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2D metal-organic frameworks from organic carbonitrile molecules on weakly interacting substrates
Kurowská, Anna ; Torre, Bruno de la (referee) ; Blatnik, Matthias (advisor)
Samouspořádávání je proces spontánního uspořádávání molekul do definovaných supra-molekulárních struktur na površích. Organické molekuly vykazující schopnost samouspořádání mohou být použity jako stavební prvky pro výrobu struktur přístupem "bottom-up", který umožňuje syntézu atomárně přesných dvourozměrných (2D) struktur. Začleníme-li do molekulárního uspořádání atomy kovu může dojít k vytvoření 2D sítí organika-kov (2D MOF). Atomy kovu jsou v nich periodicky uspořádány díky organickým molekulám, které je vzájemě spojují. Takovéto struktury na povrchu materiálů mohou vést k zajímavým vlastnostem, např. změně elektrických vlastností materiálů, nebo použítí nových exotických stavů hmoty v technologických zařízeních. Tato práce se zabývá studiem struktur na bázi karbonitrilových molekul a atomů přechodných kovů na povrchu ušlechtilých kovů a topologického izolantu. Vybrané molekuly, u nichž budeme studovat možnosti využití jako ligandu, jsou HATCN a DCA. Práce představuje výsledky z metod LEEM a STM pro molekulární samouspořádání na obou typech povrchů, a pro systémy organika-kov jen na ušlechtilých kovech; zejména DCA se ukazuje jako slibná molekula pro tvorbu 2D MOFs. Úspěšně jsme vytvořili periodicky uspořádané MOF s atomy Fe na povrchu Ag(111) a molekulární samouspořádání DCA molekul na povrchu Bi2Se3.
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Modeling electroacoustic systems in COMSOL
Hanuš, Jan ; Honzík,, Petr (referee) ; Schimmel, Jiří (advisor)
The thesis aims to explore the simulation software COMSOL Multiphysics with relevance to the field of electroacoustics. The work covers general introduction to the software, including an outline of the principles of finite element method, which is the most widely used numerical method in COMSOL Multiphysics. It also includes a clear description of the individual steps required to create a simulation. Furthermore, the Acoustics Module is described, Pressure Acoustics physics interface in particular as it is used later on in the simulations. The AC/DC Module and its physical interface Electric Circuit is mentioned briefly as well. Finally, the simulations created by the author are explained in a step-by-step manner. These look at the impact of the membrane’s and waveguide’s geometries on the radiation of the speaker driver, and the shapes of the loudspeaker system’s enclosure with the edge diffraction phenomena in mind. The results of the individual simulations are presented using graphs and discussed afterwards.
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A sampler of diffraction and refraction optically variable image elements
Horáček, Miroslav ; Krátký, Stanislav ; Matějka, Milan ; Chlumská, Jana ; Meluzín, Petr ; Pirunčík, J. ; Aubrecht, I. ; Kotrlý, M. ; Kolařík, Vladimír
Diffraction and refraction optically variable image elements are basic building blocks of planar structures for advanced security of documents and valuables. A sampler formed by an array of 36 diffraction structures binary, tertiary, quaternary and blazed gratings (period range 400 nm 20,000 nm) represents a cross-section throughout technological steps mastering, galvanic replication and embossing. Electron-beam writing technology with Gaussian beam and electron energy of 100 keV, with very small forward scattering of high energy electrons and with the possibilities to create a linear grating with the minimal period of 100 nm, was used to create the master. An important advantage of high-resolution electron-beam lithography is its substantial flexibility in combining possible planar structures with significantly different parameters, such as very dense and relatively shallow structures together with deep structures (approx. 10 microns) with precise shapes (micro-lenses or Fresnel structures). For protection of documents and valuables, interesting results are induced with planar optical structures consisting of non-periodic arrangements, which are characterized by high robustness to counterfeiting and imitation. While the origination process is available for grating period down to 100 nm, the mass replication technology appears to be a bottleneck of the entire technological process. Measurement of topology and profiles of the structures by atomic forces microscope and documenting the quality of technological process of the three steps of replication of planar optically variable elements was performed for all 36 structure types of sampler.
