El t
Electron Microscopy Mi
SEM and TEM
SEM and TEM
Content
1. Introduction: Motivation for electron microscopy
2 Interaction with matter
2.
Interaction with matter
3. SEM: Scanning Electron Microscopy 3.1 Functional Principle
3.2 Examples
3.3 EDX (Energy‐Dispersive X‐ray spectroscopy)
4 TEM: Transmission Electron Microscopy
4.
TEM: Transmission Electron Microscopy
4.1 Functional Principle
4.2 Examples
4.3 Comparing SEM and TEM d
4.4 HAADF (High Angle Annular Dark‐Field Imaging)
1 Motivation for EM
1. Motivation for EM
Resolution of light microscope is limited:
λ
sin Θ = 1.22 ⋅
D
• wavelenght of visible light
wavelenght of visible light
• less diffraction for smaller wavelenghts
¾ possible magnification: ~ 2 000
[ ]
[1]
1 Motivation for EM
1. Motivation for EM
Different approach: use electrons instead of light
• Access
Access to much smaller wavelengths
to much smaller wavelengths
h
λ=
(3.7 pm for 100 keV)
p
• electrostatic/electromagnetic lenses l t t ti / l t
ti l
instead of glass lenses
¾ possible magnification: ~ 2 000 000
[2]
2 Interaction with matter
2. Interaction with matter
Backscattered electrons
Secondary electrons
y
Auger electrons
Transmitted electrons
Transmitted electrons
X‐Rays
specimen
phonons
2 Interaction with matter
2. Interaction with matter
Topography and composition Topography
p g p y
Structure and composition
Structure and composition
Composition
Backscattered electrons
Secondary electrons
y
Transmitted electrons
Transmitted electrons
X‐Rays
2 Interaction with matter
2. Interaction with matter
2 different approaches:
Backscattered and B
k
d d
secondary electrons
SEM
T
Transmitted electrons
i d l
TEM
3 SEM
3. SEM
Scanningg
Electron
Microscopy
3 1 Functional Principle
3.1 Functional Principle
Electron source
Condenser lens
Scan coil
Objective lens
Specimen + Detectors
2‐25 kV
e‐
3 1 Functional Principle
3.1 Functional Principle
e‐
Electron gun
Condenser lens
Scan coil
Objective lens
Specimen + Detectors
coils
N
N
S
coils
3 1 Functional Principle
3.1 Functional Principle
Electron gun
e‐
Condenser lens
Scan coil
Objective lens
Specimen + Detectors
Waveform generator
Detector signal
3 1 Functional Principle
3.1 Functional Principle
Electron gun
e‐
Condenser lens
Scan coil
Objective lens
Specimen + Detectors
coils
coils
f
3 1 Functional Principle
3.1 Functional Principle
Electron gun
Condenser lens
Scan coil
Objective lens
Specimen + Detectors
e‐
El t
Electron‐
and
d
Lightdetectors
3 2 Examples
3.2 Examples
Photonic crystal in silicon substrate
WSI, D. Dorfner
Nanowires in silicon substrate WSI, D. Pedone
3 3 Energy Dispersive Systems (EDX)
3.3 Energy Dispersive Systems (EDX)
e‐
e‐
Bremsstrahlung
→ X‐ray Continuum
Electron filling holes
→ Characteristic X‐rays
Information about chemical composition
p
3 3 Energy Dispersive Systems (EDX)
3.3 Energy Dispersive Systems (EDX)
Solid state X‐ray
Solid state X
ray Detector
Detector
N2
Si(Li)
coldfinger
X‐ray
‐X‐ray creates hole/electron pairs (3.8 eV necessary per pair)
‐Number
Number of pairs and current are a measure for X
of pairs and current are a measure for X‐ray
ray energy
energy
3 3 Energy Dispersive Systems (EDX)
3.3 Energy Dispersive Systems (EDX)
Alloy of aluminum and tungsten
[3]
reminder
2 different approaches:
Backscattered and B
k
d d
secondary electrons
SEM
T
Transmitted electrons
i d l
TEM
4 TEM
4. TEM
Transmission
Electron
Microscopy
4 1 Functional principles
4.1 Functional principles
Electron gun
Condenser lenses
Object
Objective lens + intermediate lens + projective lense
l
50‐ 400 kV
e‐
4 1 Functional principles
4.1 Functional principles
Electron gun
Condenser lenses
Object
Objective lens + intermediate lens + projective lense
l
e‐
4 1 Functional principles
4.1 Functional principles
e‐
Electron gun
Condenser lenses
~100nm
specimen
p
Object
Objective lens + intermediate lens + projective lense
l
scattered
direct beam
4 1 Functional principles
4.1 Functional principles
Electron gun
Condenser lenses
Object
Objective lens + intermediate lens + projective lense
l
4 2 Example
4.2 Example
Crossectional analysis of a conductor nanogap device
WSI, S. Strobel
WSI, D. Pedone
4 3 Comparison of SEM and TEM
4.3 Comparison of SEM and TEM
SEM: scans with a focused point
TEM: illumantes whole sample
4.4 High Angle Annular Dark‐Field 4
4 High Angle Annular Dark Field
Imaging (HAADF)
g g(
)
‐ used in STEM (scanning transmission electron microscopy)
‐ rayleigh scattering at high angles
rayleigh scattering at high angles
‐Angle depends on the atomic number Z: ‐electron intesity: I ∝ Z 2
¾ by messuring the electron intensity, while scanning over the sample, information about the chemical compositio can be aquired
can be aquired
Thanks for your attention.
reference
‐ TUM chemie department: http://www.ch.tum.de/em/emlabor/methoden/rem.htm
http://www ch tum de/em/emlabor/methoden/tem htm
http://www.ch.tum.de/em/emlabor/methoden/tem.htm
‐wikipedia:
http://en.wikipedia.org/wiki/Electron_microscopy
http://en wikipedia org/wiki/Transmission electron microscope
http://en.wikipedia.org/wiki/Transmission_electron_microscope
http://en.wikipedia.org/wiki/Scanning_Electron_Microscope
http://en.wikipedia.org/wiki/Energy‐dispersive_X‐ray_spectroscopy
http://en wikipedia org/wiki/HAADF
http://en.wikipedia.org/wiki/HAADF
http://en.wikipedia.org/wiki/EELS
‐ Transmission Electron Microscopy, D. B. Williams and C. B. Carter
‐ Scanning electron microscopy and X‐ray Microanalysis, G. Lowes
g
py
y
y ,
‐ electron microscopy in solid state physics, H. Bethge and J. Heydenreich
reference
[1] http://en.wikipedia.org/wiki/Optical_microscope
[2] http://de.wikipedia.org/wiki/Elektronenmikroskop
[3] http://www ch tum de/em/emlabor/methoden/rem edx htm
[3] http://www.ch.tum.de/em/emlabor/methoden/rem‐edx.htm