Light measurements are widely used in physics experiments and medical applications. It is possible to nd many of them in High{Energy Physics, Astrophysics and Astroparticle Physics experiments and in the PET or SPECT medical techniques. Two different types of light detectors are usually used: thermal detectors and photoelectric effect based detectors. Among the rst type detectors, the Bolometer is the most widely used and developed. Its invention dates back in the nineteenth century. It represents a good choice to detect optical power in far infrared and microwave wavelength regions but it does not have single photon detection capability. It is usually used in the rare events Physics experiments. Among the photoelectric effect based detectors, the Photomultiplier Tube (PMT) is the most important nowadays for the detection of low-level light flux. It was invented in the late thirties and it has the single photon detection capability and a good quantum efficiency (QE) in the near-ultraviolet (NUV) and visible regions. Its drawbacks are the high bias voltage requirement, the diculty to employ it in strong magnetic field environments and its fragility. Other widely used light detectors are the Solid-State detectors, in particular the silicon based ones. They were developed in the last sixty years to become a good alternative to the PMTs. The silicon photodetectors can be divided into three types depending on the operational bias voltage and, as a consequence, their internal gain: photodiodes, avalanche photodiodes (APDs) and Geiger-mode detectors, Single Photon Avalanche Diodes (SPADs). The first type detector does not have internal gain, thus its signal is proportional to the number of incoming photons that are converted in electron-hole pairs. The detector and the read-out circuit noises limit the detector sensitivity to, at least, some hundreds of photons. The APD exploits the impact ionisation effect to have an internal gain up to some hundreds or more. The internal gain allows the detector to improve the performance with respect to a similar area photodiode reducing the sensitivity limit to some tens of photons. Operating the APDs with a bias voltage larger than the breakdown one, the Geiger-mode operation range can be reached. In this case, the detectors have a very high gain, in the order of (10^5-10^7), but their signal is not proportional to the number of the incoming photons, it is always the same. The SPAD (or GM-APD) is a typical Geiger-mode silicon detector. It has the single photon detection capability as the PMT, due to the high gain, but its signal is digital: it is fired or not by the incoming photons. The capability to give a signal proportional to the number of photons is lost in a SPAD. To recover this property, a matrix of independent SPADs connected in parallel is built. These matrices are called Silicon Photomultipliers, SiPMs (or Multi-Pixel Photon Counters, MPPCs). In a typical SiPM, the output signal is the sum of the SPAD ones, thus, although the digital nature of the SPAD signal, it is analogue and ranges from zero to the maximum number of cells composing the matrix. The detector response can be considered linear if the number of incoming photons is much smaller than the total number of cells because the probability that two photons arrive on the same cell is negligible. Main features of the SiPMs are the low bias voltage (<100 V typically), a high Photo-Detection Efficiency (PDE) in NUV and visible range (usually larger than the PMT QE), compactness, insensitivity to magnetic elds and high internal gain. The noise sources are the Dark Count Rate (DCR), the optical Cross-talk (CT) and the Afterpulsing (AP). The first is called primary noise and mainly depends, at room temperature, on the thermal generation of electron-hole pairs that can travel to the high-field region triggering a cell. The others are collectively called correlated noise because they can happen only after a primary signal, caused both by a photon or by a spontaneous carrier generation. In this thesis, the focus is on the characterisation of one SiPM technology produced in Fondazione Bruno Kessler (FBK) in Trento, Italy, named NUV-SiPMs. This technology, implementing the p-on-n concept, showed, from the beginning, a high PDE spectrum peaked in the NUV to violet region exceeding the 30 %, a very low DCR, typically below 100 KHz/mm^2 in the operating voltage range, and a total correlated noise probability under the 50 %. In the last years, the technology was developed modifying the silicon wafer substrate properties, reducing the delayed correlated noise probabilities, and adopting the so-called High-Density concept. In this last version, named NUV-HD, a new layout, with a narrower border region around the cell active area and deep trenches to electrically and optically isolate the cells, is employed. The first improvement has a direct influence on the PDE because it increases the Fill Factor (FF), the ratio between the active to the total cell area. The second layout change reduces the probability that a secondary photon can travel from a cell to a neighbouring one, reducing the cross-talk probability. Possible applications of the NUV-HD devices are: medical application (e.g. the Time of Flight PET, ToF-PET, scanners), the rare events Physics experiments (e.g. NEXT and DarkSide) and Astroparticle Physiscs experiments (e.g. the Cherenkov Telescope Array Observatory, CTA). The ToF-PET scanners are promising medical techniques with the goal of improving the spatial resolution of the classical PET scanners measuring the gamma rays time of flight. For this reason, these scanners require very fast photodetectors with coincidence time resolution (CTR) less or equal to 100 ps. NEXT and DarkSide are low temperature experiments with the main goal of observe rare events as the neutrinoless double beta decay and the Dark Matter particles. Due to the signal rarity, the detector noise requirements are very stringent. CTA will be a future ground-based Imaging Atmospheric Cherenkov Telescope (IACT) observatory, with the goal to track very high energy cosmic gamma rays, up to hundreds of TeV, to their galactic sources. It will consist of two matrices of telescopes