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Application of Kelvin Probe Force Microscopy on Two-Dimensional Structures
Švarc, Vojtěch ; Kunc,, Jan (referee) ; Kolařík, Vladimír (referee) ; Bartošík, Miroslav (advisor)
The presence of water molecules strongly influences the function of solution-based biosensors and ambient operating gas sensors. Water molecules accelerate the charge diffusion on the surface of insulating parts, induce sensor hysteresis, and affect sensors' stability, resistance response, and sensitivity. Therefore, it is essential to understand the behaviour of charge motion influenced by water on the sensor surface. To better understand sensor behaviour and its immediate surroundings under controlled humidity, this study utilizes measurements of transport properties and simultaneous measurement of macroscopic resistance response with mapping of the local surface potential using Kelvin probe force microscopy (KPFM). As a chosen model, the 2D graphene Hall bar structure in the field-effect transistor (FET) architecture was fabricated and optimized. The results indicate that the charge dissipation from the main graphene channel to its insulating surroundings exponentially increases with relative humidity. The amount of this leakage charge can be further tuned by the gate voltage of the FET sensor. Further findings show that the charge diffusing into adjacent SiO2 parts minimally influences the conductivity of the graphene main channel. Simultaneous measurements of resistivity and KPFM on graphene-based sensors deepen the understanding of water's impact on the sensor's active parts and the diffusion of charge on passive insulating parts. These findings could benefit future designs of active graphene parts of the sensor and surface modifications of its insulating parts.
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Adaptive scanning based on lower resolution images
Dymáček, Michal ; Klapetek, Petr (referee) ; Pavera, Michal (advisor)
Tato diplomová práce se zabývá vývojem metody adaptivního skenování založené na obrázcích s nižším rozlišením, která má za cíl zkrátit dobu měření a otevřít tak nové možnosti metod SPM, konkrétně mikroskopie atomárních sil (AFM), pro aplikace např. v biologii a polovodičovém průmyslu. V prvním kroku navrhovaného přístupu je pořízen obrázek s nižším rozlišením, který je uměle zvětšen s využitím interpolace a dále zpracován pro tvorbu rychlostní mapy, která určuje rychlost skenování pro jednotlivé řádky druhého měření. Řádky protínající vyvýšené struktury jsou skenovány pomalu, čímž je zachována nutná přesnost, ale celková doba měření je snížena, jelikož jsou řádky obsahující pouze povrch substrátu skenovány zvýšenou rychlostí. Na základě rešeršní studie a provedených experimentů byl navržen přístup adaptivního skenování využívající skriptovací modul SPM mikroskopu LiteScope založený na programovacím jazyce Python. S využitím tohoto přístupu bylo dosaženo redukce doby měření o 30 % pro kalibrační mřížku TGQ1.
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The utilization of atomic force miscroscopy to study of selected bacterial strain
Nováková, Simona ; Slaninová, Eva (referee) ; Smilek, Jiří (advisor)
The subject of the bachelor’s thesis was the study of selected bacterial strains by a selected method of atomic force microscopy. Thermophilic purple bacteria – Rhodoblastus acidophilus, Rhodobaca barguzinensis – were investigated. The main aim of this theses was focused on optimizing the usage of this microscopic method for imaging in an aqueous environment with the most appropriate fixation of sample. Focusing on bacterial strains demanded to preserve the viability of microorganisms and to observe optimal conditions for maintaining the native state during the measurement process. Furthermore, mechanical properties were evaluated – Young’s modulus and adhesion. The morphology of individual samples was compared for samples of the same species in different pH liquid environments and in environments with different concentrations of dissolved NaCl salt. The ability to produce PHA granules in purple bacteria was also targeted, however, due to the absence of first-class PHA synthase, PHA was not detected. The effects of different cultivation parameters such as different cultivation time or different pH of the environment were compared. Imaging of bacteria was carried out using the SNL-10 tip, which is suitable for bacterial samples in a liquid environment, and the measurement itself was carried out in QITM mode. A glass substance covered with a layer of Poly-L-lysin was used for immobilization. Finally, the mechanical properties were evaluated through Young’s modulus and adhesion for samples with various environmental factors.
