Noise Analysis of a SFS Algorithm Formulated under Various Imaging Conditions

1973 ◽

Vol 31 ◽

pp. 228-229

Author(s):

L. E. Thomas ◽

J. S. Lally ◽

R. M. Fisher

Keyword(s):

High Voltage ◽

Chromatic Aberration ◽

Crystalline Materials ◽

Resolution Parameter ◽

Instrument Resolution ◽

Imaging Conditions ◽

Beam Excitation ◽

Optimum Imaging

In addition to improved penetration at high voltage, the characteristics of HVEM images of crystalline materials are changed markedly as a result of many-beam excitation effects. This leads to changes in optimum imaging conditions for dislocations, planar faults, precipitates and other features.Resolution - Because of longer focal lengths and correspondingly larger aberrations, the usual instrument resolution parameter, CS174 λ 374 changes by only a factor of 2 from 100 kV to 1 MV. Since 90% of this change occurs below 500 kV any improvement in “classical” resolution in the MVEM is insignificant. However, as is widely recognized, an improvement in resolution for “thick” specimens (i.e. more than 1000 Å) due to reduced chromatic aberration is very large.

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Analysis of Dark-Field Images of Disordered Materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096059 ◽

1972 ◽

Vol 30 ◽

pp. 560-561

Author(s):

J. M. Cowley

Keyword(s):

Amorphous Materials ◽

Careful Analysis ◽

Dark Field ◽

Minimum Diameter ◽

Statistical Fluctuations ◽

Bright Spots ◽

Sufficient Detail ◽

Random Arrangement ◽

Diffraction Patterns ◽

Imaging Conditions

Recently a number of authors have reported detail in dark-field images obtained from diffuse-scattering regions of electron diffraction patterns. Bright spots in images from short-range order diffuse peaks of disordered binary alloys have been interpreted as evidence for the existence of microdomains of ordered lattice or of segragated clusters of one component. Spotty contrast in dark field images of near-amorphous materials has been interpreted as evidence for the existense of microcrystals. Without a careful analysis of the imaging conditions such conclusions may be invalid. Usually the conditions of the experiment have not been specified in sufficient detail to allow evaluation of the conclusions.Elementary considerations show that even for a completely random arrangement of atoms the statistical fluctuations of density will give a spotty contrast with spots of minimum diameter determined by the dark field aperture size and other factors influencing the minimum resolvable distance under darkfield imaging conditions, including fluctuations and drift over long exposure times (resolution usually 10Å or more).

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Black-white contrast of dislocation loops

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108787 ◽

1978 ◽

Vol 36 (1) ◽

pp. 328-329

Author(s):

J. J. Hren ◽

W. D. Cooper ◽

L. J. Sykes

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Dislocation Loops ◽

Major Premise ◽

Burgers Vector ◽

Transmission Electron ◽

Primary Means ◽

Contrast Analysis ◽

Dot Product ◽

Imaging Conditions

Small dislocation loops observed by transmission electron microscopy exhibit a characteristic black-white strain contrast when observed under dynamical imaging conditions. In many cases, the topography and orientation of the image may be used to determine the nature of the loop crystallography. Two distinct but somewhat overlapping procedures have been developed for the contrast analysis and identification of small dislocation loops. One group of investigators has emphasized the use of the topography of the image as the principle tool for analysis. The major premise of this method is that the characteristic details of the image topography are dependent only on the magnitude of the dot product between the loop Burgers vector and the diffracting vector. This technique is commonly referred to as the (g•b) analysis. A second group of investigators has emphasized the use of the orientation of the direction of black-white contrast as the primary means of analysis.

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Computer averaging of lattice images of poly-4-methyl-pentene-1 (P4mp1): Noise created artifacts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126731 ◽

1987 ◽

Vol 45 ◽

pp. 388-389

Author(s):

P. Pradère ◽

J.F. Revol ◽

R. St. John Manley

Keyword(s):

Low Dose ◽

Polymer Concentration ◽

Processing System ◽

Limiting Factor ◽

Dilute Solution ◽

New Techniques ◽

Dose Unit ◽

Lattice Images ◽

Dose Imaging ◽

Imaging Conditions

Although radiation damage is the limiting factor in HREM of polymers, new techniques based on low dose imaging at low magnification have permitted lattice images to be obtained from very radiation sensitive polymers such as polyethylene (PE). This paper describes the computer averaging of P4MP1 lattice images. P4MP1 is even more sensitive than PE (total end point dose of 27 C m-2 as compared to 100 C m-2 for PE at 120 kV). It does, however, have the advantage of forming flat crystals from dilute solution and no change in d-spacings is observed during irradiation.Crystals of P4MP1 were grown at 60°C in xylene (polymer concentration 0.05%). Electron microscopy was performed with a Philips EM 400 T microscope equipped with a Low Dose Unit and operated at 120 kV. Imaging conditions were the same as already described elsewhere. Enlarged micrographs were digitized and processed with the Spider image processing system.

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A method for direct measurement of specimen noise in HREM images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100148125 ◽

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.

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HREM image simulations for supported metal particle catalysts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100149519 ◽

1993 ◽

Vol 51 ◽

pp. 736-737 ◽

Cited By ~ 1

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.

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