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## Nejdůležitější publikace 2. období (MATE)

Nejdůležitější odborné publikace vydané během druhého období (do 31. září 2019). Seznam všech publikací výzkumného programu MATE vydaných v rámci projektu CAAS najdete na zvláštní stránce, seznam nejdůležitějších publikací za první období pak zde.

Nanoscale frictional properties of ordered and disordered MoS2
Elisabetta Serpini; Alberto Rota; Sergio Valeri; Egor Ukraintsev; Bohuslav Rezek; Tomas Polcar; Paolo Nicolini
Tribology International; Volume 136, August 2019
The present work aims to understand the sliding of ordered/disordered molybdenum disulfide against itself by combination of nanoscale sliding experiments and atomistic simulations. Tribological experiments were performed using lateral force microscopy with tips covered by a thin sputtered MoS2film. Nanoscale contact area between the MoS2-coated tips and MoS2 samples opened up the possibility for close comparison with classical molecular dynamics simulations. Our simulations replicated well the coefficient of friction obtained by experiments for various contact conditions and shed light on nanoscale sliding of both crystalline and amorphous MoS2. Experimental sliding at humid environment demonstrated detrimental effect of water molecules on friction. However, such effect was much less pronounced when compared to that observed in macroscopic sliding experiments.

Increasing Fatigue Endurance of Hydroxyapatite and Rutile Plasma Sprayed Biocomponents by Controlling Deposition In-Flight Properties
J. Cizek; O. Kovarik; F. Siska; J. Bensch; J. Cupera; M. Matejkova; J. Siegl; T. Chraska; K. A. Khor
ACS Biomater. Sci. Eng. 2019, 5, 4, 1703-1714, Publication Date: March 12, 2019
Three sets of hydroxyapatite and rutile-TiO2 coatings were plasma sprayed onto metallic substrates. The spray parameters of the sets were modified so as to obtain different in-flight temperatures and velocities of the powder particles within the plasma jet (ranging from 1778 to 2385 K and 128 to 199 m s–1, respectively). Fatigue endurance of the coated specimens was then tested. The samples were subjected to a symmetric cyclical bend loading, and the crack propagation was monitored until it reached a predefined cross-section damage. The influence of the coating deposition was evaluated with respect to a noncoated reference set and the in-flight characteristics. Attributed to favorable residual stress development in the sprayed samples, it was found that the deposition of the coatings generally led to a prolongation of the fatigue lives. The highest lifetime increase (up to 46% as compared to the noncoated set) was recorded for the coatings deposited under high in-flight temperature and velocity. Importantly, this was achieved without significantly compromising the microstructure or phase composition of the deposited HA and TiO2 layers.

Microstructural evolution of helium-irradiated 6H–SiC subjected to different irradiation conditions and annealing temperatures: A multiple characterization study
N. Daghbouj; LiB. S.; M. Callisti; H. S. Sen; M. Karlik; T. Polcar
Acta Materialia; Volume 181, December 2019
The microstructural phenomena occurring in 6H–SiC subjected to different irradiation conditions and annealing temperatures were investigated to assess the suitability of 6H–SiC as a structural material for nuclear applications. To this aim, a single crystal of 6H–SiC was subjected to He<sup>+</sup> irradiation at 300 keV with different fluences and at temperatures ranging from 25 to 750 °C. Rutherford backscattering/channeling (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were combined to shed light on the microstructural changes induced by irradiation and subsequent annealing (750 to 1500 °C). At room temperature, amorphization starts to occur at a fluence of 2.5 × 1016 cm−2 (0.66 dpa). On the contrary, amorphization was prevented at high irradiation temperatures and fluences. Furthermore, a thin and highly strained region located around the maximum He concentration (Rp) formed. This region results from the accumulation of interstitial atoms which are driven toward the highly damaged region under the actions of a strain gradient and high temperature. Regardless of the fluence and irradiation temperature, the material stores elastic energy, which leads to the trapping of He in dissimilar defect geometries. For irradiation temperatures below 750 °C, helium was accumulated in bubbles which coarsened after annealing. On the other hand, for an irradiation temperature of 750 °C, helium was trapped in platelets (even for medium fluence), which evolved into a homogeneous dense array of cavities during annealing. DFT calculations show that the bubbles are under high pressure and contribute to developing the overall tensile strain in the single crystal 6H–SiC.

## 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.

## Materiálová věda a inženýrství (MATE)

Koordinátor programu: prof. Dr. RNDr. Miroslav Karlík

Skupina materiálové vědy CAAS dále rozvine svou vynikající kompetenci ve studiích materiálové struktury a vlastností, přípravy nových materiálů a také porozumění vazeb mezi strukturou a vlastnostmi materiálů, například v pokročilé tribologii a biologických aplikacích materiálů. Fyzika pevných materiálů a fyzika materiálů je převážně předmětem studia na FJFI