Number of found documents: 647
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Automation of metallographic sample cleaning process
Čermák, Jan; Ambrož, Ondřej; Jozefovič, Patrik; Mikmeková, Šárka
2022 - English
Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual sample handling. An etchant or electrolyte results in inhomogeneous surface quality because the solution runs off the specimen surface during its removal from the beaker. High-quality specimen cleaning is absolutely crucial for the acquisition of the specimen suitable for characterization by a scanning electron microscope operated at very low landing energies of the primary electrons (SLEEM). The SLEEM technique is a powerful tool for the characterization of advanced steels, as described by many scientific papers. The SLEEM requires the specimen absolutely free of water and any organic residues on the surface. This work presents a novel unique apparatus enabling automatic specimen cleaning and drying after the etching or electropolishing processes. Automation reduces the influence of dependent variables that would be introduced into the process by the metallographer. These variables include cleaning time, kinematics, and motion dynamics, but the process can also be affected by variables that are not obvious. Performed experiments clearly demonstrate our in-house designed apparatus as a useful tool improving efficiency and consistency of the sample cleaning process. The high quality of the specimen surface is verified using a light optical microscope, an electron scanning microscope, and above mentioned SLEEM technique. Keywords: metallography; sample cleaning; process automation; repeatability Fulltext is available at external website.
Automation of metallographic sample cleaning process

Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual ...

Čermák, Jan; Ambrož, Ondřej; Jozefovič, Patrik; Mikmeková, Šárka
Ústav přístrojové techniky, 2022

16th Multinational Congress on Microscopy, 16MCM, 04-09 September 2022, Brno, Czech Republic. Book of abstracts
Krzyžánek, Vladislav; Hrubanová, Kamila; Hozák, Pavel; Müllerová, Ilona; Šlouf, Miroslav
2022 - English
Fulltext is available at external website.
16th Multinational Congress on Microscopy, 16MCM, 04-09 September 2022, Brno, Czech Republic. Book of abstracts

Krzyžánek, Vladislav; Hrubanová, Kamila; Hozák, Pavel; Müllerová, Ilona; Šlouf, Miroslav
Ústav přístrojové techniky, 2022

Correction of gradient pulse shape distortions in radial MRI
Vitouš, Jiří
2022 - English
This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may produce phase distortion in the resulting image and also signal loss in the acquired signal. A method for correction is proposed based on the Nelder-Mead algorithm followed by coordinate ascent search in the neighborhood of the found solution. The adjustment is evaluated using a simple Fast low angle shot (FLASH) sequence with radial readout. The results show a significant improvement in the Free induction decay (FID) signal magnitude, echo stability, and an improvement in the homogeneity of image phase. Keywords: MRI; gradient; Nelder–Mead; slice; adjustment Fulltext is available at external website.
Correction of gradient pulse shape distortions in radial MRI

This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may ...

Vitouš, Jiří
Ústav přístrojové techniky, 2022

Gold nanosystems for the detection of molecules using surface-enhanced Raman scatterings (SERS)
Benešová, Markéta
2022 - English
Raman spectroscopy is a non-destructive analytical technique to analyze the chemical structure of molecules by a phenomenon known as Raman scattering, which occurs by an inelastic interaction of photons with the valence electrons in molecular bonds. However, Raman scattering can be hard to observe due to other, more frequent phenomena, such as Rayleigh scattering or fluorescence. SERS (surface-enhanced Raman spectroscopy) uses localized surface plasmon resonance (LSPR) of metal nanostructures to amplify Raman scattering. LSPR is a coherent oscillation of conduction electrons that arises from the interaction of electromagnetic radiation with metal nanostructures. The amplification of Raman scattering occurs when the analyte is adsorbed on the surface of such nanostructure and the strong localized electric field interacts with the electrons in its molecular bonds. Signal amplification of several orders of magnitude can be achieved, commonly 103 or more. In our work, we determined the presence of a selected bacterial species by multi-functionalized golden nanoparticles called SERS-tags, which have their surface modified with an antibody and a Raman reporter. The antibody allows the nanoparticles to bind to the surface of a concrete bacterial species based on the antigen-antibody affinity. When the targeted bacterium is covered with the nanoparticles, the Raman reporter signal is amplified by SERS, providing specific and strong Raman response. Therefore, when the Raman reporter signal is detected in a sample, it confirms the presence of the specific bacterium on a single-cell level. Keywords: surface-enhanced Raman spectroscopy; SERS-tag Available at various institutes of the ASCR
Gold nanosystems for the detection of molecules using surface-enhanced Raman scatterings (SERS)

