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Methods of Preparation and Characterization of Experimental Field-Emission Cathodes
Knápek, Alexandr ; Luňáček, Jiří (oponent) ; Lazar, Josef (oponent) ; Grmela, Lubomír (vedoucí práce)
This PhD thesis describes, and covers the preparation of field-emission cathodes that represent a high-quality, inexpensive source of electrons for devices that work with a focused electron beam. In this work, an improved method of electrochemical fabrication is used for the preparation of a composite field-emission cathode. The composite structure improves current stability in comparison to tungsten-based pure field-emission cathodes. Improvements to the technology used were implemented on the basis of findings obtained using spectrum noise diagnostics, which are based on measuring and evaluating the emission current in the time and in frequency domains. Additionally, noise spectroscopy provides important information about charge transport, electron mobility, and lifespan, which is essential for future research. Results obtained using the experimental method have been further supplemented with theoretical data provided by a computer simulation in order to establish characterization procedures for improved field-emission cathodes.
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Defectoscopy of thin polymer layers using computer vision
Podstránský, Jáchym ; Sobola, Dinara (oponent) ; Knápek, Alexandr (vedoucí práce)
In the electron beam lithography process, one of the first steps is to coat the substrate, the wafer, with a thin layer of polymer resist. During the coating process, defects occur that can affect the exposure and therefore the functionality of the final nanostructure. By checking the quality of the deposited resin prior to exposure, these defect sites can be avoided. This process can be done manually using a light microscope, but it is a time consuming process. In the framework of this bachelor thesis, a device has been developed that can detect these defects automatically. It is a rasterising device that, by combining two stepper motors and an optical camera, takes images of the desired area of the wafer and then analyses these with the help of artificial intelligence. The user is then provided with a document in which the size, position and type of each defect found is recorded.
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Analysis and characterisation of spirally-arranged field-emission nanostructure
Ondříšková, Martina ; Sobola, Dinara (oponent) ; Knápek, Alexandr (vedoucí práce)
Cathodes containing arrays of high aspect ratio field emitters are of great interest as sources of electron beams for vacuum electronic devices. The desire to maximize current and current density leads to the design of denser arrays. However, denser arrays lead to undesirable field shielding effects caused by the presence of surrounding emitters in the array. To reduce the shielding effect and thus maximize the field enhancement, an array of emitters was designed with an arrangement inspired by the natural phenomenon of phyllotaxis. The structure thus designed was created using electron beam lithography and reactive ion etching to form micropillars. A black silicon etching technique was used to create ultra-sharp tips with a radius in the order of tens of nanometers on the top of each micropillar. Analysis of the sample topography was performed by Scanning electron microscopy. Ultraviolet photoelectron spectroscopy was used to determine the work function. To find out the emission properties of the fabricated structures, a Field emission microscope was constructed and its electron gun was modified to experimentally use the fabricated structure as the cathode. A Murphy-Good plot was used to analyze the field emission data, to which the orthodoxy test was applied to check the validity of the experimental I-V data. Current stability measurement was performed to observe current fluctuations.
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Methodics of characterisation for the cold field-emission sources intended for electron microscopy
Štrbková, Lenka ; Grmela, Lubomír (oponent) ; Knápek, Alexandr (vedoucí práce)
The master’s thesis deals with the characterization method of the electron emitter for an electron microscope – Fowler-Nordheim analysis. The method is based on the presence of quantum tunnelling, which occurs during the field emission of electrons. The work contains the theoretical background to the topic, as well as the practical part. The theoretical introduction describes the electron emission, quantum tunnelling phenomenon and the parameters of the electron emitters. In the second part, the thesis focuses on the experimental study of the field-emission cathode. The essential characteristics of the emitter are computed. These characteristics determine the overall quality of electron emission, as well as provide information about the actual condition of the emitter. The results of the F-N analysis are subsequently compared with the results of the computer simulation of the field-emission. The simulation is performed in COMSOL Multiphysics software using the finite element method (FEM) and enables to assess the relevance and accuracy of the F-N analysis.
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Korelativní měření katodoluminiscence za použití technik SEM a SPM
Černek, Ondrej ; Knápek, Alexandr (oponent) ; Spousta, Jiří (vedoucí práce)
Diplomová práca sa zaoberá kombinovaným použitím techník SEM a SPM za použitia optického vlákna, ktoré slúži k zberu katódoluminiscenčného signálu v tesnej blízkosti vzorky. Práca taktiež obsahuje rešeršnú časť, v ktorej je uvedený popis CPEM techniky, ďalej sú uvedené použité techniky potrebné pre úpravu optického vlákna, teoretický úvod do katódoluminiscencie a zaužívané techniky pre jej meranie. V praktickej časti sú diskutované získané výsledky meraní a problémy, ktoré nastali počas procesu úpravy optického vlákna, jeho použití ako sondy SPM a pri samotnom meraní materiálov vykazujúcich katódoluminiscenciu.
