Scanning electron microscopy (SEM) is a technique used to image surfaces at high magnifications. SEM can be used to examine biological tissues, polymers, and metals. Environmental SEM allows imaging of non-conductive wet samples in low vacuum or gas conditions. Atomic force microscopy (AFM) provides complementary high-resolution topographic information to SEM. While SEM provides faster wide-area imaging, AFM enables manipulation and analysis of samples at the nanoscale. Various techniques like stereo-photogrammetry and stacked images allow generating 3D surface representations from SEM data.

1. Scanning Electron Microscope
IH2652- Methods and Instruments of Analysis
Prof. Henry H Radamson
Prepared by:
Sumit Mohanty – Mohamed Atwa – Ahmed Al-Askalany
KTH Royal Institute of Technology
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2. Agenda
Introduction and Applications
Environmental SEM
Complementarity of SEM and AFM
SEM vs. TEM
3D Imaging with SEM
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3. Introduction and Applications
3

4. SEM-Structure
SEM Introduction
4

5. Interaction volume
• The generated radiation will not be detected unless
it escapes from the SP.
• Electrons will not backscattered out of SP if they
have penetrated more than a fraction of micrometers,
Therefore the BS signal come from a much smaller area
SEM Introduction
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6. The affect of accelerating voltage
SEM Introduction
6

7. Biology
Lung tissue
Embryo limbs
Núria Cortadellas, Eva Fernández, and Almudena Garcia;Biomedical and Biological Applications of Scanning Electron Microscopy,
Handbook of instrumental techniques.
RBCs: Chris Toumey, Nature Nanotechnology 6, 191–193 (2011) doi:10.1038/nnano.2011.55
Parasites
Red blood cells
SEM Applications
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8. Fig.1
Fig.1: S. Zhou et al. / Biomaterials 24 (2003) 3563–3570
Fig.2: D.R. Chen et al. / Polymer Degradation and Stability 67 (2000) 455-459
Fig.2 a
b
SEM Applications
8

9. Environmental SEM
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10. Gaseous Electron Microscopy
• Conventional and Auger
SEM Require Vacuum
(Usually in the range of 10-5
mBar)
• Sample Charging
• Sample Bursting
http://www.ammrf.org.au/myscope/images/sem/pump-evac.png
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11. Gaseous SEM (Environmental SEM)
• Works in:
• Air
• Low Vacuum
• High Pressure
• Variable Pressure
• Gases Used Include:
• N2
• O2
• Ar, He, H2O...
http://www.phy.cam.ac.uk/research/research
-groups-images/bss/images/esem.jpg
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12. GSEM Image Quality Factors
Image quality and microanalysis results depend on:
• The size of the electron beam
• The accelerating voltage
• Sample nature
• Pressure in different parts of the chamber
• Type of gas
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13. Use of Gas in Imaging
• Gas atoms or molecules interact with
the primary electron beam and
produce positive ions.
• Positive ions neutralize the negative
charge on the surface of the insulating
sample
• Gas atoms can also aid the imaging
process through avalanche electron
generation http://www.azom.com/work/Environm
ental%20Scanning%20Electron%20Micr
oscopy%20-
%20ESEM_files/image004.gif 13

14. Typical Operation Parameters
“Wet” Mode (Condensed Water)
• Electron Beam Energy: 20 kV
• Emission Current: 49 μA.
• SE Detection Method: Gaseous detector
• Working distance: 19 mm (Compensates for Skirting Beam)
V. Kazmiruk -Scanning Electron Microscopy -Intech (2012)
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15. Gaseous Detector
https://en.wikipedia.org/wiki/Gaseous_detection
_device#mediaviewer/File:GDD_principle.svg
• Probe electrons ionize gas
atoms/molecules
• Electric field “pulls”
secondary and backscattered
electrons towards plate
electrodes
• Electrons are multiplied in
collisions with gas
atoms/molecules
• Location and energy of
electrons used to form image
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16. Skirting Beam Phenomenon
• PLA1: Final Aperture
• Z: Distance which electrons scatter
• Θ: Solid angle of scattering
• Sf: Scattered fraction of electrons
(Skirt)
• UnSf: Unscattered fraction of
electrons
• rs+dr: Scattering radius
V. Kazmiruk -Scanning Electron Microscopy -
Intech (2012)
16

