Por ser um semicondutor de elevado número atômico, elevada densidade de massa e largo gap de energia, o brometo de tálio (TlBr) é um material promissor para a detecção da radiação à temperatura ambiente. Entretanto, existem poucos trabalhos relacionados ao estudo deste material sob forma de filme fino policristalino para produção em grandes áreas como desejado para aplicações médicas. Neste trabalho, as técnicas de spray pyrolysis e evaporação térmica foram avaliadas como métodos alternativos para a deposição de filmes de TlBr policristalinos. Ambas as técnicas apresentam relativo baixo custo e podem facilmente ser expandidas para grandes áreas. O objetivos deste trabalho é o estudo da influência das principais condições de crescimento nas propriedades (estruturais, ópticas e elétricas) finais dos filmes de TlBr. Para os filmes produzidos por spray pyrolysis água mili-Q foi utilizada como solvente. A solução (0,10 g de TlBr dissolvidos em 100 g de água) foi agitada à temperatura de 70ºC. Cada deposição foi realizado mantendo os substratos (1cm x 1cm) à temperatura de 100ºC, com um fluxo de nitrogênio (N2) de 8 1/min e um fluxo de solução de aproximadamente 1/90 (ml/s). A distância bico de spray-substrato utilizada foi de 19 cm. Os filmes de TlBr evaporados foram crescidos pela evaporação térmica do material a partir de um cadinho de tungstênio. Um sistema de aquecimento dos substratos foi implantado e permitiu a variação da temperatura destes durante a deposição desde a temperatura ambiente até 200ºC. A separação substrato-superfície de evaporação, h, e o número de deposições por filme, n, também foram variados no intervalo de 3 a 9 cm e 1 a 4, respectivamente. A estrutura dos filmes foi investigada por Difração de Raio-x, a morfologia por Microscopia Eletrônica de Verredura e a composição através da Espectroscopia de Dispersão de Energia (EDS). Experimentos ópticos de transmitância em função do comprimento de ondas foram realizados para estimar o gap ótico dos filmes.As resistividades foram medidas a partir de experimentos de corrente em função da voltagem aplicada fluorescente (20 watts). Por fim, algumas amostras selecionadas foram expostas aos raios-X na faixa de diagnóstico mamográfico. As melhores propriedades foram obtidas para os filmes crescidos por evaporação térmica. A maior compactação e o maior gap óptico foram encontrados para os filmes produzidos a partir de h= 9 cm, os quais garantiram a maior sensibilidade para estes filmes quando expostos aos raios-X. Para os filmes produzidos pela deposição sequencial de várias camadas, a estrutura colunar dos filmes foi mantida para camadas superiores e resultados semelhantes para todas as amostras foram obtidos em relação ao gap óptico e à resistividade elétrica. Além disso, a sensibilidade a partir da utilização de raio-X na faixa mamográfica foi quadruplicada para o filme mais espesso. O aumento da temperatura do substrato resultou na maior compactação e homogeneidade no recobrimento do substrato. Entretanto, uma perda significativa de material durante a evaporação determinou filmes menos espessos em relação aos depósitos à temperatura ambiente. Variações cristalográficas e morfológicas foram obtidas entre os filmes depositados a diferentes temperaturas. Maiores valores gap foram obtidos para 150 e 200ºC. A caracterização elétrica dos filmes depositados a diferentes temperaturas foi limitada, neste trabalho, pela baixa pureza do pó utilizado para produção destes filmes. / Due to its high atomic number, high mass density and intrinsic band gap, thallium bromide (TlBr) is a promising semiconductor for room temperature operation for ionizing radiation detection. However, there are few works related to the study of this material in the polycrystalline thin film form for production in large areas (~ 40 x 40 cm2 ), as desired by medical applications. In this work, spray pyrolysis and thermal evaporation were used as alternative methods for the deposition of polycrystalline TlBr films. Both techniques present relative low cost and can be expanded for large areas. The aim of this work is to investigate the influence of the main growth conditions on the final structural, optical and electrical TlBr films properties. Films produced by spray pyrolysis used mili-Q water as solvent. The solution (0,10g of TlBr dissolved in 100g of water) was stirred at 70o C. Each deposition was performed maintaining the substrates (1cm2 ) at 100o C, the nitrogen rate at 8l/min and the solution flow at 1/90 ml/s approximately. The nozzle-spray to substrate distance was 19 cm. Evaporated TlBr films were grown by resistive thermal evaporation of purified material from a tungsten crucible. The substrate temperature was evaluated from room temperature to 200°C. The separation between