceptions had cached 91% of the desirable levels frequency had cached 81% and cutoff potential, 64%. Considering that 60% of the answers analyzed were acceptable, it is believed that the usage of Kelly’s Experience Cycle as a methodological tool is extremely effective. / Este trabalho tem o objetivo de investigar o comportamento dual da luz devido a implementação de uma nova abordagem baseada na Teoria dos Construtos Pessoais de George Kelly, mais especificamente, no Ciclo da Experiência. As cinco etapas desse ciclo (antecipação, investimento, encontro, validação e revisão construtiva) foram distribuídas em três aulas durante as quais foram acompanhadas as concepções dos alunos, desde as iniciais, detectadas através de um pré-teste e da produção de um cartaz, até as concepções mantidas ao término da intervenção didática, através de um pós-teste e da produção de um novo cartaz. Foram investigados os conceitos de onda, partícula, freqüência e comprimento de onda, além de fotoelétrons, potencial de corte e freqüência de corte com o intuito de retratar o fenômeno do Efeito Fotoelétrico. Na produção dos cartazes, as respostas consideradas aceitáveis passaram de 64% para 100% no que diz respeito ao conceito de onda. Em relação ao conceito de partícula na produção dos cartazes, os resultados foram ainda mais relevantes, nenhuma resposta foi aceita, inicialmente, contra a aceitação de todas as respostas após a aplicação do ciclo. Estes resultados indicaram a clareza que os alunos passaram a ter ao distinguir onda e partícula, o que foi complementado com a compreensão de conceitos essenciais relacionados com o fenômeno do Efeito Fotoelétrico. Assim, os alunos passaram a compreender o comportamento corpuscular da luz, no referido fenômeno, e ondulatório, em outros fenômenos (reflexão, refração, difração e interferência), como se pôde verificar nos resultados do pré-teste e pós-teste. Em relação aos conceitos de comprimento de onda, freqüência de corte e fotoelétrons, todas as respostas atingiram níveis aceitáveis. Além disso, as respostas a respeito dos conceitos de quantum e fóton atingiram 91% dos níveis desejáveis, freqüência, 82%, e potencial de corte, 64%. Como todos os dados analisados atingiram níveis acima de 60% daqueles desejáveis, acredita-se que a utilização do Ciclo da Experiência de Kelly, como ferramenta metodológica, apresentou-se com bastante eficácia.

The varied properties of Silicon Carbide (SiC) are helping to launch the material into many new applications, particularly in the field of novel semiconductor devices. In this work, the cubic form of SiC is of interest as a basis for developing integrated optical components. Here, the formation of a suitable SiO2 buried cladding layer has been achieved by high dose oxygen ion implantation. This layer is necessary for the optical confinement of propagating light, and hence optical waveguide fabrication. Results have shown that optical propagation losses of the order of 20 dB/cm are obtainable. Much of this loss can be attributed to mode leakage and volume scattering. Mode leakage is a function of the effective oxide thickness, and volume scattering related to the surface layer damage. These parameters have been shown to be controllable and so suggests that further reduction in the waveguide loss is feasible. Analysis of the layer growth mechanism by RBS, XTEM and XPS proves that SiO2 is formed, and that the extent of formation depends on implant dose and temperature. The excess carbon generated is believed to exit the oxide layer by a number of varying mechanisms. The result of this appears to be a number of stable Si-C-O intermediaries that form regions to either depth extreme of the SiO2 layer. Early furnace tests suggest a need to anneal at temperatures approaching the melting point of the silicon substrate, and that the quality of the virgin material is crutial in controlling the resulting oxide growth.

