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7/23/2019 rutherford electron model
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Scanning electronmicroscope (SEM)
ELECTRON SOURCES
Ruth Jaimes 2013
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Hitachi S-4800 !el" emission scanning electron microscope
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1. What is the main idea of S!"
2. lectron gun
3. Ho# is a $ne electron %ean formed"
4. Ha# can #e o%tain an e&en $ner electron %ean"
'. What (inds of electron guns )electron sources* are used inthe S!"
+. What are the di,erences %et#een the (inds of electronsguns"
ELECTRON SOURCES
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SEM ELECTRON SOURCES
Te electron g#n are locatedeither at the &er top region of the
S! that generates a %eam ofelectrons
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scanning electron microscope )S!*is a tpe of electron microscope thatproduces images #ith a focused%eam of electrons.
/he electrons interact #ith electronsin the sample
/he electron %eam is generation
b$ electrons so#rces%
on$guration ofS!
/he mechanism that emits electronsform a metal and accelerates tema strong electric !el"%
1. What is the main idea of S!"
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Ho# is a $ne electron %ean formed"
/he electron source )diameterdo* formed % electron gun isreduced and made into a $neelectron %ean )diameter dk* %the condenser lens ando%ecti&e lens.
Ha# can #e o%tain ane&en$ner electron %ean"
n order to o%tain a $ne electron %eanthe instrument utilies an electron gun featuring5 a small electron source a large current densit )current )in 6cm2* per unit areaand
a small energ #idth )energ &itiating )in e7* ofdischarged electrons.
SEM ELECTRON SOURCES
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W$ is important teelectron so#rces&
/he simplest and cheapest gun uses aheated tungsten #ire to produce electrons.
generates a %eam of electrons
Wat kin" of electron so#rces is #se"
in te SEM&
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ield emission guns create a strongelectrical $eld to pull electronsa#a from the atoms.
/hermionic guns tpe appl thermalenerg to a $lament )usuall made oftungsten #hich has a high meltingpoint* - cold $eld emission
- Schott(
- tungsten
- 9a:+ )lanthanumhe;a%oride
/here are three tpes of electron gunaccording to the method of emission5 - $eld emission tpe )*electron gun - Schott( electron gun
and - thermal electron gun.
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Wat kin" of electron so#rces is #se"in te SEM&)a* /hermionic gun
)tungsten*
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Wat kin" of electron so#rces is #se"in te SEM&)%* 9a:+ gun
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Wat kin" of electron so#rces is #se"in te SEM&
)c* cold $eld emission )* electron gun
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Wat kin" of electron so#rces is #se"in te SEM&
)d* Schott( electron gun
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What are the di,erences %et#een the (inds ofelectrons guns"
SEM ELECTRON SOURCES
7/23/2019 rutherford electron model
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