Scanning Electron Microscopes (SEM) and Electron Sources
Scanning electron microscope (SEM)
ELECTRON SOURCES
Ruth Jaimes
2013
CAMTEC Nanofabrication Workshop
Hitachi S-4800
field emission
scanning electron microscope
CAMTEC Nanofabrication Workshop
1.
What is the main idea of SEM?
2.
Electron gun
3.
How is a fine electron bean formed?
4.
Haw can we obtain an even finer electron bean?
5.
What kinds of electron guns (electron sources) are used in the SEM?
6.
What are the differences between the kinds of electrons guns?
ELECTRON SOURCES
SEM ELECTRON SOURCES
The electron gun
are located either at the
very top region of the SEM that generates a
beam of electrons
CAMTEC Nanofabrication Workshop
A scanning electron microscope (SEM) is a type
of electron microscope that produces images
with a focused beam of electrons.
The electrons interact with electrons in the
sample
The electron beam is generation
by
electrons sources.
These electrons don't
naturally go where
they need to,
however, which gets
us to the next
component of SEMs.
Configuration of SEM
The mechanism that
emits electrons
form a metal and
accelerates them
a strong electric field.
1.
What is the main idea of SEM?
CAMTEC Nanofabrication Workshop
How is a fine electron bean formed?
The electron source (
diameter do
)
formed by electron gun is reduced and
made into a fine electron bean
(
diameter dk
) by the condenser lens
and objective lens.
Haw can we obtain an even
finer electron bean?
In order to obtain a fine electron bean,
the instrument utilizes an electron gun featuring:
a small electron source,
a large current density (current (in A/cm
2
) per unit area, and
a small energy width (energy vitiating (in eV) of discharged electrons.
SEM ELECTRON SOURCES
Why is important the electron sources?
The simplest and cheapest gun uses a heated tungsten
wire to produce electrons.
generates a beam of electrons
What kind of electron sources is used in the SEM?
Em um MEV típico, os
elétrons
são
emitidos termionicamente a partir
de um
cátodo
(filamento) de
tungstênio
ou hexaboreto de
lantânio (LaB
6
) e acelerados através
de um
ânodo
, sendo também
possível obter elétrons por efeito de
emissão de campo. O tungstênio é
tipicamente usado por ser o metal
com mais alto
ponto de fusão
e mais
baixa pressão de vapor, permitindo
que seja aquecido para a emissão de
elétrons.
CAMTEC Nanofabrication Workshop
Field emission guns
, create a strong
electrical field to pull electrons away from
the atoms.
Thermionic guns type
, apply thermal energy to
a filament (usually made of tungsten, which
has a high melting point)
- cold field emission,
- Schottky,
- tungsten,
- LaB6 (lanthanum hexaboride)
There are three types of electron gun
according to the method of emission:
- field emission type (FE) electron gun,
- Schottky electron gun and,
- thermal electron gun.
CAMTEC Nanofabrication Workshop
What kind of electron sources is used in the SEM?
(a) Thermionic gun (tungsten)
CAMTEC Nanofabrication Workshop
What kind of electron sources is used in the SEM?
(b) LaB6 gun
CAMTEC Nanofabrication Workshop
What kind of electron sources is used in the SEM?
(c) cold field emission (FE) electron gun
CAMTEC Nanofabrication Workshop
What kind of electron sources is used in the SEM?
(d) Schottky electron gun
CAMTEC Nanofabrication Workshop
What are the differences between the kinds of electrons guns?
SEM ELECTRON SOURCES
CAMTEC Nanofabrication Workshop
CAMTEC Nanofabrication Workshop
Thanks for attention
Canada
Brazil
Victoria BC
Scanning Electron Microscopes (SEMs) utilize focused electron beams to produce high-resolution images by interacting with a sample's electrons. The electron source, such as the electron gun, plays a crucial role in forming fine electron beams for imaging purposes. Different types of electron sources, including field emission and thermionic guns, are employed in SEMs to generate electron beams efficiently. Understanding how electron sources work is essential for achieving finer imaging resolutions in nanofabrication workshops.
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Presentation Transcript
CAMTEC Nanofabrication Workshop Scanning electron microscope (SEM) ELECTRON SOURCES Hitachi S-4800 field emission scanning electron microscope Ruth Jaimes 2013
CAMTEC Nanofabrication Workshop ELECTRON SOURCES 1. What is the main idea of SEM? 2. Electron gun 3. How is a fine electron bean formed? 4. Haw can we obtain an even finer electron bean? 5. What kinds of electron guns (electron sources) are used in the SEM? 6. What are the differences between the kinds of electrons guns?
http://bits.wikimedia.org/static-1.21wmf7/skins/common/images/magnify-clip.pnghttp://bits.wikimedia.org/static-1.21wmf7/skins/common/images/magnify-clip.png CAMTEC Nanofabrication Workshop SEM ELECTRON SOURCES 1. What is the main idea of SEM? Configuration of SEM A scanning electron microscope (SEM) is a type of electron microscope that produces images with a focused beam of electrons. The electrons interact with electrons in the sample The electron gun are located either at the very top region of the SEM that generates a beam of electrons The mechanism that emits electrons form a metal and accelerates them a strong electric field. The electron beam is generation by electrons sources.
CAMTEC Nanofabrication Workshop SEM ELECTRON SOURCES How is a fine electron bean formed? The electron source (diameter do) formed by electron gun is reduced and made into a fine electron bean (diameter dk) by the condenser lens and objective lens. Haw can we obtain an even finer electron bean? In order to obtain a fine electron bean, the instrument utilizes an electron gun featuring: a small electron source, a large current density (current (in A/cm2) per unit area, and a small energy width (energy vitiating (in eV) of discharged electrons.
CAMTEC Nanofabrication Workshop Why is important the electron sources? generates a beam of electrons The simplest and cheapest gun uses a heated tungsten wire to produce electrons. What kind of electron sources is used in the SEM? There are three types of electron gun according to the method of emission: - field emission type (FE) electron gun, - Schottky electron gun and, - thermal electron gun. Thermionic guns type, apply thermal energy to a filament (usually made of tungsten, which has a high melting point) Field emission guns, create a strong electrical field to pull electrons away from the atoms. - tungsten, - LaB6 (lanthanum hexaboride) - cold field emission, - Schottky,
CAMTEC Nanofabrication Workshop What kind of electron sources is used in the SEM? (a) Thermionic gun (tungsten)
CAMTEC Nanofabrication Workshop What kind of electron sources is used in the SEM? (b) LaB6 gun
CAMTEC Nanofabrication Workshop What kind of electron sources is used in the SEM? (c) cold field emission (FE) electron gun
CAMTEC Nanofabrication Workshop What kind of electron sources is used in the SEM? (d) Schottky electron gun
CAMTEC Nanofabrication Workshop SEM ELECTRON SOURCES What are the differences between the kinds of electrons guns?
CAMTEC Nanofabrication Workshop Thanks for attention Canada Victoria BC Brazil
