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Self-assembled molecular layers on epitaxial graphene
Kovařík, Štěpán ; Švec, Martin (referee) ; Čechal, Jan (advisor)
Samouspořádání organických molekul je spontánní proces tvorby nanostruktur, při kterém je výsledná struktura určena mezimolekulárními and molekulárně-substrátovými interakcemi. Pochopení principů samouspořádávání je klíčem k přípravě funkčních nanostruktur s atomární přesností. Tato diplomová práce se zaměřuje na přípravu a studium samouspořádaných molekulárních struktur 4,4’-diphenyl dikarboxylové kyseliny na povrchu grafenu připraveného na Ir(111). Pro studium vlastností molekulárních struktur je využito rastrovací tunelovací mikroskopie a nízkoenergiové elektronové mikroskopie. Tato kombinace umožňuje získat informace z oblastí o velikosti v řádu nanometrů až milimetrů. V práci je popsána molekulární strukuktura stabilní při pokojové teplotě. Vazebný motiv této struktury je dán interakcí karboxylových skupin sousedních molekul.
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Hydrogen quantification by electron spectroscopy
Endstrasser, Zdeněk ; Polčák, Josef (referee) ; Čechal, Jan (advisor)
The absence of hydrogen in the photoelectron spectrum remains one of the greatest limitations of X-ray photoelectron spectroscopy. The main aim of this work is therefore to determine the concentration of hydrogen atoms in the near surface region of a sample. The REELS electron spectroscopic method based on quasi-elastic electron scattering is used for this purpose. The choice of this method was given mainly by the fact that the photoelectron spectrometers has an electron source in the basic equipment, so there is no requirement to purchase additional equipment. In our case, measurements were realized using the AXIS Supra photoelectron spectrometer in CEITEC laboratories. We were primarily focused on the study of polymer samples in this work. The gus cluster ion source was used for sputter cleaning of the sample surface. Then the XPS and REELS measurements were performed on such cleaned samples. The obtained data were subsequently evaluated, and the results discussed. The most important output of this work was to develop the methodology of detection and quantification of hydrogen atoms. However, the theoretical description of the methods used, and the appreciation of critical aspects associated with the use of the REELS method are also embraced. In particular, the effect of sample charging and electron dose on measurement results is discussed.
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2D molecular systems at surfaces
Kormoš, Lukáš ; Mysliveček,, Josef (referee) ; Schlickum, Uta (referee) ; Čechal, Jan (advisor)
Molekulárne systémy predstavujú jeden zo smerov súčasného výskumu nových nanoelektronických zariadení. Organické molekuly nachádzajú uplatnenie v rôznych aplikáciách, ako sú napríklad solárne články, displeje alebo kvantové počítače. Rast vysokokvalitných molekulárnych vrstiev s požadovanými vlastnosťami často vyžaduje využitie samousporiadavaných štruktúr, hlboké pochopenie rozhrania kovu a organických molekúl a tiež dynamiky rastu molekulárnych vrstiev. Predkladaná práca sa zaoberá predovšetkým samousporadanými štruktúrami bifenyl-dikarboxylovej kyseliny (BDA) na Cu (1 0 0) a Ag (1 0 0), ktoré boli skúmané v UHV s využitím STM, XPS a LEEM. V prípade BDA-Ag je podrobne opísaných niekoľko chemicky a štrukturálne odlišných molekulárnych fáz. Ďalej boli BDA a TCNQ molekuly skúmané na grafene pripravenom na Ir (1 1 1). Okrem toho sa organo-kovové systémy syntetizovali depozíciou atómov Ni a Fe s molekulami TCNQ a BDA. Záverečná časť tejto práce popisuje povrchovú syntézu grafénových nanoribonov (7-AGNR) na špecicky štrukturovanom substráte Au (16 14 15) z prekurzorových molekúl DBBA. Rekonštrukcia povrchu po raste bola analyzovaná pomocou STM a elektronické vlastnosti 7-AGNRs pomocou ARPES.
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Germanium island morphology in the presence of Gallium and Gold
Pejchal, Tomáš ; Čechal, Jan (referee) ; Kolíbal, Miroslav (advisor)
This bachelor's thesis deals with germanium island morphology in the presence of gold, silver and gallium. The islands were grown on Ge(111) surface by means of evaporation under the UHV conditions. In the paper a background research on the surface reconstructions of the metals on Ge(111) is presented. It is demonstrated that the island concentration, size and shape are affected by the presence of metals and the deposition temperature. The surface structure and the morphology of the samples were investigated by RHEED and SEM.
