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Synthesis, characterization and applications of new types of fiberous structures
Hromádko, Luděk ; Kočí,, Kamila (oponent) ; Pekař, Miloslav (oponent) ; Macák, Jan (vedoucí práce)
This thesis presents a comprehensive investigation of centrifugal spinning and in particular the novel synthetic approaches for nano- and microfibers by this highly interesting technology. New types of polymeric fibers and also inorganic (ceramic) fibers are presented, along with their characterization and their use in various applications. In the first section, many available techniques for fibers preparation are introduced and explained. Their advantages and drawbacks are described and discussed. A comparably large attention is given to electrostatic spinning and centrifugal spinning, which belong between mostly used techniques for industrial production of the fibers. The sub-section on applications describes the main applications of the fibers, for example air/water filtration, tissue engineering, drug delivery and Li-ion battery separators. The second section presents a large experimental and comparative study of the two most used techniques for fiber preparation, the electrospinning and centrifugal spinning. Polyvinyl pyrrolidone (PVP) and polyvinyl acolhol (PVA), as some of the mostly used polymers for fibers preparation, were used for comparison of these techniques. Many parameters (air temperature, humidity, rotations etc.) were exploited and their influence on the fibers´ quality was investigated. Such a large comparatiove study of electrospinning and centrifugal spinning has not yet been conducted before us and this particular effort. The third section presents the preparation of WO3 fibers by centrifugal spinning. New, simple and green recipe of the spinning solution based on the ammonium metatungstate (NH4)6H2W12O40.xH2O and polyvinyl pyrrolidone (PVP) is demonstrated. Influence of variations of the concetration of the polymer and precursor on the properties of resulting fibers is shown. The resulting fibers with the best photocatalytic performance is compared with the fibers prepared by electrospinning and commercialy available nanoparticles. The centrifugal spun fibers showed the 1.4 up to 4 time higher photocatalytic activity. The centrifugaly spun fibers also has higher specific surface (SBET = 22.3 m2/g) compared to electrospun fibers (SBET = 7.4 m2/g) and nanoparticles (SBET = 6.4 m2/g). The fourth section shows the preparation of the amorphous SiO2 fibers. The new recipe for centrifugal spinning has been developed. The spinning solution was based on the tetraethyl orthosilicate (TEOS) and polyvinyl pyrrolidone (PVP). The calcination profile has been tuned to reach the SiO2 fibers with 824 m2/g of specific surface. The prepared SiO2 fibers had pore size distribution in 2 – 10 nm and volume of pores 0.547 cm3/g. The prepared fibers possessed superior adsorption capacity of the water comparing to silicagel of the same textural type. The fifth section presents the preparation of the ZrO2 fibers with addition of yttrium (Y). Two different precursors were used to prepare ZrO2 fibers. The use of pure Zr precursor led to fibers containing the mixture of monoclinic and tetragonal structure. The addition of about 3 mol.% of yttrium led to fibers that consist of tetragonal single phase, which is stabilized by Y. The yttrium addition also led to smaller crystallite size comparing to pure ZrO2 fibers.
