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Wyświetlanie 1-15 z 16
Tytuł:
Positron Scattering at Thermal Energies
Autorzy:
Fedus, K.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1340032.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
34.80.-i
34.80.Bm
34.80.Uv
Opis:
Modified effective range theory in analytical form is used to extrapolate elastic cross-sections down to thermal energies for positron scattering from five atomic and molecular targets including Ar, $H_2$, $N_2$, $C_6H_6$ (benzene) and $C_6H_{12}$ (c-hexane). The derived scattering parameters are then used to estimate the annihilation rates for chosen elements using a simple formula by Gribakin. We show that a combination of two simple models has a potential for accurate parameterization of coefficients describing the interaction of thermal positrons with non-polar targets of low polarizability such as Ar and $N_2$.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 829-832
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Annihilation Studies of Czochralski-Grown Silicon Annealed Under Pressure
Autorzy:
Karwasz, G. P.
Brusa, R. S.
Misiuk, A.
Zecca, A.
Powiązania:
https://bibliotekanauki.pl/articles/2008074.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
71.55.Cn
Opis:
Two positron techniques have been applied to study dynamics of oxygen precipitation in Czochralski-grown silicon, annealed under high (up to 1.4 GPa) pressure. Lifetime measurements were performed with 180 ps resolution; Doppler broadening with a variable-energy slow-positron beam. Different thermal treatings rise the mean lifetime of positrons from 222 ps in as-grown samples up to 227 ps. In samples with a high (up to 85%) amount of oxygen precipitated, an intermediate (550-800 ps) lifetime is observed.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 575-580
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Porosity of Low-κ Materials Studied by Slow Positron Beam
Autorzy:
Brusa, R. S.
Macchi, C.
Mariazzi, S.
Karwasz, G. P.
Powiązania:
https://bibliotekanauki.pl/articles/2042213.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
68.60.Dv
68.90.+g
Opis:
The information about porosity in low-κ materials obtainable by depth profiling with positron annihilation spectroscopy is reviewed. In particular we focus on Doppler broadening spectroscopy and 2-3γ ratio of positronium measurements on SiOCH and amorphous carbon a-C:F:H thin films produced by plasma enhanced chemical vapour deposition.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 702-711
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation in Organic Liquids
Autorzy:
Karbowski, A.
Fedus, K.
Służewski, K.
Bruzdowska, J.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1030028.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
82.30.Gg
36.10.Dr
Opis:
This paper reports on the results of positron annihilation lifetime measurements of three organic liquids: benzene (C₆H₆), cyclohexane (C₆H₁₂), and methanol (CH₃OH). The lifetime spectra are acquired at different temperatures for non-degassed, degassed, and oxygen-saturated samples, at temperatures between 5°C and 25°C. The spectra are analyzed using a standard three-exponential model. The influence of oxygen on each lifetime and intensity component is discussed.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1466-1469
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Low Energy Cross-Sections for Positron Interactions with Cyclic Hydrocarbons
Autorzy:
Karwasz, G. P.
Pliszka, D.
Brusa, R. S.
Perazzolli, C.
Powiązania:
https://bibliotekanauki.pl/articles/2042198.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
34.85.+x
39.90.+d
Opis:
We report total cross-section measurements for positron scattering on cyclic hydrocarbons: benzene, aniline, and cyclohexane. Measurements were done by an absolute transition method in the energy range 1.5-20 eV (0.4-20 eV for cyclohexane). High cross-sections for all measured molecules were observed at low energies. In the case of cyclohexane the cross-section in the zero energy limit tends to a constant value. In aniline a weakly accented peak slightly above the positronium formation threshold is observed. Similar but less visible bump was observed in the case of benzene. Measurement of total cross-sections in nitrogen and argon used for calibration of the apparatus are also presented.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 666-672
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Genetic Algorithms for Positron Lifetime Data
Autorzy:
Karbowski, A.
Fisz, J.
Karwasz, G.
Kansy, J.
Brusa, R.
Powiązania:
https://bibliotekanauki.pl/articles/1812491.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
71.55.Cn
Opis:
Recently, genetic algorithms have been applied for ultrafast optical spectrometry in systems with several convoluted lifetimes. We apply these algorithms and compare the results with POSFIT (by Kirkegaard and Eldrup) and LT programme (by Kansy). The analysis was applied to three types of samples: molybdenum monocrystals, Czochralski-grown silicon with oxygen precipitates, Si with under-surface cavities obtained by He + H ion co- implantation. In all three tests, the genetic algorithm performs very well, in particular for short lifetimes. Further developments to model the resolution function in genetic algorithms are needed.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1365-1372
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Toward a European Network of Positron Laboratories
Autorzy:
Karwasz, G. P.
Brusa, R. S.
Egger, W.
Ogorodnikova, O. V.
