Working Principle of AFM

1. Fundamentals of Atomic Force Microscope
(AFM)
Md Ataul Mamun
BSc. in EEE
Bangladesh University of Engineering and
Technology (BUET), Dhaka, Bangladesh
Instructor: Dr. Nirmal Adhikari

2. Outline
• Introduction
– Background
– Motivation
– Objectives
• Theory
– Working principle
– Operating modes
• Results and Analysis
• Conclusion
• Future Work

3. Introduction
• AFM is one kind of scanning probe microscope
that possesses a very high resolution (on the order
of fractions of nanometers)
• Operates by measuring force between its probe
and the sample
• Can measure local properties, such as height,
friction, magnetism with the probe
• Unlike the electron microscope, AFM provides a
3-D surface profile
Source: https://en.wikipedia.org/wiki/Atomic-force_microscopy

4. Introduction
• In the field of solid state physics, it can be used
for identification of atoms at a surface, and to find
interactions between a specific atom and its
neighboring atoms.
• Besides solid state physics, the AFM is applied in
molecular engineering, polymer engineering,
polymer chemistry etc.
• Due to its versatility, science and research
students should know the working principle and
applications of the AFM.

5. • AFM was invented by IBM Scientists in 1982
• Improved AFM was invented and used by Gerd
Binnig et al. in 1980s which earned them noble
prize in 1986
• The first commercially available AFM was
introduced in 1989.
Background
Source: https://en.wikipedia.org/wiki/Atomic-force_microscopy

6. Objective
• To learn AFM working principle, application, and
study of images
Motivation
• Need to understand how to use AFM to study dye
monolayer on TiO2 surface

7. Theory
• AFM consists of a cantilever with a sharp tip
(probe) at its end that is used to scan the specimen
surface.
• The cantilever is typically silicon with a tip radius
of curvature on the order of nanometers.
• When the tip is brought into proximity of a
sample surface, forces between the tip and the
sample lead to a deflection of the cantilever
according to Hooke’s law
F = -kx

8. Theory
Figure: AFM probe tip (on the order of nanometers) and cantilever
Source: https://en.wikipedia.org/wiki/Atomic-force_microscopy

9. Working principle
Figure: Working principle of AFM

10. Working principle
Feedback loop:

11. AFM Modes of Operation
AFM has 3 modes of operation
• Contact mode
• Non contact mode
• Tapping mode
(Tapping mode provides higher
resolution with minimum sample
damage)

12. AFM Modes of Operation
Contact Mode:
• Measures repulsion between tip and sample
• Force of tip against sample remains constant (With
Feedback)
• Feedback regulation keeps cantilever deflection constant
Non Contact Mode:
• Measures attractive forces between tip and sample
• Tip doesn’t touch sample
• Van der Waals forces between tip and sample detected
• Doesn’t degrade or interfere with sample- better for soft
samples

13. Tapping (Intermittent Contact) Mode:
• Tip vertically oscillates 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
• Tapping mode provides higher resolution with minimum
sample damage
• More effective for larger scan sizes
AFM Modes of Operation

14. Results and Analysis

15. Conclusions
Future Work
• Characterize dye monolayer on TiO2 with AFM
• AFM has diverse applications in research areas
• It is capable to produce 3-D images with high
resolution

16. Acknowledgements
• SDSU EE&CS Dept.
• Dr. Qiquan Qiao
• Dr. Nirmal Adhikari