This document describes the components and operation of a scanning electron microscope (SEM) used to evaluate the properties of bulk nanostructured materials. It discusses the electron beam energy levels of SEMs compared to other techniques, advantages of electron microscopes like high resolution and depth of focus. Sample preparation techniques like cutting, mounting, grinding, polishing and etching are outlined. Applications of SEM like topography, chemistry analysis via EDX, crystallographic analysis with EBSD, and in-situ experiments are described. The document explains how SEM images are formed through electron beam and sample interactions and detection of signals. It details the major components of an SEM including the electron gun, electromagnetic lenses, detectors, and vacuum system.

1. ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Bulk Materials – Experimental
Techniques
Main Outcome:
Evaluation of properties of bulk nanostructured materials
Mohammad Omar Abuelnaga
AMT–506 Bulk Materials – Experimental Techniques 1

2. ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Scanning Electron Microscope
(SEM)
AMT–506 Bulk Materials – Experimental
2
Techniques

3. ADVANCED MATERIALS & TECHNOLOGY
Contents POSTGRADUATE DIPLOMA
1. Electron Beam Energy
2. Advantages of Electron Microscope
(Wave length–Resolving power–Depth of focus)
3. SEM Sample Preparation
4. What can we use a SEM for?
5. How do we get an image?
6. Electron beam-sample interactions
7. Components of the SEM
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4. 1. Electron Beam Energy
e- beam energy ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
SEM TEM synchrotron
0.2 keV to 40 keV ›100 KeV 1 GeV
Microstructure Crystal structure Particle Physics Research
Synchrotron Images
http://www.xente.mundo-r.com/rcid/pages/phy_9.html
http://www.desy.de/news/news/archive_before_2010/2007/photon_219/index_eng.html
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5. 2. Adv. of Electron Microscope ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
•Wavelength:
Visible light: 400-700 nm
Electron Beam: 0.001-0.01 nm
•Resolving power:
The closest spacing of two points clearly
as separate entities.
http://www.olympusmicro.com/primer/anatomy/numaperture.html
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6. 2. Adv. of Electron Microscope ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
•Resolving power:
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7. 2. Adv. of Electron Microscope ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
•Resolving power:
In practice:
Magnification of LOM ≈ 1000 X Magnification of TEM ≈ 2,000,000 X
Magnification of SEM ≈ 500,000 X
AMT–506 Bulk Materials – Experimental Techniques 7

8. 2. Adv. of Electron Microscope ADVANCED MATERIALS & TECHNOLOGY
Depth of focus POSTGRADUATE DIPLOMA
http://www.emal.engin.umich.edu/courses/sem_lecturecw/SEM_DepthofFocus.html
•At some distance D/2 above and below the focus plane the diameter of the beam
becomes twice the pixel diameter for the magnification being used, whereupon
the signals from adjacent pixels overlap enough to cause the image to appear
blurred.
•Over the distance D between these limits, however, the image will appear to be in
acceptably sharp focus, and so this distance is called 'the depth of field' or 'the
depth of focus'.
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9. 2. Adv. of Electron Microscope ADVANCED MATERIALS & TECHNOLOGY
Depth of focus POSTGRADUATE DIPLOMA
Optical microscopy vs SEM
Depth of focus
Magnification
Optical SEM
10 60 μm 1000 μm
100 8 μm 100 μm
1000 0.2 μm 10 μm
10000 --- μm 1 μm
Screw length: ~ 0.6 cm
Images: the A to Z of Materials
• A SEM typically has orders of magnitude better depth of
focus than a optical microscope making SEM suitable
for studying rough surfaces.
• The higher magnification, the lower depth of focus.
AMT–506 Bulk Materials – Experimental Techniques 9

10. 3. SEM Sample Preparation ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
• General characteristics for sample preparation:
– Must be conductive to prevent charging
– Must be vacuum compatible
– Dependent on material properties (beam sensitivity,
hardness, etc.)
AMT–506 Bulk Materials – Experimental Techniques 10