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Dynamic in-situ experiments utilizing probe microscopy
Patočka, Marek ; Frank, Otakar (referee) ; Kolíbal, Miroslav (advisor)
V této práci je uvedeno několik případových studií dynamických in-situ experimentů s využitím skenovací sondové mikroskopie. Nejprve je zkoumána elektrodepozice lithia v baterii s pevným elektrolytem bez kladné elektrody. Na tento experiment navazuje obdobné měření, při kterém jsou jako materiál kladné elektrody použity částice MXene. Druhá část práce se zabývá grafenem plovoucím na kapalném kovu. Je zde prezentováno zkoumání přítomnosti menisku okolo grafenových vloček.
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Characterization of surface and mechanical properties of microbial cells
Khýrová, Markéta ; Lukeš,, Jaroslav (referee) ; Plichta, Tomáš (advisor)
The subject of this diploma thesis is the characterization of bacterial strains capable of polyhydroxyalkanoates (PHA) production in terms of morphology and mechanical properties. With this aim, an atomic force microscope (AFM) was used together with a nanoindentation instrument to perform microcompression tests on selected microorganisms. The model bacterial strains, Cupriavidus necator and Rhodospirillum rubrum, were tested in their PHA-producing form and in their mutant non-producing variant, in order to study the effect of PHA amount on bacterial morphology and mechanical properties. In the experimental part of this work, the preparation of native bacterial samples for both techniques were first optimised. Glass substrates were treated with plasma and the cells were subsequently fixed with poly-L-lysine. In addition, sample preparation including fluorescent staining was optimized for the microcompression tests in order to easily detect cells and determine their size. Finally, the impact of different measurement parameters and mathematical models for calculating Young's modulus on the AFM data were evaluated. The results revealed the effect of PHA on bacterial cell morphology and showed that PHA producers exhibit higher Young´s modulus on average compared to their mutant. It was also shown experimentally that microcompression tests provide significantly higher Young's modulus values than those obtained by AFM.
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Controlled modification of tips usable for selected measurement modes of atomic force microscopy
Lišková, Kateřina ; Szabová, Jana (referee) ; Smilek, Jiří (advisor)
This master's thesis deals with the modification of tips commonly used in atomic force microscopy and their following utilization for determining the mechanical properties of selected hydrogel systems at the local level. For targeted modification, a method of micro-particle fixation on a cantilever was chosen, which was successfully modified using melamine resin particles. Initially, the mechanical properties of a selected representative of physically cross-linked hydrogels (agarose polysaccharide) were measured, which were evaluated based on the Young's modulus of elasticity, adhesive force, and work. The obtained results were compared with values measured using two commercially available cantilevers differing in both shape and basic parameters such as spring constant and resonance frequency. Subsequently, the influence of the setpoint force applied to the sample by the cantilever was verified. The usability of modified cantilevers was also tested on a selected representative of ionically cross-linked hydrogels (sodium alginate cross-linked with multivalent ions). Within the experimental part of the master's thesis, it was verified that the use of cantilevers with a higher contact area leads to more reliable results in terms of reliability and reproducibility, considering that the final value of the Young's modulus includes not only the contribution of the polymer chain but also the pores. When determining mechanical values, it is important to specify not only the cantilever used and its properties but also all other experimental parameters, the change of which may affect the final values of the Young's modulus determined at the micro level by atomic force microscopy.
