EELS Fine Structure Research Articles

Short-range-order in (ZnSnN2)1-x (ZnO)2x as Examined by EELS Fine Structure

Short-range-order in (ZnSnN2)1-x (ZnO)2x as Examined by EELS Fine Structure

Atomically Resolved EELS Elemental and Fine Structure Mapping via Multi-Frame and Energy-Offset Correction Acquisition

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Towards atomically resolved EELS elemental and fine structure mapping via multi-frame and energy-offset correction spectroscopy

Electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy are two of the most common means for chemical analysis in the scanning transmission electron microscope. The marked progress of the instrumentation hardware has made chemical analysis at atomic resolution readily possible nowadays. However, the acquisition and interpretation of atomically resolved spectra can still be problematic due to image distortions and poor signal-to-noise ratio of the spectra, especially for investigation of energy-loss near-edge fine structures. By combining multi-frame spectrum imaging and automatic energy-offset correction, we developed a spectrum imaging technique implemented into customized DigitalMicrograph scripts for suppressing image distortions and improving the signal-to-noise ratio. With practical examples, i.e. SrTiO3 bulk material and Sr-doped La2CuO4 superlattices, we demonstrate the improvement of elemental mapping and the EELS spectrum quality, which opens up new possibilities for atomically resolved EELS fine structure mapping.

EFTEM Contrast Tuning and EELS Fine Structure Analysis for Characterization of Carbon Containing Ultra-Low-k Dielectric Materials

Journal Article EFTEM Contrast Tuning and EELS Fine Structure Analysis for Characterization of Carbon Containing Ultra-Low-k Dielectric Materials Get access Brenda Prenitzer, Brenda Prenitzer NanoSpective, Inc., Orlando, Florida, USA Search for other works by this author on: Oxford Academic Google Scholar Stephen Schwarz, Stephen Schwarz NanoSpective, Inc., Orlando, Florida, USA Search for other works by this author on: Oxford Academic Google Scholar Brian Kempshall, Brian Kempshall NanoSpective, Inc., Orlando, Florida, USA Search for other works by this author on: Oxford Academic Google Scholar Imen Rezadad Imen Rezadad NanoSpective, Inc., Orlando, Florida, USAPhysics Department, University of Central Florida, Orlando, Florida, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 831–832, https://doi.org/10.1017/S143192761500495X Published: 23 September 2015

Performances of an 80–200 kV microscope employing a cold-FEG and an aberration-corrected objective lens

The performances of a newly developed 80-200 kV cold field emission gun (CFEG) transmission electron microscope (TEM) integrating a spherical aberration corrector for a TEM image-forming lens have been evaluated. To begin, we show that the stability of both emission and probe currents makes use of this new CFEG much friendlier. The energy spread of electrons emitted from the CFEG has been measured as a function of emission current and shows a very last 0.26 eV energy resolution at 200 kV and even 0.23 eV at 80 kV. The combination of the CFEG and the CEOS™ aberration corrector, associated with enhanced mechanical and electrical stabilities of this new microscope, allows reaching an information transfer below 75 pm at 200 and 80 pm at 80 kV. This unseen resolution at 200 kV has allowed us to study the structure of CoPt nanoparticles by observing direct images of their atomic arrangement along the high indexes zone axis. We have evidenced the presence of defects in these nanostructures that are not parallel to the electron beam. The precise stoichiometry of two iron oxides, FeO and Fe2O3, has been determined from an analysis of iron valence state that was obtained from a direct analysis of EELS fine structures spectrum of the two oxides.

Characterisation of Exsolution Phenomena by Mapping Eels Fine Structure

Characterisation of Exsolution Phenomena by Mapping Eels Fine Structure

Evaluation of Methods for Extracting Chemical Information from Eels Line-Spectra Across Interfaces

EELS fine structures on characteristic core edges are closely related to the bonding type and structural environment around the excited atoms. Consequently, they constitute useful hints for investigating the electronic properties at interfaces. One major difficulty then lies in the extraction of the information relevant to the involved atoms, from that due to neighbouring atoms on both sides of the selected interface seen end on by the impinging electrons. We have investigated possible ways to reach this goal, using the spectrum-line method, which consists in acquiring sequences of spectra at well defined increments (0.3 nm) while scanning a subnanometer electron probe (0.7 nm) across the interface. This approach constitutes one step forward with respect to the spatial-difference (SD) method which processes spectra acquired on two adjacent areas, one encompassing the interface, the other one on a reference area nearby. A normalized version (NSD) has been introduced to extend its field of application from grain boundaries to heterophase interfaces in order to enhance their specific ELNES contribution

EELS as a Probe of Local Electronic Structure and Cohesion

There is an intimate connection between the electronic structure of a material and its physical properties. to change one, is to change the other. Some of the most striking illustrations of this relationship can be found at grain boundaries in metals and their alloys. Here, the most important changes in cohesion can be described by changes in the local density of states (LDOS), which in turn can be measured using EELS [1]. The first demonstration that EELS could be used to connect the electronic and mechanical properties of a material was in revealing the role that boron has in restoring a bulk-like bonding to grain boundaries in Ni3Al [2,3]. Boron was known to change the fracture mode in Ni3Al from intergranular to transgranular, possibly by enhancing grain boundary cohesion.What interested me in this project, when John Silcox first suggested it as a thesis topic, was the potential of using the EELS fine structure to measure materials properties directly.

