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Condensing Steam Turbine with superheating
Urbánek, Martin ; Weber, Norbert (referee) ; Weber, Norbert (referee) ; Fiedler, Jan (advisor)
The thesis is focused on designing of condensing steam turbine with reheating for combustion of biomass. The turbine is developed to be tandem compound-regenerative with five uncontrolled extraction points. Optimization of reheating pressure is made in the turbine's cycle. The turbine outlet is constructed to lead down to the water cooled condenser. Thesis includes the calculation of heat cycle with the draft of flow channel of high pressure and middle-low pressure turbine. Detailed calculation of middle-low pressure turbine, including stress-strength analysis, is performed. The thesis provides an evaluation of flow scheme of 100 % and 75 % of generator’s power output and the drawing of middle-low pressure turbine in longitudinal section.
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Characterization of magnetic nanostructures by magnetic force microscopy
Staňo, Michal ; Vetushka,, Aliaksei (referee) ; Urbánek, Michal (advisor)
The thesis deals with magnetic force microscopy of soft magnetic nanostructures, mainly NiFe nanowires and thin-film elements such as discs. The thesis covers almost all aspects related to this technique - i.e. from preparation of magnetic probes and magnetic nanowires, through the measurement itself to micromagnetic simulations of the investigated samples. We observed the cores of magnetic vortices, tiny objects, both with commercial and our home-coated probes. Even domain walls in nanowires 50 nm in diameter were captured with this technique. We prepared functional probes with various magnetic coatings: hard magnetic Co, CoCr and soft NiFe. Hard probes give better signal, whereas the soft ones are more suitable for the measurement of soft magnetic structures as they do not influence significantly the imaged sample. Our probes are at least comparable with the standard commercial probes. The simulations are in most cases in a good agreement with the measurement and the theory. Further, we present our preliminary results of the probe-sample interaction modelling, which can be exploited for the simulation of magnetic force microscopy image even in the case of probe induced perturbations of the sample.
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Magnetic transformation of metastable fcc Fe/Cu(100) films by focused ion beam
Gloss, Jonáš ; Cháb, Vladimír (referee) ; Urbánek, Michal (advisor)
Metastable paramagnetic face-centered cubic (fcc) Fe thin films deposited on a Cu(100) single-crystal are good candidates for focused ion-beam magnetic patterning, due to their structural and magnetic phase transformation to ferromagnetic body-centered cubic (bcc) Fe upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni, that stabilizes the fcc phase. The amount of Ni necessary to stabilize non-magnetic, metastable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phase diagram revealing the metastable region is presented. It is also shown that the stabilizing effect of CO can be removed by artificial O saturation of the surface and thus the Ni-stabilized films can be grown also in systems with lower vacuum. Finally, we present fabrication of micro- and nanostructures in 44 ML thick films of Fe alloyed with Ni on Cu(100) by focused ion beam.
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Switching vortex chirality in magnetostatically coupled permalloy nanodisks
Balajka, Jan ; Nebojsa, Alois (referee) ; Urbánek, Michal (advisor)
The diploma thesis is concerned with switching of vortex circulation in magnetic nanodisks. The results of micromagnetic simulations of hysteresis loops of individual disks with different degrees of asymmetry are presented. The influence of geometric asymmetry of the disk on the shape of the hysteresis loop is discussed as well as switching of vortex circulation in asymmetric nanodisks by external in-plane magnetic field. Simulations of pairs of magnetostatically coupled nanodisks were carried out for different interdisk distances and degrees of asymmetry. By analysing the results of the simulations, the effects of magnetostatic coupling and the asymmetry on resultant circulation of individual vortices were compared and the range of magnetostatic interaction between nanodisks of given dimensions and asymmetry was estimated. Experimental techniques used for fabrication and measurement of the samples are briefly summarized.
