Národní úložiště šedé literatury Nalezeno 28 záznamů.  1 - 10dalšíkonec  přejít na záznam: Hledání trvalo 0.00 vteřin. 
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.
SMV-2023-06: Vývoj testovacích preparátů pro REM
Matějka, Milan ; Krátký, Stanislav ; Meluzín, Petr ; Košelová, Zuzana ; Chlumská, Jana ; Horáček, Miroslav ; Kolařík, Vladimír ; Knápek, Alexandr
Studie se zaměřuje na výzkum a vývoj přesných kalibračních vzorků s reliéfními strukturami. Tyto vzorky jsou navrženy ke kalibraci zobrazování ve skenovacích elektronových mikroskopech (SEM). Testovací vzory umožňují ověření a kalibraci zvětšení, ortogonality a geometrického zkreslení. Příprava kalibračních vzorků využívá mikro litografické techniky přizpůsobené pro zpracování křemíku a dalších související technologické postupy.
SMV-2023-05: DI2023
Matějka, Milan ; Krátký, Stanislav ; Meluzín, Petr ; Košelová, Zuzana ; Chlumská, Jana ; Horáček, Miroslav ; Kolařík, Vladimír ; Knápek, Alexandr
Výzkum se soustředí na zkoumání a vývoj precizních kalibračních vzorků s reliéfními strukturami. Tyto vzorky jsou koncipovány pro kalibraci parametrů ve skenovacích elektronových mikroskopech (SEM). Testovací vzory umožňují ověření kvality zobrazovaní danou mikroskopickou technikou jako je celkové zvětšení, velikost zorného, rozlišení, deformace zobrazení v laterárních osách a další geometrická zkreslení. Pro přípravku jsou využívány precizní litografické techniky a další techniky vycházející z technologií zpracování křemíku z polovodičového průmyslu. Vývoj byl zaměřen na optimalizaci záznamu leptacích masek před přenosem obrazu do monokrystalické křemíkové podložky.
Influence of High Concentration of Silica Nanoparticles on the Dielectric Spectra
Soud, Ammar Al ; Daradkeh, Samer ; Knápek, Alexandr ; Liedermann, Karel ; Holcman, Vladimír ; Sobola, Dinara
In the presented work, we report the dielectricbehavior of epoxy–silicon oxide composites in the temperaturerange 240– 300 K, over the frequency range 10-2 Hz – 107 Hz. Themeasuring apparatus was based on the Novocontrol AlphaAnalyser and the measured data were analyzed and interpretedusing the Havriliak – Negami equation. The master curves of thereal part of permittivity and the dielectric loss number wereobtained by time–temperature superposition principle, and theresults showed that the nano-composite had a much higher lossfactor. Through the analysis of the origin of the dielectric responsein epoxy/silica composite, the reason for the different dielectricrelaxation behaviors of the nano-composite, and the pure epoxywas discussed.
Field emission characteristics and analysis of chargé flow through graphite based cathodes
Allaham, Mohammad M. ; Burda, Daniel ; Sobola, Dinara ; Knápek, Alexandr
This paper studies the performance of differenttypes of graphite cathodes when operated as field emissionelectron sources. The tested cathodes were prepared in theform of bulk polymer graphite, bulk pure graphite, and polymergraphite coated with thin layer of insulating material(epoxy resin). The obtained results include X-Ray photoelectronspectroscopy analysis, scanning electron micrographs, the fieldemission microscope patterns and current-voltage characteristics,and the orthodoxy test analysis results. The importance of thisstudy is summarized in following the pursuit of finding cheapand green electron sources. Moreover, to present a new exoticfield emission behavior in the form of emission pulses.
SMV-2023-03: Držák autoemisních katod
Knápek, Alexandr ; Horáček, Miroslav ; Klein, Pavel
Smluvní výzkum (SMV) se zabývá vývojem modulárního držáku pro vývoj a testování auto-emisních katod v podmínkách ultra-vysokého vakua. Výzkum kombinuje znalosti z vakuové techniky, silnoproudé elektrotechniky a povrchové fyziky k dosažení spolehlivého zařízení, které umožňuje pracovat s polně-emisními katodami ve vakuových podmínkách, a to v diodové a triodové konfiguraci. Hlavním výstupem pro objednavatele je výkresová dokumentace, která umožňuje aparaturu replikovat a dále jeden kus funkčního prototypu, který byl v rámci SMV zkonstruován k ověření funkcionality.
Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters
Burda, Daniel ; Knápek, Alexandr
This research aims to obtain a more in-depth understanding of the field emission properties of tungsten single-tip field emitters (STFEs) coated with a several tens of nanometer thin barrier of Al2O3. The introduction of an additional barrier into the metal-vacuum interface system of the emitter can be beneficial to improve its performance. The tungsten emitters were prepared using a two-step electrochemical drop-off etching technique. Thin oxide barrier coatings were prepared by using low-temperature atomic layer deposition (ALD), a chemical vapor deposition technique. Field emission was studied in an internally developed field emission microscope (FEM) working in UHV vacuum (< 1·10−7 Pa), and the experimental field emission data were analyzed by the so-called Murphy-Good plotsThe value of the local work function of the grown oxide layer were investigated using Ultra-violet photoelectron spectroscopy (UPS).
Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters
Burda, Daniel ; Knápek, Alexandr
This research aims to obtain a more in-depth understanding of the field emission properties of tungsten single-tip field emitters (STFEs) coated with a several tens of nanometer thin barrier of Al2O3. The introduction of an additional barrier into the metal-vacuum interface system of the emitter can be beneficial to improve its performance. The tungsten emitters were prepared using a two-step electrochemical drop-off etching technique. Thin oxide barrier coatings were prepared by using low-temperature atomic layer deposition (ALD), a chemical vapor deposition technique. Field emission was studied in an internally developed field emission microscope (FEM) working in UHV vacuum (< 1·10−7 Pa), and the experimental field emission data were analyzed by the so-called Murphy-Good plotsThe value of the local work function of the grown oxide layer were investigated using Ultra-violet photoelectron spectroscopy (UPS).
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.
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.

Národní úložiště šedé literatury : Nalezeno 28 záznamů.   1 - 10dalšíkonec  přejít na záznam:
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