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Scintilační detektor sekundárních elektronů pro ESEM
Čudek, Pavel ; Špinka, Jiří (oponent) ; Jirák, Josef (vedoucí práce)
Práce se zabývá úpravou a stavbou scintilačního detektoru sekundárních elektronů pro enviromentální rastrovací elektronový mikroskop. Popisuje problematiku rastrovací enviromentální elektronové mikroskopie, typy detektorů a detekci sekundárních elektronů. Obsahem praktické části je návrh a stavba nového scintilačního detektoru na základě simulací drah sekundárních elektronů. U realizovaného detektoru pak proměření jeho parametrů, proměření tlakových závislostí a optimalizace elektrodového systému.
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Determination of titanium dioxide nanoparticles in personal care products
Košík, Juraj ; Čáslavský, Josef (oponent) ; Vávrová, Milada (vedoucí práce)
The following master thesis deals with extraction of titanium dioxide nanoparticles (TiO2 NPs) from consumer care products, concretely sunscreens, and subsequent characterization of these particles. TiO2 nanoparticles are present in an increasing number of commercially available products. Therefore, there is an increasing need to evaluate the potential fate and indirect exposure of TiO2 NPs of different sizes and shapes and investigate their entire life cycle. Feasibility of using ultrafiltration and ultracentrifugation as an extraction method were investigated. Two extraction method for extracting TiO2 nanoparticles were developed and applied to sunscreen samples. Extracted particles can be used for ecotoxicological and mesocosmos experiments. Secondly, size of extracted particles was determined using dynamic light scattering (DLS) and transmission electron microscopy (TEM).
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Gecko mimicking surfaces
Fecko, Peter ; Boušek, Jaroslav (oponent) ; Pekárek, Jan (vedoucí práce)
Adhesive capabilities of a gecko lizard have been the subject of many studies and an inspiration for many artificial imitations and inventions. This work proposes a design version of synthetic gecko structures in a form of micro-pillars, that would have similar adhesion capabilities as gecko setae. Structures made of Parylene C polymer have been created using photolithography and silicon etching techniques. Following focus was on various methods of surface modifications and characterisation of these structures to determine the adhesion forces on their surface, before and after modifications.
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Elektronová litografie na nevodivých substrátech
Hovádková, Zuzana ; Šamořil, Tomáš (oponent) ; Dvořák, Petr (vedoucí práce)
Elektronová litografie zažívá v posledních letech velký rozmach, zejména díky možnosti vytvořit velké struktury s přesným rozlišením. Tato práce se zabývá elektronovou litografií na nevodivých substrátech, a to konkrétně na skle. Litografie na skle má využití zejména v biologii, kde je potřeba transparentních substrátů pro světlo, které jsou zároveň netoxické pro růst buněk. V experimentální části jsou ukázány dva způsoby kompenzace akumulovaného náboje a porovnány možnosti jejich dalšího využití.
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Surface analysis of xGnP/PEI nanocomposite
Červenka, Jiří ; Klapetek, Petr (oponent) ; Čech, Vladimír (vedoucí práce)
This Diploma thesis deals with surface analysis of nanocomposite foil – polyetherimide matrix (PEI) reinforced by exfoliated graphite nanoplatelets (xGnP). The PEI foil without reinforcement and separate xGnP particles were also analysed. Samples of the nanocomposite and the PEI foil were etched for various times by argon plasma. Scanning electron microscopy (SEM) was used to characterize xGnP agglomerates dispersed over silicon wafer and pristine/etched samples of PEI foil and nanocomposite xGnP/PEI foil. Graphite nanoplatelets were identified at surface of etched nanocomposite foil. Atomic force microscopy (AFM) was used for surface topography imaging of separate nanoplatelets and those uncovered at the surface of etched nanocomposite. Surface roughness (root mean square, peak to peak) of etched nanocomposite increased with prolonged etching time. Atomic force acoustic microscopy (AFAM) was used to characterize elastic anisotropy of etched nanocomposite. Nanoindentation measurements were employed to characterize the local mechanical properties of PEI and nanocomposite foils.
