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Surface acoustic waves in the layered systems
Tarasenko, Alexander; Boháč, Petr; Jastrabík, Lubomír
2016 - anglický
The laser acoustic method was used for analysis of two layered systems: thin titanium and diamond like carbon films both deposited on silicon. The film and substrate parameters are determined by fitting the theoretical curve to the measured dispersion curve. The fit software seeks that set of the system parameters whose theoretical curve coincides the best with the experimental data. For the titanium film the best root-mean square deviation was 2.04 m/s with the relative error < O.I % and for the DLC system the corresponding value was 0.30 m/s (the relative error < O.O1 % ).
Klíčová slova:
laser acoustic method; surface acoustic waves; layered systems; Ti films; diamond-like carbon films
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Surface acoustic waves in the layered systems
The laser acoustic method was used for analysis of two layered systems: thin titanium and diamond like carbon films both deposited on silicon. The film and substrate parameters are determined by ...
Laser-driven ablation through fast electrons in PALS experiment
Gus'kov, S. Yu.; Chodukowski, T.; Demchenko, N.; Kalinowska, Z.; Kasperczuk, A.; Krouský, Eduard; Pfeifer, Miroslav; Pisarczyk, P.; Pisarczyk, T.; Renner, Oldřich; Skála, Jiří; Šmíd, Michal; Ullschmied, Jiří
2016 - anglický
Energy transfer to shock wave in Al and Cu targets irradiated by a laser pulse with intensity of I~1-50 PW/cm2 and duration of 250 ps was investigated at Prague Asterix Laser System (PALS). The iodine laser provided energy in the range of 100-600 J at the first and third harmonic frequencies. The focal spot radius of laser beam on the target was varied from 160 to 40 µm. The dominant contribution of fast electron energy transfer into the ablation process was found when using the first harmonic radiation, the focal spot radius of 40-100 µm, and the energy of 300-600 J. The fast electron heating results in the growth of ablation pressure from 60 Mbar at the intensity of 10 PW/cm2 to 180 Mbar at the intensity of 50 PW/cm2 and in the growth of the efficiency of the energy conversion into the shock wave from 2 to 7 % under the conditions of 2D ablation.
Klíčová slova:
laser-produced plasma; ablation pressure
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Laser-driven ablation through fast electrons in PALS experiment
Energy transfer to shock wave in Al and Cu targets irradiated by a laser pulse with intensity of I~1-50 PW/cm2 and duration of 250 ps was investigated at Prague Asterix Laser System (PALS). The iodine ...
Geometric resonances in reflectivity spectra of lead zirconate
Dočekalová, Zuzana; Hlinka, Jiří
2016 - anglický
The paper deals with effects of domain boundaries on the THz–frequency range dispersion of the complex dielectric permitivity tensor of lead zirconate. In the case of a sufficiently narrow domain widths (in comparison to the wave–length of the light used in the experiment), the effective–medium average permittivity shows additional peaks identified as geometric resonances, i.e. extraneous excitations created by thematerial interface. Features of the far–infrared reflectivity spectra of the twinned lead zirconate crystal in the limit of narrow and wide domains are estimated with the\nhelp of the damped harmonic oscillator model with paramaters fully determined fromrecent experiments.
Klíčová slova:
geometric resonances; lead zirconate; antiferroelectrics; reflectivity; phonon
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Geometric resonances in reflectivity spectra of lead zirconate
The paper deals with effects of domain boundaries on the THz–frequency range dispersion of the complex dielectric permitivity tensor of lead zirconate. In the case of a sufficiently narrow domain ...
Cryogenic cooling system Brayton for 10 J/10 Hz Yb:YAG multi-slab based laser system at ELI-Beamlines project
Schustr, P.; Fibrich, Martin; Polan, Jiří; Rus, Bedřich; Dostálová, M.; Valdislav, P.; Simek, J.
2016 - anglický
We present design and operational prototype of cryogenic cooling system based on Bryton's cycle for 10J/10Hz Yb:YAG multi-slab laser system at ELI-Beamlines project.
