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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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Study of manganese segregation in Mn-doped transparent alumina ceramics
Pišťák, Jan ; Maca, Karel (referee) ; Drdlík, Daniel (advisor)
This work deals with the preparation of Al2O3 ceramics doped with manganese, the study of basic physical and microstructural properties and the description of the dissolution kinetics of manganese in the Al2O3 matrix. Al2O3 ceramics and Al2O3 ceramics doped with 1 and 5 at.% Mn3O4 with different dopant particle sizes were successfully prepared by the slip casting method. The prepared ceramic materials were sintered at temperatures of 1100 and 1150 °C with different dwell times. The density in sintered samples was monitored depending on the preparation parameters and thermal treatment conditions. It was found during the microstructure observation that even at a relatively low temperature, the rapid dissolution of the dopant in the Al2O3 matrix occurred, while in the samples containing 1 at.% Mn3O4, this dopant was already completely dissolved. In the case of samples with a concentration of 5 at.% Mn3O4, a spinel phase was identified in the matrix. In addition, some samples were found to have unreacted dopant particles excreted from the matrix during ceramographic processing. Therefore, the goal of the bachelor thesis could not be completely fulfilled, i.e. the kinetics of dopant dissolution could not be studied for objective reasons.
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Fabrication and properties of doped piezoceramics based on BaTiO3
Mařák, Vojtěch ; Chlup, Zdeněk (referee) ; Drdlík, Daniel (advisor)
This diploma thesis deals with the preparation of doped piezoceramic materials based on BaTiO3 using electrophoretic deposition. Five rare earth oxides, i.e. Er2O3, Dy2O3, Eu2O3, Tb407 and CeO2, were used as dopants in amounts of 1, 3, and 5 wt. %. The prepared deposits were evaluated in terms of preparation methodology, high temperature dilatometry, X-ray diffraction analysis, relative density, mean grain size, hardness and fractographic analysis. The study of dilatometric curves described the sintering behavior and its changes at different material compositions. X-ray diffraction analysis revealed a tetragonal phase in all samples; the tetragonality of the BaTiO3 crystalline cell decreased with dopant content. By a suitable choice of dopant, it was possible to significantly increase the relative density of sintered samples, their hardness and at the same time prevent the samples from coarsening of the microstructure during heat treatment. A relative density up to 98 %, a mean grain size below 1 m and a hardness of over 10 GPa were achieved. Analysis of the fracture surfaces revealed that the fracture mode was transcrystalline for the most of studied materials; only the samples doped with cerium dioxide had fracture surfaces with both transcrystalline and intercrystalline fracture modes. Based on the obtained results, a suitable composition of the material for the intended use in a layered piezoceramic harvester was identified, which, in addition to the BaTiO3 layers, consists of functionally-protective Al2O3 and ZrO2 layers.
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Processing and properties of transparent polycrystalline ceramic materials
Tásler, Jan ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
The presented diploma thesis is focused on the preparation and properties of transparent polycrystalline ceramic materials based on Al2O3. Theoretically, the most important technological aspects of the processing of these materials are presented. Detailed attention is given to transparent Al2O3 polycrystalline ceramics doped with rare earth elements. The influence of microstructural parameters on the optical properties (represented by RIT) is investigated on Al2O3 samples doped and codoped with dysprosium, terbium and chromium. A significant effect of the average grain size on the light transmittance of all samples is observed. The highest RIT = 55 % (measured by a laser beam with a wavelength of 632,8 nm) was achieved by an optimized preparation process for a sample doped with 0,05 at. % of dysprosium. For all samples photoluminescent properties are also analysed. The photoluminescent emission spectra correspond to the activation of doping elements. In case of the terbium and chromium codoped samples, the differences in the activation of individual dopants depending on different excitation wavelengths were demonstrated, resulting in different colour emissions for different excitation wavelengths.