of different type and size, each one having a camera. In the small size telescopes, the possibility to use the SiPMs to build the camera is under investigation. Since the cosmic gamma rays are detected through the secondary Cherenkov photons, produced by the accelerated electrons in the Earth atmosphere, the camera photosensors must have a very high detection efficiency from 300 nm to 600 nm, and, possibly, a low sensitivity in the NIR region to reject the night sky background. In addition, they must have good timing properties and high granularity. To fully characterise the SiPM, measurements of signal properties, noise parameters and PDE are needed. The set-ups and analysis of the characterisation procedure are fully described. In particular, the optical set-up, with its calibration procedures, and the analysis methods, with the definition of the possible uncertainty sources, are the central point of this work. During the dark characterisation, the SiPM is enclosed in a light-tight climatic chamber. An oscilloscope acquires and sends to a PC software millisecond-long SiPM waveforms. The software implements a Differential Leading Edge Discriminator (DLED) algorithm to better distinguish the SiPM pulses with time separation larger than a few nanoseconds. This analysis allows to count the primary pulses, due to the thermal/tunnelling excitations, obtaining the DCR, and measure the correlated noise probabilities. In addition, signal parameters as amplitude, gain and cell recharge time are measured. The PDE measurements require a set-up in which the number of impinging photons to the device is precisely known. For this reason, a compact set-up, consisting of an integrating sphere inside a light-tight box, a series of LEDs with peak wavelength ranging from NUV to NIR, fully characterised before use, a monochromator, equipped with a tungsten lamp, and a transparent optical fibre, was developed. Along with the set-up, a light calibration procedure, taking into account different uncertainty sources (LED wavelength shift, light uniformity at the device position, etc.), was also developed. Three different analysis techniques can be used to obtain the technology PDE. Each technique has its own benets and error sources. The equivalence among the different methods is shown. Moreover, measuring the PDE on SPADs with the same layout of single SiPM cells, identical results are obtained. This fact shows the equivalence between the single cell device and its larger counterpart, opening the possibility to measure the PDE of a new technology on SPADs. This is a very important result because the SPAD is a simpler device, with lower correlated noise, because it has no CT, and negligible primary one, often less than 1 kHz. Measurements are more precise, faster and it is possible to apply larger bias voltage, obtaining more information on the technology in such conditions at which no SiPM can be tested any more. A rst version NUV-HD technology characterisation is shown. In this version, the NUV-HD SiPMs have cell pitch ranging from 25 um to 40 um. A typical primary noise lower than 100 KHz/mm^2 and a delayed correlated noise probability less than 5 % are measured, up to 10 V of overvoltage. In the same bias voltage range, a direct CT probability lower than 45 % is measured in the largest cell devices (25 % in the smallest ones). The PDE spectrum has the expected shape with the maximum in the NUV-violet region. A maximum value exceeding the 60 % is measured in the largest cell devices (45 % in the smallest ones). To investigate possible variations of the measured features on the wafer, devices taken from different wafer points are measured and compared finding no difference but the primary noise. This parameter shows a variation by a factor up to about three on the wafer level. To compare the different cell devices, all the measured parameters are plotted as a function of the peak PDE, about 400 nm. During this comparison, the smallest device reveals worse than the others having a larger noise, both primary and correlated, at the same PDE value. The other three devices are comparable within the measurement errors. From the PDE measurements, a comparison between the measured FF and the expected one, as dened by the design, is obtained. In the smallest cell device, this comparison shows an unexpected discrepancy leading to the possibility that the expected FF is larger than the effective one. This possibility is investigated in the last part of this thesis in which a complete study of the factors contributing to the PDE is shown. This study is performed on a new NUV-HD version employing a photodiode with equal dopant prole of the SiPMs, a circular SPAD having 100 % FF and a square one with 35 um cell size and a nominal FF equal to 81 %. A developed box model is used to describe the electric eld inside the cell. The calculated effective FF is always different from the expected one. The reason of the measured difference is the electric field transition from the constant high value to zero occurring at the active area border region. This partially efficient region has an effect similar to an added completely ineffective region of 1-1.5 um size inside the expected active area. The transition region effect is critical for the smallest cells because it strongly reduces the effective FF with respect to the design one. The study of the factors contributing to the PDE of the NUV-HD SiPMs is very important. Through the obtained results, it is confirmed that the technology QE is just maximised in the wavelength range of interest, NUV to blue, and, at the same wavelengths, the triggering probability saturation rate is very small allowing the detectors to reach the maximum PDE when biased with a few volts of overvoltage. This operating condition has also the effect to employ the detector having low noise, both primary and correlated one. The best solution to further improve the technology PDE is a redesign of the electric field border region to reduce the gap between the expected FF and the effective one. This is more important for the smallest cell devices in which the actual transition region effect reduces the PDE performance to about the 50-60 % of the expected values.

