Number of found documents: 597
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In vivo study of diatom assemblages using low temperature method for ESEM
Tihlaříková, Eva; Neděla, Vilém; Fránková, Markéta
2017 - English
Diatoms are the most species-rich algal group represented by 12 000 described species and are recognized as powerful bio indicators and used for water quality monitoring. Diatom taxonomy is predominantly based on the morphology of ornate silicified cell wall called frustule composed of two overlapping parts (thecae). This frustule displays intricate patterns and designs unique to each species. For these studies conventional scanning electron microscopy (SEM) was and still is widely used. This method requires cleaning of diatom frustules in strong acids and peroxides followed by conductive coating.This aggressive procedure removes protoplast and damages delicate structures. Environmental scanning electron microscopy (ESEM) brings advantages of observation of fresh diatom material that are presence of whole intact diatom cells, not only empty diatom frustules, extracellular mucilaginous diatom secrets (e.g. pads, stalks, tubes) and whole diatom assemblages directly in situ together with other algal assemblages (e.g. cyanobacteria or green algae). However, in diatom research, ESEM is used mainly for elimination of conductive coating and observation of these organisms in their native wet state adhered directly on the host plant is not yet common. The ESEM observation of native aquatic samples is usually affected with radiation damage that can be lovered by the use of special methods like the Low Temperature Method (LTM) for the ESEM. Keywords: ESEM; diatom; morphology; LTM Available at various institutes of the ASCR
In vivo study of diatom assemblages using low temperature method for ESEM

Diatoms are the most species-rich algal group represented by 12 000 described species and are recognized as powerful bio indicators and used for water quality monitoring. Diatom taxonomy is ...

Tihlaříková, Eva; Neděla, Vilém; Fránková, Markéta
Ústav přístrojové techniky, 2017

Nanopatterning of Silicon Nitride Membranes
Matějka, Milan; Krátký, Stanislav; Řiháček, Tomáš; Kolařík, Vladimír; Chlumská, Jana; Urbánek, Michal
2017 - English
Membranes are typically created by a thin silicon nitride (SIN) layer deposited on a silicon wafer. Both, top and bottom side of the wafer is covered by a thin layer of the silicon nitride. The principle of silicon nitride membranes preparation is based on the wet anisotropic etching of the bottom side of the silicon wafer with crystallographic orientation (100). While the basic procedure for the preparation of such membranes is well known, the nano patterning of thin membranes presents quite important challenges. This is partially due to the mechanical stress which is typically presented within such membranes. The resolution requirements of the\nmembrane patterning have gradually increased. Advanced lithographic techniques and etching procedures had to be developed. This paper summarizes theoretical aspects, technological issues and achieved results. The application potential of silicon nitride membranes as a base for multifunctional micro system (MMS) is also\ndiscussed. Keywords: e-beam writer; silicon nitride membranes; nano patterning; anisotropic etching Available at various institutes of the ASCR
Nanopatterning of Silicon Nitride Membranes

Membranes are typically created by a thin silicon nitride (SIN) layer deposited on a silicon wafer. Both, top and bottom side of the wafer is covered by a thin layer of the silicon nitride. The ...

Matějka, Milan; Krátký, Stanislav; Řiháček, Tomáš; Kolařík, Vladimír; Chlumská, Jana; Urbánek, Michal
Ústav přístrojové techniky, 2017

Effect of gold coating on emissivity and absorptivity of Ti-6Al-4V alloy
Frolec, Jiří; Králík, Tomáš; Musilová, Věra; Urban, Pavel
2017 - English
The article provides experimental analysis of total hemispherical emissivity and absorptivity of Ti-6Al-4V alloy before and after deposition of 1-2 .pí.m gold layer. We measured their dependences on the temperature of thermal radiation (varying from 20 K to 320 K) and confronted these results with mechanically polished copper, i.e. with material known for extremely low emissivity and absorptivity. Galvanic deposition of pure gold resulted in significant lowering of original emissivity of Ti-6Al-4V bare surfaces from 15.8 percent to 3.4 percent at 300 K and from 4.1 percent to 1.1 percent at 20 K. Our findings about thermal-radiative properties have practical relevance for an improvement of a low temperature part of an ultra-high vacuum scanning probe microscope\n(UHV-SPM) designed by our group and could also be useful for other applications and low temperature systems. Keywords: cryogenics; gold films; heat transfer; thermal radiation Available at various institutes of the ASCR
Effect of gold coating on emissivity and absorptivity of Ti-6Al-4V alloy

The article provides experimental analysis of total hemispherical emissivity and absorptivity of Ti-6Al-4V alloy before and after deposition of 1-2 .pí.m gold layer. We measured their dependences on ...

