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Microscopic and spectroscopic analysis of elementary 2D materials
Jeřábek, František ; Procházka, Pavel (referee) ; Kolíbal, Miroslav (advisor)
Tato práce se zabývá analýzou struktur tvořených při depozici fosforu na monokrystal mědi Cu(111) za podmínek ultravysokého vakua. Součástí práce je komplexní shrnutí aktuálního pokroku v oblasti syntézy černého a modrého fosforenu. Kromě samotných metod přípravy je diskutována také předpovězená stabilita těchto struktur. V práci jsou prezentovány výsledky analýzy tří struktur pomocí skenovací tunelové mikroskopie a spektroskopie, prokazující možnost přípravy jednovrstvého modrého fosforenu na měděném substrátu. In-situ analýza stability připravených struktur pomocí skenovací tunelovací mikroskopie prokazuje velmi rychlou degradaci modrého fosforenu i za podmínek ultravysokého vakua.
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Deposition of Molecular Magnets on „2D“ Materials
Vavrečková, Šárka ; Musálek, Tomáš (referee) ; Hrubý, Jakub (advisor)
This thesis deals with deposition of single-molecule magnets on 2D materials and studies their behavior on surfaces. Theoretical part contains information about properties of single-molecule magnets, deposition methods and also information about chosen 2D materials – graphene and molybdenum disulfide. Further, the physical principles of the selected characterization methods (atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and electron paramagnetic resonance) are described. In the experimental part graphene and molybdenum disulfide were exfoliated. Afterwards, depositions of single-molecule magnets from solution and by thermal sublimation were made. After that, samples were analyzed using the mentioned methods and results were discussed.
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Preparation of elemental 2D materials
David, Jiří ; Čechal, Jan (referee) ; Kolíbal, Miroslav (advisor)
This thesis is focused on searching suitable experimental conditions for epitaxial growth of silicene, multilayer silicene and phosphorene, and their analysis by LEED and LEEM. Composition was analyzed by XPS. In the first part, a summary of literature research on properties and structure of these materials is presented. The second part describes experiments attemping to prepare these materials. Silicene was the only successfully-prepared material. It was imposible to reach suitable experimental conditions for multilayer silicene growth in the available experimetal setup. Deposition of phosphorus led only to formation of phosphorene precursor.
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Luminescence of semiconductors studied by scanning near-field optical microscopy
Těšík, Jan ; Klapetek, Petr (referee) ; Křápek, Vlastimil (advisor)
This work is focused on the study of luminescence of atomic thin layers of transition metal chalkogenides (eg. MoS2). In the experimental part, the work deals with the preparation of atomic thin layers of semiconducting chalcogenides and the subsequent manufacturing of plasmonic interference structures around these layers. The illumination of the interference structure will create a standing plasmonic wave that will excite the photoluminescence of the semiconductor. Photoluminescence was studied both by far-field spectroscopy and near-field optical microscopy.
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Gas sensors based on 1D and 2D materials
Brodský, Jan ; Glowacki, Eric Daniel (referee) ; Gablech, Imrich (advisor)
In this work, general properties of fundamental gas sensors are described. Thesis is mainly focused on chemoresistive and ChemFET types, which are further used in experimental part. Subsequently, properties, preparation and transfer methods of chosen 1D and 2D materials are described. Experimental part of this work describes design and fabrication of chips, which combine the sensing principals mentioned above for utilization of 1D and 2D materials as an active layer. Transfer methods of individual materials on fabricated chips are described and these materials are characterized by Raman spectroscopy and field effect transistor characteristics measurements. Finally, the response of chosen materials to oxidative and reductive gases is measured.
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Fabrication and characterization of atomically thin layers
Tesař, Jan ; Kunc, Jan (referee) ; Procházka, Pavel (advisor)
Tato práce se zabývá oblastí dvourozměrných materiálů, jejich přípravou a analýzou. Pravděpodobně nejznámějším zástupcem dvourozměrných materiálů je grafen. Tento 2D allotrop uhlíku, někdy nazývaný „otec 2D materiálů“, v sobě spojuje neobyčejnou kombinaci elektrických, tepelných a mechanických vlastností. Grafen získal mnoho pozornosti a byl také připraven mnoha metodami. Jedna z těchto metod však stále vyniká nad ostatními kvalitou produkovaného grafenu. Mechanická exfoliace je ve srovnání s jinými technikami velmi jednoduchá, takto připravený grafen je však nejkvalitnější. Práce je také zaměřena na optimalizaci procesu tvorby heterostruktur složených z vrstev grafenu a hBN. Dle prezentovaného postupu bylo připraveno několik van der Waalsových heterostruktur, které byly analyzovány Ramanovskou spektroskopií, mikroskopií atomových sil a nízkoenergiovou elektronovou mikroskopií. Měření pohyblivosti nosičů náboje bylo provedeno v GFET uspořádání. Získané hodnoty pohyblivosti prokázaly vynikající transportní vlastnosti exfoliovaného grafenu v porovnání s grafenem připraveným jinými metodami. V práci popsaný proces přípravy je tedy vhodný pro výrobu kvalitních heterostruktur.
