Nejdůležitější publikace 1. období (MATE)

Nejdůležitější odborné publikace vydané během prvního období (do 31. března 2019). Seznam všech publikací výzkumného programu MATE vydaných v rámci projektu CAAS najdete v předchozím příspěvku.

Thermoelectric properties of the tetrahedrite–tennantite solid solutions Cu12Sb4−xAsxS13 and Cu10Co2Sb4−yAsyS13 (0 ≤ xy ≤ 4)
Petr Levinsky, Christophe Candolfi, Anne Dauscher, Janusz Tobola, Jiří Hejtmánek, Bertrand Lenoir
Physical Chemistry Chemical Physics, Issue 8, 2019
Tetrahedrites, a class of copper- and sulfur-rich minerals, exhibit inherently very low lattice thermal conductivity and adjustable electronic properties that make them interesting candidates for thermoelectric applications. Here, we investigate the influence of isovalent As substitution on the Sb site on the structural and transport properties (5–700 K) of the two solid solutions Cu12Sb4−xAsxS13 and Cu10Co2Sb4−yAsyS13 (0 ≤ xy ≤ 4). Electronic band structure calculations predict that As has only a weak influence on the valence bands and hence, on the p-type metallic character of Cu12Sb4S13. In agreement with these predictions, all the samples of the series Cu12Sb4−xAsxS13 exhibit p-type metallic behavior with relatively low electrical resistivity and moderate thermopower values that only slightly evolve with the As content. In contrast, the substitution of Co for Cu in As-rich samples seems less favorable as suggested by a decrease in the Co concentration with increasing the As content. This trend leads to a concomitant increase in the electrical resistivity and thermopower leaving the ZTvalues practically unchanged with respect to purely Cu-based samples. As a result, peak ZT values ranging between 0.60 and 0.75 are achieved at 700 K for both series. The lack of significant variations in the ZT values confirms the robustness of the thermoelectric performances of tetrahedrites with respect to variations in the Sb-to-As ratio.

Atomic-scale design of friction and energy dissipation
Antonio Cammarata, Paolo Nicolini, Kosta Simonovic, Egor Ukraintsev, Tomas Polcar
Phys. Rev. B 99, 094309 – Published 25 March 2019
Study of friction and energy dissipation always relied on direct observations. Actual theories provide limited prediction on the frictional and dissipative properties if only the material chemistry and geometry are known. We here develop a framework to study intrinsic friction and energy dissipation based on the only knowledge of the normal modes of the system at equilibrium. We derive an approximated expression for the first anharmonic term in the potential energy expansion which does not require the computation of the third-order force constants. Moreover, we show how to characterize the frequency content of observed physical quantities and individuate the dissipative processes active during experimental measurements. As a case study, we consider the relative sliding motion of atomic layers in molybdenum disulfide dry lubricant, and we discuss how to extract information on the energetics of sliding from atomic force microscopy signals. The presented framework switches the investigation paradigm on friction and energy dissipation from dynamic to static studies, paving avenues to explore for the design of alternative anisotropic tribological and thermal materials.

A high sensitivity UV photodetector with inkjet printed ZnO/nanodiamond active layers
Josef Nahlik, Alexandr Laposa, Jan Voves, Jiri Kroutil, Jan Drahokoupil, Marina Davydova
IEEE Sensors Journal, Volume: 19, Issue: 14, July 15, 2019
The single- and double-layered photodetectors based on ZnO and/or detonation nanodiamond (DND) have been developed via a sequential inkjet printing on the interdigital electrode platform using a diamond and zinc oxide precursor ink. The morphological structure of the deposited materials was visualized and analyzed by scanning electron microscopy and atomic force microscopy. The crystalline configuration and structural quality of ZnO and nanodiamond were investigated by X-ray diffraction and Raman spectroscopy. The response, response time, and recovery time were measured for different UV wavelengths (365, 385, and 405 nm), light intensities, temperatures, and bias voltages. The ZnO/DND structure shows more than ten times higher response and faster reactivity in comparison with a single-layered photodetector. Photoresponsivity of the double-layered photodetector (ZnO/DND) is 0.35 A $\cdot \,\,\text{W}^{ {-1}}$ , whereas bare ZnO is about 0.039 A $\cdot \,\,\text{W}^{{-1}}$ . The interaction between UV light and ZnO/DND grains was investigated by two dimensional Silvaco TCAD simulation.

Nejdůležitější publikace 1. období (PARTPHYS)

Nejdůležitější odborné publikace vydané během prvního období (do 31. března 2019). Seznam všech publikací výzkumného programu PARTPHYS vydaných v rámci projektu CAAS najdete v předchozím příspěvku.

