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V-pit Defects in InGaN/GaN Studied by X-ray Diffraction
Stránská Matějová, Jana ; Holý, Václav (advisor) ; Dopita, Milan (referee) ; Rafaja, David (referee)
V-pit defects in InGaN/GaN heterostructures were studied by high-resolution x-ray diffraction accompanied by numerical simulations. The work is focused on the role of the V-pits in strain relaxation, on their impact on the appearance of the x-ray reciprocal- space maps and on their relation to the threading dislocations. Analysis of the diffuse part of the diffracted intensity by kinematical scattering theory, together with principal strains and their directions in the vicinity of the V-pit, explains why the lateral position of the InGaN peak is not affected by the V-pits presence. The strain relaxation by V-pit formation was confirmed, while plastic relaxation by misfit dislocations was not observed. The density of the V-pits in the epilayer turned out to be given by the content of threading dislocation with a screw component in the substrate. Pure edge threading dislocations do not affect the V-pit density. The In concentration has an influence on the size of the V-pits, but not their density. 1
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Vibron states in cerium crystalline compounds
Doležal, Petr ; Javorský, Pavel (advisor) ; Detlefs, Blanka (referee) ; Rafaja, David (referee)
This thesis is focused on study of the vibron state in Ce intermetallics. The presence of a vibron state is a consequence of an enhanced magneto-elastic interaction, between phonons and 4f electrons of the Ce ion. The magneto-elastic interaction is usually weak and can be neglected, but here in CeAl2, CePd2Al2, CeCuAl3 and CeAuAl3 is considered to be strong enough, which leads to a bound state called the vibron state. A well determined crystal structure of these compounds is a necessary prerequisite to discuss this unique behaviour. Therefore our investigation is performed on the following levels: A crystal structure study of (Ce,La)Pd2Al2-xGax and CePt2Al2, by low temperature and high temperature X-ray powder diffraction; Investigation of bulk and transport properties of a CePt2Al2 single crystal using the specific heat, magnetisation and electrical resistivity measurements; Symmetry analysis of phonon modes and angular momentum operators in the model Hamiltonian, based on group theory; And finally the study of phonon dispersion curves in CePd2Al2 and LaPd2Al2 single crystals using inelastic X-ray scattering. All these results and preformed analyses lead to the following conclusions: The CePd2Al2 and LaPd2Al2 are incongruently melting phases. We found and described the way which has allowed us to...
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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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