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2-D simulations of electromigration processes
Kolivoška, Viliam ; Gaš, Bohuslav (vedoucí práce) ; Koval, Dušan (oponent)
6 Abstract In the presented thesis we introduce a computational model that can be used for 2-D and 3-D computer simulations of experiments in electrophoresis. The simulations are carried out by the aid of the finite element method (FEM). In particular, commercially available program Comsol Multiphysics 3.3 is employed. A general shape of continuity equation is chosen to express the mass, electric charge, momentum and energy conservation law. Diffusion, migration and convection terms are taken into account when formulating the mass conservation law. Both external (driving voltage) and internal (diffusion currents) terms are considered in the electric charge conservation law. Both constant voltage mode and constant current mode can be handled. A solvent is regarded as an incompressible Newtonian fluid. Both pressure-driven and electroosmotic flows can be taken into consideration. The heat convection as well as the heat diffusion is governed by the energy conservation law. Both strong and weak electrolytes (of any attainable valency) may be regarded as system constituents. Furthermore, the model can handle the ionic strength correction if desired. A task may be assigned either in Cartesian or cylindrical coordinates. The presented model was employed to solve four particular tasks. The first one inspects the...
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Preparation, characterization and study of electron transfer in self-organized structures on solid electrodes
Kolivoška, Viliam
Předkládaná dizertační práce se zaměřuje na elektrochemické, spektroelektrochemické, adsorpční, komplexační a vodivostní vlastnosti prodloužených viologenů různé délky (sloučeniny 1 až 6). Jejich molekuly by v budoucnosti mohli sloužit jako vodivé molekulární dráty v přístrojích molekulární elektroniky. Všechny studované sloučeniny vytvářejí na rozhraní rtuť/elektrolyt kompaktní monovrstvu paralelně ležících molekul s difúzně řízeným vznikem. Přítomnost adsorbovaných molekul na povrchu Au(111) byla potvrzena pomocí technik STM a PM IRRAS. Molekula prodlouženého viologenu obsahující jednu opakující se jednotku (sloučenina 1) reverzibilně přijímá čtyři elektrony, jako plně delokalizovaný systém. Molekula sloučeniny 2 však přijímá dva elektrony nezávisle a má proto dvě nekomunikující centra. Molekuly obsahující větší počet jednotek (n) přijímají v prvních dvěch redukčních krocích 2(n-1) elektronů (n-1 v každém). Chemická stabilita redukovaných forem sloučenin 1 až 6 byla potvrzena pomocí in-situ UV/VIS/NIR spektroelektrochemických technik. Vodivost elektrických spojů obsahujících molekuly prodloužených viologenů (měřena Taovou metodou) klesá exponencielně s délkou molekuly. V případě jiných typů prodloužených viologenů (sloučeniny 1' a 4') se zjistilo, že na jejich elektrochemické chování má výrazný...
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Charge Transport through Molecular Towers Based on Tetraphenyhmethane Tripods
Kolivoška, Viliam ; Šebera, Jakub ; Lindner, M. ; Valášek, M. ; Mayor, M. ; Mészáros, G. ; Gasior, Jindřich ; Hromadová, Magdaléna
Molecular platforms with multiple anchors were introduced recently to provide robusi coupling between molecular electronic components and metallic electrodes. In this work, charge transport in tower-shaped single molecule conductors based on tetraphenylmethane tripod possessing three thiol anchors is investigated by scanning tunneling microscopy break junction technique. The effect of tripod substitution pattern and number of repeating units in molecule is addressed. The substitution was found to influence conductance value in early stages of molecular junction evolution, where tower lays parallel to surface. In late stages, the charge is transported through principal molecular axis and junction breaks thermally in tilted configuration.
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Charge Transport in Single Oligophenylene Molecular Wires with Different Anchoring Groups
Hromadová, Magdaléna ; Kolivoška, Viliam ; Šebera, Jakub ; Sebechlebská, Táňa ; Gasior, Jindřich ; Nováková Lachmanová, Štěpánka ; Mészáros, G. ; Lindner, M. ; Mayor, M. ; Valášek, M.
This work compares single molecule conductance measurements of selected organic systems containing identical oligophenylene molecular wires and different tripodal anchoring groups. Single molecule conductance G was obtained by a scanning tunneling microscopy break junction technique complemented by theoretical calculations based on the density functional theory and non-equilibrium Green’s function formalism. Two molecules were compared where the same oligophenylene wire is connected to one of the electrodes via a tripod substituted on each leg by a thiol group either in the meta or para position. By combined experimental and theoretical analysis it was possible to confirm that single molecule conductance in the metal-molecule-metal junction of both molecules corresponds to a fully extended molecular wire, which is attached to one of the electrodes by all three thiolate bonds of the tripod. Experimental results confirmed that G value of meta-connected molecules is lower than that of para, whereas junction formation probability was higher for meta functionalization.
