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Study of valence band structure of transition metals and alloys by ARUPS method
Pira, Peter ; Matolín, Vladimír (advisor) ; Libra, Jiří (referee)
Heterogeneous catalysis is one of many interesting part of physics, witch surface science study. Knowing of importance of processes in catalytic reaction should predict properties of new bimetallic systems. The main task of this diploma thesis was the study of valence band of transition metals. In this diploma thesis we studied bimetallic system of palladium and tin by ARUPS. We also used methods XPS, XPD and LEED, which are classical applications in surface physics.
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Microstructure and Properties of Nanocrystalline Hard Coatings and Thin Film Nanocomposites
Dopita, Milan ; Rafaja, David (advisor) ; Richter, Frank (referee) ; Šutta, Pavol (referee)
In this work, microstructure and properties of M-Al-(Si-)N nanocrystalline hard coatings and thin film nanocomposites deposited by cathodic arc evaporation (CAE) process at different positions of substrates in the deposition apparatus were investigated using the combination of electron probe microanalysis, X-ray diffraction, transmission electron microscopy with high resolution and hardness measurement. Six series of specimens that differed in the transition metal type (Cr, Ti and Zr) and in the amount of Si and Al were deposited using the CAE process in the deposition apparatus π-80 produced by Platit AG. The essential microstructural parameters; the chemical and phase composition, the residual stress, preferred orientation of crystallites, crystallite size and mutual disorientation of crystallites were determined in all coatings under study. The derived microstructural parameters were correlated with the hardness of coatings. Finally, the microstructural model of the nanocrystalline hard coatings and thin film nanocomposites formation was developed. Depending on the sample chemical composition, three regions with different phase compositions exist in the coatings. In the transition metal richest samples, a single fcc M1-x- yAlxSiyN phase exists in the coating. With increasing Al content,...
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Theoretical studies of rolled-up and wrinkled nanomembranes
Čendula, Peter ; Holý, Václav (advisor) ; Fedorchenko, Alexander I. (referee) ; Onck, Patrick N. (referee)
Title: Theoretical studies of rolled-up and wrinkled nanomembranes Author: Mgr. Peter Cendula Department: Department of Condensed Matter Physics Thesis Supervisors: Prof. Dr. Oliver G. Schmidt, Prof. RNDr. Václav Holý, CSc. Abstract : The thesis is devoted to three similar topics from the field of rolled-up and wrinkled nanomembranes. We start by recalling classical theory of thin plates, which will be used to describe deformation of nanomembranes. In the first topic, relaxation of internal strain is studied when a flat film is partially released from the substrate by etching the sacrificial layer underneath. Energetic competition of the tube and wrinkle shape is quantitatively investigated. Similar model is used to investigate the limiting maximum value of tube rotations. In the second topic, roll-up of initially wrinkled film is shown to favor tubes forming on the flat edge of rectangular wrinkled pattern, enabling precise control of tube position. Experiment is provided to justify our theoretical predictions. In the third topic, quantum well is assumed inside a wrin- kled nanomembrane. Shift of transition energy induced by lateral modulation due to bending strain is quantified, being of interest for strain-sensitive optical detectors and emitters. In addition, lateral localization of electron and hole due to...
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Bacterial role in silicate mineral alteration in near-neutral pH conditions
Duchoslav, Vojtěch ; Falteisek, Lukáš (advisor) ; Seydlová, Gabriela (referee)
It is well established that bacteria are able to catalyze dissolution of silicate minerals. Bacteria may dissolve silicates for two different purposes. They may use certain elements that can undergo redox transitions as substrates for their energetic metabolism or they can leach nutrients, that are otherwise unaccessible in their habitat. The main mechanisms of bacterially mediated silicate leaching are acidic or basic catalysis and surface complexation. The main nutrients extracted are K, Mg, P and Fe. The only element significantly exploited as substrate for dissimilative energetic metabolism is iron. In order to leach iron as a nutrient, even extremely strong complexants (i.e. siderophores) may be employed. However, only moderate complexing agents can serve to obtain iron as terminal electron acceptor. The second possibility is to reduce iron directly in the crystal grid by means of the conductive nanofibres. The oxidative dissolution of silicates by chemoautotrophs is rare, in contrast to that of sulfides. Bacterial dissolution of silicates leaves morphological and geochemical signatures, but it is still problematic to recognize and interpret them. Although it is well-known that bacteria can dissolve most of the rock-forming minerals in diverse environments we are unable to quantify their contribution...
