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1
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Extended X-Ray Absorption Fine Structure Studies of Co Doped ZnS and ZnSe Alloys

100%
Ławniczak-Jabłońska K., Gołacki Z.
Acta Physica Polonica A
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1994
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vol. 86
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issue 5
727-735
EN
X-ray absorption experiments were performed at the Kedge of Co and Zn in Zn_{1-x}Co_{x}S and Zn_{1-n}Co_{x}Se compounds with x = 0.25, 0.16, 0.10, 0.05, 0.00 in the sulphides samples and x = 0.07, 0.02, 0.00 in the selenide ones. Analysis of the extended X-ray absorption fine structure oscillations using phase and amplitudes either from McKale code or from standard samples, gave the distance, number of atoms and the Debye-Waller factors for nearest neighbours. We found that the cation-anion distances Zn-S(Se) or Co-S(Se) are systematically shorter in ZnS than in ZnSe matrix, the Zn-anion distance is always larger than the Co-anion one without any significant Co content dependence. This allowed us to estimate the covalent radius of Co in the studied matrices to be 0.025 Å smaller than the Zn covalent radius and stated that covalent radius of Co is independent of the type of surrounding atoms. In addition the Debye-Waller factors indicated a better ordering in ternary compounds than in the binary standard ones in agreement with rocking curve measurements.
2
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Valency of Yb in PbS and PbTe Determined by XPS

100%
Gołacki Z., Heinonen M.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
775-778
EN
X-ray photoelectron spectroscopy experiments on PbTe:Yb, PbS:Yb, PbTe, and PbS crystals have been performed using the monochromatized Al K_{α} radiation. The valence band spectrum of PbTe:Yb exhibits one set of peaks associated with divalent Yb initial states, but two sets associated with divalent and trivalent Yb are observed for PbS:Yb. The valency of Yb in PbTe:Yb is 2 (within an accuracy of the experiment) but in PbS:Yb the mixed valency of Yb is seen. These conclusions are confirmed by an analysis of Yb 4d spectra in PbTe:Yb and PbS:Yb crystals.
3
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Valency of Selected Rare-Earth Ions in SnTe Matrix

100%
Gołacki Z., Heinonen M.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
779-782
EN
X-ray photoelectron spectroscopy experiments on SnTe crystals doped by Sm, Eu, and Yb were performed to determine the valency of these ions in the SnTe matrix. The analysis of the X-ray photoelectron spectroscopy valence-band spectra revealed that Eu and Yb are divalent while Sm is trivalent in SnTe. These conclusions were confirmed by studies of the binding energies of core levels (4d-levels of Yb and 3d -levels of Sm and Eu), which are not presented here.
4
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Reflectivity Spectra of CdTe Implanted at Room and Liquid Nitrogen Temperature

81%
Czarnecka-Such E., Kisiel A., Rodzik A., Gołacki Z.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
781-784
EN
The fundamental reflectivity spectra of monocrystalline CdTe, implanted with Ag ions at room temperature and with Er ions at liquid nitrogen temperature, are investigated in the 0.5-6.0 eV energy range. The analysis of the obtained spectra leads to the suggestion that temperature of implantation influences the obtained results much more decisively than values of other parameters. For the implantation carried out at 300 K no significant changes in reflectivity spectra are observed regardless of magnitude of the ion dose (up to 5 × 10^{15}/cm^{2}) and this fact, in our opinion, is due to the self-annealing effect. For samples implanted at temperature 77 K with comparable doses of ions, however, the characteristic changes of shape and intensity of reflection coefficient spectra appear. The manner of this changes gives evidence that temperature 77 K is low enough to make the radiation induced lattice defects stable (frozen-in) which are responsible for the observed behaviour of CdTe fundamental reflectivity spectra.
5
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Reflectivity Study of the Zn_{1-x}Co_{x}Se Crystals

