Introduction to EM
Light microscopy - limitation
resolution
magnification
depth of focus
visible light - > λ = 390 – 760 nm
0.61 /
Abbe, Airy
dd  =
2
U=10kV (SEM) -> λ = 0.01226 nm
U=100kV (TEM) -> λ = 0.0039 nm
Visible light - > λ = 390 – 760 nm
Fotons
Electrons
Neutrons
3
Electron microscopy
SEM TEM
4
Specimens
SEM
Conductive specimens! (C, Au coatings)
Polished or electropolished metalographic cuts
Fracture surfaces
Tensile, fatigue, creep,… specimens
Powders
TEM
Specimens transparent for electrons! (~ 100 nm)
Thin foils – electropolished, Ar ions bombardment
Surface or extraction replica
Nanopowders
FIB
5
1931: 16x
1933: 12000x 1965: Oatley, first commercial SEM Stereoscan
Berlin early 1930s: Ruska and Knoll
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Vacuum system
Ion pump
Turbomolecular
Rotary/scroll pump
Diffusion pumps
10-1 Pa
10-2 – 10-9 Pa 10-5 Pa
10-9 Pa
7
Electron sources
(La,Ce)B6W
Field emission gun (FEG)
W wire + ZrO layer 8
Electron sources
W (La,Ce)B6
FEG
W wire +
ZrO layer
9
Magnetic lenses
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Magnetic lenses – expectation vs. reality
expectation reality
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Abberations Spherical abberation
Chromatic abberation
Astigmatism Coma abberation
- +
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U=10kV (SEM) -> λ = 0.01226 nm Typical SEM -> dd ~ 1 nm
expectation reality
U=100kV (TEM) -> λ = 0.0039 nm
Visible light - > λ = 390 – 760 nm
Typical TEM -> dd ~ 0.1 nm
High-end TEM (300 kV) -> dd ~ 0.05 nm
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Interactions
14
Interactions
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Primary beam - AZ91 magnesium alloy
SE
EverhartThornley
SE
In – lens SE
BSE
Annular BSE
In – lens BSE
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5 mm
5 kV
10 kV
5 mm
20 kV
5 mm
Secondary electrons
In – lens SE Everhart-Thornley SE
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1 mm
ECCI – Electron channeling contrast imagining
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19
304L – after fatigue (specimen cross-cut)
20 mm
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21
Energy and wave dispersive spectroscopy
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Energy dispersive spectroscopy - EDS
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Wave dispersive spectroscopy - WDS
2d sin q = n.λ
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25
element wt. %
Cu 60.1
Zn 27.5
Mn 6.5
Si 2.6
Al 1.3
Ni 1.1
Fe 1.0
lead-free brass
Electron backscattered diffraction - EBSD
crystallographic information, crystal orientation
26
Examples
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Examples
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Ni Cu Fe Ti
Examples
29
Examples
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Examples
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Examples
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Examples Band contrast
Map Z
Map XMap Y
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Transmission electron microscopy - diffraction
2 sinhkld nq =
Bragg law
Diffraction - reciprocal space
Cubic, tetragonal and orthorhombic lattice Hexagonal and trigonal lattice
Diffraction is a 2D cut of crystal in reciprocal space
Diffraction patterns – single crystal / one grain
Diffraction patterns
Nanocrystals
Amorphous
Transmission electron microscopy – Imagining
2
cos
g ik r
g
F n
d i e q
 
q
= 
quite complicated….
Kinematic approximation
2
g 2
0
sin( ) sin ( )
exp( ), Intenzita I
( )
 

  
 =  = − 
t
g g
g g g
g g g g
ts tsi
d is t
s s
0
2 2
0
0
0
0
0
( ) ( )exp(2 )
( )exp(2 )
2
,
( )
( ) ( )exp(2 ( ) )
( )
( ) ( )exp(2 ( ) )
g
g
g
g
g
g
r z i r
z i r
h
eE
m
g s
d z i i
z z i r
dz
d z i i
z z i r
dz
  
 

   
 
  
 
 
  
 
= 
+ 
=
 = + + =

=  +  −

=  +  −
Dynamic theory
Transmission electron microscopy – Imagining
TEM – Monel – FIB lamella
Very high dislocation density. Black dots are probably prizmatic dislocation loops
TEM – Kanthal powder
TEM – Monel - bulk
Cold spray - austenitic steel
Cold spray - austenitic steel