Multiple scattering calculations at the oxygen K-edge for SiO2

1995 ◽  
Vol 53 ◽  
pp. 602-603
Author(s):  
DJ Wallis ◽  
R Brydson ◽  
PH Gaskell
Keyword(s):  
Multiple Scattering ◽  
Structural Information ◽  
Core Loss ◽  
Calculated Data ◽  
Real Space ◽  
Edge Structure ◽  
Exchange Correlation ◽  
Valence Electrons ◽  
Electron Energy Loss ◽  
Atom Energy

Electron Energy Loss Spectroscopy (EELS) in the STEM is potentially a very powerful technique for studying the structure of materials. The Near Edge Structure (NES) in core loss edges carries information about triplet, and higher order correlation functions and under certain conditions is sensitive to long range atomic correlations. However, since the NES contains strong contributions due to multiple elastic scattering, a simple interpretation in terms of atomic structure is not possible. It is therefore necessary to perform some form of modeling to obtain structural information. One approach to modeling NES is Multiple Scattering (MS) theory.MS calculations have been performed to model the O K-edge ELNES for the α-quartz phase of SiO2 The calculations use a real-space atomic cluster and model the atomic potentials using the Muffin Tin approximation. Effects of the core hole produced upon excitation were accounted for using the (Z+1)* approximation for the excited atom. Energy scales of the calculated data have also been compressed to correct for the energy dependence of the exchange correlation between the photoelectron and the valence electrons which is not accounted for in the calculation.

Probing vacancies and structural distortions at individual defects in ceramics using EELS

1996 ◽  
Vol 54 ◽  
pp. 678-679
Author(s):  
D. J. Wallis ◽  
N. D. Browning
Keyword(s):  
Structural Information ◽  
Core Loss ◽  
Nearest Neighbors ◽  
Ceramic Materials ◽  
Scanning Transmission Electron Microscope ◽  
Real Space ◽  
Atomic Scale ◽  
Structure Property ◽  
Scanning Transmission ◽  
Key Issues

In electron energy loss spectroscopy (EELS), the near-edge region of a core-loss edge contains information on high-order atomic correlations. These correlations give details of the 3-D atomic structure which can be elucidated using multiple-scattering (MS) theory. MS calculations use real space clusters making them ideal for use in low-symmetry systems such as defects and interfaces. When coupled with the atomic spatial resolution capabilities of the scanning transmission electron microscope (STEM), there therefore exists the ability to obtain 3-D structural information from individual atomic scale structures. For ceramic materials where the structure-property relationships are dominated by defects and interfaces, this methodology can provide unique information on key issues such as like-ion repulsion and the presence of vacancies, impurities and structural distortion.An example of the use of MS-theory is shown in fig 1, where an experimental oxygen K-edge from SrTiO3 is compared to full MS-calculations for successive shells (a shell consists of neighboring atoms, so that 1 shell includes only nearest neighbors, 2 shells includes first and second-nearest neighbors, and so on).

The Effect of Local Symmetry on Atomic Resolution EELS Near-Edge Structures: Predictions for Grain Boundaries In NiAl

2000 ◽  
Vol 6 (S2) ◽  
pp. 186-187
Author(s):  
D. A. Pankhurst ◽  
G. A. Botton ◽  
C. J. Humphreys
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Local Density ◽  
Spherical Aberration ◽  
Core Loss ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Atomic Column ◽  
Edge Structure ◽  
Electron Energy Loss

It has been demonstrated that electron energy loss spectrometry (EELS) can be used to probe the electronic structure of materials on the near-atomic scale. The electron energy loss near edge structure (ELNES) observed after the onset of a core edge reflects a weighted local density of final states to which core electrons are excited by fast incident electrons. Lately ‘atomic resolution EELS’ and ‘column-by-column spectroscopy’ have become familiar themes amongst the EELS community. The next generation of STEMs, equipped with spherical aberration (Cs) correctors and electron beam monochromators, will have sufficient spatial and energy resolution, along with the superior signal to noise required, to detect small changes in the ELNES from atomic column to atomic column.Core loss ELNES provides information about unoccupied states, but the structure observed in spectra is sensitive to changes in the underlying occupied states, and thus to the bonding in the material.

