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Nanostructured metal substrates for model electrocatalysis
Škvára, Jan ; Mysliveček, Josef (advisor) ; Stetsovych, Oleksandr (referee)
This thesis studies preparation of nanostructured Pt(111) surfaces for usage in model electrocatalytic experiments. A method is presented, that uses ion erosion of the sur- face at elevated temperature for surface preparation. The results of the thesis suggest, that comparing to other methods of nanostructured surface preparation in present elec- trochemical practice the ion erosion is an effective and practical tool for preparation of surfaces with morphology controlled at the atomic level and that it has a potential to accelerate the development of knowledge in this area. 1
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STM study of growing 1D nanostructures composed by III and IV group atoms
Kučera, Michael ; Ošťádal, Ivan (advisor) ; Mysliveček, Josef (referee)
In the presented work we study Al and Sn on a Si(100)2$\times$1 surface by means of STM. Peculiarities of displaying and morphology of metallic structures are investigated. Utilizing the STM to investigate Al and Sn, we obtain the growth characteristics for various coverage and temperatures at deposition. It is shown, that island size distribution is scalable for both metals and has a qualitatively different character. In order to interpret the growth characteristics and obtain unknown microscopic parameters, a new software tool for kinetic Monte Carlo (kMC) simulations of aluminum was conceived.
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Role of surface defects in ceria-based catalysis
Tovt, Andrii ; Mysliveček, Josef (advisor) ; Čechal, Jan (referee) ; Švec, Martin (referee)
Title: Role of surface defects in ceria-based catalysis Author: Andrii Tovt Department: Department of Surface and Plasma Science Supervisor of the doctoral thesis: doc. Mgr. Josef Mysliveček Ph.D., Department of Surface and Plasma Science Abstract: This work concentrates on the analysis of fundamental physicochemical properties of Pt-CeOx, single-atom Pt1 /CeOx, and inverse CeOx/Cu(111) catalysts. Preparation method for stabilized atomically-dispersed Pt2+ ions on ceria was developed and adsorption sites for Pt ions were thoroughly studied using advanced surface science techniques supported by theoretical methods. The mechanism of Pt2+ stabilization on ceria steps was revealed and the step capacity towards Pt2+ ions was estimated. Also, the preparation method for well-ordered cerium oxide ultrathin films with different stoichiometry and ordering of surface oxygen vacancies was developed, and the Ceria/Cu(111) interaction was investigated. Key words: heterogeneous catalysis, model systems, single-atom catalysis, platinum ions, cerium oxide.
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STM study of metal adatom mobility on Si(100) surface
Rozbořil, Filip ; Ošťádal, Ivan (advisor) ; Mysliveček, Josef (referee)
Surface diffusion of group III and IV metals on Si(100) is studied. Three methods for obtaining diffusion barriers are presented and discrepancies in published results are discussed. Room temperature growth of Al on Si(100) is studied using STM, observing a monomodal scaled island size distribution function. A Kinetic Monte Carlo simulation model is employed to obtain bonding energies and diffusion barriers for Al/Si(100). The best agreement between the measured and simulated characteristics is found for strongly anisotropic diffusion with barriers 0.60 eV in the direction orthogonal to the Si dimer rows and 0.80 eV in the parallel direction. Modifications of the cooling system required for observing metal adatom diffusion on Si(100) using STM are described and the first low-temperature experiment is carried out.
