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Noise, Transport and Structural Properties of High Energy Radiation Detectors Based on CdTe
Šik, Ondřej ; Lazar, Josef (referee) ; Navrátil, Vladislav (referee) ; Grmela, Lubomír (advisor)
Poptávka ze strany vesmírného výzkumu, zdravotnictví a bezpečnostního průmyslu způsobila v posledních letech zvýšený zájem o vývoj materiálů pro detekci a zobrazování vysokoenergetického záření. CdTe a jeho slitina CdZnTe. jsou polovodiče umožnují detekci záření o energiích v rozsahu 10 keV až 500 keV. Šířka zakázaného pásma u CdTe / CdZnTe je 1.46 -1.6 eV, což umožňuje produkci krystalů o vysoké rezistivitě (10^10-10^11 cm), která je dostačující pro použití CdTe / CdZnTe při pokojové teplotě. V mé práci byly zkoumány detektory CdTe/CdZnTe v různých stádiích jejich poruchovosti. Byly použity velmi kvalitní spektroskopické detektory, materiál s nižší rezistivitou a výraznou polarizací, detektory s asymetrií elektrických parametrů kontaktů a teplotně degenerované vzorky. Z výsledků analýzy nízkofrekvenčního šumu je patrný obecný závěr, že zvýšená koncentrace defektů způsobí změnu povahy původně monotónního spektra typu 1/f na spektrum s výrazným vlivem generačně-rekombinačních procesů. Další výrazná vlastnost degenerovaných detektorů a detektorů nižší kvality je nárůst spektrální hustoty šumu typu 1/f se vzrůstajícím napájecím napětí se směrnicí výrazně vyšší než 2. Strukturální a chemické analýzy poukázaly, že teplotní generace detektorů způsobuje difuzi kovu použitého při kontaktování a stopových prvků hlouběji do objemu krystalu. Část mé práce je věnována modifikaci povrchu svazkem argonových iontů a jejímu vlivu na chemické složení a morfologii povrchu.
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Optimization of thin films of metal oxide materials
Vítek, Jiří ; Šimonová, Lucie (referee) ; Šubarda, Jiří (advisor)
This thesis is focused on the description of the method of reactive sputtering of thin films. Currently, there are many ways how to create thin films and there are many applications of thin films in various industrial sectors. In this paper at the first are listed the issue of thin films, followed by an overview of the deposition techniques and of the chemical analysis of deposited thin films. It also describes the four-point measurement method of sheet resistance, mechanical test of adhesion and optical properties. At the end of the theoretical part are described the material composition of the deposited films. The goal of the practical part is to optimize the deposition process of the mixed layer of indium tin oxide (In2O3: SnO2) and contribute to the overall understanding of the influence of annealing on the layer. There were created six series of samples with that applied layers. First, the work focused on examining of the influence of annealing on the throughput in the whole measuring range, and then comparing the series due to the transmittance in the visible light spectrum. Furthermore were compared the value of sheet resistance of unannealed and subsequently annealed samples.
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The effect of modification of cermic surface on the sintering of advanced ceramic materials
Vykydal, Adam ; Spusta, Tomáš (referee) ; Pouchlý, Václav (advisor)
This thesis is focused on the effect of modification of ceramic surface on the sintering of the advanced ceramic materials. To modify the surface of ceramic materiál was used method atomic layer deposition. For the research we used materiál TiO2 and materiál TiO2, which was modified using gas in an ALD chamber. To determine the appropriate sintering temperature we used high-temperature dilatometry, where we found that the sintering temperature is about 800 °C. Moreover, the coefficient of thermal expansion (CTE) was determined using subsequent calculation with the data of shrinkage from sintering densification curve. The samples were placed in a kiln where they were sintered on the mentioned temperature on four different dwell times to find effective dwell time for the best value of density of material. Using a scanning electron microscope, the surface-modified material was found to have a uniform structure when sintered to 800 ° C. At a sintering temperature of 1500 ° C, it can be observed that the ZrO2 did not remain only at the grain boundaries, but is more or less evenly distributed. The core-shell structure was not preserved in the structure, however ZrO2 was agglomerated into particles and in the vicinity of these particles titanium dioxide and zirconia react according to the phase diagram. Based on the diagram, it can be stated that this is the ZrTiO4 phase. The occurrence and size of this pase can be verified by RTG analysis.
