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Low-temperature emissivity of thin Al2O3 layers deposited on copper substrate
Frolec, Jiří; Králík, Tomáš; Nyman, L.; Pudas, M.; Kallio, E.
2021 - anglický
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.
Klíčová slova:
heat transfer; thermal radiation; cryogenics; surface finish
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Nanostructured layer enhancing light extraction from GaN-based scintillator using MOVPE
Vaněk, Tomáš; Hubáček, Tomáš; Hájek, František; Dominec, Filip; Pangrác, Jiří; Kuldová, Karla; Oswald, Jiří; Hospodková, Alice
2021 - anglický
Light extraction (LE) efficiency of GaN buffer layer was studied by angle-resolved photoluminescence. We measured enhancement of light extraction efficiency (LEE) up to 154% by introducing the SiNx layer atop the GaN buffer and subsequent GaN light extraction layer (LEL) overgrowth. Morphological properties of GaN.
Klíčová slova:
MOVPE; GaN; light extraction; SiNx; scintillator
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Nanostructured layer enhancing light extraction from GaN-based scintillator using MOVPE
Light extraction (LE) efficiency of GaN buffer layer was studied by angle-resolved photoluminescence. We measured enhancement of light extraction efficiency (LEE) up to 154% by introducing the SiNx ...
Structural and magnetic properties of Fe-oxide layers prepared by inkjet printing on Si-substrate
Zažímal, František; Svoboda, T.; Dzik, P.; Homola, T.; Jirásková, Yvonna
2021 - anglický
Magnetic films with two, four, six, and eight layers were prepared using 2D inkjet printing on the 333 K heated Si-substrates at ambient conditions. The microstructure, phase composition of layers, and magnetic studies were investigated using wide spectrum of experimental methods with the aim to find the optimal conditions for producing magnetic sensors by digital printing technology in the near future. As the magnetic compound, the hematite powder was chosen and its milling with Si-binder dissolved in dowanol using glass balls and vial to prevent contamination was done to prepared suspension appropriate for printing. It is shown that hematite transformed markedly into maghemite, thus the layers consisted of small amount hematite and dominant maghemite phases determining the magnetic properties. From the viewpoint of magnetic behavior, the highest saturation magnetization and the lowest coercivity was obtained at the sample with 8 layers.
Klíčová slova:
Inkjet printing; hematite; physical properties; testing methods
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Structural and magnetic properties of Fe-oxide layers prepared by inkjet printing on Si-substrate
Magnetic films with two, four, six, and eight layers were prepared using 2D inkjet printing on the 333 K heated Si-substrates at ambient conditions. The microstructure, phase composition of layers, ...
Patterning of conductive nano-layers on garnet
Chlumská, Jana; Lalinský, Ondřej; Matějka, Milan; Krátký, Stanislav; Kolařík, Vladimír
2021 - anglický
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.
Klíčová slova:
Electron beam lithography; nano-patterning; yttrium aluminium garnet
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Solving the moving mass problem on large finite element models with modal analysis – estimation of the discrete movement error
Bayer, Jan
2021 - anglický
Solving transient dynamic problems on large finite element (FE) models using a direct integration requires a high sampling rate and therefore also considerable computing times because of the large system matrices. Movement of a mass on a FE model has to follow the discrete pattern of the FEs, and is therefore of a discrete character. This introduces an unknown\nerror into the analytical results. Applying modal analysis (MA) reduces the number of equations used in the subsequent numerical integration by orders of magnitude. Resampling of the mode shapes to the required sampling rate makes it possible to solve the moving mass problem much more quickly and quasi-continuously. The performed comparative analytical study using ANSYS and MATLAB showed that using a discrete movement on the FE mesh when solving a moving mass problem can cause a considerable error.
Klíčová slova:
moving mass; FE analysis; modal analysis; discret-movement error; ANSYS & MATLAB
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Solving the moving mass problem on large finite element models with modal analysis – estimation of the discrete movement error
Solving transient dynamic problems on large finite element (FE) models using a direct integration requires a high sampling rate and therefore also considerable computing times because of the large ...
Description of the quasi-periodic response caused by combined harmonic and random excitation
Náprstek, Jiří; Fischer, Cyril
2021 - anglický
The generalized van der Pol equation exposed to combined harmonic and random excitation can exhibit a quasi-periodic response. The existence of this particular type of response depends on the detuning between the driving and resonance frequencies. The response is stationary for a ”small” or ”large” value of detuning. The contribution specifies in detail the detuning interval in which the quasi-periodic response occurs.
Klíčová slova:
van der Pol equation; resonance; vibrations
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Description of the quasi-periodic response caused by combined harmonic and random excitation
The generalized van der Pol equation exposed to combined harmonic and random excitation can exhibit a quasi-periodic response. The existence of this particular type of response depends on the detuning ...
