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AFM (Atomic Force Microscopy)
1. ATOMIC FORCE MICROSCOPY
SUBMITTED TO DR. Shazia Abrar
SUBMITTED BY Sohaib Hasnain
PROGRAMME M.Phil
SUBJECT :
Instrumental Analysis for Process Industries
2. History
Atomic force microscopy (AFM) was developed
when people tried to extend STM technique to
investigate the electrically non-conductive
materials, like proteins.
In 1986, Binnig and Quate demonstrated for the
first time the ideas of AFM, which used an ultra-
small probe tip at the end of a cantilever.
3. What isAFM
AFM is a type of scanning probe
microscopy (SPM), with demonstrated
resolution on the order of fractions of
a nanometer, more than 1000 times better than
the optical diffraction limit.
The information is gathered by "feeling" or
"touching" the surface with a mechanical
probe
4. AFM provides a 3D profile of the surface on a
nanoscale, by measuring forces between a sharp
probe and the surface.
The AFM has three major abilities:
force measurement, imaging, and manipulation.
It is powerful because an AFM can generate
images at atomic resolution with angstrom scale
resolution height information, with minimum
sample preparation.
5. Principle Of AFM
Surface Sensing
An AFM uses a cantilever with a very sharp tip to
scan over a sample surface. As the tip approaches
the surface, the close-range, attractive force
between the surface and the tip cause the
cantilever to deflect towards the surface.
However, as the cantilever is brought even closer
to the surface, such that the tip makes contact
with it, increasingly repulsive force takes over
and causes the cantilever to deflect away from the
surface.
6. Detection Method
A laser beam is used to detect cantilever
deflections towards or away from the surface.
By reflecting an incident beam off the flat top
of the cantilever, any cantilever deflection will
cause slight changes in the direction of the
reflected beam. A position-sensitive photo
diode (PSPD) can be used to track these
changes. Thus, if an AFM tip passes over a
raised surface feature, the resulting cantilever
deflection (and the subsequent change in
direction of reflected beam) is recorded by the
PSPD.
7.
8. Imaging
An AFM images the topography of a
sample surface by scanning the
cantilever over a region of interest. The
raised and lowered features on the
sample surface influence the deflection
of the cantilever, which is monitored by
the PSPD. The AFM can generate an
accurate topographic map of the surface
features.
9. How Are Force Measured
The probe is placed on the end of a cantilever
(which one can think of as a spring).
The amount of force between the probe and
surface is dependant on the spring constant
(stiffness of the cantilever and the distance
between th probe and the sample surface.
This force can be described using Hooke’s
Law:
F= -k·x
10. F = Force
k = spring constant
x = cantilever deflection
• If the spring constant of
cantilever (typically ~ 0.1-1
N/m) is less than surface,
the cantilever bends and the
deflection is monitored.
•This typically results in
forces ranging from nN (10
) to µN (10-6) in the open
air.
11.
12. What Are Probes Made Of?
They are generally made up
of Silicon or Si3N4.
Probes may be coated with
other materials for the
addiontal SPM application
such as CFM(Chemical
force Microscopy) and
MFM(Magnetic Force
Microscopy)
13. Why is different from optical microscopy
No lenses are needed.
No need of light source to illuminate the
sample.
No eyeplece to look through the sample.
Itself imaging device technique which is able
to measure the very small forces b/w the atom
or molecules
14. Why AFM is better than STM
It give information about the conducting
and non-conducting surfaces.
3-D image of surfaces are obtained by
this techniques.
Sample can be analyzed in open Air.
15. Application
The AFM has been applied to problems in a wide
range of disciplines of the natural sciences,
including solid-state physics, semiconductor
science and technology, molecular engineering,
polymer chemistry and physics, surface
chemistry, molecular biology, cell biology,
and medicine.
It gives information about the toughness,
roughness and smoothness value of surface.
16. Applications in the field of solid state physics
include (a) the identification of atoms at a
surface, (b) the evaluation of interactions
between a specific atom and its neighboring
atoms.
In molecular biology, AFM can be used to
study the structure and mechanical properties
of protein complexes and assemblies. For
example, AFM has been used to
image microtubules and measure their
stiffness.
17. In cellular biology, AFM can be used to
attempt to distinguish cancer cells and normal
cells based on a hardness of cells, and to
evaluate interactions between a specific cell
and its neighboring cells in a competitive
culture system.
Soft surfaces are analyzed by this technique
without damaging it like Lipids.
Covalent bond strength is measured by this
Technique
19. The Hessian Blob Algorithm: Precise Particle
Detection in Atomic Force Microscopy
Imagery.
Atomic-resolution three-dimensional
hydration structures on a heterogeneously
charged surface