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Transparent polycrystalline ceramic materials with cubic lattice structure
Kučera, Jan ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
The presented work is focused on the study of the influence of preparation parameters on the optical properties of polycrystalline cubic ZrO2 (stabilized with 8 mol.% Y2O3). Furthermore, the work deals with the doping of c-ZrO2 with TiO2 and its effect on the luminescence properties of ZrO2. The examined samples were prepared by uniaxial pressing (10 MPa), followed by a cold isostatic pressing (300 and 700 MPa), pressureless sintering (1340–1380 °C, 10 min), and hot isostatic pressing (1200–1400 °C, 4 h, 200 MPa). In this work, it is shown that the optical properties are significantly affected by the temperature of the hot isostatic pressing, the thickness of the sample, and also by the wavelength of the incident light. A maximum real in-line transmission of 68.8 % was achieved, which is 90.5 % of the theoretical limit for c-ZrO2 at an incident radiation wavelength of 632.8 nm. A low-pressure infiltration method and a powder mixing method were used to prepare the doped ZrO2 ceramic sample. With doping, the maximum of the excitation spectrum shifted from 295 nm (4.20 eV) for the undoped ZrO2 to 320 nm (3.87 eV) for the doped samples. Doping led to an increase in emission intensity compared to a pure ZrO2 by up to 23 times. The maximum emission intensity at 545 nm wavelength was achieved for samples doped by infiltration method with a nominal 0.1 mol.% TiO2 content.
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Preparatin of dopped lead-free piezoceramic materials by non-conventional sintering methods
Žaludek, Jakub ; Kachlík, Martin (referee) ; Pouchlý, Václav (advisor)
Piezoceramics BaTiO3 doped with ZrO2 was studied in this thesis. Six different compositions were prepared from base powders of BaTiO3 and ZrO2. with 10, 20, 40, 60, 80 and 90 wt% ZrO2. These mixtures were sintered using convetional sintering method and by Spark Plasma Sintering. Resuting ceramic compacts were subjected to measuring of density, dielectric constant, permitivity, polarization P-E curves, piezoelekctric faktor, loss factor and dilatometric measurements. From these results can be said that i tis possible to create piezoceramic BaTiO3 doped by ZrO2 with relative density higher than 94 %t.d. and these ceramics can possess piezoelectric properties. Value of highest piezoelectrick factor 33=9 / was achieved with addition of 20 wt% ZrO2. Dilatometric measurements discovered effect of increasing ammount of ZrO2 in BaTiO3. Rising amount of ZrO2 had a lowering effect on initial sintering temperature and materials achieved higher relative densities. This was also true for samples sintered using SPS, where it was less obvious. Measuring of electrical properties discoverad electric conductivity for SPS sintered samples, which was most probably caused by carbon introduced into samples during SPS cycle.
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Doped ceramic substrates for plasma aplications
Hliničan, Jan ; Šťastná, Eva (referee) ; Šťastný, Přemysl (advisor)
This bachelor thesis summarizes findings on subject: Doped ceramic substrates for plasma aplications. The thesis is divided into two parts. The first part is a literary research focused on topic: production of thin ceramic tapes by tape casting and their use. The second part is experimental. It deals with the preparation of alumina tapes doped with magnesium spinel (MgAl2O4) in different amounts. Phase composition and microstructure will be evaluated on prepared structures. The prepared samples will be used for the production of electrodes for atmospheric plasma discharge.
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Printed transparent oxide conductors
Bartoš, Radim ; Pekárková, Jana (referee) ; Dzik, Petr (advisor)
Thin films of tin oxide doped by fluorine or antimony were prepared by spincoating technique and material printing technique. Plenty of inorganic and organic coumpouds were used as precursors of fluorine and antimony. Sheet resistence of films were measured by 4-probe method and film thickness were determined by contact profilometer. Films were analyzed by Xray diffraction (XRD) and scan electron microscopy (SEM).
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The hydrogen modification of the graphene structures for field effect transistors
Kurfürstová, Markéta ; Čermák,, Jan (referee) ; Mach, Jindřich (advisor)
This master’s thesis is focused on the subject of graphene modified with atomic hydrogen and its electronic transport properties. Structural and electronic properties of graphene and hydrogenated graphene are compared in the theoretical part of the thesis. The Raman spectroscopy technique is described, including characterization of typical Raman spectra of both unmodified and modified graphene. Samples used during experimental part of the thesis are prepared via laser and electron lithography, and are set to be measured in a vacuum chamber. Subsequently, electronic transport properties are measured before and after hydrogen modification of graphene. Finally, hydrogenated graphene is irradiated using electron beam and changes in its structure are analyzed with Raman spectroscopy techniques.
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