2. Atomic force microscopy (AFM) is a very-high-
resolution type of scanning probe
microscopy(SPM), with high resolution on the order
of fractions of a nanometer, more than 1000 times
better than the optical microscopy.
The information is gathered by "feeling" or
"touching" the surface with a mechanical probe.
3. Background and History
1981 – Swiss scientists Gerd Binnig
and Heinrich Rohrer- Atomic
resolution microscopy,
simple
1986 – Nobel prize
4. 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
Nano
resolution and
also measure
force at the
nano- scale.
2
Used to study
phenomena of:
Abrasion,
corrosion,
etching (scratch),
friction,
lubricating,
plating, and
polishing.
6. Parts of AFM
1. Laser (Illumination)– 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- amplifies the signal
5. Recorder
6. Sample
7. Probe –tip that scans sample
made of Si
8.Cantilever –moves as scanned
over sample and deflects laser beam
7.
8. Principle
The 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 or silicon nitride with a tip radius of
curvature on the order of nanometers.
When the tip is brought into proximity of a sample surface, laser beam
activates the forces between the tip and the sample lead to a deflection of
the cantilever.
Depending on the situation, forces that are measured in AFM include
mechanical contact force, van der Waals forces, capillary forces, chemical
bonding, electrostatic forces.
8
11. Scanners
AFM scanners are made
from piezoelectric material, which expands and
contracts proportionally to an applied voltage.
Peizo electric material- Barium titanate,
Zirconium titanate
Whether they elongate or contract depends upon
the voltage applied.
Traditionally the tip or sample is mounted on a
'tripod' of three piezo crystals, with each
responsible for scanning in
the x,y and z directions.
Because of differences in material or size, the
sensitivity varies from scanner to scanner.
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
17. THREE Modes: Contact mode,
Non-contact, mode, Tapping Mode
A.Contact Mode; hard, stable samples in air or liquid
B. Non-Contact Mode: non- invasive sampling.
C. Tapping (Intermittent contact): No shear and damaging samples
18. A. Contact
Mode
Measures repulsion between tip and sample
Force of tip against sample remains constant
Problems: excessive tracking forces
applied by probe to sample- sample will destroy.
19. 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
20. 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
24. 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