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Charge Transport in Single Oligophenylene Molecular Wires with Different Anchoring Groups
Hromadová, Magdaléna ; Kolivoška, Viliam ; Šebera, Jakub ; Sebechlebská, Táňa ; Gasior, Jindřich ; Nováková Lachmanová, Štěpánka ; Mészáros, G. ; Lindner, M. ; Mayor, M. ; Valášek, M.
This work compares single molecule conductance measurements of selected organic systems containing identical oligophenylene molecular wires and different tripodal anchoring groups. Single molecule conductance G was obtained by a scanning tunneling microscopy break junction technique complemented by theoretical calculations based on the density functional theory and non-equilibrium Green’s function formalism. Two molecules were compared where the same oligophenylene wire is connected to one of the electrodes via a tripod substituted on each leg by a thiol group either in the meta or para position. By combined experimental and theoretical analysis it was possible to confirm that single molecule conductance in the metal-molecule-metal junction of both molecules corresponds to a fully extended molecular wire, which is attached to one of the electrodes by all three thiolate bonds of the tripod. Experimental results confirmed that G value of meta-connected molecules is lower than that of para, whereas junction formation probability was higher for meta functionalization.
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Electrochemical Investigation of Polylactic Acid/Carbon Black Composite Filament for the Manufacture of 3D Printed Electrodes
Sebechlebská, Táňa ; Vaněčková, Eva ; Shestivska, Violetta ; Kolivoška, Viliam
Fused deposition modeling 3D printing has recently attracted increasing attention as an inexpensive, fast, reliable, adaptable and environmentally friendly tool to fabricate electrodes and electrochemical cells from composites of thermoplastics and carbon nanostructures. In this work, we use electric conductance measurements and cyclic voltammetry employing Ru(acac)30/1- as an electroactive probe to demonstrate that commercial polylactic acid(PLA)/carbon black composite filaments may be readily used as functional working electrodes in aqueous electrolytes. We further devise a procedure that leads to an improvement of their electrochemical performance. Characteristics of composite filaments treated by the optimized procedure approach those of classical metallic electrodes.
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Charge Transport in Single Oligophenylene Molecular Wires with Different Anchoring Groups
Hromadová, Magdaléna ; Kolivoška, Viliam ; Šebera, Jakub ; Sebechlebská, Táňa ; Gasior, Jindřich ; Nováková Lachmanová, Štěpánka ; Mészáros, G. ; Lindner, M. ; Mayor, M. ; Valášek, M.
This work compares single molecule conductance measurements of selected organic systems containing identical oligophenylene molecular wires and different tripodal anchoring groups. Single molecule conductance G was obtained by a scanning tunneling microscopy break junction technique complemented by theoretical calculations based on the density functional theory and non-equilibrium Green’s function formalism. Two molecules were compared where the same oligophenylene wire is connected to one of the electrodes via a tripod substituted on each leg by a thiol group either in the meta or para position. By combined experimental and theoretical analysis it was possible to confirm that single molecule conductance in the metal-molecule-metal junction of both molecules corresponds to a fully extended molecular wire, which is attached to one of the electrodes by all three thiolate bonds of the tripod. Experimental results confirmed that G value of meta-connected molecules is lower than that of para, whereas junction formation probability was higher for meta functionalization.
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Determination of Roughness Factor and Fractal Dimension of Zirconium in its Native and Surface Modified State using Atomic Force Microscopy. Effect of the Hydrogen Evolution Reaction on the Surface Structure
Novák, M. ; Kocábová, Jana ; Kolivoška, Viliam ; Pospíšil, Lubomír ; Macák, J. ; Cichoň, Stanislav ; Cháb, Vladimír ; Hromadová, Magdaléna
Atomic force microscopy (AFM) was used to characterize surface morphology of pristine zirconium, Si modified and FeSi modified zirconium electrodes prior and after hydrogen evolution at potentials negative of the open circuit potential value. Two main characteristic parameters were obtained from the ex situ AFM height images, namely, the roughness factor and fractal dimension of the studied surface. The effect of hydrogen evolution reaction on the electrode surface morphology was discussed. Fractal dimension values were used successfully to explain the non ideality of the interfacial capacitance.
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Investigation of Single Molecule Charge Transport Properties and Geometrical Arrangement in Terpyridine Architectures Supported by the Tetraphenylmethane Tripod
Kolivoška, Viliam ; Sebechlebská, Táňa ; Šebera, Jakub ; Gasior, Jindřich ; Lindner, M. ; Lukášek, J. ; Valášek, M. ; Mayor, M. ; Mészáros, G. ; Hromadová, Magdaléna
Tripodal platforms were engineered recently to realize a well-defined directional contact between metallic electrodes and molecular architectures dedicated to serve as working elements for electronic applications. In this work we employ cyclic voltammetry, scanning tunneling microscopy break junction technique and theoretical approaches based on the combination of density functional theory and non-equilibrium Green´s function to investigate the geometrical arrangement and single molecule charge transport in terpyridine-based architectures supported by tetraphenylmethane tripod. We demonstrate that this architecture adopts a favorable geometrical arrangement capable of forming highly conductive molecular junctions and is thus suitable to serve as a basis for working molecular switches.
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