11. 3. SEM Sample Preparation ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
1. Cutting
•Conventional Sample
Preparation procedures:
1. Cutting
2. Mounting
(Conductive mounting material for SEM)
3. Grinding 2. Mounting
Hot Mounting
4. Polishing Machine
5. Etching Hot Mount
Cold Mounts
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12. 3. SEM Sample Preparation ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
AMT–506 Bulk Materials – Experimental Techniques 12

13. 3. SEM Sample Preparation
ADVANCED MATERIALS & TECHNOLOGY
3. Grinding POSTGRADUATE DIPLOMA
Grinder/Polisher preparation machine
Polishing Paper Grinding Paper
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14. 3. SEM Sample Preparation
4. Polishing ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Colloidal Silica for sample polishing
•Abrasive Powders in a colloidal suspension /
slurry / Paste.
•Commonly used polishing Materials are:
1. Alumina
2. Silica
3. Diamond paste
DIAMOND PASTE with different particle sizes
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15. 5. Etching
ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
• The purpose of etching is to optically enhance microstructural features such as grain size
and phase features.[Metallography & Ceramography]
1. Chemical etching.
(e.g.: Nital [95 % Alcohol + 5 % Nitric Acid] for 30 seconds is used for steel etching)
2. Molten salt etching.
(e.g.: Al2SiO5 in Potassium hydrogen fluoride melt in a Platinum crucible for 5-10 minutes)
3. Electrolytic etching.
4. thermal etching .
(e.g.: heating Si3N4 in vacuum at 1250 ⁰C for 15 minutes)
5. plasma etching.
• For difficult to etch specimens, the etching rate can be enhanced with temperature,
ultrasonic, electrolytic or microwave energy.
AMT–506 Bulk Materials – Experimental Techniques 15

16. 3. SEM Sample Preparation ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
SEM Gold Sputtering System
A spider coated in gold to prepare it as a
specimen for Scanning electron microscopy.
http://en.wikipedia.org/wiki/Scanning_electron_microscope
Silver Paint
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17. 3. SEM Sample Preparation ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
SEM Sample Holders
holding specimen and shorter
screws with Allen wrench
AMT–506 Bulk Materials – Experimental Techniques 17

18. 3. SEM Sample Preparation ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
This dovetail is on the bottom of all of the http://www.azonano.com/news.aspx?newsID=13399
holders. It fits onto the SEM motorized
stage dovetail mount.
http://www.efjeld.com/P_S-hold.htm
AMT–506 Bulk Materials – Experimental Techniques 18

19. ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
4. What can we use a SEM for?
What can we study in a SEM?
1. Topography and morphology
2. Chemistry
3. Crystallographic Orientation of grains
(EBSD- Kikuchi bands)
4. In-situ experiments
Effects of temperature (Hot Stage)
AMT–506 Bulk Materials – Experimental Techniques 19

20. 1. Topography and morphology ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
AMT–506 Bulk Materials – Experimental Techniques 20

21. 2. Chemistry (EDX Mapping) ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
CK
line
Pb L lines
X-Ray Generation
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22. 2. Chemistry (EDX Mapping) ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
CK
line
Pb L lines
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23. 2. Chemistry (EDX Mapping) ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Carbon
Manganese
Pb M Lead
CK
lines
line
Mn K
lines
Pb L lines
0 2 4 6 8 10 12 14 16 18 20
Full Scale 143608 cts Cursor: 19.997 (142 cts) keV
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24. 2. Chemistry (EDX Mapping) ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Ce
Fe Sr
AMT–506 Bulk Materials – Experimental Techniques 24

25. 3. Crystallographic Orientation of grains
ADVANCED MATERIALS & TECHNOLOGY
(EBSD- Kikuchi bands) POSTGRADUATE DIPLOMA
http://www.stanford.edu/group/snl/SEM/OIMIntro.htm
AMT–506 Bulk Materials – Experimental Techniques 25