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Study of the influence of geometrical parameters of phase binary gratings on their optical response for the preparation of optical fiber sensors
Krátký, Stanislav ; Kolařík, Vladimír ; Mikel, Břetislav ; Helán, R. ; Urban, F.
For exposure to optical fibers through a phase grating, it is necessary to tune the geometrical parameters of the grating very well. In this paper, we study the effect of the grating period, grating diameter, grating depth, and polarisation of the incident laser beam on the efficiency of diffraction orders. A suitably tuned grating generates diffraction orders with the desired efficiency, thereby guaranteeing the formation of the desired motif in the exposed optical fiber.
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Compensation of loudspeaker measurements using standard baffle
Štěpáník, Jiří ; Schimmel, Jiří (referee) ; Balík, Miroslav (advisor)
The frequency response of the loudspeaker is one of the key data that needs to be known, for example, when designing a speaker cabinet or speaker system. The frequency response should be achieved with the highest possible accuracy and with a minimum of distortion. How to achieve such characteristics is described in the standard ČSN EN 60268-5, which states as one of the ways the use of standard enclosures. Except for the standard baffle, these baffles have correction curves for the measured characteristics described in the standard. However, this does not mean that the standard baffle does not distort the measurement. The aim of this work is to analyze the distortion of measurements caused by this baffle and other elements and their compensation. The work contains a description of certain parts of the standard ČSN EN 60268-5 with focus on the standard baffle. Especially on its construction and methods of measuring the speakers mounted on it. Several test measurements were performed within the work. These measurements were performed in a anechoic chamber with speakers mounted on a modular standard baffle, which is a modification of the standard baffle which is also described in the work. The measurements performed include the measurement of frequency characteristics at different distances of the microphone from the speaker at different positions of the baffle in the anechoic chamber. The test measurements show that the modular standard baffle and anechoic chamber cause measurement distortion. In other measurements, the distortion by the anechoic chamber is minimized and the distortion caused by the base of the modular standard baffle is completely eliminated. The thesis then presents the theory of sound diffraction at the edges of a standard baffle and the theory of the extended Biot-Tolstoy-Medwin method of modeling these diffractions using numerical calculations. Based on this theory, software compensation of diffraction distortion was performed in Matlab. It is not entirely clear from the results of the compensation to what extent it can be considered successful. It can be speculated that it only works on certain frequencies. It is necessary to verify the functionality of this compensation method by another test measurement.
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Structure and magnetic interactions in nanomaterials with application potential
Pacáková, Barbara ; Kalbáčová Vejpravová, Jana (advisor) ; Jirásková, Yvona (referee) ; Svoboda, Pavel (referee)
The thesis is focused on the physics of magnetic nanoparticles (NPs), starting from the solution of magnetic structure, internal alignment within the single particle and role of interactions and particle structure in magnetic response of systems of the NPs. Moreover, the macroscopic arrangement of the NPs and its effect on the properties of system containing the NPs are discussed. The work brings several new results and concepts, such as the solution of magnetic structure of the ε-Fe2O3 phase, methods of proper detection and description of magnetic metal catalyst in carbon nanotubes and role of the NP arrangement and their effect on graphene placed on the top of substrates decorated with the NPs. 1
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Metal-organic networks on graphene surfaces
Kurowská, Anna ; Průša, Stanislav (referee) ; Čechal, Jan (advisor)
Molecular self-assembly is a spontaneous association of molecules and atoms into well-defined supramolecular structures. Understanding this process is key for preparation of structures with atomic precision. This thesis studies the supramolecular structure of tetrakyanochinodimetan molecules (TCNQ) and iron atoms on graphene grown on iridium crystal with the (111) surface. The surface analysis was performed by scanning tunneling microscopy, low-energy electron microscopy and x-ray photoelectron spectroscopy. The thesis introduces the growth process of a good quality graphene on Ir(111) and the synthesis of Fe-TCNQ networks 20 nm x 20 nm large and describes their structural properties. Three preferential orientations of Fe-TCNQ on graphene were identified. The networks will be used in follow-up studies targeting their magnetic properties.