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PROGRESS TOWARD THE DEVELOPMENT OF SINGLE NANOWIRE-BASED ARRAYS FOR GAS SENSING APPLICATIONS
Chmela, Ondřej ; Vrňata, Martin (oponent) ; Macák, Jan (oponent) ; Hubálek, Jaromír (vedoucí práce)
This thesis presents the development of silicon-based platforms for selective integration of semiconducting metal oxide (MOX) nanostructures and their use as highly sensitive and selective elements for the detection of gas analytes in prospective mobile devices. Semiconducting MOX nanostructures, for instance nanowires, have proved better gas sensing properties including sensitivity, stability and to a certain extent also selectivity as compared to their bulk counterparts. The use of single (or few) nanowire structures connected in parallel has also shown to be the ideal architecture to achieve well-defined conduction channel easy to modulate by the gas-solid interactions. However, yet current methods for the integration of single nanowire structures in functional devices represent a technological challenge, with most of the methods needing the assistance of techniques, such as focused-ion beam (FIB), which restricts the scalability of the process and increases the cost and time of fabrication. In this context, this work is focused on the search and optimization of technological processes to fabricate gas sensing systems based on arrays of single semiconducting nanowires. In this thesis, three versions of electrode platforms were developed for the selective integration of single gas-sensitive metal oxide nanowires. State-of-the-art multistep throughput fabrication techniques, as well as electron-beam lithography (nanofabrication), were used as crucial fabrication technologies allowing the development of arrays with faced nanoelectrodes and other functional nanostructures. Results show the fabrication of electrode platform with faced nanoelectrodes (100 – 300 nm width) framed in narrow dielectric windows close to the nanowire diameter (100 – 200 nm approx.). These nanoelectrodes were used as both mechanical support to align the single nanowire, and electrical contacts to measure the electrical change along the nanowire during gas detection. Results also include the optimization of techniques for removal and redeposition of nanowires to achieve single nanowire interconnections in the array of parallel electrodes using an alternating electric field as a simple and effective technique for nanowires alignment (dielectrophoresis). The validation of these systems toward various gaseous species (oxidizing and reducing gases) was performed using non-functionalized and Pt-functionalized WO3 nanowires synthesized by aerosol-assisted chemical vapor deposition (AACVD) and backside ceramic heaters (with the operating temperature at 250 °C) assembled on TO-8 package. The sensing parameters of such systems showed better sensing responses in resistive regime to nitrogen dioxide (NO2) and ethanol (EtOH) than their counterparts based on multiple nanowire-based films. The last version of gas sensing systems developed in this thesis (described as third chip generation) includes a third insulated electrode buried under the gas sensitive nanowire for enhanced gas sensing regime. Gas sensing tests of this system to hydrogen (H2) and nitrogen dioxide (NO2) corroborated the enhanced functionality of these systems and the modulation of sensor response by applying external electrical stimuli on the buried electrode.
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Most přes silnici I/11
Macák, Jan ; Šrubař, Jiří (oponent) ; Panáček, Josef (vedoucí práce)
Tato diplomová práce se zabývá návrhem silničního mostu. Objekt se nachází na silnici II. třídy S 7,5/50 a je veden přes silnici I/11 a přeložku MK v Bystřici. Byly vypracovány tři varianty, z nichž byl vybrán spojitý desko-trámový nosník o 6-ti polích pro podrobné zpracování. K této variantě je zpracován statický výpočet nosné konstrukce, ve kterém je zahrnuta i časová analýza konstrukce (jednotlivé fáze výstavby). Statický výpočet je posouzen na mezní stavy dle platných evropských norem. Součástí diplomové práce je také výkresová dokumentace, časový harmonogram výstavby a 3D vizualizace mostního objektu.
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APLIKACE GRAFENU V ELEKTRONICE A TECHNOLOGIE PŘÍPRAVY
Zahradníček, Radim ; Sofer,, Zdeněk (oponent) ; Macák, Jan (oponent) ; Hubálek, Jaromír (vedoucí práce)
Tato dizertační práce je zaměřena na studium aplikace grafenu v elektronice a technologii přípravy. Teoretická část práce popisuje kromě základních vlastností grafenu také metody jeho přípravy, přenosu, charakterizace a možnosti uplatnění v elektronice. Experimentální část je rozdělena do tří kapitol. První kapitola se zabývá výrobou grafenu pomocí depozice z plynné fáze, jeho přenosem a aplikací v oblasti solárních článků. K přenosu grafenu byl nejprve použit polymer polymetylmetakrylát, který byl posléze nahrazen kalafunou z důvodu menší kontaminace grafenu na konci přenosového procesu. Druhá kapitola se zabývá přípravou kvantových teček pomocí exfoliace v kapalné fázi z grafitu a jeho aplikaci ve voltametrii. Voltametrie byla využita v této práci k detekci peroxidu vodíku pomocí zlaté elektrody modifikované kvantovými tečkami z grafenu a jiných dichalkogenů (MoS2, MoSe2, WS2, WSe2). V poslední kapitole je studován vliv substrátu a depozičních podmínek grafenu, vytvářeného plazmou podpořenou depozicí z plynné fáze, na růst, přičemž připravený grafen byl charakterizován pomocí zobrazovacích a spektroskopických metod. Celý experimentální růst grafenu byl řízen a vyhodnocen pomocí plánovaného experimentu.
