Search results for "K-edge"
showing 10 items of 34 documents
Structural disorder and electronic hybridization in NicMg1−cO solid solutions probed by XANES at the oxygen K edge
2007
A series of NicMg1−cO solid solutions has been studied for the first time looking at the structural disorder by means of x-ray absorption near-edge-structure (XANES) spectroscopy at the oxygen K edge. The experimental XANES signals were analysed within the full multiple scattering formalism and were interpreted taking into account clusters of up to 15 coordination shells around an absorbing oxygen atom. The substitution of nickel atoms by magnesium atoms results in a dramatic decrease of the empty density of states in the conduction band close to the Fermi level due to an exchange of the 3d(Ni)–2p(O) interaction with 3p(Mg)–2p(O). Besides, a simultaneous small decrease of the 3d(Ni)–2p(O) h…
Interpretation of the Cu K-edge EXAFS spectra of Cu3N using ab initio molecular dynamics
2020
Financial support provided by ERDF project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity “Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. This work was supported by a grant from the Swiss National Supercomputing Centre (CSCS) under the project ID s681 .
Cationic vacancies and anomalous spectral-weight transfer in Ti1−xTaxO2thin films studied via polarization-dependent near-edge x-ray absorption fine …
2013
We report the electronic structures of Ta-doped anatase TiO 2 thin films grown by pulsed laser deposition (PLD) with varying magnetization using a combination of first-principles calculations and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. The roles of Ta doping and Ti vacancies are clarified, and the observed room-temperature ferromagnetism is attributed to the localized magnetic moments at Ti vacancy sites ferromagnetically ordered by electron charge carriers. O K -edge spectra exhibit significant polarization dependence which is discussed and supported by first-principles calculations in relation to both the crystal symmetry and the formation of defects. In particula…
Influence of nanoscale order–disorder transitions on the magnetic properties of Heusler compounds for spintronics
2017
Modifications in nanoscale chemical order are used to tune the magnetic properties, namely T-C, of Co2FeSixAl1-x (0 < x < 1). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast reveals nanoscale regions of L2(1) order within a B2 matrix in the off-stoichiometry samples. Perhaps surprisingly, the latter, more chemically disordered structure, exhibits a higher T-C. Upon annealing, the off-stoichiometry samples become more homogeneous with the fraction of L2(1) order decreasing. The short-range order was also investigated using X-ray absorption fine structure (XAFS) measurements at the Co and Fe K edges. Since the local atomic environments of C…
Oxygen K-edge x-ray absorption near-edge structure in crystalline and amorphous molybdenum trioxides
2004
X-ray absorption near-edge structure (XANES) signals at the oxygen K edge in polycrystalline α-MoO3 and amorphous a-MoO3 thin film were analysed within the full-multiple-scattering (FMS) formalism. Significantly different XANES signals were found for non-equivalent oxygen atoms in low-symmetry layered-type α-MoO3 structure. The obtained results are in agreement with the experimental data and allow us to interpret all XANES peaks for α-MoO3. Besides, the FMS XANES simulations, performed for several fragments of α-MoO3 structure, allowed us to explain the O K-edge XANES in amorphous a-MoO3 thin film. We found that although the crystallographic structures of α-MoO3 and a-MoO3 are strongly diff…
Muon spin rotation studies in single crystals of Zn and Cd
1981
Effect of atomic vibrations in XANES: polarization-dependent damping of the fine structure at the Cu K-edge of (creat)2CuCl4
2016
Polarization-dependent damping of the fine structure in the CuK-edge spectrum of creatinium tetrachlorocuprate [(creat)2CuCl4] in the X-ray absorption near-edge structure (XANES) region is shown to be due to atomic vibrations. These vibrations can be separated into two groups, depending on whether the respective atoms belong to the same molecular block; individual molecular blocks can be treated as semi-rigid entities while the mutual positions of these blocks are subject to large mean relative displacements. The effect of vibrations can be efficiently included in XANES calculations by using the same formula as for static systems but with a modified free-electron propagator which accounts f…
When are thin films of metals metallic? Part III
1996
Abstract A large amount of experimental information has indicated that very thin films of metallic elements can exhibit nonmetallic behavior, even on metal substrates. These films undergo a gradual nonmetal to metal transition with increasing film density or thickness. The nonmetallic behavior can be related to electron localization due to strong electron-electron correlation in low dimensional systems, as indicated by the strong enhancement of electron effective mass. The evolution in the electronic structure associated with the nonmetal to metal transition bears a striking resemblance to the behavior observed for free metal clusters. Part I [1], outlined the general concepts of a nonmetal…
Probing the Thermochromic Phase Transition in CuMoO 4 by EXAFS Spectroscopy
2018
The work was supported by philanthropist MikroTik and administrated by the University of Latvia Foundation. The experiment at HASYLAB/DESY was performed within the project I-20160149 EC.
QUADRUPOLAR CHARACTER OF THE Ti K-EDGE PREPEAKS IN TiO2 BY RESONANT AUGER
2002
Resonant spectroscopies offer a new opportunity to get more insight into excited electronic states by studying line shapes and intensities of decay processes. For photon excitations in the pre-K-edge region, the Ti KL 2,3 L 2,3 Auger spectra in TiO 2 show additional peaks when an electron is promoted in localized d-like states via a quadrupolar transition. This resonant process is used to unravel the respective contributions of quadrupolar and dipolar transitions to the absorption edge prepeaks.