82 research outputs found
Laboratory von H\'amos X-ray Spectroscopy for Routine Sample Characterization
High energy resolution, hard X-ray spectroscopies are powerful element
selective probes of the electronic and local structure of matter, with diverse
applications in chemistry, physics, biology and materials science. The routine
application of these techniques is hindered by the complicated and slow access
to synchrotron radiation facilities. Here we propose a new, economic, easily
operated laboratory high resolution von H\'amos type X-ray spectrometer, which
offers rapid transmission experiments for X-ray absorption, and is also capable
of recording X-ray emission spectra. The use of a cylindrical analyzer crystal
and a position sensitive detector enabled us to build a maintenance free,
flexible setup with low operational costs, while delivering synchrotron grade
signal to noise measurements in reasonable acquisition times. We demonstrate
the proof of principle and give examples for both measurement types. Finally,
tracking of a several day long chemical transformation, a case better suited
for laboratory than synchrotron investigation, is also presented
Channelling study of LaSrCoO films on different substrates
The cobalt oxide system LaCoO and its Sr-doped child compounds have been
intensively studied for decades due to their intriguing magnetic and electronic
properties. Preparing thin LaSrCoO (LSCO) films on different
substrates allows for studies with a new type of perturbation, as the films are
subject to substrate-dependent epitaxial strain. By choosing a proper substrate
for a thin film grow, not only compressing but also tensile strain can be
applied. The consequences for the fundamental physical properties are dramatic:
while compressed films are metallic, as the bulk material, films under tensile
strain become insulating. The goal of this work is to determine the strain
tensor in LSCO films prepared on LaAlO and SrTiO substrates by pulsed
laser deposition using RBS/channelling methods. Apart from the composition and
defect structure of the samples, the depth dependence of the strain tensor, the
cell parameters, and the volume of the unit cell are also determined.
Asymmetric behaviour of the strained cell parameters is found on both
substrates. This asymmetry is rather weak in the case of LSCO film grown on
LaAlO, while stronger on SrTiO substrate. The strain is more effective
at the interface, some relaxation can be observed near to the surface
Hard x-ray spectroscopy in NaxCoO2 and superconducting NaxCoO2 - yH2O: A view on the bulk Co electronic properties
The electronic properties of Co in bulk Na0.7CoO2 and the superconducting
hydrated compound Na0.35CoO2 - y H2O have been investigated by x-ray absorption
spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) using hard
x-rays. The XAS spectra at the Co K-edge were measured in both compounds with
two different polarization directions. The changes in the XAS spectra upon
hydration and their polarization dependence are well accounted for by linear
muffin- tin orbital calculations in the local density approximation. The
underlying electronic structure indicates the strong hybridization between the
Co 3d and O 2p states in both compounds, while the electron localization is
enhanced in the hydrated compound due to the increase of the Co-Co interplanar
distance. The Co K pre-edge further highlights the splitting of the d band as a
result of the crystal field effect and demonstrates the Co valency increase
when Na0.7CoO2 is hydrated. The RIXS spectra measured at the Co K-edge show an
energy loss feature around 10 eV in both compounds in fair agreement with the
calculated dynamical structure factor. The RIXS feature is associated to a
damped plasmon excitation.Comment: 8 page
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Site-Selective Real-Time Observation of Bimolecular Electron Transfer in a Photocatalytic System Using L-Edge X-Ray Absorption Spectroscopy
Time-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [IrIII (ppy)2 (bpy)]+ photosensitizer, in combination with triethylamine as a sacrificial reductant and Fe3(CO)12 as a water reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X-ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations. The presented methods and results will enhance our understanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance
Evolution of Fe Species During the Synthesis of Over-Exchanged Fe/ZSM5 Obtained by Chemical Vapor Deposition of FeCl3
Abstract The evolution of iron in over-exchanged Fe/ZSM5 prepared via chemical vapor deposition of FeCl 3 was studied at each stage of the synthesis. Different characterization techniques (EXAFS, HR-XANES
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