Current Limits in Predicting Eels Fine Structure

Electron energy loss spectroscopy (EELS) probes electronic excitations of a solid on the atomic scale. The widespread availability of first-principles calculations has lead to an explosion of theoretical calculations of EELS spectra. Agreement between theory and experiment is generally reported to be good at the typical energy resolutions in commercial microscopes of 0.7-1.3 eV. However a brief survey of the X-ray absorption literature suggests that the anticipated introduction of monochromators, along with improvements in energy stability, and spectrometer resolution will unmask many more effects that cannot be predicted as precisely as they can be measured.The shape and binding energy of a core excitation is determined by both the ground state electronic structure (initial state effects) and the reponse to the excited electron-hole (final state effects) (Fig. 1). Errors in the initial state, such as the systematic errors in band gaps (and hence band offsets) are inherent in the local density approximation eigenvalues used to simulate EELS spectra.

New Approaches for Energy Filtered Imaging and EELS Analysis

Abstract Electron energy-loss spectroscopy imaging is now becoming an established and indispensable tool in high-resolution materials characterization. Whether the imaging approach is based on post column filters attached to a conventional transmission electron microscope (TEM) or on parallel spectrometers on a scanning (field emission) TEM, energy filtered (EF) microscopy is having a significant impact in materials science (e.g. Ref. 1). Elemental mapping, however, is not the only imaging tool accessible with EF microscopy. EELS images and spectra are often only part of the data that is obtained when samples are characterized in an analytical TEM. Complementary information is also obtained from EDS spectra which are often analyzed independently from the EELS data and from EELS near edge structures. When the EELS fine structure is altered due to changes in chemical state of the probed atoms, additional information is accessible and can potentially be used in novel methods of image acquisition.

Using EELS fine structures: understanding the chemical bond and obtaining spectroscopic images

Using EELS fine structures: understanding the chemical bond and obtaining spectroscopic images

Beyond fingerprinting: simple but quantitative models of EELS fine structure and the cohesion of interfaces

Spatially resolved EELS in a STEM provides unique opportunities to examine how local structural and electronic properties can affect macroscopic properties of a solid. Perhaps nowhere else are these connections as pronounced as at interfaces. For instance, H embrittles and B strengthens the grain boundaries in Ni3Al, a prototypical high-temperature intermetallic. EELS measurements of these boundaries have revealed the changes in electronic structure that correlate with the altered mechanical properties of the material.The interfacial states, which rarely extend more than an atomic layer or so from the boundary, can only be observed with great care. Not only is a stable microscope and very efficient detector required, but also a good understanding of how the probe interacts with the specimen. Artifacts due to radiation damage are a real possibility. If the boundary is examined in a strongly diffracting orientation (as is often the case with special boundaries) probe dechanneling can profoundly alter the measured spectra. This can be avoided by tilting the boundary a few mrad away from the zone axis, which limits the spatial resolution to being sub-nanometer, but not atomic.

Analyses of EELS fine structures of different silicon compounds

Electron energy loss spectra of different silicon compounds, in particular, silicon carbide, dioxide, and oxycarbide, are analysed experimentally as well as theoretically. For this purpose features measured of both the low-loss region and the SiL 23 inner-shell excitation are compared with results of corresponding calculations. In the theoretical treatment the features of the low-loss region are interpreted as superpositions of plasmon and interband excitations. On the basis of the energy eigenvalues E m and the occupation densities of the occupied valence states attained by MNDO (modified neglect of diatomic overlap) calculations the scattering function Im {-1/e(E)} in the low-loss region is simulated. The low-loss features attained both experimentally and theoretically agree quite well. The fine structure of the SiL 23 ionization edge is interpreted using densities of unoccupied states obtained by MNDO calculations, too. The density of states calculated depends on the chemical bonding as experimentally proved. The calculations enable predictions concerning the electronic structure of the silicon compounds under investigation, whereas the limits of LCAO (linear combination of atomic orbitals) methods have to be considered if inelastic electron scattering processes are described.

Combined HRTEM, X-ray microchemical and EELS fine structure analysis of planar defects in YBa 2Cu 3O 7−δ

High temperature superconductors in the systems YBa 2Cu 3O 7−δ (123) and decomposed YBa 2Cu 4O 7−δ (124) often contain planar faults with (001) as the nominal fault plane. Such planar defects have been analyzed using a unique combination of high resolution TEM (HRTEM) imaging and high resolution analytical electron microscopy (HRAEM). HRTEM confirmed that these planar faults are stacking faults with double or multiple insertion of crystal planes parallel to the c-plane of the crystal, most probably CuO planes. X-ray microanalysis clearly showed enrichment of copper associated with these defects. EELS fine structure of CuL 23 edge from the fault regions resembled that of pure CuO. The combined results indicate that the planar defects are in fact insertions of extra CuO planes in an otherwise regular 123 crystal unit cell.

Site symmetry effects in the EELS fine structure of Be2C

A relationship between observed electron energy loss near edge fine structure (ELNES) and the local site symmetry of the excited atomic species has recently been demonstrated by Taftϕ and Zhu. These workers have shown that the K edge ELNES (0 to 20 eV above threshold) of Mg and Al octahedrally coordinated by oxygen is dominated by a single peak approximately 10eV wide, while the K edge ELNES of Mg, Al, and Si at tetrahedral sites exhibit one or two narrow (width 5eV) features. We present here an initial study of similar behavior in the antifluorite structure crystal Be2C. This system was selected because C is at an octahedral site and Be is at a tetrahedral site (see Fig.1) Furthermore, the light elements involved make acquisition of the ELNES signal less difficult than for heavier elements.