scholarly journals Multislice image simulations of sheared needle‐like precipitates in an Al‐Mg‐Si alloy

2020 ◽  
Vol 279 (3) ◽  
pp. 265-273
Author(s):  
E. CHRISTIANSEN ◽  
I.G. RINGDALEN ◽  
R. BJØRGE ◽  
C.D. MARIOARA ◽  
R. HOLMESTAD
Keyword(s):  
Image Simulations

Computers and diffraction analysis

1989 ◽  
Vol 47 ◽  
pp. 44-45
Author(s):  
J. A. Eades
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
Diffraction Analysis ◽  
Electron Diffraction Analysis ◽  
Image Simulation ◽  
Correct Interpretation ◽  
High Profile ◽  
High Resolution Images ◽  
Image Simulations

For well over two decades computers have played an important role in electron microscopy; they now pervade the whole field - as indeed they do in so many other aspects of our lives. The initial use of computers was mainly for large (as it seemed then) off-line calculations for image simulations; for example, of dislocation images.Image simulation has continued to be one of the most notable uses of computers particularly since it is essential to the correct interpretation of high resolution images. In microanalysis, too, the computer has had a rather high profile. In this case because it has been a necessary part of the equipment delivered by manufacturers. By contrast the use of computers for electron diffraction analysis has been slow to prominence. This is not to say that there has been no activity, quite the contrary; however it has not had such a great impact on the field.

A method for direct measurement of specimen noise in HREM images

1993 ◽  
Vol 51 ◽  
pp. 458-459
Author(s):  
Sidnei Paciornik ◽  
Roar Kilaas ◽  
Ulrich Dahmen ◽  
Michael Adrian O'Keefe
Keyword(s):  
Random Noise ◽  
Image Interpretation ◽  
Thin Foil ◽  
High Resolution Electron Microscopy ◽  
Black Dot ◽  
Atomic Column ◽  
Amorphous Oxide ◽  
Resolution Electron ◽  
Imaging Conditions ◽  
Image Simulations

High resolution electron microscopy (HREM) is a primary tool for studying the atomic structure of defects in crystals. However, the quantitative analysis of defect structures is often seriously limited by specimen noise due to contamination or oxide layers on the surfaces of a thin foil.For simple monatomic structures such as fcc or bcc metals observed in directions where the crystal projects into well-separated atomic columns, HREM image interpretation is relatively simple: under weak phase object, Scherzer imaging conditions, each atomic column is imaged as a black dot. Variations in intensity and position of individual image dots can be due to variations in composition or location of atomic columns. Unfortunately, both types of variation may also arise from random noise superimposed on the periodic image due to an amorphous oxide or contamination film on the surfaces of the thin foil. For example, image simulations have shown that a layer of amorphous oxide (random noise) on the surfaces of a thin foil of perfect crystalline Si can lead to significant shifts in image intensities and centroid positions for individual atomic columns.

Atomic chemistry by HREM and image simulations?

1986 ◽  
Vol 44 ◽  
pp. 828-829
Author(s):  
J.M. Howe ◽  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Resolution Electron ◽  
Image Simulations

The technique of high-resolution electron microscopy (HREM) is invaluable to the materials scientist because it allows examination of microstructural features at levels of resolution that are unobtainable by most other methods. Although the structural information which can be determined by HREM and accompanying image simulations has been well documented in the literature, there have only been a few cases where this technique has been used to reveal the chemistry of individual columns or planes of atoms, as occur in segregated and ordered materials.

HREM image simulations for supported metal particle catalysts

1993 ◽  
Vol 51 ◽  
pp. 736-737 ◽  
Author(s):  
Ming-Hui Yao ◽  
David J. Smith
Keyword(s):  
Fine Particles ◽  
Amorphous Material ◽  
Chemical Properties ◽  
Morphological Features ◽  
Metal Particles ◽  
Plan View ◽  
Profile View ◽  
Imaging Conditions ◽  
Image Simulations ◽  
Supported Metal

The chemical properties of catalysts often depend on the size, shape and structure of the supported metal particles. To characterize these morphological features and relate them to catalysis is one of the main objectives for HREM study of catalysts. However, in plan view imaging, details of the shape and structure of ultra-fine supported particles (<2nm) are often obscured by the overlapping contrast from the support, and supported sub-nanometer particles are sometimes even invisible. Image simulations may help in the interpretation at HREM images of supported particles in particular to extract useful information about the size, shape and structure of the particles. It should also be a useful tool for evaluating the imaging conditions in terms of visibility of supported particles. P. L. Gai et al have studied contrast from metal particles supported on amorphous material using multislice simulations. In order to better understand the influence of a crystalline support on the visibility and apparent morphological features of supported fine particles, we have calculated images of Pt and Re particles supported on TiO2(rutile) in both plan view and profile view.

Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

Critical image formation parameters in thermal hyperspectral image simulations

1998 ◽  
Author(s):  
Scott D. Brown ◽  
John R. Schott ◽  
Rolando V. Raqueno
Keyword(s):  
Hyperspectral Image ◽  
Image Formation ◽  
Image Simulations

scholarly journals Image Simulations of Ge Twin Boundaries.

1992 ◽  
Vol 295 ◽  
Author(s):  
Stuart Mckernan ◽  
C. Barry Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Angle ◽  
Structural Units ◽  
Twin Boundaries ◽  
Large Unit ◽  
Unit Cells ◽  
The Individual ◽  
Image Simulations

AbstractGeneral high-angle tilt grain boundaries may be described by an arrangement of repeating structural units. Some grain-boundary defects may also be modeled by the incorporation of structural units of related boundary structures into the boundary. The simulation of these structures requires the use of prohibitively large unit cells. The possibility of modeling these boundaries by the superposition of image simulations of the individual structural units isinvestigated.

Crystallographic Origin of the Alternate Bright/Dark Contrast in 6H-SiC and other Hexagonal Crystal HREM Images

1996 ◽  
Vol 2 (2) ◽  
pp. 63-78
Author(s):  
J.S. Bow ◽  
R.W. Carpenter ◽  
M.J. Kim
Keyword(s):  
Crystal Thickness ◽  
Material System ◽  
Hrem Image ◽  
Hexagonal Crystal ◽  
Cubic Crystals ◽  
Unit Cells ◽  
Crystal Model ◽  
Scattering Potential ◽  
Diffraction Patterns ◽  
Image Simulations

Alternating bright/dark anomalous subunitcell contrast in HREM images along or near the close-packed direction of 6H-SiC, Ti5Si3, α-Ti, and 4H-SiC, all of which are hexagonal, was examined using computer-generated crystal models, HREM image simulations, and digital diffractograms from the corresponding experimental images. The primary variables were crystal tilt and thickness. Crystal model projections showed that the scattering potential was smeared anisotropically within the unit cells by small crystal tilts, which reproduced the experimentally observed anomalous subunit-cell contrast modulations in the corresponding simulations. The effect increased with thickness, but it did not occur in exact zone axis simulations for any crystal thickness. Structural considerations indicated that the contrast resulted from tilt-induced violations of Gjonnes-Moodie dynamical extinctions and excitation of kinematically forbidden reflections in the imaging zone. Digital diffractograms from experimental HREM images confirmed their presence in the imaging zone diffraction patterns. These effects were absent in HREM images from cubic crystals in this material system because the structurally induced requisite kinematically forbidden reflections do not occur in the imaging zone.

In-Situ Transmission Electron Microscopy and Computer Simulation Study of the Kinetics of Oxygen Loss in Yba2Cu3OZ

1989 ◽  
Vol 169 ◽  
Author(s):  
C. P. Burmester ◽  
L. T. Wille ◽  
R. Gronsky ◽  
B. T. Ahn ◽  
V. Y. Lee ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Computer Simulation Study ◽  
Oxygen Loss ◽  
Domain Structures ◽  
Transmission Electron ◽  
Kinetics Of ◽  
Image Simulations

AbstractHigh resolution transmission electron microscopy during in‐situ quenching of YBa2Cu3Oz is used to study the kinetics of microdomain formation during oxygen loss in this system. Image simulations based on atomic models of oxygen‐vacancy order in the basal plane of this material generated by Monte Carlo calculations are used to interpret high resolution micrographs of the structures obtained by quenching. The observed domain structures agree well with those obtained from the simualtions.

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