evaporation source and substrates, h, and the number of depositions, n, were also varied from 3 cm up to 9 cm and from 1 up to 4, respectively. The structure of the crystals was investigated by X-ray Diffraction, the morphology by Scanning Electron Microscopy and the composition by Energy Dispersive X-Ray Spectroscopy. Optical experiments of absorbance as a function of wavelength were performed to estimate the optical gap of the TlBr films. Electrical resistivities were measured using current versus voltage experiments. The dark current was compared to the current under illumination with a fluorescent lamp (20 watts). Finally, some selected samples were exposed to X-ray in the range of mammography diagnosis. The best properties were obtained for films produced by resistive thermal evaporation. This technique allowed the production of films with thickness of approximately 28 µm, for a unique deposition of 12 minutes. However, bromine has lower vapor pressure than the thallium, what leads to a Br loss of about 10% in the composition of evaporated films. The smallest distribution of cracks and the largest optical gap were obtained for films produced at the lowest deposition rates. This leads also to a higher increase of the ratio between current under irradiation and in the dark, when the films were exposed to X-rays. For films produced at room temperature using sequential depositions, the columnar structure was kept for the superior layers and similar results for all samples were obtained in relation to optical gap and electrical resistivity. Moreover, for the thicker film, an increase of a factor 4 was observed for the ratio between current under irradiation using X-rays in the mammography range in relation to the dark. The higher substrate temperature leads to significant material loss during the evaporation and determined less thick films in relation to the ones deposited at room temperature. Structural and morphological variations were verified for films deposited at different temperatures. Larger gap values were found for 150 and 200ºC. For the electrical characterization of the films deposited at different temperatures an original powder with higher purity would be necessary. Moreover, due to the significant difference between bromine and thallium vapor pressures, better results would probably be obtained by a change to the hot-wall evaporation technique.

Por ser um semicondutor de elevado número atômico, elevada densidade de massa e largo gap de energia, o brometo de tálio (TlBr) é um material promissor para a detecção da radiação à temperatura ambiente. Entretanto, existem poucos trabalhos relacionados ao estudo deste material sob forma de filme fino policristalino para produção em grandes áreas como desejado para aplicações médicas. Neste trabalho, as técnicas de spray pyrolysis e evaporação térmica foram avaliadas como métodos alternativos para a deposição de filmes de TlBr policristalinos. Ambas as técnicas apresentam relativo baixo custo e podem facilmente ser expandidas para grandes áreas. O objetivos deste trabalho é o estudo da influência das principais condições de crescimento nas propriedades (estruturais, ópticas e elétricas) finais dos filmes de TlBr. Para os filmes produzidos por spray pyrolysis água mili-Q foi utilizada como solvente. A solução (0,10 g de TlBr dissolvidos em 100 g de água) foi agitada à temperatura de 70ºC. Cada deposição foi realizado mantendo os substratos (1cm x 1cm) à temperatura de 100ºC, com um fluxo de nitrogênio (N2) de 8 1/min e um fluxo de solução de aproximadamente 1/90 (ml/s). A distância bico de spray-substrato utilizada foi de 19 cm. Os filmes de TlBr evaporados foram crescidos pela evaporação térmica do material a partir de um cadinho de tungstênio. Um sistema de aquecimento dos substratos foi implantado e permitiu a variação da temperatura destes durante a deposição desde a temperatura ambiente até 200ºC. A separação substrato-superfície de evaporação, h, e o número de deposições por filme, n, também foram variados no intervalo de 3 a 9 cm e 1 a 4, respectivamente. A estrutura dos filmes foi investigada por Difração de Raio-x, a morfologia por Microscopia Eletrônica de Verredura e a composição através da Espectroscopia de Dispersão de Energia (EDS). Experimentos ópticos de transmitância em função do comprimento de ondas foram realizados para estimar o gap ótico dos filmes.As resistividades foram medidas a partir de experimentos de corrente em função da voltagem aplicada fluorescente (20 watts). Por fim, algumas amostras selecionadas foram expostas aos raios-X na faixa de diagnóstico mamográfico. As melhores propriedades foram obtidas para os filmes crescidos por evaporação térmica. A maior compactação e o maior gap óptico foram encontrados para os filmes produzidos