A.E. GunnsMENA3100 V08 Electron Diffraction (ED) in the transmissions electron microscope.
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A.E. Gunnæs MENA3100 V08 Electron Diffraction (ED) in the transmissions electron microscope
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A.E. GunnæsMENA3100 V08 Basic TEM Electron source (HV= 200kV) Apertures Sample holder Fluorescence screen Film box Pedals for tilting the sample Magnetic lenses Vacuum in the column better than Pa
Transcript of A.E. GunnsMENA3100 V08 Electron Diffraction (ED) in the transmissions electron microscope.
A.E. Gunnæs MENA3100 V08
Electron Diffraction (ED) in the transmissions electron microscope
A.E. Gunnæs MENA3100 V08
JEOL 2010F in the Research park
A.E. Gunnæs MENA3100 V08
Basic TEMElectron source (HV= 200kV)
Apertures
Sample holder
Fluorescence screen
Film box
Pedals for tilting the sample
Magnetic lenses
Vacuum in the columnbetter than 10-6 Pa
A.E. Gunnæs MENA3100 V08
The lenses and apertures in a TEM
Sample
Filament
Anode
ΔU= ~100-1000 kV
1. and 2. condenser lenses
Objective lens
Intermediate lenses
Projector lens
Selected area aperture(diffraction aperture)
Objective aperture
Condenser aperture
Electron source:
●Tungsten, W
● LaB6
● FEG
ImageFluorescence Screen (ZnS or ZnS/CdS powder)
Recording media:
●Film
● Imaging plates
● CCD camera
●TV camera
λ= h/(2meV)0.5
(NB non rel. Expr)
A.E. Gunnæs MENA3100 V08
Simplified ray diagram
Objective lense
Diffraction plane(back focal plane)
Image plane
Sample
Parallel incoming electron beamSi
a
b
cPow
derCell 2.0
1,1 nm
3,8
Å
Convergent beam -Discs in diffraction -Micro diffraction -STEM mode -Chemical analysis
A.E. Gunnæs MENA3100 V08
Electron diffraction
Elastic scattered electronsOnly the direction of v is changing.(Bragg scattering)
Elastic scattering is due to Coulomb interaction between the incident electrons and the electric charge of the electron clouds and the nucleus. (Rutherford scattering).
The elastic scattering is due to the average position of the atoms in the lattice.
Reflections satisfying Braggs law:
2dsinθ=nλ
Inelastic scattered electronsDirection and magnitude of v change.
Energy is transferred to electrons and atoms in the sample.
-It is due to the movements of the atoms around their average position in the lattice.
- It give rise to a diffuse background in the diffraction patterns.
Electrons interacts 100-1000 times stronger with matter than X-rays-more absorption (need thin samples)-can detect weak reflections not observed with x-rays
A.E. Gunnæs MENA3100 V08
Sample preparationTEM grids
3 mm
A.E. Gunnæs MENA3100 V08
Sample holders
Sample positions
Cooling
Standard
Heating