The Near Edge Structure of Hexagonal Boron Nitride

2014 ◽  
Vol 20 (4) ◽  
pp. 1053-1059 ◽  
Author(s):  
Nicholas L. McDougall ◽  
Rebecca J. Nicholls ◽  
Jim G. Partridge ◽  
Dougal G. McCulloch
Keyword(s):  
Boron Nitride ◽  
Density Functional ◽  
Light Emission ◽  
Hexagonal Boron Nitride ◽  
Core Loss ◽  
Experimental Studies ◽  
Stacking Faults ◽  
Edge Structure ◽  
Deep Ultraviolet ◽  
Electron Energy Loss

AbstractHexagonal boron nitride (hBN) is a promising material for a range of applications including deep-ultraviolet light emission. Despite extensive experimental studies, some fundamental aspects of hBN remain unknown, such as the type of stacking faults likely to be present and their influence on electronic properties. In this paper, different stacking configurations of hBN are investigated using CASTEP, a pseudopotential density functional theory code. AB-b stacking faults, in which B atoms are positioned directly on top of one another while N atoms are located above the center of BN hexagons, are shown to be likely in conventional AB stacked hBN. Bandstructure calculations predict a single direct bandgap structure that may be responsible for the discrepancies in bandgap type observed experimentally. Calculations of the near edge structure showed that different stackings of hBN are distinguishable using measurements of core-loss edges in X-ray absorption and electron energy loss spectroscopy. AB stacking was found to best reproduce features in the experimental B and N K-edges. The calculations also show that splitting of the 1s to π* peak in the B K-edge, recently observed experimentally, may be accounted for by the presence of AB-b stacking faults.

scholarly journals Real-space multiple-scattering calculation and interpretation of x-ray-absorption near-edge structure

1998 ◽  
Vol 58 (12) ◽  
pp. 7565-7576 ◽  
Author(s):  
A. L. Ankudinov ◽  
B. Ravel ◽  
J. J. Rehr ◽  
S. D. Conradson
Keyword(s):  
Multiple Scattering ◽  
Real Space ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

scholarly journals A primordial 15N-depleted organic component detected within the carbonaceous chondrite Maribo

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Christian Vollmer ◽  
Jan Leitner ◽  
Demie Kepaptsoglou ◽  
Quentin M. Ramasse ◽  
Ashley J. King ◽  
...  
Keyword(s):  
Organic Matter ◽  
Interstellar Medium ◽  
Structural Information ◽  
Carbonaceous Chondrite ◽  
Carbonaceous Chondrites ◽  
Local Interstellar Medium ◽  
Edge Structure ◽  
Electron Energy Loss ◽  
Cm Chondrite ◽  
X Ray Absorption

AbstractWe report on the detection of primordial organic matter within the carbonaceous chondrite Maribo that is distinct from the majority of organics found in extraterrestrial samples. We have applied high-spatial resolution techniques to obtain C-N isotopic compositions, chemical, and structural information of this material. The organic matter is depleted in 15N relative to the terrestrial value at around δ15N ~ -200‰, close to compositions in the local interstellar medium. Morphological investigations by electron microscopy revealed that the material consists of µm- to sub-µm-sized diffuse particles dispersed within the meteorite matrix. Electron energy loss and synchrotron X-ray absorption near-edge structure spectroscopies show that the carbon functional chemistry is dominated by aromatic and C=O bonding environments similar to primordial organics from other carbonaceous chondrites. The nitrogen functional chemistry is characterized by C-N double and triple bonding environments distinct from what is usually found in 15N-enriched organics from aqueously altered carbonaceous chondrites. Our investigations demonstrate that Maribo represents one of the least altered CM chondrite breccias found to date and contains primordial organic matter, probably originating in the interstellar medium.

