|
|
Rtg difrakce a difuzní rozpyl na Heuslerových slitinách
Cejpek, Petr ; Holý, Václav (advisor)
Recently, Heusler alloys are studied for their interesting magnetic and electronic properties. These properties are strongly dependent on the crystallographic struc- ture. This work deals with Heusler alloys of the A2BC type. We have powder samples and single-crystaline samples for our study as well. An object of interest was a description of crystallographic structure of the samples, site occupation numbers of each type of atoms and their possible occupation disorder. Pow- der difraction and EXAFS have been measured on the powder samples. Clasical single-crystal diffractions has been meassured on the single-crystaline samples. In the case of a modulated structure in the samples, satelite difractions have been measured too. 1
|
|
|
Rtg difrakce a difuzní rozpyl na Heuslerových slitinách
Cejpek, Petr ; Holý, Václav (advisor)
Recently, Heusler alloys are studied for their interesting magnetic and electronic properties. These properties are strongly dependent on the crystallographic struc- ture. This work deals with Heusler alloys of the A2BC type. We have powder samples and single-crystaline samples for our study as well. An object of interest was a description of crystallographic structure of the samples, site occupation numbers of each type of atoms and their possible occupation disorder. Pow- der difraction and EXAFS have been measured on the powder samples. Clasical single-crystal diffractions has been meassured on the single-crystaline samples. In the case of a modulated structure in the samples, satelite difractions have been measured too. 1
|
|
|
High-temperature X-ray Diffractometry of Thin Layers
Valeš, Václav ; Holý, Václav (advisor) ; Jergel, Matej (referee) ; Nižňanský, Daniel (referee)
In this work, the crystallographic structure and its changes under thermal treatment of different systems consisting of metal oxide nanoparticles is studied. The principal method used throughout the thesis is x-ray powder diffraction enriched with grazing incidence small angle x-ray scattering when the nanoparticles form an ordered structure or with x-ray absorption spectroscopy when additional information on local crystallographic structure is required. For all the systems the preparation conditions were optimized according to the crystallographic data for further applications.
|
|
|
Rtg difrakce a difuzní rozpyl na Heuslerových slitinách
Cejpek, Petr ; Holý, Václav (advisor) ; Kriegner, Dominik (referee)
Recently, Heusler alloys are studied for their interesting magnetic and electronic properties. These properties are strongly dependent on the crystallographic struc- ture. This work deals with Heusler alloys of the A2BC type. We have powder samples and single-crystaline samples for our study as well. An object of interest was a description of crystallographic structure of the samples, site occupation numbers of each type of atoms and their possible occupation disorder. Pow- der difraction and EXAFS have been measured on the powder samples. Clasical single-crystal diffractions has been meassured on the single-crystaline samples. In the case of a modulated structure in the samples, satelite difractions have been measured too. 1
|
|
|
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.
|
|
|
Study of the structure of ferromagnetic semiconductors by x-ray scattering methods
Horák, Lukáš ; Holý, Václav (advisor) ; Mikulík, Petr (referee) ; Stangl, Julian (referee)
We studied epitaxial layers of Gallium Manganese Arsenide by various x-ray scattering methods. Since the positions of the Mn dopant in the a host GaAs lattice are crucial for magnetic properties of this material, we focused mainly on a development of the laboratory diffraction method capable to identify Mn in particular crystallographic positions. From the measured diffracted intensity distributed along Crystal Truncation Rods, it is possible deduce the density of Mn interstitials in two non-equivalent crystallographic positions. It is possible to decrease the interstitial Mn density by annealing. We demonstrated our method on severally annealed epitaxial layer. The depth profile of interstitial density was determined after each annealing. The annealing process was simulated by the solving of the Drift- Diffusion equations. From the comparison with the experimentally determined interstitial densities, we estimated the diffusivity of Mn interstitials in the GaAs lattice. Powered by TCPDF (www.tcpdf.org)
|
|
|
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
|
|
|
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...
|
|
|
Dynamics of structural defects in CdTe-based semiconductors
Bugár, Marek ; Belas, Eduard (advisor) ; Holý, Václav (referee) ; Fochuk, Petro (referee)
Title: Dynamics of structural defects in CdTe-based semiconductors Author: RNDr. Marek Bugár Institute: Institute of Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. Ing. Eduard Belas CSc.; Institute of Physics, Charles University in Prague Abstract: The work was aimed at investigation of the effect of annealing on structural, electrical and optical properties of CdZnTe epitaxial substrates and CdTe-based and CdZnTe-based X-ray and gamma-ray detectors. The first part of the work is focused on investigation of structural properties of one type of second phase defects - inclusions - present in the material, which degrade the material quality. Consequent annealing experiments were aimed at reduction of these defects. In case of CdZnTe substrates, an annealing treatment leading to increase of the infrared transmittance was investigated. On the other hand, annealing experiments on the detectors of high-energetic radiation were focused on preservation of the high-resistive state. Moreover, the work contains detailed measurements of transport properties of CdTe taken directly at high temperatures. Key words: CdTe, annealing, inclusions, detectors, defects
|
|
|
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.
|
guest ::
RSS feed.