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Deskový předpjatý most
Macák, Jan ; Suza, Dominik (oponent) ; Panáček, Josef (vedoucí práce)
Tato bakalářská práce se zabývá návrhem silničního mostu. Objekt se nachází na komunikaci 1. třídy I/39 a je veden přes vodoteč Polečnice. Křížení os komunikace a vodoteče se nachází na 22,783 km výše uváděné komunikace. Jsou vypracovány 3 varianty. 1. varianta je deska z dodatečně předpjatého betonu o výšce 0,85 m. 2. varianta se skládá z prefabrikovaných nosníků DS-PP1 40/85 spřažených s železobetonovou deskou o minimální tloušťce 0,2m. 3.varianta je opět deska z dodatečně předpjatého betonu ovšem se zešikmeným čelem.
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Příprava vysoce dopovaných ZnO nanodrátů
Andrýsek, Michal ; Macák, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Tato diplomová práce se zabývá přípravou ZnO nanodrátů, jejich dopováním a analýzou. Nanodráty byly připraveny oxidací mosazné fólie za vyššího tlaku a teploty a pomocí depozice zinku v oxidační atmosféře. V práci je popsán vliv teploty a tlaku na růst těchto nanodrátů. Ukázalo se, že za jistých experimentálních podmínek lze nanodráty připravit prvním uvedeným postupem. Pomocí efúzní cely se nanodráty připravit nepodařilo.
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Electrochemical synthesis, characterization and applications of new types of 1D valve metal oxide nanostructures
Alijani, Mahnaz ; Prof. Lluis F. Marsal (oponent) ; Tsuchiya, Hiroaki (oponent) ; Macák, Jan (vedoucí práce)
This thesis presents a comprehensive investigation of the growth of high-aspect-ratio (HAR) TiO2 nanotube (TNT) layers and their application in advanced light sensing technologies. The research outputs achieved during this Ph.D. study encompass a series of papers that collectively explore the synthesis and characterization of HAR TNT layers on one hand side, and performance evaluation of these layers in various sensing modalities on the other side. The initial study focuses on the successful anodization of Ti foil to obtain HAR TNT layers using a specially formulated electrolyte containing NH4F/H2O/ethylene glycol, with the addition of lactic acid (LA). The results demonstrate that by controlling the electrolyte age and composition, together with the application of sufficiently high potentials, HAR TNT layers with high aspect ratio (of approximately 450) can be achieved within remarkably short anodization times ( 15 minutes) compared to the literature available before the work on this thesis begun. This approach offers a promising pathway to obtain robust TNT layers without dielectric breakdown, eliminating the need for additional process control, such as heating or cooling of the electrolyte. Building up on the successful anodization results, the subsequent investigation explored the galvanostatic anodization for obtaining HAR TNT layers in an LA-containing electrolyte. It was observed that lactic acid effectively prevents dielectric breakdown when high current densities are applied. This finding highlights the potential of galvanostatic anodization to produce HAR TNT layers in significantly reduced anodization times at room temperature. Expanding the research scope, the thesis delves into the microwave photoconductivity of TNT layers with different thicknesses (15, 50, 80, and 110 m) at X-band frequencies (~8 GHz) for applications in sensing and wireless space communication. The integration of anatase TNT layers with a planar split ring resonator (SRR) microwave resonator enables the evaluation of their microwave photoconductivity performance. Experimental results revealed significant variations in the resonant amplitude and frequency responses of the TNT layers, with the 80 m thick TNT layers demonstrating the highest sensitivity. Correlations were established between the photoconductivity efficiency, crystallite size, and thickness of the TNT layers, supporting the development of optimized TNT layers for enhanced microwave sensing capabilities. Furthermore, the thesis explores TNT layers on SRR for visible light detection. By sensitizing the TNT layers to the visible spectral region through the deposition of a CdS coating using Atomic Layer Deposition (ALD), the results demonstrate effective detection of ultraviolet (UV) light, visible (VIS) light and light-induced variations in the dielectric properties of TNT layers. The experimental findings align with theoretical models and highlight the clearly outstanding potential of TNT-based sensors in hazard detection, pollution monitoring, material analysis, and light-based satellite-to-satellite communication. Overall, this thesis provides a comprehensive understanding of HAR TNT layers and their capabilities for advanced sensing applications. The knowledge gained from this research will contribute to the advancement of nanomaterial-based sensors and opens up new possibilities for their utilization in various industries and emerging technologies.
