Direct observation of strain-stored grains in electrodeposited nanocrystalline Ni-W alloys by low-angle annular dark field diffraction contrast imaging

2019 ◽  
Vol 166 ◽  
pp. 29-33 ◽  
Author(s):  
Isao Matsui ◽  
Yorinobu Takigawa ◽  
Takahisa Yamamoto
Keyword(s):  
Direct Observation ◽  
Dark Field ◽  
Contrast Imaging ◽  
Diffraction Contrast ◽  
Stored Grains ◽  
Annular Dark Field

scholarly journals Microstructure study of a severely plastically deformed Mg-Zn-Y alloy by application of low angle annular dark field diffraction contrast imaging

2016 ◽  
Vol 17 (1) ◽  
pp. 115-127 ◽  
Author(s):  
Dudekula Althaf Basha ◽  
Julian M. Rosalie ◽  
Hidetoshi Somekawa ◽  
Takashi Miyawaki ◽  
Alok Singh ◽  
...  
Keyword(s):  
Dark Field ◽  
Contrast Imaging ◽  
Diffraction Contrast ◽  
Annular Dark Field

Atomic resolution Z-contrast imaging of bulk crystal surfaces in Scanning Reflection Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 414-415
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
Electron Microscopy ◽  
Elastic Scattering ◽  
Dark Field ◽  
Contrast Imaging ◽  
Crystal Lattices ◽  
Small Probe ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Image Position ◽  
Z Contrast

The success of obtaining atomic-number-sensitive (Z-contrast) images in scanning transmission electron microscopy (STEM) has shown the feasibility of imaging composition changes at the atomic level. This type of image is formed by collecting the electrons scattered through large angles when a small probe scans across the specimen. The image contrast is determined by two scattering processes. One is the high angle elastic scattering from the nuclear sites,where ϕNe is the electron probe function centered at bp = (Xp, yp) after penetrating through the crystal; F denotes a Fourier transform operation; D is the detection function of the annular-dark-field (ADF) detector in reciprocal space u. The other process is thermal diffuse scattering (TDS), which is more important than the elastic contribution for specimens thicker than about 10 nm, and thus dominates the Z-contrast image. The TDS is an average “elastic” scattering of the electrons from crystal lattices of different thermal vibrational configurations,

Incoherent High-Resolution Z-Contrast Imaging of Silicon and Gallium Arsenide Using HAADF-STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y Kotaka ◽  
T. Yamazaki ◽  
Y Kikuchi ◽  
K. Watanabe
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Contrast Imaging ◽  
High Spatial Resolution Image ◽  
Transmission Electron ◽  
Eigen Value ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Convergent Beam ◽  
Z Contrast

AbstractThe high-angle annular dark-field (HAADF) technique in a dedicated scanning transmission electron microscope (STEM) provides strong compositional sensitivity dependent on atomic number (Z-contrast image). Furthermore, a high spatial resolution image is comparable to that of conventional coherent imaging (HRTEM). However, it is difficult to obtain a clear atomic structure HAADF image using a hybrid TEM/STEM. In this work, HAADF images were obtained with a JEOL JEM-2010F (with a thermal-Schottky field-emission) gun in probe-forming mode at 200 kV. We performed experiments using Si and GaAs in the [110] orientation. The electron-optical conditions were optimized. As a result, the dumbbell structure was observed in an image of [110] Si. Intensity profiles for GaAs along [001] showed differences for the two atomic sites. The experimental images were analyzed and compared with the calculated atomic positions and intensities obtained from Bethe's eigen-value method, which was modified to simulate HAADF-STEM based on Allen and Rossouw's method for convergent-beam electron diffraction (CBED). The experimental results showed a good agreement with the simulation results.

scholarly journals Direct observation and catalytic role of mediator atom in 2D materials

2020 ◽  
Vol 6 (24) ◽  
pp. eaba4942
Author(s):  
Gun-Do Lee ◽  
Alex W. Robertson ◽  
Sungwoo Lee ◽  
Yung-Chang Lin ◽  
Jeong-Wook Oh ◽  
...  
Keyword(s):  
Direct Observation ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Tight Binding ◽  
Structural Evolution ◽  
Dark Field ◽  
Bond Rotation ◽  
Annular Dark Field ◽  
Catalytic Role ◽  
Type Bond

The structural transformations of graphene defects have been extensively researched through aberration-corrected transmission electron microscopy (AC-TEM) and theoretical calculations. For a long time, a core concept in understanding the structural evolution of graphene defects has been the Stone-Thrower-Wales (STW)–type bond rotation. In this study, we show that undercoordinated atoms induce bond formation and breaking, with much lower energy barriers than the STW-type bond rotation. We refer to them as mediator atoms due to their mediating role in the breaking and forming of bonds. Here, we report the direct observation of mediator atoms in graphene defect structures using AC-TEM and annular dark-field scanning TEM (ADF-STEM) and explain their catalytic role by tight-binding molecular dynamics (TBMD) simulations and image simulations based on density functional theory (DFT) calculations. The study of mediator atoms will pave a new way for understanding not only defect transformation but also the growth mechanisms in two-dimensional materials.