Proton therapy is a recent type of radiotherapy that uses high-energy proton beams, and more recently carbon ion beams, to benefit of their physical selectivity. The energy deposited by these particle beams is inversely proportional to their velocity. Therefore they release most of the energy at the end of their path into the tissue. The energy is deposited in a few millimeters, in a zone called the Bragg peak. Before and after the Bragg peak the energy deposition is minimal. The depth and the width of the Bragg peak depends on the beam energy and on the density of tissues located along the beam path. By setting the beam energy, the Bragg peak can be positioned in the tumor site, avoiding the healthy tissues. Because of the sharpness of the Bragg peak zone, proton therapy is advantageous for tumors located near to important body part, such as the brain, spine, and neck. The drawback is that small uncertainties on particle range can have a serious impact on treatment and limit the efficiency of the proton therapy. To obtain more effective treatments in proton therapy real-time range verifications are necessary to perform on-line corrections of the delivered treatment. Among different techniques presented in the literature, positron emission tomography (PET) and prompt gamma imaging (PGI) are the most promising methods for in vivo range verification. PET and PGI are indirect approaches to measure protons penetration depth inside patients because they aim to detect secondary particles resulting from the interaction between proton beams and tissue nuclei. PET imaging detects coincidence gamma rays due to the production of positron emitters and requires some minutes to achieve enough statistics to have a sufficient signal to noise ratio. PGI instead uses prompt gamma rays generated by de-excitation of target nuclei; the quantity of these rays and their temporal emission (few nanoseconds) allow to perform a range verification during treatment with the PGI. Several research groups are evaluating different approaches to realize a prompt gamma imaging system suitable for the use in clinical condition and the optimization of a gamma-ray detector for PGI is still ongoing. The Gammarad project works in this direction and aims to develop an high-performance and solid-state gamma ray detection module (GDM) with a slit camera design. The project is based on a collaboration among Fondazione Bruno Kessler (FBK, Trento, Italy), Politecnico di Milano (Milano, Italy), the Trento Institute for Fundamental Physics and Applications (TIFPA, Trento, Italy ), and the Proton Therapy Center of Trento (Italy). The project is divided into two parts. The first part focuses on the technological development of a gamma-ray imaging module. This module is composed by a gamma-ray detector, based on a solid-state silicon sensor, and an integrated circuit. They are assembled into a compact module with data and control systems. The second part of the project will be dedicated to the experimental validation of the system both in laboratory with radioactive sources and in a real environment, that of proton therapy. The most innovative part of the gamma-ray detector developed for the project is the photo-sensor used for the scintillation light readout. In traditional applications it is a photomultiplier tube (PMT). However, in recent years, Silicon Photomultiplier (SiPM) has become increasingly popular in a variety of applications for its promising characteristics. Among them, current-generation SiPMs offer high gain, high Photon Detection Efficiency (PDE), excellent timing performance, high count-rate capability and good radiation hardness. Due to these characteristics they are used as PMTs replacement in several applications, such as in nuclear medicine (PET), in high-energy physics (calorimeters), astrophysics (Cherenkov telescopes) and in others single-photon or few-photon applications. For its characteristics, the SiPM is also very promising for the scintillator readout in prompt gamma imaging and in high energy gamma-ray spectroscopy. Detectors for these applications must be compact, robust, and insensitive to the magnetic field. They have to provide high performance in terms of spatial, temporal, and energy resolution. SiPMs can satisfy all these requirements but typically they have been used with relatively low energy gamma rays and low photon flux, so manufacturers have optimized them for these conditions. Because of the limited number of micro-cells in a standard SiPM, 625 cells/mm^2 with 40 μm cells, the detector response is non-linear in high energies condition. Increasing the cell density is extremely important to improve the linearity of the SiPM and to avoid the compression of the energy spectrum at high energies, which worsens the energy resolution and makes difficult the calibration of the detector. On the other hand, small cells provide a lower Photon Detection Efficiency (PDE) because of the lower Fill Factor (FF) and as a consequence a lower energy resolution. Summarizing, the energy resolution at high energies is a trade-off between the excess noise factor (ENF) caused by the non-linearity of the SiPM and the PDE of the detector. Moreover, the small cell size provides an ultra-fast recovery time, in the order of a few of nanosecond for the smallest cells. A short recovery time together with a fast scintillator such a LYSO, reduces pile-up in high-rate applications, such as PGI. Based on the above considerations, the aim of this thesis is to develop an optimized gamma-ray detector composed of SiPMs for high-dynamic-range application, such as the scintillation light readout in prompt gamma imaging and in high-energy gamma-ray spectroscopy. SiPMs evaluated for the detector are High-Density (HD) and Ultra-High-Density (UHD) SiPM technologies recently produced at Fondazione Bruno Kessler (FBK). Instead of standard SiPMs, HD and UHD SiPMs have a very small micro-cell pitch, from 30 μm down to 5 μm with a cell density from 1600 cells/mm^2 to 46190 cells/mm^2, respectively. HD SiPMs are produced using a lithography technology with smaller critical dimensions and designed with trenches among SPADs. Small cells