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Analysis of locally modified surfaces for selective growth of cobalt
Krajňák, Tomáš ; Bábor, Petr (referee) ; Čechal, Jan (advisor)
In this thesis the chemical composition of silicon substrates locally modified by focused gallium ion beam by X-ray photoelectron spectroscopy is determined. In order to determine the influence of focused ion beam, the sample comprising sputtered square areas with nominal depths in range of 1 to 10 nm was prepared. Next, the sample was heated to elevated temperatures (500 - 700 °C) to reveal changes in the sputtered areas induced by annealing. In this work by X-ray photoelectron spectrometer Kratos Supra and electron microscope Tescan LYRA3 with focused ion beam were used. From the measured spectra of the Si 2p and Ga 2p3/2 peaks measured as a function of nominal sputtering depth and annealing temperature the following main observations were obtained. First, there is the additional peak component in the Si 2p peak, which can be assigned to the amorphous silicon. The second important finding is that gallium can be removed from near surface volume by annealing at temperatures beyond 700 °C.
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Interaction of low-energy electrons with graphene field effect transistors
Vysocký, Filip ; Kunc, Jan (referee) ; Čechal, Jan (advisor)
This diploma thesis is focused on fabrication of graphene field-effect transistors, characterisation of their transport properties and investigation of low-energy electron beam influence on the devices' properties under UHV conditions. The theoretical part of this work describes graphene fabrication methods, options of graphene transfer onto the substrates for graphene field-effect transistor manufacture. Furthermore, model of graphene doping via electrostatic interaction or photon, resp. electron beam exposition is explained. The experimental part of this work consist of manufacture of the graphene field-effect transistor in order to examine the change of its transport properties induced by doping of the graphene via low-energy electron beam exposition.
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Epitaxial growth of cobalt islands via oxide mediated epitaxy
Stará, Veronika ; Kolíbal, Miroslav (referee) ; Čechal, Jan (advisor)
This bachelor thesis deals with preparation, growth and analysis of cobalt thin films. The films are formed on silicon (111) samples covered with a thin layer of native oxide SiO2. Cobalt thin films were prepared using oxide mediated epitaxy method with the effusion cell as a source of cobalt atoms. Composition and morphology of the resulting Co system was studied as a function of the annealing temperature. Another goal of this research was to determine the dependence of the final island shape on the amount of deposited material and substrate orientation. The prepared structures were analyzed using X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. To determine the thickness of subsurface islands the samples were etched in buffered hydrofluoric acid and analyzed using above mentioned methods.
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An influence of electron beam on thin oxide films
Kostyal, Michal ; Průša, Stanislav (referee) ; Čechal, Jan (advisor)
This bachelor work deals with a study of the influence of electron beam of scanning electron microscope on the surface of the SiO2/Si (100) – sample. In the work the electron and atomic force microscopy briefly described. The main objective of experimental part is to describe variation in the brightness of sample SiO2/Si (100) in Scanning electron microscope images. In this study is found that on the sample surface are created objects few nm high. The rest of the work is then devoted to measuring the dependence of the object’s high on different variables. Experiments are generally based on the selective irradiation of the sample surface by scanning electron microscope, measurement of irradiated parts using atomic force microscope and evaluation in the application Gwyddion.
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Single Atomic Catalysts
Závodný, Adam ; Švec,, Martin (referee) ; Čechal, Jan (advisor)
Single atom catalysts are prospective class of materials, which holds promises to reach the ultimate limit of improvement in catalyst performance, selectivity, lifetime and cost reduction. The ability to efficiently capture the adsorbates at the active sites is the key prerequisite for catalytic transformation to the products. In this respect, our experimental study aims to describe the interaction of gas molecules (H2O, CO, O2 and NO) with single metal atoms (Rh, Ir, Cu) on the magnetite surface employing scanning tunneling microscopy.
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Non-thermal dehydrogenation of carboxylic acids on metal surfaces
Kugler, David ; Kolíbal, Miroslav (referee) ; Čechal, Jan (advisor)
Molecular self-assembly is the process of spontaneous arrangement basic adsorbate units into complex structures. Self-assembly systems could be used for atomically precise fabrication of functional nanostructures in the future. One of the possibilities to fabricate self-assembled molecular networks is to deposit the simple carboxylic acid molecules onto a clean metal substrate. The aim of this work is to describe the kinetics of the deprotonation process of 4,4´-biphenyldicarboxylic acid on Ag(100) due to CO exposure. A low-energy electron microscope was used to monitor phase transitions induced by changes in binding properties of molecules. The result of the work is a comprehensive view on the deprotonation process induced by exposure to CO. We found out that the deprotonation reaction depends on the shape and size of molecular islands, and we described the kinetics of individual phase transitions for different molecular coverages. We have also described the correlation between CO pressure and the rate of deprotonation.
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