fiber characterization under atomic force microscopy

1. Prepared by Amare Worku
(MSC in Tex. Eng.)
November 2015
Seminar Title on: Atomic Force Microscopy (AFM)

2. LOGO
Atomic Force Microscopy

3. Contents/ Outlines
1. Background and History
2. General Applications
3. How Does AFM Work?
4. Parts of AFM
5. THREE Modes: Contact mode,
Non-contact mode, Tapping Mode

4. Contents/ Outlines
6. What are the limitations of AFM?
7. Advantages and Disadvanteges of AFM
8. The future of AFM

5. 1. Background and History
Scanning tunneling microscopy
 1981 – Swiss scientists Gerd Binnig
and Heinrich Rohrer
 Atomic resolution, simple
 1986 – Nobel prize

6. 2. General Applications
1
Materials
Investigated: Thin
and thick film
coatings,
ceramics,
composites,
glasses, synthetic
and biological
membranes,
metals, polymers,
and
semiconductors.
3
AFM can image
surface of
material in
atomic
resolution and
also measure
force at the
nano-Newton
scale.
2
Used to study
phenomena of:
Abrasion,
corrosion,
etching (scratch),
friction,
lubricating,
plating, and
polishing.

7. Further Applications

8. 3. How Does AFM Work?

9. Tip vibrates (105 Hz) close to specimen surface
(50-150 Å) with amplitude 10-100 nm, May at
times lightly contact surface
Two ways - 'constant force' ……. feedback system
moves tip in z direction to keep force
constant.
'constant height'……. no feedback system -
usually used when surface roughness small
higher scan speeds possible.
3. Continued…

11. Hooke’s Law
x= the vertical
displacement of the
end of the cantilever.
k = the cantilever
spring constant
F = the force acting
On the cantilever
F = -kx
Hooke’s Law

12. 3. 1 Experimental Procedures
Sample preparation
Thin layer of wax on steel disk Measuring
3-D Imaging
Manipulating/Analyzing

13. Diagram
3-D
Imaging
Measuring
3-D Imaging
Manipula
ting/Anal
yzing
Manipulating/
Analyzing

14. Scanning the Sample/measure
 Tip brought within
nanometers of the sample
(van der Waals)
 Radius of tip limits the
accuracy of analysis/
resolution
 Stiffer cantilevers protect
against sample damage
because they deflect less in
response to a small force
 This means a more
sensitive detection
scheme is needed

15. Data Analysis
Morphology Characterization/
Sub microscopic level
Surface roughness
quantification
Physical properties/
Swelling, cohesiveness,
smoothness
Will be
analyzed

16. AFM Tips

17. 4. Parts of AFM
1. Laser – deflected off cantilever
2. Mirror –reflects laser beam to
photo detector
3. Photo detector –dual element
photodiode that measures
differences in light intensity and
converts to voltage
4. Amplifier
5. Register
6. Sample
7. Probe –tip that scans sample
made of Si
8. Cantilever –moves as scanned
over sample and deflects laser
beam

19. 1. Z-Piezo Calibration: by scanning a sample of known
height (calibration grating)
In contact mode
2. Cantilever deflection calibration
3. Cantilever stiffness, k, calibration
Calibration Every month

20. 5. THREE Modes: Contact mode,
Non-contact, mode, Tapping Mode
A.Contact Mode Mode; hard,
stable samples in air or
liquid
B. Non-Contact Mode: non-
invasive sampling.
C. Tapping (Intermittent
contact): No shear and
damaging samples

21. A. Contact Mode
 Measures repulsion between tip and sample
 Force of tip against sample remains constant
 Feedback regulation keeps cantilever deflection
constant
 Voltage required indicates height of sample
 Problems: excessive tracking forces applied by
probe to sample

22. B. Non-Contact Mode
 Measures attractive forces between tip and
sample
 Tip doesn’t touch sample
 Van der Waals forces between tip and
sample detected
 Problems: Can’t use with samples in fluid
 Used to analyze semiconductors
 Doesn’t degrade or interfere with sample-
better for soft samples

23. C. Tapping (Intermittent-
Contact) Mode
 Tip vertically oscillates between contacting sample
surface and lifting of at frequency of 50,000 to
500,000 cycles/sec.
 Oscillation amplitude reduced as probe contacts
surface due to loss of energy caused by tip
contacting surface
 Advantages: overcomes problems associated with
friction, adhesion, electrostatic forces
 More effective for larger scan sizes

25. 6. What are the limitations
of AFM?
 AFM imaging is not ideally sharp

26. 7. Advantages and Disadvanteges
of AFM

27. Comparison b/n AFM vs. SEM

28. 8. The future of AFM
 Sharper tips by improved micro-fabrication
processes: (tip – sample interaction tends to
distort or destroy soft biological molecules )
 development of more flexible cantilever
springs and less damaging and non-sticky
probes needed

29. Nano-Identification on Fiber surface
MMF
Viscose
Rayon
Cotton

30. TYPES OF FIBER UNDER AFM
AFM
topographical
scan of a glass
surface.
Clean glass surface:
roughness ~ 0.8 nm

31. AFM images of the samples:
a)Cotton topography and phase (5 μm × 5 μm),
b) Cotton topography and phase (2 μm × 2 μm),

32. c)Wool topography and phase (5 μm × 5 μm)
d)Wool topography and phase (2 μm × 2 μm).

33. AFM images of the
samples:
a) PET,
b)Antistatic PET,
c) Antibacterial PET.

34. AFM images of the cross sections of the fibers:
a)Antibacterial PET friction,
b)Antistatic PET friction.

36. In general

37. LOGO