Crossing the boundary between face-centred cubic and hexagonal close packed: the structure of nanosized cobalt is unraveled by a model accounting for shape, size distribution and stacking faults, allowing simulation of XRD, XANES and EXAFS

The properties of nanostructured cobalt in the fields of magnetic, catalytic and biomaterials depend critically on Co close packing. This paper reports a structural analysis of nanosized cobalt based on the whole X-ray diffraction (XRD) pattern simulation allowed by the Debye equation. The underlying structural model involves statistical sequences of cobalt layers and produces simulated XRD powder patterns bearing the concurrent signatures of hexagonal and cubic close packing (h.c.p. and f.c.c.). Shape, size distribution and distance distribution between pairs of atoms are also modelled. The simulation algorithm allows straightforward fitting to experimental data and hence the quantitative assessment of the model parameters. Analysis of two samples having, respectively, h.c.p. and f.c.c. appearance is reported. Extended X-ray absorption fine-structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra are simulated on the basis of the model, giving a tool for the interpretation of structural data complementary to XRD. The outlined structural analysis provides a rigorous structural basis for correlations with magnetic and catalytic properties and an experimental reference forab initiomodelling of these properties.

Download Full-text

Local structure of Ge quantum dots determined by combined numerical analysis of EXAFS and XANES data

Journal of Synchrotron Radiation ◽

10.1107/s160057751501913x ◽

2016 ◽

Vol 23 (1) ◽

pp. 253-259 ◽

Cited By ~ 5

Author(s):

Yuanpeng Zhang ◽

Osman Ersoy ◽

Ali Karatutlu ◽

William Little ◽

Andrei Sapelkin

Keyword(s):

Quantum Dots ◽

Structural Model ◽

Volume Ratio ◽

Local Symmetry ◽

Coordination Shell ◽

Edge Structure ◽

X Ray ◽

Ge Quantum Dots ◽

X Ray Absorption ◽

Diamond Type

The sensitivity of X-ray absorption near-edge structure (XANES) to the local symmetry has been investigated in small (∼4 nm) matrix-free Ge quantum dots. TheFDMNESpackage was used to calculate the theoretical XANES spectra that were compared with the experimental data of as-prepared and annealed nanoparticles. It was found that XANES data for an as-prepared sample can only be adequately described if the second coordination shell of the diamond-type structural model is included in theFDMNEScalculations. This is in contrast to the extended X-ray absorption fine-structure data that show only the first-shell signal. These results suggest that, despite the high degree of disorder and a large surface-to-volume ratio, as-prepared small Ge quantum dots retain the diamond-type symmetry beyond the first shell. Furthermore, we utilized this sensitivity of XANES to the local symmetry to study annealed Ge quantum dots and found evidence for significant structural distortion which we attribute to the existence of surface disorder in the annealed oxygen-free Ge quantum dots.

Download Full-text

X-ray absorption spectroscopy principles and practical use in materials analysis

Physical Sciences Reviews ◽

10.1515/psr-2017-0181 ◽

2020 ◽

Vol 5 (4) ◽

Author(s):

Wolfgang Grünert ◽

Konstantin Klementiev

Keyword(s):

Fine Structure ◽

Structural Analysis ◽

Disordered Systems ◽

Structural Information ◽

Research Strategies ◽

Edge Structure ◽

X Ray ◽

Absorption Fine ◽

Wide Range ◽

X Ray Absorption

AbstractThe X-ray Absorption Fine Structure (XAFS) with its subregions X-ray Absorption Near-edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for the structural analysis of materials, which is nowadays a standard component of research strategies in many fields. This review covers a wide range of topics related to its measurement and use: the origin of the fine structure, its analytical potential, derived from the physical basis, the environment for measuring XAFS at synchrotrons, including different measurement geometries, detection modes, and sample environments, e. g. for in-situ and operando work, the principles of data reduction, analysis, and interpretation, and a perspective on new methods for structure analysis combining X-ray absorption with X-ray emission. Examples for the application of XAFS have been selected from work with heterogeneous catalysts with the intention to demonstrate the strength of the method providing structural information about highly disperse and disordered systems, to illustrate pitfalls in the interpretation of results (e. g. by neglecting the averaged character of the information obtained) and to show how its merits can be further enhanced by combination with other methods of structural analysis and/or spectroscopy.

Download Full-text

Chemical and orientational imaging of polymeric samples

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168074 ◽

1994 ◽

Vol 52 ◽

pp. 68-69

Author(s):

H. Ade ◽

B. Hsiao ◽

G. Mitchell ◽

E. Rightor ◽

A. P. Smith ◽

...

