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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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Magnetic nanostructures with application potential
Bittová, Barbara ; Kalbáčová Vejpravová, Jana (advisor) ; Holý, Václav (referee)
The thesis is mainly focused on the investigation of macroscopic and microscopic magnetic properties of selected nanomaterials containing cobalt and iron, and also the capability of our new device, scanning probe microscope Multimode V by Veeco, to directly visualise morphology and magnetic structure of these samples (Magnetic Force Miscroscopy, MFM). Investigated materials, such as CoFe2O4 nanoparticles and SiO2_Co_Si(111) thin films and multilayers are in general promising materials in many fields. In the medicine, the nanoparticles are used as the drug targets or contrast agents whereas in electronics, the (nano)granular thin films are the starting point in fabrication of high density storage media. The macroscopic magnetic properties of our samples are discusses in a view of superparamagnetic phenomena. The interactions in systems of nanoparticles are presented theoretically within the up-to date knowledge and also experimentally by demonstrating the behavior of the strongly-interacting, uper-spin-glass system. The thin films are studied in term of their granular structure and magnetic anisotropy. The morphology and the microscopic domain structure, respectively, are studied with use of the MFM. The first successful results obtained in our lab by this method are presented.
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Diffuse x-ray scattering from GaN epitaxial layers
Barchuk, Mykhailo ; Holý, Václav (advisor) ; Caha, Ondřej (referee) ; Pietsch, Ulrich (referee)
Real structure of heteroepitaxial GaN and AlGaN layers is studied by diffuse x-ray scattering. A new developed method based on Monte Carlo simulation enabling to determine densities of threading dislocations in c-plane GaN and stacking faults in a-plane GaN is presented. The results of Monte Carlo simulations are compared with ones obtained by use of other conventional techniques. The advantages and limitations of the new method are discussed in detail. The methods accuracy is estimated as about 15%. We have shown that our method is a reliable tool for threading dislocations and stacking faults densities determination.
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X-ray investigation of defects in graded SiGe/Si thin layers
Endres, Jan ; Daniš, Stanislav (advisor) ; Holý, Václav (referee)
The goal of presented work is a study of defects in graded Si1xGex/Si thin layers. Misfit dislocations are dominant type of defects in this kind of layers. Diffuse scattering of radiation, which is caused by the presence of defects, was measured with high-resolution diffractometer. Misfit dislocations arrangement in the layers was determined from measured reciprocal space maps. Misfit dislocations distribution is discussed within the scope of two models. Equilibrium one, which is based on energy minimization, and kinetic one, which considers thermally activated movement of dislocations. Measured reciprocal space maps were compared with simulations, which were realized via kinematic theory of X-ray radiation scattering.
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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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Diffusion x-ray reflection from rough multilayers
Cejpek, Petr ; Holý, Václav (advisor) ; Daniš, Stanislav (referee)
This bachelor work follows with the theory of diffusion x-ray scattering from rough multilayers. In the first chapter we will recap some basic principles - statitistic properties of interfaces, Fresnell coefficients, scattering theory, etc. - this stuff we will use to derive the expressions for specular reflection and diffusion scattering from rough interfaces, which we will consider as the random fractals. We will demonstrate the use of these derived expressions at a measurement on the multilayers coumpounded from and layers and substrate of mineral glass. Fitting of the measured data on the derived expressions will be done with Matlab software. Moreover, we will measure the roughness of interfaces with AFM microscope and we will compare these two measuring metodes. 2SiO 2ZrO
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Hegel's criticism of the German historical law school in the Philosophy of Law
Holý, Václav ; Sobotka, Milan (advisor) ; Karásek, Jindřich (referee)
This work deals with the problem of hi s tory and historicity of man, society and laws. Hegel stands at the end of a long philosophical tradition and has developed a complex framework, which allows the explanation of all these phenomena and their development. The care of this explanation i s the understanding of the world as rational - the world is the product of the self-conscious idea. And more, the hi s tory is progress of the very same idea towards its own realisation in this world. Hegel sees the whole scenery from the point of view of "the end of history" and it is this position, which allows him to understand the laws governing it. Hegel likes to call his philosophy science and system and as such is this philosophy justifiable only on the grounds of its explicative power. Central terms of Hegels understanding of the society and laws are freedom, will, person and personality, which are again manifestations of the sole idea of reason. The work deals with their conception in Hegels philosophy and their functioning in the explanation of the development of the human society towards reason. Hegel sees the historical law school as an enemy of this development, as an effort to save the past. -we have tried to show that the historical law school is a much more complex phenomenon. Hugo and Savigny have tried...
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