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Wyszukujesz frazę "Čížek, J." wg kryterium: Autor


Wyświetlanie 1-5 z 5
Tytuł:
Defects Studies of ZnO Single Crystals Prepared by Various Techniques
Autorzy:
Lukáč, F.
Čížek, J.
Procházka, I.
Melikhova, O.
Anwand, W.
Brauer, G.
Powiązania:
https://bibliotekanauki.pl/articles/1196118.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.J-
Opis:
The aim of the present work was a comparison of defects in ZnO crystals grown by various techniques available nowadays, namely hydrothermal growth, pressurized melt, Bridgman method growth and vapor phase growth. Positron annihilation spectroscopy was employed as a principal tool for characterization of defects in ZnO crystals grown by above mentioned various techniques. ZnO crystals can be divided into two groups: (i) hydrothermal grown crystals, which exhibit positron lifetime of 179-182 ps and (ii) ZnO crystals grown by the other techniques (pressurized melt, Bridgman method, vapor phase growth) which are characterized by the lower lifetimes falling in the range of 160-173 ps. Comparison of experimental data with ab initio theoretical calculations revealed that HT grown ZnO crystals contains Zn vacancies associated with hydrogen atom in a bond-centered site. On the other hand, ZnO crystals prepared by other techniques contain most probably stacking faults created by stresses induced by temperature gradients in the melt.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 748-751
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation in Nanostructured Metals
Autorzy:
Čížek, J.
Melikhova, O.
Hruška, P.
Vlček, M.
Anwand, W.
Liedke, M.
Novotný, M.
Bulíř, J.
Powiązania:
https://bibliotekanauki.pl/articles/1033937.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
41.75.Fr
36.10.Dr
Opis:
Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1579-1584
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hydrogen Interaction with Vacancies in Electron Irradiated Niobium
Autorzy:
Čižek, J.
Procházka, I.
Brauer, G.
Anwand, W.
Gemma, R.
Nikitin, E.
Kirchheim, R.
Pundt, A.
Powiązania:
https://bibliotekanauki.pl/articles/1812478.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.72.-y
Opis:
Defect studies of Nb irradiated with 10 MeV electrons were performed in the present work by means of positron annihilation spectroscopy. The lattice defects were characterized by positron lifetime spectroscopy. Moreover, defect depth profiles were studied by slow positron implantation spectroscopy. The experimental investigations were accompanied by first principles theoretical calculations of positron parameters. It was found that irradiation-induced vacancies in Nb specimens are surrounded by H, which causes a shortening of the lifetime of trapped positrons. The influence of a Pd and Cr over-layer on the H concentration in the Nb specimens was examined.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1293-1299
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Probing of Pores in Zirconia Nanopowders
Autorzy:
Prochazka, I.
Cizek, J.
Lukac, F.
Melikhova, O.
Hruska, P.
Anwand, W.
Liedke, M.
Konstantinova, T.
Danilenko, I.
Powiązania:
https://bibliotekanauki.pl/articles/1033930.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.07.Wx
61.46.Hk
78.70.Bj
Opis:
In the present paper, conventional positron lifetime measurements on selected zirconia-based nanopowders are reported. The nanopowders were doped with various metal cations (Y³⁺, Eu³⁺, Gd³⁺, Lu³⁺ and Mg²⁺). Lifetime experiments were conducted in air and supplemented with mass density measurements. In a range of lifetimes, from a few ns to ≈70 ns, up to two individual lifetime components could be identified. Such observations confirmed positronium (Ps) formation with subsequent ortho-Ps pick-off annihilation as well as the occurrence of pores of different size. Pore sizes were estimated using a shape-free model of the correlation between pore size and ortho-Ps lifetime. The origins of pores are discussed on the basis of the ortho-Ps data in combination with the results of mass density measurements.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1564-1567
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultra Fine-Grained Metals Prepared by Severe Plastic Deformation: A Positron Annihilation Study
Autorzy:
Čížek, J.
Procházka, I.
Kužel, R.
Matĕj, Z.
Cherkaska, V.
Cieslar, M.
Smola, B.
Stulíková, I.
Brauer, G.
Anwand, W.
Islamgaliev, R. K.
Kulyasova, O.
Powiązania:
https://bibliotekanauki.pl/articles/2043303.pdf
Data publikacji:
2005-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
79.60.Jv
Opis:
Recent investigations of ultra fine-grained metals (Cu, Fe, Ni) performed within a Prague-Rossendorf-Ufa collaboration will be reviewed. The specimens were prepared by severe plastic deformation: the high-pressure torsion and equal channel angular pressing. Positron annihilation spectroscopy was used as the main method including (i) the conventional lifetime and the Doppler broadening measurements with $\text{}^{22}$Na and (ii) the slow-positron implantation spectroscopy with the Doppler broadening measurement. Other methods were also involved: transmission electron microscopy, X-ray diffraction, and microhardness. First, the mean grain size was determined and defects were identified in the as-deformed materials. Defects concentration and spatial distribution were studied in detail. Dislocations situated in distorted regions along grain boundaries, and a few-vacancy clusters distributed homogeneously inside dislocations-free grains, were observed in the ultra fine-grained Cu, Fe, and Ni. Subsequently, the thermal evolution of the ultra fine-grained structures during isochronal annealing was studied.
Źródło:
Acta Physica Polonica A; 2005, 107, 5; 745-752
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-5 z 5

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