Powiązania:
https://bibliotekanauki.pl/articles/146548.pdf
Data publikacji:
2015
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
positron beams
material science
thermonuclear reaction
Opis:
Some applications of controlled-energy positron beams in material studies are discussed. In porous organic polysilicates, measurements of 3γ annihilation by Doppler broadening (DB) method at the Trento University allowed to trace pore closing and filling by water vapor. In silicon coimplanted by He+ and H+, DB data combined with positron lifetime measurements at the München pulsed positron beam allowed to explain Si blistering. Presently measured samples of W for applications in thermonuclear reactors, irradiated by W+ and electrons, show vast changes of positron lifetimes, indicating complex dynamics of defects.
Źródło:
Nukleonika; 2015, 60, No. 4, part 1; 733-739
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Scattering on Atoms and Molecules in the Limit of Low Energy
Autorzy:
Karwasz, G. P.
Brusa, R. S.
Pliszka, D.
Idziaszek, Z.
Nowakowska, H.
Powiązania:
https://bibliotekanauki.pl/articles/2047133.pdf
Data publikacji:
2006-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
34.85.+x
39.90.+d
Opis:
Starting from experimental cross-sections for positron scattering in argon and nitrogen, we examine different energy ranges. In the zero-energy limit the cross-section falls with energy and can be described by modified effective range theory for polarization potential. In a few eV range the cross-sections are constant vs. energy. As far as it is possible to force the elastic scattering phase shifts in a way that both experimental differential cross-sections are reproduced and the total cross-section remains constant in energy, such a model lacks the physical justification. Only the virtual-positronium model, developed recently by Gribakin, reproduces a constant dependence of the total cross section in a few eV energy range.
Źródło:
Acta Physica Polonica A; 2006, 110, 5; 605-614
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Systematic Measurements of Doppler-Coincidence Spectra for Positron Annihilation in Pure Metals and Semiconductors
Autorzy:
Deng, W.
Pliszka, D.
Brusa, R. S.
Karwasz, G. P.
Zecca, A.
Powiązania:
https://bibliotekanauki.pl/articles/2030758.pdf
Data publikacji:
2002-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Doppler-broadening measurements of the electron-positron annihilation line in twenty six elements are presented. The adopted coincidence technique allows to reduce the background and point out the contribution of positron annihilation with core electrons. The changes of the high momentum contribution is presented for selected examples and a semiempirical analysis of the dependence on electronic structure is performed. Measured data are in a good agreement with recent theoretical calculations and can be used to identification of impurities surrounding open volume defects.
Źródło:
Acta Physica Polonica A; 2002, 101, 6; 875-892
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Photoluminescence and positron annihilation lifetime studies on pellets of ZnO nanocrystals
Autorzy:
Karbowski, A.
Fedus, K.
Patyk, J.
Bujak, Ł.
Służewski, K.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/148001.pdf
Data publikacji:
2013
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
photoluminescence (PL)
positron annihilation lifetime spectroscopy (PALS)
X-ray diffraction (XRD)
ZnO nanocrystals
Opis:
We explore the interrelationships between the X-ray diffraction patterns, the photoluminescence spectra and the positron lifetimes obtained from circular pellets composed of commercial ZnO nanoparticles. The experimental results are studied as a function of thermal treatment at different temperatures. X-ray diffractograms reveal the temperature- independent wurtzite phase structure of nanocrystals and show huge enlargement of ZnO grains after annealing at temperatures higher than 700 centigrade. Photoluminescence measurements exhibit two emission bands : a near band edge emission in UV (small tilde 378 nm) and a defect-related broad visible peak with a maximum in the green region ( small tilde 502 nm). The significant enhancement of the green emission at the expense of UV luminescence is observed after sample sintering at 800 and 1000 centigrade. The positron annihilation lifetime spectroscopy (PALS) is applied in order to study the thermally induced evolution of defects. The lifetime components show a step-like dependence on the thermal treatment, but do not follow exactly the variation in crystallographic phases and only vaguely follow differences in photoluminescence. The positron data indicate therefore some additional structural and/or defect changes. The possible origin of green luminescence from ZnO pellets is discussed.
Źródło:
Nukleonika; 2013, 58, 1; 189-194
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron-annihilation and photoluminescence studies of nanostructured ZrO2
Autorzy:
Fidelus, J. D.
Karbowski, A.
Mariazzi, S.
