Atomic Scale Characterization of Vacancy Ordering in Oxygen Conducting Membranes

2002 ◽  
Vol 8 (6) ◽  
pp. 475-486 ◽  
Author(s):  
Robert F. Klie ◽  
Nigel D. Browning
Keyword(s):  
Defect Formation ◽  
Bulk Material ◽  
Electronic Conductivity ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Atomic Scale ◽  
Structure Property ◽  
Dark Field Imaging ◽  
Scanning Transmission ◽  
Scale Characterization

This article presents a comprehensive investigation of (La, Sr)FeO3 by correlated atomic resolution annular dark field imaging and electron energy loss spectroscopy. Here, the ability of these techniques to characterize point defect formation and phase transitions under reducing conditions in situ in the scanning transmission electron microscope is evaluated and the influence of oxygen vacancies on the structure–property relationships is discussed. In particular, the evolution of the Ruddlesden–Popper, Brownmillerite, and Aurivillius phases can be associated directly with the ionic and electronic conductivity of the bulk material under different thermodynamic conditions. These results lead naturally to an atomistic defect chemistry model to explain the high temperature ionic and electronic conductivity in this and other perovskite materials.

scholarly journals Atomic-Scale Characterization of Commensurate and Incommensurate Vacancy Superstructures in Natural Pyrrhotites

2021 ◽  
Vol 106 (1) ◽  
pp. 82-96 ◽  
Author(s):  
Lei Jin ◽  
Dimitrios Koulialias ◽  
Michael Schnedler ◽  
Andreas U. Gehring ◽  
Mihály Pósfai ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Atomic Scale ◽  
Past Century ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Local Measurements ◽  
Scale Characterization

Abstract Pyrrhotites, characterized by the chemical formula Fe1–δS (0 < δ ≤ 1/8), represent an extended group of minerals that are derived from the NiAs-type FeS aristotype. They contain layered arrangements of ordered Fe vacancies, which are at the origin of the various magnetic signals registered from certain natural rocks and can act as efficient electrocatalysts in oxygen evolution reactions in ultrathin form. Despite extensive studies over the past century, the local structural details of pyrrhotite superstructures formed by different arrangements of Fe vacancies remain unclear, in particular at the atomic scale. Here, atomic-resolution high-angle annular dark-field imaging and nanobeam electron diffraction in the scanning transmission electron microscope are used to study natural pyrrhotite samples that contain commensurate 4C and incommensurate 4.91 ± 0.02C constituents. Local measurements of both the intensities and the picometer-scale shifts of individual Fe atomic columns are shown to be consistent with a model for the structure of 4C pyrrhotite, which was derived using X-ray diffraction by Tokonami et al. (1972). In 4.91 ± 0.02C pyrrhotite, 5C-like unequally sized nano-regions are found to join at anti-phase-like boundaries, leading to the incommensurability observed in the present pyrrhotite sample. This conclusion is supported by computer simulations. The local magnetic properties of each phase are inferred from the measurements. A discussion of perspectives for the quantitative counting of Fe vacancies at the atomic scale is presented.

Atomic Scale Characterization Of Interfaces And Defects In Non-Stoichiometricmulticomponent Oxides

1999 ◽  
Vol 5 (S2) ◽  
pp. 106-107
Author(s):  
S. Stemmer ◽  
S. K. Streiffer ◽  
A. Sane ◽  
T. J. Mazanec ◽  
N. D. Browning
Keyword(s):  
Dark Field ◽  
Atomic Scale ◽  
Chemical Information ◽  
Structure Property ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Scale Characterization ◽  
Electron Microscopes

The ability to obtain chemical information with (near) atomic resolution has recently become possible by a combined approach of Z-contrast imaging with electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopes. This method is particularly interesting for the characterization of structure-property relationships in novel multicomponent oxides, which possess added functionality due to their high nonstoichiometry.In this paper we demonstrate the capabilities of this method in analyzing the microstructural mechanisms of accommodation of non-stoichiometry, using two example systems: (Ba,Sr)TiO3thin films for DRAM applications, grown by MOCVD with different amounts of excess titanium, and an oxygen-deficient perovskite ceramic, SrCoOx. The experiments were performed in a JEOL JEM 201 OF field emission transmission electron microscope, operating at 200 kV, equipped with an annular dark-field detector, scanning unit and a post-column imaging filter (Gatan GIF 200). This microscope has been demonstrated to achieve probe sizes of under 1.5 Å .

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).

Stem Without Spherical Aberration

1999 ◽  
Vol 5 (S2) ◽  
pp. 670-671 ◽  
Author(s):  
O.L. Krivanek ◽  
N. Dellby ◽  
A.R. Lupini
Keyword(s):  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Operating Voltage ◽  
Resolution Limit ◽  
New Paradigm ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Two Generations

Even though two generations of electron microscopists have come to accept that the resolution of their instruments is limited by spherical aberration, three different aberration correctors showing that the aberration can be overcome have recently been built [1-3]. One of these correctors was developed by us specifically for forming small electron probes in a dedicated scanning transmission electron microscope (STEM) [3, 4]. It promises to revolutionize the way STEM instruments are built and the types of problems that they are applied to.As was the case with the Berlin Wall, when a barrier that was once thought immovable finally crumbles, many of the consequences can be quite unexpected. For STEM, the removal of spherical aberration (Cs) as the main resolution limit is likely to lead to a new paradigm in which:1) The resolution at a given operating voltage will improve by about 3x relative to today's best. When Cs can be adjusted arbitrarily in a STEM being used for microanalysis or dark field imaging, defocus and Cs are set to values that optimally oppose the effect of the 5th-order spherical aberration C5.

