S1007 Doing structural biology
with the electron microscope
Lecture 3: Electron Microscope
2
Optical vs. TEM microscope
3
Optical vs. TEM microscope
source
condensor
objective
detector
4
Electron source
- thungsten filament
- LaB6 crystal
- Field Emission
Gun
Probe sizeWork function
5
Electron source
- thungsten filament
- LaB6 crystal
- Field Emission
Gun
6
Electron source - LaB6
7
Electron source - FEG
8
Electron source - accelerator
E=U.e
U=300kV => λ=1.97pm
U=200kV ??
9
Lenses – ray diagram
10
Electromagnetic lenses
Lorentz force:
Magnetic lenses rotate image
11
Electromagnetic lenses
Power of the magnetic lens can be changed
12
Electromagnetic lenses
Illumination on the detector changes with change of lens power
13
Lens assembly - appertures
Apperture size: ~100um
14
Lens assembly - appertures
15
Lens assembly - stigmators
16
Lens aberrations - chromatic
17
Lens aberrations - spherical
18
Detectors
CCD – charge coupled device
CMOS – complementary metal oxide semiconductor
19
Detectors
DQE – detective quantum efficiency
- probability to detect an electron
- DQE ~ sin(x)/x
20
Vacuum system
- roughing pump (105
– 10-4
Pa)
- turbo molecular pump (10-2
– 10-8
Pa)
- ion getter pump ( up to 10-9
Pa)
21
Vacuum system
- roughing pump (105
– 10-4
Pa)
- turbo molecular pump (10-2
– 10-8
Pa)
- ion getter pump ( up to 10-9
Pa)
90.000 rpm
22
Vacuum system
- roughing pump (105
– 10-4
Pa)
- turbo molecular pump (10-2
– 10-8
Pa)
- ion getter pump ( up to 10-9
Pa)
23
Vacuum system
24
TEM
25
TEM
26
TEM
27
TEM
Differential pumping apperture
28
TEM
29
TEM
30
SEM
31
SEM
32
Dual beam FIB/SEM
33
SEM - detection
- Everhart-Thornley Detector (ETD)
- Ion Convertion to Electron Detector (ICE)
34
SEM - detection
- Concentric Backscatter detector