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Preparation of InAs nanowires by MBE
Stanislav, Silvestr ; Maniš, Jaroslav (referee) ; Musálek, Tomáš (advisor)
The bachelor’s thesis deals with growth of InAs nanowires grown on silicon substrate by molecular beam epitaxy. The emphasis is mainly layed on fabrication of nanowires grown via Vapour-Liquid-Solid mechanism using gold catalytic nanoparticles. There is a brief description of two most common mechanisms of nanowire growth in the first part of the thesis. The text also discusses crystal structure of InAs and doping options of InAs nanowires. The experimental part is aimed at deposition and the impact of different growth conditions on both growth mechanism and nanowire morphology.
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Preparation of contacts to one-dimensional nanostructures
Citterberg, Daniel ; Procházka, Pavel (referee) ; Kolíbal, Miroslav (advisor)
This bachelor thesis deals with methodology of contacting one-dimensional nanostructures. Theoretical part of the thesis defines the concept of one-dimensional nanostructures, then it deals with the potential of their usage, especially in field effect transistors. This part also deals with the possibility of measuring the electrical properties of one-dimensional nanostructures and the possibility of fabricating contacts with sufficiently small sizes using litographic approach. Experimental part gives a brief overview of the tasks that need to be done during the contact fabrication. Subsequently, the individual steps are described in more detail and, finally, initial results of electrical characterization are shown.
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Oxidation barriers prepared by electrochemical procedures
Šťastná, Eva ; Pouchlý, Václav (referee) ; Jan, Vít (advisor)
A process with aim to prepare an oxidically and thermal resistant layer was performed on the samples from clear aluminium (99,99+ %, VÚK čisté kovy, s. r. o.) and on the samples from clear titanium (99,95 % Goodfellow) with a layer from sputtered aluminium (99,99 %, VÚK čisté kovy, s. r. o.), An oxidic layer was prepared on the samples by anodization in the oxalic acid. The layer had fine, hexagonally organized pores with the diameter of 30 nm. During the following processing was the structure prepared for the electrochemical deposition of copper to the pores. The aim of the electrodeposition was preparation of copper nanowires deposited into the pores of the oxidic layer. The process was performed in the solution of copper sulfate and sulfuric acid in water. The controlling parameter of the deposition was voltage which had a very asymmetric period. The period had to be optimized for a successful preparation of the wires. The result of the whole process was structure with oxidic matrix whose most of the pores were filled with copper.
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Substrate-controlled nucleation of the magnetic phase transition in nanostructures
Hajduček, Jan ; Procházka, Pavel (referee) ; Uhlíř, Vojtěch (advisor)
Properties of the phase transition in iron-rhodium (FeRh) from the antiferromagnetic (AF) to ferromagnetic phase (FM) are largely affected by lattice defects in FeRh. Epitaxial layers of FeRh are grown on monocrystalline MgO (001) substrates. Surface atomic terraces of the substrate can induce defects in epitaxial layers and modify electronic and magnetic properties. In this thesis the effect of surface atomic terraces on the width and the hysteresis of the metamagnetic phase transition in FeRh thin layers and nanostructures is studied. The amount and character of defects in FeRh are also affected by mutual orientation of terraces and FeRh nanowires, which changes the number of discrete jumps in FM-AF transition. The nanowires have been fabricated by electron-beam lithography. FM domains in in FeRh have been observed by magnetic force microscopy and electrical transport properties of differently oriented nanowires have been studied by 2-probe measurements. Higher density of surface atomic terraces significantly increases the number of discrete jumps in the FM-AF transition.
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Transport properties of one dimensional magnetic nanostructures
Holobrádek, Jakub ; Liška, Jiří (referee) ; Vaňatka, Marek (advisor)
Magnetic nanowires have been recently under the scope for their specic properties and applications in microelectronics and sensors. This work deals with measurement of transport properties of nanowires in magnetic field. Nanowires prepared in the range of the thesis were grown by the physical vapor deposition method in colaboration with the University of Technology Sydney. The main task of the thesis was to develop a process of contacting single nanowires by electron beam lithography and measuring them using anisotropic magnetoresistance in angle dependent magnetic field. Characterization techniques such as transmission electron microscopy, energy-dispersive X-ray spectroscopy and magnetic force microscopy were used to provide further analysis.
