- Atomic force microscopy (AFM) uses a sharp tip to scan over a sample surface and measure forces between the tip and sample. Gerd Binning invented the AFM in 1986. - There are three main imaging modes: contact mode, tapping mode, and non-contact mode. Non-contact mode operates with the tip oscillating above the surface without touching. - Advantages of non-contact AFM include that it exerts low forces and avoids damaging soft samples or contaminating the tip. Disadvantages include lower resolution and slower scanning speeds. Applications include analyzing surface roughness, thin film growth, and material properties like stiffness.

1. Presented by:-
DHRUBAJYOTI SADHUKHAN
CUJ/I/2015/INT/04

3. Content
 Introduction
 Advantage and disadvantage of AFM
 Experimental setup
 Imaging methods
 Force vs Distance curve
 Mode of AFM
 Contact mode
 Tapping Mode
 Non-contact mode
 Components of NC-AFM
 Mode of Operation
 Comparison between Modes of AFM
 Application

4. Invention
 Gerd Binning in 1986 invented
the AFM
 1st Experimental implementation
made by Gerd Binning,
Christoph Gerber and Calvin
Quate (1986)
 The first Non-Contact AFM
(NC-AFM) was developed by
Martin et al in 1987.

5. Introduction
 The STM measures the tunneling
current (conducting surface).
 The AFM measures the forces
acting between a fine tip and a
sample.
 The tip attached to the free
end of a cantilever and
brought very close to a
surface.
 Attractive or repulsive forces
resulting interactions between
the tip

6. ▪ High resolution type of scanning
probe microscopy.
▪ Measures surface structure in length
scale 10nm-100μm.
▪ Provides height information of the
sample
▪ Can be imaged, very hard (ceramic
material) or very soft (human cells,
individual molecules of DNA)
▪ Used in all fields of science
Introduction
Atomic force microscope

8. ADVANTAGES AND DISADVANTAGES
OF AFM
ADVANTAGES
 Does not require a conductive
sample
 Ability to magnify in the X,Y,Z axes
 Works in ambient air or in a liquid
environment
 Cheap
 Small size advantage.
DISADVANTAGES
• Cannot be used for size
greater than 100μm
• Limited scanning speed
• Possibility of image variation
▪ Image does not reflect the
true sample topography,

9. Experimental setup of AFM

10. Working of AFM

11. Imaging methods
Contact mode
 Tip is in contact with the substrate
 High resolution
 Can damage surfaces
Non-contact mode (NCM)
▫ Tip is oscillating and not touching the
sample
Tapping mode
 Tip is oscillating and taps the surface
Lateral force microscopy (LFM)
 Tip is scanned sideways
 used to measure friction forces on the
nanoscale
Force Modulation Microscopy
 Rapidly moving the tip up and down
while pressing it into the sample.
 Possible to measure the hardness of
the surface and characterize it
mechanically

12. Forces versus distance curve
 The force measured by AFM can
be classified into long-range forces
and short-range forces.
 When scan at large distances from
the surface
 Van der Waals force,
capillary forces (due to the
water layer often present in an
ambient environment).
 When the scanning is in contact
with the surface the short range
forces
 quantum mechanical forces
or repulsive vander waal force
(Pauli Exclusion Principle
forces).

13. Modes of AFM
Contact mode
 (< 0.5 nm probe
surface separation
Tapping mode
 (0.5-2 nm probe-
surface separation)
Non contact Mode
 (0.1-10 nm probe-
surface separation)

14. Contact Mode
 Tip is dragged over the surface of the
sample.
 Cantilever bends, as the spring
constant of cantilever is less than
surface.
 Repulsive force on the tip
 The force between the probe and the
sample remains constant by
maintaining a constant deflection and
an image of the surface is obtained.
 The deflection of the cantilever Dx is
proportional to the force acting on the
tip,
▫ via Hook’s law, F=-k. x,

15. Tapping mode
 Cantilever oscillates close to
its resonance frequency.
 feedback loop ensures the
constant oscillation amplitude.
 Forces cause a change in the
 oscillation amplitude,
 resonant frequency
 phase of the cantilever.

16. Non-Contact Mode AFM
▪ To avoid problems caused by
capillary forces, the sample is
immersed in a liquid.
▪ This procedure is especially
beneficial for biological
samples.
▪ The probe operates in the
attractive force region and the
tip sample interaction is
minimized.

17.  Allowed scanning without influencing the shape of the sample by
the tip-sample forces.
 The cantilever of spring constant of 20- 100 n/m
 Non-contact mode: amplitude set as ~ 100% of “free” amplitude; •
Non-Contact Mode AFM
Tapping vs NC AFM Contact vs NC AFM

18. Non-Contact Mode AFM

19. Components Of The Microscope
▪ Piezocrystals
▫ ceramic materials
▫ develop an electrical potential in
response to mechanical
pressure.
▪ Probe
▫ The probe represents a micro-
machined cantilever with a sharp
tip at one end, which is brought
into interaction with the sample
surface.