Organic electronic devices are sustainable alternatives to the conventional electronics, due to their advantages of low cost, mechanical flexibility and wide range of applications. With the myriad list of organic materials available today, the opportunities to imagine new innovative devices are immense. Organic electronic devices such as OLEDs (organic light emitting diode), OPVs (Organic photovoltaics) and OFETs (organic field effect transistors) are among the leading device categories. Although OLED’s have been a huge commercial success, other categories are not lagging. Radical thinking is necessary to improve on the current performances of these devices. One such thinking is to combine the versatile ZnO (Zinc Oxide) material to organic semiconductors. This can be achieved by exploiting the dual nature of ZnO’s semiconducting and piezoelectric property. Many devices have used ZnO in combination with organic semiconductors for applications ranging from sensors, photovoltaics, OFET’s, memory and many others. The goal of the work is to incorporate the piezoelectric nature of hydrothermally grown ZnO nanowires for Opto-electronic applications. Although the initial research work was done on incorporating the piezo effect of bulk grown ZnO nanowires in improving the efficiency of an OPV, we discovered a unique memory effect in this device by incorporating ZnO nanowires in an inverted organic photovoltaic architecture. The device switched between a rectifying response in dark to resistive behavior under illumination with a finite transition time and was reversible. Since then we decided to explore few of the opto-electronic applications of this technology. The synthesis and characterization of crystalline ZnO nanowires, nanoforest and planar ZnO nanofilm are reported along with the application of these ZnO nanostructures in optoelectronic devices. Noncentro symmetry of crystalline ZnO nanostructures makes it an excellent candidate to be used as piezo functional material and these nanostructures are characterized using electrochemical cell containing ZnO electrode as the working electrode. ZnO nanostructures like nanowires, nanoforest and planar nanofilm are similarly characterized for piezo property using electrochemical technique. Different devices require distinguishing physical and electrical properties of ZnO nanostructures, hence morphology, effect of pre-strain, surface area, surface coverage and thickness of these nanostructures were evaluated for its piezoresponse. It is shown that it was possible to obtain similar piezoresponse among different ZnO nanostructures in addition to taking advantage of the structural benefits among various categories of nanostructures as per requirement. The presented research can be used as the proof-of-the-concept that ZnO nanostructures can be designed and fabricated with a prestrain to adjust the piezo response of the material under external forces. Therefore, the structure with the prestrain can be employed in various electronic and optical devices where the piezo voltage can be used for adjusting the energy band bending at an interface.

The COmpton Spectrometer and Imager (COSI) is a space telescope that aims to study the soft gamma regime (0.2-5 MeV), capable of performing spectroscopy, imaging and polarimetry of cosmic gamma sources. COSI will use an active shield made of Bismuth Germanium Oxide (BGO), a known scintillator material, in order to reduce the instrumental background produced by primary and secondary particles. When a cosmic ray particle or gamma interacts with the active shield, they will produce scintillation photons. Thanks to the optical coupling of photomultipliers tubes (PMT) to the BGO walls, it is possible to detect these scintillation photons and remove the background events from the analysis with the Compton telescope. IRAP (Research Institute in Astrophysics and Planetology) is the organization responsible of providing the photodetector (PMT with its electronics and mechanics) design to the COSI mission. The main objective of my internship is to study the performance of the photodetector of the active shield, focusing on the development of simulations with Geant4. The first study investigates the propagation of optical photons inside a PMT, comparing an analytical method versus a Geant4 simulation. Geant4 perfectly simulates the transmission and reflection of photons. However, if some of the photons are absorbed by the materials, Geant4 starts to slightly differ. This happens because the absorption is computed with different physic processes in both models. The second study is focused on obtaining measurements from the PMTs at the laboratory. The pulse amplitude at the preamplifier level is analysed, as well as the transmission of the Si pad. The third and fourth studies are focused on the simulation, with Geant4, of the performance of a PMT optically coupled to two different scintillator materials, CsI(Tl) and BGO, respectively. The correct set-up of a simulation is always critical, especially for a space mission like COSI. Both studies aim to find the correct set-up in order to get the most precise simulation. The results are great, showing a really good correlation between the simulation and the real data. During the fifth study, I updated the photodetector engineering model, called DACS (Detector for the AntiCoincidence System), taking into consideration the new electronic board designs and the previous engineering models. The results obtained in this thesis help to understand the performance of the photodetectors that will be used on the COSI telescope, as well as to show the benefits of using a toolkit like Geant4 in projects with propagation of scintillation photons.

