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Atomic structure of FeRh(001) surface
Ondračka, Václav ; Bábor, Petr (referee) ; Čechal, Jan (advisor)
Alloy of iron-rhodium, Fe50Rh50, shows a low-temperature metamagnetic phase transition between its antiferromagnetic and ferromagnetic state. A detailed description of this transition using the tools of surface analysis has not yet been done. This bachelor’s thesis focuses on preparation and characterisation of the alloy’s clean surface using X-ray photoemission spectroscopy and low-energy electron diffraction. A flat field correction and a diffraction measurement callibration is done using a sample with known crystal lattice in order to quantify the diffraction results.
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Organic materials for molecular quantum bits: deposition and chemical and morphological analysis
Komora, Mojmír ; Mach, Jindřich (referee) ; Čechal, Jan (advisor)
This bachelor thesis deals with an experimental preparation and analysis of ultra thin films of iron phtalocyanines on silicon substrates with goal to describe parameters of films prepared under different conditions, e.g deposition time or substrate temperature. Preparation of samples was done using MBE method under conditions of ultrahigh vacuum in vacuum chamber. Analysis of chemical composition and morfology of prepared films was done with methods of X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and Atomic Force Microscopy, respectively.
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Fabrication of Nanowires into Porous Alumina by Electrolysis
Staňo, Michal ; Čechal, Jan (referee) ; Škoda, David (advisor)
This thesis deals with preparation of metal nanowires based on electrodeposition from aqua solution of metallic salts into porous dielectric aluminium oxide templates. The theoretical part covers various bottom-up methods of nanowire preparation using a template, electrochemistry and electrodeposition overview. The Experimental part is focused on the nanowire (Ag, Cu, Ni-H) preparation by means of direct current and alternating current electrodepositon and geometrical characterization of fabricated nanowires by scanning electron and atomic force microscopy. Defects of commercially available and prepared porous alumina templates are mentioned. Branching and coalescence of nanowires are briefly discussed as well.
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Growth of 3D Structures Induced by Electron Beam on Ceramic Substrates
Bukvišová, Kristýna ; Čechal, Jan (referee) ; Salamon, David (advisor)
Vystaví-li se vzorek působení elektronového svazku, dojde na jeho povrchu ke strukturním změnám. Jednou z těchto změn je vertikální růst 3D struktur na keramických materiálech. V práci jsou zkoumány podmínky nutné pro takový proces. Nárůst teploty často zapříčiní povrchové změny, proto je v práci proveden výpočet ohřevu materiálu elektronovým svazkem. Dále je zkoumán vliv různých parametrů svazku na růst 3D struktur, závislost objemu a rozměrů je analyzována pomocí AFM. Výsledný odhad nárůstu teploty se pohybuje v řádech jednotek, maximálně desítek K. Výrazný objemový růst je pozorován pro nízká urychlovací napětí a malé proudy. Výška vzniklých struktur dosahuje 100 nm za minutu a je nepřímo úměrná velikosti proudu.
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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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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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