Raman spectroscopy is a non-destructive analytical technique to analyze the chemical structure of molecules by a phenomenon known as Raman scattering, which occurs by an inelastic interaction of ...

Benešová, Markéta
Ústav přístrojové techniky, 2022

Unfolded Low-rank + Sparse Reconstruction for MRI
Mokrý, O.; Vitouš, Jiří
2022 - English
We apply the methodology of deep unfolding on the problem of reconstruction of DCE-MRI data. The problem is formulated as a convex optimization problem, solvable via the primal-dual splitting algorithm. The unfolding allows for optimal hyperparameter selection for the model. We examine two approaches - with the parameters shared across the layers/iterations, and an adaptive version where the parameters can differ. The results demonstrate that the more complex model can better adapt to the data. Keywords: DCE-MRI; proximal splitting algorithms; deep unfolding; L+S model Fulltext is available at external website.
Unfolded Low-rank + Sparse Reconstruction for MRI

We apply the methodology of deep unfolding on the problem of reconstruction of DCE-MRI data. The problem is formulated as a convex optimization problem, solvable via the primal-dual splitting ...

Mokrý, O.; Vitouš, Jiří
Ústav přístrojové techniky, 2022

Electron beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy
Rončák, Ján; Adam, O.; Müller, P.; Zobač, Martin
2022 - English
Eutectic high-entropy alloys have become a significantly studied type of material due to their combination of strength and ductility. However, previous research has focused primarily on manufacture, solidification behaviour and mechanical properties. Only a small part of the research has been devoted to welding. This paper is focused on evaluating the weldability of eutectic high-entropy alloy AlCoCrFeNi2.1 in the as-cast state without further heat treatment. The electron beam welding process was performed twice at the same parameters, except for the beam current. Properties such as the depth of the remelted layer, the formation of the heat-affected zone, and the presence of undesirable defects in the welded joints were observed using light and electron microscopy. At the same time, material properties in the form of microstructural stability, chemical composition, and hardness of the welded joints were evaluated. Keywords: AlCoCrFeNi2.1; electron beam welding; eutectic high-entropy alloys; microstructure Fulltext is available at external website.
Electron beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy

Eutectic high-entropy alloys have become a significantly studied type of material due to their combination of strength and ductility. However, previous research has focused primarily on manufacture, ...

Rončák, Ján; Adam, O.; Müller, P.; Zobač, Martin
Ústav přístrojové techniky, 2022

Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters
Burda, Daniel; Knápek, Alexandr
2022 - English
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). Keywords: Cold field emission; single-tip field emitters; tungsten tip; aluminum oxide; dielectric coatings; Murphy-Good plot Fulltext is available at external website.
Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters

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. ...

Burda, Daniel; Knápek, Alexandr
Ústav přístrojové techniky, 2022

Low-temperature emissivity of thin Al2O3 layers deposited on copper substrate
Frolec, Jiří; Králík, Tomáš; Nyman, L.; Pudas, M.; Kallio, E.
2021 - English
Copper is commonly used in cryogenic systems due to its high thermal and electrical conductivity along with excellent solderability. Very low emissivity values of copper surface also reduce in cryogenic systems heat load transferred by thermal radiation. These values may be, however, enhanced by a prospective coating, deposited usually in order to prevent chemical changes on highly reactive copper surface. This paper focuses on protective layers of Al2O3 with thicknesses up to 28 nm, deposited on polished copper. We measured total hemispherical emissivity at cryogenic temperatures before and after the coating process. Contribution of Al2O3 layer to original copper emissivity increased with rising temperature of the layer and with the layer thickness. However, emissivity of the coated copper stayed below 2%, allowing usage of the coated copper in systems where low heat load by thermal radiation is needed. Preliminary tests with oxygen plasma shows that deposited layers can effectively protect the copper surface against oxidation and maintain the original thermal-radiative properties. Keywords: heat transfer; thermal radiation; cryogenics; surface finish Available at various institutes of the ASCR
Low-temperature emissivity of thin Al2O3 layers deposited on copper substrate

Copper is commonly used in cryogenic systems due to its high thermal and electrical conductivity along with excellent solderability. Very low emissivity values of copper surface also reduce in ...

