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Combined X-Ray Diffraction and Absorption Study οf Crystalline Vanadium-Doped Lithium Disilicate

100%
Paszkowicz W., Wolska A., Klepka M., abd el All S., Ezz-Eldin F.
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issue 2
315-318
EN
Structure of vanadium-doped lithium disilicate, Li_{2}Si_{2}O_{5} (Ccc2 space group) is studied. This crystalline phase is obtained by annealing of the doped lithium disilicate glass for 4 h at 550°C. X-ray diffraction and X-ray absorption near-edge structure analysis indicate location of vanadium atoms at Si sites. the lattice parameters are found to increase isotropically with increasing vanadium content. the valency of vanadium ions is discussed on the basis of X-ray absorption near-edge structure results.
2
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Study of the Local Environment of Mn Ions Implanted in GaSb

86%
Wolska A., Lawniczak-Jablonska K., Klepka M., Barcz A., Hallen A., Arvanitis D.
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issue 2
286-292
EN
The first attempts to establish an implantation process leading to formation of ferromagnetic inclusions inside the GaSb matrix are presented. Gallium antimonide containing ferromagnetic MnSb precipitations is considered as a promising material for novel spintronic applications. It is possible to obtain such inclusions during the molecular beam epitaxy (MBE) growth. However, for commercial application it would be also important to find an optimal way of producing this kind of inclusions by Mn ions implantation. In order to achieve this goal, several parameters of implantation and post annealing procedures were tested. The ion energy was kept at 10 keV or 150 keV and four different ion doses were applied, as well as various annealing conditions. The analysis of X-ray absorption spectra allowed to estimate the local atomic order around Mn atoms. Depending on the implantation energy and annealing processes, the manganese oxides or manganese atoms located in a heavily defected GaSb matrix were observed. The performed analysis helped in indicating the main obstacles in formation of MnSb inclusions inside the GaSb matrix by Mn ion implantation.
3
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X-ray Absorption Fine Structure Investigation of the Low Temperature Grown ZnCoO Films

86%
Wolska A., Klepka M., Witkowski B., Witkowski M., Guziewicz E., Godlewski M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
883-887
EN
ZnO based diluted magnetic semiconductors are intensively investigated for possible spintronic applications. In the present work we investigate the ZnCoO layers grown at low temperature by atomic layer deposition. The local atomic structure of a series of layers with different Co concentration is investigated by the X-ray absorption fine structure measurements. Two groups of ZnCoO layers are investigated - the ones with an uniform Co distribution and highly nonuniform films. For uniform samples we observe that a majority of Co atoms is built into the ZnO matrix substituting the Zn atoms. In contrast, for the nonuniform samples, metallic Co inclusions are also observed. These results are in strong correlation with the magnetic properties of the films studied separately. Samples with the uniform Co distribution (Co substitutes Zn in ZnO) are paramagnetic, whereas the nonuniform ones show a ferromagnetic response.
4
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XANES Studies of Mn K and L_{3,2} Edges in the (Ga,Mn)As Layers Modified, by High Temperature Annealing

73%
Wolska A., Lawniczak-Jablonska K., Klepka M., Jakieła R., Demchenko I., Sadowski J., Holub-Krappe E., Persson A., Arvanitis D.
Acta Physica Polonica A
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2008
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vol. 114
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issue 2
357-366
EN
Ga_{1-x}Mn_xAs is commonly considered as a promising material for microelectronic applications utilizing the electron spin. One of the ways that allow increasing the Curie temperature above room temperature is to produce second phase inclusions. In this paper Ga_{1-x}Mn_xAs samples containing precipitations of ferromagnetic MnAs are under consideration. We focus on the atomic and electronic structure around the Mn atoms relating to the cluster formation. The changes in the electronic structure of the Mn, Ga and As atoms in the (Ga,Mn)As layers after high temperature annealing were determined by X-ray absorption near edge spectroscopy. The experimental spectra were compared with the predictions of ab initio full multiple scattering theory using the FEFF 8.4 code. The nominal concentration of the Mn atoms in the investigated samples was 6% and 8%. We do not observe changes in the electronic structure of Ga and As introduced by the presence of the Mn atoms. We find, in contrast, considerable changes in the electronic structure around the Mn atoms. Moreover, for the first time it was possible to indicate the preferred interstitial positions of the Mn atoms.
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