Frolec, Jiří; Králík, Tomáš; Musilová, Věra; Urban, Pavel
Ústav přístrojové techniky, 2017

Role of the superconductivity in radiative heat transfer
Králík, Tomáš; Musilová, Věra; Srnka, Aleš; Fořt, Tomáš; Frolec, Jiří
2017 - English
The absorption and emission of thermal radiation by metals is related to their electrical properties that are influenced by impurities, defects and temperature. We show by some examples of measurements on common metals how different can be the thermal radiative properties. When the heat is transferred across a microscopic vacuum gap in the near field regime, it is possible to achieve a step-like change of the heat\ntransfer based on a superconducting transition. An interesting feature of this effect is the nonlinear thermal conductivity effecting a change of the sign of the differential thermal conductivity across the vacuum gap. Keywords: thermal radiation; near field; superconductivity Available at various institutes of the ASCR
Role of the superconductivity in radiative heat transfer

The absorption and emission of thermal radiation by metals is related to their electrical properties that are influenced by impurities, defects and temperature. We show by some examples of ...

Králík, Tomáš; Musilová, Věra; Srnka, Aleš; Fořt, Tomáš; Frolec, Jiří
Ústav přístrojové techniky, 2017

Parameter Optimization of Multi-Level Diffraction Gratings
Matějka, Milan; Kolařík, Vladimír; Horáček, Miroslav; Král, Stanislav
2017 - English
Originally, the e-beam lithography (EBL) is a technique for creating high-resolution black and white masks for the optical lithography. Multi-level relief structures can be also prepared using EBL patterning. Their preparation is based on the image patterning with a gradient of exposure doses. Large-area multi-level structures can be effectively prepared using the electron beam pattern generator with a variable shaped beam. We present several writing strategies. Basically, the main writing strategy uses one stamp (i.e. one elementary exposure of the shaped electron beam) per one elementary area with the same exposure dose. This simple approach is fast and flexible, however it does not guarantee optimal results. The main problem is an imperfection of the stamps (size, shape, and homogeneity). Advanced algorithms are based on multiple\nexposure of the same elementary area, the total local exposure dose is a sum of several different elementary exposures (stamps). Using these algorithms, a smoother surface of the structure can be achieved. On the other hand, the writing speed is considerably decreased. Tradeoff between the achieved parameters and the writing speed is discussed for selected set of writing strategy algorithms. Keywords: e-beam pattern generator; variable shaped beam; grayscale lithography; multi-level grating Available at various institutes of the ASCR
Parameter Optimization of Multi-Level Diffraction Gratings

Originally, the e-beam lithography (EBL) is a technique for creating high-resolution black and white masks for the optical lithography. Multi-level relief structures can be also prepared using EBL ...

Matějka, Milan; Kolařík, Vladimír; Horáček, Miroslav; Král, Stanislav
Ústav přístrojové techniky, 2017

Noise behaviour of field emission cathode based on lead pencil graphite
Knápek, Alexandr; Horáček, Miroslav; Hrubý, František; Šikula, J.; Kuparowitz, T.; Sobola, D.
2017 - English
The paper describes electrical noise of experimental field emission cathodes based on “polymer” pencil leads which have a high content of hybridized carbon with a low degree of surface oxidation and silicon monoxide (SiO). Charge transport within experimental samples is evaluated based on results provided by the noise spectroscopy method. The paper also briefly describes the experimental preparation method of graphite tips based on ion milling which allow obtaining ultrasharp tips of a diameter lower than 100 nm. Keywords: field emission; lead pencil graphite; noise spectroscopy Available at various institutes of the ASCR
Noise behaviour of field emission cathode based on lead pencil graphite

The paper describes electrical noise of experimental field emission cathodes based on “polymer” pencil leads which have a high content of hybridized carbon with a low degree of surface oxidation and ...

