S1007 Doing structural biology
with the electron microscope
Lecture 3: Electron Microscope
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Optical vs. TEM microscope
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Optical vs. TEM microscope
source
condensor
objective
detector
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Electron source
- thungsten filament
- LaB6 crystal
- Field Emission
Gun
Probe sizeWork function
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Electron source
- thungsten filament
- LaB6 crystal
- Field Emission
Gun
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Electron source - LaB6
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Electron source - FEG
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Electron source - accelerator
E=U.e
U=300kV => λ=1.97pm
U=200kV ??
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Electron source - accelerator
Task 1: What is the electron wavelength at acceleration voltage of 200kV?
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Lenses – ray diagram
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Electromagnetic lenses
Lorentz force:
Magnetic lenses rotate image
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Electromagnetic lenses
Power of the magnetic lens can be changed
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Electromagnetic lenses
Illumination on the detector changes with change of lens power
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Lens assembly - appertures
Apperture size: ~100um
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Lens assembly - appertures
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Lens assembly - stigmators
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Lens aberrations - chromatic
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Lens aberrations - spherical
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Detectors
CCD – charge coupled device
CMOS – complementary metal oxide semiconductor
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Detectors
DQE – detective quantum efficiency
- probability to detect an electron
- DQE ~ sin(x)/x
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Vacuum system
- roughing pump (105
– 10-4
Pa)
- turbo molecular pump (10-2
– 10-8
Pa)
- ion getter pump ( up to 10-9
Pa)
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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
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Vacuum system
- roughing pump (105
– 10-4
Pa)
- turbo molecular pump (10-2
– 10-8
Pa)
- ion getter pump ( up to 10-9
Pa)
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Vacuum system
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TEM
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TEM
Task 2: How many electron are there in the microscope at one point? (U=300kV, I=1nA,
column length: 2m)
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TEM
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TEM
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TEM
Differential pumping apperture
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TEM
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TEM
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SEM
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SEM
Task 3: What is the radiation damage (electron dose in e-/A2) of the specimen in SEM?
(U=2kV, I=5pA, dwell time: 1us, spot size: 5nm)
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SEM
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Dual beam FIB/SEM
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SEM - detection
- Everhart-Thornley Detector (ETD)
- Ion Convertion to Electron Detector (ICE)
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SEM - detection
- Concentric Backscatter detector