have a lower gain which helps to reduce correlated noise, such as After-Pulse and Cross-Talk. Trenches provide an optical and electrical cell isolation, and a smaller dead border around cells which increase the FF limiting PDE losses. UHD SiPMs push the limits of the HD technology even further, by reducing all the feature sizes, such as contacts, resistors and border region around cells. UHD SiPMs have hexagonal cells in a honeycomb configuration which generate a circular active area and a dead border around cells lower than 1 μm. The reduction of this dead boarder can improve the FF in smaller cells although it usually decrease with cell sizes. It is necessary understand how these significant layout changes affect the optical properties of SiPMs to evaluate which SiPM technology provides best performance in high-energy gamma-ray applications. In the first part of the thesis, I presents the characterization of HD and UHD SiPM technologies in terms of PDE, gain, Dark Count Rate, and correlated noise for the cell sizes between 30 and 7.5 μm. The most important markers of SiPMs performance in gamma-ray spectroscopy are however the energy resolution and the linearity when coupled to the scintillator for the detection of high-energy gamma-rays. A typical characterization of the energy resolution of SiPMs, coupled to scintillator crystals, is performed with radioactive source up to 1.5 MeV. However, PGI features gamma ray-energies up to 15 MeV which are not easily provided by the usual laboratory calibration sources. Extrapolating the behaviour of the detector from the "low" energy data is not correct and leads to unreliable data for calibration and performance estimation. Therefore, I developed a novel setup that simulates the LYSO light emission in response to gamma photons up to 30 MeV. A LED (emitting at 420 nm) is driven by a pulse generator, emulating the light emitted by a LYSO scintillator when excited by gamma rays. The pulse generator parameters (amplitude, duration, rise and fall time constants) are adjusted so that the LED emitted photons match the intensity and time distribution of the LYSO emission. The photon number in each light pulse is calibrated from the measurements at 511 keV obtained with a ^(22)Na source and a LYSO crystal coupled to the SiPMs. Using this LED setup I characterized the energy resolution and non-linearity of HD and UHD SiPMs in high-energy gamma-ray conditions. The second part of the thesis provides a detailed description of the scintillator setup and of the setup for the simulation of high-energy gamma-ray response, followed by the results of the characterization performing with these setups. Summarizing the results, the lowest non-linearity is provided by the technology with highest cell density, the RGB-UHD. For the 10 and 12.5 μm-cells we obtained values of 4.5% and 5% respectively at 5 MeV and 6 V over-voltage. On the other hand, we measured the best energy resolution of 2.6% and 2.3% at 5 MeV for the largest SiPM cells of 20 and 25 μm respectively, without the intrinsic term of the scintillator crystal and at 6 V over-voltage. This is due to the dependence of the energy resolution on the photon detection efficiency, which increases with the size of the SiPM cell. The optimal performance of the detector in high-dynamic-range applications, which depends on the several SiPM parameters, such as excess noise factor, photon detection efficiency, and cell sizes of the SiPM, is a trade off between non-linearity and energy resolution. At 5 MeV, the best trade-off for prompt gamma imaging application is reached by the 15 μm-cell. At 10 MeV the 12.5 μm-cell provides the best trade-off, because of the higher number of photons emitted by the scintillator. Furthermore, I distinguish the different components of the energy resolution (intrinsic, statistical, detector and electronic noise) as a function of cell sizes, over-voltage and energy, thanks to the combination of the scintillator and LED setups. The estimation of the intrinsic contribution of the scintillator crystal, coupled to the HD SiPMs, getting consistent results among the several cell sizes. On the basis of previous characterization, HD SiPMs with dimensions of 4x4 mm^2 and 15 μm-cell were chosen to produce the photo-detector module of the gamma camera, optimized for an energy range between 2 and 8 MeV. This module is a 8x8 array of SiPMs which is called tile. The production of the tile requires research on packaging techniques to solve two main challenges: the maximization of the photo-sensitive area and the application of a protective resin, transparent in the near UV to maximize light collection from the LYSO. After some R&D on packaging, I obtained a fully functional tile with 64 SiPMs with a fill factor, ratio between the photo-sensitive area and the total area, of about 86%. This fill factor is comparable to the values obtained when a Through Silicon Vias (TSVs) technique is used to connect SiPMs but without the high production cost and the additional fabrication process complexity of the TSV. It should be highlighted that packaging operations is very critical because it is necessary to produce a tile with all working SiPMs, since defective items can not be replaced in the tile. The last part of the thesis presents the packaging procedure that I have defined to produce photo-detector modules and the characterization of the photo-detector array in terms of energy resolution, position sensitive and non-linearity. The measurements on the tile were carried out jointly with the Gammarad partner of Politecnico di Milano, which provided the ASIC and DAQ for the readout. In conclusion, the R&D activity carried out during this thesis has provided to Gammarad project the final photo-detection module with state of the art performance for high-energy gamma-ray spectroscopy. The characterization of the module shows also a position sensitivity that matches with the SiPM dimensions, and a proper acquisition of high-energy gamma-ray events from 800 keV to 13 MeV. This module will be tested on beam in an experimental treatment room at the Proton therapy facility in Trento by the Gammarad project partners.