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APLIKACE GRAFENU V ELEKTRONICE A TECHNOLOGIE PŘÍPRAVY
Zahradníček, Radim ; Sofer,, Zdeněk (oponent) ; Macák, Jan (oponent) ; Hubálek, Jaromír (vedoucí práce)
Tato dizertační práce je zaměřena na studium aplikace grafenu v elektronice a technologii přípravy. Teoretická část práce popisuje kromě základních vlastností grafenu také metody jeho přípravy, přenosu, charakterizace a možnosti uplatnění v elektronice. Experimentální část je rozdělena do tří kapitol. První kapitola se zabývá výrobou grafenu pomocí depozice z plynné fáze, jeho přenosem a aplikací v oblasti solárních článků. K přenosu grafenu byl nejprve použit polymer polymetylmetakrylát, který byl posléze nahrazen kalafunou z důvodu menší kontaminace grafenu na konci přenosového procesu. Druhá kapitola se zabývá přípravou kvantových teček pomocí exfoliace v kapalné fázi z grafitu a jeho aplikaci ve voltametrii. Voltametrie byla využita v této práci k detekci peroxidu vodíku pomocí zlaté elektrody modifikované kvantovými tečkami z grafenu a jiných dichalkogenů (MoS2, MoSe2, WS2, WSe2). V poslední kapitole je studován vliv substrátu a depozičních podmínek grafenu, vytvářeného plazmou podpořenou depozicí z plynné fáze, na růst, přičemž připravený grafen byl charakterizován pomocí zobrazovacích a spektroskopických metod. Celý experimentální růst grafenu byl řízen a vyhodnocen pomocí plánovaného experimentu.
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PROGRESS TOWARD THE DEVELOPMENT OF SINGLE NANOWIRE-BASED ARRAYS FOR GAS SENSING APPLICATIONS
Chmela, Ondřej ; Vrňata, Martin (oponent) ; Macák, Jan (oponent) ; Hubálek, Jaromír (vedoucí práce)
This thesis presents the development of silicon-based platforms for selective integration of semiconducting metal oxide (MOX) nanostructures and their use as highly sensitive and selective elements for the detection of gas analytes in prospective mobile devices. Semiconducting MOX nanostructures, for instance nanowires, have proved better gas sensing properties including sensitivity, stability and to a certain extent also selectivity as compared to their bulk counterparts. The use of single (or few) nanowire structures connected in parallel has also shown to be the ideal architecture to achieve well-defined conduction channel easy to modulate by the gas-solid interactions. However, yet current methods for the integration of single nanowire structures in functional devices represent a technological challenge, with most of the methods needing the assistance of techniques, such as focused-ion beam (FIB), which restricts the scalability of the process and increases the cost and time of fabrication. In this context, this work is focused on the search and optimization of technological processes to fabricate gas sensing systems based on arrays of single semiconducting nanowires. In this thesis, three versions of electrode platforms were developed for the selective integration of single gas-sensitive metal oxide nanowires. State-of-the-art multistep throughput fabrication techniques, as well as electron-beam lithography (nanofabrication), were used as crucial fabrication technologies allowing the development of arrays with faced nanoelectrodes and other functional nanostructures. Results show the fabrication of electrode platform with faced nanoelectrodes (100 – 300 nm width) framed in narrow dielectric windows close to the nanowire diameter (100 – 200 nm approx.). These nanoelectrodes were used as both mechanical support to align the single nanowire, and electrical contacts to measure the electrical change along the nanowire during gas detection. Results also include the optimization of techniques for removal and redeposition of nanowires to achieve single nanowire interconnections in the array of parallel electrodes using an alternating electric field as a simple and effective technique for nanowires alignment (dielectrophoresis). The validation of these systems toward various gaseous species (oxidizing and reducing gases) was performed using non-functionalized and Pt-functionalized WO3 nanowires synthesized by aerosol-assisted chemical vapor deposition (AACVD) and backside ceramic heaters (with the operating temperature at 250 °C) assembled on TO-8 package. The sensing parameters of such systems showed better sensing responses in resistive regime to nitrogen dioxide (NO2) and ethanol (EtOH) than their counterparts based on multiple nanowire-based films. The last version of gas sensing systems developed in this thesis (described as third chip generation) includes a third insulated electrode buried under the gas sensitive nanowire for enhanced gas sensing regime. Gas sensing tests of this system to hydrogen (H2) and nitrogen dioxide (NO2) corroborated the enhanced functionality of these systems and the modulation of sensor response by applying external electrical stimuli on the buried electrode.
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