Atomic-resolution eels for composition and 3-D coordination determination at interfaces and defects

1996 ◽  
Vol 54 ◽  
pp. 530-531
Author(s):  
N. D. Browning ◽  
D. J. Wallis ◽  
S. Sivananthan ◽  
P. D. Nellist ◽  
S. J. Pennycook
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Structure Property ◽  
Contrast Imaging ◽  
Angle Scattering ◽  
Structural Differences ◽  
Scanning Transmission ◽  
Composition Structure ◽  
Z Contrast

Materials properties associated with interfaces and defects are dominated by atomic scale fluctuations in composition, structure and bonding. Although electron energy loss spectroscopy (EELS) provides a powerful tool to probe these features, low signal, lens aberrations, image coherence and specimen drift preclude the use of spectrum imaging and energy filtered imaging for these high-resolution problems. However, by utilizing Z-contrast imaging in conjunction with EELS in the scanning transmission electron microscope (STEM), these limitations are largely overcome and EELS appears capable of providing fudamental 3-D characterization of defect and interface structures with atomic resolution and sensitivity.The main premise in utilizing these combined techniques is that the properties of defects and interfaces must be associated with structural differences relative to the bulk. If those structural differences can be located, then it is only necessary to perform spectroscopy in their vicinity to understand the structure property relationship. For crystalline materials in zone-axis orientations, the Z-contrast image provides this atomic resolution structural map. As this direct image is generated with only the high-angle scattering, it can be used to position the electron probe with atomic precision and does not interfere with the low-angle scattering for spectroscopy.

Atomic-Resolution Z-Contrast Imaging and its Application to Compositional Ordering and Segregation

1999 ◽  
Vol 583 ◽  
Author(s):  
S. J. Pennycook ◽  
Y. Yan ◽  
A. Norman ◽  
Y. Zhang ◽  
M. Al-Jassim ◽  
...  
Keyword(s):  
High Resolution Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Ferroelectric Materials ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
High Angle ◽  
Contrast Imaging ◽  
Resolution Electron ◽  
Scanning Transmission ◽  
Z Contrast

AbstractIn the last ten years, the scanning transmission electron microscope (STEM) has become capable of forming electron probes of atomic dimensions making possible a new approach to high-resolution electron microscopy, Z-contrast imaging. Formed by mapping the intensity of high-angle scattered electrons as the probe is scanned across the specimen, the Z-contrast image represents a direct map of the specimen scattering power at atomic resolution. It is an incoherent image, and can be directly interpreted in terms of atomic columns. High angle scattering comes predominantly from the atomic nuclei, so the scattering cross section depends on atomic number (Z) squared. Z-contrast microscopy can therefore be used to study compositional ordering and segregation at the atomic scale. Here we present three examples of ordering: first, ferroelectric materials, second, III-V semiconductor alloys, and finally, cooperative segregation at a semiconductor grain boundary, where a combination of Z-contrast imaging with first principles theory provides a complete atomic-scale view of the sites and configurations of the segregant atoms.

Analysis of the Atomic Scale Defect Chemistry in Oxygen Deficient Materials by STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y. Ito ◽  
S. Stemmer ◽  
R. F. Klie ◽  
N. D. Browning ◽  
A. Sane ◽  
...  
Keyword(s):  
Preliminary Investigation ◽  
High Mobility ◽  
Scanning Transmission Electron Microscope ◽  
Defect Chemistry ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Separation Membranes ◽  
Oxidation Reduction ◽  
Scanning Transmission ◽  
Z Contrast

AbstractThe high mobility of anion vacancies in oxygen deficient perovskite type materials makes these ceramics potential candidates for oxygen separation membranes. As a preliminary investigation of the defect chemistry in these oxides, we show here the analysis of SrCoO3−σ using atomic resolution Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope. In particular, after being subjected to oxidation/reduction cycles at high temperatures we find the formation of ordered microdomains with the brownmillerite structure.

