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Dislocation
lines act as a trapping location for impurity atoms in a crystal. A method
of locating dislocation lines in transparent materials entails "decorating"
them with such impurity atoms. These particles scatter light and the defect
can then be viewed with a high powered microscope.
In
silver chloride, the material may be decomposed to yield metallic silver
when exposed to light in the fundamental absorption edge. The interstitial
silver migrates to dislocation lines and may be seen by viewing the crystal
in non-photoactive light. The top photograph shows a dislocation network
in silver chloride made visible in this way. Materials that do not photodecompose
may have their dislocations decorated with impurity atoms. The lower photograph
shows dislocations in KCl decorated with silver impurities. |
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