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Thermionic generators
Primes, Alois ; Pospíšil, Jiří (referee) ; Brázdil, Marian (advisor)
This bachelor thesis deals with thermionic generators. In the first part of the thesis thermionic conversion principle and related physical phenomena are described. In the next part, the distribution of thermionic generators according to the construction is presented. The performed research shows that currently vacuum thermionic generators are being tested. This is followed by an overview of selected thermionic generators, and the purpose for which they were designed and the results achieved. It has been found that electric heating was used for experimental purposes, which can artificially increase the efficiency of the tested devices. The conclusion is dedicated to the performance and efficiency of thermionic devices and their possible use in the near future. It can be assumed that some types of thermionic generators will be used in power plants using high-temperature heat sources to increase their efficiency.
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Analysis of locally modified surfaces for selective growth of cobalt
Krajňák, Tomáš ; Bábor, Petr (referee) ; Čechal, Jan (advisor)
In this thesis the chemical composition of silicon substrates locally modified by focused gallium ion beam by X-ray photoelectron spectroscopy is determined. In order to determine the influence of focused ion beam, the sample comprising sputtered square areas with nominal depths in range of 1 to 10 nm was prepared. Next, the sample was heated to elevated temperatures (500 - 700 °C) to reveal changes in the sputtered areas induced by annealing. In this work by X-ray photoelectron spectrometer Kratos Supra and electron microscope Tescan LYRA3 with focused ion beam were used. From the measured spectra of the Si 2p and Ga 2p3/2 peaks measured as a function of nominal sputtering depth and annealing temperature the following main observations were obtained. First, there is the additional peak component in the Si 2p peak, which can be assigned to the amorphous silicon. The second important finding is that gallium can be removed from near surface volume by annealing at temperatures beyond 700 °C.
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Characterisation for the cold field-emission sources intended for electron microscopy
Vašíček, Martin ; Tománek, Pavel (referee) ; Grmela, Lubomír (advisor)
This work deals with the theoretical foundations of electron emission into vacuum, various types of emissions, focused on the cold-emission and Schottky emission and the principle of quantum tunneling. The next part deals with the technical implementation of electron sources with a detailed study of the methodology of laboratory production of cathodes by electrochemical etching and construction of electron microscopes, using field-emission sources. This work also contains methods for measuring, processing and evaluation of electrical characteristics of emission sources.
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Coulomb Interactions in Electron Beams
Jánský, Pavel ; Janík,, Ján (referee) ; Kolařík,, Robert (referee) ; Lencová, Bohumila (advisor)
The thesis deals with numerical simulations of a hairpin thermionic electron gun, an electron source of the electron-beam welding machine. Simulations showed that the space charge in the electron gun has a significant influence on the beam current and electron trajectories. Simulation outputs are in a sufficient agreement with the experimental measurements.
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Thermionic generators
Primes, Alois ; Pospíšil, Jiří (referee) ; Brázdil, Marian (advisor)
This bachelor thesis deals with thermionic generators. In the first part of the thesis thermionic conversion principle and related physical phenomena are described. In the next part, the distribution of thermionic generators according to the construction is presented. The performed research shows that currently vacuum thermionic generators are being tested. This is followed by an overview of selected thermionic generators, and the purpose for which they were designed and the results achieved. It has been found that electric heating was used for experimental purposes, which can artificially increase the efficiency of the tested devices. The conclusion is dedicated to the performance and efficiency of thermionic devices and their possible use in the near future. It can be assumed that some types of thermionic generators will be used in power plants using high-temperature heat sources to increase their efficiency.
|
|
|
Analysis of locally modified surfaces for selective growth of cobalt
Krajňák, Tomáš ; Bábor, Petr (referee) ; Čechal, Jan (advisor)
In this thesis the chemical composition of silicon substrates locally modified by focused gallium ion beam by X-ray photoelectron spectroscopy is determined. In order to determine the influence of focused ion beam, the sample comprising sputtered square areas with nominal depths in range of 1 to 10 nm was prepared. Next, the sample was heated to elevated temperatures (500 - 700 °C) to reveal changes in the sputtered areas induced by annealing. In this work by X-ray photoelectron spectrometer Kratos Supra and electron microscope Tescan LYRA3 with focused ion beam were used. From the measured spectra of the Si 2p and Ga 2p3/2 peaks measured as a function of nominal sputtering depth and annealing temperature the following main observations were obtained. First, there is the additional peak component in the Si 2p peak, which can be assigned to the amorphous silicon. The second important finding is that gallium can be removed from near surface volume by annealing at temperatures beyond 700 °C.
|
|
|
Coulomb Interactions in Electron Beams
Jánský, Pavel ; Janík,, Ján (referee) ; Kolařík,, Robert (referee) ; Lencová, Bohumila (advisor)
The thesis deals with numerical simulations of a hairpin thermionic electron gun, an electron source of the electron-beam welding machine. Simulations showed that the space charge in the electron gun has a significant influence on the beam current and electron trajectories. Simulation outputs are in a sufficient agreement with the experimental measurements.
|
|
|
Characterisation for the cold field-emission sources intended for electron microscopy
Vašíček, Martin ; Tománek, Pavel (referee) ; Grmela, Lubomír (advisor)
This work deals with the theoretical foundations of electron emission into vacuum, various types of emissions, focused on the cold-emission and Schottky emission and the principle of quantum tunneling. The next part deals with the technical implementation of electron sources with a detailed study of the methodology of laboratory production of cathodes by electrochemical etching and construction of electron microscopes, using field-emission sources. This work also contains methods for measuring, processing and evaluation of electrical characteristics of emission sources.
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