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Study of catalytic oxidation of carbon monoxide by AFM/SEM
Hrůza, Dominik ; Janák, Marcel (referee) ; Bábor, Petr (advisor)
This diploma thesis focuses on the study of carbon monoxide oxidation on platinum using correlative AFM/SEM microscopy, which has been overlooked in the literature in this field of research. In the introduction is provided a description of the functioning of the used methods. Furthermore, the investigated reaction is theoretically explained, the oxides on platinum are described, and current directions of scientific research are discussed. The experimental part closely follows the theoretical section, where is described the transfer of the experiment between electron microscopes and the challenges associated with this transfer. This is followed by in-situ observations of the influence of ion beam modifications on the studied reaction. These measurements are compared by using electron and ion beams, and is provided a description of individual surface processes. The experimental results demonstrate new possibilities for influencing chemical reactions through surface modification and provide evidence supporting the theory of subsurface forms of oxides. Subsequently, the effects of the tip on the reaction are investigated, presenting the possibility of direct surface modification by engraving. In conclusion, time-resolved spectroscopy and surface mapping of the desorption reaction wave is carried out to elucidate the influence of the chemical wave passing under the tip. The thesis also includes surface spectroscopic analyses to support the conclusions drawn in this thesis.
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Preparation of magnetic nanoparticles by hydrothermal method
Repko, Anton ; Nižňanský, Daniel (advisor) ; Buršík, Josef (referee) ; del Puerto Morales, Maria (referee)
Hydrothermal method of nanoparticle preparation, involving oleic acid, has received certain attention in the last years. However, the published works lack systematic approach to the subject, and the mechanism was not thoroughly investigated, so as to achieve a predictable outcome of the synthesis. The present work investigated the influence of composition of organic and water phase on the synthesis of cobalt ferrite (cobalt(II)-iron(III) oxide) and magnetite nanoparticles, and the mechanism of nanoparticle formation was proposed. Organic phase was based on pentanol, octanol or toluene, containing the precursor - metal oleate. Besides hydrophobic particles, it was even possible to directly prepare hydrophilic oleate-coated particles by using water phase with sodium oleate. Synthetic procedure was then simplified by a separate preparation of cobalt-iron oleate, which led also to a product of narrower size distribution and better phase purity. Size control in the range of 6-11 nm and a batch yield of ca. 500 mg was achieved. Attention was given also to the surface modification of the particles, thus imparting them hydrophilicity. Small di- or tricarboxylic acids were utilized, as well as carboxylmethyl dextran and titanium dioxide. Titanium dioxide required additional protection with...
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The effect of modification of cermic surface on the sintering of advanced ceramic materials
Vykydal, Adam ; Spusta, Tomáš (referee) ; Pouchlý, Václav (advisor)
This thesis is focused on the effect of modification of ceramic surface on the sintering of the advanced ceramic materials. To modify the surface of ceramic materiál was used method atomic layer deposition. For the research we used materiál TiO2 and materiál TiO2, which was modified using gas in an ALD chamber. To determine the appropriate sintering temperature we used high-temperature dilatometry, where we found that the sintering temperature is about 800 °C. Moreover, the coefficient of thermal expansion (CTE) was determined using subsequent calculation with the data of shrinkage from sintering densification curve. The samples were placed in a kiln where they were sintered on the mentioned temperature on four different dwell times to find effective dwell time for the best value of density of material. Using a scanning electron microscope, the surface-modified material was found to have a uniform structure when sintered to 800 ° C. At a sintering temperature of 1500 ° C, it can be observed that the ZrO2 did not remain only at the grain boundaries, but is more or less evenly distributed. The core-shell structure was not preserved in the structure, however ZrO2 was agglomerated into particles and in the vicinity of these particles titanium dioxide and zirconia react according to the phase diagram. Based on the diagram, it can be stated that this is the ZrTiO4 phase. The occurrence and size of this pase can be verified by RTG analysis.
