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Optimization of thermal dissociation atomic hydrogen source for use SEM
Melichárek, Václav ; Polčák, Josef (referee) ; Mach, Jindřich (advisor)
The focus of this bachelor's thesis is the optimization of a thermal dissociation monoatomic hydrogen source. The project entailed the design and construction of a new control electronics for the thermal dissociation source, because the source has been powered using universal laboratory power supplies until now. The thesis begins with a brief introduction into the interaction of graphene with monoatomic hydrogen, the operational principle and construction of the monoatomic hydrogen source. Furthermore, the requirements on the design of the electronics are specified. A more detailed analysis of possible solutions, and the selection of the optimal solution were also conducted. The practical part discusses the conceptual designs in detail and describes the selection of the optimal solution. It follows by elaborating on the implementation of the control electronics in detail, its design and construction, and the electrical circuit in particular.
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Examination of 2D crystals in a low voltage SEM/STEM
Mikmeková, Eliška ; Frank, Luděk ; Polčák, J. ; Paták, Aleš ; Lejeune, M.
Development of new types of materials such as 2D crystals (graphene, MoS2, WS2, h-BN, etc.) requires emergence of new surface-sensitive techniques for their characterization. As regards the “surface” sensitivity, the (ultra) low energy electron microscopy can become a very powerful tool for true examination of these atom-thick materials, capable of confirming physical phenomena predicted to occur on their surfaces. Modern commercial scanning electron microscopes enable imaging and analyses by low energy electrons even at very high magnification. In the case of the SEM, resolution even below 1 nm can be achieved at low landing energy of electrons. Since specimen contamination increases with increasing electron dose and decreasing landing energy, specimen cleanness is a critical factor in obtaining meaningful data. A range of various specimen cleaning methods can be applied to selected samples. Typical cleaning methods, such as solvent rinsing, heating, bombarding with ions and plasma etching have their limitations. Electron-induced in situ cleaning procedure can be gentle, experimentally convenient and very effective for wide range of specimens. Even a small amount of hydrocarbon contamination can severely impact on the results obtained with low energy electrons, as illustrated in Figure 1A. During the scanning of surfaces by electrons, the image usually darkens because of a carbonaceous layer gradually deposited on the top from adsorbed hydrocarbon precursors.
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Study of chemical cleaning of surfaces by LEIS method
Staněk, Jan ; Polčák, Josef (referee) ; Bábor, Petr (advisor)
This thesis deal with studying chemical etched surfaces of cadmium telluride crystals (CdTe crystals) by low-energy ion scattering spectroscopy (LEIS method). In the theoretical part, there is description of physical essence of LEIS method, including experimental arrangement of Qtac100 instrument, on which the experiment is measured. The LEIS method is also compared with X-ray photoelectron spectroscopy (XPS). There is summary of properties and structure of CdTe crystals including principle of X-ray detectors, which are the primary use of the crystals. In experimental part there is a description of measuring process, starting with a calibration measurement, ongoing with a chemical etching and ending with a surface analysis. There are examples of LEIS spectra with comments and interpretation including comparison with XPS data.
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SiO2 etching by Si deposition
Pokorný, David ; Bábor, Petr (referee) ; Polčák, Josef (advisor)
This bachelor thesis deals with one of the most interesting reactions taking place in the solid phase in UHV conditions and that is decomposition of SiO2 according to the equation Si + SiO2 = 2SiO. It was used the previously untested procedure - providing Si atoms not from substrate, but by direct deposition on the surface of the oxide. As a source of silicon atoms was used effusion cell. Deposition of silicon on SiO2 substrate was used at room temperature and at elevated temperature to clarify the principle of this reaction. The activation energy and temperature dependence of the reaction rate was determined. It was also verified the possibility of etching SiO2 by Si deposition in UHV conditions. The prepared samples were examined by x-ray photoelectron spectroscopy and atomic force microscopy.
