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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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EXAFS Determination of Bond Lengths in Zn_{1-x}Fe_{x}S Ternary Alloys

100%
Iwanowski R. J., Ławniczak-Jabłońska K.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
797-801
EN
Studies of local atomic structure in the zinc-blende Zn_{1-x}Fe_{x}S (x=0.11-0.50) diluted magnetic semiconductors with the use of the EXAFS technique are reported for the first time. They include the K-edge EXAFS measurements for both cationic elements (Zn, Fe). The experiment was carried out at room temperature in the transmission mode using synchrotron radiation of the DCI storage ring in Orsay, France. A detailed EXAFS analysis for different crystal compositions (x) gave a convincing evidence for a bimodal distribution of the nearest-neighbour interatomic distances in Zn_{1-x}Fe_{x}S within the iron solid-solubility limit. It has also revealed, within the accuracy of this method, constancy of both the nearest-neighbour cation-anion distances (i.e. Zn-S and Fe-S) in the composition range studied.
3
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Lattice Site Occupancy in Ternary Ordered Ni_{3}Al_{1-x}Fe_{x} Alloys Estimated by EXAFS

81%
Ławniczak-Jabłońska K., Pascarelli S., Boscherini F., Kozubski R.
Acta Physica Polonica A
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1992
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vol. 82
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issue 2
315-322
EN
Extended X-ray absorption fine structure (EXAFS) spectroscopy offers additional experimental evidence to the solution of site occupancy problem in ternary NiAlX alloys. A study of local order in the stoichiometric Ni_{3}Al_{1-x}Fe_{x} ternary alloys (x = 0.02, 0.05, 0.10, 0.15, and 0.25) by EXAFS at the K-edge of Fe in the energy range from 7000 eV to 7600 eV are presented. Three models of substitutional behavior are considered - the preferential substitution of Fe atoms in: 1) Ni sites, 2) Al sites, 3) both sites. Data analysis was performed with theoretical and experimentally determined scattered photoelectron phases and amplitudes. The results of the EXAFS analysis are consistent with the picture in which most of the Fe atoms substitute Al sites and less than 25% of Fe atoms substitute Ni sites. Alloys with more than 10 at% of Fe showed higher tendency for ordering than those containing less than 10 at% Fe.
4
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Chemical Shifts at K-Absorption Edges of Transition Metals Admixed To ZnS and ZnSe

81%
Iwanowski R. J., Ławniczak-Jabłońska K., Traverse A.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
803-808
EN
This paper gives the experimental evidence of systematic X-ray K-absorption edge studies in an effort to analyse the effect of cation chemical shift in the group of compounds type Zn_{1-x}M_{x}A (M = Mn, Fe, Co, Ni; A = S, Se). The observed chemical shift was found practically independent of the choice of anion, whereas it revealed a noticeable decrease when passing from Mn to Zn. The effect was ascribed to the change of the 3d shell occupation. The calculations of the effective cation charge (based on the theoretical approach of Kitamura and Chen, 1991) have shown that in the case of transition metals admixed to ZnS and ZnSe there is a contribution of the 3d electrons to the overall charge transfer, which indicates that the ability of 3d electrons to participate in predominantly ionic bond decreases with 3d orbit filling.
5
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Study of Mo-Ni Alloys by X-Ray Spectroscopies

81%
Ławniczak-Jabłońska K., Heinonen M., Inoue J., Tohyama T.
Acta Physica Polonica A
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1993
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vol. 83
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issue 1
115-124
EN
Band structure investigations of the random MoNi_{4} and MoNi_{3} alloys, performed by emission and photoelectron spectroscopy, is reported. The X-ray emission and X-ray photoelectron spectra allowed to study the occupied valence band states below Fermi level. These techniques gave the full description of changes in the density of valence electron states distribution due to substitution of Mo atoms into the fcc Ni lattice up to 25 at%. The analysis of the emission and photoelectron spectra led to clear distinction between the changes in spectra caused by density of states structure and by additional effects involved in creation of the particular spectra. The experimental data are compared with the density of states calculated using coherent potential approximation and linear muffin-tin orbital methods.
6
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X-Ray Photoelectron Spectroscopy and X-Ray Diffraction Studies of Zn_{1-x}Co_{x}S Diluted Magnetic Semiconductor Crystals

61%
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.
7
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X-Ray Absorption Studies of Ge Layers Buried in Silicon Crystal

61%
Demchenko I., Ławniczak-Jabłońska K., Zhuravlev K., Piskorska E., Nikiforov A., Welter E.
Acta Physica Polonica A
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2002
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vol. 101
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issue 5
709-717
EN
Polarization-dependent X-ray absorption spectroscopy was used to study the local microstructure of Ge layers buried in silicon. The layers with thickness from 6 to 20 monolayers of Ge were grown by molecular beam epitaxy on Si substrate and were covered by Si (20 nm). To investigate the morphology of grown structures, X-ray absorption near edge structure and extended X-ray absorption fine structure analysis of the Ge K-edge was done. The performed qualitative analysis proves that X-ray absorption spectra are very sensitive to the local order in the formed structures and are sources of unique information about morphology of the buried Ge layers. Using these techniques we were able to observe the changes in atomic order around the Ge atoms in investigated buried layers and compare the formed atomic order with that in crystalline Ge. A substantial increase in intensity, broadening and chemical shift of the X-ray absorption near edge structure spectrum for 8 ML were observed. It can be related to the increase in density of electron states caused by increase in the localization of the states due to potential appearing at the Ge island boundaries and indicated the formation of quantum dots. The observed in-plane modulations of radial distribution and out-of-plane for different layers were discussed.
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