Klíčová slova:
Brayton; cryogenics; laser; cooling; ytterbium; design; prototype
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Cryogenic cooling system Brayton for 10 J/10 Hz Yb:YAG multi-slab based laser system at ELI-Beamlines project
We present design and operational prototype of cryogenic cooling system based on Bryton's cycle for 10J/10Hz Yb:YAG multi-slab laser system at ELI-Beamlines project.
Microscopic characterization of graphene material and electronic quality across neighbouring, differently oriented copper grains
Čermák, Jan; Yamada, T.; Ganzerová, Kristína; Rezek, Bohuslav
2015 - anglický
We study graphene grown across the boundary of three such grains having bright, medium, and dark color in reflection. Raman micro-spectroscopy proves presence of mostly a monoor bi-layer graphene on all the grains. Yet intensity of Raman 2D band is grain-dependent: highest at the darkest grain and lowest at the brightest one. Contrary, conductive atomic force microscopy detects the highest conductivity at the brightest grain and the lowest current at the darkest grain. This is attributed to dominant electrical current path through graphene and underlying oxide thickness of which also depends on the type of copper grain. We correlate and discuss the results with view to better understanding of graphene growth and electronic properties on large area copper substrates.
Klíčová slova:
graphene; chemical vapor deposition; atomic force microscopy; Raman spectroscopy; electronic properties
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Microscopic characterization of graphene material and electronic quality across neighbouring, differently oriented copper grains
We study graphene grown across the boundary of three such grains having bright, medium, and dark color in reflection. Raman micro-spectroscopy proves presence of mostly a monoor bi-layer graphene on ...
Magnetic domains under mechanical stress in single crystal Ni-Mn-Ga
Kopecký, Vít; Heczko, Oleg
2015 - anglický
The complexity of Ni-Mn-Ga single crystal lies in combination of ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure for different twinned microstructure was studied using magneto-optical indicator film. Different orientations of magnetic domains can be observed at the same place of the sample thanks to magnetically induced structural reorientation by movement of twin boundaries. We investigated experimentally the changes of magnetic domain structure in the vicinity of mobile a/c twin boundary.
Klíčová slova:
Ni-Mn-Ga; magnetic domains; twin boundary
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Magnetic domains under mechanical stress in single crystal Ni-Mn-Ga
The complexity of Ni-Mn-Ga single crystal lies in combination of ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure for different twinned ...
Diamond coated AlGaN/GaN high electron mobility transistors - effect of deposition process on gate electrode
Vanko, G.; Ižák, Tibor; Babchenko, O.; Kromka, Alexander
2015 - anglický
We studied the influence of the diamond deposition on the degradation of Schottky gate electrodes (i.e. Ir or IrO2) and on the electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs). In present study, the diamond films were selectively deposited on the AlGaN/GaN circular HEMT by focused (ellispoidal cavity reactor) and linear antenna (surface wave) microwave plasma at different temperatures from 400°C to 1100°C. The preliminary results on electrical measurements on the diamond-coated c-HEMTs showed degraded electrical properties comparing to c-HEMTs before deposition process, which was attributed to degradation of the Ir gate electrodes even at temperatures as low as 400°C. On the other hand, metal oxide gate electrode layer (IrO2) can withstand diamond CVD process even at high temperatures (~900°C) which make it suitable for fabrication of all-in-diamond c-HEMT devices for high-power applications.
Klíčová slova:
GaN HEMT; CVD diamond; iridium oxide; thermal stability; IV characteristics
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Diamond coated AlGaN/GaN high electron mobility transistors - effect of deposition process on gate electrode
We studied the influence of the diamond deposition on the degradation of Schottky gate electrodes (i.e. Ir or IrO2) and on the electrical characteristics of AlGaN/GaN high electron mobility ...