Knápek, Alexandr; Horáček, Miroslav; Hrubý, František; Šikula, J.; Kuparowitz, T.; Sobola, D.
Ústav přístrojové techniky, 2017

Resampling in magnetic resonance spectroscopy-A less model-dependent quantitation quality assessment method
Jabłoński, Michal; Starčuková, Jana; Starčuk jr., Zenon
2017 - English
In this paper we propose a novel method for magnetic resonance spectroscopy (MRS) fitting quality assessment based on time domain resampling of acquired spectra and bootstrapping of the obtained results. The authors introduce two resampling strategies and example results are shown. The proposed method requires MRS data without averaging. Keywords: magnetic resonance spektroscopy; quantitation; fitting Quality Assessment Available at various institutes of the ASCR
Resampling in magnetic resonance spectroscopy-A less model-dependent quantitation quality assessment method

In this paper we propose a novel method for magnetic resonance spectroscopy (MRS) fitting quality assessment based on time domain resampling of acquired spectra and bootstrapping of the obtained ...

Jabłoński, Michal; Starčuková, Jana; Starčuk jr., Zenon
Ústav přístrojové techniky, 2017

Examination of 2D crystals in a low voltage SEM/STEM
Mikmeková, Eliška; Frank, Luděk; Polčák, J.; Paták, Aleš; Lejeune, M.
2017 - English
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. Keywords: low voltage SEM/STEM; 2D crystals; contamination Available at various institutes of the ASCR
Examination of 2D crystals in a low voltage SEM/STEM

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” ...

Mikmeková, Eliška; Frank, Luděk; Polčák, J.; Paták, Aleš; Lejeune, M.
Ústav přístrojové techniky, 2017

K-space trajectory calibration for improved precision of quantitative ultrashort echo time imaging
Latta, P.; Starčuk jr., Zenon; Gruwel, M.; Tomanek, B.
2017 - English
Ultrashort echo time imaging (UTE) is often the method of choice for measurement of short-lived T2 signals from biological tissues. The UTE acquisition is based on radial or spiral sampling schemes which, in general, are sensitive to small discrepancies between prescribed and actual trajectories. Such errors are usually observed as image quality degradation, visible as ghosting or intensity variation. This is even more serious for quantitative applications when intensity variation can cause serious bias in the estimation of measured parameters such as proton density (PD). Here we investigate such behavior of UTE acquisition and demonstrate that proper calibration of the gradient channels could minimize these type of the errors. Phantom experiments proved the efficiency of the application trajectory calibration approach. Keywords: ultrashort Echo Time (UTE); K-space Trajectory Calibration; proton Density Available at various institutes of the ASCR
K-space trajectory calibration for improved precision of quantitative ultrashort echo time imaging

Ultrashort echo time imaging (UTE) is often the method of choice for measurement of short-lived T2 signals from biological tissues. The UTE acquisition is based on radial or spiral sampling schemes ...

Latta, P.; Starčuk jr., Zenon; Gruwel, M.; Tomanek, B.
Ústav přístrojové techniky, 2017

Effect of thermal radiation on low temperature measurement for various types of temperature sensor installations
Urban, Pavel; Hanzelka, Pavel; Králík, Tomáš; Vlček, Ivan; Srnka, Aleš
2017 - English
We investigated an effect of thermal radiation (300 K) on precision of low temperature measurement of a sample holder (or sample) in an UHV SEM/SPM microscope working at range down to 20 K for various ways of temperature sensor mounting. We designed a special copper casing for installation of Lake Shore\ntemperature sensors (CernoxTM and Si diodes) encapsulated in SD packages. The sensor body is attached direct to the casing using indium solder. The current leads pertaining to the sensor are thermally anchored but electrically insulated from the casing. Quality of sensors installation in the casing was tested for various ways of mounting on a cooled plate. Insufficient thermal anchoring of electrical wires and thermal shielding were imitated. Comparative measurement was also performed with sensors in SD package mounted without\ncasing. The experiments proved that our special design of temperature sensors casing is adequate for intended application of temperature measurement of sample holder in UHV SEM/SPM microscope. In contrary, measurement precision of unprotected sensors was absolutely unsuitable. Keywords: low temperature; temperature sensor; thermal radiation Available at various institutes of the ASCR
Effect of thermal radiation on low temperature measurement for various types of temperature sensor installations

We investigated an effect of thermal radiation (300 K) on precision of low temperature measurement of a sample holder (or sample) in an UHV SEM/SPM microscope working at range down to 20 K for various ...

Urban, Pavel; Hanzelka, Pavel; Králík, Tomáš; Vlček, Ivan; Srnka, Aleš
Ústav přístrojové techniky, 2017

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