Crystal Structure Evolution of La2Ni7 during Hydrogenation

2013 ◽  
Vol 1516 ◽  
pp. 183-188 ◽  
Author(s):  
Yuki Iwatake ◽  
Kyosuke Kishida ◽  
Haruyuki Inui
Keyword(s):  
Hydrogen Absorption ◽  
Dark Field ◽  
Atomic Scale ◽  
Structure Evolution ◽  
Desorption Process ◽  
Atomic Arrangement ◽  
Anisotropic Expansion ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Scale Characterization

ABSTRACTAtomic scale characterization of the La2Ni7 hydrides by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that not only the anisotropic expansion of the La2Ni4 unit layer previously reported but also the shearing on the basal plane of the La2Ni4 unit layers occur during one-cycle of hydrogen absorption/desorption process. Two different types of orthorhombic La2Ni7 hydrides with the same atomic arrangement of La and different atomic arrangement of Ni were observed depending on the maximum hydrogen concentration achieved during one hydrogen absorption/desorption cycle.

Atomic scale study of polar Lomer–Cottrell and Hirth lock dislocation cores in CdTe

2014 ◽  
Vol 70 (6) ◽  
pp. 524-531 ◽  
Author(s):  
Tadas Paulauskas ◽  
Christopher Buurma ◽  
Eric Colegrove ◽  
Brian Stafford ◽  
Zhao Guo ◽  
...  
Keyword(s):  
Elastic Energy ◽  
Semiconductor Devices ◽  
Dislocation Core ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Atomic Scale ◽  
Formation Mechanisms ◽  
Atomic Column ◽  
Dark Field Imaging ◽  
Zinc Blende

Dislocation cores have long dominated the electronic and optical behaviors of semiconductor devices and detailed atomic characterization is required to further explore their effects. Miniaturization of semiconductor devices to nanometre scale also puts emphasis on a material's mechanical properties to withstand failure due to processing or operational stresses. Sessile junctions of dislocations provide barriers to propagation of mobile dislocations and may lead to work-hardening. The sessile Lomer–Cottrell and Hirth lock dislocations, two stable lowest elastic energy stair-rods, are studied in this paper. More specifically, using atomic resolution high-angle annular dark-field imaging and atomic-column-resolved X-ray spectrum imaging in an aberration-corrected scanning transmission electron microscope, dislocation core structures are examined in zinc-blende CdTe. A procedure is outlined for atomic scale analysis of dislocation junctions which allows determination of their identity with specially tailored Burgers circuits and also formation mechanisms of the polar core structures based on Thompson's tetrahedron adapted to reactions of polar dislocations as they appear in CdTe and other zinc-blende solids. Strain fields associated with the dislocations calculatedviageometric phase analysis are found to be diffuse and free of `hot spots' that reflect compact structures and low elastic energy of the pure-edge stair-rods.

Theoretical considerations in lattice resolution high-angle annular dark-field imaging

1992 ◽  
Vol 50 (2) ◽  
pp. 1226-1227
Author(s):  
Adam Amali ◽  
Peter Rez
Keyword(s):  
Large Angle ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Theoretical Interpretation ◽  
High Angle ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Lattice Resolution

The highly coherent probe in the scanning transmission electron microscope(STEM) equipped with a with high angle annular dark field (HAADF) detector has become an important tool for high resolution work in the study of crystals.with potential for providing chemically sensitive information.The results of Pennycook and Boatner and the calculations of Kirkland et al clearly demonstrated that lattice resolution was possible using HAADF imaging.There has been other contributions since then.The theoretical interpretation of these images however remains controversial and other contributions have focussed on whether the imaging is coherent or incoherent.In the present work we analyse the various mechanisms that contribute to the large angle signal obtained in the HAADF detector.Bloch waves are used to describe the elastic dynamical scattering; and in the abscence of any strong Bragg reflections.the amplitude observed in the detector plane in the STEM may be represented by a simple convolution between the scattering function of the object and the probe.

Quantitative Strain Mapping Applied to Aberration-Corrected HAADF Images

2006 ◽  
Vol 12 (4) ◽  
pp. 285-294 ◽  
Author(s):  
Ana M. Sanchez ◽  
Pedro L. Galindo ◽  
Slawomir Kret ◽  
Meiken Falke ◽  
Richard Beanland ◽  
...  
Keyword(s):  
Quantitative Measure ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Internal Strain ◽  
Atomic Scale ◽  
Strain Mapping ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Free Material ◽  
Aberration Corrected

A systematic distortion in high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, which may be caused by residual electrical interference, has been evaluated. Strain mapping, using the geometric phase methodology, has been applied to images acquired in an aberration-corrected STEM. This allows this distortion to be removed and so quantitative analysis of HAADF-STEM images was enabled. The distortion is quantified by applying this technique to structurally perfect and strain-free material. As an example, the correction is used to analyse an InAs/GaAs dot-in-quantum well heterostructure grown by molecular beam epitaxy. The result is a quantitative measure of internal strain on an atomic scale. The measured internal strain field of the heterostructure can be interpreted as being due to variations of indium concentration in the quantum dot.

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