scholarly journals The Reconstruction of Displacement Fields of Defects in Crystals from Electron Micrographs. I. Analytic Fields

1969 ◽  
Vol 22 (1) ◽  
pp. 43 ◽  
Author(s):  
AK Head
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Approximation Theory ◽  
Displacement Field ◽  
Image Formation ◽  
Defects In Crystals ◽  
Electron Micrograph ◽  
Phase Information ◽  
Displacement Fields ◽  
Electron Microscope Image

The following theorem and corollaries are proved. If the two-beam column approximation theory of electron microscope image formation is assumed and if the displacement field of the object is analytic with zero derivative at infinity, and such that there is a direction in the object along which displacements are constant, then from an electron micrograph that records intensities but no phase information there is an explicit and unique reconstruction of the component of the displacement field of the object in the direction of the diffracting vector, except possibly in some specified singular cases for which the reconstruction cannot be started uniquely.

scholarly journals The Reconstruction of Displacement Fields of Defects in Crystals from Electron Micrographs

1969 ◽  
Vol 22 (3) ◽  
pp. 345 ◽  
Author(s):  
AK Head
Keyword(s):  
Electron Micrographs ◽  
Displacement Field ◽  
Defects In Crystals ◽  
Displacement Fields ◽  
Beam Diffraction

It is shown that the theorem of Part I, namely, that there is a unique reversible connection between displacement fields and electron micrographs for the case of two-beam diffraction and analytic displacement fields, can be extended to many-beam diffraction conditions. The case of a systematic set of diffracting vectors is parallel to the two-beam case with a unique reversible connection between one component of the displacement field and one micrograph. In the general many-beam case there is a unique reversible connection between the vector displacement field and three micrographs.

Electron microscope image contrast of small dislocation loops and stacking-fault tetrahedra

1979 ◽  
Vol 292 (1397) ◽  
pp. 523-537 ◽  
Keyword(s):  
Electron Microscope ◽  
Numerical Solutions ◽  
Preceding Paper ◽  
Stacking Fault ◽  
Image Contrast ◽  
Dislocation Loops ◽  
Displacement Fields ◽  
Microscope Image ◽  
Stacking Fault Tetrahedra ◽  
Electron Microscope Image

With the use of the method described in the preceding paper (to be referred to subsequently as I) for constructing the displacement fields, the electron microscope image contrast of small dislocation loops and of stacking-fault tetrahedra has been computed from numerical solutions of the Howie-Whelan (1961) equations. The computer-simulated images, displayed in the form of half-tone pictures, have been used to identify the nature and geometry of such defects in ion-irradiated foils. A systematic study of the contrast of small Frank loops in Cu + ion irradiated copper under a wide variety of diffraction conditions is reported. In particular the variations of the contrast of loops edge-on and inclined to the electron beam with the operating Bragg reflexion, the thickness and inclination of the foil, depth of the defect in the foil and deviation from the Bragg-reflecting condition have been studied. Methods of obtaining useful information, such as the diameters of the loops, are suggested. The contrast of stacking-fault tetrahedra, and of non-edge perfect dislocation loops in ion-irradiated molybdenum is also investigated.

Wiener Processing of Phase Contrast Electron Micrographs

1973 ◽  
Vol 31 ◽  
pp. 270-271
Author(s):  
T. A. Welton ◽  
Frances L. Ball ◽  
W. W. Harris
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Phase Contrast ◽  
Preliminary Test ◽  
Electron Micrograph ◽  
Theoretical Reason ◽  
Oak Ridge ◽  
Thin Carbon ◽  
High Coherence

Previously reported work has given some theoretical reason to believe that the effective resolution of an electron micrograph can, under suitable conditions, be enhanced by computation. The Oak Ridge High Coherence Electron Microscope, described elsewhere in these proceedings, will attempt to exploit this concept to its logical limit, but a preliminary test has been thought worthwhile. For this purpose, a series of micrographs has been made of TMV on thin carbon, negatively stained with PTA. The Siemens 1A was used at 100 μ and magnification 150,000, with condenser aperture 100/tand no objective aperture. The defocus was exaggerated to imitate the effect of sphercal aberration in the High Coherence Microscope. Figure 1 is a portion of one member of the focal series, with a size of 425Å square.

