Atomic force microscopy (AFM) is a technique for imaging surfaces at the nanoscale. It works by measuring the force between a sharp probe and the sample surface. The key parts of an AFM include a laser, photodetector, cantilever with a probe tip, amplifier and scanner. There are three main imaging modes - contact mode, non-contact mode, and tapping mode. AFM can provide three-dimensional topographic information about a sample and operates in air, liquid or vacuum. Proper sample preparation and calibration of the AFM are required to obtain high resolution images.

1. By: Seyoum Kebede (PhD)
April. 2019
Introduction to Atomic Force Microscope (AFM)

2. Contents
Introduction
General Applications
Parts of AFM and their functions
THREE Modes of Contacts
What are the limitations of AFM?
Advantages and Disadvantages of AFM
Steps to use AFM
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3. Introduction
• Atomic force microscopy (AFM) is a very high-resolution non optical-based microscopy, with
demonstrated resolution on the order of fractions of a nanometer.
• The AFM is one of the foremost tools for imaging, measuring, and manipulating matter at the
nanoscale.
• The information is gathered by feeling the surface with a mechanical probe. Piezoelectric elements
that facilitate tiny but accurate and precise movements on electronic command enable very precise
scanning.
• One extra ordinary feature of AFM is that is fully working in liquid environment.
Relative terms:-
STM: scanning tunneling microscope tunneling of electrons between probe and surface
AFM: atomic force microscope measuring of the force on the probe tip
OFM: Optical force microscope measuring of the force on the optically trapped particle
MFM: magnetic force microscope is AFM with magnetical probe
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4. General Applications
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The General Applications we need to find from AFM are:-
• Materials Investigated:
 Thin and thick film coatings, ceramics, composites, glasses, synthetic and
biological membranes, metals, polymers, and semiconductors.
• Used to study those phenomenon's of:
 Abrasion, corrosion, etching (scratch), friction, lubricating, plating, and polishing. And generally, uses
for study of Topology, Morphology, composition, and Crystallographic information of material surfaces.
NB:- Topography-the surface features of an object or how it looks, its texture is.
- Morphology–the shape and size of the particles making up the object.
- Composition-The elements and compounds that the object is composed of and the relative amount
of them.
- Crystallographic information–How the atoms are arranged in the object.
• AFM can image surface of material in atomic resolution and also measure force at the
nano-Newton scale.

5. Parts of AFM and their functions
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1. Laser – 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
5. Register
6. Sample
7. Probe –tip that scans sample.
8. Cantilever –moves as scanned over sample
and deflects laser beam

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7. Cont.
• The AFM brings a probe in close proximity to the
surface
• The force is detected by the deflection of a spring,
usually a cantilever (diving board)
• Forces between the probe tip and the sample
are sensed to control the distance between
the tip and the sample.
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8. Cont.
• Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100
nm, May at times lightly contact surface
• Two ways of scanning the sample surface:-
 constant force:- feedback system moves tip in z direction to keep force constant.
 constant height:- no feedback system usually used when surface roughness is
small and higher scan speeds possible.
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9. Comparison between Constant-force scan and constant-height scan modes
Constant-force
 Advantages:
 Large vertical range
 Constant force (can be optimized
to the minimum)
 Disadvantages:
 Requires feedback control
 Slow response
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Constant-height
Advantages:
Simple structure(no feedback control)
Fast response
Disadvantages:
Limited vertical range(cantilever
bending and detector dynamic range)
Varied force

10. AFM Imaging modes
• Contact mode:- imaging is heavily influenced by frictional and adhesive forces, and can
damage samples and distort image data.
• Non-contact:- imaging generally provides low resolution and can also be hampered by a
contaminant such as liquid which can interfere with oscillation.
• Tapping Mode:- imaging takes advantages of the two modes. It eliminates frictional
forces by intermittently contacting the surface and oscillating with sufficient amplitude
to prevent the tip from being trapped by adhesive meniscus forces from a contaminant
layer.
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11. Limitations of AFM?
• AFM imaging is not ideally sharp
• But for each pixel there is real 3D image of studied surface with
X,Y,Z coordinates.
• And samples that can not be exposed to vacuum can also be
studied on AFM. 11

12. Advantages and Disadvantages of AFM
Advantages
 Easy sample preparation
 Works in Air, Vacuum, and Liquids
 Gives an accurate height information
of the surface morphology
 Living system can be studied
 Can show 3D imaging
 Best in dynamic environment
 Can show best surface roughness
quantification
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Disadvantages
 Limited vertical range
 Limited magnification range
 In/out put Data not independent of Tip
 Tip or Sample can be damaged
 Has Limited Scanning speed

13. Cont.
AFM is versatile tool to investigate
 Topography of surfaces
 Properties of surfaces
 Properties of single molecules
 Forces with molecules
But, we need to consider experimental conditions and artifacts on measurement of
those parameters listed above.
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14. What are the experimental steps to be followed while using AFM?
1. Turn on the circuit
breaker (main) located
on the rear panel of
the Nano Navi Real
station.
2. Turn on the power switch
located on the front panel of the
Nano Navi Real station.
3. Start-up Windows/computer.
4. Start-up the SPIWin Software.
5. Select the unit to use.
6. Select the measurement mode.
7. Select the language
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NB:Steps 2 to 4 are required only when the turbo-molecular pump is connected. Go to step 5
when there is no connection with turbo-molecular pump.