Formation of methane and (per)chlorates on Mars
Svatopluk Civiš, Antonín Knížek, Paul B. Rimmer, Martin Ferus, Petr Kubelík, Markéta Zukalová, Ladislav Kavan, Elias Chatzitheodoridis
CS Earth Space Chem. 201932221-232, Publication Date:December 17, 2018
Methane, perchlorates, chlorates, and methyl chlorides have all been detected on Mars. The origin of these species has never been adequately explained. In this paper, we irradiated mixtures of CO2, HCl, and a mineral catalyst—anatase, rutile, montmorillonite, and the Nakhla meteorite—with soft UV radiation for up to 3500 h and observed the formation of perchlorates, chlorates, methyl chlorides, and methane in a single experiment. Additionally, the methanogenesis for anatase was observed at −196 °C. Further, we propose that while methane is decomposed relatively quickly and therefore attains a steady-state concentration (0.41 ± 0.16 ppbv), the chlorinated compounds are much more stable and therefore would have accumulated throughout the Martian history. We estimate that this mechanism would be sufficient in the course of Martian history to accumulate perchlorate in the soil in 0.5 wt % in 5–50 cm depth, which is in accordance with the observed perchlorate content on Mars. This predicted perchlorate gradient may be observed with the Insight rover. Further, if microbes are present on Mars, they will likely inhabit depths below the perchlorate (i.e., 5–50 cm). This chemistry likely still continues on Mars to a certain extent, and any future exploration by rovers or planetary models should account for this process during their analyses.

Anisotropic flow in Xe-Xe collisions at root s(NN)=5.44 TeV
ALICE Collaboration
Physics Letters B, Volume 784, 10 September 2018, Pages 82-95
The first measurements of anisotropic flow coefficients for mid-rapidity charged particles in Xe–Xe collisions at sNN=5.44 TeV are presented. Comparing these measurements to those from Pb–Pb collisions at sNN=5.02 TeV, v2 is found to be suppressed for mid-central collisions at the same centrality, and enhanced for central collisions. The values of v3 are generally larger in Xe–Xe than in Pb–Pb at a given centrality. These observations are consistent with expectations from hydrodynamic predictions. When both v2 and v3 are divided by their corresponding eccentricities for a variety of initial state models, they generally scale with transverse density when comparing Xe–Xe and Pb–Pb, with some deviations observed in central Xe–Xe and Pb–Pb collisions. These results assist in placing strong constraints on both the initial state geometry and medium response for relativistic heavy-ion collisions.

Nejdůležitější publikace 1. období (APPLICATIONS)

Nejdůležitější odborné publikace vydané během prvního období (do 31. března 2019). Seznam všech publikací výzkumného programu APPLICATIONS vydaných v rámci projektu CAAS najdete v předchozím příspěvku.

Mediaeval metal threads and their identification using micro-XRF scanning, confocal XRF, and X-ray micro-radiography
M. Hložek, T. Trojek, R. Prokeš, V. Linhart
Radiation Physics and Chemistry, Volume 155, February 2019, Pages 299-303
Fabrics with metal threads were discovered in mediaeval well during excavations in the Mečová 2 Street in Brno. These are thin braids woven of metal threads using a small loom and sewed together into a broader strip. The textile materials are in a relatively good state, because the environment of the well preserved organic materials (fabrics, leather, wood). Furthermore, the positive effect of metal corrosion on the preservation of organic parts of the fabric occurred here. If metal threads are found in graves or dwelling backfills, only spiral-shaped metal fragments with microscopic relics of organic fibers are preserved. Based on microphotographs, we assume that metal threads were made by cutting or scissoring thin strips of metal sheets. The strips were spirally wound on a textile thread. The excavated fabric was deposited in a museum collection storage room for 20 years unnoticed, because its surface was covered with a layer of sediment and corrosion products. During the systematic research of mediaeval fabrics from Brno, it was found out that relics of gold are present in the ends of some of the threads. The fabrics were examined by non-destructive analytical methods. Metal threads covered with sediment and corrosion products were studied using X-ray fluorescence and radiography methods. The concentrations of elements in the individual layers show that the centre of the metal thread is formed by a silver strip. A thin layer of gold was laid on the silver strip. Silver was alloyed with copper, which corrosion products covered the whole metal strip and solidified the layer of sediments in the surface. XRF elemental mapping was employed to find out whether the metal threads pass through the whole braid. The results show that the braids are composed of silver threads with gold deposited on their rims and some central parts only.