O interesse em óxidos dopados com metais de transição tem crescido muito rapidamente nos últimos anos em função da previsão teórica de ordenamento ferromagnético a temperatura ambiente nestes sistemas. Entretanto, apesar do grande número de relatos experimentais e teóricos, a natureza das propriedades magnéticas frequentemente observadas continua um tema controverso. Muitos trabalhos recentes relatam que ordenamento ferromagnético é função direta de defeitos estruturais. Resultados experimentais obtidos em nosso grupo de pesquisas demonstram que defeitos no sítio do oxigênio não são efetivamente responsáveis por promover o ferromagnetismo desejado. Neste contexto, propomos aqui o estudo relacionado a síntese e caracterizações estrutural e magnética de amostras óxidas a partir da matriz de TiO2 na fase anatásio, dopada com Co e Sb. O objetivo da co-dopagem com Sb é introduzir defeitos no sítio do Ti através de um processo de compensação de carga devido a diferenças nos estados de oxidação. Neste trabalho preparamos pós nanoestruturados de Ti1-x-yCoxSbyO2-δ na fase anatásio com x = 0; 0,03 e y = 0; 0,04; 0,08; 0,12 e 0,16. As amostras foram preparadas pelo método dos precursores polimérico, o Pechini. A caracterização estrutural foi realizada através das técnicas de difração de raios-X, espectroscopia de espalhamento Raman, absorção de raios-X e microscopia eletrônica de transmissão de alta resolução. Obtivemos uma granulometria inferior a 10 nm. Os dados estruturais confirmam a inserção do Co e do Sb na matriz de TiO2 em caráter substitucional ao Ti, sem a formação de segregados ou fases secundárias. Com a co-dopagem com Sb a estrutura das amostras gradativamente se degrada. Os resultados das análises de absorção de raios-X revelam a presença de Sb tanto com oxidação 3+ quanto 5+, levando ao aumento das concentrações das vacâncias de O e de Ti concomitantemente. A caracterização magnética se deu por magnetometria SQUID. Os resultados obtidos a temperatura ambiente demonstram a presença de uma fase ferromagnética potencialmente relacionada às vacâncias de Ti. / The interest in transitional metal doped oxides has been grown very fast in the last years since the theoretical prediction of room temperature ferromagnetism for such kind of systems. However, in spite of the great number of experimental and theoretical reports in this research area, the nature of the often observed magnetic properties still remain a controversial issue. Several recent works has been shown that ferromagnetic ordering depends on structural defects. Our recent experimental results demonstrates that defects at the anion sites (oxygen) are not effective to promote the desired ferromagnetism. In this context, we propose here the study related to the synthesis and the structural and magnetic characterization of oxide samples based on the nanostructured anatase TiO2 matrix doped with Co and Sb. The purpose of the co-doping with Sb is to introduce defects at the Ti due the process of charge compensation associated to the differences in the states of oxidation. In this work we prepared nanostructured anatase Ti1-x-yCoxSbyO2-δ samples with x = 0; 0.03 and y = 0.04; 0.08; 0.12; and 0.16. The samples were prepared by the Pechini method. The structural characterization were conducted by X-ray diffraction, Raman scattering spectroscopy, X-ray absorption and high-resolution transmission electron microscopy. The granulometry is lower than 10 nm. The structural data confirms the Co and the Sb incorporation into the anatase TiO2 matrix with no segregated related phases. With the Sb co-doping the structure of the samples are gradually degraded. X-ray absorption results reveals the presence of Sb3+ and Sb5+ in the samples and an induced growing concentration of both O and Ti vacancies. The magnetic characterization were conducted by using a SQUID magnetometer. The results present a room temperature ferromagnetic phase for all the samples closely related to the concentration of Ti vacancies.