26. 3. Crystallographic Orientation of grains
ADVANCED MATERIALS & TECHNOLOGY
(EBSD- Kikuchi bands) POSTGRADUATE DIPLOMA
OIM scan progress and data review
AMT–506 Bulk Materials – Experimental Techniques 26

27. 3. Crystallographic Orientation of grains
ADVANCED MATERIALS & TECHNOLOGY
(EBSD- Kikuchi bands) POSTGRADUATE DIPLOMA
EBSD detector
SEM System that provides simultaneous EDS,
EBSD and WDS data collection detectors.
AMT–506 Bulk Materials – Experimental Techniques 27

28. 4. In-situ experiments:
Effects of temperature (Hot Stage) ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
• A modern SEM can be equipped with various accessories, e.g. a hot stage
AMT–506 Bulk Materials – Experimental Techniques 28

29. 5. How do we get an image?
ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Electrons out
Electrons in
or: x-rays out
• In brief: we shoot high-energy electrons and analyze
the outcoming electrons/x-rays
AMT–506 Bulk Materials – Experimental Techniques 29

30. 5. How do we get an image?
ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
The instrument in brief
AMT–506 Bulk Materials – Experimental Techniques 30

31. 5. How do we get an image?
ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
Electron gun 288 electrons!
156 electrons!
Detector
Image
AMT–506 Bulk Materials – Experimental Techniques 31

32. 5. How do we get an image?
ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
AMT–506 Bulk Materials – Experimental Techniques 32

33. ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
6. Electron beam-sample interactions
AMT–506 Bulk Materials – Experimental Techniques 33

34. ADVANCED MATERIALS & TECHNOLOGY
6. Electron beam-sample interactions POSTGRADUATE DIPLOMA
Auger elect rons
Secondary elect rons
Backscat t ered elect rons
Charact erist ic X-rays
Cont inuum X-rays
Fluoresecent X-rays
AMT–506 Bulk Materials – Experimental Techniques 34

35. 7. Components of the SEM ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
AMT–506 Bulk Materials – Experimental Techniques 35

36. 7. Components of the SEM ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
1. Electron Gun Types
2. Lenses
3. Detectors
4. Vacuum
AMT–506 Bulk Materials – Experimental Techniques 36

37. 7. Components of the SEM ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
1. Electron Gun Types
With field emission guns we get a smaller spot and
higher current densities compared to thermionic guns
Vacuum requirements are tougher for a field emission
guns
Single crystal of LaB6 Tungsten wire Field emission tip
AMT–506 Bulk Materials – Experimental Techniques 37

38. 7. Components of the SEM ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
1. Electron Gun Types
The Electron Gun
-emitter
-Wehnelt cap or grid
-anode
-first “lens” in the SEM
Emitter/Wehnelt cap assembly Anode [Hitachi S2300]
[from Hitachi S2300]
AMT–506 Bulk Materials – Experimental Techniques 38

39. 7. Components of the SEM ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
2. Lenses
Cross-section of Electromagnetic Lens from an SEM
-note the copper wire turns & power leads
AMT–506 Bulk Materials – Experimental Techniques 39

40. 7. Components of the SEM ADVANCED MATERIALS & TECHNOLOGY
POSTGRADUATE DIPLOMA
3. Detectors
Backscattered electron
detector:
(Solid-State Detector)
Secondary electron detector:
(Everhart-Thornley)
Image: Anders W. B. Skilbred, UiO
AMT–506 Bulk Materials – Experimental Techniques 40

41. 7. Components of the SEM
3. Vacuum SEM Vacuum System
-multistage system:
1.) low-vac [“roughing”]
2.) high-vac [“diff pump”]
Oil Diffusion pump
-high-vac
[Rotary] Mechanical pump
-”roughing” or low-vac