Dislocation imaging

The characteristic K line consists of a closely spaced doublet with a 2 1 intensity ratio between the K i and K 2 lines. This not a problem if a low spatial resolution recording medium, such as a fluorescent screen and image intensifier, is used but is a problem if high resolution nuclear emulsion plates are used. Then individual dislocation images are doubled because the diffracted beams from the two lines make different directiorrs in space, giving rise to a type... 

Figure 8.3 Berg-Barrett topograph showing individual dislocation images in a single crystal of zinc. (Courtesy B.Roessler)...

However, for quantitative calculations and simulation of dislocation images we... 

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

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

The dislocation image lies to one side of the dislocation, in agreement with the intuitive explanation of the origin of dislocation contrast given in Section 5.1. 

Experience has shown that BF dislocation images formed under diffraction conditions approximating those in Figure 5.19(c) - particularly when the structure factor of the first-order reflection g is much larger than that of the second-order reflection 2g (e.g., g = lOTl in quartz) - have... 

Howie, A., Whelan, M. J. (1962). Diffraction contrast of electron microscope images of crystal lattice defects. 111. Results and experimental confirmation of the dynamical theory of dislocation image contrast. Proc. Roy. Soc., (London), A267, 206-30. 

Figure 3.48 Formation of a dislocation image by deflection of transmitted electrons due to local diffraction near the core of an edge dislocation. BF, bright-field.

Figure 3.49 Configuration of dislocations in a thin foil when they line up in a single slip plane (a) orientation relation between primary electron beam and dislocations in a crystal plane and (b) the dislocation images projected on a TEM image plane.

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. 

FIGURE 17.4 CFR UHMWPE (Poly II) tibial component (A) and patellar component (B) retrieved after 32 years of implantation. Implanted in 1975, this Total Condylar knee replacement was revised in 2006 for instability and patellar dislocation. Image provided courtesy of Francisco Medel, PhD, Drexel University. 

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