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The preparation and study of catalytic system Cu(O)-CeO2 using surface analytical methods
Šmíd, Břetislav
Title: The preparation and study of catalytic system Cu(O)-CeO2 using surface analytical methods Author: Břetislav Šmíd Department: Department of Surface and Plasma Science Supervisor of the doctoral thesis: Doc. Mgr. Iva Matolínová, Dr. Abstract: This work is concerned with a study of copper/copper oxide - cerium dioxide systems and their interaction with CO and H2O molecules. Investigated samples were prepared in the form of powder catalysts and also as very well defined model inverse systems. The low temperature CO oxidation powder catalysts were studied by means of XPS, XRD, SEM, TEM and in micro-reactor system allowing the CO oxidation examination. The study of H2O adsorption and co-adsorption of H2O with CO were carried out on model inverse systems CeOx(111)/Cu(111) in ultra-high vacuum conditions using X-ray, synchrotron radiation (SRPES), resonant (RPES) photoelectron spectroscopies and LEED. It was observed on the stoichiometric surface water adsorbs molecularly at 120 K while on the reduced surface and surface of CeO2 islands on Cu(111) the H2O adsorption is partially dissociative with formation of OH groups. The increase of Ce3+ species (i.e. surface reduction) observed after H2O adsorption was explained as an electronic effect of the Ce 4f charge accumulation and Ce 5d charge depletion....
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Study of diffractive processes at the ATLAS Experiment
Kůs, Vlastimil
Title: Study of diffractive processes at the ATLAS Experiment Author: Vlastimil Kůs Department: Institute of Particle and Nuclear Physics Supervisor: Mgr. Marek Taševský, Ph.D. Institute of Physics of the Academy of Sciences of the CR, v.v.i. Abstract: A data sample of pp collisions corresponding to an integrated lumi- nosity of 6.75 nb−1 was collected at √ s = 7 TeV using the ATLAS detector at the Large Hadron Collider. Collision events with at least two jets with pT > 20 GeV are used to measure the differential cross section of the diffractive dijet production as a function of the rapidity gap size ∆ηF , the largest forward region extending from |η| = 4.8 devoid of particle activity above threshold momentum cuts, and an estimator of the fractional momentum loss of the scattered proton assuming the single diffractive dissociation (pp → pX), ˜ξ± . Comparisons with various Monte Carlo models reveal that though the region of small ˜ξ± and large rapidity gaps is dominated by diffraction, a contribution form non-diffractive events cannot be neglected. The rapidity gap survival probability is estimated based on data to Monte Carlo comparisons in the −3.2 < log10 ˜ξ± < −2.5 region of the ˜ξ± distri- bution with the ∆ηF > 2 requirement. 1
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Investigation of dislocation structure evolution in advanced magnesium alloys
Šimko, Pavol ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
: This thesis deals with evolution of dislocation structures in mag- nesium alloys containing long-period stacking ordered phase (LPSO). Before de- formation the samples were studied by optical light microscopy, in the process of deformation by neutron diffraction. Obtained diffraction profiles were of two types, axial and radial diffraction profiles (created by planes oriented in the di- rection of deformation and orthogonally to the direction of deformation). Profiles were evaluated by Convolutional Multiple Whole Profile method and by Hexbur- ger program. This work is focused on the role of LPSO phase in the evolution of dislocation density and population of dislocations in slip systems depending on the composition of alloys and on the volume fraction of LPSO phase. 1
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