The document provides information about atomic force microscopy (AFM). It describes the key components of an AFM, including a laser, photodetector, cantilever with a sharp tip, and piezoelectric crystals that control tip movement. The document explains that in AFM, the tip is brought close to the sample surface and interactions between tip and sample result in cantilever bending that is measured by reflecting a laser off the cantilever into a photodetector. Different AFM modes are also summarized, such as contact mode, non-contact mode, and tapping mode.

1. CHARECTERISATION
TECHNIQUES

2. Parts of AFM
• 1. Laser – deflected off cantilever
• 2. Mirror –reflects laser beam to
photodetector
• 3. Photodetector –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

3. Atomic force microscope
• The AFM combines the principles of the STM and the stylus
profiler .
• During initial contact, the atoms at the end of the tip experience
a very weak repulsive force due to electronic orbital overlap with
the atoms in the sample surface. The force acting on the tip
causes a cantilever deflection which is measured by tunneling,
capacitive, or optical detectors.
• In an AFM, the force between the sample and tip is detected,
rather than the tunneling current.
• The deflection can be measured to within 0.02 nm, so for typical
cantilever spring constant of 10N/m a force as low as 0.2 nN can
be detected.
• The AFM can be used either in a static or dynamic mode.

4. Two Modes
Repulsive (contact)
• At short probe-sample distances,
the forces are repulsive
Attractive Force (non-contact)
• At large probe-sample distances,
the forces are attractive
The AFM cantelever can be used to
measure both attractive force
mode and repulsive forces.

5. Raster the Tip: Generating an Image
ScanningTipRasterMotion
• The tip passes back and forth in a
straight line across the sample
(think old typewriter or CRT)
• In the typical imaging mode, the
tip-sample force is held constant by
adjusting the vertical position of the
tip (feedback).
• A topographic image is built up by
the computer by recording the
vertical position as the tip is
rastered across the sample.

6. Scanning electron microscope

7. The Scanning Electron Microscope, or SEM, is an incredible tool
for seeing the unseen worlds of micro space.
The Scanning Electron Microscope creates the magnified images
by using electrons instead of light waves
The SEM shows very detailed 3-dimensional images at much
higher magnifications than is possible with a light microscope.
Samples have to be prepared carefully to withstand the vacuum
inside the microscope.
The sample is placed inside the microscope's vacuum column
through an air-tight door.

9. An electron gun [at the top] emits a
beam of high energy electrons. This
beam travels downward through a
series of magnetic lenses designed
to focus the electrons to a very fine
spot.

10. Near the bottom, a set of
scanning coils moves the
focused beam back and
forth across the specimen,
row by row.

11. As the electron beam hits each
spot on the sample, secondary
electrons are knocked loose from
its surface. A detector counts
these electrons and sends the
signals to an amplifier

12. The final image is built up from
the number of electrons emitted
from each spot on the sample.

13. Advantages;
 They have a higher resolution.
Electron microscopes allow for the visualization of structures
that would normally be not visible by optical microscopy.
it is possible to view the three dimensional external shape of an
object (Scanning Electron Microscope, SEM).
In scanning electron microscopy (SEM), due to the nature of
electrons, electron microscopes have a greater depth of field
compared to light microscopes.
The higher resolution may also give the human eye the
subjective impression of a higher depth of field.

14. Disadvantages
They are extremely expensive.
The sample must be completely dry.
It is not possible to observe moving specimens (they are dead).
It is not possible to observe color. The image is only black/white.
They require more training and experience
The space requirements are high.
Maintenance costs are high.

15. ATOMIC FORCE
MICROSCOPY

16. AFM

17. The atomic force microscope (AFM) was invented by
Binning et al. in 1986.
1.AFM measures the forces acting between a fine tip and a
sample.
2.The tip is attached to the free end of a cantilever and is
brought very close to a surface.
3.Attractive or repulsive forces resulting from interactions
between the tip and the surface will cause a positive or
negative bending of the cantilever.
4.The bending is detected by means of a laser beam, which
is reflected from the back side of the cantilever.

18. Piezocrystals
Piezocrystals are ceramic materials
that expand or contract in the
presence of voltage gradient and
conversely, they develop an
electrical potential in response
to mechanical pressure.
In this way, movements in x, y and z
direction are possible.

19. cantilever have a sharp tip at
one end, which is brought
into interaction with the
sample surface.
To detect the displacement of
the cantilever, a laser is
reflected off the back of the
cantilever and collected in a
photodiode.
cantilever

20. The diode is divided into four
parts,
1.When the laser is displaced
vertically along the positions
top (B-A) and bottom (D-C),
there exists a bending due to
topography,
2.while if this movement is
horizontal left (B-D) and right
(A-C), it produces a torsion due
to “friction” (lateral force).

21. Modes of operation

22. Contact Mode Non Contact Mode Tapping Mode
(intermittent contact
Mode)
In this mode, the tip
makes soft “physical
contact” with the surface
of the sample.
In this mode, the tip
cannot make any contact
with the surface of the
sample.
The cantilever should be
soft enough to be
deflected by very small
forces and has a high
enough resonant
frequency to not be
susceptible to vibrational
instabilities.
The cantilever for this
mode is the one having
high spring constant of
20- 100 N/m so that it
does not stick to the
sample surface at small
amplitudes.
The cantilever for this
mode is oscillating close
to its resonance
frequency.
Such that amplitude
remains constant, so that
a constant tip-sample
interaction is maintained
during scanning.

23. Contact Mode Non Contact Mode Tapping Mode (intermittent
contact Mode)
Advantages:
- High scan speeds.
- “Atomic resolution” is
possible.
-Easier scanning of
rough samples.
Advantage:
- Low force is exerted
on the sample surface
and no damage is
caused to
soft samples
Advantages:
- Higher lateral
resolution (1 nm to 5
nm).
- Lower forces and less
damage to soft samples
in air.
- Almost no lateral
forces.
Disadvantage:
- Slower scan speed
than in contact mode.
Disadvantages:
- Lower lateral
resolution, .
-Slower scan speed to
avoid contact with fluid
layer.
Disadvantage:
- Slower scan speed
than in contact mode.