Investigation of color layers of Bohemian panel paintings by confocal micro-XRF analysis
Radek Prokeš, Václava Antušková, Radka Šefců, Tomáš Trojek, Štěpánka Chlumská, Tomáš Čechák
Radiation Physics and Chemistry, Volume 151, October 2018, Pages 59-64
Confocal micro X-ray fluorescence spectroscopy (confocal micro-XRF) has recently become a significant instrumental method for analyses of cultural heritage as it provides depth-resolved information on elemental distribution of the investigated samples. This work describes results of confocal micro-XRF analyses of paint layers of two Bohemian panel paintings from the half of the 15th century that are part of the collections of the National Gallery in Prague. All the measurements were performed using a table top confocal micro-XRF setup designed at the Czech Technical University in Prague. A depth-profiling was used for investigation of red and blue paint layers in order to compare the composition and structure of the used pigments. Obtained results were compared with findings from the material survey on the sample taken from the painting Assumpta from Deštná (ca 1450, inv. no. O 724) to verify their origin in the same workshop. Confocal micro-XRF provides satisfactory data to specify the art workshop.

Tissue-equivalence of 3D-printed plastics for medical phantoms in radiology
J. Solca, T. Vrba, L. Burianova
Journal of Instrumentation, Volume 13, September 2018, Published 20 September 2018
The paper describes measurement of the linear attenuation coefficients for 59.5 keV, 122.0 keV and 344.5 keV photons and Hounsfield units for 80 kVp and 120 kVp computed tomography imaging of a large set of commercially 3D-printed test samples of different plastic materials aiming to provide a basis for a selection of a suitable and available material for 3D printing of medical phantoms used in radiology, and specifically for imaging in targeted radionuclide therapy. The results were compared to ICRU44 skeletal muscle and adipose tissues. The results also showed large differences between photon attenuation properties of the same type of plastic material printed by different companies on different printers using filaments from different manufacturers. As a result, it is highly recommended to print a medical phantom on the same printer, with the same settings, and with the same filament as the test sample.

Nejdůležitější publikace 1. období (LASE)

Nejdůležitější odborné publikace vydané během prvního období (do 31. března 2019). Seznam všech publikací výzkumného programu LASE vydaných v rámci projektu CAAS najdete v předchozím příspěvku.

Wave-based laser absorption method for high-order transport–hydrodynamic codes
Jan Nikl, Milan Kuchařík, Jiří Limpouch, Richard Liska, Stefan Weber
First Online: 18 February 2019
Models of the laser propagation and absorption are a crucial part of the laser–plasma interaction models. Hydrodynamic codes are afflicted by usage of the simplified, not self-consistent, models of the geometrical optics, limiting their physical accuracy. A robust and efficient method is presented for computing the stationary wave solution, not restricted to this field of application exclusively. The method combines the semi-analytic and high-order differential approaches to benefit from both. Flexibility of the discretization is maintained, including the discontinuous methods. Performance of the model is evaluated for the problem of a transition layer by comparison with the analytic solution. Reliable results on coarse computational meshes and high convergence rates on fine meshes are obtained. The relevance to the current fusion research and non-local energy transport is pointed out.

Nejdůležitější publikace 1. období (PLASMA)

Nejdůležitější odborné publikace vydané během prvního období (do 31. března 2019). Seznam všech publikací výzkumného programu PLASMA vydaných v rámci projektu CAAS najdete v předchozím příspěvku.

Features of fast deuterons emitted from plasma focus discharges editors-pick
Physics of Plasmas 26, 032702 (2019); https://doi.org/10.1063/1.5080974
P. Kubes, M. Paduch, M. J. Sadowski, J. Cikhardt, B. Cikhardtova1, D. Klir, J. Kravarik, R. Kwiatkowski, V. Munzar, K. Rezac, E. Skladnik-Sadowska, A. Szymaszek, K. Tomaszewski, D. Zaloga, and E. Zielinska
Published Online: 01 March 2019 Accepted: February 2019
This paper presents the discussion concerning the characteristics of the fast deuterons which have energy above 30 keV and are recorded during high-current plasma-focus (PF) discharges, by means of PM-355 plastic track-detectors placed inside ion pinhole cameras. The fast deuterons evoke D-D fusion reactions, mainly by a beam-target mechanism. The distribution of the magnetic field, which influences the trajectories of the recorded deuterons, is discussed. It is found that the fast deuterons are produced in various local sources and their motion is strongly influenced by a circular symmetry of the local magnetic field, which increases their radial shift with a decrease in their energy. The sources of these deuterons are probably located inside the plasmoids and in some local regions of the ring-shaped plasma structures. These ring-structures can be formed outside the dense pinch column, up to a radius of 5 cm. Global magnetic fields, associated with the total current flow in the PF discharge, have a weaker influence. The observed radial shift of the recorded fast deuterons is interpreted as a result of their deflection by magnetic fields which have opposite orientations of the azimuthal components, associated with the currents flowing in directions towards and from the applied ion detectors. The local sources of the recorded fast deuterons correspond to filamentary structures, in which the stored magnetic energy (having the local high density) can be released in induced electric fields accelerating the deuterons during the magnetic reconnections.