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Preparation and characterization of nanostructured III-V semiconductor materials
Maniš, Jaroslav ; Kostelník,, Petr (referee) ; Hospodková,, Alice (referee) ; Šikola, Tomáš (advisor)
Předkládaná dizertační práce se zabývá výrobou a analýzou gallium nitridových (GaN) nanostruktur ve třech odlišných formách. V prvním případě byl zkoumám trojdimenzionální GaN ve formě nanokrystalů rostených na grafenu. Nanokrystaly byly připraveny s využitím techniky droplet epitaxy, která mimo jiné umožňuje růst nanostruktur za nízké teploty substrátu (T = 200°C). Studium se zaměřovalo jak na charakterizaci kvality připravených nanokrystalů, tak na statistický popis růstu. V dalším kroku byly připravené struktury využity pro výrobu fotodektoru citlivého na ultrafialové světlo. Výroba fotodektoru a jeho úspěšné použití slouží jako základ pro navazující výzkum. Ve druhém případě byly studovány dvoudimenzionální GaN nanostruktury, které byly rovněž připraveny za nízké teploty křemíkového substrátu. Následná analýza se soustředila na popis krystalové struktury a prvkovou analýzu, neboť byly takovéto struktury pozorovány vůbec poprvé. Další rozvoj možností přípravy těchto nanostruktur je předmětem navazujícího výzkumu. Ve třetím případě byly zkoumány jednodimenzionální GaN nanodráty připravené na safírovém substrátu. Účelem tohoto projektu bylo získání datasetu pro ověření teoretického modelu, který popisuje růst horizontálních nanodrátů. Na základě sběru a analýzy dat se podařilo modelovat růstovou dynamiku GaN nanodrátů, která byly v souladu s teoretickým modelem.
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Utilization of various methods of porosimetry in investigation of internal structure of biopolymer hydrogels
Zahrádka, Jan ; Pekař, Miloslav (referee) ; Sedláček, Petr (advisor)
The main aim of the thesis was to select, optimize and test suitable methods for studying inner structure of hydrogel materials. The study of the size of pores with potential use in fundamental and applied research of these materials is the central focus of the thesis. Firstly, a literature search was done in order to collect basic information about usefulness of the individual methods. On the basis of this literature search, the experimental part of the work was divided into several steps. First, selected methods of conventional porosimetry (mercury intrusion porosimetry, BET analysis and DSC thermoporometry) were applied on reference porous materials and the results obtained by the individual methods were compared. The methods optimized with the use of these reference materials were then utilized in the analysis of porosity of model hydrogels based on polyvinyl alcohol. Based on the results of this analysis, the usability and benefits of the individual methods were discussed with respect to the sample preparation, time and financial demands, and also from the viewpoint of compliance of the determined pore sizes with the range of sizes declared for the physical PVA gels.
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The Use of AFM Measurement Method in Crystalline Silicon Solar Cells Technology
Mojrová, Barbora ; Boušek, Jaroslav (referee) ; Hégr, Ondřej (advisor)
This thesis deals with the use of Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) in solar cells production. Both techniques measure surface properties using interactions between surface and tip that progressively scans entire surface of the sample. Atomic force microscopy allows three dimensional imaging of surface structure. Kelvin probe force microscopy is used to measure the contact potential difference on the sample surface. There are described experimental measurements of monocrystalline and multicrystalline substrates after various etching processes using AFM. By using KPFM the contact potential difference was measured on dielectric layers PSG, SiOX, SiNX and Al2O3 and on selective emitter structures. All experiments described in this work were carried out at the Solartec Ltd. workplace and they completely correspond with the actual technology of crystalline solar cells production.
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Atomic force microscopy of soft materials
Šudáková, Anna ; Havlíková, Martina (referee) ; Smilek, Jiří (advisor)
This bachelor thesis focuses on atomic force microscopy (AFM), mainly on studying the measurement procedure and optimalization of measurement conditions with future perspective on imaging hydrogels and measuring mechanical properties (such as adhesion or stiffness) of hydrogels and semi-rigid materials at the microlevel. Atomic force microscopy is gaining significant importance in research due to its versatility, when it can provide topographical image of conductive and non-conductive samples while measuring mechanical properties of the samples, such as adhesion, elasticity or stiffness. Advantage of AFM method is that it can provide mechanical properties of the samples not only on macro levels as we are used to, for example, from rheology, but also on local level. Optimalization was performed on standard sample, one micrometre polystyrene nanoparticles , when the individual modes were measured, such as non-contact (AC Mode Imaging) mode and quantitative mode (QITM Advanced Imaging). This was followed by the measurement of a PVA foils, the measurement was performed because they are xerogels and will be studied more in the future. They were made with polyvinyl alcohol and chitosan. The internal environment of the hydrogels has been modified by adjusting the pH (NaOH) or by changing the ionic strength (NaCl). Furthermore, the effect of freezing on the PVA foils was observed, it is one of the possible ways of preparation of physically linked hydrogels. This work also examines the effect of porosity on concentration of physically linked thermoreversible agarose gels.
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