Keyword(s):

Ethylene Terephthalate ◽

National Laboratory ◽

Brookhaven National Laboratory ◽

Carbonyl Groups ◽

Aromatic Rings ◽

Edge Structure ◽

X Ray ◽

Scanning Transmission ◽

Polymeric Samples ◽

X Ray Absorption

We have used the Scanning Transmission X-ray Microscope at beamline X1A (X1-STXM) at Brookhaven National Laboratory (BNL) to acquire high resolution, chemical and orientation sensitive images of polymeric samples as well as point spectra from 0.1 μm areas. This sensitivity is achieved by exploiting the X-ray Absorption Near Edge Structure (XANES) of the carbon K edge. One of the most illustrative example of the chemical sensitivity achievable is provided by images of a polycarbonate/pol(ethylene terephthalate) (70/30 PC/PET) blend. Contrast reversal at high overall contrast is observed between images acquired at 285.36 and 285.69 eV (Fig. 1). Contrast in these images is achieved by exploring subtle differences between resonances associated with the π bonds (sp hybridization) of the aromatic groups of each polymer. PET has a split peak associated with these aromatic groups, due to the proximity of its carbonyl groups to its aromatic rings, whereas PC has only a single peak.

Download Full-text

In Vivo Investigation of the Distribution and the Local Speciation of Selenium inAlliumcepa L. by Means of Microscopic X-ray Absorption Near-Edge Structure Spectroscopy and Confocal Microscopic X-ray Fluorescence Analysis

Analytical Chemistry ◽

10.1021/ac060380s ◽

2006 ◽

Vol 78 (22) ◽

pp. 7616-7624 ◽

Cited By ~ 49

Author(s):

Ewa Bulska ◽

Irena A. Wysocka ◽

Małgorzata H. Wierzbicka ◽

Kristof Proost ◽

Koen Janssens ◽

...

Keyword(s):

Fluorescence Analysis ◽

Edge Structure ◽

X Ray ◽

X Ray Absorption

Download Full-text

Full-Field Calcium K-Edge X-ray Absorption Near-Edge Structure Spectroscopy on Cortical Bone at the Micron-Scale: Polarization Effects Reveal Mineral Orientation

Analytical Chemistry ◽

10.1021/acs.analchem.5b04898 ◽

2016 ◽

Vol 88 (7) ◽

pp. 3826-3835 ◽

Cited By ~ 12

Author(s):

Bernhard Hesse ◽

Murielle Salome ◽

Hiram Castillo-Michel ◽

Marine Cotte ◽

Barbara Fayard ◽

...

Keyword(s):

Cortical Bone ◽

Edge Structure ◽

Full Field ◽

Polarization Effects ◽

X Ray ◽

X Ray Absorption

Download Full-text

Local structure and cation distribution analysis of Mn1-xZnxFe2O4 powders by X-ray Absorption Near Edge Structure Spectroscopy

Radiation Physics and Chemistry ◽

10.1016/j.radphyschem.2021.109628 ◽

2021 ◽

pp. 109628

Author(s):

Jaru Jutimoosik ◽

Pinit Kidkhunthod ◽

Theerachai Bongkarn ◽

Rattikorn Yimnirun

Keyword(s):

Cation Distribution ◽

Local Structure ◽

Distribution Analysis ◽

Edge Structure ◽

X Ray ◽

X Ray Absorption

Download Full-text

Database of ab initio L-edge X-ray absorption near edge structure

Scientific Data ◽

10.1038/s41597-021-00936-5 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Yiming Chen ◽

Chi Chen ◽

Chen Zheng ◽

Shyam Dwaraknath ◽

Matthew K. Horton ◽

...

Keyword(s):

High Throughput ◽

Scattering Theory ◽

Research Community ◽

Metal Compounds ◽

Edge Structure ◽

X Ray ◽

Initial Release ◽

Computational Workflow ◽

X Ray Absorption

AbstractThe L-edge X-ray Absorption Near Edge Structure (XANES) is widely used in the characterization of transition metal compounds. Here, we report the development of a database of computed L-edge XANES using the multiple scattering theory-based FEFF9 code. The initial release of the database contains more than 140,000 L-edge spectra for more than 22,000 structures generated using a high-throughput computational workflow. The data is disseminated through the Materials Project and addresses a critical need for L-edge XANES spectra among the research community.

Download Full-text

Theoretical and experimental investigation of point defects in cubic boron nitride

MRS Advances ◽

10.1557/adv.2017.53 ◽

2017 ◽

Vol 2 (29) ◽

pp. 1545-1550 ◽

Cited By ~ 1

Author(s):

Nicholas L. McDougall ◽

Jim G. Partridge ◽

Desmond W. M. Lau ◽

Philipp Reineck ◽

Brant C. Gibson ◽

...

Keyword(s):

Boron Nitride ◽

Cubic Boron Nitride ◽

Optical Emission ◽

Wide Band ◽

Wide Band Gap ◽

Edge Structure ◽

X Ray ◽

Substitutional Defects ◽

X Ray Absorption ◽

Annealing Experiments

ABSTRACTCubic boron nitride (cBN) is a synthetic wide band gap material that has attracted attention due to its high thermal conductivity, optical transparency and optical emission. In this work, defects in cBN have been investigated using experimental and theoretical X-ray absorption near edge structure (XANES). Vacancy and O substitutional defects were considered, with O substituted at the N site (ON) to be the most energetically favorable. All defects produce unique signatures in either the B or N K-edges and can thus be identified using XANES. The calculations coupled with electron-irradiation / annealing experiments strongly suggest that ON is the dominant defect in irradiated cBN and remains after annealing. This defect is a likely source of optical emission in cBN.

Download Full-text