Annular Dark Field Imaging in Stem

1994 ◽  
Vol 332 ◽  
Author(s):  
Sean Hillyard ◽  
John Silcox
Keyword(s):  
Phonon Scattering ◽  
Dark Field ◽  
Probe Intensity ◽  
Dark Field Imaging ◽  
Quantitative Measurements ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Computer Based ◽  
Diffraction Patterns

ABSTRACTAnnular dark field scanning transmission electron microscopy (ADF STEM) is chemically sensitive at high spatial resolution (e.g., 1.8ë at 100keV). Images can be digitally acquired and recorded, permitting quantitative analysis. It is particularly powerful when used in combination with complementary analysis modes such as x-ray microanalysis and transmission electron energy loss spectroscopy. Critical to the interpretation of these data is an understanding and determination of the electron probe intensity, shape and propagation characteristics inside the specimen. Quantitative measurements of diffraction patterns and images in comparison with computer-based simulations (including phonon scattering) provide a basis for developing that information. Results of a series of studies are reviewed that address questions such as defocus and other instrumental factors, and also the formation of channeling peaks that appear on the atomic columns along zone axes. For example, along Si(100) a peak forms and penetrates over 500ë whereas along Ge(100) it developes rapidly but disappears in less than 200ë. In higher atomic number elements, the penetration is even less (e.g. 1 O0ë for In).

Direct observation ofB-site cation displacements in Pb-based complex perovskite relaxor oxides

2010 ◽  
Vol 44 (1) ◽  
pp. 111-121 ◽  
Author(s):  
K. Z. Baba-Kishi
Keyword(s):  
Long Range ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Unit Cells ◽  
Annular Dark Field ◽  
Pb Ions ◽  
Diffraction Patterns ◽  
Spatial Displacements

Electron diffraction patterns recorded using a scanning transmission electron microscope (STEM) from PbMg1/3Nb2/3O3(PMN) crystallites and PbZn1/3Nb2/3O3(PZN) crystals show weak and systematic continuous diffuse streaking along the 〈110〉 directions. Detailed high-angle annular dark-field (HAADF) images recordedviaan aberration-corrected STEM show that theB-site cations in PMN and PZN undergo correlated and long-range displacements towards the Pb2+ions on the (110) planes. The planarB-site displacement measured from the centres of the octahedra is about 0.3–0.5 Å in PMN and about 0.20–0.4 Å in PZN. In the HAADF images of the PMN crystallites and PZN crystals studied, there is insufficient evidence for systematic long-range planar displacements of the Pb2+ions. The observed Pb2+ion displacements in PMN and PZN appear randomly distributed, mostly displaced along 〈110〉 towards theB-site columns. There is also evidence of possible stress-related distortion in certain unit cells of PMN. In the relaxors studied, two distinct types of displacements were observed: one is the long-range planarB-site spatial displacement on the (110) planes, correlated with the Pb2+ions, possibly resulting in the observed diffuse streaking; the other is short-range Pb2+ion displacement on the (110) planes. The observed displacement status indicates a mutual attraction between the Pb ions and theB-site cations in which theBsites undergo the largest spatial displacements towards the Pb ions along 〈110〉.

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.

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.

Environmental Optimization for Sub-0.2NM Scanning Transmission Electron Microscopy

2000 ◽  
Vol 6 (S2) ◽  
pp. 110-111
Author(s):  
D. A. Muller ◽  
J. Grazul ◽  
F. H. Baumann ◽  
R. Hynes ◽  
T. L. Hoffman
Keyword(s):  
Electromagnetic Interference ◽  
Dark Field ◽  
Limiting Factors ◽  
Scanning System ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Electrical Loads ◽  
Field Imaging

Sub-0.2 nm probes can now be readily obtained on Schottky field-emission microscopes[1]. However environmental instabilities are proving to be the limiting factors for atomic resolution spectroscopy and distortion-free annular-dark field imaging, as a result of the long acquisition times (comparable to those required for inline holography[2]), and from the serial nature of the scanning system where instabilities result in image distortions rather than reductions in contrast. Troubleshooting the two most common environmental problems are discussed here.Electromagnetic interference can cause beam deflections in both the scanning system and the spectrometer [3](< 0.3 mG r.ms for 0.3nm, < 0.2 mG for 0.2 nm). These are most easily dealt with before the machine is installed, as substantial rewiring may be necessary. There is little that can be done about quasi-DC fields, such as from elevators and nearby trains and buses. Major sources of AC electromagnetic interference are unbalanced electrical loads.

scholarly journals Bi8Te3, the 11-Atom Layer Member of the Tetradymite Homologous Series

Minerals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 980
Author(s):  
Cristiana L. Ciobanu ◽  
Ashley D. Slattery ◽  
Nigel J. Cook ◽  
Benjamin P. Wade ◽  
Kathy Ehrig
Keyword(s):  
Homologous Series ◽  
Layer Structure ◽  
Stoichiometric Composition ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions ◽  
Atom Layer

Bi8Te3 is a member of the tetradymite homologous series, previously shown to be compositionally and structurally distinct from hedleyite, Bi7Te3, yet inadequately characterized structurally. The phase is identified in a sample from the Hedley district, British Columbia, Canada. Compositions are documented by electron probe microanalysis and structures are directly imaged using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Results confirm that Bi8Te3 has an 11-atom layer structure, in which three Bi-Bi pairs are placed adjacent to the five-atom sequence (Te-Bi-Te-Bi-Te). Bi8Te3 has trigonal symmetry (space group R3¯m) with unit cell dimensions of a = ~4.4 Å and c = ~63 Å calculated from measurements on representative electron diffraction patterns. The model is assessed by STEM simulations and EDS mapping, all displaying good agreement with the HAADF STEM imaging. Lattice-scale intergrowths are documented in phases replacing Bi8Te3, accounting for the rarity of this phase in nature. These results support prior predictions of crystal structures in the tetradymite homologous series from theoretical modeling and indicate that other phases are likely to exist for future discovery. Tetradymite homologues are mixed-layer compounds derived as one-dimensional superstructures of a basic rhombohedral sub-cell. Each member of the series has a discrete stoichiometric composition and unique crystal structure.

scholarly journals Fabrication of Maghemite Nanoparticles with High Surface Area

Nanomaterials ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 1004 ◽  
Author(s):  
Yulia Trushkina ◽  
Cheuk-Wai Tai ◽  
German Salazar-Alvarez
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Dark Field ◽  
Maghemite Nanoparticles ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Powerful Approach ◽  
Scanning Transmission ◽  
Annular Dark Field

Maghemite nanoparticles with high surface area were obtained from the dehydroxylation of lepidocrocite prismatic nanoparticles. The synthesis pathway from the precursor to the porous maghemite nanoparticles is inexpensive, simple and gives high surface area values for both lepidocrocite and maghemite. The obtained maghemite nanoparticles contained intraparticle and interparticle pores with a surface area ca. 30 × 103 m2/mol, with pore volumes in the order of 70 cm3/mol. Both the surface area and pore volume depended on the heating rate and annealing temperature, with the highest value near the transformation temperature (180–250 °C). Following the transformation, in situ X-ray diffraction (XRD) allowed us to observe the temporal decoupling of the decomposition of lepidocrocite and the growth of maghemite. The combination of high-angle annular dark-field imaging using scanning transmission electron microscopy (HAADF-STEM) and surface adsorption isotherms is a powerful approach for the characterization of nanomaterials with high surface area and porosity.

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