81%
Kowalski B., Gołacki Z., Orłowski B.
Acta Physica Polonica A
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1991
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vol. 80
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issue 3
393-396
EN
The room temperature reflectivity spectra of the Zn_{1-x}Co_{x}Se (x = 0, 0.03, 0.05) crystals have been measured in the visible and ultraviolet range from 1.7 to 12 eV. The structure of the spectra was interpreted in terms of the electronic band structure of the binary material (ŻnSe). The experimental results were compared with the reflectivity spectra of the Fe-based semi magnetic semiconductors [1], and the interpretation was confronted with the conclusions derived from the photoemission experiments performed for Cd_{1-x}Co_{x}Se [2] and the tight-binding CPA calculations of the band structure of Zn_{1-x}Co_{x}Se [3].
6
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Magnetic Susceptibility of Sn_{1-x}Au_{x}Te

81%
Górska M., Anderson J., Peng J., Gołacki Z.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
665-668
EN
The magnetic susceptibility of Bridgman-grown Sn_{1-x}Eu_{x}Te with nominal values of x up to 0.095 was measured over a temperature range from 2 to 385 K. The samples were p-type with hole concentrations up to 1.5 × 10^{21} cm^{-3}. The susceptibility data above 50 K followed the Curie-Weiss relation with a small Curie temperature. At about 10 K a small cusp in susceptibility was observed in samples with the higher range of x values. The data indicate a presence of both antiferromagnetic and ferromagnetic exchange interactions, with some paramagnetic contributions from charged defects. There is also evidence of Eu going into the lattice both as Eu^{2+} and Eu^{3+} ions.
7
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Gd 4f and 5d Electrons in Sn_{0.96}Gd_{0.04}Te Valence Band

71%
Orłowski B. A., Kowalski B. J., Gołacki Z., Story T., Johnson R. L.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
857-860
EN
The synchrotron radiation was applied to measure resonant photoemission spectra (Fano-type Gd 4d-4f resonance), constant initial states and constant final states to study the valence band electronic structure of Sn_{0.96}Gd_{0.04}Te crystal. The resonant energy was found equal to 150.3 eV. The electrons 4f were found to contribute to the valence band of the crystal with the maximum located at 9.5 eV below the valence band edge whereas 5d electrons contribute at the crystal valence band edge.
8
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Analysis of 4f Level in Samarium-Rich MBE Grown CdSmTe Sample

71%
Szamota-Sadowska K., Gołacki Z., Orłowski B., Boyn R., Johnson R.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
560-564
EN
Electronic states of 4f samarium ions were investigated by photoemission spectroscopy in samarium-rich CdSmTe sample obtained by MBE. The photon energy of synchrotron radiation allowed to investigate Fano-type resonance and antiresonance. The energy distribution curve spectra were attributed to the Sm 4d-4f transition. The shape of the constant initial states spectra was compared with this one obtained for atomic samarium.
9
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4f Shell of Gd^{2+} and Gd^{3+} Ions in Sn_{1-x}Gd_{x}Te - Resonant Photoemission Study

71%
Kowalski B. J., Gołacki Z., Guziewicz E., Orłowski B. A., Johnson R. L.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
875-878
EN
Resonant photoemission spectra of Sn_{1-x}Gd_{x}Te (x=0.02 and 0.08) measured for the photon energy range 142 to 151 eV show the valence band density of states distribution and the Gd 4f derived maximum. The energy position of the J=0 component of the Gd 4f maximum was determined and used as a measure of the Gd 4f shell binding energy. The electrostatic model of core level shifts was used to interpret the difference in the Gd 4f binding energies observed for x=0.02 and x=0.08.
10
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Cd_{1-x}Fe_{x}Te Ternary Crystal Formation Studied by Resonant Photoemission

62%
Guziewicz E., Kowalski B. J., Gołacki Z., Orłowski B. A., Johnson R. L., Masek J.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
793-796
EN
A resonant photoemission was used to study the ternary crystal formation, when small amount of Fe atoms was deposited (in one monolayer range of thickness) on the clean CdTe(100) surface. The constant initial state spectra taken near the Fe 3p-3d transition after Fe deposition and then again after heating process show the existence of two Fano-like resonance. The differences of the energy distribution curves taken for both resonance and antiresonance, respectively, allow us to distinguish two kind of Fe 3d contributions to the valence band: one derived from the metallic Fe islands on the surface and the second - derived from the Fe atoms built into the Cd_{1-x}Fe_{x}Te crystal.
11
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Content available