17. Skirting Phenomenon (Continued)
V. Kazmiruk -Scanning Electron Microscopy -Intech (2012)
• rs is the skirt radius
• Z the gas atomic number
• E the incident beam energy
• P is the pressure
• T the temperature
• GPL the gas path length
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18. Sample Image
• Plant material:
• Insulating
• Fragile
• White circles are “Stomata,” pores
for gas-exchange
• Imaged using the “wet mode”
parameters mentioned before
V. Kazmiruk -Scanning Electron Microscopy -
Intech (2012)
18

19. Complementary techniques AFM
and SEM
1. Surface Structure
2. Composition
3. Environment
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20. Surface structure
Principle difference  process vertical changes in
topography
Atomically smooth surfaces
AFM
• Vertical resolution of <0.5Å
• Resolve the 1.4Å monoatomic
silicon steps
SEM
• Difficulty resolving these features due to the subtle
variations in height.
Russell, Phil, Dale Batchelor, and J. Thornton. "SEM and AFM: complementary techniques for high resolution surface investigations." Veeco
Instruments Inc., AN46, Rev A 1 (2001): 2004.
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21. Subtle roughness (<1µm)
• AFM  3-D nature changes in roughness
• Surface area variations  differences in deposition
parameters (<0.5Å)
• SEM, a large area view of variations in surface structure
acquired all at once
Strausser, Y.E., Schroth, M., Sweeney, J.J., Characterization of the low-pressure chemical vapor deposition grown rugged polysilicon surface using
atomic force microscopy,” J. Vas. Sci. Technol. A 15, 1997, 1007
SEM and AFM (tapping mode) images of Poly-silicon thin film
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22. SEM
• Depth of field and small beam size dominant
• Millimeters of vertical information
AFM
• Probe length 5-6 µm
• Obtuse angles, enclosed structures  vertical limitation
Not so subtle roughness!! (<1mm)
Russell, Phil, Dale Batchelor, and J. Thornton. "SEM and AFM: complementary techniques for high resolution surface investigations." Veeco
Instruments Inc., AN46, Rev A 1 (2001): 2004.
22

23. Bumps or Pits???
SEM
• Change in electron intensity  slope
• Sloping up or down? :/
AFM
• Subtle heights/depths  straightforward (e.g. 70nm)
SEM and AFM (tapping mode) showing growth of GaP by chemical beam epitaxy
Kelliher, J.T., Thornton, J., Dietz, N., Lucovsky, G., Bachmann, K.J., “Low temperature chemical beam epitaxy ofgallium phosphide/silicon
heterostrucutres, Materials Science and Engineering, B22 (1993) 97.
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24. High aspect ratio structures
SEM
• Trenches and via holes
• Cleaving cross section of the wafer  destructive
AFM
• Scanning undercuts & section analysis
• Tip choice – crucial
Russell, Phil, Dale Batchelor, and J. Thornton. "SEM and AFM: complementary techniques for high resolution surface investigations." Veeco
Instruments Inc., AN46, Rev A 1 (2001): 2004.
SEM and AFM showing undercutting in Poly-silicon lines by reaction ion etching
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25. Composition
AFM
• Compositional information based on physical properties
• Stiffness, elasticity, friction, adhesion, magnetic field
carrier concentration
SEM
• Elemental analysis using X-ray
detection
• Back scattered electrons 
Atomic number.
Backscattered SEM image of an PbSn
alloy showing contrast based on the atomic number
Russell, Phil, Dale Batchelor, and J. Thornton. "SEM and AFM: complementary techniques for high resolution surface investigations." Veeco
Instruments Inc., AN46, Rev A 1 (2001): 2004.
25

26. Environment
SEM
 Traditionally vacuum
 Hydrated environment –
scattering e beam
 Resolution degraded
AFM
 Traditionally ambient
 Hydrated environment –
scanning unperturbed
 Resolution preserved
Mou, J., Czajkowsky, D.M., Sheng, S., Ho, R., Shao, Z., “High resolution surface structure of E. coli GroeS Oligomer by Atomic Force Microscopy,”
FEBS Letters 381 (1996) 161.
Russell, Phil, Dale Batchelor, and J. Thornton. "SEM and AFM: complementary techniques for high resolution surface investigations." Veeco
Instruments Inc., AN46, Rev A 1 (2001): 2004.
26

27. SEM vs AFM
• SEM can analyze a larger surface area compared to
AFM.
• SEM can perform faster scanning than AFM.
• SEM only for imaging, AFM manipulate the molecules in
addition to imaging.
www.researcher.ibm.com www.zurich.ibm.com chemistry.oregonstate.edu 27