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Exchange bias in metamagnetic heterostructures
Zadorozhnii, Oleksii ; Schneeweiss, Oldřich (referee) ; Uhlíř, Vojtěch (advisor)
Výměnná anizotropie je zajímavý fyzikální jev vznikající na rozhraní antiferomagnetických (AF) a feromagnetických (FM) materiálů, který již je široce používán v elektronickém průmyslu a magnetickém záznamu. Přestože byl tento jev dlouhou dobu intenzivně studován, jeho přesný mechanizmus zatím nebyl uspokojivě vysvětlen. V této práci je představen přehled studií dokumentujících výměnnou anizotropii v tenkých dvojvrstvách, včetně experimentálních výsledků a teoretických modelů. Experimentální úkoly této diplomové práce zahrnovaly jak výrobu, tak měření různých modelových systémů vykazujících výměnnou anizotropii. Dvojvrstva Fe/FeRh, kde vrstva FeRh prochází fázovou přeměnou z AF fáze na FM fázi při 360 K, poskytuje možnost nastavení parametrů výměnné anizotropie. Dále byly zkoumány účinky výměnné anizotropie a tvarové anizotropie v mikrostrukturách Fe/FeRh. Konečně, přítomnost výměnné anizotropie byla zkoumána mezi FM a AF fází koexistujícími během fázové přeměny v nanodrátech FeRh. Vzorky byly vyrobeny pomocí magnetronového naprašování a elektronové litografie. Všechny prezentované systémy byly analyzovány pomocí magnetooptické Kerrovy mikroskopie. Výměnná anizotropie byla úspěšně nalezena v systému Fe/FeRh, přičemž její velikost byla téměř identická co do rozsahu i orientace s výsledky v literatuře, přestože námi vyrobená dvojvrstva měla horší kvalitu FM-AF rozhraní. Bylo také prokázáno, že v tomto systému existuje tzv. tréninkový efekt (Training effect), což je výrazným důkazem existence výměnné anizotropie. U nanodrátů bylo změřena významná výměnná anizotropie mezi koexistujícími fázemi FM a AF během fázové přeměny.
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Investigation of nanomaterials for their nuclear power and research utilization
Jelínek, Martin ; ČEZ,, Jiří Skalička, (referee) ; Katovský, Karel (advisor)
This bachelor thesis provides a comprehensive overview of the properties of various nanomaterials and summarizes the latest findings and knowledge of advanced applications in all sectors of nuclear power engineering from construction materials through nuclear fuel, fuel cladding, neutron moderator and coolant to the advanced methods for detection of ionizing radiation ad its direct utilization for electricity production. A significant space is devoted to the applications in safety systems of nuclear power plants. The experimental part of the thesis deals with the possibility of using carbon nanofibers as an additive to the coolant in VVER reactor type in order to improve the thermal properties of the coolant. So far a very little examined issues of neutron balance changes due to interaction with nanoparticles was experimentally verified on the paraffin wax mixture of two different concentrations. The comparison with the reference sample of pure paraffin was also made.
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Correlated probe and electron microscopy for the study of modern magnetic nanomaterials
Novotný, Ondřej ; Flajšman, Lukáš (referee) ; Pavera, Michal (advisor)
High pressure on the development of new magnetic materials and their miniaturization also emphasizes the development of new analytical techniques. This diploma thesis deals with the development and demonstration of correlated magnetic force and electron microscopy, which is a promising tool for the characterization of magnetic nanomaterials. The first part of this thesis describes the fundamental physics of micromagnetism with a focus on cylindrical nanofibers. The following pages describe optic, probe, electron, and synchrotron methods for mapping the magnetic properties of materials. The next part describes magnetic domain wall motion in cylindrical nanowires performed as a part of a more extensive material study. The last part of the thesis describes the development of correlated magnetic force and electron microscopy on LiteScope device. A production of magnetic probes was designed and successfully tested. Probes were fabricated by focused electron beam-induced deposition from the Co2(CO)8 precursor. Further, the developed correlated microscopy is demonstrated on a multilayer PtCo sample, magnetic cylindrical nanofibers, NiFe vortex structures, and FeRh metamagnetic nano-islands.
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Optical characterization of InAs nanowires
Hošková, Michaela ; Ligmajer, Filip (referee) ; Musálek, Tomáš (advisor)
This bachelor thesis deals with the fabrication and optical characterization of InAs nanowires. Physical vapor deposition is used for the fabrication of nanowires via method selective epitaxy in the MBE chamber. The growth conditions for the formation of nanowires are optimized and their dimensions are characterized by a scanning electron microscope. Confocal spectroscopy and electron energy loss spectroscopy are employed for measurement of the optical response and the influence of the geometry of individual nanowires is studied. The motivation is the development of a new optical method that monitors nanowires directly during growth in the MBE apparatus.
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