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Preparation of elementary 2D materials and heterostructures
David, Jiří ; Redondo,, Jesús Rubén López-Roso (referee) ; Kolíbal, Miroslav (advisor)
This thesis is focused on the preparation of blue phosphorene on Ag(111) and Cu(111) substrates and on the preparation of heterostructure graphene/blue phosphorene on Cu(111) substrate. The structural properties of these materials were analyzed by LEED, LEEM, and STM. Chemical composition was measured by XPS. The first chapter describes the properties of blue phosphorene, the influence of the substrates on its growth, the current experimental state, and the advantages of heterostructures from 2D materials. The second chapter is focused on the optimization of blue phosphorene’s growth conditions. Next, a successful preparation of blue phosphorene on Cu(111) substrate is demonstrated. Additionally, a new growth mechanism of 2D materials is described. In the end, an attempt to prepare a heterostructure of blue phosphorene and graphene was made. The results show a possible feasibility of demonstrated approach.
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Microscopic and spectroscopic analysis of elementary 2D materials
Jeřábek, František ; Procházka, Pavel (referee) ; Kolíbal, Miroslav (advisor)
Tato práce se zabývá analýzou struktur tvořených při depozici fosforu na monokrystal mědi Cu(111) za podmínek ultravysokého vakua. Součástí práce je komplexní shrnutí aktuálního pokroku v oblasti syntézy černého a modrého fosforenu. Kromě samotných metod přípravy je diskutována také předpovězená stabilita těchto struktur. V práci jsou prezentovány výsledky analýzy tří struktur pomocí skenovací tunelové mikroskopie a spektroskopie, prokazující možnost přípravy jednovrstvého modrého fosforenu na měděném substrátu. In-situ analýza stability připravených struktur pomocí skenovací tunelovací mikroskopie prokazuje velmi rychlou degradaci modrého fosforenu i za podmínek ultravysokého vakua.
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Dynamic Processes in Porous Nanomaterials: Adsorption and Diffusion
Trachta, Michal ; Bludský, Ota (advisor) ; Heard, Christopher James (referee) ; Čičmanec, Pavel (referee)
Dynamical processes in porous nanomaterials (adsorption, diffusion, separation) play a significant role in many industrial applications. Modeling of these applications theoretically provides atomistic details of adsorption and diffusion phenomena - information that is often difficult to obtain using contemporary experimental methods. Theory may thus provide a deeper insight into these processes, e.g., explaining the mechanisms and assisting in the search for new materials suited for a specific application through material screening. In this work, the dynamical processes in porous materials were investigated by means of force field and ab initio modeling. On a set of relevant simulation data, two particular problems related to the modeling of such processes are thoroughly addressed: (i) the sensitivity of the results to material geometry, and (ii) the accuracy of the potential energy surface description. Regarding the structure description, the reliability of theoretically-predicted structures is still limited, despite the significant increase in computational power and algorithm development. The drawbacks of individual methods are identified; even state-of-the-art density functional theory approaches suffer from inaccuracies, e.g., due to an imbalance between the semi-local (GGA) functional and...
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Plasmon-mediated electrocatalytic activity of TiB2 towards water splitting
Buravets, V. ; Zabelina, A. ; Miliutina, E. ; Popelková, Daniela ; Henych, J. ; Šťastný, Martin ; Švorčík, V. ; Lyutakov, O.
Environmental problems related to the economy based on fossil fuels are of paramount importance. However, transition to renewable energy sources is restrained by the availability of storage technologies. Electrochemistry is a widely recognized prominent tool to achieve this goal by converting renewable energy into the form of chemical bonds accessible further as fuels, such as hydrogen produced by water splitting. Crucial losses in such process are caused by the high overpotentials, required for water splitting as a hydrogen source. To achieve required efficiency of water splitting appropriate catalysts have to be found with the suitable combination of activity, stability and cost. Nano-structured, two-dimensional materials (2D) are attractive candidates due possessing many of the desired properties and highly tunable characteristics. Employing light allows additional degree of freedom to boost conventional photo-electrocatalysis, in particular plasmonmediated electrocatalysis. Enhancement of the catalytic activity can be increased even further if the catalytic system absorbs wide range of light spectrum. In this study, we combine plasmon-active Au grating with 2D flakes of TiB2, to perform plasmon-mediated water splitting half-reaction – hydrogen evolution.
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