Editing Dislocation (section)

==Observation==
=== Transmission electron microscopy (TEM) ===
[[Image:TEM micrograph dislocations precipitate stainless steel 1.jpg|right|thumb|[[Transmission electron micrograph]] of dislocations]]
[[Image:TEM micrograph dislocations precipitate stainless steel 2.jpg|right|thumb|Transmission electron micrograph of dislocations]]

[[Transmission electron microscopy]] can be used to observe dislocations within the [[microstructure]] of the material.<ref>{{cite journal|last1=Spence|first1=J.C.H.|s2cid=135976739|author-link1 = John C. H. Spence|title=Imaging dislocation cores – the way forward|journal=Philosophical Magazine|date=2006|volume=86|issue=29–31|pages=4781–4796|doi=10.1080/14786430600776322|display-authors=etal|bibcode = 2006PMag...86.4781S }}</ref>  Thin foils of material are prepared to render them transparent to the electron beam of the microscope. The [[electron]] beam undergoes [[diffraction]] by the regular crystal lattice planes into a diffraction pattern and contrast is generated in the image by this diffraction (as well as by thickness variations, varying strain, and other mechanisms). Dislocations have different local atomic structure and produce a strain field, and therefore will cause the electrons in the microscope to scatter in different ways. Note the characteristic 'wiggly' contrast of the dislocation lines as they pass through the thickness of the material in the figure (dislocations cannot end in a crystal, and these dislocations are terminating at the surfaces since the image is a 2D projection).

Dislocations do not have random structures, the local atomic structure of a dislocation is determined by the Burgers vector. One very useful application of the TEM in dislocation imaging is the ability to experimentally determine the Burgers vector. Determination of the Burgers vector is achieved by what is known as <math>\vec{g} \cdot \vec{b}</math> ("g dot b") analysis.<ref>{{Cite book|title=Transmission electron microscopy : a textbook for materials science|first1=David B. |last1=Williams |first2=C. Barry |last2=Carter |date=2008|publisher=Springer|isbn=9780387765020|oclc=660999227}}</ref> When performing [[dark field microscopy]] with the TEM, a diffracted spot is selected to form the image (as mentioned before, lattice planes diffract the beam into spots), and the image is formed using only electrons that were diffracted by the plane responsible for that diffraction spot. The vector in the diffraction pattern from the transmitted spot to the diffracted spot is the <math>\vec{g}</math> vector. The contrast of a dislocation is scaled by a factor of the [[dot product]] of this vector and the Burgers vector (<math>\vec{g} \cdot \vec{b}</math>). As a result, if the Burgers vector and <math>\vec{g}</math> vector are perpendicular, there will be no signal from the dislocation and the dislocation will not appear at all in the image. Therefore, by examining different dark field images formed from spots with different g vectors, the Burgers vector can be determined.

=== Other methods ===
[[Image:Silicon dislocation orientation 111 mag 500x.png|right|thumb|Etch Pits formed on the ends of dislocations in silicon, orientation (111)]]

[[Field ion microscopy]] and [[atom probe]] techniques offer methods of producing much higher magnifications (typically 3 million times and above) and permit the observation of dislocations at an atomic level. Where surface relief can be resolved to the level of an atomic step, screw dislocations appear as distinctive spiral features – thus revealing an important mechanism of crystal growth: where there is a surface step, atoms can more easily add to the crystal, and the surface step associated with a screw dislocation is never destroyed no matter how many atoms are added to it.

==== Chemical etching ====
When a dislocation line intersects the surface of a metallic material, the associated strain field locally increases the relative susceptibility of the material to acid [[industrial etching|etching]] and an [[etch pit density|etch pit]] of regular geometrical format results. In this way, dislocations in silicon, for example, can be observed ''indirectly'' using an interference microscope. Crystal orientation can be determined by the shape of the etch pits associated with the dislocations.

If the material is deformed and repeatedly re-etched, a series of etch pits can be produced which effectively trace the movement of the dislocation in question.