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Víceelektrodový systém ionizačního detektoru pro environmentální rastrovací elektronový mikroskop
Uhlář, Vít ; Špinka, Jiří (oponent) ; Jirák, Josef (vedoucí práce)
Diplomová práce se zabývá problematikou environmentální rastrovací elektronové mikroskopie a detekce signálních elektronů s použitím ionizačního detektoru. První část práce hovoří o principu a uspořádání environmentálního rastrovacího elektronového mikroskopu. Druhá část práce popisuje druhy rozptylu a jednotlivé signály, které vznikají při interakci primárního elektronového svazku se vzorkem. Třetí část práce vysvětluje problematiku nárazové ionizace a ionizačního detektoru. Experimentální část práce se zabývá použitím segmentového ionizačního detektoru a stanovením zesílení výsledného signálu z mědi a platiny v závislosti na zapojení elektrod detektoru. Dále práce zkoumá vliv uspořádání elektrod ionizačního detektoru na materiálový kontrast a na změny napěťového kontrastu na přechodu báze emitor bipolárního tranzistoru typu NPN. Všechny experimenty byly prováděny v závislosti na tlaku nasycených par v komoře vzorku.
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Fatigue resistance and mechanisms of the fatigue damage in materials for high temperatures
Petráš, Roman ; Kohout,, Jan (oponent) ; Weidner, Anja (oponent) ; Polák, Jaroslav (vedoucí práce)
Superaustenitic stainless 22Cr25NiWCoCu steel designed for high temperature applications in power generation industry was investigated in terms of low cycle fatigue at room and elevated temperature. Individual specimens were subjected to different loading procedures in order to study the material response along with the mechanism of fatigue damage. Cyclic hardening/softening curves, Coffin-Manson and cyclic stress-strain curves were evaluated. Life-time behavior for various types of loading procedures was discussed with respect to the effective damage mechanisms developed under specific loading conditions. Standard isothermal low cycle fatigue tests at room and elevated temperature were conducted. Hysteresis loops recorded during cycling were analyzed by means of generalized statistical theory of hysteresis loop. The probability density distribution function of the internal critical stresses and its evolution during cycling straining was derived for different strain amplitudes. Evolution of the surface relief along with the internal dislocation arrangement for both temperatures was assessed in relation to the development of the probability density function of internal critical stresses. Surface relief evolution using SEM equipped with FIB revealed the early fatigue crack formation. Cyclic loading at room temperature resulted in the localization of the cyclic plastic strain into persistent slip bands and formation of surface persistent slip marking consisting of extrusions and intrusions. Deepening of an intrusion leads to the initiation of the fatigue crack from the tip of the deepest intrusion. Distinctive mechanism of the early crack formation was found in test at elevated temperature where the effect of environment is crucial. Rapid oxidation of the grain boundaries and subsequent cracking of the oxidized grain boundaries represent effective mechanisms of the nucleation of I-stage fatigue crack. Additional 10 minute tensile dwells implemented into the loading cycle led to the internal damage evolution. To reveal internal damage the longitudinal cross-sections parallel to the stress axis of the tested specimen were produced. The crack paths and their relation to the grain and twin boundaries were studied using electron back-scattered diffraction (EBSD) technique. The influence of dwells introduced in the loading cycle on fatigue life is assessed in relation to the evolution of the surface relief and internal damage. Specimens were also exposed to more complex loading procedures where the load along with the temperature varies with time simultaneously. In-phase and out-of-phase type thermomechanical fatigue (TMF) tests with or without dwells were conducted. Rapid cyclic hardening was observed in all tests regardless of the strain amplitude applied while tendency to saturation was found primarily in out-of-phase loading with/without dwells. Investigation of the surface relief by means of SEM along with FIB cutting revealed the preferential oxidization and cracking of the grain boundaries perpendicular to the loading axis. Dwells implemented in maximum tension resulted in the enlargement of the plastic strain amplitude and to the additional creep damage in the form of internal cracks. Intergranular crack propagation was observed for in-phase cycling with/without dwells. Damage evolution in out-of-phase cycling was found to be principally similar for straining with and without dwell.
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Analysis and characterisation of spirally-arranged field-emission nanostructure
Ondříšková, Martina ; Sobola, Dinara (oponent) ; Knápek, Alexandr (vedoucí práce)
Cathodes containing arrays of high aspect ratio field emitters are of great interest as sources of electron beams for vacuum electronic devices. The desire to maximize current and current density leads to the design of denser arrays. However, denser arrays lead to undesirable field shielding effects caused by the presence of surrounding emitters in the array. To reduce the shielding effect and thus maximize the field enhancement, an array of emitters was designed with an arrangement inspired by the natural phenomenon of phyllotaxis. The structure thus designed was created using electron beam lithography and reactive ion etching to form micropillars. A black silicon etching technique was used to create ultra-sharp tips with a radius in the order of tens of nanometers on the top of each micropillar. Analysis of the sample topography was performed by Scanning electron microscopy. Ultraviolet photoelectron spectroscopy was used to determine the work function. To find out the emission properties of the fabricated structures, a Field emission microscope was constructed and its electron gun was modified to experimentally use the fabricated structure as the cathode. A Murphy-Good plot was used to analyze the field emission data, to which the orthodoxy test was applied to check the validity of the experimental I-V data. Current stability measurement was performed to observe current fluctuations.
