National Repository of Grey Literature 413 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Preparation of LiNbO3 nanostructures and their characterization
Pikna, Štěpán ; Jelínek, Michal (referee) ; Dvořák, Petr (advisor)
This master thesis is focused on the deposition of LiNbO3 on c-cut Al2O3 substrate. This material exhibits an electro-optic effect, which refers to the change in the refractive index upon the application of an external voltage, and it has extensive applications in electro-optic modulators. Currently, there is significant interest in miniaturizing these devices for use in the fields of meta-optics and photonics, where its transparency is also advantageous. The first part of this thesis is dedicated to a review of the electro-optic effect and its application in optical metasurfaces. Subsequently, the review addresses the pulsed laser deposition of LiNbO3. The practical part begins with the optimization of target fabrication from LiNbO3 wafers using a laser cutter. Following this, the measurement of the electro-optic effect from a monocrystalline LiNbO3 wafer is discussed. The final section is devoted to the deposition of this material onto a sapphire substrate and further analysis using SPM, XPS, XRD, and SEM. Monocrystalline growth of 30 nm grains was observed, and the physical dependencies of the growth was studied.
Anion-exchange enabled tuning of caesium lead mixed-halide perovskites for high-energy radiation detection
Matula, Radovan ; Friák, Martin (referee) ; Dvořák, Petr (advisor)
Olovnato-halogenidové perovskity (OHP) se svými bezprecedentními funkčními vlastnostmi, které umocňuje jednoduché ladění zakázaného pásma, vzaly svět polovodičů útokem. Proces aniontové výměny, možný i po syntéze, umožňuje ladění zakázaného pásu OHP, což vede k olovnato-mix-halogenidovým perovskitům (OMHP), čímž se rozšiřuje jejich potenciál pro aplikace, zejména v oblasti laditelných detektorů. Širokému přijetí LMHP však brání jejich chemická nestabilita, která vede k segregaci halogenidů v materiálu, což zásadně omezuje spolehlivý provoz zařízení na bázi OMHP. Pochopení kinetiky segregace halogenidu přes delší časové intervaly zůstává výzvou, nabízi se tak použití teoretických simulací, jako jsou metody Monte Carlo (MC). Avšak MC simulace spoléhají na dobře definované povrchy potenciální energie (PPE), typicky odvozené z výpočetně náročných výpočtů teorie funkcionálu hustoty (DFT). V této práci navrhujeme nový přístup pro konstrukci dobře definovaných PPE z vysoce přesných DFT dat se zlomkem výpočetního zatížení. Využitím activation-relaxation technique noveau (ARTn) pro motivaci hledání přechodových bodů v PPE v kombinaci s nejmodernějšími přístupy strojového učení se snažíme výrazně snížit výpočetní náklady. Navíc s využitím klasické teorie hodnotíme detekční schopnosti vybraných OMHP.
Preparation and characterization of optical metasurfaces
Weiss, Vlastimil ; Čižmár, Tomáš (referee) ; Dvořák, Petr (advisor)
This thesis presents a comprehensive study on the preparation and characterization of dielectric optical metasurfaces. Optical metasurfaces, which are artificially structured surfaces, enable precise manipulation of electromagnetic waves at a subwavelength scale, surpassing conventional optics in terms of spatial resolution and the complexity of optical transformations. The work is conducted at the Institute of Physical Engineering, Brno University of Technology in colaboration with CEITEC, and involves the use of advanced techniques such as ion beam etching through masks created via electron beam lithography (EBL) and the deposition of optically active materials into EBL matrices. The primary objectives include a thorough literature review, the fabrication of dielectric metasurfaces based on phase control mechanisms, and the detailed morphological and optical characterization of the produced structures. The research employs digital holographic microscopy and confocal optical spectroscopy for optical characterization, as well as numerical and semi-analytical simulations. The results contribute to the ongoing development of high-efficiency optical components and highlight the potential applications of biophotonic devices in the field of nano-optics.