Scanning thermal microscopy of thermoelectric pulsed laser deposited nanostructures
Vaniš, Jan; Zelinka, Jiří; Zeipl, Radek; Jelínek, Miroslav; Kocourek, Tomáš; Remsa, Jan; Navrátil, Jiří
2015 - anglický
New materials with high possible figure of merit ZT are of high interest as a promising candidates for thermoelectric applications such as energy harvesting. Miniaturization of such systems tends toward developing of the suitable characterization method with nanometer resolution ability. In our contribution, we present the development and experimental results of a simple scanning probe microscopy method for the relative thermal conductivity characterization. The possibility of the setup is demonstrated on the set of different thin thermoelectric layers grown from hot pressed targets by pulsed laser deposition on the reference Si substrate. All the measurements were performed on the commercial Veeco Multimode scanning AFM/STM microscope with home developed controller and by using PicoCal Inc. bolometer probes with tungsten resistive path. All the experiments were done in the air at the ambient condition. Additional sample treatment for the measurement will be also briefly described
Klíčová slova:
Scanning thermal microscopy; figure of merit; thermoeletric materials
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Scanning thermal microscopy of thermoelectric pulsed laser deposited nanostructures
New materials with high possible figure of merit ZT are of high interest as a promising candidates for thermoelectric applications such as energy harvesting. Miniaturization of such systems tends ...
Modeling of nanofibers interaction with the environment
Klicmanová, I.; Sveshnikov, Alexey
2015 - anglický
Nanomaterials change our life. Every day they find applications in new branches of technology. At the same time, some branches of technology, like civil engineering, are rather conservative and do not accept new approaches lightly. Nanotextiles exhibit a number of qualities that make them a promising material for civil engineering applications. They can potentially play a role of filters, protective layers, armature and others. Properties of the nanotextiles can be significantly influenced by parameters of technological process. Pure experimental search of the optimal technological parameters to achieve the desired properties of the final material can be very tedious. Thus, a theoretical dependence of the properties of the nanotextile on parameters of the technological process must be established. Two independent tasks must be solved for this: the dependence of nanotextile structure on technological parameters, and determination of physical, chemical or biological properties of a nanotextile of a given structure. In this paper we discuss steps necessary for the solution of the second task.
Klíčová slova:
Van der Waals; DLVO potential; Monte Carlo simulations
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Modeling of nanofibers interaction with the environment
Nanomaterials change our life. Every day they find applications in new branches of technology. At the same time, some branches of technology, like civil engineering, are rather conservative and do not ...
Study of photocatalytic activity of Zn.sub.x./sub.Cd.sub.1-x./sub.S quantum dots in dependence on their composition using methylene blue
Praus, P.; Svoboda, L.; Hospodková, Alice; Mamulová Kutláková, K.
2015 - anglický
ZnCdS quantum dots (QDs) with the different composition were prepared by precipitation of zinc and cadmium acetates with sodium sulphide in the presence of cetyltrimethylammonium bromide (CTAB) used for stabilization of their aqueous colloid dispersions. Transition energies of these quantum dots were determined from the UV-VIS spectra of QDs colloid dispersions and consequently used for calculation of the QDs sizes according to the Schrodinger equation. The ZnCdS QDs size was found to be significantly influenced by their composition: the QDs size decreased with the increasing Zn content. The photocatalytic activity of the ZnCdS QDs was studied using the methylene blue decomposition under UV irradiation. Different photocatalytic activity depending on the composition x was observed and explained. The maximal photocatalytic activity was achieved for x = 0.6 when the energy of the irradiation photons was still sufficient to generate electron-hole pairs in majority of the QDs and at the same time the photocatalytic surface area was maximal.\n
Klíčová slova:
quantum dots; ZnCdS; photocatalysis; UV-VIS absorption; x-ray diffraction
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Study of photocatalytic activity of Zn.sub.x./sub.Cd.sub.1-x./sub.S quantum dots in dependence on their composition using methylene blue
ZnCdS quantum dots (QDs) with the different composition were prepared by precipitation of zinc and cadmium acetates with sodium sulphide in the presence of cetyltrimethylammonium bromide (CTAB) used ...
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