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Design and verification of low temperature part of UHV – STM microscope
Voňka, Jakub ; Rotter, Miloš (referee) ; Urban, Pavel (advisor)
The diploma thesis addresses the design and experimental verification of cooling system and low temperature part of UHV - STM working in temperature range of 20K - 300K. Due to the demand of variable temperature, the flow cooling system with cryogenic (~5 K) helium (He) is used. Two variants of the low temperature part of the microscope are studied. First the version with cooling only the sample holder, and second with cooling of the whole STM. Designed cooling system consists of He flow cryostat allowing to connect it to the Dewar vessel with liquid helium (LHe) using a low-loss transfer line. The cryostat consists of He inlet and outlet, heat exchangers and copper strains (i.e. braids) for the thermal connection of the sample holder/STM and radiation shield around the STM with the heat exchangers. The thesis describes the design of the flow cryostat and its initial tests in the designed vacuum chamber. Heat flow through a spot contact is also discussed to estimate thermal conductance of insulation supports based on thermal resistance of spherical contacts. The thesis was elaborated in collaboration with the Institute of Scientific Instruments of the ASCR, v.v.i.
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Low temperature scanning tunneling microscopy
Sojka, Antonín ; Havlíček,, Marek (referee) ; Pavera, Michal (advisor)
The diploma thesis is divided into two main parts. The first part describes the production of chrome and cobalt tips for SP-STM with subsequent testing of chrome tips on the Fe-Ir system (111). Furthermore, the first results from the growth studies of niobium on iridium(111) are presented. In the second part is described in detail the experimental LT-STM microscope of the Faculty of Physical Engineering. The chapter deals with the development of the microscope and its testing on a HOPG sample under atmospheric and vacuum conditions. The chapter describes the biggest problems which were solved when the microscope was puting into operation state. The second part also introduces the design of a new vacuum transport system, which consists of a tip and sample transport pallet. At the end of the second part is described the testing of cooling systems for LT-STM and the design of their modifications.
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SMV-2023-38: Testing of surfaces for cryogenics
Frolec, Jiří
The ordering party required an analysis of the thermal-radiative characteristics of several different metallic materials, from which several special samples were designed and manufactured in cooperation with ISI Brno. These were tested in a special low-temperature apparatus. As part of the contract research, the relative rate of thermal radiation emission, the so-called total hemispheric emissivity, was determined at temperatures ranging from -268 °C up to room temperature. By comparing the results with each other, the client will be able to determine the optimal variant for the intended application, both in terms of the material itself as well as the applied surface finish.
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SMV-2023-37: CRYSA project - cryostat of the space probe 2
Frolec, Jiří
The goal of the project CRYSA is the selection and testing of three composite materials suitable for fixation of a low temperature device (cryostat), which will be part of the upcoming Athena space probe from the European Space Agency (ESA). The Cryogenics and Superconductivity group at the Institute of Scientific Instruments of the Czech Academy of Sciences (ISI Brno), OHB Czechspace, 5M s.r.o. and the Institute of Physics of Materials of the CAS (IPM) collaborate on this project. The aforementioned contractual researches carried out at ISI Brno in 2023 were focused on the partial goals of the project. Specifically, the selection of the three best materials, which will be tested in the future, was finalized. Further, detailed procedures for the planned measurements of the thermal conductivity of the samples and the method of their temperature cycling at low temperatures were developed. The members of the Cryogenics and Superconductivity Group also performed optimization of the measuring devices and measured thermal conductivities of several dummy samples. The outputs of this project will help ESA with the selection of the optimal material for the construction of the mechanical supports for the cryostat in the Athena telescope.
