Transmission Electron Microscopy Image Contrast

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PASI
Santiago, 07/06
Transmission Electron Microscopy Image Contrast
I.G. Solórzano
Dept . of Materials Science and Metallurgy - PUC
- Rio de Janeiro, Brazil
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After D.B. Williams and C.B. Carter Plenum Press
1996 A note on wording
Change in intensity
Contrast
Beware of digital images or good darkroom
technicians
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STEM is a serial technique
Some special features (e.g., Z contrast)
Note comparison to TEM
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Mass-Thickness contrast
Tricky because we are talking about several
concepts at once.
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Shadowed
Mass-Thickness contrast
Shadow with Au/Pd, Al, Pt, Cr, etc
C film
Thickness contrast
Shadows are dark !
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Staining is much more important in Biology
Beware of safety wjen using OsO4
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Another reason for TEM prefered over STEM
Image processing is now easy and TEM has better
resolution - Why?
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TEM DF versus STEM ADF
Thinkwhy there is a difference
TEM DF. Better resolution
STEM ADF. More signal less noise
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C replica
C replica plus shadowing
Extraction replica of Cr-Mo steel
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Z contrast of PT atoms or groups of atoms
Why is this STEM better? .... FEG
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The Principle of HAADF
Current research topic
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TEM BF
Z contrast
Bi-implanted Si
Z contrast
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High Resolution
TEM
HAADF
How do we interpret this?
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2-beam DPs
Beware when you read about CDF
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Which is BF which is DF ?
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Relate image DP
Tilting the beam. Here, the specimen is not moving
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Regular STEM
STEM with smaller ?
TEM
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For 2-beam conditions BF DF images are
complementary
Thickness Contours
Thickness Fringes
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Two thickness effects
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Why contours? ... Like a map but both sides vary!
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Howie Whelan equations
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When the surfaces is faceted This is what we
actually calculate
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BENDING
Really important Learn this
Much to think about with this figure
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ZAPs
Example of using the schematic
Bend contour
Bend contour
How can you recognise them?
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c
f
e
d

• Bend contours AA and bend centres in aluminium
  with associated SADP inset
• 100, (c) 110, (d) 112, (e) 111, (F)
  114, (g) 003

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Identifying bend contours
Use displacement-aperture DF images
Notice
Then use the schematic
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Using the 90 wedge
Why do the fringes disappear?
?g was due to k(1) - k (2). We have lost a k.
Why the change? Ans ?g
Be careful. Look at the edge.
OK
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300kV
100kV
Would you be able to tell which is which?
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Note the arrows
Bending and thickness can occur at the same time!
cknowledgements
Acknowledgements Illustrations from the book ,
Transmisison Electron Microscopy by D.B.
Williams ab C.B. Carter (Plenum Press, 1996)