Editing Microscope (section)

===Electron microscope===

[[File:Cytokinesis-electron-micrograph.jpg|thumb|Transmission electron micrograph of a dividing cell undergoing cytokinesis]]{{main|Electron microscope}}
The two major types of electron microscopes are [[transmission electron microscope]]s (TEMs) and [[scanning electron microscope]]s (SEMs).<ref name=":0" /><ref name=":1">{{Cite journal|last1=Alberts|first1=Bruce|last2=Johnson|first2=Alexander|last3=Lewis|first3=Julian|last4=Raff|first4=Martin|last5=Roberts|first5=Keith|last6=Walter|first6=Peter|date=2002|title=Looking at the Structure of Cells in the Microscope|url=https://www.ncbi.nlm.nih.gov/books/NBK26880/|journal=Molecular Biology of the Cell. 4th Edition|language=en}}</ref> They both have series of electromagnetic and electrostatic lenses to focus a high energy beam of electrons on a sample. In a TEM the electrons pass through the sample, analogous to [[bright field microscopy|basic optical microscopy]].<ref name=":0"/> This requires careful sample preparation, since electrons are scattered strongly by most materials.<ref name=":1"/> The samples must also be very thin (below 100&nbsp;nm) in order for the electrons to pass through it.<ref name=":0"/><ref name=":1"/> Cross-sections of cells stained with osmium and heavy metals reveal clear organelle membranes and proteins such as ribosomes.<ref name=":1"/> With a 0.1&nbsp;nm level of resolution, detailed views of viruses (20 – 300&nbsp;nm) and a strand of DNA (2&nbsp;nm in width) can be obtained.<ref name=":1"/> In contrast, the SEM has raster coils to scan the surface of bulk objects with a fine electron beam. Therefore, the specimen do not necessarily need to be sectioned, but coating with a nanometric metal or carbon layer may be needed for nonconductive samples.<ref name=":0"/> SEM allows fast surface imaging of samples, possibly in thin water vapor to prevent drying.<ref name=":0"/><ref name=":1"/>