Made available in DSpace on 2016-04-28T14:16:12Z (GMT). No. of bitstreams: 1 Arthur Issa Mangili.pdf: 986316 bytes, checksum: 5bd8636e8f419fb55e6f9132606a92dc (MD5) Previous issue date: 2011-05-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study aimed to analyze the experiments made by Heinrich Rudolph Hertz about the photoelectric effect. To this end, we consulted the work Electric Waves: Being Researches On The Propagation Of Electric Action With Finite Velocity Through Space, mainly the part in which the experiment that refers to the photoelectric effect is described. So we want to understand in which context such effect is discussed, looking for evidence that has arisen its discovery / Este estudo teve por objetivo analisar os experimentos realizados por Heinrich Rudolph Hertz relativos ao efeito fotoelétrico. Para tanto, consultamos a obra Electric Waves: Being Researches on the Propagation of Electric Action With Finite Velocity Through Space, principalmente a parte em que o experimento que se refere ao efeito fotoelétrico é descrito. Buscamos assim compreender em que contexto tal efeito é abordado, procurando indícios que sugiram a sua descoberta

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-10-19T12:34:29Z No. of bitstreams: 1 PDF - Joana Menara Souza Soares.pdf: 2514459 bytes, checksum: 19c69f29bb7ad433f442d2f53400b037 (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-10-19T17:11:24Z (GMT) No. of bitstreams: 1 PDF - Joana Menara Souza Soares.pdf: 2514459 bytes, checksum: 19c69f29bb7ad433f442d2f53400b037 (MD5) / Made available in DSpace on 2016-10-19T17:11:24Z (GMT). No. of bitstreams: 1 PDF - Joana Menara Souza Soares.pdf: 2514459 bytes, checksum: 19c69f29bb7ad433f442d2f53400b037 (MD5) Previous issue date: 2016-08-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Currently, much has been discussed about the presence and importance of the History of Science (HC) in teaching physics. Associado a essa premissa, temos visto uma crescente produção de trabalhos acadêmicos, na qual se tem enfatizado uma abordagem histórica e filosófica inserida em conteúdos dessa disciplina. It is clear, however, that some of these jobs do not come to the teacher, leaving them at the mercy of distorted stories and / or simplified, present in most textbooks (LD), which ends up reinforcing some known scientific myths, transmitting false historical concepts to students and teachers. So, considering the importance of HC, we highlight the importance of examining the presence of this interrelationship in Physics textbooks for higher education by checking whether or not a historical proper transpositions on the photoelectric effect and how these materials, which They aim to train the teacher present the historical context of the phenomenon in question. Analysis and discussion of the results presented here should be based on some criteria that take into account historical aspects of the phenomenon as well as science, noting the presence of scientific myths and distorted bibliographic reports on the scientists involved. / Atualmente, muito se discute sobre a presença e a importância da História da Ciência (HC) no ensino de Física. Associada a essa premissa, temos visto uma crescente produção de trabalhos acadêmicos, na qual se tem enfatizado uma abordagem histórica e filosófica inserida em conteúdos dessa disciplina. Percebe-se, por outro lado, que alguns desses trabalhos não chegam ao professor, deixando-os a mercê de histórias distorcidas e/ou simplificadas, presentes na maioria dos livros didáticos (LD), o que termina por reforçar alguns conhecidos mitos científicos, transmitindo falsas concepções históricas a estudantes e professores. Assim, considerando a importância da HC, destacamos a relevância de se examinar a presença dessa inter-relação nos livros didáticos de Física para o ensino superior, verificando se há ou não umas transposições históricas adequadas, sobre o efeito fotoelétrico e como esses materiais, que visam formar o professor apresentam o contexto histórico do fenômeno em questão. A análise e discussão dos resultados aqui apresentados tomam como base alguns critérios que levam em consideração aspectos históricos do fenômeno e bem como da ciência, atentando para presença de mitos científicos e de relatos bibliográficos distorcidos sobre os cientistas envolvidos.