|
|
SiO2 etching by Si deposition
Pokorný, David ; Bábor, Petr (referee) ; Polčák, Josef (advisor)
This bachelor thesis deals with one of the most interesting reactions taking place in the solid phase in UHV conditions and that is decomposition of SiO2 according to the equation Si + SiO2 = 2SiO. It was used the previously untested procedure - providing Si atoms not from substrate, but by direct deposition on the surface of the oxide. As a source of silicon atoms was used effusion cell. Deposition of silicon on SiO2 substrate was used at room temperature and at elevated temperature to clarify the principle of this reaction. The activation energy and temperature dependence of the reaction rate was determined. It was also verified the possibility of etching SiO2 by Si deposition in UHV conditions. The prepared samples were examined by x-ray photoelectron spectroscopy and atomic force microscopy.
|
|
|
Preparation of Ag/Co/Ag Trilayers
Burda, Pavel ; Kolíbal, Miroslav (referee) ; Čechal, Jan (advisor)
The Bachelor's thesis is aimed to the preparation of silver and cobalt ultrathin films. The films are formed on modified surfaces of crystalline silicon substrates (SiO2/Si(111), Si(111) ?H, Si(111) 7×7) and amorphous SiO2 in a form of a quartz glass. Thin films are grown using an effusion cell for Molecular Beam Epitaxy (MBE). Surface modified surfaces are covered subsequently by a silver, cobalt and silver thin layer. The individual film thickness is 6 nm. Consequently the samples are studied by the X-ray Photoelectron Spectroscopy (XPS) and the Atomic Force Microscopy (AFM). The morphology of thin films and growth modes are compared among the substrates. Growth modes change with the surface modification type. Complete trilayer system Ag/Co/Ag was prepared on SiO2/Si(111) and Si(111) 7×7. Such system can be employed in plasmonics in order to allow the control of surface plasmon polariton properties by an external magnetic field.
|
|
|
Development of methodology for study of mechanical activation of chemical reactions at phase boundaries
Matoušek, David ; Kalina, Lukáš (referee) ; Šoukal, František (advisor)
This Bachelor thesis deals with impact of mechanochemical activation on a nature of interphase region in macro-defect-free composites (MDF). MDF composites are highly perspective material on a polymer-cement basis. The most significant advantage of this material is high flexural strength (cca 150 MPa). High strength is caused by high-shear mixing of mixture of cement, polymer, water and plasticiser in twin-roll mill. High-shear stress leads to mechanical activation of reactions between cement and polymer and creation of weak or even strong interactions in interphase region. This work aimed on creation of interphase region by contact of surfaces of two moulded tablets – polyvinyl alcohol and monocalcium aluminate. Next step was construction of simple apparatus, able to define the rate of mechanical activation in interphase region. The most important part of this work concentrated on analysis of activated interphase region by XPS.
|
|
|
Selective growth of GaN on SiN
Hulva, Jan ; Kolíbal, Miroslav (referee) ; Mach, Jindřich (advisor)
This bachelor's thesis deals with the selective growth of gallium and gallium nitride on silicon nitride (SiN) substrates. Thin silicon nitride layers are deposited on silicon substrates. Oxide structures are prepared by the local anodic oxidation method (LAO) on SiN substrates. These surfaces can be editionally modified by etching in hydrofluoric acid. Modified substrates are used for the deposition of gallium or gallium nitride under ultra-high vacuum conditions. Consequently, ordering of deposited material was studied in areas modified by LAO. Chemical state of layers is studied by X-ray photoelectron spectroscopy. Morphology of surfaces is measured by the atomic force microscope (AFM).
|
|
|
High Performance Polymer Composites
Bábík, Adam ; Lapčík,, Lubomír (referee) ; Prokeš, Jan (referee) ; Čech, Vladimír (advisor)
High performance polymer composites are materials with emphasis on specific chemical and mechanical properties due to their broad scope of applications. The main advantages are high strenght and toughness in comparison with their low weight and density. An increased adhesion at composite interfaces is important to ensure excellent composite properties. Bundles of glass fibers were coated by plasma-polymerised interlayers of tetravinylsilane (pp-TVS) of different thicknesses and at different effective powers. The prepared interlayers of pp-TVS were analyzed to evaluate chemical composition (RBS, FTIR, XPS) and mechanical properties (NI-AFM). Microindentation test and fiber-bundle pull-out test were used to determine the interfacial shear strenght.
|
|
|
Study of chemical cleaning of surfaces by LEIS method
Staněk, Jan ; Polčák, Josef (referee) ; Bábor, Petr (advisor)
This thesis deal with studying chemical etched surfaces of cadmium telluride crystals (CdTe crystals) by low-energy ion scattering spectroscopy (LEIS method). In the theoretical part, there is description of physical essence of LEIS method, including experimental arrangement of Qtac100 instrument, on which the experiment is measured. The LEIS method is also compared with X-ray photoelectron spectroscopy (XPS). There is summary of properties and structure of CdTe crystals including principle of X-ray detectors, which are the primary use of the crystals. In experimental part there is a description of measuring process, starting with a calibration measurement, ongoing with a chemical etching and ending with a surface analysis. There are examples of LEIS spectra with comments and interpretation including comparison with XPS data.