Submitted by Edisangela Bastos (edisangela@ufpa.br) on 2018-04-11T18:09:47Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_ProcessosRelaxacaoSistemas.pdf: 1260132 bytes, checksum: ad4fe6b7c854c1f14a57345a390d826a (MD5) / Approved for entry into archive by Edisangela Bastos (edisangela@ufpa.br) on 2018-05-04T13:56:21Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_ProcessosRelaxacaoSistemas.pdf: 1260132 bytes, checksum: ad4fe6b7c854c1f14a57345a390d826a (MD5) / Made available in DSpace on 2018-05-04T13:56:21Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_ProcessosRelaxacaoSistemas.pdf: 1260132 bytes, checksum: ad4fe6b7c854c1f14a57345a390d826a (MD5) Previous issue date: 1985-08-16 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo / Utilizamos o método do operador estatístico de não-equilíbrio desenvolvido, por D. N. Zubarev, baseado no formalismo da entropia máxima de E. T. Jaynes, para derivar um conjunto de equações de transporte que descrevem a evolução temporal de um plasma de semicondutor altamente excitado. A partir deste conjunto de equações obtemos a evolução temporal das variáveis termodinâmicas intensivas de interesse para a descrição do processo de relaxação do plasma, e aplicamos ao estudo dos semicondutores GaAs, CdS e CdSe.

This work shows that it is possible to fabricate phosphate-based planar wave-guides activated by rare earth ions both by sol-gel and RF-sputtering techniques. The objective of this thesis has been to evaluate various methodologies for fab-rication Phosphorous-based planar waveguides. In this context sol-gel and RF-sputtering techniques for planar waveguides fabrication has been investigated. RF-process has been optimized. In case of sol-gel technique a further thermo-dynamical study is required. Each of technique has drawbacks, in sol-gel method the principal question is related to the kinetics of the reaction, since it is too fast, to better control of the reaction rates, and better adjustment of the technological films fabrication, which effects on spectroscopic properties of the waveguiding systems: losses, refractive index. In case of RF-sputtering is no-ticeable that the refractive index is low, and the losses are less than 0.2 dB/cm, however the multicomponent target material increase the complexity of the structure.

Submitted by Jaqueline Silva (jtas29@gmail.com) on 2014-09-15T18:48:07Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Ademar Paulo Júnior.pdf: 470454 bytes, checksum: ca666cb4df9cfed260dd792d9b884664 (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2014-09-15T18:48:28Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Ademar Paulo Júnior.pdf: 470454 bytes, checksum: ca666cb4df9cfed260dd792d9b884664 (MD5) / Made available in DSpace on 2014-09-15T18:48:28Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Ademar Paulo Júnior.pdf: 470454 bytes, checksum: ca666cb4df9cfed260dd792d9b884664 (MD5) Previous issue date: 2014-02-17 / The Quantum Chromodynamics (QCD) is the current theory that aim to describe the strong interactions in the Standard Model. It is a non-abelian gauge theory where quarks and gluons are the fundamental particles. However, QCD exhibits difficulties when low energy regimes are considered and perturbative methods cannot be employed. Thus, effective models are extremely important and useful when low energy limits are considered. Starting with QCD we develop an effetive model taking into account the second order gluon condensate, ⟨Aa A a ⟩, and quark-antiquark, ⟨ qq⟩. The coupled GAP equations are derived for Ns = 3 and numerical solutions are found for that. Furthermore, a functional expansion from effective potencial to the sixth order is calculated and contributions from that terms inserted into the effective lagrangian. / A Cromodin^amica Qu^antica (QCD) e a atual teoria que busca descrever as intera c~oes fortes dentro do modelo padr~ao. Trata-se de uma teoria de calibre n~ao-abeliana em que os quarks e gl uons constituem as part culas fundamentais. Entretanto, a QCD apresenta di - culdades quando consideram-se regimes de baixas energias em que t ecnicas n~ao perturbativas devem ser utilizadas. Assim, o uso de modelos efetivos e de extrema import^ancia e utilidade para os regimes de baixas energias que s~ao os de interesse deste trabalho. Partindo da QCD desenvolveremos um modelo efetivo para intera c~oes entre quarks levando em conta a presen ca dos condensados de gl uons de ordem dois, ⟨Aa A a ⟩, e de quark-antiquark, ⟨ qq⟩. As equa c~oes do GAP acopladas s~ao obtidas para Ns = 3 e suas solu c~oes num ericas s~ao encontradas. Al em disso, a expans~ao funcional do potencial efetivo at e sexta ordem no campo dos quarks e calculada e as contribui c~oes destes termos consideradas na lagrangeana efetiva.

