scholarly journals Fullerite C60 optical constants in the C 1s NEXAFS region

2021 ◽  
Vol 2103 (1) ◽  
pp. 012168
Author(s):  
D V Sivkov ◽  
S V Nekipelov ◽  
O V Petrova ◽  
D V Bogachuk ◽  
R N Skandakov ◽  
...  
Keyword(s):  
Cross Sections ◽  
Optical Constants ◽  
Absorption Cross ◽  
X Ray ◽  
Carbon Absorption ◽  
Cross Section Spectrum ◽  
Integral Relations ◽  
Atomic Form Factor ◽  
Using Data ◽  
X Ray Absorption

Abstract Using data on the absorption cross sections the refraction coefficient spectral dependence n(E) and the spectra of the remaining optical coefficients (reflection coefficient, phase shift, and atomic form factor) in the fullerite C60 C 1s near edge X-ray absorption fine structure (NEXAFS) region (280–350 eV) were determined. For the n(E) calculations the Kramers-Kronig integral relations (KKRs) were used. The KKR computations were performed using data on atomic carbon absorption cross sections in the 10–30000 eV range and on solid and gaseous C60 – in the 0–120 eV. Absorption cross section spectrum in the fullerite C60 C 1s NEXAFS region were measured.

scholarly journals Cr L-Edge X-ray Absorption Spectroscopy of CrIII(acac)3 in Solution with Measured and Calculated Absolute Absorption Cross Sections

2018 ◽  
Vol 122 (29) ◽  
pp. 7375-7384 ◽  
Author(s):  
Markus Kubin ◽  
Meiyuan Guo ◽  
Maria Ekimova ◽  
Erik Källman ◽  
Jan Kern ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Cross Sections ◽  
Absorption Cross ◽  
X Ray ◽  
X Ray Absorption

Photoelectric Atomic Absorption Cross Sections for Elements 2 = 6 to 54 in the Medium Energy X-ray Range 5 to 25 keY

1975 ◽  
Vol 30 (9) ◽  
pp. 1133-1142 ◽  
Author(s):  
J. D. Stephenson
Keyword(s):  
Atomic Absorption ◽  
Cross Sections ◽  
Absorption Cross ◽  
Medium Energy ◽  
Absorption Coefficients ◽  
X Ray ◽  
Rigorous Theory ◽  
Mass Absorption ◽  
X Ray Absorption

A comparison is made between recent computations of X-ray photoeffect absorption cross sections, using screened hydrogen-like eigenfunctions, given in Part I1, and those of an alternate more rigorous theory together with those estimable from experimental X-ray absorption coefficients. Some inherent limitations, which restrict the present results, are discussed. Photoeffect mass absorption coefficients for a limited number of elements between Z = 10 and 39 are determined from the hydrogen-like theory, using five characteristic X-ray energies from NiLa 1 (0.852 keV) to TiLa 1 (4.511 keV)

scholarly journals Relativistic Corrections to Phase Shift Calculation in the GNXAS Package

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1021
Author(s):  
Nodoka Hara ◽  
Andrea Di Di Cicco ◽  
Georghii Tchoudinov ◽  
Keisuke Hatada ◽  
Calogero Renzo Natoli
Keyword(s):  
Phase Shift ◽  
Multiple Scattering ◽  
Cross Sections ◽  
Basic Structure ◽  
Absorption Cross ◽  
Structural Refinement ◽  
Relativistic Case ◽  
X Ray ◽  
Relativistic Corrections ◽  
X Ray Absorption

Modern XAFS (X-ray Absorption Fine Structure) data-analysis is based on accurate multiple-scattering (MS) calculations of the x-ray absorption cross-section. In this paper, we present the inclusion and test of relativistic corrections for the multiple-scattering calculations within the GnXAS suite of programs, which is relevant to the treatment of the XAFS signals when atoms with high atomic number are contained into the system. We present a suitable strategy for introducing relativistic corrections without altering the basic structure of the programs. In particular, this is realized by modifying only the Phagen program calculating the atomic absorption cross sections and scattering t-matrices for the selected cluster. The modification incorporates a pseudo-Schrödinger Equation (SE) replacing the Dirac relativistic form. The phase-shift calculations have been put to a test in two known molecular and crystalline cases: molecular bromine Br2 and crystalline Pb. Calculations in an extended energy range have been shown to be very close to the non-relativistic case for Br2 (Br K-edge) while corrections have been found to exceed 25% for amplitude and phases of the XAFS multiple-scattering signals (Pb L3-edge). Benefits in the structural refinement using relativistic corrections are discussed for crystalline Pb at room temperature.

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

scholarly journals Anisotropy of X-ray Absorption Cross Section in CeCoGe3 Single Crystal

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 544
Author(s):  
Andrei Rogalev ◽  
Fabrice Wilhelm ◽  
Elena Ovchinnikova ◽  
Aydar Enikeev ◽  
Roman Bakonin ◽  
...  
Keyword(s):  
Cross Section ◽  
Absorption Cross Section ◽  
Linear Dichroism ◽  
X Rays ◽  
Absorption Cross ◽  
X Ray ◽  
Measured Absorption ◽  
Linearly Polarized ◽  
X Ray Absorption ◽  
Absorption Edges

Absorption spectra of two orthogonal linearly polarized x-rays in a single CeCoGe3 crystal were measured at the ID12 beamline of the ESRF for the energies near the K-edges of Ge, Co and near the L23 edges of Ce. The X-ray natural linear dichroism (XNLD) was revealed in the vicinity of all the absorption edges, which indicates a splitting of electronic states in a crystalline field. Mathematical modelling in comparison with experimental data allowed the isotropic and anisotropic parts of atomic absorption cross section in CeCoGe3 to be determined near all measured absorption edges. The calculations also show that the “average” anisotropy of the cross section close to the Ge K-edge revealed in the experiment is less than the partial anisotropic contributions corresponding to Ge atoms in two different Wyckoff positions.

scholarly journals FDMX: extended X-ray absorption fine structure calculations using the finite difference method

2016 ◽  
Vol 23 (2) ◽  
pp. 551-559 ◽  
Author(s):  
Jay D. Bourke ◽  
Christopher T. Chantler ◽  
Yves Joly
Keyword(s):  
Fine Structure ◽  
Energy Range ◽  
Cross Sections ◽  
Full Potential ◽  
Final State ◽  
X Ray ◽  
Complete Representation ◽  
Absorption Fine ◽  
Energy Dependent ◽  
X Ray Absorption

A new theoretical approach and computational package,FDMX, for general calculations of X-ray absorption fine structure (XAFS) over an extended energy range within a full-potential model is presented. The final-state photoelectron wavefunction is calculated over an energy-dependent spatial mesh, allowing for a complete representation of all scattering paths. The electronic potentials and corresponding wavefunctions are subject to constraints based on physicality and self-consistency, allowing for accurate absorption cross sections in the near-edge region, while higher-energy results are enabled by the implementation of effective Debye–Waller damping and new implementations of second-order lifetime broadening. These include inelastic photoelectron scattering and, for the first time, plasmon excitation coupling. This is the first full-potential package available that can calculate accurate XAFS spectra across a complete energy range within a single framework and without fitted parameters. Example spectra are provided for elemental Sn, rutile TiO2and the FeO6octahedron.

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