Imaging dislocations with an annular dark-field detector

1992 ◽  
Vol 50 (2) ◽  
pp. 1224-1225 ◽  
Author(s):  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Supported Catalysts ◽  
Dark Field ◽  
Contrast Effects ◽  
Thermal Diffuse Scattering ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Active Research ◽  
Thermal Diffuse

High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) has been recently the subject of active research because of its successful applications to the characterization of supported catalysts, interface problems in MBE grown semiconductors, superconductors and X-ray multilayers. The characteristics of HAADF images are different from those of the TEM images. For perfect single crystals the HAADF signal is mainly generated from thermal diffuse scattering. HAADF technique has also been used to study dopant contrast effects in semiconductors and dislocations have also been observed with an ADF detector. In this paper we report a study of dislocation contrasts and their dependence on the inner collection angle of the ADF detector.The STEM instrument used for the observations was the HB5 from VG Microscopes, Ld., modified by the addition of an ultra-high resolution pole piece (Cs = 0.8 mm) and a two-dimensional detector system. Post specimen lenses and various beam stops were used to change the inner (α) and outer (β) collection angles of the ADF detector.

Design of a new objective lens for an HB-501A STEM

1991 ◽  
Vol 49 ◽  
pp. 416-417
Author(s):  
Earl J. Kirkland ◽  
Robert J. Keyse
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Microscopy

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

Intergrowth of niobium tungsten oxides of the tetragonal tungsten bronze type

2020 ◽  
Vol 75 (11) ◽  
pp. 913-919
Author(s):  
Frank Krumeich
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Tungsten Bronze ◽  
Structural Complexity ◽  
Dark Field ◽  
Tetragonal Tungsten Bronze ◽  
Tungsten Oxides ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractSince the 1970s, high-resolution transmission electron microscopy (HRTEM) is well established as the most appropriate method to explore the structural complexity of niobium tungsten oxides. Today, scanning transmission electron microscopy (STEM) represents an important alternative for performing the structural characterization of such oxides. STEM images recorded with a high-angle annular dark field (HAADF) detector provide not only information about the cation positions but also about the distribution of niobium and tungsten as the intensity is directly correlated to the local scattering potential. The applicability of this method is demonstrated here for the characterization of the real structure of Nb7W10O47.5. This sample contains well-ordered domains of Nb8W9O47 and Nb4W7O31 besides little ordered areas according to HRTEM results. Structural models for Nb4W7O31 and twinning occurring in this phase have been derived from the interpretation of HAADF-STEM images. A remarkable grain boundary between well-ordered domains of Nb4W7O31 and Nb8W9O47 has been found that contains one-dimensionally periodic features. Furthermore, short-range order observed in less ordered areas could be attributed to an intimate intergrowth of small sections of different tetragonal tungsten bronze (TTB) based structures.

Atomic-scale structural and compositional analyses of Ruddlesden-Popper planar faults in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics

2009 ◽  
Vol 24 (8) ◽  
pp. 2596-2604 ◽  
Author(s):  
Sašo Šturm ◽  
Makoto Shiojiri ◽  
Miran Čeh
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dark Field ◽  
Atomic Scale ◽  
Transmission Electron ◽  
Initial Stage ◽  
Final Microstructure ◽  
Scanning Transmission ◽  
The Matrix ◽  
Annular Dark Field

The microstructure in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics is strongly affected by the formation of Ruddlesden-Popper fault–rich (RP fault) lamellae, which are coherently intergrown with the matrix of the perovskite grains. We studied the structure and chemistry of RP faults by applying quantitative high-resolution transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy analyses. We showed that the Sr2+ and Ca2+ dopant ions form RP faults during the initial stage of sintering. The final microstructure showed preferentially grown RP fault lamellae embedded in the central part of the anisotropic perovskite grains. In contrast, the dopant Ba2+ ions preferably substituted for Sr2+ in the SrTiO3 matrix by forming a BaxSr1−xTiO3 solid solution. The surplus of Sr2+ ions was compensated structurally in the later stages of sintering by the formation of SrO-rich RP faults. The resulting microstructure showed RP fault lamellae located at the surface of equiaxed BaxSr1-xTiO3 perovskite grains.