Z-Contrast Imaging of Heavy Metal Particles Supported in A Zeolitic Matrix Via High-Resolution Stem

1987 ◽  
Vol 45 ◽  
pp. 204-205
Author(s):  
J. H. Butler ◽  
G. M. Brown
Keyword(s):  
High Resolution ◽  
Incident Beam ◽  
Dark Field ◽  
Irradiation Damage ◽  
Contrast Imaging ◽  
Vacuum Oven ◽  
Annular Dark Field ◽  
Resolution Imaging ◽  
Beam Currents ◽  
Z Contrast

High resolution Imaging of zeolites is difficult because these materials are very susceptible to Irradiation damage. It is now well known that dehydrated samples are more stable under the electron beam. Thus the most successful high resolution studies of zeolites to date have been on samples which were freeze-fractured and subsequently dehydrated via heating in a vacuum oven. Electron microscopy was then performed using a combination of low Incident beam currents and sensitive detectors. One problem with this method is that zeolites fracture along cleavage planes and therefore are deposited on microscope grids In a particular orientation. This limits the range of viewing angles. Here we describe a method of sample preparation via ultramlctrotomy as well as the establishment of suitable FEG/STEM Imaging conditions which permit the observation of small (7-14 A diameter) Pt particles within Individual zeolite channels using the method of Z-contrast as applied with a high-angle annular dark field detector. This method allows observation over all crystalline orientations for relatively long exposures to the beam.

High-Resolution Bright-Field and Dark-Field Hollow Cone Illumination

1990 ◽  
Vol 48 (1) ◽  
pp. 36-37
Author(s):  
R.A. Herring ◽  
M.E. Twigg
Keyword(s):  
Large Angle ◽  
Dark Field ◽  
Hollow Cone ◽  
Contrast Imaging ◽  
Lattice Image ◽  
Dark Field Imaging ◽  
Annular Dark Field ◽  
Lattice Images ◽  
Z Contrast ◽  
Field Imaging

Hollow cone illumination using a large C2 blocked-aperture (bl apt) in the conventional TEM (CTEM) can remove the beams within the zero-order Laue zone (ZOLZ) thereby making lattice images more simply interpretable. Dark-field (DF) hollow cone illumination has the added advantage of enhancing the Z-contrast within the lattice image, since the electrons contributing to the image must be scattered over a large angle (approximately 10 mrad). Both of these imaging methods have been explored, using a 600 um C2 bl apt and objective aperture sizes of 70, 20 and 10 um, and are reported in this paper.Much interest has been generated by the report of Pennycook [1] on STEM Z-contrast imaging using annular dark-field. In earlier work ,it was noted that CTEM hollow cone imaging and STEM annular dark-field imaging are related via reciprocity [2] (Fig. 1). In addition, Zernike has shown the advantages of hollow cone illumination in optical phase-contrast microscopy [3]. The electron-optical analogues to these optical techniques are now possible because of the low Cs values achieved in modern TEMs.

Structural Insights of Supported Nanoparticles By Z-Contrast and High Resolution Electron Microscopy

2001 ◽  
Vol 7 (S2) ◽  
pp. 1102-1103
Author(s):  
Judith C. Yang ◽  
Erin Devlin ◽  
William Rhodes ◽  
Steven Bradley
Keyword(s):  
Electron Microscopy ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Contrast Imaging ◽  
Essential Information ◽  
Support Materials ◽  
Annular Dark Field ◽  
Z Contrast ◽  
Structural Insights

A vital component to nanoparticle science will be the three dimensional (3-D) characterization of both structure and chemistry of these nanoparticles on their supports at the nanometer scale and below. to achieve this goal, quantitative Z-contrast and atomic resolution will provide essential information about their structure. Z-contrast imaging is ideal for imaging these large Z nanoparticles on low Z supports. in this proceedings, we present a quantitative Z-contrast method to determine number of atoms and a few examples of a combination of electron microscopy methods to gain structural insights into supported nanoparticle, such as Pt on different support materials, PtRu5 on C and Pt-Sn on SiO2.A relatively new and powerful method is to determine the number of atoms in a nanoparticle, by very high angle annular dark-field (HAADF) imaging or Z-contrast technique [1, 2]. We have shown that quantification of the absolute image intensity from very HAADF microscopy will provide the number of atoms in very small particles of high atomic number to ±2 atoms for Re6 nanoparticles supported on carbon [3].

Which is Better for Protein Imaging: Phase Contrast TEM or Annular Dark Field STEM?

2001 ◽  
Vol 7 (S2) ◽  
pp. 382-383
Author(s):  
P. Rez
Keyword(s):  
Phase Contrast ◽  
Protein Structure Determination ◽  
Dark Field ◽  
Biological Molecules ◽  
Contrast Imaging ◽  
Bright Field ◽  
Low Contrast ◽  
X Ray ◽  
Contrast Microscopy ◽  
Annular Dark Field

In a landmark paper Henderson compared X-ray, neutrons and electrons for protein structure determination. He showed that electron microscopy should be superior to X-ray or neutron diffraction in terms of dose for a given resolution. in addition he presented a theoretical analysis to determine the smallest size molecule whose structure could be determined by phase contrast microscopy. Although he qualitatively considered amplitude contrast mechanisms and concluded they were inferior to phase contrast, no explicit numerical analysis was performed. It has been implicitly assumed that bright field phase contrast imaging is the optimal technique for imaging small biological molecules. Protein specimens are usually embedded in some medium such as ice or glucose. Since they must give a very low contrast it seems reasonable to expect that bright field techniques for these weakly scattering objects would be inferior, given that a weak signal is sitting on large background.

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