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Atomic Force MicroscopyAl-Karawi, Dheyaa

Western Kentucky University WKU- Chemistry department- instrumental analysis “chem 435”

11/30/2015

2https:/www.pinterest.com/lictorn/gary-larson-the-far-side/

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Brief History of Microscopes

• 1590’s – Zacharias Jansen and his father Hans

• Several lenses in a tube– Enlarged objects only ~9X

http://www.history-of-the-microscope.org/history-of-the-microscope-who-invented-the-microscope.php

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• Anton van Leeuwenhoek (1632-1723)– 1st to make a “real” microscope– 1st to see and describe bacteria, yeast plants…– Developed superior lenses

• 270X magnifying power

• Robert Hooke (1635-1703)– Verified van Leeuwenhoek’s work– Published Micrographia, 1665

• Observed pores in cork, called them “cells”

IMAGE: http://www.nlm.nih.gov/exhibition/hooke/hookesbooks.html

Brief History of Microscopes

• Nobel Prize in Physics, 1984– Ernst Ruska

• German physicist– Fundamental work in electron optics– Designed 1st electron microscope

– Gerd Binnig , Heinrich Rohrer– Design of scanning tunneling microscope.

• A few years later, the first Atomic Force Microscope (AFM) was developed by G. Binnig, Ch. Gerber, and C. Quate at Stanford University by gluing a tiny shard of diamond onto one end of a tiny strip of gold foil

• Currently AFM is the most common form of scanning probe microscopy

5http://ernst.ruska.de/daten_e/library/documents/999.nobellecture/lecture.html

Brief History of Microscopes

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Atomic Force Microscopy AFM

• Basic components of AFM:• Cantilever and Tip• Laser• A scanner that controls the x-y-

z position • Detector and the feedback

control

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Probe

• Probe: Si or Si3N4

• Only part that contacts sample-> shape is critical! -> Resolution depends on it

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Cantilever

The cantilever is designed with a very low spring so it is very sensitive to any forces.

• Spring system/Force Sensor• Bends in presence of attractive/repulsive forces• Cantilever deflection converted to force using:

Hooke’s Law! s : deflectionk : spring constant

Piezoelectric transducers

• Scanner. The movement of the tip or sample in the x, y, and z-directions is controlled by a piezo-electric tube scanner.

• amorphous lead barium titanate, PdBaTiO3 or lead zirconate titanate.

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Feedback control

Feedback control is used to maintain a fixed force between the probe and the sample.

11http://www.edinformatics.com/nanotechnology/atomic_force_microscope.htm

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Interaction force between probe and sample

Deflection of cantilever

Changes of the laser signal to the photosensitive position detector

Electric signal

Signal processing to generate image

Change of the surface properties along the scan line

Different modes of operation

Mode of Operation Force of Interaction

Contact mode strong (repulsive) - constant force or constant distance.

Non-contact mode weak (attractive) - vibrating probe

Tapping mode strong (repulsive) - vibrating probe

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Modes of Imaging

Repulsive

Attractive

Tapping Mode

Non-Contact ModeContact Mode

http://virtual.itg.uiuc.edu/training/AFM_tutorial/

ADVANTAGES AND DİSADVANTAGES OF AFM

Adv: Easy sample preparation Non-destructive imaging Accurate height information Works in vacuum, air, and liquids Living systems can be studied Sample not required to be conductive

Polymers, ceramics, glassMetalsBiological samples

Dis-adv: Limited vertical range Limited magnification range Highly Dependent on AFM probes. Tip or sample can be damaged

OU NanoLab/NSF NUE/Bumm & Johnson

Application• Digitally image a topographical surface

• Determine the roughness of a surface sample or to measure the thickness of a crystal growth layer

• Any sample like ceramic material, human cells or individual molecules of DNA.

• In biological applications: Image non-conducting surfaces such as proteins and DNA Study Unfolding Of Proteins Imagining Of Biomolecules Force Measurements In Real Solvent Environments Antibody-Antigen Binding Studies Ligand-Receptor Binding Studies Binding Forces Of Complimentary DNA Strands

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Example of contact mode

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Tapping mode

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Non- contact mode

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References• Atomic force Microscopy by Peter Eatson and Paul West.

• http://hansmalab.physics.ucsb.edu/afmapp.html

• Quazar Technologies Pvt., LTd. Guide section.

• Astrid Kronenberger School of Engineering and Science. (2006) Atomic Force Microscopy-Basics and Applicationshttp://www.faculty.jacobs-university.de/mwinterhalter/yannic/alex%20summer%20school/Talks/kronenberger.pdf

• West, E.P. Introduction to Atomic Force Microscopy: Theory, Practice, Applications” http://www.paulwestphd.com/download.html

• http://www.edinformatics.com/nanotechnology/atomic_force_microscope.htm