Editing Scanning electron microscope (section)

==Environmental SEM==
{{Main|Environmental scanning electron microscope}}
Conventional SEM requires samples to be imaged under [[vacuum]], because a gas atmosphere rapidly spreads and [[attenuation|attenuates]] electron beams. As a consequence, samples that produce a significant amount of [[vapour pressure|vapour]], e.g. wet biological samples or oil-bearing rock, must be either dried or cryogenically frozen. Processes involving [[phase transition]]s, such as the drying of [[adhesive]]s or melting of [[alloy]]s, liquid transport, chemical reactions, and solid-air-gas systems, in general cannot be observed with conventional high-vacuum SEM. In environmental SEM (ESEM), the chamber is evacuated of air, but water vapor is retained near its saturation pressure, and the residual pressure remains relatively high. This allows the analysis of samples containing water or other volatile substances. With ESEM, observations of living insects have been possible.<ref>{{cite journal |last1=Takaku |first1=Yasuharu |last2=Suzuki |first2=Hiroshi |last3=Ohta |first3=Isao |last4=Tsutsui |first4=Takami |last5=Matsumoto |first5=Haruko |last6=Shimomura |first6=Masatsugu |last7=Hariyama |first7=Takahiko |date=7 March 2015 |title=A 'NanoSuit' surface shield successfully protects organisms in high vacuum: observations on living organisms in an FE-SEM |journal=Proceedings of the Royal Society of London B: Biological Sciences |language=en |volume=282 |issue=1802 |pages=20142857 |doi=10.1098/rspb.2014.2857 |issn=0962-8452 |pmc=4344158 |pmid=25631998}}</ref>

The first commercial development of the ESEM in the late 1980s<ref>{{cite book
|last = Danilatos
|first = G. D.
|year = 1988
|chapter = Foundations of environmental scanning electron microscopy
|volume = 71
|pages = 109–250
|doi = 10.1016/S0065-2539(08)60902-6
|isbn = 9780120146710
|title = Advances in Electronics and Electron Physics Volume 71
}}</ref><ref>{{US patent reference|number=4823006|issue-date=18 April 1989|title=Integrated electron optical/differential pumping/imaging signal detection system for an environmental scanning electron microscope|inventor=Danilatos, Gerasimos D. and Lewis, George C.}}</ref> allowed samples to be observed in low-pressure gaseous environments (e.g. 1–50 [[Torr]] or 0.1–6.7&nbsp;kPa) and high relative [[humidity]] (up to 100%). This was made possible by the development of a secondary-electron detector<ref>{{cite book
|last = Danilatos
|first = G. D.
|year = 1990
|title = Theory of the Gaseous Detector Device in the ESEM
|volume = 78
|pages = 1–102
|doi = 10.1016/S0065-2539(08)60388-1
|series = Advances in Electronics and Electron Physics
|isbn = 9780120146789
}}</ref><ref>{{US patent reference|number=4785182|issue-date=15 November 1988|title=Secondary Electron Detector for Use in a Gaseous Atmosphere|inventor=Mancuso, James F.; Maxwell, William B. and Danilatos, Gerasimos D.}}</ref> capable of operating in the presence of water vapour and by the use of pressure-limiting apertures with differential pumping in the path of the electron beam to separate the vacuum region (around the gun and lenses) from the sample chamber. The first commercial ESEMs were produced by the ElectroScan Corporation in USA in 1988. ElectroScan was taken over by Philips (who later sold their electron-optics division to FEI Company) in 1996.<ref>[http://www.sfc.fr/Material/hrst.mit.edu/hrs/materials/public/ElectronMicroscope/EM1990s.htm History of Electron Microscopy 1990s] {{Webarchive|url=https://archive.today/20070304091710/http://www.sfc.fr/Material/hrst.mit.edu/hrs/materials/public/ElectronMicroscope/EM1990s.htm |date=4 March 2007 }}. sfc.fr</ref>

ESEM is especially useful for non-metallic and biological materials because coating with carbon or gold is unnecessary. Uncoated [[plastics]] and [[elastomers]] can be routinely examined, as can uncoated biological samples. This is useful because coating can be difficult to reverse, may conceal small features on the surface of the sample and may reduce the value of the results obtained. X-ray analysis is difficult with a coating of a heavy metal, so carbon coatings are routinely used in conventional SEMs, but ESEM makes it possible to perform X-ray microanalysis on uncoated non-conductive specimens; however some specific for ESEM artifacts are introduced in X-ray analysis. ESEM may be the preferred for electron microscopy of unique samples from criminal or civil actions, where [[forensic analysis]] may need to be repeated by several different experts. It is possible to study specimens in liquid with ESEM or with other [[Liquid-Phase Electron Microscopy|liquid-phase electron microscopy]] methods.<ref>{{cite journal |last1=de Jonge|first1= N.|last2= Ross|first2= F.M.|date=2011 | title=Electron microscopy of specimens in liquid | journal= Nature Nanotechnology |volume=6 |issue= 8| pages= 695–704 | doi=10.1038/nmat944|pmid= 12872162|bibcode=2003NatMa...2..532W|s2cid= 21379512}}</ref>