A software package for the analysis of X-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data analysis using theoretical standards from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of atomic absorption data. These programs enable high-quality data analysis that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.

http://cars9.uchicago.edu/xafs_school/Material/Articles/Horae%20JSR2005.pdf

ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT.

Highly active catalysts for the oxygen evolution reaction (OER) are required for the development of photoelectrochemical devices that generate hydrogen efficiently from water using solar energy. Here, we identify the origin of a 500-fold OER activity enhancement that can be achieved with mixed (Ni,Fe)oxyhydroxides (Ni(1-x)Fe(x)OOH) over their pure Ni and Fe parent compounds, resulting in one of the most active currently known OER catalysts in alkaline electrolyte. Operando X-ray absorption spectroscopy (XAS) using high energy resolution fluorescence detection (HERFD) reveals that Fe(3+) in Ni(1-x)Fe(x)OOH occupies octahedral sites with unusually short Fe-O bond distances, induced by edge-sharing with surrounding [NiO6] octahedra. Using computational methods, we establish that this structural motif results in near optimal adsorption energies of OER intermediates and low overpotentials at Fe sites. By contrast, Ni sites in Ni(1-x)Fe(x)OOH are not active sites for the oxidation of water.

/pdf/identification-of-highly-active-fe-sites-in-ni-fe-ooh-for-1kxniexq7l.pdf

Identification of Highly Active Fe Sites in (Ni,Fe)OOH for Electrocatalytic Water Splitting

SIXPack (Sam's Interface for XAS analysis Package), a graphical user interface that allows users simple manipulation and analysis of data, is presented. The modules of SIXPack allow users to: (1) load, calibrate, and average raw data files; (2) perform background subtractions; (3) perform principal component analysis and target transforms; (4) perform least squares fitting of data to standards and functions; (5) perform EXAFS fitting to FEFF phase and amplitude files; (6) create single scattering FEFF phase and amplitude files using a periodic table interface. Novel features of the program allow for the fitted correction of XANES spectra due to self-absorption effects in unknown matrices, which is particularly useful for analysis of geochemical and environmental systems. The core of the XAS analysis routine uses IFEFFIT. SIXPack is developed in Python, is installable across many operating systems and platforms, and is freely available with an Open Source license.

https://iopscience.iop.org/article/10.1238/Physica.Topical.115a01011/pdf

SIXpack: A Graphical user interface for XAS analysis using IFEFFIT

Reference LPI-ARTICLE-1999-017View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

/pdf/metal-oxide-surfaces-and-their-interactions-with-aqueous-22jt31pax0.pdf

Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms.

In this paper, we report the complete synthesis and characterization procedures to generate highly organized and oriented mesoporous titania thin films, using poly(ethylene oxide) (PEO)-based templates. Controlled conditions in the deposition, postsynthesis, and thermal treatment steps allow one to tailor the final mesostructure (2D hexagonal, p6m, or 3D cubic, Im3m). Various techniques were used to determine the time evolution of the mesostructure. Spectroscopic techniques (UV/vis, (17)O NMR) and EXAFS/XANES have been used to follow the chemical changes in the Ti(IV) environment. Crossing these techniques spanning all ranges permits a complete description of the chemistry all the way from solution to the mesostructured metal oxide. A critical discussion on all important chemical and processing parameters is provided; the understanding of these features is essential for a rational design and the reproducible construction of mesoporous materials.

Controlled formation of highly organized mesoporous titania thin films: from mesostructured hybrids to mesoporous nanoanatase TiO2.

A high-order multiple-scattering (MS) approach to the calculation of polarized x-ray-absorption spectra, which includes both x-ray-absorption fine structure and x-ray-absorption near-edge structure, is presented. Efficient calculations in arbitrary systems are carried out by using a curved-wave MS path formalism that ignores negligible paths, and has an energy-dependent self-energy and MS Debye-Waller factors. Embedded-atom background absorption calculations on an absolute energy scale are included. The theory is illustrated for metallic Cu, Cd, and Pt. For these cases the MS expansion is found to converge to within typical experimental accuracy, both to experiment and to full MS theories (e.g., band structure), by using only a few dozen important paths, which are primarily single-scattering, focusing, linear, and triangular.

M. J. Eller

Papers

Multiple-scattering calculations of x-ray-absorption spectra