Analysis of Nanometer Sized Pyrogenic Particles by Scanning Transmission Electron Microscopy

1995 ◽  
Vol 53 ◽  
pp. 218-219
Author(s):  
DJ Wallis ◽  
ND Browning ◽  
CM Megaridis
Keyword(s):  
Operating Conditions ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Chemical Mechanisms ◽  
Transmission Electron ◽  
Angle Scattering ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Physical And Chemical ◽  
Electron Energy Loss

Iron is a ubiquitous element on the earth's surface, and is thus involved in most naturally occurring fires. Iron organometalic compounds have also been known to suppress carbonaceous soot emissions under certain operating conditions of practical combustors. In order to unravel the physical and chemical mechanisms of influence, of iron on the emission of carbonaceous pyrogenic particles, finescale characterization techniques need to be implemented.The combined techniques of Z-contrast imaging and electron energy loss spectroscopy (EELS) in a VG HB-501 dedicated STEM are ideally suited to study such a system. The sensitivity of the Z-contrast imaging technique to high-Z materials makes it ideal for location of the iron particles within the much lower atomic number matrix. As only the high-angle scattering is used in the image formation, EELS can be performed simultaneously from a position defined in the image. This accurate positioning of the probe by the Z-contrast image permits both compositional and bonding information to be obtained with a spatial resolution approaching the atomic scale.

Atomic resolution determination of the structure and chemistry of ceramic grain boundaries

1995 ◽  
Vol 53 ◽  
pp. 320-321
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
Grain Boundaries ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Secondary Phases ◽  
Contrast Imaging ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Contrast Technique ◽  
Z Contrast

Characterization of grain boundaries in ceramics is complicated by the multicomponent nature of the materials, the presence of secondary phases, and the tendency for the grain boundary plane to “wander” on the length scale of a few nanometers. However, recent developments in the scanning transmission electron microscope (STEM) have now made it possible to correlate directly the structure, composition and bonding at grain boundaries on the atomic scale. This direct experimental characterization of grain boundaries is achieved through the combination of Z-contrast imaging (structure) and electron energy loss spectroscopy (EELS) (composition and bonding). For crystalline materials in zone-axis orientations, where the atomic spacing is larger than the probe size, the Z-contrast technique provides a direct image of the metal (high Z) columns. This image, being formed from only the high-angle scattering, can be used to position the electron probe with atomic precision for simultaneous EELS. Under certain collection conditions, the spectrum can have the same atomic spatial resolution as the image, thus permitting the spectra to be correlated with a known atomic location.

Z-Contrast Imaging in the Scanning Transmission Electron Microscope

1995 ◽  
Vol 1 (6) ◽  
pp. 231-251 ◽  
Author(s):  
S.J. Pennycook ◽  
D.E. Jesson ◽  
M.F. Chisholm ◽  
N.D. Browning ◽  
A.J. McGibbon ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Entropy Analysis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Angle Scattering ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Annular Detector ◽  
Incoherent Imaging ◽  
Z Contrast

Z-contrast STEM using an annular detector can provide an intuitively interpretable, column-by-column, compositional map of crystals. Incoherent imaging reduces dynamical effects to second order so that the map directly reflects the positions of the atomic columns and their relative high-angle scattering power. This article outlines how these characteristics arise, presents some examples of the insights available from a direct image, and discusses recent developments of atomic-resolution microanalysis, direct structure retrieval by maximum entropy analysis, and Z-contrast imaging at 1.4 Å resolution using a 300-kV STEM.

Analysis of the Atomic Scale Oxygen Vacancy Ordering by EELS and Z-Contrast Imaging

2000 ◽  
Vol 6 (S2) ◽  
pp. 192-193
Author(s):  
Y. Ito ◽  
S. Stemmer ◽  
R.F. Klie ◽  
N.D. Browning ◽  
T.J. Mazanec
Keyword(s):  
Ceramic Membranes ◽  
Scanning Transmission Electron Microscope ◽  
Defect Chemistry ◽  
Atomic Scale ◽  
Successful Implementation ◽  
Contrast Imaging ◽  
Valence States ◽  
Scanning Transmission ◽  
Before And After ◽  
Z Contrast

Perovskite-type oxides with high electronic and ionic conductivity are very promising materials for use as dense ceramic membranes for oxygen separation. For the successful implementation of practical ceramic membranes, a full understanding of the parameters controlling the degree of non-stoichiometry, i.e. the defect chemistry is essential. A combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) can be used to directly image crystal and defect structures and the effect of the structures on the local electronic properties (i.e. oxygen coordination and cation valence). Here the defect chemistry in SrCoO3-δ before and after a reduction treatment at high temperatures is investigated in the JEOL 201 OF STEM. This material is known to exist in a wide a variety of phases with different crystal structures, compositions and valence states of cobalt, and can be highly oxygen deficient.