a partir de h= 9 cm, os quais garantiram a maior sensibilidade para estes filmes quando expostos aos raios-X. Para os filmes produzidos pela deposição sequencial de várias camadas, a estrutura colunar dos filmes foi mantida para camadas superiores e resultados semelhantes para todas as amostras foram obtidos em relação ao gap óptico e à resistividade elétrica. Além disso, a sensibilidade a partir da utilização de raio-X na faixa mamográfica foi quadruplicada para o filme mais espesso. O aumento da temperatura do substrato resultou na maior compactação e homogeneidade no recobrimento do substrato. Entretanto, uma perda significativa de material durante a evaporação determinou filmes menos espessos em relação aos depósitos à temperatura ambiente. Variações cristalográficas e morfológicas foram obtidas entre os filmes depositados a diferentes temperaturas. Maiores valores gap foram obtidos para 150 e 200ºC. A caracterização elétrica dos filmes depositados a diferentes temperaturas foi limitada, neste trabalho, pela baixa pureza do pó utilizado para produção destes filmes. / Due to its high atomic number, high mass density and intrinsic band gap, thallium bromide (TlBr) is a promising semiconductor for room temperature operation for ionizing radiation detection. However, there are few works related to the study of this material in the polycrystalline thin film form for production in large areas (~ 40 x 40 cm2 ), as desired by medical applications. In this work, spray pyrolysis and thermal evaporation were used as alternative methods for the deposition of polycrystalline TlBr films. Both techniques present relative low cost and can be expanded for large areas. The aim of this work is to investigate the influence of the main growth conditions on the final structural, optical and electrical TlBr films properties. Films produced by spray pyrolysis used mili-Q water as solvent. The solution (0,10g of TlBr dissolved in 100g of water) was stirred at 70o C. Each deposition was performed maintaining the substrates (1cm2 ) at 100o C, the nitrogen rate at 8l/min and the solution flow at 1/90 ml/s approximately. The nozzle-spray to substrate distance was 19 cm. Evaporated TlBr films were grown by resistive thermal evaporation of purified material from a tungsten crucible. The substrate temperature was evaluated from room temperature to 200°C. The separation between evaporation source and substrates, h, and the number of depositions, n, were also varied from 3 cm up to 9 cm and from 1 up to 4, respectively. The structure of the crystals was investigated by X-ray Diffraction, the morphology by Scanning Electron Microscopy and the composition by Energy Dispersive X-Ray Spectroscopy. Optical experiments of absorbance as a function of wavelength were performed to estimate the optical gap of the TlBr films. Electrical resistivities were measured using current versus voltage experiments. The dark current was compared to the current under illumination with a fluorescent lamp (20 watts). Finally, some selected samples were exposed to X-ray in the range of mammography diagnosis. The best properties were obtained for films produced by resistive thermal evaporation. This technique allowed the production of films with thickness of approximately 28 µm, for a unique deposition of 12 minutes. However, bromine has lower vapor pressure than the thallium, what leads to a Br loss of about 10% in the composition of evaporated films. The smallest distribution of cracks and the largest optical gap were obtained for films produced at the lowest deposition rates. This leads also to a higher increase of the ratio between current under irradiation and in the dark, when the films were exposed to X-rays. For films produced at room temperature using sequential depositions, the columnar structure was kept for the superior layers and similar results for all samples were obtained in relation to optical gap and electrical resistivity. Moreover, for the thicker film, an increase of a factor 4 was observed for the ratio between current under irradiation using X-rays in the mammography range in relation to the dark. The higher substrate temperature leads to significant material loss during the evaporation and determined less thick films in relation to the ones deposited at room temperature. Structural and morphological variations were verified for films deposited at different temperatures. Larger gap values were found for 150 and 200ºC. For the electrical characterization of the films deposited at different temperatures an original powder with higher purity would be necessary. Moreover, due to the significant difference between bromine and thallium vapor pressures, better results would probably be obtained by a change to the hot-wall evaporation technique.