Magnetic Specific Heat of Pb_{1-x}Eu_xTe

62%
Górska M., Łusakowski A., Jędrzejczak A., Gołacki Z., Anderson J., Balci H.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
631-636
EN
The temperature dependence of the magnetic specific heat was studied experimentally and theoretically in the semimagnetic semiconductor Pb_{1-x}Eu_xTe for x=0.027 and x=0.073, over the temperature range from 0.5 K to 15 K, in magnetic fields up to 2 T. In zero magnetic field at about 2 K there was a broad maximum in the magnetic specific heat, which was much higher than that predicted by the model of superexchange interaction between nearest neighbors; the maximum values increased with magnetic field. The experimental data were analyzed in the framework of a model which takes into account the spin splitting of the ground state of a single Eu2+ ion in the presence of local lattice distortions in the Pb_{1-x}Eu_xTe mixed crystal. The model describes well the experimental data, especially for lower x-values, where the contribution from singlets dominates.
12
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Raman Spectroscopy of Co-Doped ZnO Bulk Crystals

62%
Szuszkiewicz W., Morhange J., Gołacki Z., Łusakowski A., Schumm M., Geurts J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
363-368
EN
Low-temperature Raman spectra of a bulk mixed crystal Zn_{1-x}Co_xO (x = 0.016) are shown and analyzed. Besides the common modes of the ZnO host lattice, electronic transitions related to the presence of Co^{2+} ions at the Zn sites are observed. In spite of the low Co concentration the presence of collective excitations corresponding to Co and CoO precipitates is also revealed.
13
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Resonant Photoemission Study of Gd 4f States in IV-VI Crystals

62%
Kowalski B. J., Gołacki Z., Guziewicz E., Orłowski B. A., Ghijsen J., Johnson R. L.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
819-823
EN
Resonant photoemission experiments were performed in order to reveal the contributions of half-filled Gd 4f^{7} shell to the electronic structures of Sn_{0.95}Gd_{0.05}Te and Pb_{0.95}Gd_{0.05}S crystals. The influences of the Gd 4f^{6} final-state multiplet splitting and f-ligand hybridization on the shapes of the spectra are discussed.
14
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4f Contribution to Valence Band of Pb_{1-x}RE_{x}S (RE = Eu,Gd) Studied by Resonant Photoemission

62%
Kowalski B., Gołacki Z., Guziewicz E., Orłowski B., Ghijsen J., Johnson R.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
1035-1039
EN
Resonant photoemission experiments were carried out in order to reveal the contributions of partly filled Eu 4f^{7} and Gd 4f^{7} shells to the valence bands of Pb_{0.95}Eu_{0.05}S and Pb_{0.95}Gd_{0.05}S crystals. The coupling between these orbitals and the host electronic states is discussed.
15
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X-Ray and Electron-Optical Characterization of ZnSe(Co) Crystal with Natural Face

62%
Auleytner J., Domagała J., Gołacki Z., Pawłowska M., Pełka J., Regiński K.
Acta Physica Polonica A
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1993
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vol. 83
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issue 6
759-768
EN
Using complementary X-ray and electron-optical methods, a ZnSe(Co) crystal with natural face was investigated. X-ray diffraction methods such as double-crystal X-ray reflection topography, double-crystal diffractometry for rocking curve measurements, precise lattice constant measurements by the Bond technique were used for crystal structure characterization and X-ray fluorescence method for studies of chemical composition along the crystal. The scanning electron microscopic image of the crystal surface and reflection diffraction of the high-energy electrons enriched the crystal structure characterization. It was shown that X-ray characterization and reflection high-energy electron diffraction can be regarded as very important complementary tools for non-destructive investigation of the ZnSe(Co) crystal surface layers.
16
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X-Ray Photoelectron Spectroscopy and X-Ray Diffraction Studies of Zn_{1-x}Co_{x}S Diluted Magnetic Semiconductor Crystals