Brusa, R. S.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/146313.pdf
Data publikacji:
2010
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
positron annihilation
zirconia nanopowders
photoluminescence
Opis:
In the present work, photoluminescence and Doppler broadening depth-resolved positron annihilation spectroscopy was performed on pure zirconia nanopowders. Zirconia nanopowders were grown by a hydrothermal microwave-driven process followed by annealing in oxygen atmosphere. Photoluminescence under 274 nm wavelength excitation from a 150 W high-pressure Xe exhibits similar spectra, in the region from 320 to 820 nm, although its intensity depends on the annealing. Positron annihilation Doppler-broadening spectra show low values of the normalized S-parameter, varying little with the depth, from 0.495 on the surface to 0.47-0.49 in bulk. Both high the annealing temperature and oxygen concentrations, lead to low bulk S-values. The ortho-positronium (o-Ps) fraction is about 10-11% for all samples on the surface, whereas it is reduced to 7-8% in the bulk for samples annealed at 700°C and 5-6% for samples annealed at 800°C. Both photoluminescence (PL) and positron studies show the presence of defects in all samples. The o-Ps signal suggests a high porosity of samples, particularly at a depth down to 10 nm.
Źródło:
Nukleonika; 2010, 55, 1; 85-89
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Depth Profiling of Defects in He Implanted $SiO_2$
Autorzy:
Mariazzi, S.
Toniutti, L.
Brusa, R.
Duarte Naia, M.
Karbowski, A.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1812538.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
68.55.-a
61.82.Ms
61.72.J-
Opis:
Thin layer of $SiO_2$ thermally grown on p-type Si was implanted with $He^+$ ions at 30 keV with a dose of $5×10^{15}$ ions/$cm^2$. $SiO_2//Si$ samples were depth profiled by Doppler broadening positron annihilation spectroscopy to identify induced defects in the silicon oxide, at the interface and in the Si substrate. In one sample the silicon dioxide layer was removed by etching after implantation. It is shown that removing the silicon dioxide layer some more information about defects into the substrate can be found.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1447-1453
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron-Annihilation, Structural and Optical Studies on Properties of Nanostructured $ZrO_2,$ $ZnO,$ $Bi_2O_3$ and $ZnO-Bi_2O_3$
Autorzy:
Fidelus, J.
Karbowski, A.
Grabis, J.
Jusza, A.
Piramidowicz, R.
Brusa, R.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1492669.pdf
Data publikacji:
2011-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
71.55.Cn
Opis:
Nanostructured oxides, like $ZrO_2,$ on $ZnO$ and $Bi_2O_3$ show interesting electronic and photovoltaic properties. Pressed and annealed samples were obtained from nanopowders grown in hydrothermal or plasma processes. Positron annihilation (the Doppler broadening depth-resolved, positron lifetime) techniques were used to trace structural changes in samples after annealing. Photoluminescence spectra of all investigated samples show broad-band emission in the visible, with intensity depending on annealing temperature. The change in nanoporosity and positron lifetimes correlate well with changes in photoluminescence properties. The nature of broad photoluminescence bands is to be understood; further positron studies via the Doppler coincidence method would help in identifying the nature of defects in these samples.
Źródło:
Acta Physica Polonica A; 2011, 120, 6A; A-066-A-068
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Structural Studies of Titanium Oxide Multilayers
Autorzy:
Karwasz, G. P.
Miotello, A.
Zomer, E.
Brusa, R. S.
Kościelska, B.
Armellini, C.
Kuzmin, A.
Powiązania:
https://bibliotekanauki.pl/articles/2043379.pdf
Data publikacji:
2005-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.47.Jk
78.70.Bj
61.10.Nz
Opis:
Multilayers of titanium oxide on conductive glasses (silica, covered with indium/tin and tin oxides) were obtained by different methods (from suspension, by sol-gel, by vacuum sputtering). X-ray diffraction and positron annihilation depth-resolved characterization of these samples are presented. The data allow us to determine optimal deposition parameters, in order to obtain the anatase phase, important in practical applications in photoelectrochemical cells.
Źródło:
Acta Physica Polonica A; 2005, 107, 6; 977-982
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Amorphous Carbon Thin Films Deposited on Si and PET: Study of Interface States
Autorzy:
Mariazzi, S.
Macchi, C.
Karwasz, G. P.
Brusa, R. S.
Laidani, N.
Bartali, R.
Gottardi, G.
Anderle, M.
Powiązania:
https://bibliotekanauki.pl/articles/2043339.pdf
Data publikacji:
2005-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
68.55.Ac
71.60.+z
73.20.At
78.70.Bj
Opis:
Thin carbon films with various thicknesses, deposited on different substrates (Si and poly-ethylene-terephthalate) at the same operating conditions in a radio frequency plasma enhanced chemical vapour deposition system were characterized by Doppler broadening spectroscopy. The films and the substrates were depth profiled by a slow positron beam. The aim of these measurements was to study the open volume structure and the interface of the films. It was found that, independently from the substrate, the films were homogeneous and exhibited the same open volume distribution. On the contrary, the effective positron diffusion length in the Si substrate was found to change with the thickness of the carbon films. This behaviour was interpreted as a change in the electric field at the carbon/silicon interface.
Źródło:
Acta Physica Polonica A; 2005, 107, 5; 842-847
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 16

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