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Analysis of Trench Insulated Gate Bipolar Transistors
Karlovský, Juraj ; Polčák, Josef (referee) ; Bábor, Petr (advisor)
This thesis is focused on the selection and optimalization of suitable analytical methods for study of TIGBT (Trench Insulated Gate Bipolar Transistor) structures with a use of methods, that depict material composition of the studied sample. The theoretical part contain explana-tions of the analytical methods used for measurements and basic principle of operation of an TIGBT transistor. The practical part contain the methodic of measurements and the evaluation of the obtained data and design of optimal procedures in done experiments.
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Surface Analysis by Photoelectrons – Computer Control of Experiments
Polčák, Josef ; Zemek, Josef (referee) ; Cháb, Vladimír (referee) ; Šikola, Tomáš (advisor)
Doctoral thesis is dealing with the methods for analysis of surfaces by photoelectrons being emitted by X-ray radiation. The methods are: X-ray Photoelectron Spectroscopy - XPS, Angle-resolved XPS - ARXPS and X-ray Photoelectron Diffraction - XPD. The work is especially focused on a method of ARXPS, which is used for the depth compositional analysis of sample surfaces. To obtain an information about the depth composition from the measured ARXPS spectra, a calculation software in the Matlab environment has been developed. The software has been tested both for simulated and real sample data. For an experimental implementation of these methods, a complete manipulation system has been developed. It ensures the transport of samples inside a vacuum apparatus and the experiment itself. The system is controlled mainly by a software and enables to run the experiments automatically.
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Passivation of germanium surface using ALD
Kuba, Jakub ; Polčák, Josef (referee) ; Kolíbal, Miroslav (advisor)
The thesis deals with passivation of germanium surfaces by chemical etching and atomic layer deposition (ALD). Attention was paid to the rate of oxidation of germanium surfaces after selected passivation methods and the composition of the germanium suboxides. In the thesis selected methods for germanium oxide removal are reviewed and a brief description of the methods used for analysis (XPS) and thin film deposition (ALD) is given.
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Upgrade of the UHV manipulator for SIMS and LEIS methods
Dao, Tomáš ; Polčák, Josef (referee) ; Bábor, Petr (advisor)
This bachelor’s thesis deals with the design and the construction of the manipulator, which operates under ultra high vacuum. In the first section, the original design and realization of the manipulator with six motion axis is introduced. Second section deals with the modifications of the manipulator. Advantages and disadvantages of the design are discussed and a new design of the manipulator, based on the experience from manipulator operation, is projected. Section is mainly focused on the design of the sample rotation using a stepper motor working in the ultra high vacuum. The new Faraday cup was also designed and tested. The last section contains the LEIS structural analysis measurement using the manipulator.
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Imaging of SiCN thin films on silicon substrate in the scanning low energy electron microscope
Zobačová, Jitka ; Hüger, E. ; Urbánek, Michal ; Polčák, J. ; Frank, Luděk
The Si-C-N materials have been attracting growing interest due to their excellent physical properties. They are hard, possess a large band gap, resist harsh and high temperature environments, and exhibit interesting nanostrucrures such as turbosrtatic-carbon and nanopores. Their range of application includes anti-erosive turbines and cutting tools, opto-electronic materials, sensors and special drug delivery pharamaceutical products. Most of their interesting properties stems from carbon-nitrogen bonds. Hence, Si-C-N materials with a high content of carbon and nitrogen are of interest. Up to date, the highest carbon and nitrogen content could be synthesised in SiC2N4 and Si2CN4. Both chemical compositions are stable and possess the highest achieved carbon-nitrogen bond. Two different nitride bonding configuration was measured to be present.
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Imaging of thermal treated thin films on silicon substrate in the scanning low energy electron microscope
Zobačová, Jitka ; Mikmeková, Šárka ; Polčák, J. ; Frank, Luděk
Structure of thin films usually requires to be examined on microscopic level. The research topics like growth and stability of thin films, phase transitions and separation, crystallization, diffusion and defect formation has a need for LEED or XPS as techniques adequate for investigation of atomic transport processes on short length scales. The low energy electron microscopy is a complementary solution for imaging of samples with special concern for knowledge of surface physics and material science. In this contribution the microscopic examination of as-deposited and thermal treated thin films on Si substrates is performed.
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