1. The Principle of Microscopy : SEM, TEM, AFM
Tuesday seminar
The Principle of Microscopy : SEM, TEM, AFM
So-Yeon Park

2. Contents Introduction : Motivation for Microscopy Electron Microscopy
- interaction with matter
- SEM : Scanning Electron Microscopy
- TEM : Transmission Electron Microscopy
AFM : Atomic Force Microscopy

3. Motivation of microscopy
Resolution of light microscope is limited
▶ possible magnification : ~ 2 000
Different approach : use electrons instead of light
▶ access to much smaller wavelengths
▶ electrostatic lenses instead of glass lenses
▶ possible magnification : ~

4. Interaction with matter

5. Interaction with matter

6. SEM
Scanning
Electron
Microscopy

7. Electrons for SEM image
Secondary electrons (SE)
Backscattered electrons (BSE)

8. Electrons for SEM image
Electron beam
Electron beam

9. Electrons for SEM image
The intensity of emitted secondary electron for a line scan over some different surface features
Edge effect

10. Functional principle

11. Functional principle

12. Functional principle

13. Functional principle

14. Functional principle
Electron detector

15. Main concern of SEM
High vacuum : to avoid crashing into air Edge effect

16. Main concern of SEM
Charging effect ▶ non-conductive material ▶ no electrons escaping from specimen ▶ Gold coating
More electron
Diffraction
Au, Pd, Pt

17. Gold coating EBT2 with Au coating
Graduate School of Convergence Science and Technology. Seoul National University

18. Example
EBT2

19. TEM
Transmission
Electron
Microscopy

20. Functional principle

21. Functional principle

22. Functional principle

23. Functional principle

24. Example
Lung cell

25. AFM
Atomic
Force
Microscopy

26. Principle
Position-sensitive photodetector
Laser diode
Cantilever spring
Tip
Tip
by measuring forces between a sharp probe (<10 nm) and surface at very short distance

27. Mode of operation (1) Contact AFM < 0.5 nm probe-surface separation
(2) Intermittent contact (tapping mode AFM)
0.5-2 nm
(3) Non-contact AFM nm

28. Contact mode The force on the tip is repulsive.
Advantage: fast scanning, good for rough samples
Disadvantage : at time forces can damage/deform soft samples

29. Intermittent mode(Tapping)
The cantilever is oscillated at this resonant
Frequency.
Advantage: high resolution of samples that are easily damaged, good for biological samples
Disadvantage : more challenging to image in liquids, slower scan speeds needed

30. Non-contact mode The force on the tip is attractive.
Advantage: VERY low force exerted on the sample, extended probe lifetime
Disadvantage : lower resolution, usually need ultra high vacuum to have best imaging

31. Limitations of AFM
Used to study a wide variety of samples. The physical probe is not ideally sharp. An AFM image dose not reflect the true sample topography.

32. Limitations of AFM
For water droplet(물방울)

33. Example
Lung cell
Collagen matrices
EBT2 film

34. Thank you for attention :D