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Detection and analysis of crystal defects in Si wafer for electronics
Páleníček, Michal ; Tichopádek, Petr (referee) ; Urbánek, Michal (advisor)
The thesis deals with the study and analysis of crystallographic defects on the surface of silicon wafers produced by Czochralski method. It focuses primarily on growth defects and oxygen precipitates, which play an important role in the development of appropriate nucleation centers for growth of stacking faults. The growth of stacking faults near the surface of silicon wafers is supported by their oxidation and selective etching. Such a highlighted stacking faults are known as the OISF (Oxidation Induced Stacking Fault). Spatial distribution of OISF on the wafer gives feedback to the process of pulling silicon single crystal and wafers surface quality. Moreover the work describes the device for automatic detection and analysis of OISF, which was developed for ON Semiconductor company in Rožnov Radhoštěm.
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Switching of spin vortices in magnetic nanodiscs
Hladík, Lukáš ; Pekárková, Jana (referee) ; Urbánek, Michal (advisor)
The diploma thesis deals with the switching of spin vortices in magnetic nanodisks. First, the basic concepts of (micro)magnetism are defined and existing theoretical and experimental achievements in the field of switching of the two basic characteristics (chirality and polarity) of magnetic vortex are summarized. Then the principle of dynamic switching of magnetic vortex chirality using in-plane magnetic field pulse with a well defined amplitude and duration is presented. There is no need to use a certain shape of nanodisks or asymmetry in magnetic field distribution. Nanostructures were prepared by the multi-step electron beam lithography and ion beam sputtering. Individual steps of sample preparation and optimization for the magnetization dynamics measurements are described. Finally, the experimental measurements of the dynamic switching of chirality on prepared samples obtained by transmission x-ray microscopy at the synchrotron Advanced Light Source at Berkeley, USA are presented and discussed.
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Automation and control of multilayers deposition by IBS/IBAD
Pavera, Michal ; Sobota, Jaroslav (referee) ; Urbánek, Michal (advisor)
This diploma thesis deals with the automation of the deposition process by ion beam sputtering and ion beam assisted deposition. This work contains drawings of mechanical adjustments of the deposition chamber designed to control shutter and rotation of the target using stepper motors. There are presented ways to control stepper motors and troubleshoot their exact settings. Another task is to design a system for computer control of the deposition process. There are discussed ways to control the ion sources, pressure meter, flow meter and thickness meter, and their connection to a PC via RS-232 and analog-digital converters. It is also designed control program in LabVIEW, which allow automated multilayer deposition. Last part of the thesis deals with testing automatic deposition and results are commented.
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Electrotransport properties of the nanostructures fabricated by the FIB
Ostřížek, Petr ; Kolíbalová, Eva (referee) ; Urbánek, Michal (advisor)
The aim of this work is fabrication of nanostructures and measurement of their electrotransport properties. There are two different methods used for fabrication - electron beam lithography with sputtering of thin films and focused ion beam with deposition from gas phase. I-V characteristic was measured for characterisation of as prepared nanostructures - wires. Material of wires prepared by using of electron beam lithography was permalloy - an alloy of iron and nickel. Second types of wires prepared by using of chemical vapor deposition induced by focused ion beam was platinum based.
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Study of magnetic nanostructures for spintronics
Kameš, Jaroslav ; Nebojsa, Alois (referee) ; Urbánek, Michal (advisor)
The Cu/NiFe/Cu/Co/(CoOx) spin-valves have been prepared by the ion-beam sputtering method. Their GMR ratio and the time stability have been investigated by the magnetoresistance and the MOKE measurements at room temperature. The reproducibility of the preparation of the samples have been studied as well, i.e. two identically configurations of the layers should have the same magnetotransport properties.
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Fabrication of micro- and nanostructures by different etching methods
Těšík, Jan ; Urbánek, Michal (referee) ; Šamořil, Tomáš (advisor)
The selective etching is currently very widely used method for the preparation of micro- and nanostructures. This thesis deals with the principles of the etching methods, their applications and also the possibilities of dry and wet etching at the Institute of Physical Engineering. The experimental part is devoted to the preparation of the etching masks to ensure etching selectivity and to the preparation of pre-defined micro- and nanostructures. Important parameters were determined from the results, e.g. Si etch rate, selectivity of the masks etc. Further, the suitability of the used methods and etching masks were compared.
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