Frolec, Jiří; Králík, Tomáš; Nyman, L.; Pudas, M.; Kallio, E.
Ústav přístrojové techniky, 2021

Patterning of conductive nano-layers on garnet
Chlumská, Jana; Lalinský, Ondřej; Matějka, Milan; Krátký, Stanislav; Kolařík, Vladimír
2021 - English
Synthetic crystalline materials of the garnet group are used as scintillators in scanning electron microscopy. If a thick conductive layer is applied on the garnet surface, slower electrons don't have enough energy to pass through this relatively thick conductive layer on the scintillator surface. Therefore, either thinner conductive layer or appropriate patterning of the thicker layer has to be used. Within this contribution we study the patterning process of such conductive nano-layer. Resolution of the patterning process is of high interest. Two approaches are compared: direct writing electron beam lithography and mask projection UV lithography. Keywords: Electron beam lithography; nano-patterning; yttrium aluminium garnet Available at various institutes of the ASCR
Patterning of conductive nano-layers on garnet

Synthetic crystalline materials of the garnet group are used as scintillators in scanning electron microscopy. If a thick conductive layer is applied on the garnet surface, slower electrons don't have ...

Chlumská, Jana; Lalinský, Ondřej; Matějka, Milan; Krátký, Stanislav; Kolařík, Vladimír
Ústav přístrojové techniky, 2021

A sampler of diffraction and refraction optically variable image elements
Horáček, Miroslav; Krátký, Stanislav; Matějka, Milan; Chlumská, Jana; Meluzín, Petr; Pirunčík, J.; Aubrecht, I.; Kotrlý, M.; Kolařík, Vladimír
2021 - English
Diffraction and refraction optically variable image elements are basic building blocks of planar structures for advanced security of documents and valuables. A sampler formed by an array of 36 diffraction structures binary, tertiary, quaternary and blazed gratings (period range 400 nm 20,000 nm) represents a cross-section throughout technological steps mastering, galvanic replication and embossing. Electron-beam writing technology with Gaussian beam and electron energy of 100 keV, with very small forward scattering of high energy electrons and with the possibilities to create a linear grating with the minimal period of 100 nm, was used to create the master. An important advantage of high-resolution electron-beam lithography is its substantial flexibility in combining possible planar structures with significantly different parameters, such as very dense and relatively shallow structures together with deep structures (approx. 10 microns) with precise shapes (micro-lenses or Fresnel structures). For protection of documents and valuables, interesting results are induced with planar optical structures consisting of non-periodic arrangements, which are characterized by high robustness to counterfeiting and imitation. While the origination process is available for grating period down to 100 nm, the mass replication technology appears to be a bottleneck of the entire technological process. Measurement of topology and profiles of the structures by atomic forces microscope and documenting the quality of technological process of the three steps of replication of planar optically variable elements was performed for all 36 structure types of sampler. Keywords: diffraction; refraction; e-beam writer; embossing; galvanic replication; mastering; optically variable image element; security; valuables Available at various institutes of the ASCR
A sampler of diffraction and refraction optically variable image elements

Diffraction and refraction optically variable image elements are basic building blocks of planar structures for advanced security of documents and valuables. A sampler formed by an array of 36 ...

Horáček, Miroslav; Krátký, Stanislav; Matějka, Milan; Chlumská, Jana; Meluzín, Petr; Pirunčík, J.; Aubrecht, I.; Kotrlý, M.; Kolařík, Vladimír
Ústav přístrojové techniky, 2021

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