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Design and synthesis of surface architectures on fluorescent nanodiamonds
Havlík, Jan
anks to their unique properties and high biocompatibilities, fluorescent nanodiamonds are promising representatives of modern carbon nanomaterials with a broad range of applications. Nevertheless, their wider use is limited because of weak fluorescence intensity and low colloidal stability in the biological environment. e optimization of treatment procedures and development of new suitable surface designs is therefore critically needed. In this study, several key steps for fluorescent nanodiamond treatment have been optimized, leading to both a substantial increase in fluorescence intensity and to significantly lower surface damage caused by graphitization. Further, a new high-throughput irradiation technique was developed. e influence of surface chemistry on the fluorescence parameters was studied using partial fluorination of the functional groups on the nanodiamond surface. A novel method which significantly affects the interaction of nanodiamonds with biological systems by increasing of the homogeneity and circularity was developed. e potential of nanodiamonds for future medical and biological research was demonstrated on particles with complex surface architectures that enabled targeting and therapy of tumor cells. Moreover, a strong and highly selective affinity of fibroblast growth factors to diamond...
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Design and synthesis of surface architectures on fluorescent nanodiamonds
Havlík, Jan
anks to their unique properties and high biocompatibilities, fluorescent nanodiamonds are promising representatives of modern carbon nanomaterials with a broad range of applications. Nevertheless, their wider use is limited because of weak fluorescence intensity and low colloidal stability in the biological environment. e optimization of treatment procedures and development of new suitable surface designs is therefore critically needed. In this study, several key steps for fluorescent nanodiamond treatment have been optimized, leading to both a substantial increase in fluorescence intensity and to significantly lower surface damage caused by graphitization. Further, a new high-throughput irradiation technique was developed. e influence of surface chemistry on the fluorescence parameters was studied using partial fluorination of the functional groups on the nanodiamond surface. A novel method which significantly affects the interaction of nanodiamonds with biological systems by increasing of the homogeneity and circularity was developed. e potential of nanodiamonds for future medical and biological research was demonstrated on particles with complex surface architectures that enabled targeting and therapy of tumor cells. Moreover, a strong and highly selective affinity of fibroblast growth factors to diamond...
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Design and synthesis of surface architectures on fluorescent nanodiamonds
Havlík, Jan ; Kotek, Jan (advisor) ; Lang, Kamil (referee) ; Štěpánek, František (referee)
anks to their unique properties and high biocompatibilities, fluorescent nanodiamonds are promising representatives of modern carbon nanomaterials with a broad range of applications. Nevertheless, their wider use is limited because of weak fluorescence intensity and low colloidal stability in the biological environment. e optimization of treatment procedures and development of new suitable surface designs is therefore critically needed. In this study, several key steps for fluorescent nanodiamond treatment have been optimized, leading to both a substantial increase in fluorescence intensity and to significantly lower surface damage caused by graphitization. Further, a new high-throughput irradiation technique was developed. e influence of surface chemistry on the fluorescence parameters was studied using partial fluorination of the functional groups on the nanodiamond surface. A novel method which significantly affects the interaction of nanodiamonds with biological systems by increasing of the homogeneity and circularity was developed. e potential of nanodiamonds for future medical and biological research was demonstrated on particles with complex surface architectures that enabled targeting and therapy of tumor cells. Moreover, a strong and highly selective affinity of fibroblast growth factors to diamond...
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