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Pyroelectric detector signal measurement and processing
Knápek, Alexandr ; Sedláková, Vlasta (oponent) ; Majzner, Jiří (vedoucí práce)
The thesis analyzes the physical properties of the pyroelectric sensors and its practical use. Essential part of the work is the design and realization of the measuring set-up, which is used for the measurements of the sensors physical properties. With this workbench, main parameters of the pyroelectric sensors have been obtained. The second part of the work deals with a low noise preamplifier designing. This device was designed for the pyroelectric sensor signal measurements. The amplifier is designed to be used for a low noise, wide band measuring. During the process of amplifier designing, all the noise components have been investigated separately, using operational amplifiers models. The objective of the last part of this work is to develop the system, which would be able to localize an infrared (IR) emitting source located somewhere in the space between the installed pyroelectric sensors. For this purpose, classical localization methods could be used as well as the artificial neural networks (ANN), which are becoming still more popular these days. The system is able to detect the exact placement of the IR radiation source.
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Design of automated set-up intended for inspection of PMMA coated silicon wafers
Drozd, Michal ; Sobola, Dinara (oponent) ; Knápek, Alexandr (vedoucí práce)
During the coating the substrate with a thin layer of polymer resist several defects can to occur which could damage an exposure by electron beam lithography. The quality of the resist-coated surface prior to the exposure is also very important in terms of the final functionality of the fabricated micro device. The quality of the resist-coated surface can be measured by means of human visual inspection with a visible-light microscope. This bachelor's thesis is focused on the design and assembly of the automated set-up to do this inspection automatically. More precisely, the designed set-up is called WaferScan and it allows to scan a silicon wafer coated with a resist layer. The wafer surface is scanned with an optical camera and the taken images are analyzed using computer to determine the location and the size of the defects and the dust particles in the resist layer. The entire device consists of two moving axes, x and y, (that allow the movement of the camera) and a control electronic circuitry. Software to control the scanning device and the image processing tool were also developed.
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Metody zobrazování a analýzy biologických vzorků
Novotná, Veronika ; Tománek, Pavel (oponent) ; Knápek, Alexandr (vedoucí práce)
Bakalářská práce se věnuje vlastnostem lidských tkání a bakterií z mikroskopického hlediska. Dále popisuje fyzikální principy mikroskopovacích technik SNOM a elektronové mikroskopie (TEM, SEM, ESEM) a jejich vhodnost pro pozorování biologických preparátů. Následující část se zabývá transformací dat z elektronového mikroskopu z časové do obrazové roviny a práci se vzniklými obrazy. Další kapitola je věnována experimentální přípravě preparátů pro SEM/ESEM a SNOM. Protože jsou zde v současné době tendence využít mikroskopovací techniku SNOM v biologické výzkumu je cílem práce srovnání možností zmíněných mikroskopovacích technik pro pozorování biologických vzorků a zhodnocení, zda je možné pro tyto účely nahradit obecně drahý EM levnějším SNOM. EM i SNOM totiž umožňují získat rozdílnou nicméně srovnatelnou a komplementární informaci o zkoumaném vzorku.
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Functional Tungsten-based thin films and their characterization
Košelová, Zuzana ; Horáková, L. ; Sobola, Dinara ; Burda, Daniel ; Knápek, Alexandr ; Fohlerová, Z.
Anodizing is a technique by which thin oxide layers can be formed on a surface. Thin oxide layers have been found to be useful in a variety of applications, including emitters of electrons. Tungsten is still a common choice for cold field emitters in commercial microscopy applications. Its suitable quality can be further improved by thin film deposition. Not only the emission characteristic can be improved, but also the emitter operating time can be extended. Tungsten oxide is known for its excellent resistance to corrosion and chemical attack due to its stable crystal structure and strong chemical bonds between tungsten and oxygen atoms. Many techniques with different advantages and disadvantages have been used for this purpose. Anodization was chosen for this work because of the controllable uniform coverage of the material and its easy availability without the need for expensive complex equipment. The anodizing process involves applying an electrical potential to tungsten while it is immersed in an electrolyte solution. This creates a thin layer of tungsten oxide on the surface of the metal. The thickness and properties of the resulting oxide layer can be controlled by adjusting the anodization conditions, such as the electrolyte solution, voltage, and the duration of the process. In this work, H3PO4 was used as the electrolyte to test whether these tungsten oxide layers would be useful for electron emitters, for use in electron guns and other devices that require high-quality electron emitters. The properties were evaluated using appropriate techniques. In general, anodization of tungsten to form thin layers of tungsten oxide layers is a promising technique for producing high quality electron emitters.
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