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Organic materials for molecular quantum bits
Tuček, Marek ; Bábor, Petr (referee) ; Čechal, Jan (advisor)
In this thesis we briefly outline the properties and utilization of metal phthalocyanines, the procedure of iron phthalocyanine thin film deposition on Si(100), the supplementary post-deposition analysis by XPS and the equipment used to measure X-ray reflectivity. Further we describe the theoretical description of physical background of X-ray diffraction on a crystal, the measurement of X-ray reflectivity and evaluation of acquired data, focusing on determination of the thin film thickness, identification of its crystal structure and lattice parameters. It has been found out that iron phthalocyanine thin films deposited on a substrate at room temperature grow as an alpha-phase in the shape of needles perpendicular to substrate surface, so the film thickness, due to high rougness of the film, can be only estimated with the help of Scherrer equation for long depositions. In the case of shorter depositions (and thus lower roughness) the Kiessig fringes method can be used. By the post-deposition annealing we were not able to induce a phase transition; at required temperatures all the material on the substrate evaporated. By a deposition on a substrate heated to 160°C we acquired considerably rough film with unclear crystalline phase.
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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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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.
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Calibration and interpretation of images measured by LEEM
Endstrasser, Zdeněk ; Novák, Jiří (referee) ; Čechal, Jan (advisor)
This thesis deals with the software development to calibration and interpretation of image data measured by a LEEM device. As the imaging technique is uniquely suited for in-situ studies of surface dynamical processes, the attention is mainly paid to methods enabling the evaluation of measurement time series. The phase correlation method based on Fourier transform of images is proposed to temperature shift correction between consecutive frames. The thesis describes the methods of additive and impulse noise filtering, image visualization, the filtration of secondary electrons and the determination of I-V curves from measured image data. Implemented methods are described not only in terms of their mathematical origin, but also with emphasis on the revealing of critical aspects associated with their use. The thesis also focuses on the application of the created algorithm to image data capturing the spatial and temporal evolution of 4,4’-biphenyl-dicarboxylic acid surface phases induced by sample annealing. Based on these evaluations, a suitable procedure is then determined to perform accurate detection and compensation of temperature shift said.
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Optical response of asymmetric plasmonic structures
Babocký, Jiří ; Kolařík, Vladimír (referee) ; Čechal, Jan (advisor)
This diploma thesis deals with study of resonance modes of plasmonic structures. First part provides an overview of theoretical models, which explain the resonanace modes in plasmonic structures. Next part describes technology of electron beam lithography. First section of experimental part deas with technological processes leading to an improvement of resulting structures made by electron beam lithography that is followed by lift-off process. Last part focuses on a study of reflectance spactra of plasmonic antenas and the identification of resonance modes.
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Ostwald ripening – theoretical description and simulation.
Čechal, Tomáš ; Šikola, Tomáš (referee) ; Čechal, Jan (advisor)
Tato práce se zabývá popisem Ostwaldova zrání trojrozměrných ostrůvků deponovaných na rovinných površích. V první kapitole jsou představeny dvě teorie Ostwaldova zrání: LSW teorie založená na aproximaci středního pole a mnohačásticová teorie vycházející z řešení difuzní rovnice v kvazistatické aproximaci. Ve druhé kapitole je popsán algoritmus numerického řešení rovnic získaných z mnohačásticové teorie. Výsledky numerického řešení jsou ve třetí kapitole srovnány s předpověďmi LSW modelu. Bylo zjištěno, že předpovědi standardní LSW teorie popisující systémy s dvourozměrným transportem hmoty jsou v ostrém protikladu jak s výsledky získanými z dokonalejšího mnohačásticového modelu, tak s experimenty popsanými v uvedených pramenech. Mnohačásticový model založený na difuzní rovnici poskytuje výsledky konzistentní s jinými teoriemi i experimentem.