Measurement and compensation of defocusing and aberrations by Fourier processing of electron micrographs

1971 ◽  
Vol 261 (837) ◽  
pp. 105-118 ◽  
Keyword(s):  
Electron Microscope ◽  
Spherical Aberration ◽  
Image Formation ◽  
Order Theory ◽  
First Order Theory ◽  
The Fourier Transform ◽  
Electron Microscope Image ◽  
Contrast Image ◽  
Thin Crystal ◽  
Conventional Electron Microscopy

The effects of defocusing and spherical aberration in the electron microscope image are most simply and directly displayed in the Fourier transform of the image. We have investigated the process of image formation by determining the changes in the transform of the image of a thin crystal of catalase, which has discrete diffraction maxima in the resolution range of 10 to 2.5 nm, as a function of defocusing. The changes in amplitude and phase of these diffraction maxima have been measured and compared with the predictions of a first-order theory of image formation. The theory is generally confirmed, and the transfer function of the microscope is completely determined by finding the relative contributions from phase and amplitude contrast. A ‘true’ maximum contrast image of the catalase crystal, compensated for the effects of defocusing, is reconstructed from the set of micrographs in the focal series. The relation of this compensated image to individual underfocused micrographs, and the use of underfocus contrast enhancement in conventional electron microscopy, are discussed. This approach and the experimental methods can be extended to high resolution in order to compensate for spherical aberration as well as defocusing. In as much as spherical aberration is the factor presently limiting the resolution of electron lenses, this could provide a considerable extension of the resolution of the electron microscope.

Utilizing Dark Field Electron Microscopy to Produce Lantern Slides

1974 ◽  
Vol 32 ◽  
pp. 116-117
Author(s):  
J. N. Meador ◽  
C. N. Sun ◽  
H. J. White
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Dark Field ◽  
Limiting Factor ◽  
Clinical Laboratories ◽  
Field Electron ◽  
Time Element ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Dark Field Micrographs

The electron microscope is being utilized more and more in clinical laboratories for pathologic diagnosis. One of the major problems in the utilization of the electron microscope for diagnostic purposes is the time element involved. Recent experimentation with rapid embedding has shown that this long phase of the process can be greatly shortened. In rush cases the making of projection slides can be eliminated by taking dark field electron micrographs which show up as a positive ready for use. The major limiting factor for use of dark field micrographs is resolution. However, for conference purposes electron micrographs are usually taken at 2.500X to 8.000X. At these low magnifications the resolution obtained is quite acceptable.

Light Optical Diffraction Studies of Macromolecular Ultrastructure

1970 ◽  
Vol 28 ◽  
pp. 258-259
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
Electron Micrograph ◽  
Its Analysis ◽  
Resolution Electron ◽  
Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

On an Application of the Metallurgical Stage to Chromosome Morphology

1967 ◽  
Vol 25 ◽  
pp. 28-29
Author(s):  
Godfrey C. Hoskins
Keyword(s):  
Human Chromosome ◽  
Electron Micrographs ◽  
Chromosome Morphology ◽  
Electron Optics ◽  
Electron Micrograph ◽  
Photographic Evidence ◽  
Sophisticated Equipment ◽  
Periodic Arrangement

The first serious electron microscooic studies of chromosomes accompanied by pictures were by I. Elvers in 1941 and 1943. His prodigious study, from the manufacture of micronets to the development of procedures for interpreting electron micrographs has gone all but unnoticed. The application of todays sophisticated equipment confirms many of the findings he gleaned from interpretation of images distorted by the electron optics of that time. In his figure 18 he notes periodic arrangement of pepsin sensitive “prickles” now called secondary fibers. In his figure 66 precise regularity of arrangement of these fibers can be seen. In his figure 22 he reproduces Siegbahn's first stereoscopic electron micrograph of chromosomes.The two stereoscopic pairs of electron micrographs of a human chromosome presented here were taken with a metallurgical stage on a Phillips EM200. These views are interpreted as providing photographic evidence that primary fibers (1°F) about 1,200Å thick are surrounded by secondary fibers (2°F) arranged in regular intervals of about 2,800Å in this metanhase human chromosome. At the telomere the primary fibers bend back on themselves and entwine through the center of each of each chromatid. The secondary fibers are seen to continue to surround primary fibers at telomeres. Thus at telomeres, secondary fibers present a surface not unlike that of the side of the chromosome, and no more susceptible to the addition of broken elements from other chromosomes.

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