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A field emission gun (FEG) is a type of electron gun in which a sharply pointed Müller-type^{[clarification needed]} emitter^[1]^: 87–128 is held at several kilovolts negative potential relative to a nearby electrode, so that there is sufficient potential gradient at the emitter surface to cause field electron emission. Emitters are either of cold-cathode type, usually made of single crystal tungsten sharpened to a tip radius of about 100 nm, or of the Schottky type,^[1]^: 1–28 in which thermionic emission is enhanced by barrier lowering in the presence of a high electric field. Schottky emitters are made by coating a tungsten tip with a layer of zirconium oxide (ZrO₂) decreasing the work function of the tip by approximately 2.7 eV.^[2]

In electron microscopes, a field emission gun is used to produce an electron beam that is smaller in diameter, more coherent and with up to three orders of magnitude greater current density or brightness than can be achieved with conventional thermionic emitters such as tungsten or lanthanum hexaboride (LaB
₆)-tipped filaments. The result in both scanning and transmission electron microscopy is significantly improved signal-to-noise ratio and spatial resolution, and greatly increased emitter life and reliability compared with thermionic devices.

References

^ ^a ^b Orloff, John, ed. (24 October 2008). "Review of ZrO/W Schottky Cathode". Handbook of Charged Particle Optics (2nd ed.). CRC Press. ISBN 978-1420045543. LCCN 2008013026. OCLC 778264838. OL 11816479M.
^ "Keywords | Glossary of TEM Terms | JEOL". www.jeol.co.jp.

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[2008_Orloff-1] Orloff, John, ed. (24 October 2008). "Review of ZrO/W Schottky Cathode". Handbook of Charged Particle Optics (2nd ed.). CRC Press. ISBN 978-1420045543. LCCN 2008013026. OCLC 778264838. OL 11816479M.

[2] "Keywords | Glossary of TEM Terms | JEOL". www.jeol.co.jp.

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+{{Short description|Type of electron gun}}
-A '''field emission gun''' is a type of [[electron gun]] in which a sharply-pointed Müller-type emitter is held at several kilovolts negative [[potential]] relative to a nearby [[electrode]], so that there is sufficient potential [[gradient]] at the emitter surface to cause [[field electron emission]]. Emitters are either of [[cold-cathode]] type, usually made of single crystal tungsten sharpened to a tip radius of about 100 nm, or of the [[Walter H. Schottky|Schottky]] type, in which [[thermionic emission]] is enhanced by barrier lowering in the presence of a high electric field. Schottky emitters are made by coating a tungsten tip with a layer of [[zirconium oxide]], which has the unusual property of increasing in [[electrical conductivity]] at high temperature.
+{{More citations needed|date=December 2019}}
+[[File:Schottky-Emitter 01.jpg|thumb|Schottky-emitter electron source of an [[Electron microscope]]]]
+A '''field emission gun''' ('''FEG''') is a type of [[electron gun]] in which a sharply pointed Müller-type{{clarify|reason=what is this?|date=July 2014}} emitter<ref name="2008_Orloff" />{{rp|pages=87–128}} is held at several [[kilovolts]] negative [[potential]] relative to a nearby [[electrode]], so that there is sufficient potential [[gradient]] at the emitter surface to cause [[field electron emission]]. Emitters are either of [[cold-cathode]] type, usually made of single crystal [[tungsten]] sharpened to a tip radius of about 100&nbsp;nm, or of the [[Walter H. Schottky|Schottky]] type,<ref name="2008_Orloff" />{{rp|pages=1–28}} in which [[thermionic emission]] is enhanced by barrier lowering in the presence of a high [[electric field]]. Schottky emitters are made by coating a tungsten tip with a layer of [[zirconium oxide]] (ZrO<sub>2</sub>) decreasing the [[work function]] of the tip by approximately 2.7 [[electronvolt|eV]].<ref>{{Cite web|url=https://www.jeol.co.jp/en/words/emterms/search_result.html?keyword=Schottky-type+electron+gun|title=Keywords &#124; Glossary of TEM Terms &#124; JEOL|website=www.jeol.co.jp}}</ref>
-In  [[electron microscope]]s, a field emission gun is used to produce an electron beam that is smaller in diameter, more coherent and with up to three orders of magnitude greater current density or brightness than can be achieved with conventional [[thermionic emission|thermionic emitters]] such as tungsten or [[lanthanum hexaboride]] (LaB<sub>6</sub>)-tipped filaments. The result in both [[scanning electron microscope|scanning]] and [[transmission electron microscope|transmission electron microscopy]] is significantly improved [[signal-to-noise ratio]] and spatial resolution, and greatly increased emitter life and reliability compared with thermionic devices.
+In  [[electron microscope]]s, a field emission gun is used to produce an electron beam that is smaller in diameter, more [[Coherence (physics)|coherent]] and with up to three orders of magnitude greater [[current density]] or [[brightness]] than can be achieved with conventional [[thermionic emission|thermionic emitters]] such as tungsten or [[lanthanum hexaboride]] ({{chem|LaB|6}})-tipped [[Electrical filament|filaments]]. The result in both [[scanning electron microscope|scanning]] and [[transmission electron microscope|transmission electron microscopy]] is significantly improved [[signal-to-noise ratio]] and [[spatial resolution]], and greatly increased emitter life and reliability compared with thermionic devices.
 ==References==
-{{reflist}}
+{{reflist|refs=
+<ref name="2008_Orloff">{{cite book | date = 2008-10-24 | chapter = Review of ZrO/W Schottky Cathode | editor1-last = Orloff | editor1-first = John | editor1-link = Jon Orloff | title = Handbook of Charged Particle Optics | language = en | edition = 2nd | publisher = [[CRC Press]] | isbn = 978-1420045543 | lccn = 2008013026 | oclc = 778264838 | ol = OL11816479M | ref = 2008_Orloff | df = dmy-all}}</ref>
-[[Category:Technology]]
+}}
+{{Electron microscopy}}
+[[Category:Vacuum tubes]]
 [[Category:Tungsten]]
 {{tech-stub}}