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Towards highly-doped Ge and ZnO nanowires: Growth, characterization and doping level analysis
Pejchal, Tomáš ; Mikulík,, Petr (referee) ; Grym,, Jan (referee) ; Kolíbal, Miroslav (advisor)
Vysoce dopovaná polovodičová nanovlákna představují nadějnou třídu nanostruktur pro budoucí aplikace v elektronice, optoelektronice nebo bio-senzorice. Tato práce se zaměřuje na přípravu a charakterizaci nanovláken germania a oxidu zinečnatého s cílem dosáhnout vysoké úrovně dopování. Úvodní část dizertační práce se zabývá přípravou germaniových nanovláken metodou VLS (pára – kapalina – pevná látka). Nejprve jsou popsány faktory ovlivňující růst nanovláken a jejich morfologii – složení katalytické částice, vliv adsorbovaných atomů či molekul a potenciální inkorporace atomů katalyzátoru do objemu nanovláken. Nanovlákna připravená ze zlatých katalytických nanočástic v podmínkách ultravysokého vakua (tzv. MBE metodou) a za přítomnosti atomárního vodíku (proces napodobující podmínky CVD metod) vykazují odlišnou morfologii a směr růstu. Tyto rozdíly odhalují kombinovaný účinek adsorpce atomárního vodíku a šíření zlatého katalyzátoru na stěny nanovláken. Tento efekt je klíčový pro vysvětlení rozdílů ve výsledné morfologii nanovláken připravených MBE a CVD metodami. Další část práce se věnuje přípravě Ge nanovláken z katalyzátorů obsahujících prvky III. skupiny a studiu jejich případné inkorporace, která by mohla vést k dopování nanovláken. Bylo zjištěno, že in-situ připravené směsné Au–Ga nanočástice lze úspěšně využít pro růst germaniových nanovláken, přestože stabilita katalyzátoru je nižší než v případě čistého zlata. I přes vysokou koncentraci gallia v katalytické částici nebyla pozorována inkorporace gallia do objemu nanovlákna. Tato metoda dopování nanovláken se tedy pro uvedenou materiálovou kombinaci ukázala jako nevhodná. Ve třetí části práce jsou popsány výsledky charakterizace ZnO nanodrátů a vývoj metody jejich difuzního dopování galliem. Je prokázán vliv žíhání nanodrátů na koncentraci kyslíkových vakancí (VO) – ve srovnání s žíháním v podmínkách vysokého vakua se koncentrace VO snižuje žíháním v plynném peroxidu vodíku. Dále je zdokumentována inkorporace gallia do ZnO nanodrátů při teplotě nad 350 °C – pozorováno pomocí in-situ SEM. Při teplotě nad 450 °C dochází ke galliem indukované dekompozici ZnO nanodrátů. K určení koncentrace a prostorového rozložení Ga atomů v nanovláknech je využito teoretického difuzního modelu a STEM EDS měření nanovláken. Byla nalezena korelace mezi koncentrací kyslíkových vakancí a inkorporací gallia do objemu ZnO nanovláken. Koncentrace gallia dosahuje řádově 10^21 cm^-3, což dokazuje vhodnost použité metody pro dosažení vysokých úrovní dopování, které jsou potřebné pro budoucí bio-senzorické aplikace v infračervené oblasti.
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The Study of ZnO Crystal Growth in Supersaturated Alkaline Solution
Bannert, Tomáš ; Máca, Josef (referee) ; Chladil, Ladislav (advisor)
This thesis deals with the study of growth of zinc oxide crystals from supersaturated solutions using a scanning electron microscope and XRD methods. The work is divided into a theoretical and an experimental part. The theoretical part analyses issues related to the principle of operation of electrochemical cells with an emphasis on Ni-Zn batteries and phenomena limiting the life and efficiency of Ni-Zn batteries with a focus on phenomena that affect precipitation processes of zinc oxide crystals. It also analyses and compares the appropriateness of the methods that have been used to study the growth of the prepared zinc oxide crystals. The experimental part describes the preparation of a supersaturated solution, the process of each analysis and its evaluation. The results of each method are compared with the theoretical assumptions and among themselves. The experimental part also contains a chapter dealing with the design of in situ X-ray diffraction analysis methods of the obtained zinc oxide crystals.
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The influence of zinc oxide on the cement composite with silica fume.
Dobiáš, Jiří ; Koutný, Ondřej (referee) ; Šiler, Pavel (advisor)
The aim of this work was to investigate the influence of zinc oxide on the properties of blended Portland cement mixed with silica fume. On the pastes were monitored flow properties and by using of isoperibolic calorimetry process of the hydration. On the prepared samples were studied mechanical properties of obtaining values of compressive and flexural strength after 1, 7 and 28 days. By using of XRD were measured phase composition and microstructure development war observed by SEM. The elemental composition of cement leaches was measured by using of ICP-OES.
