409 research outputs found
Operando X-ray Absorption Spectroscopy for the study of charge transfer in electrodes for photo-electrochemical water oxidation.
Lecture for students of the doctorate in chemical sciences, Perugia University (cycles XXXV-XXXVI- XXXVII) hold on march 17, 2022
Operando X-ray Absorption Spectroscopy for the study of charge transfer in electrodes for photo-electrochemical water oxidation.
Lecture for students of the doctorate in chemical sciences, Perugia University (cycles XXXV-XXXVI- XXXVII) hold on march 17, 2022.PGP Key: 6A7C CB93 F409 EEE1 86B7 E3F9 98D1 318C 0436 39E
Multi-scale theoretical approach to X-ray absorption spectra in disordered systems: an application to the study of Zn(II) in water
We develop a multi-scale theoretical approach aimed at calculating from first
principles X-ray absorption spectra of liquid solutions and disordered systems.
We test the method by considering the paradigmatic case of Zn(II) in water
which, besides being relevant in itself, is also of interest for biology. With
the help of classical molecular dynamics simulations we start by producing
bunches of configurations differing for the Zn(II)-water coordination mode.
Different coordination modes are obtained by making use of the so-called dummy
atoms method. From the collected molecular dynamics trajectories, snapshots of
a more manageable subsystem encompassing the metal site and two solvation
layers are cut out. Density functional theory is used to optimize and relax
these reduced system configurations employing a uniform dielectric to mimic the
surrounding bulk liquid water. On the resulting structures, fully quantum
mechanical X-ray absorption spectra calculations are performed by including
core-hole effects and core-level shifts. The proposed approach does not rely on
any guessing or fitting of the force field or of the atomic positions of the
system. The comparison of the theoretically computed spectrum with the
experimental Zn K-edge XANES data unambiguously demonstrates that among the
different a priori possible geometries, Zn(II) in water lives in an octahedral
coordination mode.Comment: 8 pages, 3 figure
Response to W. K. Warburton's Comments on Treatment of EXAFS data taken in the fluorescence mode in non-linear conditions
Role of CaO addition in the local order around Erbium in SiO2 –GeO2 –P2O5 fiber preforms
International audienceThe development of materials for optical signal processing represents a major issue in present technology. In this contribution we present a study on Er-doped fiber preforms where particular attention is devoted on how the addition of CaO in the glass modifies the local environment of the rare earth. The results from photoluminescence and Extended X-ray Absorption Fine Structure (EXAFS) are compared and a clear link between the width of the emission line at 1.5 µm and the amorphous/crystalline local structure around the Er3+ ion is evidenced
Comment on a recent sensitivity analysis of radial base function and multi-layer feed-forward neural network models - Response
Contains fulltext :
112420.pdf (publisher's version ) (Open Access
Interface-driven phase separation in multifunctional materials: the case of GeMn ferromagnetic semiconductor
We use extensive first principle simulations to show the major role played by
interfaces in the mechanism of phase separation observed in semiconductor
multifunctional materials. We make an analogy with the precipitation sequence
observed in over-saturated AlCu alloys, and replace the Guinier-Preston zones
in this new context. A new class of materials, the phases, is proposed
to understand the formation of the coherent precipitates observed in the GeMn
system. The interplay between formation and interface energies is analyzed for
these phases and for the structures usually considered in the literature. The
existence of the alpha phases is assessed with both theoretical and
experimental arguments
Archaeometric studies at the GILDA beamline at the European Synchrotron Radiation Facility
In the latest years archaeometry scientists have directed a growing interest to synchrotron radiation techniques. The Italian CRG beamline GILDA at the European Synchrotron Radiation Facility provides to the users the access to
experimental techniques like X-ray absorption spectroscopy and diffraction that are of great potential usefulness in this field. Here we give a technical overview of the
instrumentation available as well as some examples among the archaeometry studies presently in progress on the beamline
- …