Moiré patterns in electron diffraction from lanthanum oxide iodide (LaOI)

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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Dynamical theory of electron diffraction for the electron microscopic image of crystal lattices II. Image of superposed crystals (moiré pattern)

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1961.0007 ◽

1961 ◽

Vol 253 (1033) ◽

pp. 490-516 ◽

Cited By ~ 19

Keyword(s):

Electron Diffraction ◽

Present Theory ◽

Dynamical Theory ◽

Bragg Angle ◽

Electron Microscopic ◽

Microscopic Images ◽

Electron Microscopic Image ◽

Moire Patterns ◽

Lattice Images ◽

Moiré Patterns

The dynamical theory of electron diffraction is applied to the interpretation of electron microscopic images of moire patterns. Two cases often observed are treated. One is the case where two plate-shaped crystals are superposed closely without a vacuum layer between them and another is the case where two crystals are superposed with a vacuum layer between them. Resolved lattice images of two superposed crystals are also interpreted. The intensity profiles of the images vary with the thicknesses of the crystals and vacuum layer and with the deviation from the Bragg angle. The shifts of the fringes and anomalies of the contrast which are expected from the present theory were observed in the electron microscopic images of moire patterns of cupric sulphide, palladiumgold and platinum-phthalocyanine. The relation between moiré patterns and crystal structure is also discussed.

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Calculations of the Contrasts of Moiré Patterns from Twisted Lattices by the Dynamical Theory of Electron Diffraction

physica status solidi (b) ◽

10.1002/pssb.19690350249 ◽

1969 ◽

Vol 35 (2) ◽

pp. 973-981

Author(s):

K. Izui ◽

T. Nishida

Keyword(s):

Electron Diffraction ◽

Dynamical Theory ◽

Moire Patterns ◽

Moiré Patterns

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Moiré Patterns with Display‐Type Low‐Energy Electron Diffraction Apparatus

Journal of Applied Physics ◽

10.1063/1.1708199 ◽

1966 ◽

Vol 37 (2) ◽

pp. 473-479 ◽

Cited By ~ 4

Author(s):

R. E. McCurry

Keyword(s):

Electron Diffraction ◽

Low Energy ◽

Energy Electron ◽

Display Type ◽

Low Energy Electron Diffraction ◽

Moire Patterns ◽

Low Energy Electron ◽

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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