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Design of a nitrogen Dewar vessel for electron microscopes
Brauner, Tomáš ; Voňka,, Jakub (referee) ; Urban, Pavel (advisor)
Observation of biological samples in electron microscopes in a state closest to the native state requires reaching cryogenic temperatures, most often with the use of liquid nitrogen (LN2). For this purpose a Dewar vessel with cooled copper thumb for cooling the sample holder and anticontamination shield inside the vacuum chamber of the scanning electron microscope (SEM) and focused ion beam (FIB) source was designed. Characteristics of the designed LN2 Dewar vessel were validated by measuring executed on the real functional sample. The reached temperature at the tip of the thumb under estimated heat load 2 W was 90,8 K. Corresponding refilling interval of LN2 is about 11 h. Experimentally measured data correlate with theoretically calculated characteristics. The designed Dewar vessel with a cooled thumb fulfills the required properties specified in the thesis assignment with a margin.
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SMV-2022-43: Absorptivity and emissivity of materials for use in space
Králík, Tomáš
This contractual research was aimed at verifying the thermal radiation properties of the emissivity of coatings and covering foils for space probes. Half of the experiments were focused on thermal regulation coatings, the purpose of which is to passively maintain the optimal temperature of the device, the balance between thermal radiation and absorption of visible radiation. Some foils had unique thermochromic properties, where their thermal radiative properties change sharply with their own temperature. The second part of the research was focused on the effect of contamination of a clean metal surface with dust simulating lunar regolith on the absorption of thermal radiation. As part of this research, five differently contaminated surfaces were measured. This unique data will enable the contractor to better design apparatus for work on the surface of the Moon or other planets. The contractor selected and supplied\nsamples of materials in the form of foils and coated sheets, which had to be modified into a sample suitable for the apparatus operated at the ISI Brno. A material labelled EAC‐1A was used as a lunar regolith simulant. The goal of the project was to evaluate the so‐called total hemispheric emissivity or absorptivity in the temperature range from 20 K to 300 K.
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SMV-2022-42: Emissivity of coatings for space mission ARIEL
Králík, Tomáš
This contractual research was aimed at verifying the thermal emissivity of materials planned for use in the optical system of the ARIEL infrared telescope located in orbit around the earth. The contractor selected several samples of the coating with high light absorption. However, the thermal radiation properties of this coating were not yet known. The goal of the project was to evaluate the so-called total hemispheric emissivity in the temperature range from 20 K to 300 K. The results will enable the customer to model the temperature distribution inside the optical path of the telescope.
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SMV-2022-10: CRYSA project – CRYostat Straps for the Athena space telescope
Frolec, Jiří
The goal of the project, from the point of view of the Cryogenics and Superconductivity group at the Institute of Scientific Instruments of the Czech Academy of Sciences (ISI Brno), resides in a cooperation with OHB Czechspace and the Institute of Physics of Materials of the CAS (IPM) in order to select and experimentally measure the properties of materials suitable for mounting a device at a very low temperature (cryostat straps), which will be part of the upcoming Athena space telescope of the European Space Agency (ESA). The project consortium will conduct a survey of available materials and, based on this review, will select two most suitable and commercially available materials, which will be later tested in individual CAS institutes. Materials must meet two basic properties – high mechanical stiffness and low thermal conductivity. Members of the Cryogenics and Superconductivity group at ISI Brno will perform, with the help of special equipment and cooling using liquid helium bath, thermal conductivity measurements and the exposure of selected materials to low temperatures for next mechanical tests at the IPM. The outputs of this project will help ESA with the selection of the optimal material for the construction of the straps supporting the given Athena cryostat.
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SMV-2022-09: Special coatings for a radio-frequency absorber
Frolec, Jiří
As part of the upcoming mission of the European Space Agency, the space-probe JUICE, the task of the Max Planck Institute for Solar System Research is to determine the thermal radiation properties of the coatings intended for the radio-frequency absorber of this probe. In frame of this project, there was an experimental verification of the relative rate of thermal radiation emission, so-called emissivity, of two different coatings deposited on the surface of the developed samples. The main output of the research is the low-temperature tests of these samples carried out using a unique measuring apparatus, cooled by a bath of liquid helium. The emissivity of thermal radiation of both surfaces was determined in the temperature range from 20 K to 300 K. As part of the project, we also assessed, in addition to the thermal-radiative properties, the mechanical stability of the sample at low temperatures. All data have been submitted to the Max Planck Institute in the form of research reports.
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