Editing Electron diffraction (section)

== A primer on electron diffraction ==
All matter can be thought of as [[matter wave]]s,<ref name="Broglie" />{{Rp|location=Chpt 1-3}} from small particles such as electrons up to macroscopic objects – although it is impossible to measure any of the "wave-like" behavior of macroscopic objects. Waves can move around objects and create interference patterns,<ref name="Born & Wolf">
{{cite book
 |last1=Born |first1=M. |author1-link=Max Born
 |last2=Wolf |first2=E. |author2-link=Emil Wolf
 |year=1999
 |title=[[Principles of Optics]]
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-64222-4
}}</ref>{{Rp|location=Chpt 7-8}} and a classic example is the [[Young's two-slit experiment]] shown in [[#Figure 2|Figure 2]], where a wave impinges upon two slits in the first of the two images (blue waves). After going through the slits there are directions where the wave is stronger, ones where it is weaker – the wave has been [[Diffraction|diffracted]].<ref name="Born & Wolf"/>{{Rp|location=Chpt 1,7,8}} If instead of two slits there are a number of small points then similar phenomena can occur as shown in the second image where the wave (red and blue) is coming in from the bottom right corner. This is comparable to diffraction of an [[#Waves, diffraction and quantum mechanics|electron wave]] where the small dots would be atoms in a small crystal, see also note.{{efn|name=Diff}} Note the strong dependence on the relative orientation of the crystal and the incoming wave.{{anchor|Figure 2}}

{{multiple image
| direction         = horizontall
| align             = right
| height            = 150
| image1            = Doubleslit.gif
| image2            = Bragg Diffraction.gif
| footer            = Figure 2: Young's double slit experiment, showing the wave in blue and the two slits in yellow; the other Figure with red and blue waves is similar from a small array of white atoms.
| alt1              = An image showing the result of a double-slit diffraction and interference experiment
| alt2              = An image that illustrates electron diffraction from a very small, ordered array of atoms.
| total_width       = 
}}
Close to an aperture or atoms, often called the "sample", the electron wave would be described in terms of near field or [[Fresnel diffraction]].<ref name="Born & Wolf"/>{{Rp|location=Chpt 7-8}} This has relevance for imaging within [[electron microscope]]s,<ref name="Cowley95"/>{{Rp|location=Chpt 3}}<ref name="Reimer"/>{{Rp|location=Chpt 3-4}} whereas electron diffraction patterns are measured far from the sample, which is described as far-field or Fraunhofer diffraction.<ref name="Born & Wolf"/>{{Rp|location=Chpt 7-8}} A map of the directions of the [[#Plane waves, wavevectors and reciprocal lattice|electron waves]] leaving the sample will show high intensity (white) for favored directions, such as the three prominent ones in the Young's two-slit experiment of [[#Figure 2|Figure 2]], while the other directions will be low intensity (dark). Often there will be an array of spots (preferred directions) as in [[#Figure 1|Figure 1]] and the other figures shown later.