15. Cont.
 after deciding to open the software frame the SPIWin main window below will
display on the screen.
 When SPIWin starts, set the scanner, sample, and cantilever.
 Press on the four corners of the anti-vibration platform to check for floating.
 This is supported by nitrogen, so that it is connected to the gage.
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16. Cont.
• Prepare the cantilever.
 Select an appropriate tip for work
 Set to appropriate position and
direction.
NB:- Be careful not to grip more, and
touch the tip with holder since the
tip can easily get damage.
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17. Cont.
Cleaning for sample
1. Use a little Ethanol in a cup and put a sample
inside.
2. Clean sample using magnetic vibrator for about 3-5
minutes.
3. Use a cotton feared stick to make sure the sample
cleaned well.
4. Wash the sample using water
5. Make sure that the sample surface is clean and dry;
then Glue the sample on the sample stage.
NB:-but, before putting the sample; make sure that you
Set the sample stage with magnet on the scanner.
- be sure that the leak valve is normally closed.
Since we are not using turbo molecular pump.
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18. Cont.
Positioning:
 Find and set for position of sample and
cantilever tip
– Start up the USB Camera image monitor
– Turn on the light of the optical microscope.
– Click on ‘CCD Monitor (D)’; and Confirm the
cantilever and sample by USB Camera image to
adjust the laser position
– Better to get sample age to have better
position using piezolight.
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19. Cont.
Set the light strength
 Change the SELECT switch in the front panel of
the Adapter BOX to "ADD(first); DIF; then
FEM”.
_ Confirm that the EXT FB switch of the Adapter BOX front
is “OFF”.
– ADD depends on tip we are using and
varying >0.5 (i.e. approximately 3.5 for SiO2
& 4.0-6.0/7.0 for Silica nitride, and most of
the time the more higher value is required)
– DIF value is >0.1 (i.e. this is a value of force
containing the sample. So, if we set this
value <0.10 the Tip can’t approach. So it is
from 0.12-0.20 for silica Tip)
– FEM has a value of =0.00
NB: After adjusting the value of ADD turn of
light of the optical microscope. b/s of
the Light have an effect on DIF and FEM
values.
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20. Cont.
• On approaching stage we need to take care of
Tip and sample distance not to join with high
speed (i.e. Move In/Move Out).
• If we want to approach safely to the Tip,
better to use Auto Approach method and
wait for a minutes
• Before starting we need to check for selector
on adapter. If there is some change we have
to ‘PRESET’ it and adjust for values of
ADD,DIF, and FEM; and finally Approach it
again.
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21. Cont.
Adjusting for magnitudes on Scan Console
• The Pixel parameter should be 256, but, if we make it very high
we have to set the scan speed lower (i.e. Pixel=256 implies that
the image quality is 256).
• To Auto set the sensitivity value be sure to set it 40.00mV/Nm as
standard, and auto set it. And finally we get a sensitivity value for
our setup.
• Set the position of Tip on X&Y=0.00 nm.
• We can also check for monitor for better setup of Tip and
Sample.
• The lower scan speed helps as to get a better image.
• Then click start button to start for analysis and scanning the
surface.
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22. Cont.
• When we are starting scanning the sample, the following
will appear on the window.
 Monitor console setup
 Friction force Analysis
 Adhesion force analysis
 Result calculation
 Image orientation
 Auto/manual tones
 Graphic console
 Depth/width/morphology of surface analysis
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23. We use those steps only when the turbo-molecular pump is not connected.
When there is turbo-molecular pump, we need to check for parameters:-
• Turn on the rotary pump.
• Turn on the turbo molecular pump
• Press the START switch of the turbo-molecular controller (blue button)
• Verify that the rated rotation number is attained.
“NORMAL: 48000rpm” is displayed in the Liquid crystal panel (green circle in the photo below).
• Exhaust the vacuum until the desired vacuum level is attained.
• Go to laser axis adjustment after the desired vacuum level is attained.
• Then the same process with previous work is done.
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24. If we are using variations in relative humidity
• We know that the chamber has space and there are vacuum/air
inside. So, we need to let the air to leave the chamber just opening
the leak valve.
• To be sure that the humidity in chamber should not be equal to that
of environment, we have to let in Nitrogen to the chamber using
those pumps shown.
• Check for better Hydrogen flow, Adjust for dry and warm air.
• NB: to make zero relative Humidity we have to close the leak valve
and turn on the rotary pump and do it open without clothing.
- to break the vacuum we do have to options.
1. open the leak valve and let the air in to a chamber
2. disconnect the nitrogen valve from Humidity
adjustment set.
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25. END
Thank you
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