|
|
|
Deposition and analysis of DLC thin films
Rudolf, Miroslav ; Čech, Vladimír (referee) ; Šikola, Tomáš (advisor)
Diplomová práce nastiňuje problémy spojené s výrobou a analýzou tenkých vrstev DLC:H. Tyto vrstvy jsou ve středu zájmu mnoha vědeckých pracovníků již po několik desetiletí. V současné době existuje mnoho technik pro přípravu a analýzu. Příprava DLC vrstev má zásadní vliv na jejich vlastnosti a možnosti použití. Je zde mnoho kritérií jak vrstvy posuzovat. V této práci jsou studovány vlastnosti DLC:H vrstev připravených na substrát krystalického křemíku metodou RF-PECVD a následně jsou studovány mechanické, tribologické a optické vlastnosti. Jsou zde využity techniky jako XPS, Ramanova spektroskopie, reflektometrie, měření tvrdosti a adheze. Část práce se zabývá modelováním DLC z prvních principů. Pro tento účel je využito prvoprincipiálního programu Abinit který je šířen pod GPL. Je studována otázka přípravy vstupních dat s ohledem na konvergenci výsledků. Pozornost je také věnována výpočtu vibračních spekter ve středu Brillouinovy zóny ( bod) a celkové hustotě elektronových stavů clusteru DLC v supercele tvaru krychle. Tyto výsledky mohou být porovnány s experimentálně získanými daty z Ramanovy spektroskopie, respektive z XPS spektra valenčního pásu
|
|
|
Soil gel as a suitable matrix for the study of humic substances in the soil ecosystem
Černý, Pavol ; Pekař, Miloslav (referee) ; Enev, Vojtěch (advisor)
This master's thesis deals with a complex issue of soil gels. The main goal of this work is to optimize the process of isolation of soil gels out of the soil matrix. Isolation is carried out using only water and therefore represents a promising method for study of humic substances (HS) in natural form. Modal brown earth from the area of Veverské Kninice was used as a soil matrix for isolation. The isolated soil gel was phisicochemically characterized by thermal and spectroscopic methods. By using EA and TGA, the content of biogenic elements in the organic component of soil gel and the content of the inorganic component was determined. The inorganic component represents a majority share in structure of soil gel with values up to 90 % w/w. Mineralogical composition of the inorganic component was described using XRD, with quartz being the most represented. Chosen macro and microelements were determined by ICPOES and the results show a noticeable increase in the content of some elements, that form complexes with HS. Organic component was studied using spectroscopic methods FTIR and XPS, which clearly showed that the primary components of the organic matrix are HSs. For this reason, absorption coefficients EET/EBZ, E2/E3 a E2/E4 were determined using UV/Vis spectrometry. Morphology of isolated soil gels was studied by using SEM and the photographs show mineral particles covered with clusters of humic matrix.
|
|
|
Mechanical activation of chemical reactions at interfaces of MDF composites
Matoušek, David ; Másilko, Jiří (referee) ; Šoukal, František (advisor)
The thesis deals with study of mechnochemical activation of chemical reactions at interphase of MDF composites. MDF composites are high-perspective composite materials on polymer-cement base. They excel especially in terms of flexural strengths. High flexural stregth is caused by binding interactions between the polymer and the cement. This interactions arise due to mechanochemical activation of raw material mixture at the stage of production. This work focuses on the creation of artificial cement-polymer interphase by contacting the surfaces of two molded tablets (polyvinyl alcohol and monocalcium aluminate), activation of chemical reactions at interphase by means of specially designed appartus, which achieves good plane-parallelism of activation surfaces and good definability of activation conditions (shear rate, pressure). After experiments under different conditions, the activated surfaces are analyzed by SEM, EDS, XPS and FT-IR.
|
|
|
Study of Behaviour of Paramagnetic Molecules on Surfaces
Bouček, Martin ; Procházka, Pavel (referee) ; Hrubý, Jakub (advisor)
This thesis deals with behaviour of paramagnetic molecules of copper(II) pthalocyanine (CuPc), hemin and bis(dibenzoylmethane)copper(II) ([Cu(dbm)2]) on surfaces of glass and polycrystalline gold. Additionally the [Cu(dbm)2] is studied on graphene surface. Molecules are deposited on substrates via wet chemistry methods. They are studied after deposition with atomic force microscopy (AFM), electron paramagnetic resonance (EPR), scanning electron microskopy (SEM) and X-ray photoemission spectroscopy (XPS).
|
guest ::