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The influence of hydration accelerators on cement doped with zinc
Beneš, Pavel ; Šilerová,, Iva (referee) ; Šiler, Pavel (advisor)
Zinc in cement has negative properties mainly due to a significant delay in hydration. This bachelor thesis deals with the study of hydration of cements containing zinc. The course of cement hydration was monitored by isoperibolic calorimetry. Zinc was doped to CEM I 42.5 R in the form of 1 weight percent zinc oxide. Calcium oxide, formic acid and calcium formate were used in various proportions as accelerators. The obtained results were compared with the measured strengths and finally the suitability of the given accelerators was discussed for use in construction application.
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Influence of zinc on mechanical properties of cement composites
Štarha, Tomáš ; Šilerová,, Iva (referee) ; Šiler, Pavel (advisor)
The theme of this bachelor thesis is to monitor the effect of zinc on mechanical properties of portland cement. Zinc was tested in the form of zinc oxide. Three acceleration additives were added, calcium oxide, formic acid and calcium formate in various proportions. Furthermore, the mechanical properties of all these mixtures were monitored by measuring flexural strength and compressive strength at 7 and 28 days after mixing and mixtures were analyzed by XRD and DTA. Also using isoperibolic calorimetry, the hydration of CEM 42.5 R cement zinc oxide was monitored.
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Zinc and its compounds
Štefka, Michal ; Kábelová, Božena (referee) ; Pilátová, Ivana (advisor)
The aim of the degree work is the preparation of three consecutive zinc compounds. The theoretical part of the work deals with the most common physical properties of some inorganic compounds of this element. These are especially those compounds that are prepared as intermediates or products in accordance with the instructions set out in the Annex to this degree work. In the experimental part is on the basis of that training described the actual behavior of zinc compared to that provided by general behavior contained in the books and there are presented procedures best saited to the conditions of preparation of individua compounds.
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Influence of ettringite formation on mechanical properties of zinc doped cements.
Kunovský, Ondřej ; Matějka, Lukáš (referee) ; Šiler, Pavel (advisor)
This bachelor thesis deals with the study of the effect of hydration accelerators in cement pastes doped with zinc ions. Their influence on hydration reactions, mechanical properties and the amount of ettringite formed was studied. CEM I 42.5 R cement was used and zinc was added in the form of ZnO in an amount of 1 wt. % of Zn relative to cement content. Strengths were measured over a time horizon of 98 days. In addition, analyzes by SEM, XRD and DTA methods were performed on selected samples to determine the amount of ettringite. It has been found that compressive strengths can also decrease during hydration. At this decrease, SEM, XRD and DTA showed a reduction in the amount of ettringite in the sample.
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Growth of highly doped ZnO nanowires
Andrýsek, Michal ; Macák, Jan (referee) ; Kolíbal, Miroslav (advisor)
This diploma thesis is about ZnO nanowires growth, their doping and analysis. High temperature and pressure oxidation of brass foil and deposition from effusion cell in oxidative atmosphere utilized for nanowires growth. The growth is affected by different temperature and pressure. It has been shown that under certain experimental conditions nanowires can be prepared by the former method. However, the growth was hindered when effusion cell was used.
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Influence of antibacterial nanomaterials on the development of bacterial resistance
Bábíková, Daniela ; Lucie,, Bozděchová (referee) ; Šmerková, Kristýna (advisor)
Bacterial resistance to antibiotics is a long-discussed problem. The use of antibiotics in primary agricultural production, especially in pig breeding. High levels of zinc subsequently seeps into the soil in the form of secondary agricultural products. Doses of effect the intestinal bacteria of pigs, but also the microorganisms in the environment which can subsequently lead to the development of resistance to metals also antibiotics. This thesis deals with the effect of ZnO and newly used nanoparticles (ZnO NPs) on bacteria S. aureus, methicilin-rezistant S. aureus and E. coli. Acquired data point to the effect of ZnO on minimal inhibition concentration of antibiotics and the development of resistance in E. coli. Based on biochemical tests, the change of metabolic pathways reacting with selected substrates was confirmed. Repeated subcultur of bacteria with tested ZnO and ZnO NPs has on the susceptibility of bacteria to antibiotics and changes their biochemical pathways. Studies dealing with the issue of long-term effect on medicinal substances are essential for the development of modern antibacterial components.
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Horizontální přenos genů rezistence mezi bakteriemi
Valach, Radek
Transfer of bacterial antibiotic resistence is highly discussed topic in past years. Its spreading is reason of creating super-resistant bacterial strains, that are resistant to a wide range of conventionally used drugs. Zinc oxide, used in pig farming as a feed supplement, has in recent years replaced antibiotics, given to prevent gastrointestinal disease and to promote growth. These substituent may increase transfer of genetic elements carying antibiotic resistence genes. This thesis is focussed on possible influence of zinc oxide and its nanoparts on Enterococcus faecalis bacteria. The aim of this work was to investigate whether the action of ZnO and ZnONPs would increase the transfer of a resistance gene plasmid between bacteria through the process of conjugation.
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