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2018-11-19T14:40:48Z No. of bitstreams: 1 wagnerdiasrocha.pdf: 3693391 bytes, checksum: ff882b197689decbd93b1281b5bf0dd5 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-11-23T13:04:01Z (GMT) No. of bitstreams: 1 wagnerdiasrocha.pdf: 3693391 bytes, checksum: ff882b197689decbd93b1281b5bf0dd5 (MD5) / Made available in DSpace on 2018-11-23T13:04:01Z (GMT). No. of bitstreams: 1 wagnerdiasrocha.pdf: 3693391 bytes, checksum: ff882b197689decbd93b1281b5bf0dd5 (MD5) Previous issue date: 2018-08-21 / Este trabalho apresenta uma proposta de abordagem experimental para o Efeito Fotoelétrico baseada em um kit didático capaz de demonstrar a ocorrência (ou não) do fenômeno em função da variação de intensidade e de frequência da luz incidente sobre um material receptor. O principal objetivo é fornecer uma alternativa diferenciada para a construção do conhecimento sobre o assunto. O kit, elaborado com LEDs e outros componentes de baixo custo presentes no cotidiano, é de fácil reprodução e operação, além de compacto o suficiente para viabilizar a execução de atividades práticas em qualquer sala de aula, sendo assim muito útil principalmente para alunos e professores do Ensino Médio, os quais muitas vezes não dispõem de laboratórios e equipamentos, seja pela restrição de acesso ou até mesmo pela inexistência destes. Com três aplicações em sala de aula, desenvolveu-se uma metodologia onde duas hipóteses excludentes entre si e que se apresentam como explicação para o fenômeno são confrontadas experimentalmente. A validade de somente uma dessas hipóteses é comprovada pelas respostas dadas a dois questionamentos pós-atividade. Os resultados obtidos demonstram que os alunos conseguiram compreender o funcionamento do kit, utilizá-lo para realizar a atividade proposta e construir eles próprios o seu conhecimento sobre o assunto. Além disso, as críticas e sugestões coletadas ao final do processo demonstram que houve uma aceitação considerável da proposta pelos mesmos. A fim de torná-la acessível aos professores de Física interessados na sua utilização, são fornecidos adicionalmente dois roteiros, sendo que um descreve passo a passo a montagem do kit e o outro dá suporte à execução da atividade experimental proposta. / This work presents a proposal for an experimental approach to the Photoelectric Effect based on a didactic kit capable of demonstrating the occurrence (or not) of the phenomenon as a function of the variation of intensity and frequency of light incident on a receiving material. The main objective is to provide a differentiated alternative for building knowledge about the subject. The kit, made with LEDs and other low-cost components present in everyday life, is easy to reproduce and operate, and compact enough to enable the execution of practical activities in any classroom, and is therefore very useful mainly for students and teachers of secondary education, which often do not have laboratories and equipment, either by the restriction of access or even by the lack of them. With three applications in the classroom, a methodology was developed where two mutually exclusive hypotheses that present themselves as an explanation for the phenomenon are confronted experimentally. The validity of only one of these hypotheses is proven by the responses given to two post-activity questions. The obtained results demonstrate that the students were able to understand the operation of the kit, use it to carry out the proposed activity and build their own knowledge about the subject. In addition, the criticisms and suggestions collected at the end of the process demonstrate that there has been considerable acceptance of the proposal by the parties. In order to make it accessible to physics teachers interested in its use, two scripts are additionally provided, one describing step by step the assembly of the kit and the other supporting the execution of the proposed experimental activity.