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STM/STS study of bimetallic nanostructures on silicon surfaces
Zimmermann, Petr ; Sobotík, Pavel (advisor) ; Mysliveček, Josef (referee)
In this study we examine linear nanostructures consisting of metals of III. (Al, In) and IV. (Sn) group on the Si(001)2×1 surface by means of scanning tunnelling microscopy & spectroscopy. Atoms on the surface align into atomic chains growing perpendicularly to the dimer rows of the surface reconstruction. The chain structure consists of dimers that adsorb in the troughs between the dimer rows of the surface reconstruction. We observe that the chains consist of sequences of homodimers of either elements combining with heterodimers. The InSn chain structure is analysed with regard to theoretical ab-initio calculations of the chain dimer structure. The model is then applied to the Al-Sn system. We observe that the Al-Sn chains tend to consist of aligned heterodimers. The appearance of heterodimers in STM depends on the chemical composition of the neighbouring dimers. We can also observe the tendency of chains to agglomerate and via Sn atoms create quasi periodic 2D structures. The electronic structure of an Al, Sn and mixed AlSn dimer is studied by means of tunnelling spectroscopy. Despite its small, nonzero density of states on the Fermi energy, the character of the mixed dimer appears to be rather non-conductive.
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Adsorption and mobility of Al adatoms on Si(100) surface
Majer, Karel ; Ošťádal, Ivan (advisor) ; Mysliveček, Josef (referee)
The subject of the thesis is growth of aluminium structures one-dimensional chains on Si(100) surface. Growth characteristics of Al on Si(100) at room temperature and at higher temperature and various coverages were measured using STM. The results are discussed with respect to previous experiments and a way to find the value of activation energy of surface migration is proposed. An important part of the thesis is preparation and tests of a new low-temperature UHV apparatus for STM experiments. Functions of the apparatus are described. A way to prepare clean Si(100) surface as well as the methods of achieving atomic-scale resolution in STM were found in conditions previously unknown. A test of evaporators for Al and Sn is described. Al deposition has not been successful in the new apparatus yet. Sn deposition has been successful and low-temperature structures of tin on Si(100) were observed. They differ from room-temperature structures and contain kinks which were previously observed only in Al structures.
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Epitaxial films of ceria for opto- electronics
Kubát, Jan ; Mysliveček, Josef (advisor) ; Antoš, Roman (referee)
This diploma thesis studies magneto-optical (MO) response of epitaxial thin films of Co-doped ceria. Thin films were characterized by XPS, LEED, STM, spectroscopic ellipsometry and measurement of MO activity. The work focuses on studying MO response of the films depending on film thickness, cobalt concentration, oxidation state of cerium and chemical state of cobalt. Spectra of MO response consist of low energy region where the MO activity is mediated by transitions from defect induced states to conduction band and high energy region where a peak of MO activity appears which we attribute to transitions from valence band to conduction band. In this work we qualitatively explain the effects of the physico- chemical states of the thin films on the structure of the obtained MO spectra, mainly on the appearance of the MO activity in the low energy region, and on the changes of the position of the MO peak. Compared to other preparation methods the epitaxial thin films allow achieving a shift of the MO peak in the direction of higher photon energy.
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Highly ordered cobalt oxide thin films for model catalysis
Ronovský, Michal ; Mysliveček, Josef (advisor) ; Švec, Martin (referee)
Hydrogen processing is becoming increasingly important not only in the production of electricity but also during its accumulation. One of the energy storage options are liquid organic hydrogen carriers (LOHC). The main drawback of LOHC is the need for a large amount of thermal energy to release molecular hydrogen. We can bypass this issue using heterogeneous catalysis by transferring hydrogen from LOHC to acetone and using the produced 2-propanol (IPA) in the fuel cell. This innovative strategy of getting electri- cal energy from LOHC can be potentially energetically neutral. In this work, we studied highly ordered Co3O4(111) model catalysts for IPA oxidation in the as-prepared state and enhanced with platinum (Pt) nanoparticles. Catalysts were prepared by Physical Vapour Deposition (PVD) and further investigated by means of Low Energy Electron Diffrac- tion (LEED), X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy (STM) and Temperature Programmed Desorption (TPD). The nucleation process of Pt on the as-prepared Co3O4(111) surface was studied by depositing low amounts 0.04 and 0.13 monolayer (ML) of Pt, that create clusters as small as 2 or 3 atoms with no need for a special nucleation site. We have identified the formation of Pt-induced defects in the atomically flat cobalt oxide...
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