Made available in DSpace on 2014-06-11T19:27:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-17Bitstream added on 2014-06-13T19:15:36Z : No. of bitstreams: 1 amorim_va_me_guara.pdf: 461720 bytes, checksum: 3b0e31ee8648d12655bf8ee9dc3a0c20 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No capítulo 2 faz-se uma breve revisão e uma generalização da estrutura matemática sob a qual a teoria da relatividade restrita se fundamenta. Indiscutivelmente esta representa a base de todo formalismo que é desenvolvido ao longo deste trabalho. Enquanto capítulo este figura um papel eminentemente didático. No capitulo 3 faz-se um estudo detalhado do formalismo Lagrangiano em teoria quântica de campos, abordando tanto o campo escalar real como o campo escalar complexo. Dá-se atenção especial às transformações globais e locais que estes campos podem sofrer, dando origem a importantes resultados que são utilizados ao longo do trabalho: resultados estes provenientes, claro, dessas análises. No capítulo 4 é desenvolvido um conceito fundamental, a ideia de quebra espontânea de simetria. Trata-se do tema evidenciando as principais características de cada caso estudado, abeliano e não-abeliano. A partir dessa estrutura, no capitulo 5, faz-se um estudo refinado da construção de Dirac acerca da possibilidade de existência de monopolos magnéticos. Constrói-se, a aprtitr do eletromagnetismo usual de Maxwell, a primeira ideia de monopolos magnéticos, conhecido como monopolo de Dirac. Por ultimo, no capitulo 6, desenvolve-se a abordagem de t’Hooft e Polyakov acerca da possibilidade de existência de monopolos magnéticos. Partindo de uma lagrangiana não abeliana obtém-se a solução, estima-se a massa, e ainda se calcula a carga de monopolo. Todos os resultados obtidos nas mais variadas seções são comentados e confrontados trazendo à tona o contexto em que as teorias estudadas têm apenas representação especulativa e ainda qual a possibilidade de se encontrar monopolos magnéticos em teorias de grande unificação / At first, in the chapter 2, we present a brief review and the generalization of the mathematical structure in which the special relativity theory is based on. This chapter plays a highly didactic role. Undoubtedly, this represents the basis of all formalism presented in this work. In chapter 3 we present the lagrangiana formalism in quantum field theory addressing the real scalar field and the complex scalar field. We pay a special attention to the global and the local transformations on the fields. in chapter 4 a fundamental concept is developed – the spontaneous breakdown symmetry. This topic in particular is treated showing the main features of each studied case – the abelian one and the non-abelian one. Based on this structure, in the chapter 5 a refined study is done about the Dirac´s Monopole. From the usual electromagnetism theory it´s buit the first idea about the magnetic monopole. In the and chapter 6, the t´Hooft and Polyakov treatment to the magnet monopole is constructed. Starting with a non-belian lagrangiana it´s obtained the solution, the mass and its charge. All the obtained results in the more variety sections in the present text are commented bringing up te context in which the studied theories have only an speculated treatment and what is the possibility in finding magnetic monopoles in grand unification theories

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-04-05T14:36:38Z No. of bitstreams: 1 MEDINA_Renato_2017.pdf: 32490687 bytes, checksum: dad854d12c7bf3ae0093f0dbc031a5b8 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-04-05T14:36:52Z (GMT) No. of bitstreams: 1 MEDINA_Renato_2017.pdf: 32490687 bytes, checksum: dad854d12c7bf3ae0093f0dbc031a5b8 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-04-05T14:37:04Z (GMT) No. of bitstreams: 1 MEDINA_Renato_2017.pdf: 32490687 bytes, checksum: dad854d12c7bf3ae0093f0dbc031a5b8 (MD5) / Made available in DSpace on 2017-04-05T14:37:14Z (GMT). No. of bitstreams: 1 MEDINA_Renato_2017.pdf: 32490687 bytes, checksum: dad854d12c7bf3ae0093f0dbc031a5b8 (MD5) Previous issue date: 2017-02-15 / Não recebi financiamento / In this work a study is presented using some teaching strategies in order to strengthen the relationship between mathematics and physics in high school. It is shown how important it is to describe mathematically a physical phenomenon to motivate students in the description and prediction of situations that can be observed in their daily lives. For this purpose, simple examples are considered in classical mechanics, such as Newton’s second law applications and uniform rectilinear and circular motions. The physical phenomena were explored through mathematical concepts which are suitable for high school level such as functions, unit vector, vectors and their projections, coordinate systems and graphs. The approach considered here can be an important step for addressing more advanced and modern topics in physics in which mathematics is imperative, such as relativity and quantum mechanics. It can also favor the understanding of more abstract concepts such as the electromagnetic field, and the modeling of systems in which the performance of experiments or its observation is impracticable, such as the movement of planets or the behavior of atoms in a gas. This proposal was applied to 35 students in the third year of high school in the Bragan¸ca Paulista city, state of S˜ao Paulo. Several calculations and the explanations developed by the students are presented, showing that the proposal was successful, being very well received by the students. The outcome educational product from this proposal consists of a booklet containing all details and the importance of quantifying physical phenomena through mathematical modeling. / Neste trabalho é apresentado um estudo com algumas estratégias de ensino na tentativa de fortalecer a relação entre a matemática e a física no ensino médio. Através de problemas simples em temas da mecânica clássica como aplicações da segunda lei de Newton e movimentos retilíneo e circular uniformes, é discutida a importância de se quantificar matematicamente fenômenos físicos para a descrição e predição de situações que podem ser observadas no dia a dia dos alunos. Para isso foi utilizada uma matemática simples e adequada para o ensino médio explorando conceitos como funções, versores, vetores e suas projeções, sistemas de coordenadas e gráficos. A forma com que os exercícios foram tratados pode ser um passo importante para abordar t´ópios mais avançados e modernos da física em que a matemática é imprescindível, como a relatividade e a mecânica quântica, ou até mesmo favorecer o entendimento de conceitos mais abstratos como o de campo em eletromagnetismo e a modelagem de sistemas em que a execução de experimentos ou a observação seja inviável, como o movimento de planetas ou o comportamento dos átomos em um gás. Esta proposta foi aplicada em uma escola da rede particular da cidade de Bragança Paulista, estado de São Paulo, em uma turma do 3? ano do ensino médio com aproximadamente 35 alunos. Vários cálculos e explicações desenvolvidos pelos estudantes são apresentados, mostrando que a proposta foi muito bem recebida pelos alunos e bem sucedida. O produto educacional proveniente da aplicação desta proposta consiste de um material paradidático no formato de um pequeno livro contendo todos os detalhes e a importância de se quantificar fenômenos físicos através da modelagem matemática.

