Dislocation image width

The width of the dislocation image D, which is twice the value of r for which and is thus... 

As seen in the last chapter, the image width is easy to quantify for a screw dislocation, where the diffraction vector is parallel to the dislocation line. Around a screw dislocation, the misorientation at a distance r from the core is given by... 

Figure 10.7 Width of a dislocation image under conditions where harmonics are strong as at the ESRF. (Courtesy F.Zontone)...

Figure 10.15 Simulated image width as a function of deviation parameter in Bragg case weak beam topographs. Here, the specimen is set off the Bragg peak and an image of the defect occurs only when the lattice planes are locally rotated or dilated back into the Bragg condition. As this occurs only close to the dislocation core, the images are narrowed from those under strong beam conditions...

The intensity profiles for pure edge dislocations calculated using a given by Eq. (5.20) for g b x u = 0 have characteristics similar to those for screw dislocations except that both the image width and the displacement are about twice that of a screw dislocation with the same n. 

Note also that for all these profiles, an increase in s causes a decrease in peak height because /g is proportional to s. Because 0 = 2wsx, an increase in s causes the image peak to move closer to the dislocation, coupled with a decrease in image width. 

Figure 5.24. Variation of the 20-percent image width with g, b, and 0 for a prismatic dislocation loop (or a platelike inclusion) in an isotropic crystal matrix for several values of / ,. Thickness of foil = s = 0 r" = 10/g,...

The width of the image can be deduced using this simple idea of contrast being formed when the misorientation around the defect exceeds the perfect crystal reflecting range. We consider the case of a screw dislocation nmning normal to the Bragg planes, where the line direction / coincides with the diffraction vector g. The effective misorientation at distance r from the core is =bH r (8.41)... 

Miltat and Bowen showed that direct images can be synthesised from the cylinders of misorientation drawn aroimd a dislocation line using continuum elasticity theory. The image full width can be calculated from the projected width circumscribed by the contour where ( ) is equal to times the reflecting range,... 

Dislocations of mixed character. Image profiles for dislocations of mixed character have been calculated by Howie and Whelan (1962). For g b = 1, the images are similar to those of screw and edge dislocations but of intermediate width. 

The displacement of the image peak from the position of the dislocation is of the same order as the width of the image. 

Fig. 9. SEM images of etched cylinder forming PS-b-PEO (PEO removed) in rectangular trenches (60 nm depth and width as shown) of various widths. The white circles show various defects present including grain boundaries, dislocations and point defects. See text for further details.

Fig. 3.85 Slip bands in the intermediate region of the indented volume, a Slip band planarity and evidence of profuse pile-ups. The dislocations exhibiting paired lines in the boxed area are not dipoles but dissociated dislocations since the distance between partials is constant whether the dipole is imaged with the g or -g reflecting plane, b Intersecting slip bands, c The slight misalignment and differences in pile-up projected widths indicate that the slip bands are parallel to at least two crystallographically distinct planes [31]. With kind permission of Elsevier...

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