Atomic force microscopy (AFM) is a very high-resolution type of scanning probe microscopy that can image surfaces at the atomic scale. An AFM works by scanning a probe with a very sharp tip over a sample surface, measuring the forces between the tip and surface. There are three main imaging modes: contact mode, non-contact mode, and tapping mode. AFMs can be used to image topography, measure forces, and manipulate samples at the nanoscale. While providing atomic resolution, AFM also has limitations such as limited range and data dependence on the tip. Future improvements may enable even sharper tips and atomic resolution of living systems.

2. Objectives
 General Applications
 Background and History
 How Does AFM Work?
 Parts of AFM
 3 Modes:
Contact mode
Non-contact mode
Tapping Mode
 What are the limitations of AFM?
 Advantages and Disadvanteges of AFM
 The future of AFM

3. Atomic Force Microscopy
Atomic force microscopy (AFM) or scanning force
Microscopy (SFM) is a very-high-resolution 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.

4. Motivation
 Digitally image a topographical surface
 Determine the roughness of a surface sample or to
measure the thickness of a crystal growth layer
 Image non-conducting surfaces such as proteins and
DNA
 Study the dynamic behavior of living and fixed cells

5. General Applications
 Materials Investigated: Thin and thick film
coatings, ceramics, composites, glasses,
synthetic and biological membranes,
metals, polymers, and semiconductors.
 Used to study phenomena of: Abrasion,
adhesion, cleaning, corrosion, etching,
friction, lubricating, plating, and polishing.
 AFM can image surface of material in
atomic resolution and also measure force
at the nano-Newton scale.

6. Background and History
 1st AFM made by Gerd Binnig and Cristoph
Gerber in 1985
 Constructed by gluing tiny shard of diamond
onto one end of tiny strip of gold foil
 Small hook at end of the tip pressed against
sample surface
 Sample scanned by tracking deflection of
cantilever by monitoring tunneling current to
2nd tip position above cantilever
 Developed in order to examine insulating
surfaces

7. How Does AFM Work?

8. 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

9. Principles
 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, forces between the tip and the sample lead to a
deflection of the cantilever according to Hooke's law.[5] Depending on
the situation, forces that are measured in AFM include mechanical
contact force, van der Waals forces, capillary forces, chemical
bonding, electrostatic forces, magnetic forces etc.
 The AFM can be operated in a number of modes, depending on the
application. In general, possible imaging modes are divided into static
(also called contact) modes and a variety of dynamic (non-contact or
"tapping") modes where the cantilever is vibrated or oscillated at a
given frequency.

10. 3 Modes of AFM
Contact Mode
Non-Contact Mode
Tapping (Intermittent
contact) Mode

11. Contact Mode
 Measures repulsion between tip and
sample
 Force of tip against sample remains
constant
 Feedback regulation keeps cantilever
deflection constant
 Voltage required indicates height of sample
 Problems: excessive tracking forces
applied by probe to sample

12. 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

13. 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

14. Abilities
The AFM has three major abilities: force measurement, imaging, and manipulation.
 In force measurement, AFMs can be used to measure the forces between the
probe and the sample as a function of their mutual separation. This can be
applied to perform force spectroscopy, to measure the mechanical properties of
the sample, such as the sample's Young's modulus, a measure of stiffness.
 For imaging, the reaction of the probe to the forces that the sample imposes on it
can be used to form an image of the three-dimensional shape (topography) of a
sample surface at a high resolution. This is achieved by raster scanning the
position of the sample with respect to the tip and recording the height of the
probe that corresponds to a constant probe-sample interaction (see section
topographic imaging in AFM for more details). The surface topography is
commonly displayed as a pseudocolor plot.
 In manipulation, the forces between tip and sample can also be used to change
the properties of the sample in a controlled way. Examples of this include atomic
manipulation, scanning probe lithography and local stimulation of cells.
 Simultaneous with the acquisition of topographical images, other properties of the
sample can be measured locally and displayed as an image, often with similarly
high resolution. Examples of such properties are mechanical properties like
stiffness or adhesion strength and electrical properties such as conductivity or
surface potential. In fact, the majority of SPM techniques are extensions of AFM
that use this modality.

15. What are the limitations of
AFM?
 AFM imaging is not ideally sharp

16. Advantages and Disadvantages
of AFM
 Easy sample
preparation
 Accurate height
information
 Works in vacuum, air,
and liquids
 Living systems can be
studied
 Limited vertical range
 Limited magnification
range
 Data not independent
of tip
 Tip or sample can be
damaged

17. The Future of Atomic Force
Microscopy
 Sharper tips by improved microfabrication
processes: tip – sample interaction tends to
distort or destroy soft biological molecules
 Atomic or angstrom resolution images of live
cell surfaces: development of more flexible
cantilever springs and less damaging and
nonsticky probes needed

23. References
Li, Hong-Qiang. “Atomic Force Microscopy”.
http://www.chembio.uoguelph.ca/educmat/chm729.afm.htm
Baselt, David. “Atomic force microscopy”.
http://stm2.nrl.navy.mil/how-afm/how-afm.html
Atomic Force Microscopy.
http://www.topometrix.com/spmguide/1-2-0.htm
An Introduction to Atomic Force Microscopy
http://www.wpi.edu/academics/Depts/Physics/AFM/Pdfs/PosterIntro
.pdf
Basic Theory Atomic Force Microscopy (AFM)
http://asdlib.org/onlineArticles/ecourseware/Bullen/SPMModule_Ba
sicTheoryAFM.pdf