Made available in DSpace on 2014-12-17T15:15:05Z (GMT). No. of bitstreams: 1 HenioHAR_dissert.pdf: 2631114 bytes, checksum: 60dff4f8aa02185a64e369badebb4290 (MD5) Previous issue date: 1998-02-20 / A linear chain do not present phase transition at any finite temperature in a one dimensional system considering only first neighbors interaction. An example is the Ising ferromagnet in which his critical temperature lies at zero degree. Analogously, in percolation like disordered geometrical systems, the critical point is given by the critical probability equals to one. However, this situation can be drastically changed if we consider long-range bonds, replacing the probability distribution by a function like . In this kind of distribution the limit α → ∞ corresponds to the usual first neighbor bond case. In the other hand α = 0 corresponds to the well know "molecular field" situation. In this thesis we studied the behavior of Pc as a function of a to the bond percolation specially in d = 1. Our goal was to check a conjecture proposed by Tsallis in the context of his Generalized Statistics (a generalization to the Boltzmann-Gibbs statistics). By this conjecture, the scaling laws that depend with the size of the system N, vary in fact with the quantitie / Uma cadeia linear n?o apresenta transi??o de fase a qualquer temperatura finita num sistema unidimensional considerando apenas intera??es entre primeiros vizinhos. Um exemplo disso ? o ferromagneto de Ising que tem o ponto cr?tico a temperatura zero. De urna maneira an?loga, no dom?nio dos sistemas geom?tricos desordenados do tipo percola??o, o ponto cr?tico ? dado pela probabilidade cr?tica igual a um. No entanto, esta situa??o pode ser drasticamente mudada se incluirmos liga??es delongo alcance, substituindo a distribui??o de probabilidade por uma fun??o do tipo: Para este tipo de distribui??o, o limite α → ∞ corresponde ao caso comum com liga??es entre primeiros vizinhos. Enquanto que α = 0 corresponde ao que conhecemos como uma situa??o de "campo molecular". Nesta tese, estudamos o comportamento de Pc como uma fun??o de α para a percola??o por liga??es especialmente no caso d = 1. Nosso prop?sito foi verificar uma conjectura formulada no contexto da Estat?stica Generalizada de Tsallis (uma extens?o da estat?stica de Boltzmann-Gibbs). Segundo esta conjectura, as leis de escala que variam com o tamanho N do sistema, dependem diretamente da Quantidade

In conventional silicon solar cell, the collection probability of light generated carries shows a drop in the high energy range 280-400nm. One of the methods to reduce this loss, is to implement nanometre sized semiconductors on top of a solar cell where high energy photons are absorbed and low energy photons are re-emitted. This effect, called luminescence down-shifter (LDS), modifies the incident solar spectrum producing an enhancement of the energy conversion efficiency of a cell. We investigate this innovative effect using silicon nanoparticles dispersed in a silicon dioxide matrix as active material. In particular, I proposed to model these structures using a transfer matrix approach to simulate its optical properties in combination with a 2D device simulator to estimate the electrical performance. Based on the optimized layer sequences, high efficiency cells were produced within the european project LIMA characterized by silicon quantum dots as active layer. Experimental results demonstrate the validity of this approach by showing an enhancement of the short circuit current density with up to 4%. In addition, a new configuration was proposed to improve the solar cell performances. Here the silicon nanoparticles are placed on a cover glass and not directly on the silicon cells. The aim of this study was to separate the silicon nanocrystals (Si-NCs) layer from the cell. In this way, the solar device is not affected by the Si-NCs layer during the fabrication process, i.e. the surface passivation quality of the cell remains unaffected after the application of the LDS layer. Using this approach, the downshifting contribution can be quantified separately from the passivation effect, as compared with the previous method based on the Si-NCs deposition directly on the solar devices. By suitable choice of the dielectric structures, an improvement in short circuit current of up 1% due to the LDS effect is demonstrated and simulated.