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Graphene doping by low-energy electrons
Stará, Veronika ; Kunc, Jan (referee) ; Čechal, Jan (advisor)
Tato diplomová práce se zabývá dotováním grafenu nízkoenergiovými elektrony. Na křemíkový substrát pokrytý vrstvou SiO2 jsou pomocí litograficky vyrobené masky nadeponované kovové kontakty z titanu a zlata. Grafen vyrobený pomocí metody depozice z plynné fáze je přenesen na substrát a slouží jako vodivé spojení kovových elektrod, které vytvářejí kolektor a emitor. Na křemík je ze spodu přivedeno napětí, které tak vytváří spodní hradlo. Takto vytvořený grafenový tranzistor je ozařován nízkoenergiovými elektrony, které mění dotování grafenu. Z polohy maxima v závislosti odporu grafenu na hradlovém napětí lze vyčíst typ dotování. Toto maximum udává napětí, při kterém Fermiho meze grafenu prochází Diracovým bodem v pásové struktuře grafenu. Velikost hradlového napětí, primární energie elektronového svazku a proud svazku jsou tři parametry, které mají velký vliv na změny dotování. Při ozařování transistoru dochází ke změně typu dotování právě tehdy, když odpor grafenu v závislosti na hradlovém napětí dosáhne maxima. Vývoj této změny je zkoumán pro různé energie a proudy primárního svazku v závislosti na hradlovém napětí i v čase. Typ dotování je také prozkoumán při zastavení ozařování v různých fázích smyčky hradlového napětí. Dopování grafenu nízkoenergiovými elektrony je popsáno v teoretickém modelu.
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Fabrication and Characterization of Templates for Fabrication of Nanowires
Lednický, Tomáš ; Čechal, Jan (referee) ; Škoda, David (advisor)
The bachelor thesis is focused on fabrication of alumina templates by anodization of pure aluminium. The theoretical part discusses the growing process of anodized oxide layers and its dependency on the crucial parameters (solutions, anodization voltage, time). The theoretical part is particularly based on literature retrieval. The experimental part is aimed to the fabrication of alumina membranes: the apparatus design, aluminium foils preparation, aluminium anodization, membrane modifications for next applications (nanowires deposition) and membrane characterization.
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Deposition of large organic molecules under UHV
Krajňák, Tomáš ; Novák,, Jiří (referee) ; Čechal, Jan (advisor)
In this thesis, large organic molecules (DM15N, DM18N, Cu(dbm)2) were deposited. These molecules are cannot be deposited by thermal sublimation due the fact that they decompose at lower temperature than they sublime. The employed molecules to single molecular magnets, which can be potentially used as quantum bites (qubit). The new method of deposition atomic layer injection made by Bihur Crystal company was introduced and tested. The method uses liquid solution with molecules which is driven by argon gas through pulse valve to the sample placed in ultra-high vacuum chamber. During the deposition, droplets of solution are formed on the sample surface. The solvent can be removed by light annealing or by keeping the sample in the vacuum for couple of days. The molecules were investigated by x-ray photoelectron spectroscopy and by scanning electron microscopy to determine fragmentation of the molecules, to study topography of the resultant surface and homogeneity of the deposited layer. We found conditions at which the intact molecules are deposited on the sample surfaces and form molecular nano- and micro- crystals.
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Preparation of graphene samples for experiments under UHV conditions
Mareček, David ; Mach, Jindřich (referee) ; Čechal, Jan (advisor)
This bachelor thesis deals with electrical conductivity of a graphene sample and preparation of a graphene field-effect transistor. In the theoretical part of the thesis, we describe electronic properties of graphene, preparation of graphene by CVD and its transfer to SiO_2. Experimental part of this thesis is focused on the preparation of a graphene field-effect transistor with long distance between Source and Drain electrodes. Thesis deals with a design of a chip expander for contact of graphene in UHV conditions. The last part describes measurement of dependency of graphene layer conductivity on the gate voltage with emphasis on the position of Dirac point during adjustments of the sample in UHV conditions.
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