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Analysis and characterisation of spirally-arranged field-emission nanostructure
Ondříšková, Martina ; Sobola, Dinara (oponent) ; Knápek, Alexandr (vedoucí práce)
Cathodes containing arrays of high aspect ratio field emitters are of great interest as sources of electron beams for vacuum electronic devices. The desire to maximize current and current density leads to the design of denser arrays. However, denser arrays lead to undesirable field shielding effects caused by the presence of surrounding emitters in the array. To reduce the shielding effect and thus maximize the field enhancement, an array of emitters was designed with an arrangement inspired by the natural phenomenon of phyllotaxis. The structure thus designed was created using electron beam lithography and reactive ion etching to form micropillars. A black silicon etching technique was used to create ultra-sharp tips with a radius in the order of tens of nanometers on the top of each micropillar. Analysis of the sample topography was performed by Scanning electron microscopy. Ultraviolet photoelectron spectroscopy was used to determine the work function. To find out the emission properties of the fabricated structures, a Field emission microscope was constructed and its electron gun was modified to experimentally use the fabricated structure as the cathode. A Murphy-Good plot was used to analyze the field emission data, to which the orthodoxy test was applied to check the validity of the experimental I-V data. Current stability measurement was performed to observe current fluctuations.
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Fatigue resistance and mechanisms of the fatigue damage in materials for high temperatures
Petráš, Roman ; Kohout,, Jan (oponent) ; Weidner, Anja (oponent) ; Polák, Jaroslav (vedoucí práce)
Superaustenitic stainless 22Cr25NiWCoCu steel designed for high temperature applications in power generation industry was investigated in terms of low cycle fatigue at room and elevated temperature. Individual specimens were subjected to different loading procedures in order to study the material response along with the mechanism of fatigue damage. Cyclic hardening/softening curves, Coffin-Manson and cyclic stress-strain curves were evaluated. Life-time behavior for various types of loading procedures was discussed with respect to the effective damage mechanisms developed under specific loading conditions. Standard isothermal low cycle fatigue tests at room and elevated temperature were conducted. Hysteresis loops recorded during cycling were analyzed by means of generalized statistical theory of hysteresis loop. The probability density distribution function of the internal critical stresses and its evolution during cycling straining was derived for different strain amplitudes. Evolution of the surface relief along with the internal dislocation arrangement for both temperatures was assessed in relation to the development of the probability density function of internal critical stresses. Surface relief evolution using SEM equipped with FIB revealed the early fatigue crack formation. Cyclic loading at room temperature resulted in the localization of the cyclic plastic strain into persistent slip bands and formation of surface persistent slip marking consisting of extrusions and intrusions. Deepening of an intrusion leads to the initiation of the fatigue crack from the tip of the deepest intrusion. Distinctive mechanism of the early crack formation was found in test at elevated temperature where the effect of environment is crucial. Rapid oxidation of the grain boundaries and subsequent cracking of the oxidized grain boundaries represent effective mechanisms of the nucleation of I-stage fatigue crack. Additional 10 minute tensile dwells implemented into the loading cycle led to the internal damage evolution. To reveal internal damage the longitudinal cross-sections parallel to the stress axis of the tested specimen were produced. The crack paths and their relation to the grain and twin boundaries were studied using electron back-scattered diffraction (EBSD) technique. The influence of dwells introduced in the loading cycle on fatigue life is assessed in relation to the evolution of the surface relief and internal damage. Specimens were also exposed to more complex loading procedures where the load along with the temperature varies with time simultaneously. In-phase and out-of-phase type thermomechanical fatigue (TMF) tests with or without dwells were conducted. Rapid cyclic hardening was observed in all tests regardless of the strain amplitude applied while tendency to saturation was found primarily in out-of-phase loading with/without dwells. Investigation of the surface relief by means of SEM along with FIB cutting revealed the preferential oxidization and cracking of the grain boundaries perpendicular to the loading axis. Dwells implemented in maximum tension resulted in the enlargement of the plastic strain amplitude and to the additional creep damage in the form of internal cracks. Intergranular crack propagation was observed for in-phase cycling with/without dwells. Damage evolution in out-of-phase cycling was found to be principally similar for straining with and without dwell.
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