Coordination “Fingerprints” of Boron Measured by EELS

1990 ◽  
Vol 48 (2) ◽  
pp. 54-55
Author(s):  
H. Sauer ◽  
R. Brydson ◽  
W. Engel ◽  
P.N. Rowley
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Excited Atom ◽  
Core Loss ◽  
High Energy ◽  
Nearest Neighbour ◽  
Final State ◽  
Edge Structure ◽  
Local Symmetries ◽  
Electron Energy Loss

The electron energy-loss near-edge structure (ELNES) associated with a core-loss edge measured using electron energy-loss spectroscopy (EELS) provides, in favourable cases, a “fingerprint” corresponding to the specific nearest-neighbour coordination of the excited atom.Boron atoms in boron-oxygen compounds occur in both trigonal (BO3) and tetrahedral (BO4) coordinations. The B K-ELNES of BO3 and BO4 units (Figs, le and 2b) are remarkably different and arise from the differing local symmetries which determine the final state molecular orbitals. The BK-ELNES of BO3 units exhibit a sharp π∗ peak at ca. 194 eV followed by a broader σ∗ peak some 9-10 eV higher in energy, which may possess a low energy shoulder. BO4 B K-ELNES show no π∗ peak and display solely a σ∗ peak at ca. 199 eV together with a high energy shoulder. Both these spectra may be modelled using multiple scattering calculations.The mineral howlite contains both BO3 and BO4 units and is sensitive to electron-beaminduced damage.

Polarisation effects in hexagonal boron nitride near-edge structure: A real-space multiple scattering approach

2000 ◽  
Vol 49 (3) ◽  
pp. 343-349 ◽  
Author(s):  
M Jaouen ◽  
G Hug ◽  
B Ravel ◽  
A. L Ankudinov ◽  
J. J Rehr
Keyword(s):  
Boron Nitride ◽  
Multiple Scattering ◽  
Hexagonal Boron Nitride ◽  
Real Space ◽  
Edge Structure

Mapping Chemical Bonds in Semiconductor Devices by Monitoring the Shifts of EELS Edges

2017 ◽  
Vol 23 (5) ◽  
pp. 926-931 ◽  
Author(s):  
Pavel Potapov ◽  
Elena L. Svistunova ◽  
Alexander A. Gulyaev
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Core Loss ◽  
Least Square ◽  
Reference Spectrum ◽  
Low Loss ◽  
Edge Structure ◽  
Simultaneous Acquisition ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electron Energy Loss

AbstractScanning transmission electron microscopy (STEM) in combination with electron energy-loss spectroscopy (EELS) can deliver information about variations of bonding at the nm scale. This is typically performed by analyzing the electron-loss near edge structure (ELNES) of given EELS edges. The present paper demonstrates an alternative way of a bonding examination through monitoring the EELS onset positions. Two conditions are essential for their accurate measurement. One (hardware) is using the dual EELS instrumentation that provides near simultaneous acquisition of low-loss and core-loss spectra. Another (software) is the least-square fitting of observed spectra to a reference spectrum. The combination of these hardware and software techniques reveals the positions of EELS onsets with the precision sufficient for mapping tiny variations of bonding. The paper shows that the method is capable of helping to solve practical tasks of nanoscale engineering like the analysis of modern CMOS devices.

Energy-filtered imaging of constituent phases in polymer blends

1996 ◽  
Vol 54 ◽  
pp. 164-165
Author(s):  
E. L. Hall ◽  
G. A. Hutchins
Keyword(s):  
Spatial Resolution ◽  
Structural Damage ◽  
Chemical Nature ◽  
Phase Distribution ◽  
Core Loss ◽  
Edge Structure ◽  
X Ray ◽  
Engineering Plastics ◽  
Electron Energy Loss ◽  
X Ray Absorption

Many engineering plastics consist of complex blends of chemically-distinct constituent polymers and other additives. These components are added in order to achieve desired performance in a variety of properties, including mechanical behavior, processability, color, fire retardency, and others. The distribution of the components, as well as the nature of the interfaces between constituents, are critically important to the performance of the engineering plastic. For many years, TEM has been the key tool in determining phase distribution. However, TEM studies are often limited by the need to stain the various constituents in order to achieve contrast, and also by the inability of TEM methods to unambiguously identify the chemical nature of the various constituents in the image. In the recent past, both electron energy loss spectroscopy (EELS) in the TEM and x-ray absorption near-edge spectroscopy (XANES) using synchrotron sources have demonstrated the ability to differentiate constituents based on characteristic carbon core loss edge structure. The EELS technique has the benefit of high spatial resolution, while the XANES method causes much less structural damage and mass loss. The advent of imaging energy filters has led to a third method for phase delineation for chemically distinct components, which combines the spatial resolution of EELS with the imaging capabilities of XANES.

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