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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

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