Atomic-resolution characterization of an SrTiO3 grain boundary in the STEM

1994 ◽  
Vol 52 ◽  
pp. 972-973
Author(s):  
M. M. McGibbon ◽  
N. D. Browning ◽  
M. F. Chisholm ◽  
A. J. McGibbon ◽  
S. J. Pennycook ◽  
...  
Keyword(s):  
High Resolution ◽  
Atomic Structure ◽  
Scanning Transmission Electron Microscope ◽  
Tilt Boundary ◽  
Atomic Scale ◽  
Chemical Information ◽  
Contrast Imaging ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image

High-resolution Z-contrast imaging in the scanning transmission electron microscope (STEM) forms an incoherent image in which changes in atomic structure and composition across an interface can be interpreted intuitively without the need for preconcieved atomic structure models. Since the Z-contrast image is formed by electrons scattered through high angles, parallel detection electron energy loss spectroscopy (PEELS) can be used simultaneously to provide complementary chemical information on an atomic scale. The fine structure in the PEEL spectra can be used to investigate the local electronic structure and the nature of the bonding across the interface. In this paper we use the complimentary techniques of high resolution Z-contrast imaging and PEELS to investigate the atomic structure and chemistry of a 25 degree symmetric tilt boundary in a bicrystal of the electroceramic SrTiO3.Figure 1(a) shows a Z-contrast image of a symmetric region of the tilt boundary. The brightest spots in the image correspond to the increased scattering power of the Sr atomic columns (Z=38) with theless bright spots corresponding to the Ti atomic columns (Z=22). The lighter O atomic columns are notvisible in a Z-contrast image.

Nanoscale Structure/Property Correlation Through Aberration-Corrected Stem And Theory

2002 ◽  
Vol 738 ◽  
Author(s):  
S.J. Pennycook ◽  
A. R. Lupini ◽  
M. Varela ◽  
A. Borisevich ◽  
M. F. Chisholm ◽  
...  
Keyword(s):  
Information Transfer ◽  
Spherical Aberration ◽  
National Laboratory ◽  
Scanning Transmission Electron Microscope ◽  
Probe Intensity ◽  
Structure Property ◽  
Contrast Imaging ◽  
Oak Ridge ◽  
Scanning Transmission ◽  
Z Contrast

The combination of atomic-resolution Z-contrast microscopy, electron energy loss spectroscopy and first-principles theory has proved to be a powerful means for structure property correlations at interfaces and nanostructures. The scanning transmission electron microscope (STEM) now routinely provides atomic-sized electron beams, allowing simultaneous Z-contrast imaging and EELS as shown in Fig. 1. The feasiblity of correcting the inherently large spherical aberration of microscope objective lenses promises to at least double the achievable resolution. The potential benefits for the STEM, however, may turn out to be much greater than those for the conventional TEM because it is very much less sensitive to chromatic instabilities. The 100 kV VG Microscopes HB501UX at Oak Ridge National Laboratory (ORNL) is now fitted with an aberration corrector constructed by Nion Co., which improved its resolution from 2.2 Å (full-width-half-maximum probe intensity) to around 1.3 Å. It is now very comparable in performance to the uncorrected 300 kV HB603U STEM at ORNL which, before correction, also had a directly interpretable resolution of 1.3 Å, although information transfer had been demonstrated down to 0.78 Å8. Initial results after installing an aberration corrector on the 300 kV STEM indicate a resolution of 0.84 Å. The theoretically achievable probe size in the absence of instabilities is predicted to be 0.5 Å.

Atomic Scale Analysis of Oxygen Vacancy Segregation At Grain Boundaries in Ceramic Oxides

2001 ◽  
Vol 7 (S2) ◽  
pp. 308-309
Author(s):  
N. D. Browning ◽  
J. P. Buban ◽  
Y. Ito ◽  
R. F. Klie ◽  
Y. Lei
Keyword(s):  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Ceramic Oxides ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Resolution Analysis ◽  
Z Contrast

The properties of ceramic oxides being developed for such varied applications as fuel cells, ionic transporting membranes, high-Tc superconductors, ferroelectrics and varistors are dominated by the presence of grain boundaries. Key to controlling the electronic properties of the grain boundaries in these materials is a fundamental understanding of the complex relationship between structure, composition and local electronic structure. The ability to characterize and directly correlate these parameters on the atomic scale is afforded by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Furthermore, the recent development of in-situ heating capabilities in the JEOL 201 OF STEM/TEM permits atomic resolution analysis to be performed at elevated temperatures and the interactions of grain boundaries with the oxygen vacancies determined.Figure 1 shows an example of the type of experiment that can be performed using these methods.

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