Editing Electron diffraction (section)

==== Formation of a diffraction pattern ====

{{anchor|Figure 10}}[[File:ElmagLensScheme.png|left|thumb|300px|Figure 10: Imaging scheme of magnetic lens (center, colored ray diagram) with image (left) and diffraction pattern (right, black background)|alt=Simple comparison of imaging, ray diagram and diffraction in an electron microscope.]]

In TEM, the electron beam passes through a thin film of the material as illustrated in [[#Figure 10|Figure 10]]. Before and after the sample the beam is manipulated by the [[electron optics]]<ref name=":8" /> including [[magnetic lens]]es, deflectors and [[apertures]];<ref name="Pella">{{Cite web |title=Apertures, Electron Microscope Apertures |url=https://www.tedpella.com/apertures-and-filaments_html/apertures-overview.aspx |access-date=2023-02-11|website=www.tedpella.com}}</ref> these act on the electrons similar to how glass lenses focus and control light. Optical elements above the sample are used to control the incident beam which can range from a wide and parallel beam to one which is a converging cone and can be smaller than an atom, 0.1&nbsp;nm. As it interacts with the sample, part of the beam is diffracted and part is transmitted without changing its direction. This occurs simultaneously as electrons are everywhere until they are detected ([[Wave function collapse|wavefunction collapse]]) according to the [[Copenhagen interpretation]].<ref name=":12" /><ref name=":13">{{Cite book |last=Gbur |first=Gregory J. |url=https://www.jstor.org/stable/j.ctvqc6g7s |title=Falling Felines and Fundamental Physics |date=2019 |publisher=Yale University Press |isbn=978-0-300-23129-8 |pages=243–263 |doi=10.2307/j.ctvqc6g7s.17|jstor=j.ctvqc6g7s |s2cid=243353224 }}</ref>

Below the sample, the beam is controlled by another set of magnetic lneses and apertures.<ref name=":8" /> Each set of initially parallel rays (a [[#Geometrical considerations|plane wave]]) is focused by the first lens ([[Objective (optics)|objective]]) to a point in the [[back focal plane]] of this lens, forming a spot on a [[Detectors for transmission electron microscopy|detector]]; a map of these directions, often an array of spots, is the diffraction pattern. Alternatively the lenses can form a magnified image of the sample.<ref name=":8" /> Herein the focus is on collecting a diffraction pattern; for other information see the pages on [[transmission electron microscopy|TEM]] and [[scanning transmission electron microscopy]].