20. ▪ Beam Deflection Detection
▫ To detect the displacement of
the cantilever, a laser is
reflected off the back of the
cantilever and collected in a
photodiode.
▪ Cantilever
▫ V-shaped cantilever-
▫ Providing low mechanical
resistance to vertical
deflection, and high resistance
to lateral torsion.
Components Of The Microscope

21. Sensors
Silicon micro cantilever
▪ Produced from etching small (~100×10×1 μm) rectangular,
triangular, or V-shaped cantilevers from silicon nitride.
▪ Tend to have a higher stiffness, ~40 N/m, and resonant frequency,
~200 kHz, than contact AFM cantilevers (with stiffness's ~0.2 N/m
and resonant frequencies ~15 kHz).
▪ The reason for the higher stiffness to stop the probe snapping to
contact with the surface due to Van der Waals forces.
▪ Tips can be coated for specific purposes, such as a ferromagnetic
coatings for use as a magnetic force microscope.
▪ By doping the silicon, the sensor can be made conductive.

22. qPlus sensor
▪ Used in many ultra-high vacuum NC-AFMs.
▪ The sensor was originally made from a quartz tuning fork from a
wristwatch, consists of two coupled lines that oscillate opposed
to each other,
▪ qPlus sensor has only one tine that oscillates.
▪ Invented in 1996 by physicist Franz J. Giessibl.
▪ Can be used for combined STM/NC-AFM operation.
▪ The tip can either be electrically connected to one of tuning fork
electrodes, or to a separate thin (~30μm diameter) gold wire.
▪ The sensor stiffness, ~1800 N/m
▪ The resonant frequency, ~25 kHz

23. Modes of operation
Frequency modulation
▪ Introduced by Albrecht, Gretter, Horne and Rugar in 1991,
▪ To maintain excitation on resonance it must keep a
90° phase difference between the excitation and response of
the sensor.
▪ This is done by driving the sensor with the deflection signal
phase shifted by 90°.
▪ The change in resonant frequency ( f) can be used, either
in feedback mode, or in constant height mode.

24. Amplitude modulation
 Introduced by binnig and quate in their seminal 1986
 The sensor is excited just off resonance to detect forces
which change the resonant frequency.
 Advantage is that there is one feedback loop (the
topography feedback loop)

25. ▪ Measures surface
topography by the
attractive inter-atomic force
between the tip and a
sample surface (Figure 1).
▪ Piezoelectric modulator is
used to vibrate the
cantilever near its resonant
frequency (Figure 2) as it
passes over a surface, and
correlate changes in the
cantilever’s vibrations to
topographical features.
Working Non-Contact Mode AFM
Figure 1
Figure 2

26. ▪ Tip approaches a sample,
the van der Waals attractive
force between the tip and
the sample causes changes
in both the amplitude and
the phase of the cantilever
vibration (see Figure 3).
▪ These changes are
monitored by a Z-servo
system feedback loop to
control the tip sample
distance (see Figure 4).
Working Non-Contact Mode AFM
Figure 3
Figure 4

27. Advantages of Non Contact AFM Modes over
Contact and Tapping Mode
 Contact Mode AFM
 Lateral forces can distort the image.
 deformation
 Capillary forces from a fluid layer can cause large forces
normal to the tip sample interaction.
 Combination of these forces reduces spatial resolution
and can cause damage to soft samples.
 High contact pressure
 Tapping Mode AFM
 Slower scan speed than in contact mode.
 contamination of the tip is possible
 tip is damaged after several scans

28. Advantages of Non Contact AFM Modes over
Contact and Tapping Mode
Advantage of Non-contact Mode AFM
 Low force is exerted on the sample surface and
 no damage is caused to soft samples
 No contamination of tip
 no limitation in tip’s sharpness

29. Disadvantages of NC-AFM
- Lower lateral resolution, limited by tip-sample
separation.
- Slower scan speed
- Usually only applicable in extremely hydrophobic
samples with a minimal fluid layer.

30. Applications of NC-AFM
Some possible application are:
- Substrate roughness analysis.
- Step formation in thin film epitaxial deposition.
- Pin-holes formation.
- Grain size analysis.
- Phase mode is very sensitive to variations in material
properties, including surface stiffness, elasticity and
adhesion.
- Comparing the tip-samples forces curves for materials to
study the ratio of Young´s Modulus (graphite as a
reference for measure of the indentation).
- Obtaining information of what happening under indentation
at very small loads.

31. Reference
▪ https://www.azonano.com/article.aspx?ArticleID=3010
▪ https://en.wikipedia.org/wiki/Non-contact_atomic_force_microscopy
▪ http://www.parksystems.com/index.php/park-spm-modes/91-standard-imaging-mode/217-true-non-
contact-mode
▪ http://www.parksystems.com/index.php/park-spm-modes/91-standard-imaging-mode/217-true-non-
contact-mode
▪ Principles of Atomic Force Microscopy (AFM) Arantxa Vilalta-Clemente Aristotle
University,Kathrin Gloystein Aristotle University
▪ Y. Martin, C.C. Williams, H.K. Wickramasinghe, J. Appl. Phys. 61, 4723 (1987).
▪ Q. Zhong, D. Innis, K. Kjoller, V.B. Elings, Surf. Sci. Lett. 290, L688 (1993).
▪ Heyde, M.; Kulawik, M.; Rust, H.-P.; Freund, H.-J. (2004). "Double quartz tuning fork sensor for
low temperature atomic force and scanning tunneling microscopy". Review of Scientific
Instruments. 75 (7): 2446

32. Thank You