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SADmicrodiffraction in Tecnai F30
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Gun lens: 1-3. Spot size: any. Small-angle ... Gun lens: 5-8. Spot size: 7-11. CBED ... Effect of gun lens. Effect of C1 lens. Smaller C2 aperture ... – PowerPoint PPT presentation
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Title: SADmicrodiffraction in Tecnai F30
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SAD/microdiffraction in Tecnai F30
- Chang-Hoon Kim
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FEG operating modes for different types of
diffraction
- Selected-area diffraction (SAD)
- Mode microprobe
- C1 2 mm
- C2 150/100/50 mm
- Extr. voltage lt4.6 kV
- Gun lens 1-3
- Spot size any
- Small-angle microdiffraction
- Mode microprobe
- C1 2 mm
- C2 30 mm
- Extr. voltage lt4.6 kV
- Gun lens 5-8
- Spot size 7-11
- ? Minimum convergence angle
- Smallest-spot microdiffraction
- Mode nanoprobe
- C1 2 mm
- C2 30 mm
- Extr. voltage lt4.6 kV
- Gun lens 5-8
- Spot size 7-11
- ? CBED
Objective getting a diffraction pattern from a
small region (5 nm)
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- Increasing gun lens and/or decreasing spot size
(C1 lens) - ? form a fine probe
Effect of gun lens
Effect of C1 lens
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- Smaller C2 aperture
- ? produce a more parallel and more
coherent beam
Effect of C2 aperture
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- How to record diffraction patterns on CCD
- Place the cursor on the image. The intensity of
the pixel under the cursor is displayed in the
image status palette (Value). - Adjust beam intensity and exposure time
- 14-bit camera 500010000 counts (in the bright
regions) - Saturation of the pixel occurs when the intensity
is over 16384 counts. - Try to record the pattern with the smallest
exposure time - Linearity of CCD recorded Intensity ? exposure
time - Adjust the pattern (brightness, contrast)
- DO ANYTHING ON TV CAMERA BEFORE SWITCHING TO CCD
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Microdiffraction and SAD pattern of Si (001) zone
axis
- Exposure time 20 sec.
- Max. intensity 10000
- Exposure time 3 sec.
- Max. intensity 4500
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Problem significant contamination due to the
focused beam
a0
a30
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Problem shimmering background
- Related to the FEG characteristics (?)
- Dependent of the specimen material
- Electron-beam interaction
MnO2
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