Dark field image dislocations

Figure 5.13. Computed image profiles for an edge dislocation. Bright field and dark field images are shown as solid and broken lines, respectively. g-b = l z = 8tg Zi = 4/g lOtg 5tg = 0. (After Hirsch et al. 1965.)...

The conditions for kinematic diffraction [160] are best approximated in the weak-beam method, which consists of making a dark-field image in a weakly excited diffraction spot. The dislocation image then consists of a narrow bright line on a darker background. 

Fig. 14. (a) Weak beam dark-field image of dislocations in biotite. The trace of the slip plane (S) is indicated as well as dislocations bowing out (X). [346]. (b) Dark-field image of screw dislocations in... 

Kinematical and weak beam dark field (WBDF) images of dislocations... 

Figure 1.11. TEM images of the calcite single crystal shocked in a laser irradiation experiment with an initial pressure of 225 GPa. (a) Dark-field TEM image of a 60-gm-deep zone in the specimen, containing numerous dislocation loops. This microstructurc indicates incipient decomposition, (b) Dark-field TEM image of tangled, curved dislocations occurring in a depth of 90 pm below the initial specimen surface, (c) Bright-field TEM image of a multiply twinned zone in a depth of 280 pm.

Figure 1.13. Dark-field TEM images of single-crystal calcite shocked to 85 GPa, displaying (a) the crossing of multiple twins, a large number of perfect dislocations and (b) numerous partial dislocations decorating the twin planes, (c) Secondary electron image of compacted calcite powder shocked to 85 GPa. The recovered specimen is composed of numerous foamy aggregates containing bubbles, voids, and crater-shaped objects.

Fig. 3.69 Representative weak-beam dark-field (WBDF) images where dislocations Burgers vectors (b) and fault vector (Rp) of fault F were determined (transmission electron microscopy) [55], With kind permission of John Wiley and Sons...

Figure 33. Schematic representation of the image formation at an edge dislocation in a thin foil The line thickness is a measure of the beam intensity. The image profiles for bright-field (BF) and dark-field (DF) images are represented schematically along with diffraction conditions in the perfect part of the foil...

Dislocations. Dislocation configurations have been studied mainly by diffraction contrast bright-field imaging since this method is very sensitive to lattice strain fields. Under these conditions, dislocations appear as dark lines when two-beam diffraction conditions close to s 0 are used. A network of dislocations in the basal plane (0001) of zinc is visible in Figure 66. 

Fig. 1. (a) Dark-field optical micrograph of an extensive dislocation network in halite revealed by the decoration of the dislocations with colloidal silver [16]. (b) Optical phase image of growth steps, one unit cell high (0.79 nm) on the prism surface of a beryl crystal. The inner step joins a pair of opposite-handed screw dislocations, which are imaged as dots. The c-axis is almost parallel to the straight steps [17]. 

Fig. 3. Dislocations in carbonates (a) Dark-field TEM image showing dislocations and stacking faults on the <2 i i 0) planes generated by basal slip in a dolomite single crystal deformed at 420°C [52]. (b) Dislocations associated with crossing mechanical twins in calcite (TEM, bright field) [161].

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