Experimental measurement of dielectric functions using ellipsometry
Slovák, Radim ; Kvapil, Michal (referee) ; Dvořák, Petr (advisor)
This work deals with the broad application of the spectral ellipsometry (SE) characterization method. It includes measurements of the dielectric function of thermal SiO2 and its thickness on a silicon substrate. Additionally, it presents diverse dielectric function of thin gold layer, highlighting its metallic and dielectric properties. The SE method is utilized for determining time-variable layers such as the growth rate of copper oxides. Furthermore, the dielectric function of the photoluminescent material CsPbBr3 is measured to identify quantum transitions within this perovskite material. Finally, a program in python is developed, enabling comprehensive analysis of ellipsometric data obtained via imaging microellipsometry on phase-change Sb2S3.
Deposition of GaN nanocrystals with Ag nanoparticles
Michalko, Matej ; Dvořák, Petr (referee) ; Čalkovský, Vojtěch (advisor)
The presented bachelor thesis deals with the preparation of GaN nanocrystals with Ag nanoparticles. In the theoretical part GaN, its properties and applications are introduced. Furthermore, possible substrates for GaN growth and preparation methods are presented, with a main focus on MBE. The thesis also discusses the basic principles of photoluminescence and its enhancement using metal nanoparticles. The experimental part deals with the preparation of GaN nanocrystals with Ag nanoparticles. First, Ga islands are deposited on Si(111) substrate, the second step is Ga nitridation. Subsequently, Ag nanoparticles of different sizes are deposited. The different steps were optimized and measured by analytical techniques such as SEM and photoluminescence. Finally, the dependence of the photoluminescence enhancement on the size of Ag nanoparticles was established.
Preparation and characterization of optically active nanorods
Gaizura, Filip ; Liška, Petr (referee) ; Dvořák, Petr (advisor)
This work focuses on the qualitative study of the preparation and optical characterization of CsPbBr3 perovskite nanorods. The first part contains a brief description of 3D, 2D and 0D perovskite nanostructures, and then focuses on the description of the 1D structure - perovskite nanorods, their possible crystal structures, stability, possible preparation methods, optical properties and use in various optoelectronic devices. The practical part discusses in detail the preparation of CsPbBr3 perovskite nanorods using colloidal synthesis based on ligand-assisted reprecipitation and chemical division at room temperature. Furthermore, the synthesized nanorods are analyzed for morphology and their absorption and photoluminescence spectra are measured with the aim of verifying the dependence of optical properties on the mentioned morphology.
Fabrication of SiC optical metasurfaces
Štálnik, Jozef ; Idesová, Beáta (referee) ; Dvořák, Petr (advisor)
The aim of this bachelor's thesis was to optimize the manufacturing process of SiC meta-surfaces, which have emerged as a revolutionary replacement for classical optical elements due to their ability to control incident light through local phase modulation. Furthermore, it discusses the utilization of silicon carbide as a platform for these photonic devices and the experimental techniques employed in the meta-surface fabrication process. The experimental section presents the results of silicon carbide nanostructure fabrication, with dry plasma etching being the key optimization step. Finally, optical measurements of the phase profile of the resulting meta-surfaces are presented using off-axis digital holography. The main outcome of this work is the creation of a library of individual building blocks crucial for future applications.
Safety assessment of the technical operation of the airport
Dvořák, Petr ; Bulíček, Petr (referee) ; Kotek, Luboš (advisor)
The thesis deals with the safety of technical operation of the airport. The different procedures and rules for safety management are described and an overview of safety incidents from airport operations in Europe is presented. Furthermore, attention is paid to the different parts of the safety issue with regard to the human factor and related events within the airport ground operations. In the final part of the thesis, a risk assessment is developed for selected airport operation procedures, using the safety risk management process based on the ICAO model.
Implementation of the virtual voice assistant
Dvořák, Petr ; Koch, Miloš (referee) ; Novák, Lukáš (advisor)
This diploma thesis focuses on the analysis of the current voice system (IVR) and subsequently the selection and implementation of a virtual voice assistant into the company's environment. The thesis includes theoretical foundations, company analysis, and a detailed description of the implementation process.
Design Computer Network in a Family House
Vala, Lukáš ; Dvořák, Petr (referee) ; Ondrák, Viktor (advisor)
This thesis deals with the entire network in a new house. The first part deals with the analysis of the current state of the house, the possibilities and requirements of the investor. The second part focuses on theoretical foundations. The third part deals with the design solutions and requirements for implementation.

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