Radiations can be classified as either ionizing or non-ionizing according to whether it ionizes or does not ionize the medium through which they propagate. X-rays photons and gamma rays are the typical examples of ionizing radiations whereas radiowave, heat or visible light are examples of non ionizing radiations. UV photons have some features of both ionizing and non-ionizing radiation. Both ionizing and non-ionizing radiation can be harmful to living organisms and to the natural environment. Hence the detection and measurement of radiation is very important for the well being of living organisms as well as the natural environment. Not only for safety reasons, have radiation detectors found their applications in various fields including medical physics, nuclear and particle physics, astronomy and homeland security. Industrial sectors that use radiation detection include medical imaging, security and baggage scanning, the nuclear power industry and defense. Gas electron multiplier (GEM) is one of the most successful representatives of gaseous detectors used for UV photon and X-ray photon detection. Recently there is a growing demand for large area photon detectors with sensitivity reaching to the level of single photon. They are used in spectroscopy and imaging in astronomy high energy physics experiments etc. Thick GEM (THGEM) is a mechanical expansion of standard GEM. It has all the necessary requirements needed for large area detector and offers a multiplication factor that permits efficient detection of light. Hence, the development and performance study of THGEM based radiation detector is chosen as the topic of study in the present thesis. The initial part of the thesis contains simulation studies carried out for the understanding the working of the detector and the effect of various design parameters of THGEM for the above said applications. Different steps for the fabrication of THGEM and the technical challenges faced during the process are discussed. In the view of application of the fabricated THGEM for UV photon detection, cesium iodide photocathode is prepared using thin film technology and characterized. The performance of the photocathode under various operating conditions is studied in terms of its photoemission property. The effect of vacuum treatment on the photoemission property of the photocathode exposed to moist air is studied in detail. A major portion of this thesis focuses on maximizing the detection efficiency of the UV photon detector realized using the fabricated THGEM coupled with the cesium iodide photocathode. Simulations are used at different stages to interpret the experimental observations. The electron spectrum obtained from the detector under study was analyzed. The dependence of secondary effect like photon feedback on the operating parameters is also discussed. The last portion of the thesis deals with the application of THGEM as an X-ray detector. The performance is evaluated in terms of the gain and energy resolution achieved. The thesis is organized as follows: Chapter 1 is divided into two sections. Section A gives a general introduction to different types of radiation detectors found in the present day and their working principles. This is followed by discussion about gas ionization based detector and its working principle in detail. A brief literature survey of the different types of micropattern gas detectors is also given in this section. In Section B of this chapter GEM and THGEM are introduced with discussion about their working principle and areas of application. Chapter 2 deals with the simulation study of THGEM undertaken to have a clear understanding of the detector’s working. Section A of this chapter gives an overview of the simulation tools used for the present thesis in particular ANSYS and GARFIELD. Section B presents the results of the simulation study highlighting the effects of different geometrical and operating parameters on the electric field distribution in and around the THGEM aperture. The relevance of the study to the detectors performance is discussed vividly for all the cases. In Chapter 3, the details of the different steps involved in THGEM fabrication are given. Design aspects involved, fabrication of the THGEM using standard PCB technology coupled with photolithography technique are discussed in this chapter. This is followed by an elaborate description of the test setup used for all the performance study. Preface In the view of application of THGEM as a UV photon detector, cesium iodide photocathode was prepared and characterized. Chapter 4 discusses about the CsI photocathode preparation and its characterization for the above said application. Photoemission property of the photocathode was analyzed under various operating parameters. The effect of vacuum treatment on the photocathode performance is a new aspect of this thesis. Its correlation with the microstructure of the film is reported for the first time. Chapter 5 deals with the application of THGEM as a UV photon detector. The study mainly focuses on the improvement of the detection efficiency of the detector. The effect of drift parameters on the electron transfer efficiency and hence on the detection efficiency of the detector is a major contribution of this thesis. There are no literature available which discusses this aspect of a UV photon detector. The experimental study has been supported with simulation results. In addition to the study on detection efficiency, electron spectrum has also been acquired from the UV photon detector. The spectrum has been analyzed under various operating conditions. Discussions about secondary effects like photon feedback prevailing in the detector output are also present in this chapter. Chapter 6 presents the results of THGEM as an X-ray detector. The performance of the detector has been evaluated in terms of the effective gain and energy resolution achieved under different operating conditions. The gain instability with time and its uniformity across the THGEM area are also studied. The effect of drift field on the energy resolution and its correlation with ETE is a new aspect of this work. Chapter 7 summarizes the salient features of the work presented in this thesis. Also the scope of future work based on this thesis is discussed at the end of the chapter.