The calculation and interpretation of high-resolution electron microscope images of lattice defects

Anstis, G. R.; Cockayne, D. J. H.

doi:10.1107/s056773947900125x

Cited by 26 publications

(8 citation statements)

References 12 publications

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“…The same modified interaction constant has been used by Anstis & Cockayne (1979), and can be expressed in terms of the wave number as m/hZk~, which shows that the specimen feels not the whole wave number k but only its component k~. This result is in accord with the boundary conditions on the entrance surface, which leave the wave component kt~ parallel to the surface unchanged.…”

Section: Discussionsupporting

confidence: 69%

Multislice formula for inclined illumination

Ishizuka¹

1982

Acta Cryst A

102

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A multislice formula for many-beam calculation of dynamical electron diffraction amplitudes which may be applied for inclined illumination has been derived based on the Schr6dinger equation. This formula clearly shows the following points: a specimen should be considered as sliced parallel to the entrance surface; a spherical propagation function should be used, giving the exact excitation error measured along the surface normal; the interaction constant in the phase-grating function should be changed; the phase grating should be projected along the beam direction. A new parameter for the strength of the upper-layer interaction in the case of the inclined illumination is proposed in terms of the excitation error of the reciprocal-lattice points used to define the projected potential. It is pointed out that the potential projected along the beam direction may better represent the upper-layer interactions for the inclined illumination.

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Section: Discussionsupporting

confidence: 69%

Multislice formula for inclined illumination

Ishizuka¹

1982

Acta Cryst A

102

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“…Earlier calculations have also been reported for STEM microdiffraction patterns from dislocations based on the technique of periodic continuation (Spence, 1978); however, this method is unnecessarily accurate and time consuming for present purposes, in which contrast arises from the long-range strain field of the dislocation rather than from the detailed atomic arrangement at the core. Under these conditions the appropriate approximation is the column approximation, which neglects high-angle diffuse elastic scattering from heavily strained material (Anstis & Cockayne, 1979).…”

Section: Resultsmentioning

confidence: 99%

Three-dimensional strain-field information in convergent-beam electron diffraction patterns

Carpenter¹,

Spence²

1982

Acta Cryst A

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IntroductionConvergent-beam electron diffraction (CBED) patterns contain diffracted beams from higher-order Laue zones (HOLZ), in addition to the more often observed diffracted beams from the zeroth-order reciprocallattice zone (ZOLZ) that contains the origin of the reciprocal lattice. Since HOLZ diffraction vectors have non-zero components along the incident electron beam direction, they can detect components of static reallattice displacement fields that lie along the incident electron beam direction, an event not possible for diffracted beams normal to the incident electron beam direction (i.e. ZOLZ diffracted beams). This effect is used in the present work to determine Burgers vectors of straight dislocations and loops in silicon from observations of splitting of HOLZ lines within the forward scattered beam Bragg disk, and from splitting of Kikuchi lines associated with HOLZ Bragg reflections. The method was also applied with limited success to dislocations in aluminum; here splitting was more difficult to observe because of the rather strong diffuse background in the CBED patterns. Calculations of HOLZ line splitting due to the presence of a dislocation in the irradiated crystal volume were in good qualitative agreement with the experimental observations. Effects on CBED patterns to be expected from some partial dislocations are discussed. This CBED method can be very useful for the determination of non-ZOLZ fault vector components in an atomicresolution" structure-imaging microscope. These instruments usually have specimen tilt ranges limited to about 10°; thus conventional Burgers-vector analysis is not generally possible. Finally, the present CBED results show clearly that the projection approximation generally used to interpret structure fringe images is not strictly valid. The changes in fringe images or weakbeam images from HOLZ excitations remain to be evaluated.

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“…With this procedure it is necessary to apply the column approximation to the outer boundary of the mesh, i.e., in equation (3) ag = 1, b = 0, and cg = cp,.is calculated at the boundary using fhe column approximation. In order to avoid distortion of the image the step-size, Az, must be chosen carefully and the distance between columns (meshsize) must be sufficiently small (Anstis and Cockayne, 1979). The other method employs "free" boundary conditions defined by ag = 0, b = 1, and dc dz = 0, and which provides automatic control of the integration (e.g., the choice of Az) and provides error-estimates.…”

Section: Methodsmentioning

confidence: 99%

A computer program for many‐beam image simulation of amplitude‐contrast images

1991

J. Elec. Microsc. Tech.

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A computer program for the simulation of amplitude-contrast electron micrographs is described. The program is based on the n-beam dynamical theory of diffraction contrast as described by Howie and Whelan (see Howie, A., and Whelan, M.J. (1961) Proc. R. Soc. Lond. [Biol]). The displacement fields associated with crystal lattice defects are calculated using linear anisotropic elasticity. The program can be used to simulate images of crystals containing line or planar defects or combinations of these defects. The line defects can be oriented freely within the foil, and are not restricted to being mutually parallel, but must be straight. Different techniques available for solving the diffraction problem, with or without the column approximation, are discussed.

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The calculation and interpretation of high-resolution electron microscope images of lattice defects

Cited by 26 publications

References 12 publications

Multislice formula for inclined illumination

Multislice formula for inclined illumination

Three-dimensional strain-field information in convergent-beam electron diffraction patterns

A computer program for many‐beam image simulation of amplitude‐contrast images

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