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Structural evolution of infra- and superstructure boundary in orogens
Peřestý, Vít ; Lexa, Ondrej (advisor) ; Franěk, Jan (referee)
ENGLISH ABSTRACT This work focuses on structural and deformational aspects of the crust development during orogeny, based on historical suprastructure/infrastructure concept. The uppermost suprastructure is dominated by steep fabrics, which evolved in a brittle regime within early stages of orogeny, and which sustain almost unchanged for the whole period of orogenic evolution. On the other hand, the infrastructure is located in the lower crust, where ductile processes dominate. Because the ductility is a thermally activated process, sufficiently long time is needed to heat the lower crust, and therefore the infrastructure is younger than suprastructure. Gently to shallowly dipping structures develop as a consequence of ductile flow. The aim of this study is to describe processes on the suprastructure/infrastructure boundary. Position of this boundary is closely related to brittle/ductile transition, and so that a brief introduction to rheology is included. Rheological boundaries are often places of high strain and high displacement gradients, which must be somehow accomodated. One possibility is to lose communication between adjacent levels and create a detachment plane, which is commonly supposed in the conventional thrust tectonics model. The other possibility is, that layers are at least partially...
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Fotoluminiscence erbiem dopovaných krystalů KTaO.sub.3./sub..
Potůček, Zdeněk ; Bryknar, Z. ; Trepakov, Vladimír
Photoluminescence emission spectra of KTaO3:Er crystals was studied within the wide temperature (12 – 300 K) and spectral (300 – 1200 nm) regions in order to reveal luminescence centers related to Er ions and to elucidate their optical properties. Under excitation with band-gap light at low temperatures, the KTaO3:Er crystals shoved a broad asymmetric emission band peaking near 490 nm at 12 K that belongs to well-known “green” photoluminescence of KTaO3 crystals. Erbium doping was accompanied by appearance of narrow structured emission bands in the vicinity of 550, 660, and 850 nm that were attributed to radiative transitions within Er3+ ions with 4f11 electron configuration.
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Modification of Isoprenoids
Eignerová, Barbara
Abstract-AJ This PhD work is focused on the development of a new methodology aiming at the introduction of the perfluoroalkylated side-chains into various types of molecules. Synthesis of perfluoroalkylated compounds, owing to their biological properties, is a frequent target of organic chemistry.1 During the last couple of decades a number of different methods enabling the perfluoroalkylation have been developed. Among the classical methods belong procedures based on nucleophilic, electrophilic, or radical reactions.2 Interestingly, only a few examples of a transition metal catalyzed perfluoroalkylation reactions have been reported.3 Despite the fact that many of these methods have wide synthetic applicability, they are not general and search for new procedures is a desirable target. One of the possible and hitherto unexplored methods for the synthesis of perfluoroalkylated compounds is a ruthenium-complex catalyzed alkene cross-metathesis. Potentially, a reaction of a suitable terminal alkene reactant bearing a perfluoroalkylated moiety with the second terminal alkene could give rise to a new and more complex internal alkene. Regarding perfluoroalkylated alkenes suitable for the cross-metathesis reactions, (perfluoroalkyl)propenes can be considered as convenient substrates that can be easily prepared from...
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Microstructure and Properties of Nanocrystalline Hard Coatings and Thin Film Nanocomposites
Dopita, Milan
In this work, microstructure and properties of M-Al-(Si-)N nanocrystalline hard coatings and thin film nanocomposites deposited by cathodic arc evaporation (CAE) process at different positions of substrates in the deposition apparatus were investigated using the combination of electron probe microanalysis, X-ray diffraction, transmission electron microscopy with high resolution and hardness measurement. Six series of specimens that differed in the transition metal type (Cr, Ti and Zr) and in the amount of Si and Al were deposited using the CAE process in the deposition apparatus π-80 produced by Platit AG. The essential microstructural parameters; the chemical and phase composition, the residual stress, preferred orientation of crystallites, crystallite size and mutual disorientation of crystallites were determined in all coatings under study. The derived microstructural parameters were correlated with the hardness of coatings. Finally, the microstructural model of the nanocrystalline hard coatings and thin film nanocomposites formation was developed. Depending on the sample chemical composition, three regions with different phase compositions exist in the coatings. In the transition metal richest samples, a single fcc M1-x- yAlxSiyN phase exists in the coating. With increasing Al content,...
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The fracture behaviour of welded joints pearlitic and bainitic rail steel
Hadraba, Hynek ; Dlouhý, Ivo ; Holzmann, Miloslav ; Zbořil, J.
The contribution is focused on analysis of welded joint made from pearlitic rail steel of type UIC 900A and newly developed cast bainitic Lo8CrNiMo steel. The lowest dynamic fracture toughness and consequently the higher risk of brittle fracture possessed the pearlitic steel and its heat affected zone (HAZ). At application temperature range the fracture toughness of this steel was on lower shelf of ductile to brittle transition, the tempering in HAZ didn't affect the toughness substantially. The dynamic fracture toughness of cast bainitic steel in joint was two times highest comparing to pearlitic one and, in addition HAZ toughness increase was found. The weld joint itself was characterised by high scatter of toughness data, nevertheless, all the values were above the scatter band characterising the more brittle pearlitic steel.
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