Parallel moiré effect in electron micrographs of crystal sandwiches. I. Moiré patterns as predicted by the theory

The ultra-microtome has been used to obtain thin sections of synthetic graphite blocks. The thickness of the sections was measured by shadowcasting and measuring the shadow length at appropriate edges. An average value of 150 Å was obtained. Transmission electron micrographs of thin sections showed moire patterns and the interrelation of these moire patterns revealed a characteristic grain structure in graphite akin to that seen in metals but with component microcrystals of smaller dimensions. The area of the individual micro - crystals forming the grain structure was measured and was found to be 0·11 + 0·074μ 2 . The boundary between neighbouring microcrystals was narrow and of around 50 A in width. Pores were visible at the junction of three or more contiguous microcrystals and were of diameter 400 to 800 Å. The selected-area electron diffraction technique was used to determine the orientation of individual microcrystals in the graphite sections. It was found that the hexagonal layer net planes were lying parallel or at a very small angle to the plane of the section. The electron diffraction patterns were also used to correlate the layer stacking faults in individual microcrystals both by counts of individual reflexions on the (1120) diffraction ring and by counts of the extra reflexions due to the long spacings between successive displaced layers. The average value of 13 Å found for the distance between successive stacking faults is equivalent to the distance between four hexagonal layer net planes. The moire patterns in the electron micrographs could be related to the long spacings in the electron diffraction patterns. It was possible to calculate the angle of twist between successive stacking faults from the long spacing or from the moire pattern. Dislocations were seen in many of the thin sections and were observed as extra terminating half-lines in the moire patterns; these dislocations were present in the hexagonal layer net planes themselves and indicated that there was in this region a considerable deformation of the benzenoid structure of the hexagonal layer nets. The measured frequency for their occurrence was 3·3 x 10 7 /cm 2 . Slip planes were also detected in some specimens.

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Moiré patterns on electron micrographs, and their application to the study of dislocations in metals

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1958.0144 ◽

1958 ◽

Vol 246 (1246) ◽

pp. 345-368 ◽

Cited By ~ 128

Keyword(s):

Electron Microscope ◽

Electron Micrographs ◽

Dislocation Line ◽

Moire Pattern ◽

Moiré Pattern ◽

Transmission Electron ◽

Crystal Films ◽

Moire Patterns ◽

The Individual ◽

Moiré Patterns

The direct resolution of a crystal lattice has already been obtained in the electron microscope, with lattice spacings down to about 7 Å. Although a metal lattice has not so far been resolved in this way, a method has been developed to allow this to be carried out in an indirect manner, by means of moiré patterns. In this way, indirect resolution of crystal planes of even less than 1Å in spacing may be obtained, and the atomic array in metal lattices may be studied. The moiré patterns are obtained on transmission electron micrographs from pairs of overlapping single-crystal films of metals, prepared in a suitable manner. The mode of formation of these moiré patterns has been interpreted in terms of the kinematical theory of electron diffraction, and the relation between the patterns and the individual lattices has been considered. If a dislocation line passes through one of the metal crystals, it may be readily detected on the moire pattern. It is shown that both edge and screw dislocations in one of the crystals will give rise to terminating half-lines in the moiré pattern: the number of these terminating half-lines has been deduced, for the f. c. c. system, for any general dislocation line. The results are completely consistent with the observations, and several examples of dislocations are illustrated in the paper. Partial dislocations and stacking faults are also observed, and a full interpretation of these is given. The moiré patterns have also been used to record dislocation movements. The smallest periodicity which we have so far succeeded in resolving in the electron microscope is a moiré pattern of spacing 5.8 Å, obtained from overlapping nickel and gold crystals. The potentialities and limitations of the technique of moiré patterns are discussed in relation to their application to various problems in the metal physics of thin films, with particular reference to the study of lattice imperfections and their effect on mechanical properties.

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Observation of Dislocations in Metals by Means of Moiré Patterns on Electron Micrographs

Nature ◽

10.1038/179752a0 ◽

1957 ◽

Vol 179 (4563) ◽

pp. 752-755 ◽

Cited By ~ 115

Author(s):

D. W. PASHLEY ◽

J. W. MENTER ◽

G. A. BASSETT

Keyword(s):

Electron Micrographs ◽

Moire Patterns ◽

Moiré Patterns

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Moiré Patterns in Transmission Electron Micrographs of Sub-Boundaries of Aluminium

Nature ◽

10.1038/1791293a0 ◽

1957 ◽

Vol 179 (4573) ◽

pp. 1293-1293 ◽

Cited By ~ 4

Author(s):

G. A. GEACH ◽

R. PHILLIPS

Keyword(s):

Electron Micrographs ◽

Transmission Electron Micrographs ◽

Transmission Electron ◽

Moire Patterns ◽

Moiré Patterns

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Moire Fringes on Precipitates in Quenched and Aged Beryllium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101888 ◽

1968 ◽

Vol 26 ◽

pp. 426-427

Author(s):

F. J. Fraikor ◽

A. W. Brewer

Keyword(s):

Ternary Phase ◽

Volume Fraction ◽

Age Hardening ◽

Orientation Relationships ◽

Solute Content ◽

Moiré Fringes ◽

Moire Patterns ◽

Total Volume Fraction ◽

Diffraction Patterns ◽

Moiré Patterns

A number of investigators have examined moire patterns on precipitate particles in various age-hardening alloys. For example, Phillips has analyzed moire fringes at cobalt precipitates in copper and Von Heimendahl has reported on moire fringes in the system Al-Au. Recently, we have observed moire patterns on impurity precipitates in beryllium quenched in brine from 1000°C and aged at various temperatures in the range of 500-800°C. This heat treatment of beryllium rolled from vacuum cast ingots produces the precipitation of both an fee ternary phase, AlFeBe4, and an hcp binary phase, FeBe11. However, unlike a typical age-hardening alloy, the solute content of this material is low (less than 1000 ppm of Fe and 600 ppm of Al) and hence the total volume fraction of precipitates is small. Therefore there is some difficulty in distinguishing the precipitates and their orientation relationships with the beryllium matrix since the weak precipitate spots generally do not appear on the diffraction patterns.

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