Dislocations Moire pattern

Figure 6.6. Facing page. Optical analogues showing the formation of a moire pattern, (a) Superposition of two gratings of unequal spacing (b) superposition of two identical gratings with a small relative rotation. The effects of an edge dislocation in one of the gratings are shown in (c) and (d).

Fig. 11a - c. STM images of Ag deposited on Cu(l 11) showing the effect of substrate temperature during deposition, (a) Deposition of 0.8 ML at 225 K leads to a moire pattern, while (b) deposition of the same amount at 300 K results in a triangular misfit dislocation structure, (c) Deposition of Ag submonolayers at 775 K leads to alloying of Ag atoms into the first Cu layer (dark spots) [97Bes]. 

Crystals oriented to satisfy Bragg s law are used as optical components in X-ray interferometry. The interference patterns are sufficiently sensitive to small displacements to allow the observation of strains and defects in crystals. Lattice rotations of 10 rad or dilations dd/d of 10 can be detected. Inhomogeneous strain produces moire fringe patterns showing dislocations and the strain-associated impurities in concentrations below one in 10 . 

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