ATOMIC FORCE MICROSCOPE
PRESENTED BY
ANAM RANA
Registration #: 2013-ag-689
MSc. CHEMISTRY 4TH SEMESTER
Layout of Presentation
Microscope
Atomic Force Microscope
Basic components of AFM
AFM Modes of Operation
AFM Applications
Learning through visualization
Optical
microscope
Electron
microscope
Scanning Probe
microscope
A person with 6/6 vision can resolve objects which are about 0.089mm ( under normal lightening conditions)
Light microscope
The optical microscope (1674)
Which uses visible light (400nm-700nm)and a system of lenses to magnify images of small samples.
Magnification about 1000-2000 times
Resolution 200 nm because of diffraction of light
Viruses, proteins, and molecules are smaller so they can not resolve
Resolution can enhance by using smaller wavelength
Image without use of visible light……how?Electron Microscopy
The electron microscope is a type of microscope that uses a beam of electrons to create an image of the specimen. It is capable of much higher magnifications and has a greater
resolving power than a light microscope, allowing it to see much smaller objects in finer detail.
* Low diffraction
* High resolution TEM(0.2nm) & SEM(5nm)
Limitations of SEM and TEM…………
SEM requires Gold or Silver coating & freezing to get good imagecontrast
TEM requires conductive sample. So fine cutting and fixation of sampleare basic requirement. Sample preparation is lengthy and also requiredexperience specialist
Living samples cannot be observedBoth require high vacuum ( 10-4 torr)and sample dehydration
Optical microscope and electronsmicroscopes are parallel……?
Both provide 2-D lateral information
The image appear flat
Difficult to obtain information in 3rd dimension
Scanning Probe microscope
Scanning probe microscope (SPM) is a type of microscope that forms images of surfaces by employing a physical probe that scans the specimen
Scanning Tunneling Microscope (STM)
1980
Atomic Force Microscope (AFM)
1986
Atomic Force Microscope Atomic force microscope(AFM) or scanning force microscope (SFM) is a very high-
resolution type of scanning probe microscope, with demonstrated resolution on the orderof fractions of a nanometre.
The AFM is one of the foremost tools for imaging, measuring, and manipulating matter atthe nanoscale.
Invented by Binning and coworker in 1986 as an advancement in Scanning tunnelingmicroscope
Let’s model an AFM…
Why AFM not SEM/TEM SEM/TEM AFM
Sample Must be conductive
Insulating/conductive
Magnification 2- Dimensional 3- Dimensional
Environment Vacuum Vacuum/air/liquid
Time for image 0.1-1minutes 1-5minutes
Horizontal resolution
0.2nm(TEM) & 5nm(SEM)
0.2nm
Vertical resolution
N/A 0.05nm
Contrast on flat surfaces
Poor Good
Working Principle of AFM
The information is
gathered by "feeling"
the surface with a
mechanical probe, A
sharpened probe drag
over surface
Force interaction
between tip and sample
give topographic
information of sample
“ A probing solution”
Basic setup of an AFM Atomic scale resolution of AFM is depends
upon following components.
Cantilever with Sharp tip
Scanner
Deflection detection
Cantilever & Tip• AFM consist a cantilever( length=3-6nm tall, radius=15-
40nm ) with Sharp tip.
• Cantilever is basically a spring with spring constant
(k=0.01N/m-1N/m)
• Si or Si3N4 are used for making tips. A thin gold
layer is deposited to upper side of Cantilever for
good reflectivity of laser
• Two types are common in use
• Beam Shape
• V-Shaped
Cantilever must have smaller spring constant and mass………….??????
• Smaller spring constant
• To deflect by smaller interaction forces
• Not to disturb atoms from their site
• Flexible cantilever exerts lower force to
sample thus less distortion and less damage.
• Low mass
• To obtain both low spring constant and high
frequency( >2KHz), the mass of cantilever
should be very small ~ 10-10
• Kg. Higher the resonance frequency of
cantilever, faster and better the imaging.
Cantilever come close to sample the interaction forces come into play
Cantilever deflection detection
• Electron tunneling
• Capacitance detection
• Optical lever detection
Scanner
AFM Schematics
Contact Mode Modes of AFM
Non Contact mode
Tapping/Intermittent mode
• Cantilever oscillate at resonant
frequency
• The oscillating tip then move
towards the sample until touch
• Eliminates frictional forces and
enables to image soft materials
AFM Applications
DATA WRITTINGForce + Heating at tip.
To write 1 , the tip is gently touching the surface causing a dent.
AFM thermo mechanical data Storage
Data Reading
Bit reading depends on the piezoresistivity ( deflection, change in resistance)of Si cantilever.
Cantilever deflection is measured as tip rides over pits. If there is a pit , probe is pushed inside it.
AFM For Macromolecular studies Macromolecules are everywhere:
from DNA / proteins in biologicalscience to polymers / detergents inmaterials science.
AFM can be used to study theconformation and interactionenergies of one macromoleculeat a time.
AFM is Space
“MARS MISSIOM 2016”
High resolution power.
Does not require sample preparation /special medium
REFRENCES: R,Wiesendanger. 2004.Scanning Probe
Microscopy and Spectroscopy, Cambridge University Press
www.nanoscience.com
www.wikipedia.com
Haugstad, G.2012. Atomic Force Microscopy: Understanding Basic Modes and Advanced Applications.Jhon Wiley and sons Inc., Publication
H,Samuel and Marcia. L. 2013.Atomic Force Microscopy and Scanning Tunneling Microscopy
Any Question………???
Any Question………???
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