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Digitale Medien

Atomic-resolution imaging and spectroscopy of semiconductor interfaces (1993)

Pennycook, S. J. ; Browning, N. D. ; Jesson, D. E. ; [weitere]

Springer

Applied physics 57 (1993), S. 385-391

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ISSN: 1432-0630

Schlagwort(e): 61.14 ; 68.48 ; 68.55

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Incoherent Z-contrast imaging uses a high-angle annular detector to collect only highly local, incoherently generated scattering with the result that images become dependent on intensities, not phases. No model structures are required for a first-order structure determination, and the images remain intuitively interpretable even at interfaces. Under suitable conditions, incoherently generated inelastic scattering may be collected simultaneously with a large-aperture axial spectrometer, and, by using the Z-contrast image to locate the scanning transmission electron microscope (STEM) probe over selected atomic columns, can provide an atomic-resolution chemical analysis. This is demonstrated with reference to an epitaxial CoSi2/Si(100) interface, achieving a 2.7 Å spatial resolution. Recent insights into the growth and relaxation of strained Si-Ge epitaxial films are described, highlighting the role of stress concentrations, and contrasting the case of a free surface with that of a surface constrained by an oxide layer.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00331776

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Digitale Medien

Atomic structure of grain boundaries in YBa2Cu3O7-δ as observed by Z-contrast imaging (1994)

Chisholm, M. F. ; Pennycook, S. J. ; Norton, D. P. ; [weitere]

Springer

Interface science 1 (1994), S. 339-345

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ISSN: 1573-2746

Schlagwort(e): grain boundaries ; Z-contrast imaging ; atomic structure ; YBa2Cu3O7-δ

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: Abstract Determination of the atomic structure of grain boundaries is the key to fundamental understanding of the critical current density in polycrystalline superconductors. High-resolution images with incoherent characteristics, obtained using a high-angle annular detector on an atomic resolution scanning transmission electron microscope, are used to study the atomic arrangements of these technologically important boundaries. The incoherent Z-contrast images do not experience contrast reversals with defocus or sample thickness and display no Fresnel Fringe effects at boundaries. Observed rigid shifts of atomic columns at grain boundaries are independent of sample thickness and objective lens defocus. These characteristics allow unambiguous and intuitive interpretations of the generated images. We find the atomic structures at grain boundaries in YBa2Cu3O7-δ are strongly influenced by the strong tendency of this compound to exist only as complete unit cells terminated at {001} and {100} planes. The weak-link behavior associated with high-angle grain boundaries may follow from this structure in which there is no clear connection between the {100} facets of adjacent grains. Symmetric grain boundaries where adjacent grains share a common boundary plane have also been observed in YBa2Cu3O7-δ. In these boundaries partial structural coupling of the grains is maintained. There is evidence that these two boundary forms produce junctions with very different superconducting properties.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00188703

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Digitale Medien

Observation of structural units at symmetric [001] tilt boundaries in SrTiO3 (1995)

Browning, N. D. ; Pennycook, S. J. ; Chisholm, M. F. ; [weitere]

Springer

Interface science 2 (1995), S. 397-423

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ISSN: 1573-2746

Schlagwort(e): grain boundaries ; atomic resolution EELS ; Z-contrast imaging ; bond-valence sums

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: Abstract Incoherent Z-contrast imaging in the scanning transmission electron microscope allows atom column positions to be deduced directly from the experimental image, including locations where the column separation is less than the resolution limit. Maximum entropy analysis applied to the incoherent image locates the high-Z columns to an accuracy of ±0.2 Å. Oxygen coordination at the boundary plane can be deduced by high spatial resolution electron energy loss spectroscopy, and approximate column positions determined by simple bond-valence sum calculations. Observations of 25° (Σ=85), 36° (Σ=5) and 67° (Σ=13) [001] symmetric tilt grain boundaries in SrTiO3 bicrystals show that “half columns” are a ubiquitous feature of grain boundary structural units. The observed structural units can be combined to produce structural models for symmetric tilt boundaries over a 0–90° range. The Σ=17 (410), Σ=5 (310), and Σ=5 (210) are found to be favored boundaries and the structures of all the other tilt boundaries are comprised of these units combined with Σ=1 (100) and Σ=1 (110) structural units. All the proposed boundary models show continuity of grain boundary structure over the entire misorientation range. The Σ=17 (410) structural unit is asymmetric which induces microfacetting on all boundaries less than the Σ=5, 36.87° misorientation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00222626

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Digitale Medien

Cell-by-cell mapping of carrier concentrations in high-temperature superconductors (1994)

Browning, N. D. ; Chisholm, M. F. ; Pennycook, S. J.

Springer

Interface science 1 (1994), S. 309-319

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ISSN: 1573-2746

Schlagwort(e): grain boundaries ; hole depletion ; carrier concentrations ; atomic resolution EELS ; Z-contrast imaging

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: Abstract The correlation between atomic and electronic structure in the vicinity of grain boundaries in YBa2Cu3O7-δ is investigated on the scale of the coherence length, using a combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope. The detector arrangement of the microscope enables both techniques to be performed simultaneously, allowing the exact crystallographic location of the probe to be determined from the image. As the pre-edge feature of the oxygen K-absorption edge is very sensitive to the partial density of unoccupied states, it can be calibrated to give an accurate measure of local hole concentrations (±5%). Spatial resolution is limited only by the 2.2 Å probe size, thus allowing the electronic properties of the material to be inferred on a scale less than the coherence length. Results are discussed from the study of YBa2Cu3O7-δ films prepared by laser ablation on yttria-stabilized-zirconia (YSZ) substrates, where a symmetric (near Σ5) grain boundary shows no significant hole depletion in the boundary region, while an asymmetric (near Σ17) boundary shows depletion extending over a region far greater than the atomic disorder shown in the image. Application of this technique to the study of interfaces in other superconducting systems is discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00188701

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