28. SEM vs TEM
• 3-D
• Beam formation
• Magnification – 2 million
• Resolution – 0.4 nm
• Scans larger areas
• Limitations – conducting
samples, charging effect
http://www.ch.tum.de/em/emlabor/methoden/tem.htm
• 2-D
• Direct imaging
• Magnification – 50 million
• Resolution – 0.5 Å
• Scans thin samples
• Limitations – magnetic
samples
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29. 3D Images with SEM
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30. Stereo-Photogrammetry
• Measurements from images,
• Failure micro-mechanisms,
• 3D multi-scale textured images,
• Global low resolution,
• High resolution for regions of
interest (ROI),
• Compared with predefined
failure models for analysis.
M. Khokhlov, A. Fischer, D. Rittel. „Multi-Scale Stereo-Photogrammetry System for Fractographic Analysis Using Scanning Electron Microscopy”. Experimental
Mechanics (2012) 52:975–991 DOI 10.1007/s11340-011-9582-0.
Stereo image
matching
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31. Stereo-Photogrammetry
M. Khokhlov, A. Fischer, D. Rittel. „Multi-Scale Stereo-Photogrammetry System for Fractographic Analysis Using Scanning Electron Microscopy”. Experimental
Mechanics (2012) 52:975–991 DOI 10.1007/s11340-011-9582-0.
Stereo
images
3D points
3D mesh
3D textured
image
Multi-scale multi-resolution
3D image
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32. Photometric Stereo – Shape From Shading
• SE directional acquisition,
• known angular distribution,
• Shape from signal distribution,
• DSP for detection error
correction,
• Lambert’s angular distribution,
J. Paluszyn´ ski, W. Slo´wko. “Surface reconstruction with the photometric method in SEM”. Vacuum 78 (2005) 533–537
Topo contrast
Compo contrast
Det. signal
Local inc.
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33. Photometric Stereo – Shape From Shading
J. Paluszyn´ ski, W. Slo´wko. “Surface reconstruction with the photometric method in SEM”. Vacuum 78 (2005) 533–537
Eduard Reithmeier, Taras Vynnyk *, Thanin Schultheis. “3D-measurement using a scanning electron microscope”. Applied Mathematics and Computation 217 (2010) 1193–1201
Emission yield vs. inclination angle
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34. 3D-Like Animations from Vertical Stack of
SEM Images
• Bloodstain microarea (strongly
uneven surface),
• Out-of-focus problem,
• Stack of partial-focused scans,
• Macrophotography and light
microscope software (non-SEM
related),
• Topography and Texture,
• 3D-Like animation from vertical
stack of SE SEM micrographs.
Policarp Hortola. “Generating 3D and 3D-like animations of strongly uneven surface microareas of bloodstains from small series of partially out-of-focus digital SEM micrographs”. Micron 41 (2010) 1–6.
(1)
(2)
(3)
2000x WD=16mm 1024x832 pixels
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35. 3D-Like Animations from Vertical Stack of
SEM Images
Policarp Hortola. “Generating 3D and 3D-like animations of strongly uneven surface microareas of bloodstains from small series of partially out-of-focus digital SEM micrographs”. Micron 41 (2010) 1–6.
Texture to topography transition animation
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36. Inverse Reconstruction – Simulated SEM
• Previous methods fail at nano-scale
due to edge and charging effects,
• Iterative update of surface,
• Refinement through comparison of
simulated and actual SEM images,
• Monte Carlo method: Models of SE
and BSE generation (statistical
measure),
• Library creation through
predefined samples,
• Forward and inverse mapping,
Leili Baghaei Rad, Hanying Feng, Jun Ye and R.F.W. Pease. “Computational Scanning Electron Microscopy”. AIP Conference Proceedings 931, 512 (2007); doi: 10.1063/1.2799427
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37. Inverse Reconstruction – Simulated SEM
SEM
Image
Line
Strength
Image
Leili Baghaei Rad, Hanying Feng, Jun Ye and R.F.W. Pease. “Computational Scanning Electron Microscopy”. AIP Conference Proceedings 931, 512 (2007); doi: 10.1063/1.2799427
Z. J. Ding∗ and H. M. Li. “Application of Monte Carlo simulation to SEM image contrast of complex structures”. Surf. Interface Anal. 2005; 37: 912–918 DOI: 10.1002/sia.2109
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