Effect of the substrate crystalline orientation on the surface morphology and boron incorporation into epitaxial diamond layers
Voves, J.; Pošta, A.; Davydova, Marina; Laposa, A.; Povolný, V.; Hazdra, P.; Lambert, Nicolas; Sedláková, Silvia; Mortet, Vincent
2021 - anglický
Epitaxial growth of diamond is critically important for the fabrication of diamond-based electronic devices. The emerging study of the epitaxial diamond growth on the (113) vicinal surfaces evidences highly needed high growth rates and low structural defects concentrations with both p- and n-type doping. In this work, we compare the morphology and dopant concentration incorporation of heavily boron-doped (113) epitaxial diamond layers with conventionally studied (100) and (111) epitaxial layers. Epitaxial layers were grown using resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) system. The surface morphology of epitaxial layers was studied by optical microscopy and atomic force microscopy, whereas the boron incorporation homogeneity was determined by Raman spectroscopy mapping.
Klíčová slova:
diamond; epitaxy; defects; boron doping; Raman mapping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Effect of the substrate crystalline orientation on the surface morphology and boron incorporation into epitaxial diamond layers
Epitaxial growth of diamond is critically important for the fabrication of diamond-based electronic devices. The emerging study of the epitaxial diamond growth on the (113) vicinal surfaces evidences ...
Deep learning methods for acoustic emission evaluation
Kovanda, M.; Chlada, Milan
2021 - anglický
The goal of this paper is to show the possibilities of state-of-the-art deep learning methods for ultrasound signals evaluation. Several neural network architectures are applied to\nacoustic emission signals measured during the tensile tests of metallic specimen to determine the beginning of plasticity in the material. Plastic deformation is accompanied by microscopic\nevents such as a slip of atomic plane dislocations which is hardly detectable by other methods. The potential of machine learning is demonstrated on two tensile tests where the material is\nstrained until it collapses. The examined networks proved well to reliably predict the risk of collapse together with changes in the ultrasound emission signals.
Klíčová slova:
acoustic emission; deep learning; machine learning; plastic deformation; time series classification
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Deep learning methods for acoustic emission evaluation
The goal of this paper is to show the possibilities of state-of-the-art deep learning methods for ultrasound signals evaluation. Several neural network architectures are applied to\nacoustic emission ...
RTIN-based strategies for local mesh refinement
Kolcun, Alexej; Sysala, Stanislav
2021 - anglický
Longest-edge bisection algorithms are often used for local mesh refinements within the finite element method in 2D. In this paper, we discuss and describe their conforming variant. A particular attention is devoted to the so-called Right-Triangulated Irregular Network (RTIN) based on isosceles right triangles and its tranformation to more general domains. We suggest to combine RTIN with a balanced quadrant tree (QuadTree) decomposition. This combination does not produce hanging nodes within the mesh refinements and could be extended to tetrahedral meshes in 3D.
Klíčová slova:
mesh refinement; longest-edge bisection; right-triangulated irregular network; balanced quadrant tree; homomorphic transformation
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
RTIN-based strategies for local mesh refinement
Longest-edge bisection algorithms are often used for local mesh refinements within the finite element method in 2D. In this paper, we discuss and describe their conforming variant. A particular ...
Nucleation criteria detection as a mean to investigate metastable state
Celný, David; Span, R.; Vrabec, J.
2021 - anglický
Focus is given to the core problematic, reaching the nucleation region and sample the relevant data for selected pure substance. This termodynamic condition required for nucleation are found in so called metastable region. Metastable region is found between binodal and spinodal line separating it from the stable and unstable system condition respectively.\nObtaining the data in this area proves to be an experimental challenge, therefore the data has to be gathered using other means. Proposed setup relies two part approach combining equation of state (EoS) and molecular simulation. The computational core is done with molecular dynamics tool combined with on the fly performing decision cluster criterion utilized is already available in previously published work. These cluster criteria ensure that the system is only calculated within targeted conditions and the sampled micro-states remain valid observations. To capture whole metastable region two criteria are present for both cluster and void case as illustrated below. Remaining part utilize the equation of state for the initial system condition sampling of the metastable region by calculating the stability line and predicting the instability line for the LJ fluid as show in Linhart et.al. . These thermodynamic condition probes are evaluated afterwards with the established simulation method. Intermediate result from simulations are collected in form of both Helmholtz energy temperature and density derivatives descriptors as well as time averages of system properties for fluids like LJ, Oxygen and Nitrogen.
Klíčová slova:
metastable state; equation of state; molecular dynamics; cluster criterion
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Nucleation criteria detection as a mean to investigate metastable state
Focus is given to the core problematic, reaching the nucleation region and sample the relevant data for selected pure substance. This termodynamic condition required for nucleation are found in so ...
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