scholarly journals Exploring the Capability of HAADF-STEM Techniques to Characterize Graphene Distribution in Nanocomposites by Simulations

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
N. Baladés ◽  
D. L. Sales ◽  
M. Herrera ◽  
A. M. Raya ◽  
J. C. Hernández-Garrido ◽  
...  
Keyword(s):  
Electron Tomography ◽  
Carbon Matrix ◽  
Reconstruction Algorithm ◽  
Dark Field ◽  
Graphene Layers ◽  
Transmission Electron ◽  
Dispersion Degree ◽  
Scanning Transmission ◽  
The Matrix ◽  
Annular Dark Field

This paper explores the capability of scanning transmission electron microscopy (STEM) techniques in determining the dispersion degree of graphene layers within the carbon matrix by using simulated high-angle annular dark-field (HAADF) images. Results ensure that unmarked graphene layers are only detectable if their orientation is parallel to the microscope beam. Additionally, gold-marked graphene layers allow evaluating the dispersion degree in structural composites. Moreover, electron tomography has been demonstrated to provide truthfully 3D distribution of the graphene sheets inside the matrix when an appropriate reconstruction algorithm and 2D projections including channelling effect are used.

scholarly journals Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4531
Author(s):  
Maria Meledina ◽  
Geert Watson ◽  
Alexander Meledin ◽  
Pascal Van Der Voort ◽  
Joachim Mayer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
Catalyst Nanoparticles ◽  
Ru Catalyst ◽  
Ru Nanoparticles ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)—MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration—the stability and lifetime of the catalyst could be improved.

Detailed Calculations of Thermal Diffuse Scattering

1997 ◽  
Vol 3 (S2) ◽  
pp. 1153-1154
Author(s):  
D.A. Müller ◽  
B. Edwards ◽  
E.J. Kirkland ◽  
J. Silcox
Keyword(s):  
Diffuse Scattering ◽  
Single Point ◽  
Scanning Transmission Electron Microscope ◽  
Diffraction Spot ◽  
Thermal Diffuse Scattering ◽  
Transmission Electron ◽  
Einstein Model ◽  
Scanning Transmission ◽  
Convergent Beam ◽  
Thermal Diffuse

Convergent beam electron diffraction (CBED) produces a diffraction pattern from a single point on the specimen using a focused probe in the scanning transmission electron microscope (STEM). Because the incident wavefunction is a focused probe, each diffraction spot is enlarged to a disk the size of the objective aperture. Thermal vibration in the specimen reduces the intensity of the diffraction disks and introduces scattering in between the disk. This normally forbidden scattering between the diffraction disks is referred to as thermal diffuse scattering (TDS). The effects are most pronounced at large scattering angles, where TDS scattering can greatly reduce the intensity of the higher order Laue zone (HOLZ) lines. Previous work on modeling the TDS intensity involved the so-called frozen phonon method and the Einstein model of lattice vibration. The Einstein model assumes that each atom in the specimen vibrates independently of every other atom in the specimen and possible correlations among adjacent atoms are ignored.

scholarly journals Synthesis of nickel/gallium nanoalloys using a dual-source approach in 1-alkyl-3-methylimidazole ionic liquids

2019 ◽  
Vol 10 ◽  
pp. 1754-1767
Author(s):  
Ilka Simon ◽  
Julius Hornung ◽  
Juri Barthel ◽  
Jörg Thomas ◽  
Maik Finze ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Dark Field ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dual Source ◽  
Induced Decomposition

NiGa is a catalyst for the semihydrogenation of alkynes. Here we show the influence of different dispersion times before microwave-induced decomposition of the precursors on the phase purity, as well as the influence of the time of microwave-induced decomposition on the crystallinity of the NiGa nanoparticles. Microwave-induced co-decomposition of all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in the ionic liquid [BMIm][NTf2] selectively yields small intermetallic Ni/Ga nanocrystals of 5 ± 1 nm as derived from transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and supported by energy-dispersive X-ray spectrometry (EDX), selected-area energy diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). NiGa@[BMIm][NTf2] catalyze the semihydrogenation of 4-octyne to 4-octene with 100% selectivity towards (E)-4-octene over five runs, but with poor conversion values. IL-free, precipitated NiGa nanoparticles achieve conversion values of over 90% and selectivity of 100% towards alkene over three runs.

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