62%
Ławniczak-Jabłońska K., Gołacki Z., Paszkowicz W., Iwanowski R., Johansson L., Heinonen M.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
633-636
EN
X-ray photoelectron spectroscopy and powder X-ray diffraction studies of diluted magnetic semiconducting alloys Zn_{1-x}Co_{x}S, in the composition range 0 ≤ x ≤ 0.18, were performed. The analysis of XPS spectra has shown that admixture of Co into ZnS lattice does not affect the shape and position of Zn 2p core level, whereas certain modification of the S 2p peak shape was observed. The detected binding energy of Co indicated similarity between Co-S and Co-O bond structure. Significant contributions of Co 3d^{7} electrons to the valence band density of states were revealed.
17
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Content available

Mechanism of Radiative Mn^{2+} Intra-Shell Recombination in Bulk ZnMnS

62%
Ivanov V., Godlewski M., Yatsunenko S., Khachapuridze A., Li M., Gołacki Z.
Acta Physica Polonica A
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2001
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vol. 100
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issue 3
351-355
EN
Origin of a fast component of the photoluminescence decay of Mn^{2+} intra-shell ^4T_1 → ^6A_1 transition is discussed based on the results of photoluminescence, photoluminescence kinetics and optically detected magnetic resonance experiments performed for bulk ZnMnS samples with about 1% Mn fraction. It is demonstrated that a fast component of the photoluminescence decay, reported previously for quantum dot structure and related to quantum confinement effects, is also observed in bulk samples and is related by us to very efficient spin cross-relaxation effects.
18
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Resonant Photoemission Spectra of Zn_{1-x}Co_{x}S Valence Band

62%
Kowalski B. J., Gołacki Z., Guziewicz A., Orłowski B. A., Mašek J., Ghijsen J., Johnson R.
|
EN
We report the results of a resonant photoemission study of Zn_{1-x}Co_{x}S. A Co 3d derived contribution to the valence band spectra was revealed as a 5 eV wide structure with two maxima: at the edge of the valence band and about 4 eV below the edge. The results were compared with the total DOS distribution resulting from tight binding-coherent potential approximation calculations.
19
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High Field Magnetization of Sn_{1-x}Gd_{x}Te

62%
Górska M., Anderson J., Wolters C., Łusakowski A., Story T., Gołacki Z.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
347-350
EN
The magnetization of p-type Sn_{1-x}Gd_{x}Te with x up to 0.045 and the hole concentration, p, varying from 2.7 to 8.3×10^{20} cm^{-3} has been measured in magnetic fields up to 27 T, at the temperatures 4.2 and 1.3 K. The data were fitted to a magnetization equation with single-ion and pair terms. From comparison of the exchange parameters determined from the high-field magnetization with those previously obtained from the high-temperature magnetic susceptibility it was found that in samples with p>5×10^{20} cm^{-3} the exchange was of a short-range type, while in samples with a lower carrier concentration the long-range exchange mechanism was observed.
20
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Magnetic Properties of Sn_{1-x}Gd_{x}Te (0.002 ≤ x ≤ 0.09)

52%
Story T., Arciszewska M., Dobrowolski W., Gołacki Z., Górska M., Grodzicka E., Łusakowski A., Dynowska E., Witkowska B.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
935-938
EN
Magnetic, transport and structural properties of bulk crystals of Sn_{1-x}Gd_{x}Te with Gd content 0.002 < x < 0.09 and varying carrier concentrations obtained by an isothermal annealing were studied in the temperature range T = 1.5 - 80 K. We found the effect of resonant increase in antiferromagnetic spin-spin exchange interactions in the crystals with 0.025 ≤ x ≤ 0.05. No effect was found in crystals either with higher (x > 0.05) or with lower (x < 0.025) Gd concentration. The observed Gd composition dependence of the magnetic and transport properties of SnGdTe can be explained in a proposed model relating these experimental properties to the Gd composition induced shift of the position of Gd^{3+/2+} level with respect to the top of the valence band of SnGdTe.
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