170 research outputs found
Hard x-ray emission spectroscopy: a powerful tool for the characterization of magnetic semiconductors
This review aims to introduce the x-ray emission spectroscopy (XES) and
resonant inelastic x-ray scattering (RIXS) techniques to the materials
scientist working with magnetic semiconductors (e.g. semiconductors doped with
3d transition metals) for applications in the field of spin-electronics. We
focus our attention on the hard part of the x-ray spectrum (above 3 keV) in
order to demonstrate a powerful element- and orbital-selective characterization
tool in the study of bulk electronic structure. XES and RIXS are
photon-in/photon-out second order optical processes described by the
Kramers-Heisenberg formula. Nowadays, the availability of third generation
synchrotron radiation sources permits applying such techniques also to dilute
materials, opening the way for a detailed atomic characterization of
impurity-driven materials. We present the K{\beta} XES as a tool to study the
occupied valence states (directly, via valence-to-core transitions) and to
probe the local spin angular momentum (indirectly, via intra-atomic exchange
interaction). The spin sensitivity is employed, in turn, to study the
spin-polarized unoccupied states. Finally, the combination of RIXS with
magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard
magnetic characterization tools.Comment: Topical review (17 pages, 13 figures, 188 references). This is an
author-created, un-copyedited version of an article accepted for publication
in Semiconductor Science and Technology. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from i
A tool to plan photon-in/photon-out experiments: count rates, dips and self-absorption.
A program that helps to plan experiments where the emitted X-rays are detected is presented. The tool is based on the standard formula for fluorescence-detected X-ray absorption spectroscopy and uses tabulated parameters to estimate count rates. The objective is to evaluate the feasibility of an experiment, estimate the influence of self-absorption on the spectral shape and investigate the possibility of range-extended EXAFS. The occurrence of `negative' edges, i.e. a decrease in the detected signal, is discussed
The magnetic exciton of EuS revealed by resonant inelastic x-ray scattering
We report the valence-to-core resonant inelastic x-ray scattering (RIXS) of
EuS measured at the L3 edge of Eu. The obtained data reveal two sets of
excitations: one set is composed of a hole in the S 3p bands and an electron
excited to extended Eu 5d band states, the other is made up from a hole in the
Eu 4f states and an electron in localized Eu 5d states bound to the 4f hole by
its Coulomb potential. The delocalized excitations arise from the
dipole-allowed 5d to 2p emissions, whereas the localized excitations result
from the dipole-forbidden (quadrupole-allowed) 4f to 2p emissions. Both these
emission channels have a comparable intensity thanks to a small number of
occupied 5d states (approximately 0.6) combined with a large number of occupied
4f states (seven). We identify the localized electron-hole pairs with the
"magnetic excitons" suggested in the past as an interpretation of the sharp
features seen in the optical absorption spectra. Our observations provide a
direct experimental evidence of these excitons which has been missing up to
now.Comment: 7 pages, 4 figures, supplemental material (PDF, 8 pages) added as an
ancillary fil
Resonant X-ray emission spectroscopy reveals d–d ligand-field states involved in the self-assembly of a square-planar platinum complex
Resonant X-ray Emission Spectroscopy (RXES) is used to characterize the ligand field states of the prototypic self-assembled square-planar complex, [Pt(tpy)Cl]Cl (tpy=2,2′:6′,2′′-terpyridine), and determine the effect of weak metal-metal and π-π interactions on their energy. © 2012 the Owner Societies
Identification of Dy3+/Dy2+ as electron trap in persistent phosphors
Laser excitation and x-ray spectroscopy are combined to settle a long-standing question in persistent luminescence. A reversible electron transfer is demonstrated, controlled by light and showing the same kinetics as the persistent luminescence. Exposure to violet light induces charging by oxidation of the excited Eu2+ while Dy3+ is simultaneously reduced. Oppositely, detrapping of Dy2+ occurs at ambient temperature or by infrared illumination, yielding afterglow or optically stimulated luminescence, respectively
Неоміфологія постсучасної особистості
У статті аналізуються тенденції деміфологізації та деконструкції особистісного буття в умовах сучасного технологічного суспільства. Результатом цих процесів стає підміна глибинності та ієрархічності особистісного само-визначення імітацією та симуляцією у різноманітних формах: імідж, маска, аватар.В статье анализируются тенденции деконструкции и демифологизации личностного бытия в условиях современного технологического общества. Результатом этих процессов стала подмена глубинности и иерархичности личностного самоопределения имитацией и симуляцией в разнообразных формах: имидж, маска, аватар.The trends of demythologization and reconstruction of personality existence in modern technological society circumstances are analyzed in the article. As a result of such processes, an imitation and simulation in their different forms, such as: image, mask, avatar — substitute the depth and hierarchy of personal self-determination
Effect of alkalis on the Fe oxidation state and local environment in peralkaline rhyolitic glasses
International audienceIron oxidation state and coordination geometry have been determined by Fe K-edge X-ray absorption near edge spectroscopy (XANES) for three sets of silicate glasses of peralkaline rhyolitic composition with different peralkalinity values. These compositions were chosen to investigate the effect of alkali content (and oxygen fugacity) on the Fe oxidation state. The samples were produced by means of hydrothermal vessels at 800 °C with oxygen fugacity conditions ranging from NNO-1.61 to NNO+2.96 log units. Comparison of the pre-edge peak data with those of Fe model compounds of known oxidation state and coordination number allowed determination of the Fe oxidation state and coordination number in all glasses analyzed. Within each group of samples, Fe tends to oxidize with increasing oxygen fugacity as expected. However, alkali content is shown to have a strong effect on the Fe3+/(Fe3++Fe2+) ratio at constant oxygen fugacity: this ratio varies from 0.25 to 0.55 (±0.05) for the least peralkaline series, and from 0.45 to 0.80 (±0.05) for the most peralkaline series. Moreover, pre-edge peak data clearly indicate that Fe3+ is in fourfold coordination in the most peralkaline glasses. Extrapolation of pre-edge peak data suggests the presence of both fourfold and fivefold coordination for trivalent Fe in the other two series. Divalent Fe is suggested to be mainly in fivefold coordination in all the three glass series. The presence of minor amounts of sixfold- and fourfold-coordinated Fe cannot be ruled out by XANES data alone. XANES data suggest that the amount of alkalis also affects the Fe3+ coordination environment resulting in a decrease in the average coordination numbers. Extended X-ray absorption fine structure (EXAFS) data of the most oxidized and peralkaline sample indicate that Fe3+ is in tetrahedral coordination with = 1.85 Å (±0.02). This value compares well with literature data for [4]Fe3+ in crystalline phases (e.g., in tetra-ferriphlogopite or rodolicoite) or in silicate glasses (e.g., phonolite glasses) supporting the XANES-determined coordination number obtained for the most peralkaline glasses. Calculated NBO/T ratios decrease slightly with Fe oxidation because of the higher fraction of network forming Fe, thus increasing the polymerization of the tetrahedral network
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